Moparts
straight vs. split pattern cams
Posted By: Fishmarket
straight vs. split pattern cams - 12/15/10 05:04 PM
Can someone explain when and why it would be advantaageous to use a split pattern cam with more exhaust duration, and when a greater exhaust duration would start to be detremental?
I can see using a split on an engine breathing through exhaust manifolds but what if your heads are ported and you have a free flowing header/exhaust set up? Can too much exhaust duration hurt power output?
Posted By: Dodgem
Re: straight vs. split pattern cams - 12/15/10 05:36 PM
Testing has show for a given intake profile they will give a little more power with a longer exhaust duration.
so lets say a standard 236/236 @ .050 110 LSA cam changing it to a 236/244 @ .050 cam will give a little more power and not effect the drive ability from where it is.
the norm seems to be 6 to 10 more on the exhaust to get rid of that expanded hot exhaust charge.
Posted By: StealthWedge67
Re: straight vs. split pattern cams - 12/15/10 06:11 PM
The magic number, here, is 75%. You want your exhaust port to flow @ 75% of your intake port. Most stock heads (especially BB mopars) don't do this, so cam manufacturers figured they can compensate for the heads shortcomings by extending the duration on the exhaust side.
What has happened now, is that split pattern cams have just become the norm, and the general public percieves they are getting a better engineered product with varying #'s on the card (not really knowing why)
Most good aftermarket heads do support the 75% number, however.
The key when choosing a cam is knowing what your heads will flow, and complimenting that curve with the cam. With good heads that flow properly, there is a strong case to be made that you'll maximize the power available from a given duration and lift spec. with a square pattern cam. Your intake, carburetor, and header selection also plays a role here.
I conferred with Member, Jeff Patterson, when choosing my cam, and we both agreed that my combo seemed to call for a square pattern cam, so that's what we dialed up from Engle.
Posted By: maximum entropy
Re: straight vs. split pattern cams - 12/15/10 06:17 PM
Quote:
The magic number, here, is 75%. You want your exhaust port to flow @ 75% of your intake port. Most stock heads (especially BB mopars) don't do this, so cam manufacturers figured they can compensate for the heads shortcomings by extending the duration on the exhaust side.
What has happened now, is that split pattern cams have just become the norm, and the general public percieves they are getting a better engineered product with varying #'s on the card (not really knowing why)
Most good aftermarket heads do support the 75% number, however.
The key when choosing a cam is knowing what your heads will flow, and complimenting that curve with the cam. With good heads that flow properly, there is a strong case to be made that you'll maximize the power available from a given duration and lift spec. with a square pattern cam. Your intake, carburetor, and header selection also plays a role here.
I conferred with Member, Jeff Patterson, when choosing my cam, and we both agreed that my combo seemed to call for a square pattern cam, so that's what we dialed up from Engle.
WHAT HE SAID. 
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/15/10 06:32 PM
Opinions are just that , here's mine FWIW.
Running too much exhaust duration with low compression engines just kills torque , exhaust valve requires a later opening to take advantage of later peak pressure associated with low compression ratios , opening exhaust valve to early won't give the expanding gasses enough time/leverage to push on piston , using a faster lobe can help regards pumping lossess , sometimes a higher ratio rocker arm on exhaust can help when going shorter on exhaust duration................the other problem with long duration exhaust lobes is the overlap period , once the piston moves away from TDC on intake stroke it's drawing on both intake & exhaust port , any spent gasses left in the exhaust port will be sucked into the cylinder along with fuel'air from intake port , the longer the exhaust valve is held open on intake stroke the more contaminated the charge will be , this is the reason tighter lobe centres produce less vaccume & run pretty rough @ idle , the cleaner the intake charge the more power the engine will produce.
Using restricted exhaust manifolds along with later closing exhaust valves (longer overlap period) makes matters worse on street engines that only spin to around 3500/4000 rpm , unless that exhaust can scavenge intake charge will be contaminated.......why is it advancing intake centreline makes more torque low down? , LESS CONTAMINATION......all you guys using split patterns (low comp) go loosen lash on exhaust valve & notice the motor pick up , will idle a bunch nicer too.
Just my
, feel free to bash the hell out of it.
Posted By: BradH
Re: straight vs. split pattern cams - 12/15/10 07:17 PM
Quote:
Testing has show for a given intake profile they will give a little more power with a longer exhaust duration.
Whose testing? I've seen some that show that the proper single-pattern cam will provide more power through the entire range. So, who do you believe?
Quote:
The magic number, here, is 75%.
Sorry, there is NO MAGIC NUMBER. That "75%" rule is outdated.
Quote:
Opinions are just that...
I won't argue that point.
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/15/10 07:22 PM
Hey Budget , what does 'do not feed the troll' mean?
Posted By: Dunnuck Racing
Re: straight vs. split pattern cams - 12/15/10 07:29 PM
If you were to ask 5 different camshaft manufaturers this question,you would get 5 different answers.
It would depend on what the engine is intended to be used for,cylinder head flow,compression ratio,etc.
As far as the 75% rule,I agree that is outdated,but something people tend to use anyway.
Posted By: BradH
Re: straight vs. split pattern cams - 12/15/10 08:12 PM
Quote:
Hey Budget , what does 'do not feed the troll' mean?
It means I'm in kind of a crappy mood and this is just the sort of thread that could cause me to post of bunch of smart@ss comments in my replies.
Posted By: AndyF
Re: straight vs. split pattern cams - 12/15/10 08:16 PM
I spent a bunch of money dyno testing camshafts on my 470 low deck motor. It had exhaust manifolds and lots of people told me that I would need extra duration on the exhaust side to compensate for the manifolds. Turns out that the very best camshaft for that engine was the old school Mopar .528 solid flat tappet.
I suppose if I was given unlimted funds I could find a camshaft that was even better than the .528. And perhaps, after hunreds of dyno pulls the very best cam might well be a split pattern cam. But I called it quits after spending a couple of grand on cams and dyno time.
As far as I know, nobody knows the answer to this question. It is fairly easy to get a 90% correct answer to the question, but I don't think anyone has ever really figured it all out. If they had, then there wouldn't be any need for all of the dyno testing that goes on every day at all of the engine shops around the world.
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/15/10 08:32 PM
Quote:
I spent a bunch of money dyno testing camshafts on my 470 low deck motor. It had exhaust manifolds and lots of people told me that I would need extra duration on the exhaust side to compensate for the manifolds. Turns out that the very best camshaft for that engine was the old school Mopar .528 solid flat tappet.
I suppose if I was given unlimted funds I could find a camshaft that was even better than the .528. And perhaps, after hunreds of dyno pulls the very best cam might well be a split pattern cam. But I called it quits after spending a couple of grand on cams and dyno time.
As far as I know, nobody knows the answer to this question. It is fairly easy to get a 90% correct answer to the question, but I don't think anyone has ever really figured it all out. If they had, then there wouldn't be any need for all of the dyno testing that goes on every day at all of the engine shops around the world.
Right then , take it the jurys out for single pattern grinds.
Used 14 degree split when on the bottle , but that's a different story. 
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/15/10 08:35 PM
Quote:
Quote:
Hey Budget , what does 'do not feed the troll' mean?
It means I'm in kind of a crappy mood and this is just the sort of thread that could cause me to post of bunch of [Email]smart@ss[/Email] comments in my replies.
I wanna know who's the TROLL.
Posted By: BradH
Re: straight vs. split pattern cams - 12/15/10 09:13 PM
Quote:
I wanna know who's the TROLL.
That refers to ME. Although I tell my kids my parenting role model is Shrek and he's an ogre, not a troll. 
Posted By: AndyF
Re: straight vs. split pattern cams - 12/15/10 09:29 PM
Single pattern cams seem to work just fine in a lot of engines including most OEM engines.
I just finished up some camshaft testing in one of my big block motors where I was using a Comp MM 293 single pattern cam. It made 660 hp which is a decent number for an inexpensive flat tappet cam. This is with Edelbrock RPM heads which aren't noted for having a fantastic exhaust port. Maybe a dual pattern cam would make more power, maybe it wouldn't. Point is that 660 hp is enough power to put most Mopar race cars into the 9's. So for a typical bracket racer, why mess around with a bunch of cam theory when a simple cam off the shelf will run plenty hard.
440Jim runs a MM 305 (single pattern, flat tappet) shelf cam and he is knocking on the 8 second door.
Posted By: polyspheric
Re: straight vs. split pattern cams *DELETED* - 12/16/10 01:39 AM
Post deleted by polyspheric
Posted By: StealthWedge67
Re: straight vs. split pattern cams - 12/16/10 03:46 AM
Quote:
Quote:
Testing has show for a given intake profile they will give a little more power with a longer exhaust duration.
Whose testing? I've seen some that show that the proper single-pattern cam will provide more power through the entire range. So, who do you believe?
Quote:
The magic number, here, is 75%.
Sorry, there is NO MAGIC NUMBER. That "75%" rule is outdated.
Quote:
Opinions are just that...
I won't argue that point.
Well, if opinions are "just that", then I'll consider yours to be the low side of the analogy. You've certainly provided plenty of facts to support your rant, there..... (oh, maybe not) Until you can show me actual numbers that say the 75% rule is untrue, I'm going to consider your opinion completely arbitrary. Perhaps I should have called it a "rule of thumb", not a "magic number", this I'll concede. But the facts remain. This number is based on the physics of volumetric transfer. I don't think these mathematical equations "expire" with time. Why does just about every internal combustion head ever manufactured feature an exhaust valve approx. 75% of the intake? You may really mean to point out that this rule of thumb isn't foolproof every time??. To which I'd still ask you to come up with a fact based equation that outweighs it. Bottom line, heated exhaust gas needs approx. 75% of the volumetric space to travel at the same velocity as the cooler, wetted intake charge. If a heads flow capability doesn't support that mathematical certainty, then adjusting the exhaust valve duration to compensate has become the accepted path that cam manufacturers have followed.
Posted By: Sport440
Re: straight vs. split pattern cams - 12/16/10 03:47 AM
Thats exactly what I was going to say, you beat me to it.
mike
Posted By: sixpackgut
Re: straight vs. split pattern cams - 12/16/10 03:59 AM
what do the FAST class guys run?
Posted By: StealthWedge67
Re: straight vs. split pattern cams - 12/16/10 04:08 AM
According to the writeup on Joel Nystrom's 67 GTX in MuscleCar Review last month, He reportedly runs heads that have been custom ported to flow 420 on the intake, and 315 on the exhaust.... (at this point I would ask you to do the math on that relationship).
The same writeup notes that he employs a camshaft that features 4% more duration on the exhaust side. This makes sense, since his hemi runs 1250 cfm worth of dual AFB on the intake side, but stock exhaust manifolds on the exhaust side.
Posted By: sixpackgut
Re: straight vs. split pattern cams - 12/16/10 04:20 AM
Quote:
According to the writeup on Joel Nystrom's 67 GTX in MuscleCar Review last month, He reportedly runs heads that have been custom ported to flow 420 on the intake, and 315 on the exhaust.... (at this point I would ask you to do the math on that relationship).
The same writeup notes that he employs a camshaft that features 4% more duration on the exhaust side. This makes sense, since his hemi runs 1250 cfm worth of dual AFB on the intake side, but stock exhaust manifolds on the exhaust side.
420/315 
what does a head done for super stock flow?
Posted By: Stanton
Re: straight vs. split pattern cams - 12/16/10 04:24 AM
The end result is that you need to use the cam profile or rocker ratios to compensate for head flow. If your heads flow less than 75% on the exhaust versus the intake then you need to compensate - i.e. Indy EZ1's from all the info I can find only flow 60% on the exhaust. A split pattern cam or a higher ratio exhaust rocker would be in order.
As for the "factory" analogy, that's just BS! The cars came off the line with enough power to get you in trouble and the engineers knew damn well that anyone wanting to improve things would have headers and a cam at the top of the list.
Posted By: BradH
Re: straight vs. split pattern cams - 12/16/10 04:32 AM
Quote:
Perhaps I should have called it a "rule of thumb", not a "magic number", this I'll concede.
Perhaps...
Quote:
This number is based on the physics of volumetric transfer. I don't think these mathematical equations "expire" with time.
What are these equations to which you refer and how do they really apply when considering that (as pointed out above in Polyspheric's reply) the conditions under which the intake and exhaust ports operate in the real world are so vastly different that it's almost a shot in the dark to try to attach an arbitrary # based on some perception of similarity?
Quote:
Why does just about every internal combustion head ever manufactured feature an exhaust valve approx. 75% of the intake?
Is this 75% of diameter, or 75% of valve curtain area? And which would really be more suited to a comparison of flow #s?
Quote:
You may really mean to point out that this rule of thumb isn't foolproof every time??. To which I'd still ask you to come up with a fact based equation that outweighs it.
There isn't one, which is why saying 75% is invalid. What do you think a modern Pro Stock head flows percentage-wise on the exhaust side? It's about 60%. If 75% was the trick to making more power, wouldn't you think those guys would find a way to increase their exhaust port efficiencies to achieve that, rather than simply adding another 10+ degrees of exhaust duration?
Quote:
Bottom line, heated exhaust gas needs approx. 75% of the volumetric space to travel at the same velocity as the cooler, wetted intake charge.
Bottom line is the exhaust needs of a Pro Stock-type high compression engine, or anything along those lines, aren't the same as something that you or I might build in our garage. Trying to box in the camshaft parameters by quoting the old 75% ratio is oversimplifying the situation and the solution.
Enough of this theoretical 
I have real engines to work on.
Posted By: StealthWedge67
Re: straight vs. split pattern cams - 12/16/10 04:57 AM
Posted By: HotRodDave
Re: straight vs. split pattern cams - 12/16/10 05:31 AM
The pro stockers would love to get more ex flow but since power is primarliy limited by the ability to get air and fuel into the engine they make a very big intake valve, this means you can only run a small ex valve and that means you have to run more ex duration.
Posted By: polyspheric
Re: straight vs. split pattern cams - 12/16/10 06:28 AM
As usual: everyone speaks, no one listens.
Posted By: gregsdart
Re: straight vs. split pattern cams - 12/16/10 02:24 PM
just an uneducated response with my
Flow sheets show different flow percentages at every level of flow, not to mention that taking the highest lift flow numbers isn't a good bench mark as most motors don't have enough lift to get there any way.
Efficiency of the motor must effect the percentage ratio needed? A highly efficient intake system with lots of inertia must have different requirements than a basic bracket motor, or worse yet a stock type motor.
Efficiency of the header design must play a big part.
In the end, every combo will be unique to itself, having its own sweet spot.
look at the number of cams that are tested on high end engine builds like Prostock or other professional or comp category's and that will give you a clue as to how well a rule like that works. Any one want to buy a used roller cam for a big block? I have three for sale,,,,,,,,,,,,
Posted By: emarine01
Re: straight vs. split pattern cams - 12/18/10 02:04 AM
I am all ears....
Posted By: dennismopar73
Re: straight vs. split pattern cams - 12/18/10 02:21 AM
sorry but im ears
i m very dumb on alot of issues
somethings i know alot
my fear is sometimes i get confused between the two
Posted By: Sport440
Re: straight vs. split pattern cams - 12/18/10 02:35 AM
Quote:
As usual: everyone speaks, no one listens.
What in particular did you think some missed.
I liked both of your posts, its ashame after all that typing that you just dumped it.
If Im to guess, you made a comment to the effect that the volume in has to match the volume out was your point. 
Thats not correct 
, But that probably wasnt it. 
mike
Posted By: 440Jim
Re: straight vs. split pattern cams - 12/18/10 04:32 PM
Quote:
440Jim runs a MM 305 (single pattern, flat tappet) shelf cam and he is knocking on the 8 second door.
Just for clarification, the Comp Cams shelf cam (grind MM305S-10, part number 23-634-5) I am running is not a single pattern cam it has the MM305 intake lobe and a different exhaust lobe. In fact it has two differences:
1) The exhaust lobe is a different intensity (less agressive)
2) The exhaust has more duration at 0.050", but about the same at 0.200" and 0.300" tappet lift.
Int/Exh:
305º/320º@.020", 279º/287º@.050", 197º/200º@.200", 143º/143º@.300", 112º/107º@.350", 0.433"/0.420" lobe lift, 110 LSA
Link to Comp Cams BB Mopar drag racing cams
Posted By: moper
Re: straight vs. split pattern cams - 12/18/10 05:56 PM
It would be nice to approach this question with an open mind. I know this is Moparts and the general feel of the site has evolved in a different direction but where better to try to revive the old atmosphere...lol
Here's my opinon...I think as with most of engine theory, one has to look at how far one is willing to go. If the one perfect lobe relationship is indeed individualistic to every engine and use, then we could use a pyramid analogy with the perfect relationship and max power is the top or point, poor relationship and lost power is the base, and we're looking to find the relationship that best fits our engine, that's affordable, and that's as close to the point as possible. In terms of techonolgy, a builder can use the port, the valve job, the manifolding, and the cam to optimize the airflow into and out of any engine. There is no perfect relationship unless you are talking identical builds, otherwise the variables add up and "your results may vary". FAST guys have to overcome a bunch of things and do some strange things to run well. I wouldnt call them, or the perfectly scienced out race engine good examples of what to do. Andy's the closest because he's testing his stuff, in a running environment, one part, one change at a time. Like Jim says, modern cam lobe designs are even making what we use to compare lobes confusing with assymetrical lobes and duration measurements that don't specify if there's more on the opening ramp or closing ramp...lol. Over all, I think in terms of exh flow out, you dont need as much lift or duration if the support parts all work well for your intended rpm range. The further you get from that point, the more generalities are assumed and generally, most engines of any sort benefit from more exh duration and lift because the rest of the parts create issues impeding exh efficiency and flow.
Posted By: moparniac
Re: straight vs. split pattern cams - 12/18/10 06:03 PM
My last cam was a straight pattern! why? cause thats what was recomended...
My new cam is a split pattern! why? cause thats what was recomended ...
Posted By: Streetwize
Re: straight vs. split pattern cams - 12/18/10 06:06 PM
My
Way too complicated and 'application specific' to discuss beyond generalities.
As the motor gets larger relative to the original port cross section (think Stroker) it's much more of a challenge to get enough air IN to the motor and if you can't get enough in there's less proportionally you have to worry about getting OUT. If VE is falling by default so are the pumping forces. The tuning objective for just about any motor is get to optimum VE as early as practical for the application/load/gearing and keep it there (as close to peak) for as long as possible/practical.
The intake closing event effects overall torque and power curves more than any other single event....for a given application you more or less select the cam for the type of engine tuning (powerband) you're looking for, the exhaust timing and lobe spreads are selected from there.
Also remeber it's harder to fill the cylinder than to empty it...you have to induce the air/fuel into the hole past the valve typically with little or nothing more than Atmospheric pressure....but once it's detonated those expanding gases are LOOKING for somewhere to go....where would they go if your exhaust valve didn't open? They'ed go out somewhere, woudn't they???? The exhaust pattern/duration is a tuning means aimed at tuning the pressure (as much as possible) and to ensure adequate evacuation without upsetting the next intake charge. Backpressure through the system (as the high pressure gases return back to atmosphereic) acts like a resistive force that somewhat slows the rate of acceleration of the crank, which in turn generates the draw on the intake charge....but that resistence is also summed along with all the other resistive forces acting on the crank....namely the recipricating/rotating masses as well as the drag from the rings, bearing and valvetrain.
Also as Jim correctly illustrates the @.050 duration only tells part of the story, many cam grinders use a "lazier" exhaust pattern in an effort to trap cylinder pressure a bit longer where as with the intake you want to snap it open to get to full lift sooner and then snap it back shut before the piston sweeping back up past BDC bleeds combustion pressure back into the intake tract.
I,ve always loved Polysheric's posts but I wish he'd get a little thicker skinned; it's a forum afterall and if I ran off every time somebody disagreed with me (even if they were wrong
), I'd have been gone a long long time ago. Or maybe in myu case I'm just too hard-headed to take a hint that nobody wants me around!!
Posted By: moper
Re: straight vs. split pattern cams - 12/18/10 06:48 PM
Quote:
My Way too complicated and 'application specific' to discuss beyond generalities.
Posted By: polyspheric
Re: straight vs. split pattern cams - 12/18/10 06:55 PM
There was an old vaudeville joke about what facts are worth vs opinions.
2 guys are hiring a new secretary, but they want to be sure she can do the job, so they devise a simple test.
Q. "how much is 4 and 4?"
Applicant #1: "8"
Applicant #2: "44"
Applicant #3: "it depends on how tall he is"
They discuss it:
"Well, only one got the right answer, but the others seemed pretty sure. What should we do?"
"Hire the blond with the big t*ts".
The answer was already given, and yet the dialogue continues...
Posted By: Streetwize
Re: straight vs. split pattern cams - 12/18/10 07:09 PM
Poly,
Well as is often the case....you delete your posts before I ever see the thread
Maybe you can repost the 'right answer' or PM it to me.
In the mean time maybe the well endowed blonde I hired as my secretary can keep me busy while I'm waiting
I do know that many generally accepted laws of physics and thermodynamics don't always (but mostly they do...and a LOT more than in other 'bowtie' car forums I've seen) seem to apply here, those professors and professional engineers I work with everyday must be idiots!!
Posted By: AndyF
Re: straight vs. split pattern cams - 12/18/10 08:46 PM
My mistake, the shelf MM 305 is a dual pattern. The MM 293 I have in the motor at the moment is a single pattern cam.
I will say that while Jim has had excellent results with that MM 305, I'd be willing to bet some bucks that a sharp cam guy could grind up a single pattern cam for Jim's motor that would make his car faster. I would also assume that another equally sharp cam guy could then figure out a dual pattern cam that would once again improve the performance.
On a related front, I've been doing some dyno testing on my 514 motor with split pattern cams and split rocker arm ratios. So the cam has different intake and exhaust lobes, and the rocker arms are 1.85 on the intake and 1.70 on the exhaust. I might drop the exhaust all the way down to 1.55 next time I run some tests. So there are a couple of more variable to be tossed into the punch bowl.
I'll go back to what I said earlier in this thread: I believe the subject is too complicated for anyone to fully understand. You can make plenty of power with either type of cam. If you have the money and time for testing then you can start to optimize around your specific combination. You can continue to optimize until you run out of money.
Posted By: Streetwize
Re: straight vs. split pattern cams - 12/18/10 11:36 PM
The question I always ask people when they say they're exhaust needs to be bigger....I say realtive to what?....maybe the intake is too small to begin with!!
Posted By: emarine01
Re: straight vs. split pattern cams - 12/18/10 11:40 PM
As this post gets kicked around, useful info pops up, Sure every statement does not apply for all & everything but one can pick thru it and see what fits, It is to bad that jeff pulled his reply, I didnt see it also
Posted By: Pacnorthcuda
Re: straight vs. split pattern cams - 12/18/10 11:44 PM
It is interesting that the big power-adders (Supercharging, Turbocharging, and NOS) all work on the principle of packing more oxygen into the combustion chamber. Turbo even does it at the detriment of exhaust flow, yet a big percentage of performance cams favor the exhaust side...
Posted By: Sport440
Re: straight vs. split pattern cams - 12/19/10 12:49 AM
I did a test one time that implied that split duration cams is not wheres its at for improved performance.
In short the split duration cam had More favored lift and 5* more duration on the exhaust then the single pattern cam.
The only advantage the single pattern cam had was the same lift on the intake as the split cam and a measly 3* more intake duration.
In the two differences of the above two cams, while the extra lift and duration of the split cam might appear to be the winner, by far the extra 3* duration on the intake of the straight pattern cam proved it to be faster by a full .1 in the 1/8th.
IMO it shows/implies the intake flow lift and duration Rules and that throwing extra duration and lift at the exhaust further then the intakes pattern is not very productive.
It doesnt mean it cant help a tiny bit, but IMO again the intake side lift and duration is the Big Dog, the exhaust side is along for the ride.
Further theres a reason why the exhaust valve is smaller in the first place. It doesnt have to be very big to do its job. Even though the volume of the gasses are much, much, greater.
The one thing I dont like about split duration cams is that the extra lift and duration isnt needed , alls its doing is mucking up the charge on overlap with the extra degrees of overlap.
Unless that extra overlap is needed to assist with scavenging {And probably not} its a waste of extra valve movement and duration IMO, for the most part. mike
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/19/10 01:21 AM
Quote:
the exhaust side is along for the ride.
The one thing I dont like about split duration cams is that the extra lift and duration isnt needed , alls its doing is mucking up the charge on overlap with the extra degrees of overlap.
Unless that extra overlap is needed to assist with scavenging {And probably not} its a waste of extra valve movement and duration IMO, for the most part. mike
& i always figured you were a split kinda guy.
There is know answer , every cam guy has differing views & will grind two different cams for the same application , some of these guys are pretty sharp , but not sharp enough to know exactly what cam that engine wants , the fast guys spend all there time on the dyno going through hundreds of cams , it's IMPOSSIBLE to spec the perfect camshaft for a given engine period.
Posted By: Sport440
Re: straight vs. split pattern cams - 12/19/10 01:29 AM
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/19/10 02:40 AM
Quote:
It is interesting that the big power-adders (Supercharging, Turbocharging, and NOS) all work on the principle of packing more oxygen into the combustion chamber. Turbo even does it at the detriment of exhaust flow, yet a big percentage of performance cams favor the exhaust side...
Motors running nitrous want that exhaust valve opening pretty soon on power stroke to avoid overheating/detonation , hence the reason for the split........
I changed out the single for a split when i started running the bottle , basicly wanted the split pattern to behave pretty similar to the single pattern on the street , here's the two camshafts , notice overlap remains the same for the two cams as does IVC , only difference being EVO , these are the #s @ 050".
#1
270/270
112lsa
110icl
IO.25/IC.65
EO.69/EC.21
#2
270/278
114lsa
110icl
IO.25/IC.65
EO.77/EC.21
both had pretty similar street manners.
Posted By: HotRodDave
Re: straight vs. split pattern cams - 12/19/10 06:47 AM
Supers and Nitrous are artificially putting more gasses in the chamber even if the intake lobe was the same as a NA motor, therefor they need more exhaust opening to expell the gasses that are much greater than the motor was expelling NA.
Posted By: Fishmarket
Re: straight vs. split pattern cams - 12/19/10 03:57 PM
Let me pose this question a little differently...
What would be the result of using a cam with more exhaust duration than was necessary? Obviously, we would have a bit more overlap and contaminated charge but how would the engine react?
Posted By: Locomotion
Re: straight vs. split pattern cams - 12/19/10 04:51 PM
Quote:
Let me pose this question a little differently...
What would be the result of using a cam with more exhaust duration than was necessary? Obviously, we would have a bit more overlap and contaminated charge but how would the engine react?
I'm curious also.
I have heard that certain heads with very good flowing exhaust ports (compared to exhaust) can over-scavenge the cylinder and actually suck a lot of the intake charge into the header, where it continues to burn and overheat the pipes. With some of the intake charge lost, power would be down.
Perhaps over-camming the exhaust would do the same.
Posted By: Tig
Re: straight vs. split pattern cams - 12/19/10 05:47 PM
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It is interesting that the big power-adders (Supercharging, Turbocharging, and NOS) all work on the principle of packing more oxygen into the combustion chamber. Turbo even does it at the detriment of exhaust flow, yet a big percentage of performance cams favor the exhaust side...
Motors running nitrous want that exhaust valve opening pretty soon on power stroke to avoid overheating/detonation , hence the reason for the split........
I changed out the single for a split when i started running the bottle , basicly wanted the split pattern to behave pretty similar to the single pattern on the street , here's the two camshafts , notice overlap remains the same for the two cams as does IVC , only difference being EVO , these are the #s @ 050".
#1
270/270
112lsa
110icl
IO.25/IC.65
EO.69/EC.21
#2
270/278
114lsa
110icl
IO.25/IC.65
EO.77/EC.21
both had pretty similar street manners.
Hey Ad How did they compare at the track? on and off the bottle?
On a side note, the vast majority of cams that Indy Cylinder Head supplies / recommends are split pattern. Whilst these guys may not be the easiest to speak to over the phone, I'd bet they've used some dyno time trying different types of cams and maybe found whats best for Indy heads. Sorta tells me something
Posted By: emarine01
Re: straight vs. split pattern cams - 12/19/10 06:49 PM
Does anyone want to take a stab @ the relationship between stroke and rod ratio <long vs short> as to the effects on split cam duration & lca, addressing the fast piston speed coming off tdc intake and the BDC to 90 on the exhaust stroke, I know 602 hev started to touch on this on a earlier post but can some one walk all the way thru it?
Posted By: BradH
Re: straight vs. split pattern cams - 12/19/10 07:12 PM
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I have heard that certain heads with very good flowing exhaust ports (compared to exhaust) can over-scavenge the cylinder and actually suck a lot of the intake charge into the header, where it continues to burn and overheat the pipes. With some of the intake charge lost, power would be down.
Perhaps over-camming the exhaust would do the same.
Absolutely. Even if the engine doesn't suffer a hit in the power department, it impacts fuel efficiency.
Posted By: Brian Hafliger
Re: straight vs. split pattern cams - 12/19/10 07:41 PM
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I spent a bunch of money dyno testing camshafts on my 470 low deck motor. It had exhaust manifolds and lots of people told me that I would need extra duration on the exhaust side to compensate for the manifolds. Turns out that the very best camshaft for that engine was the old school Mopar .528 solid flat tappet.
I suppose if I was given unlimted funds I could find a camshaft that was even better than the .528. And perhaps, after hunreds of dyno pulls the very best cam might well be a split pattern cam. But I called it quits after spending a couple of grand on cams and dyno time.
As far as I know, nobody knows the answer to this question. It is fairly easy to get a 90% correct answer to the question, but I don't think anyone has ever really figured it all out. If they had, then there wouldn't be any need for all of the dyno testing that goes on every day at all of the engine shops around the world.
Wish you would have tried a cam from me...I would love to participate next time maybe...
Brian
Posted By: blownzoom440
Re: straight vs. split pattern cams - 12/19/10 07:44 PM
wondering how effective the engine builder programs are in this case.
Posted By: Brian Hafliger
Re: straight vs. split pattern cams - 12/19/10 07:52 PM
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Let me pose this question a little differently...
What would be the result of using a cam with more exhaust duration than was necessary? Obviously, we would have a bit more overlap and contaminated charge but how would the engine react?
I can tell you Comp's thumpr line of cams make great power, wide powerbands and work with low and high compression. The have at least 18° more duration on the ex. side advertised, then at .050 it gets closer to the intake side, and by .200 they are almost equal. This works really well with the tight lsa and recommended 5° advance.
Big Joe thinks it's the tight lsa that makes the power but I think it's a combination of tight lsa, 5° advance, and smooth long lazy exhaust lobe.
And they sound nasty.
You know, there is not a single man or company that has it all figured out to the point where they can spec the PERFECT cam for an engine without some type of compromise. This could be debated for ever and ever...and probably will be...LOL!!!!!
Posted By: Pacnorthcuda
Re: straight vs. split pattern cams - 12/19/10 07:56 PM
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You know, there is not a single man or company that has it all figured out to the point where they can spec the PERFECT cam for an engine without some type of compromise. This could be debated for ever and ever...and probably will be...LOL!!!!!
Yep--fixed cams are always a compromise. Well, except for applications where an engine operates at a steady rpm and load performing some sort of work.
Thats why variable valve timing has so much potential! V-tec etc.
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/20/10 02:23 AM
How many times do you here guys on here telling others to advance the heck out of the off the shelf MP grinds? , the one's i'm talking about are the single pattern grinds , why would you want to advance more than MP recommends? , one reason maybe the cam is too big for the application? , another reason is maybe some guy fitted this cam & it ran like a dog on his combo? , maybe another guy found he picked up some advancing intake centre line? , what does all this tell you? , THE CAMSHAFT IS WRONG FOR THE APPLICATION , any time a camshaft has to be advanced more than 4 degrees from straight up then go look for another camshaft , most guys on here who found power by advancing ICL are street guys , this gets back to my earlier post of contaminated intake charge , no way that motor picked up any power going 8 degrees advanced , only benefit would be seat of the pants , mostly being idle characteristics/part to mid throttle , any torque gained down low would be killed off up top.
All you guys running excessive advance maybe go get another cam , will certainly pick up on the big end.
Ever wondered why intake cenreline has to be advanced 4 degrees on most all off the shelf grinds?.............chain stretch is poor excuse , gear wear being another poor excuse , anyone wanna touch on the real reason?.......sifting through some of these posts might give a clue.
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/20/10 02:36 AM
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On a side note, the vast majority of cams that Indy Cylinder Head supplies / recommends are split pattern. Whilst these guys may not be the easiest to speak to over the phone, I'd bet they've used some dyno time trying different types of cams and maybe found whats best for Indy heads. Sorta tells me something
Hi Tig , maybe you can ask Indy the reason for going split with their heads next time you speak to them , my bet is they don't know.
Posted By: Brian Hafliger
Re: straight vs. split pattern cams - 12/20/10 03:19 AM
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How many times do you here guys on here telling others to advance the heck out of the off the shelf MP grinds? , the one's i'm talking about are the single pattern grinds , why would you want to advance more than MP recommends? , one reason maybe the cam is too big for the application? , another reason is maybe some guy fitted this cam & it ran like a dog on his combo? , maybe another guy found he picked up some advancing intake centre line? , what does all this tell you? , THE CAMSHAFT IS WRONG FOR THE APPLICATION , any time a camshaft has to be advanced more than 4 degrees from straight up then go look for another camshaft , most guys on here who found power by advancing ICL are street guys , this gets back to my earlier post of contaminated intake charge , no way that motor picked up any power going 8 degrees advanced , only benefit would be seat of the pants , mostly being idle characteristics/part to mid throttle , any torque gained down low would be killed off up top.
All you guys running excessive advance maybe go get another cam , will certainly pick up on the big end.
Ever wondered why intake cenreline has to be advanced 4 degrees on most all off the shelf grinds?.............chain stretch is poor excuse , gear wear being another poor excuse , anyone wanna touch on the real reason?
You need to talk with some of the guys in the EM Challenge...they will change your mind about how much of a tuning tool a camshaft can be.
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/20/10 03:30 AM
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You need to talk with some of the guys in the EM Challenge...they will change your mind about how much of a tuning tool a camshaft can be.
I could'nt agree more , but these guys are trying to wring out every ounce of power & don't mind pulling the motor appart to get there , most guys on here wanna fit & forget , how much power are they leaving on the table?
Posted By: Brian Hafliger
Re: straight vs. split pattern cams - 12/20/10 03:46 AM
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You need to talk with some of the guys in the EM Challenge...they will change your mind about how much of a tuning tool a camshaft can be.
I could'nt agree more , but these guys are trying to wring out every ounce of power & don't mind pulling the motor appart to get there , most guys on here wanna fit & forget , how much power are they leaving on the table?
IMO it's the engine builders job to pick a cam that will best work with the engine they are building for their customer.
Now for the do-it-yourself'er who likes to pick his own cam, they may get lucky or they may pick a dog for a cam. It's like porting your own heads...you can do good or bad...it can go either way.
I have talked with alot of cam grinders...cam designers and engineers about cam characteristics so I can get a feel for how the lobes will work in an engine but I never let them pick it for me.
And yeah I've seen some guys pick their cams and do real well....I think more time should be spent on making the CAR work rather than the "perfect cam" or "ported head" or whatever. We race cars not engines. When you go to the races and see cars with alot of money in them and can't 60ft. their way out of a paper bag it makes you wonder why they don't research the CAR more...it took me a while to get my car to 60ft. and believe me I wanted to turn to the engine everytime I got frustrated but I just kept saying if stockers can 60ft. with less than 500HP then so can my car.
And now it does!!
Oh did I get off of the subject....ha ha!!
Brian
Posted By: Tig
Re: straight vs. split pattern cams - 12/20/10 07:10 PM
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On a side note, the vast majority of cams that Indy Cylinder Head supplies / recommends are split pattern. Whilst these guys may not be the easiest to speak to over the phone, I'd bet they've used some dyno time trying different types of cams and maybe found whats best for Indy heads. Sorta tells me something
Hi Tig , maybe you can ask Indy the reason for going split with their heads next time you speak to them , my bet is they don't know.
As long as they know from results that they worked best for those heads then that will do for me
FWIW this cam 320 / 320, 288 / 288 @ .050 .691 when installed 4 degrees retarded (@ 112) from the recommended 108 picked up 2 tenths. We were just looking for a little more top end and it worked but what was that telling us?
Posted By: moparniac
Re: straight vs. split pattern cams - 12/20/10 07:27 PM
My desktop dyno says my new split cam makes more power
Posted By: Streetwize
Re: straight vs. split pattern cams - 12/20/10 07:34 PM
Some of the EM combos run very big intake lobes and advance the heck out of them to maximize (use up) the airflow potential of the heads by the 6500 rpm Cap set by the rules...Bishoff's 433" CHI headed Ford had a 106 split in at like 100 as I remember and Kasse built a motor that had (IIRC) a 98 degree ICL...and these guys have access to anything they want.
It's an over generization to say that advancing a cam to work well means you have the wrong cam....in an overported motor it can be great way to fill the holes well and still keep the Intake closing 'streetable'. an 8 degree larger intake lobe in 4 degrees earlier will have the same closing event, so if sized right for the port and as long as the roll on torque is sufficient down low it will probably make more top end power...won't it?
Ultradyne has ground tons of 108 spread cams that went in at 102 for years and years
It's dangerous and misleading to do more than generalize, all cams are application specific and more than 1/2 of the things I've learned that worked well or better for YEARS (particularly with strokers) seemed counter-intuitive to many 'experts'....but in recent years much of what has been flushed out of these jaw dropping engine-masters contests has made me feel a lot more open about talking about them.
Lobe spread and durations with a typical pushrod single cam motor are always at best a trade off....you have to give somewthing somewhere to get more somewhere else....and as correctly pointed out with a race app in a way it's easier because the clutch/cionverter and gearing can side step over the low efficency parts of the curve....in that respect a ture street motor is a lot more difficult to get as right as possible. Ask yourselves why have all the major auto companies spent umpteen millions develop their own forms of Variable cam timing (VTEC effects lift AND durations) and variable lobe spread tuning technology over the years? To improve VE across the powerband and make more power and/or torque with less cubes.
Posted By: 602heavy
Re: straight vs. split pattern cams - 12/20/10 11:43 PM
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FWIW this cam 320 / 320, 288 / 288 @ .050 .691 when installed 4 degrees retarded (@ 112) from the recommended 108 picked up 2 tenths. We were just looking for a little more top end and it worked but what was that telling us?
......could be one of four thing....or maybe two of four things........heck it could be all of the four differing valve events.
just messing , would'nt like to speculate. ........would take a bet idle was lumpy.
Posted By: dvw
Re: straight vs. split pattern cams - 12/21/10 04:04 AM
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FWIW this cam 320 / 320, 288 / 288 @ .050 .691 when installed 4 degrees retarded (@ 112) from the recommended 108 picked up 2 tenths. We were just looking for a little more top end and it worked but what was that telling us?
......could be one of four thing....or maybe two of four things........heck it could be all of the four differing valve events.
just messing , would'nt like to speculate. ........would take a bet idle was lumpy.
I retarded my cam years ago with -1 heads. it picked up as well. my heads were unported. Not enough intake flow for the combo? That was my bet.
Doug