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What is the largest LSA you ever saw on a Solid roller
Posted By: turbobitt
What is the largest LSA you ever saw on a Solid roller - 12/08/09 05:51 PM
Just as the title says, What is the largest Lobe seperation angle you ever saw on a solid roller cam and why.
Looking for a general idea of what people have tried. I have a turbo powered car and looking for ideas and a general sense of the "Norm".
Allan G.
Posted By: Bob_Coomer
Re: What is the largest LSA you ever saw on a Mech roller - 12/08/09 05:57 PM
Howards has some pretty wide stuff.... Big Chevy 4/7 swap cam says...
Very large Cubic inch with big multi stage NOS systems... LOL
Cam part # 124093
it has a 118 LSA
It will never be as cool as my Silly cam though
Posted By: aarcuda
Re: What is the largest LSA you ever saw on a Mech roller - 12/08/09 06:02 PM
whats the advantage of wide LSA besides a nicer idle?
Posted By: Cab_Burge
Re: What is the largest LSA you ever saw on a Mech roller - 12/08/09 06:10 PM
The tighter LSA, 100 to 108, are suppose to increase the bottom end, up to 7000 RPM depending on who you talk to. The flip side of that thinking is the wider LSA will cost you bottom end but pick up the upper RPM, above 5000 RPM or even above 7000 RPM
Posted By: rtstreet
Re: What is the largest LSA you ever saw on a Mech roller - 12/08/09 06:11 PM
118
Posted By: blowndart
Re: What is the largest LSA you ever saw on a Mech roll - 12/08/09 06:16 PM
Quote:
whats the advantage of wide LSA besides a nicer idle?
Less overlap. Overlap on a turbo engine is a bad thing that leads to reversion if the pressure in the exhaust is high. Wide LSAs are desirable on turbo engines. I was kinda wondering the same thing with respect to widest LAS seen on a roller cam.
Posted By: AndyF
Re: What is the largest LSA you ever saw on a Mech roller - 12/08/09 06:37 PM
Pro Stock guys run really wide centers. 117 is common but they go on up to 120+ depending on the combination.
If you're wondering about the core avaiability then you just need to call around. There is going to be a limit to what you can put on the standard cores but with a billet cam you can do anything you want.
Posted By: sshemi
Re: What is the largest LSA you ever saw on a Mech roller - 12/08/09 06:46 PM
Quote:
whats the advantage of wide LSA besides a nicer idle?
it gives a broader powerband
Posted By: mbogina
Re: What is the largest LSA you ever saw on a Mech roll - 12/08/09 06:50 PM
A wide LSA does not affect the idle quality, the idle quality improves because of the reduction in overlap. The engine does not know or care what the LSA is, only the opening and closing events of the camshaft. You can adjust the overlap using the Intake duration, the Exhaust duration, the LSA, or all of the above in combination. Increasing LSA by 2 degrees reduces the overlap by 4 degrees total, but also moves every other timing event for the cam. The optimum overlap for any particular combo will "start" the drawdown of clean air on the intake stroke and "clean" the chamber of all residual exhaust gases on the exhuast stroke. Too much overlap leads to reversion, lazy throttle response, low dynamic compression, poor idle. Too little overlap sacrifices mid range torque and increases the sensitivity to detonation.
Posted By: moderncylinder
Re: What is the largest LSA you ever saw on a Mech roll - 12/08/09 07:07 PM
what mike said
it always bothers me when guys start talking like wide lobe centers is high rpm, or for this motor only, or that motor,, the lobe sep is the distance between the lobes, doesnt tell you how much overlap you have,, or when you open and close the valves,,, which those are the parameteres that dictate where it all happens..
example,, im making this up as i type...
open/close @.050, duration, center
non-turbo/nat aspirated
int 32/68, 280, 108
exh 78/30, 288, 114
sep 111
overlap 62
turbo/nitrous
int 22/68, 270, 113
exh 78/20, 278, 119
sep 116
overlap 42
i didnt change the int close point just for reference though in a turbo you would,, but not in a nos application
int 22/64, 266, 111
exh 84/20, 284, 122
sep 116
overlap 42
i changed the closing point on the int cause you have boost to fill the cylinder better in the intake stroke so you dont have to leave the valve open aslong in the comp stroke, though it depends on rpm, cid, and port area. i changed the exh open point cause you have more volume in the cyl in compression due to boost so there is more cyl pressure which leads to quicker/more effecient combustion, therefore gases will ne burnt quicker so you can open the valve a lil earlier..
pro stock
int 28/72, 280, 112
exh 90/26, 296, 122
sep 117
overlap 54
Posted By: turbobitt
Re: What is the largest LSA you ever saw on a Mech roll - 12/08/09 07:19 PM
My line of questioning is because of my turbo application. I know that turbo applications have backpressure and as a result, will have no exhaust scavanging effect. I'm assuming that the LSA will depend on the duration of the cam to minimize overlap to some degree.
Another thing I would like to know if there is a noticable turbo spool-up difference with wider then normal LSA's. Example, if my cam is ground @ 113 LSA, what would the gains/losses be to a 115 LSA. How much is to much ?
Posted By: mbogina
Re: What is the largest LSA you ever saw on a Mech roll - 12/08/09 08:04 PM
Too much is when you have reached the limits of the available cam cores, cores are only hardened to a depth of around .060, which limits the lobe lift, duration and LSA on that particular core. A billet core does not have the same limitations, so by playing with a little math you can go just about anywhere. Using Jeff's example above, a 266-284-116 has an overlap of 43 and when installed at 111 yields an IO 22, IC 64, EC 21 EO 83. By using the same lobes and increasing the LSA to 118, now you have 39 overlap, IO22 IC64 EC17 EO87. If you wished to keep the overlap constant but widen the LSA, the 266-284-116-43 could become a 270-288-118-43, or even a 274-292-120-43. The hard answer is to use whatever LSA suites the desired opening and closing numbers. Your cam grinder will advise you if your numbers will not fit his available core choices.
Posted By: mr_340
Re: What is the largest LSA you ever saw on a Mech roll - 12/08/09 10:18 PM
I've been over this with Mike before. Yes, the engine does see the opening and closing events, but to me either way you have four variables.
IO, IC, EO, EC
or
Int Dur, Exh Dur, LSA, adv/ret
Maybe it's easier to think about using Mike's preference. To me the cams are ground using the other parameters and that's what they give you in the catalogs. Maybe I'm more used to think of them in that way and haven't moved on to Mike's way?
In 1998, I attended the SAE Motorsports Conference in Dearborn and they had a paper on restrictor plate engines in NASCAR. They were using LSAs in the 122 degree range.
Sidebar - why do people like to put a period in front of the duration number? i.e. .286 duration. This started about ten years ago in magazines and it's plain wrong in my book. What, just over 1/4 degree of duration? I'd like to see that cam lobe. It would look like a stick on a round bar.
Posted By: Locomotion
Re: What is the largest LSA you ever saw on a Mech roll - 12/08/09 11:54 PM
Quote:
Sidebar - why do people like to put a period in front of the duration number? i.e. .286 duration. This started about ten years ago in magazines and it's plain wrong in my book. What, just over 1/4 degree of duration? I'd like to see that cam lobe. It would look like a stick on a round bar.
lol
Since there isn't a "degree" key on the keyboard, I like to use the "asterick". I.E.: 263* @ .050"
Posted By: S/ST 3040
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 01:11 AM
263º @ .050"
Good tech stuff.
Posted By: Leon441
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 01:12 AM
I liked the 118 LSA. IT ran so much better than the 115 LSA. All the durations were the same. I fealt I could loose some intake but did not want to sacrifice the exhaust duration. Cam motion then ground me a 120 LSA but the Billet core had reached it limits and they suggested cutting the exhaust duration sense they fealt it was overkill. Well that cam hurt the performance.
This was a large displacement designed to kill small block.
My NA engine runs a large LSA and I feel that it hurts the performance. But, on the dyno we found engine performance is not the problem.
Leon
Posted By: Dos Snails
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 01:41 AM
Posted By: 602heavy
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 03:24 AM
Quote:
what mike said
it always bothers me when guys start talking like wide lobe centers is high rpm, or for this motor only, or that motor,, the lobe sep is the distance between the lobes, doesnt tell you how much overlap you have,, or when you open and close the valves,,, which those are the parameteres that dictate where it all happens..
, been here not so long ago.
Great post , well written. 
Posted By: Sport440
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 04:31 AM
Quote:
A wide LSA does not affect the idle quality, the idle quality improves because of the reduction in overlap. The engine does not know or care what the LSA is, only the opening and closing events of the camshaft. You can adjust the overlap using the Intake duration, the Exhaust duration, the LSA, or all of the above in combination. Increasing LSA by 2 degrees reduces the overlap by 4 degrees total, but also moves every other timing event for the cam. The optimum overlap for any particular combo will "start" the drawdown of clean air on the intake stroke and "clean" the chamber of all residual exhaust gases on the exhuast stroke. Too much overlap leads to reversion, lazy throttle response, low dynamic compression, poor idle. Too little overlap sacrifices mid range torque and increases the sensitivity to detonation.
Your response is Both True and False! Lobe Sep, Duration, and installed Centerline work together to move all those opening and closing events around that effect Desired performance.
So a Engine Will care what its "lobe sep" is, combined with its "Duration events".
LS and Dur. makes overlap a fixed number.
Change Either one, and you Can change a engines Idle characteristics.
ICL moves that overlap point forward or back from the TDC point of the piston between the Exhaust and Intake cycle of the piston.
So a engine will also care abouts its ICL too.
One thing you are Very correct about is the overlap part.
That is a Very important part of the combo. It will have a great effect. Its the Scavenging or Reversion part of the Combo. Its the 5th. stroke, of a 4 stroke motor.
Get it wrong and you can have a less then optimized motor for its set up. NA,Turbo,Blown,Nitrous,ETC. Get it Right
Okay, what was I talking about! I was just making this up as i type.
One thing I know that we All can agree on is that
Valve Events are Effected by Lobe sep, Duration, and moved about TDC on the overlap cycle by Installed Intake centerline. And BDC with same said valve events mike
Posted By: 602heavy
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 11:47 AM
Overlap should be figured @ seat duration not .050" , which confirms the point IVO/EVC are two important events if the cylinder is to be swept clean of spent gasses ready for the incoming charge of air/fuel , the other two important valve events are IVC/EVO , ex valve opening @ seat duration will determine power/heat & blowdown , intake closure @ seat duration will determine dynamic compression & cyl fill , from these events ICL is determined , moving these OPTIMUM valve events around for a particular lobe seperation angle would be a pointless excercise , correct lobe sep had already fallen into place.
Posted By: mbogina
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 01:36 PM
I concur with 602heavy on this, but to beat it down just a little more....using Leon's example that his 118 LSA ran better than the 115 LSA, Leon stated that he kept the durations the same. Examining what happened to the valve events by doing so, and assuming that both were degreed in similarly, with the 118 LSA, the IVO is delayed 3*, the IVC delayed 3*, the EVC delayed 3*, the EXO closes 3* later, the overlap is reduced by 6*, so what appears to be a simple change is actually a completely different cam with unpredictable results- he delayed opening the intake valve, closed it later, opened the exhaust later and held it open later, plus reduced the overlap by a large amount- the question arises- which valve events helped the motor, which hurt the motor, could he have increased power even more by changing only 2 of the events instead of 5? How about 3 events? When I am testing SS camshafts, we only change 1 event at a time, so we can truly see the result of that change. For example, if we had a cam that was 280-280-108, installed at 104, we have timing events of IVO36 IVC64 EVC28 EVO 72, overlap 64. If we wanted to determine whether the motor combo would respond the closing the intake valve 4* sooner, this would require a cam that is 276-280-107, which sounds completely different, but has events that are IVO36 IVC60 EVC28 EVO72, overlap 64, so the only change was the intake closing point, allowing more time for the cylinder to compression the mixture.
Posted By: S/ST 3040
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 01:57 PM
I can see how that detailed testing would be very informitive AND expensive but, by
only changing the IC event, you also shortened the intake lobe by 4º to do it.
To me, that seems to detract from the "one event change" data.
Again, great topic.
Posted By: mbogina
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 02:11 PM
Sorry to keep beating this, but my point is that the motor ONLY knows the events, IVO, IVC, EVC, EVO, overlap, the numbers used for duration and LSA are just the tools and method to get to the events. Yes, by moving the intake closing point I reduced the duration, but the motor doesn't care what the duration is, only when I opened and closed the valve. The intake opening point determines how soon before TDC the flow starts, the intake closing point determines how long you left the valve open for cylinder filling and how long the piston has to compress the mixture. The exhaust closing determines the length of the overlap period, which cleans the cylinder of residual gasses and readies it for a new charge, the exhaust opening point determines when the blowdown of the cylinder starts to push the exhaust gasses out the exhaust port.
Posted By: S/ST 3040
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 02:17 PM
It makes sense. I guess I'll have to start looking at camshafts in a different
way. Too bad I don't have 30 cams and a dyno to know what it all means.
Posted By: RAT PATROL
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 03:22 PM
I'm not sure what it all means either, but I did try advancing my cam 4 and the results were 60'=same, MPH=slowed 2.5, ET= slowed .2 The big Hemi didn't like it at all so I put it back where it was 298 duration 108 LSA @ 111 centerline.
Posted By: maximum entropy
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 04:01 PM
Quote:
Too much overlap leads to reversion, lazy throttle response, low dynamic compression, poor idle. Too little overlap sacrifices mid range torque and increases the sensitivity to detonation.
more overlap can improve throttle response, and increases dynamic compression if the overlap increase was realized by way of lsa reduction. the old man always (always) told me, " it's all about when the intake valve closes." lsa increase will flatten the power band and reduce dynamic c/r, lowering cylinder pressure, and making the engine more resistant to detonation (in an appropriate combination).
Posted By: moderncylinder
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 04:10 PM
mr rat patrol,, for you your engine probably wanted the intake valve open longer/later so it didnt like to be advanced. most of the time the intake closing is the "trump" event.
the guy who started this post said earlier,, he wanted to "hit his turbo" harder,, therefore he wanted a wide lobe sep,, when really what he would want is an early exh open, then there is more pressure in the cylinder when the valve is opened therefore charging the turbo with more pressure, but if you do not have enough cylinder pressure to combust fuel effeciently in a short period of time you will loose power in doing so,, but im not a turbo guy..
really all lobe sep does is give you the distance between peak lifts from intake to exh
overlap should be measured at .020 tappet lift for solid rollers,, thats why my example above had an earlier int opening, that the exh closing,, usually its a 2 degree stagger to make up for the difference in ramp rate between them,, exh being slower than the intake. there can be exceptions to this, but its withiin a degree or two dependning on flow characteristics at overlap, port areas, valve sizes...
Posted By: turbobitt
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 04:55 PM
Quote:
mr rat patrol,, for you your engine probably wanted the intake valve open longer/later so it didnt like to be advanced. most of the time the intake closing is the "trump" event.
the guy who started this post said earlier,, he wanted to "hit his turbo" harder,, therefore he wanted a wide lobe sep,, when really what he would want is an early exh open, then there is more pressure in the cylinder when the valve is opened therefore charging the turbo with more pressure, but if you do not have enough cylinder pressure to combust fuel effeciently in a short period of time you will loose power in doing so,, but im not a turbo guy..
really all lobe sep does is give you the distance between peak lifts from intake to exh
overlap should be measured at .020 tappet lift for solid rollers,, thats why my example above had an earlier int opening, that the exh closing,, usually its a 2 degree stagger to make up for the difference in ramp rate between them,, exh being slower than the intake. there can be exceptions to this, but its withiin a degree or two dependning on flow characteristics at overlap, port areas, valve sizes...
My thought in regards to the turbo question is to close the exhaust valve at a given point to reduce reversion. This point is probably the most critical point in the cam. Everything else seems like it would be driven from here. To keep overlap at a minimum(at a given duration), I would theorize that the LSA would need to be determined next. Then the intake event timing would be a result of the Exhaust timing and LSA.
I'm just thinking out load and of course related to Turbo cams.
This is good discussion, Keep it going.
Allan G.
Posted By: joshking440
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 06:22 PM
I have a 500" turbo deal and my cam is 114 lsa with .715 lift and .248 duration @.050
Posted By: FlyFish
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 06:35 PM
Quote:
Quote:
Sidebar - why do people like to put a period in front of the duration number? i.e. .286 duration. This started about ten years ago in magazines and it's plain wrong in my book. What, just over 1/4 degree of duration? I'd like to see that cam lobe. It would look like a stick on a round bar.
lol
Since there isn't a "degree" key on the keyboard, I like to use the "asterick". I.E.: 263* @ .050"
Hold down Alt and press 0176, then release...it should give you the degree symbol °. ...and back to the topic at hand!
Posted By: S/ST 3040
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 06:39 PM
It's 0186.
Posted By: mr_340
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 06:57 PM
I use ALt+248 on a keyboard with a keypad. I can't make it work using the number keys at the top of the keyboard. I made a MS-Word document with some symbols I use frequently in engineering (we use Greek symbols a lot). See attachment.
Posted By: FlyFish
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 07:03 PM
Quote:
It's 0186.
Neat-o, that works too only its a little lower on the screen º°º°
Posted By: Tig
Re: What is the largest LSA you ever saw on a Mech roller - 12/09/09 07:25 PM
About 80ft
(7000rpm SB Chebbie that probably went 8000rpm, York Dragway may '95)
Posted By: 602heavy
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 08:02 PM
Quote:
I'm not sure what it all means either, but I did try advancing my cam 4 and the results were 60'=same, MPH=slowed 2.5, ET= slowed .2 The big Hemi didn't like it at all so I put it back where it was 298 duration 108 LSA @ 111 centerline.
If solid maybe tighten the lash & see if it picks up , going by you're results maybe the motor wants a larger cam , or maybe you just messed up optimum valve events.
Posted By: mbogina
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 09:05 PM
It makes sense. I guess I'll have to start looking at camshafts in a different
way. Too bad I don't have 30 cams and a dyno to know what it all means.
This brings to mind a NASCAR story. Supposedly Roush was testing NASCAR cams, when asked what they were testing- the reply was "all of them". they supposedly tested all combos of the valve events within a certain range of duration and LSA, in 1 degree increments. The story goes that they had several 55 gallon barrells of cams. Of course, Roush also has over 20 dyno's, so I guess they were busy for awhile.
Posted By: Mills
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 09:21 PM
Quote:
Quote:
Too much overlap leads to reversion, lazy throttle response, low dynamic compression, poor idle. Too little overlap sacrifices mid range torque and increases the sensitivity to detonation.
more overlap can improve throttle response, and increases dynamic compression if the overlap increase was realized by way of lsa reduction. the old man always (always) told me, " it's all about when the intake valve closes." lsa increase will flatten the power band and reduce dynamic c/r, lowering cylinder pressure, and making the engine more resistant to detonation (in an appropriate combination).
He had the Overlap info incorrect. A tight LSA will have a higher cranking compression
Posted By: Sport440
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 10:23 PM
The engine Absolutely sees the results of LSA, because that moves around the Valve Events.
Its been tested over and over and well documented over the last 50 years.
LSA can be used to Tailor your valve events.
But LSA works hand in hand with duration and overlap. As the duration increases so does overlap, that can be adjusted by Picking a Different LSA.
Leons Example just showed a example of what LSA Changes can do.
Ive Tested it my self, With the same duration LSA changes makes a Difference that You and Your engine will notice.
Knowledge learned from history shouldnt have to be relearned over and over again. But if needs to,
Its fine. mike
Posted By: moderncylinder
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 10:50 PM
no knowledge that needs to be relearned here....mills said above that a tight lsa cam will have higher cranking comp,, thats not true in all cases,,, closing the intake valev earlier will make more pressure...
when "smart" people pick cams they look where they want the four events to occur,,, then figure the durations and seperation from there,, not think they will run it high or low and determine a lsa befroe they even think of the actual events... thats all me and i think mike were saying
Posted By: 602heavy
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 10:54 PM
Sport 440 , i'm gonna have to start agreeing with you soon.
Posted By: mr_340
Re: What is the largest LSA you ever saw on a Mech roll - 12/09/09 11:48 PM
Quote:
when "smart" people pick cams they look where they want the four events to occur,,, then figure the durations and seperation from there.
Jeff, I don't think that is smart as much as someone with experience. I like to think I'm relatively smart, but don't have the experience with race engines like you and Mike have. Once you've tested cams over the years, you would develop a feel for what the engine wants. For me, I'm on the beginning side of the learning curve for SS type engines. For me it's more about planning a test of cams to get where you guys are already. My DOE software can test it either way, using the opening and closing events, or durations and LSA. Reducing the number of variables to three vs. four makes the need for half as many cams to test. Advancing and retarding the cam saves that over than grinding specific cams with specific event points. Using a two-factor DOE, it only takes eight cams vs. 16 for the methods you guys use. My plan is to use lash changes to adjust durations and that just leaves LSAs to change as a screening test. I'm thinking three cams with LSAs of 108, 110 and 112 should give me a pretty good idea of what I will need if I start pretty close to the right starting point (285* on the Hemi). Keep the lobes the same on all cams, just change the LSAs. Feel free to tell me why it won't work if you can understand my methods. 
Posted By: 602heavy
Re: What is the largest LSA you ever saw on a Mech roll - 12/10/09 12:09 AM
Quote:
A tight LSA will have a higher cranking compression
That's not always the case , take a look @ two totally different cams , one ground on a 112LSA the other ground on a 106LSA , they both have the same cranking compression...............
IO-28-IC-60--duration 268--ICL 106.
EO-76-EC-20--duration 276--ICL 118.
Lobe sep 112.
IO-28-IC-60-duration 268--ICL 106.
EO-64-EC-32-duration 276--ICL 106.
Lobe sep 106.
An interesting discussion , thanks.
Posted By: mr_340
Re: What is the largest LSA you ever saw on a Mech roll - 12/10/09 12:44 AM
I'm thinking the intake closing (and to a lesser extent, the opening event) are the same for both cams. I would expect the cranking compression to be the same. It would be interesting to see them both on a dyno to compare the torque curves. I wouldn't call that a "totally different" cam, just different LSA.
Posted By: S/ST 3040
Re: What is the largest LSA you ever saw on a Mech roll - 12/10/09 12:49 AM
It would be a big difference on a 340 though.
Posted By: Chris'sBarracuda
Re: What is the largest LSA you ever saw on a Mech roll - 12/10/09 01:13 AM
Tech Archives?...
Chris..
Posted By: polyspheric
Re: What is the largest LSA you ever saw on a Mech roller - 12/10/09 06:04 PM
I'm not really satisfied that event locations (IVC, etc.) are anything more than markers established after the fact, and are faux science as predictors.
The engine cannot see any part of the valve train, including the valve.
What does it see?
Pressure differentials (is the door open or not, and which way is the traffic going - not what the door looks like, or how big it is):
IVO = vacuum begins
IVC = flow reversal point
XVO = residual combustion pressure (balanced against pumping loss)
XVC = after the wave return has peaked
The sole purpose of the position of each event is to anticipate when this pressure change will occur (or reach an acceptable level such as EVO), and if the cam gets it wrong you have no power. Opening the door to no traffic (.800" lift and no vacuum) does nothing. Leaving the door open after traffic starts moving the other way is worse.
A prediction of where X" Hg. will occur in degrees based on a cam card is not going to work, except as a coincidence.
Posted By: DakFink
Re: What is the largest LSA you ever saw on a Mech roll - 12/11/09 07:27 AM
Quote:
I'm not really satisfied that event locations (IVC, etc.) are anything more than markers established after the fact, and are faux science as predictors.
The engine cannot see any part of the valve train, including the valve.
What does it see?
Pressure differentials (is the door open or not, and which way is the traffic going - not what the door looks like, or how big it is):
IVO = vacuum begins
IVC = flow reversal point
XVO = residual combustion pressure (balanced against pumping loss)
XVC = after the wave return has peaked
The sole purpose of the position of each event is to anticipate when this pressure change will occur (or reach an acceptable level such as EVO), and if the cam gets it wrong you have no power. Opening the door to no traffic (.800" lift and no vacuum) does nothing. Leaving the door open after traffic starts moving the other way is worse.
A prediction of where X" Hg. will occur in degrees based on a cam card is not going to work, except as a coincidence.
I see a lot of NO NO NO, so tell us some Yes Yes Yes because I am way confused. Especially on your comment that an engine doesn't see the Valves???
From my limited experience you run too small of a valve (small door) or too big (huge Garage door) and your engine will tell you so.
Now when it comes to boost, different story. Bigger is better.
Not trying to say your wrong by no means, just trying to understand your reasoning/theory/way of thinking?
Posted By: DakFink
Re: What is the largest LSA you ever saw on a Mech roll - 12/11/09 08:57 AM
well it is good to know i can get what ever Cam I need as long as i am willing to pay for the Billet stuff. I was kind of worried about that as i am going to be running a 50mm bearing cam and MaMopars stock of Blanks is limited from my understanding. Leon gave me 2 of his cams that I think will be pretty close to what I need for a Turbo SB, BUT I want to know what my options are if they happen to be way off.
Back on subject!!I am no where close to understanding Cams by any means but what I have seen and learned over the years. You really can't talk about any Cam Spec with out mentioning the others as well.
It seems companies like Comp-Cams and others have tried to simplify Cam Terminology for those of us with simple minds by reducing the terms to Duration and LSA. In reality there is a lot more to it than that.
Even though it confuses me to no-end the bare bone basics are IVO, IVC,EVO,EVC. With those set you dictate your In & Ex Durations, In & Ex Cetnerlines and LSA numbers.
IVO
IVC = IN DUR. & IN Centerline > lsa
EVO
EVC = EX DUR. & EX Centerline > lsa
Changing any 1 of the above has it's consequences on the others. And the consequences are even great as you get farther away from the basics of IVO,IVC,EVO,EVC.
Now back to Turbo cams. Turbos tend to like a wider LSA as well as more Duration in the EX for the simple fact they like an exhaust that is forced out of the cylinder. Try to force the ex out with overlap and you'll be forcing it back into the intake.
Optimally THEORY would say you want to open the intake as soon as possible @ TDC on the Int. Stroke an hold it open as long as possible until BDC and allow BOOST to fill the cylinders. NO OVERLAP at all and also open the exhaust as soon as possible @ BDC and hold it open until the piston has reached TDC on the ex stroke.
I wouldn't even try to guess what the numbers for that kind of cam would be.
I know there are some guys using a bit more overlap than you would think on Turbo Engines for racing Just to keep the EGT down.
I'm definitely keeping my eyes open and paying attention best as I can. A lot I need to still learn before I put mine together.
Posted By: Sport440
Re: What is the largest LSA you ever saw on a Mech roll - 12/11/09 11:18 PM
Quote:
Optimally THEORY would say you want to open the intake as soon as possible @ TDC on the Int. Stroke an hold it open as long as possible until BDC and allow BOOST to fill the cylinders. NO OVERLAP at all and also open the exhaust as soon as possible @ BDC and hold it open until the piston has reached TDC on the ex stroke.
I wouldn't even try to guess what the numbers for that kind of cam would be.
I wont Guess, I'll give you the numbers on that cam. As you will see that cam would Suck 
As you described it that cam would have a
90* LSA and 180* duration seat to seat.
For .050 duration numbers you need to subtract the number of degrees it takes a cam to get to its .050 numbers. With some Typical ramps thats about 60* to 65* When Added up, Both Exhaust and Intake
Lets use 60* to for a duration advantage. The numbers for same cam at .050 are
90* LSA 120* dur.@ .050
If we move the .050 numbers to TDC and BDC then the cams specs at .050 would be
90* LSA 180* @ .050 240* seat to seat.
Im just giving you the numbers, I know you just stated in THEORY mike
Posted By: 602heavy
Re: What is the largest LSA you ever saw on a Mech roll - 12/12/09 12:28 AM
I like it , would it run?
Posted By: Sport440
Re: What is the largest LSA you ever saw on a Mech roll - 12/12/09 12:56 AM
Quote:
I like it , would it run?
Oh Yea, it would run! But She wouldnt be much of a Runner though
That cam would be a down grade from any Factory Low performance production motor. mike
Posted By: DakFink
Re: What is the largest LSA you ever saw on a Mech roll - 12/12/09 01:53 PM
Thanks MIKE!!!
Yeah I figured there was a reason!! or everyone would have already been doing it. I never really seen the numbers.
That would probably make a good grunt/trq low speed cam. But not much else.
Now correct me if I'm wrong again!! But wouldn't you really want the Cam to be the last thing in your selection of parts when building a motor?
Wouldn't you want to get your bottom end and heads and intake all worked out, then select your cam?? Let the cam bring it all together, as long as the parts were made to work together in the beginning.
This is my thoughts on it. Just seeing if anyone agrees or if I'm off in left field somewhere.
Posted By: turbobitt
Re: What is the largest LSA you ever saw on a Mech roll - 12/13/09 04:55 AM
Here is some more info to throw at you guys. My turbo cam was spec'd by Kenny Duttweiler with a 242/242 dur @ .050 W/113 LSA.
Int opens @ 8 BTDC
Int closes @ 54 ABDC
Exh opens @ 54 BBDC
Exh closes @ 8 ATDC
With the above info, it looks like there is 16 degrees overlap. It also appears that the most that I should consider advancing this cam is 4 crank degrees with a resultant intake centerline of 109 degrees. This would put the exhaust closing event @ TDC.
Assuming that there is a 1:1 relationship between boost and exhaust backpressure, and also assuming that there will be no exhaust scavenging, what are your opinions on this cam ? Advance, Retard, start with a new grind ? Add more overlap ? This cam was installed straight up @ 113 intake centerline. My ultimate goal is to enhance turbo spoolup since I'm running a large turbo. My previous performance has been 9.86 @ 137 MPH in a 3700# car with a small 76 mm turbo. Engine pulled to 7500-8000 RPM so I have room to sacrifice some top end.
Allan G.
Posted By: Sport440
Re: What is the largest LSA you ever saw on a Mech roll - 12/13/09 06:08 AM
Your cam does have 16* of overlap and is mild for the combo. With turbos IMO mild is all you need.
Advancing the cam 4* would put it at a 109* ICL, but the exhaust closing point would be 4* ATDC not at TDC as you stated. Crank * not Cam *
Your interests are Spooling up the Turbo faster, So IMO Id get a Split duration cam that opens the exhaust valve sooner before BDC Or maybe Advance the cam you have now even more then its 4* Maybe like 8* for a 105* ICL
IMO even with boost a little bit of overlap scavenging isnt a bad thing. mike
Posted By: turbobitt
Re: What is the largest LSA you ever saw on a Mech roll - 12/13/09 01:49 PM
Quote:
Advancing the cam 4* would put it at a 109* ICL, but the exhaust closing point would be 4* ATDC not at TDC as you stated. Crank * not Cam *
Yes, that is correct. Had a brain fart typing so late.
AG
