Comp Cam now a Bullet
 

I got my Comp regrind back from Tim today.
Opening and closing events are virtually the same just the ramp is a little less aggressive and .015 less lift.

He uses a formula for aggressiveness of the lobe putting stock lifter bores at risk.
He subtracts the advertised duration (.020) from the @ .050 duration.
This cam comes in at 34, well his exact calculations are 33.5
He has a number of 32 that is the line where lifter bores are put at risk. The smaller the number the greater the risk and those are lifter bore brace only cams
. Comp as is was 29 and he considered it too risky for a stock block with a safety margin.
This cam got reground with a Harold B UD lobe that has proven to be safe.
His formula does seem a tad conservative to me as I am sure folks have run cams in their stock blocks with a number under 31. Even a Crower I had Dan Whitmore spec out for me had a number of 30 and he would not knowingly get me a risky cam.
This cam will give me a gross lift of .733 and it has a lash of .016.
It should work out better for me as the old cam had a gross lash of .759
I probably could have run the Comp as it was since I have a full SD brace. Just did not want to rely on it. It was just for added protection for use with a cam that did not need one.
Bullet did a nice job on this. It seems like they even polished the cam gear for me, very smooth.

The "formula" is called "major intensity"

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CAM PROFILE INTENSITY
BY HARVEY CRANE

https://4secondsflat.com/Cam_Design.html


Major Intensity. A marketing tool

https://www.yellowbullet.com/threads...g-tool.455257/


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What was the LSA before it was reground?

It was on a 112. Very little was changed. Just the steepness of the ramp and a little less lift.
Tim said I will lose 10 HP or so.
But I do not want to pucker up every time I get past the 1/8 mile.

I am wondering how aggressive cams some of you guys have gotten away with in stock blocks and the engine lived a long life ?
Any examples ?

Do you have a lobe number from the comp grind that it was. I am curious what the design lash was before. Nothing wrong with loosing 10HP for some piece of mind. Sometimes you can tighten up the lash quite a bit and soften the blow on the valve terrain on a SR, makes a 30 intensity like a 34, likely still end up loosing that 10 HP though, maybe more. The lash ramp design can make a difference also, some tight lash set ups accelerate the lifter longer and you can run more intensity early in the profile and not add a lot of stress, a comp XR street roller is an example, still probably hard on the lifter bore if it was really big. The tighter design lash moves the 34* bench mark of the intensity from .050” 020” because the tighter lash starts moving the lifter well before .020”. The major intensity and the design lash effect each other on a mechanical cam.

These Ultradyne SR’s are the biggest lobes I have ever seen used in a stock Pontiac block, 36* major intensity with not a terrible amount of negative dwell over the nose. Insanely BIG. I think the guys running the Nitros grocery getter wagon were running a grind from that series. I have one almost as big on the .050” duration on a .440” lobe that is 34* intensity that has a ton of negative duration over the nose. 200* of duration at .2” max lift is another bench mark I have a heard of for max cam size on a stock block. The examples I mentioned are past that some.

I think I have the lobe number. Tim said it was a 29. so pretty aggressive.
I will look when I get home from work. Mini shut down for us this weekend. Work at least 3 of the 4 days.
Sucks, I was to have it off to work on my car. Will have to take some extra time off next weekend and get this thing out to the track.
The Comp was a .016-.018 lash.
Its now .016-.016

The new Bullet grind has a .011” lash ramp design. Multiply .011” times the rocker ratio and that puts the lash pretty much in the middle of the lash window, but you can tighten it more if needed. With 1.7s that would be .019” lash instead of .016”. The .016” was for 1.5 rockers. You can tighten the lash .006”or .008” from there if you want, and loosen it probably .004”. Should be able to adjust the lash from .011” to .023” when hot for tuning. The 34* intensity from .050” to .020” should pretty gentle on a .011” lash ramp design. That comp probably had a .012” ramp with a 29* intensity, it sounds like it was pretty aggressive.

Somewhat related here and tid bits offered for general interest only, it does not represent any endorsement.

Years ago Jim Butler included a list of solid roller cams offered in his catalog, and with that listing of cams he mentioned specific lobes that he stated "should not be aggressive enough to break lifter bores." His opinion at the time.
They were Comp Hi-Tech .420 rollers. Those specific lobes Jim listed were from 252 at .050 (169 at .200) through the top lobe listed with 282 at .050 (195 at .200).

36 intensity number.

Regarding these Hi-Tech .420 solid rollers Comp Cams has stated "The ramp designs are easy on valve springs, yet produce good power".

Note the duration at .200" valve lift. Also an indication of the lobes' aggressiveness. Often touted that a lifter bore brace is typically not necessary until the duration at 0.200" valve lift approaches or is over 200 degrees duration.
But noted you have lifter bore bracing.

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Major intensity just another one of Harvey Cranes marketing ideas.

Remember that XX degrees major intensity doesn't tell the full story. An asymmetrical cam with XX degrees major intensity will be more aggressive on the opening side than a symmetrical cam with the same major intensity will be. Also not all asymmetrical cam are the same.

Stan

The .011” ramp design I mentioned is measured from the closing side. It I a not mistaken, the opening side acceleration and the force on the lifter at max opening pressure to control the negative acceleration over the nose is more what stress’s the lifter bores?

To illustrate Stans point. The UltraDyne solid roller cam I'm currently running is Harold's old 288R.

The intake lobe it's rated 288 at .020, 255 at .050 and 176 at .200.
However, on the opening side, it is only 282 at .020, 252 at .050, still 176 at .200. The closing side is 294 at .020, 258 at .050, still 176 at .200.

Now evaluate the intensity numbers.

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I only have data for a couple of UD lobes and both were ground by Lunati. This is a graph on lifter velocity. Notice the difference in peak velocity on open verses close and also velocity is at zero before mid lobe.

Stan

Not a bad looking cam, more lift and a little more exhaust duration would be nice imo

Pressure angle (in a roller) is what breaks lifter bores. It's the sideways force imparted by the lobe onto the roller as it is opening and closing

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Definitely worth mentioning if someone is new to Pontiacs. Some have gotten broke with even mild hyd roller set ups. Some blocks are strong than others, I did a lifter brace a few days ago, and just did it for #2 and #6.

Opening side is quite a more harsh was what I was trying to get across.

You would want more than a 9 deg split ?
The Comp had a .264 intake so it had a 10 deg split. But the intake lobe Tim Thought would work best had 265 @ .050 and he thought it was fine.
The Comp cam had .759 gross lift, .741 net lift.
My heads are done at .700 lift for all intents and purposes. 350 cfm at .700 and the only go up 9 cfm, 359 cfm at .800 lift.
So I did not see the point of hanging the valve so much when it was not going to get me anything.
Jeff at KRE said Super Stock guys open the valve way past where the heads flow all the time but its harder on things.
Not what I am after.
Just trying to open the valve enough to matter, run the biggest lobe I can with a margin of safety.
Some might have the balls to run a bigger cam in a stock block, but I just bracket race. I got away with .688 lift for years in a stock block so .731 lift is a nice jump. I know you can run a .457 lobe in a stock block like Jake ran with his SB cam but the duration was in the .250s.
Still should be close to 700 HP.

Does 2228/4267 get you what you are after ?

Forget about it’s way over his head.

One of the weakest links in stock Pontiac block #2 and #6. Their attached to the block like a coup handle is attached to a coup. Unless the block is cleaned really well and that area is Mag I’ve found two blocks with hair line crack your never see with the naked eye.