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'Myth' of Mopar lifter diameter advantage? #2678180
07/17/19 08:11 AM
07/17/19 08:11 AM
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OK, so we have all heard of, read about, perhaps experienced the presumed advantage of the wider Mopar lifter diamater...however, I have to be honest and point out that for quite some time now as I have been looking at various cam listings I have been noticing the Mopar stuff (specific to the small block use - as that is my focus) with much less lobe lift then similar, if not the same, spec'ed cam grinds for the other engine brands.

Case in point, I am focusing on the retro-fit hydraulic roller cam grinds from Comp Cams, here are three examples:

1) Mopar Small Block - Xtreme Energy Retro-Fit XR292HR-10
Adv Dur => 292/300
Dur @ 0.050 => 242 / 248
Lift => .549 / .544
LSA => 110
RPM Range => 2800-6400

2) Chevy Small Bock - Xtreme Energy XR294HR Retro-Fit
Adv Dur => 294/300
Dur @ 0.050 => 242 / 248
Lift => .540 / .562
LSA => 110
RPM Range => 2800-6100

3) Ford Windsor - Xtreme Energy XR294RFHR Retro-Fit
Adv Dur => 294/300
Dur @ 0.050 => 242 / 248
Lift => .576 / .600
LSA => 110
RPM Range => 2500-6500

Alright...so the Ford grinds in particular are something that almost always lists a higher lobe lift. The Chevy...umm...here and there, but in the case of example we have here it is actually a tad higher, not by much, but it is.

So, is this because of the roller profile? Even then would you not expect the wider lifter to provide more room for a bigger diameter roller wheel and subsequently the ability to handle steeper lobe ramps?

OK, so this is pure theory (reasoning behind why these profiles are what they are), and I feel like too often we (the Mopar fans) like to say we get ignored by the aftermarket, but I find it hard to believe that given the amount of computerized manufacturing the makers like Comp Cams would not design a lobe profile that maxes out the lift.

Oh, and btw, if you say this is due to head flow restriction, while true for stock heads I would venture a guess that anyone running this level of cam has probably moved to heavily ported street heads or aftermarket stuff anyways.

So what gives here?

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678203
07/17/19 08:56 AM
07/17/19 08:56 AM
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I don't exactly know, but it seems there are many more factors involved here rather merely lift, such as area under under the curve, valve train accelerations, etc. Seems the larger lifter always is more sought if an option, even with the trade off of additional weight and cost.

Others will expound I am sure. Out. biggrin


Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678214
07/17/19 09:23 AM
07/17/19 09:23 AM
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Flat tappet: The wider foot allows for a higher rate of acceleration to be designed into the cam lobe.
Roller tappet: The larger OD allows for using a wheel with a larger radius that translates into a small increase in lifter acceleration.

Those are the potential advantages; whether the flat-tappet cam lobe or roller lifter are designed for them is something different.

Also, a brief PSA that faster is not always or necessarily better.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678242
07/17/19 10:10 AM
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Any theoretical advantage is worthless if the cam isn't actually ground to take advantage of the lifter diameter.

We have a cam analyzer at the shop, and one of the outputs is minimum lifter diameter. The Lunati Voodoo cam I checked needed a min .88x diameter lifter, which allowing for design margin, etc indicates something that was designed and ground to take advantage of the lifter advantage.

I don't have much for comparison, almost everything we do where we bother to analyze everything to this level is .904/.937/1.00 roller tappet. Haven't seen any 1.062 yet, I think that'd be interesting. S/F....Ken M

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678250
07/17/19 10:20 AM
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Originally Posted by Diplomat360
OK, so we have all heard of, read about, perhaps experienced the presumed advantage of the wider Mopar lifter diamater...however, I have to be honest and point out that for quite some time now as I have been looking at various cam listings I have been noticing the Mopar stuff (specific to the small block use - as that is my focus) with much less lobe lift then similar, if not the same, spec'ed cam grinds for the other engine brands.

Case in point, I am focusing on the retro-fit hydraulic roller cam grinds from Comp Cams, here are three examples:

1) Mopar Small Block - Xtreme Energy Retro-Fit XR292HR-10
Adv Dur => 292/300
Dur @ 0.050 => 242 / 248
Lift => .549 / .544
LSA => 110
RPM Range => 2800-6400

2) Chevy Small Bock - Xtreme Energy XR294HR Retro-Fit
Adv Dur => 294/300
Dur @ 0.050 => 242 / 248
Lift => .540 / .562
LSA => 110
RPM Range => 2800-6100

3) Ford Windsor - Xtreme Energy XR294RFHR Retro-Fit
Adv Dur => 294/300
Dur @ 0.050 => 242 / 248
Lift => .576 / .600
LSA => 110
RPM Range => 2500-6500

Alright...so the Ford grinds in particular are something that almost always lists a higher lobe lift. The Chevy...umm...here and there, but in the case of example we have here it is actually a tad higher, not by much, but it is.

So, is this because of the roller profile? Even then would you not expect the wider lifter to provide more room for a bigger diameter roller wheel and subsequently the ability to handle steeper lobe ramps?

OK, so this is pure theory (reasoning behind why these profiles are what they are), and I feel like too often we (the Mopar fans) like to say we get ignored by the aftermarket, but I find it hard to believe that given the amount of computerized manufacturing the makers like Comp Cams would not design a lobe profile that maxes out the lift.

Oh, and btw, if you say this is due to head flow restriction, while true for stock heads I would venture a guess that anyone running this level of cam has probably moved to heavily ported street heads or aftermarket stuff anyways.

So what gives here?



There are other cam companies than Comp. Many companies grind mopar specific lobes. Even Comp does. The MM series comes to mind. Unless you have an in at Comp, good luck getting them to grind a cam with the MM series lobe. The cam I run is very close to the MM lobe. But it's not a Comp because Comp wouldn't do it.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678252
07/17/19 10:33 AM
07/17/19 10:33 AM
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you need to look at the shape of the lobe and without getting too deep into it, look at duartion @ .050 and also @.200, you have to find a lobe profile catalog usually.

here is an example from Howards.
https://www.howardscams.com/sites/default/files/lobe%20list%20email%201-20-2014.pdf

it lists regular profiles, fat rate profiles, ford profiles and mopar profiles.
just based on a quick glance it looks like the ford .875 profiles are just a tad slower than the mopar profiles...which seem to be close to some of the roller profiles. keep i mind that is still a pretty simple look at things. the nose of the roller profiles could be much different then the flat tappet cams which means more area under the curve.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: krautrock] #2678255
07/17/19 10:38 AM
07/17/19 10:38 AM
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I have no scientific data to present, just to point out that Chrysler at one time offered the mushroom lifters that have a larger diameter at the cam then the stock versions.


"We live in a time when intelligent people are being silenced so that stupid people won't be offended".
Re: 'Myth' of Mopar lifter diameter advantage? [Re: krautrock] #2678263
07/17/19 11:40 AM
07/17/19 11:40 AM
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Originally Posted by krautrock
you need to look at the shape of the lobe and without getting too deep into it, look at duartion @ .050 and also @.200, you have to find a lobe profile catalog usually.

here is an example from Howards.
https://www.howardscams.com/sites/default/files/lobe%20list%20email%201-20-2014.pdf...

YES, perfect!

This is exactly the sort of information I'm curious about, especially the theory behind things like the nose duration, etc.

So given that I picked up a custom ground CompCams hydraulic roller (thus my focus on the CompCams parts, not meaning to ignore the other guys) I actually reached out to their tech folks and asked for the grind card, which they shared. The cam has the 13084 & 3039 lobes, these are the Xtreme Energy XFI rollers:

Lobe 13084:
.006 dur is 290
.050 dur is 240
.200 dur is 163

Lobe 3039:
.006 dur is 300
.050 dur is 248
.200 dur is 169

Now, if I had that same info available for the other grinds I would have happily posted those as well, alas, I do not.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678278
07/17/19 12:18 PM
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Originally Posted by Diplomat360
Originally Posted by krautrock
you need to look at the shape of the lobe and without getting too deep into it, look at duartion @ .050 and also @.200, you have to find a lobe profile catalog usually.

here is an example from Howards.
https://www.howardscams.com/sites/default/files/lobe%20list%20email%201-20-2014.pdf...

YES, perfect!

This is exactly the sort of information I'm curious about, especially the theory behind things like the nose duration, etc.

So given that I picked up a custom ground CompCams hydraulic roller (thus my focus on the CompCams parts, not meaning to ignore the other guys) I actually reached out to their tech folks and asked for the grind card, which they shared. The cam has the 13084 & 3039 lobes, these are the Xtreme Energy XFI rollers:

Lobe 13084:
.006 dur is 290
.050 dur is 240
.200 dur is 163

Lobe 3039:
.006 dur is 300
.050 dur is 248
.200 dur is 169

Now, if I had that same info available for the other grinds I would have happily posted those as well, alas, I do not.





A hydraulic roller (or a solid roller) is a bit different. But lifter diameter still matters, maybe even more so with a roller. With a lifter bore of .842 the biggest wheel you can get in that hole is .750 and that's pretty small. I can't remember if the .875 bore will let you get a bigger wheel than .750 but I don't think so. With a .904 bore you can get an .815 wheel and that's a big deal.

So no matter how I slice it, the bigger lifter bore is always better. Comp and Pro Stock don't use 1 inch and bigger lifters because they want to spend extra money.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678316
07/17/19 02:05 PM
07/17/19 02:05 PM
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The Chrysler mushroom: .970" foot. Why this size? Used on the Ford Model T - no, I'm not kidding, that's how old this is.
There's actual math to calculate the possible rate change: V = (tappet diameter - .040”) ÷ 114.6, where .040" is an acceptable safety margin to prevent edge contact.
Maximum values by tappet diameter in lift per degree of cam lobe rotation:
Engine Tappet OD Max velocity
Chev. Gen-3 L6, V8 .842” .00700”/deg.

Ford .875” .00729”/deg.

Chrysler, A.M.C. .904” .00754”/deg.

Oldsmobile V8 .921” .00769”/deg.

Model “T” mushroom .970” .00812”/deg.

Chev. Gen-2 235, 261 .990” .00829”/deg.

VW Type I• 31mm 1.220” .01030”/deg.


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Re: 'Myth' of Mopar lifter diameter advantage? [Re: polyspheric] #2678320
07/17/19 02:28 PM
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Originally Posted by polyspheric
The Chrysler mushroom: .970" foot. Why this size? Used on the Ford Model T - no, I'm not kidding, that's how old this is.
There's actual math to calculate the possible rate change: V = (tappet diameter - .040”) ÷ 114.6, where .040" is an acceptable safety margin to prevent edge contact.
Maximum values by tappet diameter in lift per degree of cam lobe rotation:
Engine Tappet OD Max velocity
Chev. Gen-3 L6, V8 .842” .00700”/deg.

Ford .875” .00729”/deg.

Chrysler, A.M.C. .904” .00754”/deg.

Oldsmobile V8 .921” .00769”/deg.

Model “T” mushroom .970” .00812”/deg.

Chev. Gen-2 235, 261 .990” .00829”/deg.

VW Type I• 31mm 1.220” .01030”/deg.




Doesn't someone now offer a 1 inch mushroom lifter for the mopar stuff?


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: 'Myth' of Mopar lifter diameter advantage? [Re: polyspheric] #2678323
07/17/19 02:32 PM
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Forget the lifter for a moment and install those cams on a fixture and track the lift with a dial indicator on the lobe. I think you'll find they are DRASTICALLY different with the exception of max lift.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678325
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So, not to side track the conversation too much.....

But the simple geometry of a roller lifter suggest to me that a larger diameter roller (I.e. 0.815 verses 0.750) on the same lobe will move the valve faster. Correct?

If this is correct, when you order a Comp Cam roller cam with specific lobe numbers from their master lobe catalog, do they grind it differently for a Chrysler vs Chevy (0.815 verses a 0.750) lifter roller? Otherwise, their catalog specs would only be correct for one roller size.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: BSB67] #2678354
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most generic shelf cams use lobes desighned for the smallest common lifter, the chevy, so even ford and chrysler with their larger lifters typically get stuck with the smaller lobes because it is easier to just make one small lobe and use it on everything than 3 specific lobes. Also just because a ferd, chuby, mopar use similar part numbers from a common manufacturer does not mean they were made the same, differnet head flow considerations and displacements require different lobes for optimal performance. Also ferds usually use higher rocker ratios so even if they do use the same lobe they will have more lift.


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Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678364
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You have to know what you're doing to find cam lobes that take advantage of the larger Mopar diameter. The generic cams use Chevy lobes. Even the Mopar Performance cams used Ford lobes rather than Mopar lobes. Comp has lobes ground for the larger Mopar lifter but most of their shelf cams use a generic lobe. Hughes Engines sells Mopar lobe cams. I've used the MM lobes from Comp before and they are a bit radical. I doubt I'd use a MM lobe cam in a street car but it could be a decent choice for a race car. Of course, as Brad pointed out, faster isn't always better. In fact, I've proven multiple times that you can lift the valve too fast. Lifting the valve too fast can cost you power and it will also wear out parts.

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678422
07/17/19 07:43 PM
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Re: 'Myth' of Mopar lifter diameter advantage? [Re: polyspheric] #2678463
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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.
Comp, Bullet, and Engle do high acceleration lobes for 0.904" as a custom for good reason. The average guy isn't going to correct lifter bore geometry with bushes, and often the bore orientation is out of phase, resulting in lifter or camshaft failure.

Jesel make 1.25" roller wheel lifters for Pro Stock and the like these days for good reason


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Re: 'Myth' of Mopar lifter diameter advantage? [Re: LA360] #2678478
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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

Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678487
07/17/19 11:25 PM
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I use to race NHRA stock class years ago when stock meant something. Back then the fastest SB Mopar racers knew that the stock OEM heads flow the maximum at or below .500 lift so they would have the cam lobes with the most duration with the max lift allowed by NHRA custom ground for there motors and use the LSA to run as fast as they could with that lift work
Back then Isky had the hot lobes for all the 340, 318 and 360 stocker motors, most ran the best with 104 to 106 LSA shruggy If I'm remembering correctly they all had less than .460 valve lift allowed at the retainers whiney shruggy


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Re: 'Myth' of Mopar lifter diameter advantage? [Re: Diplomat360] #2678515
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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.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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