Cam Design Theory from David Vizard
Originally Posted by jimmyblue
I think that little graphic and the cam advice with it,
may not really comprehend the aggressive lobe profiles
that the LS1 crowd likes to use. This aspect lets you
have more effective duration at less real overlap, ja?
may not really comprehend the aggressive lobe profiles
that the LS1 crowd likes to use. This aspect lets you
have more effective duration at less real overlap, ja?
Jimmy, I think it has to deal more with the fact that it's a completely different engine design. Parameters that worked well on SBC and SBFs might not work on motors with much different designs.... intake manifolds, compression ratios, head ports etc...
Bret
A lot of his work was done with traditional single/dual plane intakes. I wonder if following these guidelines could improve the results with a vic jr, seeing how they lose out a lot against the fast intake in the torque department.
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Not sure where I read it but I saw an article said that optimum LSA is vastly different for carbs than for efi. As an example it said that 108° would be tame for a carbed 350 SBC but would be very rough on an efi engine.
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From: K-W, Ontario
Originally Posted by GMC_DUDE
Not sure where I read it but I saw an article said that optimum LSA is vastly different for carbs than for efi. As an example it said that 108° would be tame for a carbed 350 SBC but would be very rough on an efi engine.
I would think the opposite based on the idle manifold pressure. At idle and
low RPM (<2000 RPM) for instance, the carb needs good vacuum (low pressure)
to allow the fuel to flow into the air stream (idle and/or part throttle main
circuit).
True, it was a 224° @ .050, but it worked well and wasn't the 112°-116° LCA stuff I see offered a lot.
I guess that says there is more than one way to skin a feline...or design a cam.
I guess that says there is more than one way to skin a feline...or design a cam.
David. I was just thinking in terms of my particular case. If I were to use a
224 degree lobe @ 0.050" with 1.6 ratio rockers, on the 107 LCA I could
probably make a decent idle to 6000 RPM power curve with my set up.
Last edited by Adrenaline_Z; Feb 6, 2007 at 04:45 PM.
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From: Upstate NY
Originally Posted by Adrenaline_Z
Jon and Bret (or anyone else), I hope you didn't misread my post to slam
David. I was just thinking in terms of my particular case. If I were to use a
224 degree lobe @ 0.050" with 1.6 ratio rockers, on the 107 LCA I could
probably make a decent idle to 6000 RPM power curve with my set up.
Even the PHR editors were concerned with the 108° LCA. I guess they believe some of the stuff they have written in the past. Here is their quote:
'We knew the cam would make hard-hitting torque, but questioned whether it would have the legs to run up the rpm range, which would be vital to making big horsepower upstairs. In fact, we questioned whether the 224 degrees of duration would allow the engine to make peak power anywhere near the 6,000-rpm range, an rpm capacity we know a 350-cube engine would require to make over 400 hp.
When questioned, Vizard reassured us by stating confidently, "I've been speccing cams for well over 20 years, and haven't been wrong yet, but maybe I'm due." '
I imagined a
in DV's statement.No offense intended to carrag editors. Some are just more savvy than others. One or two come to mind.
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From: K-W, Ontario
Yes, it is about getting the valve events correct.
I should have added the info that was included within the PM to Bret.
Using my 244 degrees @ 0.050" with a 1.6 rocker ratio on a 107 LSA would
not be in my best interest.
As I was stating in the previous post, I'd have to drop some duration and
reduce the rocker ratio to make the 107 LSA work well with that specific lobe.
That could totally screw my setup for top end power.
As you suggest, with a 224 degree lobe, 107 LSA and maybe a higher ratio
rocker, I might be able to make similar numbers. I don't know, I've never tried
anything close to 107-108.
My theoretical dyno says I'd make peak torque sooner, with more average
torque down low, and I would drop some peak RPM as well as average HP
in the upper band.
What does your SOTP dyno say about that?
I should have added the info that was included within the PM to Bret.
Using my 244 degrees @ 0.050" with a 1.6 rocker ratio on a 107 LSA would
not be in my best interest.
As I was stating in the previous post, I'd have to drop some duration and
reduce the rocker ratio to make the 107 LSA work well with that specific lobe.
That could totally screw my setup for top end power.
As you suggest, with a 224 degree lobe, 107 LSA and maybe a higher ratio
rocker, I might be able to make similar numbers. I don't know, I've never tried
anything close to 107-108.
My theoretical dyno says I'd make peak torque sooner, with more average
torque down low, and I would drop some peak RPM as well as average HP
in the upper band.
What does your SOTP dyno say about that?
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Originally Posted by Adrenaline_Z
Yes, it is about getting the valve events correct.
I should have added the info that was included within the PM to Bret.
Using my 244 degrees @ 0.050" with a 1.6 rocker ratio on a 107 LSA would
not be in my best interest.
As I was stating in the previous post, I'd have to drop some duration and
reduce the rocker ratio to make the 107 LSA work well with that specific lobe.
That could totally screw my setup for top end power.
As you suggest, with a 224 degree lobe, 107 LSA and maybe a higher ratio
rocker, I might be able to make similar numbers. I don't know, I've never tried
anything close to 107-108.
My theoretical dyno says I'd make peak torque sooner, with more average
torque down low, and I would drop some peak RPM as well as average HP
in the upper band.
What does your SOTP dyno say about that?
I should have added the info that was included within the PM to Bret.
Using my 244 degrees @ 0.050" with a 1.6 rocker ratio on a 107 LSA would
not be in my best interest.
As I was stating in the previous post, I'd have to drop some duration and
reduce the rocker ratio to make the 107 LSA work well with that specific lobe.
That could totally screw my setup for top end power.
As you suggest, with a 224 degree lobe, 107 LSA and maybe a higher ratio
rocker, I might be able to make similar numbers. I don't know, I've never tried
anything close to 107-108.
My theoretical dyno says I'd make peak torque sooner, with more average
torque down low, and I would drop some peak RPM as well as average HP
in the upper band.
What does your SOTP dyno say about that?
I'd rather measure things than speculate. Thinking out of the box (TOOTB) can payback well, in some cases. Sometimes it even surprises the "experts" after they measure results. How many of us can actually TOOTB? Practicing "thought experiments" is a way to improve one's ability to do that. So is brainstorming with other TOOTB folks. It helps keep one young. At my advance age, I need that!
Fortunately I get to do that.
Originally Posted by SStrokerAce
Jimmy, I think it has to deal more with the fact that it's a completely different engine design. Parameters that worked well on SBC and SBFs might not work on motors with much different designs.... intake manifolds, compression ratios, head ports etc...
Bret
Bret
Bret,
I agree with what you're saying here. That is why I said what I did in the first paragraph of post #4 above. I wish that someone with a contemporary knowledge of powertrain technology who communicates well would really take on the task of documenting modern cam design variables, induction system optimization, etc. In today's world, this would get into the use of computer tools like engine simulation programs.
The aerodynamic design of the heads and intakes that are available today (plenums, ports, combustion chamber, etc.) coupled with the availability of PCM-controlled multi-port fuel injection and sophisticated spark control with WBAFR feed-back could not have been imagined when Vizard did most of his testing and theorizing.
I believe that GM will be turning the corner on dual cam-in-block production small block engines within the next four years. This tied with independent phasing of intake and exhaust events and perhaps variable length intake runners will further change the dynamics of cam design (both for the OEM and aftermarket companies).
Steve
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He also talks about an exhaust pulse that will give a lower pressure at the exhaust valve from the exhaust flowing threw the pipe. Sounds like a winner but i've never figured out how to calculate the weight of each exhaust molecule traveling at diverent speeds then the rate of deceloration that can make such and such amount of vacume to pull in fresh air threw the intake valve threw the overlape period. .........................if any one wants some example numbers to try this math i'd be happy to give you the specs to my motor.
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
Originally Posted by Ed Wright
With 30 degree intake valve seats, right?
Remember his "30 degree technology" deal he was so proud of?
Smart guy, but sometimes way off in left field.
Remember his "30 degree technology" deal he was so proud of?
Smart guy, but sometimes way off in left field.
I agree with most of his other stuff but the cam stuff or at least that cam stuff is all in left field in my opinion.
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
Originally Posted by SStrokerAce
Guys remember Dave had to take his dick out first before he stepped on it. There has been a lot of times that he didn't!
The low lift flow and 30° seats were not winners but some of his stuff is.
Bret
The low lift flow and 30° seats were not winners but some of his stuff is.
Bret
I did a search for Vizard LS camshafts and this thread [unfortunately] is the top hit in Google. Does anybody know of any published work done by David Vizard for LS camshafts?
Regarding this thread, the link no longer works but I assume everybody was talking about the famous "128" rule. That rule does not apply to LS engines.
Vizard did a lot of work with traditional SBC engines with 10.5 compression ratio. After hundreds (or more) of that kind of engine combination, he saw that the more healthy combinations, making ~1.4 lb-ft torque per cubic inch, had a camshaft LSA that fitted an equation now known as the "128 rule". This equation gave average people a fair shot of also making 1.4 lb-ft per cubic inch with their 10.5:1 SBC, which was better than what most people could do at the time.
Regarding this thread, the link no longer works but I assume everybody was talking about the famous "128" rule. That rule does not apply to LS engines.
Vizard did a lot of work with traditional SBC engines with 10.5 compression ratio. After hundreds (or more) of that kind of engine combination, he saw that the more healthy combinations, making ~1.4 lb-ft torque per cubic inch, had a camshaft LSA that fitted an equation now known as the "128 rule". This equation gave average people a fair shot of also making 1.4 lb-ft per cubic inch with their 10.5:1 SBC, which was better than what most people could do at the time.
Last edited by QwkTrip; Feb 18, 2024 at 03:26 PM.
