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Re: 'Myth' of Mopar lifter diameter advantage? [Re: madscientist] #2678526
07/18/19 04:37 AM
07/18/19 04:37 AM
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Sullivan, IN
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Mopar Sam Offline
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To the OP. The main reason the ford has more lift than the mopar is they have 1.6 rockers.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: madscientist] #2678537
07/18/19 06:11 AM
07/18/19 06:11 AM
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Melbourne , Australia
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Originally Posted by madscientist
Originally Posted by Diplomat360
Originally Posted by LA360
Many have already explained the larger lifter bore is an advantage and not a myth, but shelf cams are never going to push the envelope as far as acceleration etc. They are generic, high volume production camshafts, they only thing they'll tweak is the lobe separations and how the lobes are paired...

OK, fair to an extent...strangely enough somehow the Chevy and Ford grinds end up with the higher lift lobes though...presumably out of the very same lobe catalog I have here, so why isn't CompCams putting the higher lift lobes on Mopar cams???

I mean like you said:
Originally Posted by LA360
"...They are generic, high volume production camshafts, they only thing they'll tweak is the lobe separations and how the lobes are paired..."

...so what is the reason for pairing the lower lift lobes for our small block engines? Is it poor head flow? Is it bad geometry??? That's the depth of an answer I'm looking for...

Bottom line being: the "shelf cam" argument here holds no water, as I just pointed out the other guys somehow end up running those lobes...so what gives? That's really what my question is about...would you not expect any manufacturer to want to optimize their sales regardless of what engine their product goes into? Makes no sense to me to want to sell less product...after all, if more lift was a bad thing we'd all be running our stock cams! LOL





Don't confuse total lift with the lift rate of the lobe. Two seperate things. The reason all the cams for Chrysler's have low lift is the idea that the port breaks over at about .450 lift. I can make it break over much lower than that. I can also move it up, or at least flatten it out. Put an intake manifold on and it changes everything.

I run as much lift as I can get for the valve gear. I'm running (on the street) a lobe that is 281 on the seat at 255 at .050 so it's pretty close to a Comp MM lobe. With a 1.6 rocker I net about .606 at the valve. It isn't hard on parts. It will idle clean down to 700 but I don't idle it that slow. That's hard on parts. I let it idle at 1000 and it's not an issue.

As to why the manufacturer doesn't optimize lobes for a Chrysler is there is NO MONEY in it. Most guys to this day STILL buy a cam out of a catalog or worse yet, take a poll on a forum and Joe blow runs cam XXYD in his jalopy and it's the cats ass even though Joe has never done any testing. So they have to have a cam today and they buy that crap. Honestly, 98% of the guys out there won't ever know the difference.

It's economics. Simple money math. There are so many companies that will grind a custom cam with a .904 lobe on it for you there is no sense in every buying an off the shelf cam. But, you have to convince the guy on the phone why you need a faster lobe. I bought my cam from Jim at Racer Brown and before he used those lobes we had almost two hours on the phone and flow sheets plus a drawing of the cutter I used used for the valve job.


Thank you, you saved me typing a response

Shelf cams are going to be generic, the cam company will specify some basics, but they're not going to know what the intake and exhaust system comprises of etc. Results will always vary.


Alan Jones
Re: 'Myth' of Mopar lifter diameter advantage? [Re: madscientist] #2678571
07/18/19 08:09 AM
07/18/19 08:09 AM
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Originally Posted by madscientist
Originally Posted by Diplomat360
Originally Posted by LA360
Many have already explained the larger lifter bore is an advantage and not a myth, but shelf cams are never going to push the envelope as far as acceleration etc. They are generic, high volume production camshafts, they only thing they'll tweak is the lobe separations and how the lobes are paired...

OK, fair to an extent...strangely enough somehow the Chevy and Ford grinds end up with the higher lift lobes though...presumably out of the very same lobe catalog I have here, so why isn't CompCams putting the higher lift lobes on Mopar cams???

I mean like you said:
Originally Posted by LA360
"...They are generic, high volume production camshafts, they only thing they'll tweak is the lobe separations and how the lobes are paired..."

...so what is the reason for pairing the lower lift lobes for our small block engines? Is it poor head flow? Is it bad geometry??? That's the depth of an answer I'm looking for...

Bottom line being: the "shelf cam" argument here holds no water, as I just pointed out the other guys somehow end up running those lobes...so what gives? That's really what my question is about...would you not expect any manufacturer to want to optimize their sales regardless of what engine their product goes into? Makes no sense to me to want to sell less product...after all, if more lift was a bad thing we'd all be running our stock cams! LOL





Don't confuse total lift with the lift rate of the lobe. Two seperate things...............


I didn't get it, that was addressed in the first sentence of the the first reply in this thread, and its still being discussed?

Maybe somebody should have just said forget any cam change and suggest OP get 2.5:1 rockers and be in bliss with ultimate lift. laugh2

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678674
07/18/19 12:13 PM
07/18/19 12:13 PM
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Aurora, Colorado
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your comparing roller cams here, the cam lobes are likely nearly the same for each brand, with maybe a difference in roller tappet diameter and rocker ratio on the Ford.
The biggest advantage of the larger diameter lifter bore is with flat tappet lifter cams.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678689
07/18/19 12:49 PM
07/18/19 12:49 PM
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So. Burlington, Vt.
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With regards to the 3 cams listed in the OP, there are two different families of lobes in play here, with the Mopar grind using the lobes with the most area under the curve.

The Chevy and Ford cams use the same lobes, with the extra lift for the Ford coming by way of the higher OE rocker ratio.

If you look at the more “entry level” hyd roller lifters, most have .700 or .750 wheels, regardless of the lifter bore diameter.

If someone wanted to use the lobes from the Mopar grind in their Chevy or Ford build...... its no problem.
Just order it up and they’ll grind it for you.

This is not the same as having a .904 specific flat tappet profile in your Mopar, and someone wanting to use it in their Chevy.
The only way that’s going to happen is if the lifter bores are enlarged to use .904 lifters, or a mushroom style lifter with a .904 or larger foot.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678704
07/18/19 01:25 PM
07/18/19 01:25 PM
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New York
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In my above list of lift per degree: this is not the limit for the engine, or the valve, the tappet, or the lobe.
It's the limit for the pushrod and rocker arm. Harley-Davidson cams made 60 years ago had FASTER rates than anything listed - a flathead with absolutely rigid valve gear: everything is a straight column load with no extraneous vectors. A 250 lb. spring controls a 1.94" valve @ 8,000 RPM.

W/r/t roller diameter: yes a larger roller* gives faster action and greater area (1928-84 H-D rollers: .855"), but there's a penalty.
When the valve closes and the pressure on the lobe is relaxed, the lash appears under the roller. When the opening ramp comes up again, the roller has to accelerate up to speed before it rotates on its axle. Until that point it's skidding across the lobe. A larger roller has far more inertia to overcome (much more than a simple comparison of diameters), which makes this worse. The obvious cure is thinner roller "wheels" (less metal toward the axle) but I'm sure that invites crushing with those 1,000 lb. springs X 1.9:1 rocker ratio = 1,900 lbs. on the lobe. Remember your math: the locus of points in common between 2 tangent convex shapes is a line with no thickness at all.

* be very careful here: a larger roller wheel will do bad things on an inverse (concave) flank designed for a specific smaller size, and even on a conventional (convex) lobe the speed increase is not linear but varies depending on where the roller makes contact.


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Re: 'Myth' of Mopar lifter diameter advantage? [Re: polyspheric] #2678872
07/18/19 08:41 PM
07/18/19 08:41 PM
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Prospect, PA
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Originally Posted by polyspheric


W/r/t roller diameter: yes a larger roller* gives faster action and greater area (1928-84 H-D rollers: .855"), but there's a penalty.
When the valve closes and the pressure on the lobe is relaxed, the lash appears under the roller. When the opening ramp comes up again, the roller has to accelerate up to speed before it rotates on its axle. Until that point it's skidding across the lobe. A larger roller has far more inertia to overcome (much more than a simple comparison of diameters), which makes this worse. The obvious cure is thinner roller "wheels" (less metal toward the axle) but I'm sure that invites crushing with those 1,000 lb. springs X 1.9:1 rocker ratio = 1,900 lbs. on the lobe. Remember your math: the locus of points in common between 2 tangent convex shapes is a line with no thickness at all.

* be very careful here: a larger roller wheel will do bad things on an inverse (concave) flank designed for a specific smaller size, and even on a conventional (convex) lobe the speed increase is not linear but varies depending on where the roller makes contact.


Thanks for answering one of my questions.

Is it only inertia that figures into the skidding? I would think that angularity of the load and lower terminal roller rpm would favor the larger wheel.

Has this presented as an meaningful issue in the more typical hydraulic or street strip spring pressure applications?

Re: 'Myth' of Mopar lifter diameter advantage? [Re: BSB67] #2678894
07/18/19 09:16 PM
07/18/19 09:16 PM
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New York
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The RPM difference is linear and varies directly with diameter (.750 to .800" is 12.5% slower), the inertia is closer to the cube of the difference (+21% and more due to concentration of mass at the rim).
Not a common problem, but IMHO it's one reason why mfg. favor hydraulic rollers: there is no lash take-up, the roller (and needle) speed never stops but varies throughout the range.


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Re: 'Myth' of Mopar lifter diameter advantage? [Re: polyspheric] #2679111
07/19/19 01:41 PM
07/19/19 01:41 PM
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Kalispell Mt.
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Wouldn't the inertia of the spinning wheel plus friction from the oil between the wheel and base circle keep the roller spinning at or nearly the same as when it's on the lobe? I wouldn't think it stops and then starts in that very infinitesimally small fraction of time... if I'm wrong that would at least be the second time


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 'Myth' of Mopar lifter diameter advantage? [Re: HotRodDave] #2679170
07/19/19 04:33 PM
07/19/19 04:33 PM
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Originally Posted by HotRodDave
Wouldn't the inertia of the spinning wheel plus friction from the oil between the wheel and base circle keep the roller spinning at or nearly the same as when it's on the lobe? I wouldn't think it stops and then starts in that very infinitesimally small fraction of time... if I'm wrong that would at least be the second time


Kinda thought the same thing too. And oil? Also wonder if roller needles verse bushed would figure in. Inertia would go down with rollers. Probably splitting the hair of split hairs. Interesting, but so far from where I'm at with my street junk.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: BSB67] #2679186
07/19/19 05:39 PM
07/19/19 05:39 PM
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Bend,OR USA
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I've seen more than one solid roller cam that had skids marks on the back side of the lobe(shinier than the front or bottom of the lobes scope) from the lifter loosing contact with the lobe after max lift work
I suspect not enough spring pressure causes that for the intended upper RPM limits work shruggy I shoot for a little more pressure on the seats(15 to 40 Lbs) and over the nose and similar more pressure over the nose to allow for some pressure loss after engine run in time up twocents
I've seen from 10 to 40 Lbs. spring pressure loss after running the motor at the track and on the street for several years, that is on a motor that I had the rocker arms oiling full time and .039 restrictors in the oil feed circuit to the rocker arm shafts up
I sincerely believe you can do more damage to a solid roller cam and lifters by using to little pressure on the springs than by adding a bunch(40+ Lbs) more pressure with them twocents work

Last edited by Cab_Burge; 07/20/19 01:43 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: 'Myth' of Mopar lifter diameter advantage? [Re: Cab_Burge] #2679343
07/20/19 08:35 AM
07/20/19 08:35 AM
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Florida
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Having enough spring pressure is the same concern with Schubeck/Smith composite lifters. If contact is lost, there is the chance that slamming the lifter down back onto the lobe will create stresses that the lifter isn't designed for, leading to failure. Cams need pressure to control valve closure, not their opening.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Cab_Burge] #2679367
07/20/19 09:32 AM
07/20/19 09:32 AM
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Is this roller inertia issue why I have see lately pizza cutter width pro stock rollers?

Re: 'Myth' of Mopar lifter diameter advantage? [Re: jcc] #2679417
07/20/19 11:45 AM
07/20/19 11:45 AM
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Not sure, but Jerry Branch (Branch Flowmetrics) removed 2/3 of the stock H-D factory 3/8" wide roller tappet (1/3 from either side on an angle) 50 years ago. Yes, that triples the load per inch on the lobe, but evidently it was worth it because pretty common, and used (what we would regard today as) very light springs.


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