Stocker Cam Lobe Profile ?

[Aubrey N Bruneau]

Been there, and done all that, Greg ! On my old 64 Pontiac convertible, that's almost exactly how my heads were done. I sold that car to build this one !
One thing is for absolutely sure... there is no possible way on earth that I could achieve .100" piston to valve on the exhaust, without taking 20 degrees dutration out of the cam, and milling the piston a WHOLE lot !
It's all good... really. and the trouble is that it never really does "nose over"... especially down at sea level in Mission. Exhaust valve is always good... but probably due to a much more gentle lobe. No bounce.
It's just the damn intake.
BTW, the track... sea level ( as opposed to dyno )... yes, that was a lesson !

Alan, much longer valves create a new problem in geometry... particularly on the exhaust valve, because of the angles of the rocker stud in relation to the valve. Not ideal at all.
Not to mention, I already have my valves sunk into the heads at least ..050" deeper than stock ( piston to valve is a real problem )... so longer valves would be way up there.

Good news is, yes, I can fit 1.55 spring. That was my old combination.
Results were the same.
Maybe I should mention that my heads, at .510" lift, flowed 288 / 212.
Certainly not the potential of a large port BBC.

The right retainers and keepers ?
yup.... been chasing that one for a while !

When I first started racing the Firebird, I changed the rear gear in it. The first time I ran it at the Etown national event it started popping and banging at around 6700. Around 100 ft before the finish line. After the race I checked the valve springs. Found them to be at 200 and 380 open. Bingo! I thought. Changed the springs and retainers. Had 450 open. The next race I almost able to get to the traps ! I figured what is wrong now. When I got home I was going swap a fresh engine anyway.
When I took that engine apart to get the cam and lifters and other assorted parts, I found 3 loose pucks on the bottom of the lifters. The camshaft was a Bullet. I checked the numbers on the cam for the lobes. When I looked up the lobe profiles, the were dwell torque lobes . When I asked John Partrige about this, he told me those lobes were never meant to run over 6500. He told me that I need a asymmetrical rpm style lobe. So I ordered one from him. The cam he sent me went to 7400 with no problem, and I never broke any valvetrain after that. You are on the right track, sounds like you need a profile change.

[Paul Precht]

Originally Posted by Aubrey N Bruneau

Been there, and done all that, Greg ! On my old 64 Pontiac convertible, that's almost exactly how my heads were done. I sold that car to build this one !
One thing is for absolutely sure... there is no possible way on earth that I could achieve .100" piston to valve on the exhaust, without taking 20 degrees dutration out of the cam, and milling the piston a WHOLE lot !
It's all good... really. and the trouble is that it never really does "nose over"... especially down at sea level in Mission. Exhaust valve is always good... but probably due to a much more gentle lobe. No bounce.
It's just the damn intake.
BTW, the track... sea level ( as opposed to dyno )... yes, that was a lesson !

Alan, much longer valves create a new problem in geometry... particularly on the exhaust valve, because of the angles of the rocker stud in relation to the valve. Not ideal at all.
Not to mention, I already have my valves sunk into the heads at least ..050" deeper than stock ( piston to valve is a real problem )... so longer valves would be way up there.

Good news is, yes, I can fit 1.55 spring. That was my old combination.
Results were the same.
Maybe I should mention that my heads, at .510" lift, flowed 288 / 212.
Certainly not the potential of a large port BBC.

The right retainers and keepers ?
yup.... been chasing that one for a while !

Hi Aubrey, advancing the cam 4 degrees or more would give you a significant increase in exhaust V to P clearance and much more mid range torque.

[Robert Swartz]

Originally Posted by A56

Aubrey,
There is no rule that you have to have the most agressive lobe to go fast. There are so many Stock Elim. combinations that simply cant use an agressive lobe, usually due to VP clearances. I for one can use any profile I want on my Mopar 340, but you would laugh at small of a cam im using in the engine right now. Im using the header to draw the air into the engine, something you might want to consider doing. If you cant spin the engine to 7400 without problem, simply dont do it. Try to make more power in your usable RPM. I myself if I was in your shoes would keep your current lobes, or even go smaller or softer, then build a small set of headers. The engine still might sign off at 7200, but who cares. Try to make more power and TQ down low and in the mid range. Usually in our Stock combinations we dont have the cylinder heads to support high RPM anyways.

Mark Lelchook
F/SA #764

I'm not the tech expert that many on this forum are. For consideration sake, I'd explore this avenue. I bought some parts in Ohio from a guy that runs in I/SA, yes, it's a sbc. He told us he was running a real aggressive, big cam. After talking with people running similar combinations. He found that changing to a smaller cam, different headers, his car actually picked up. Food for thought. I'm finding stock to be much more challenging than running brackets. I don't even have a car ready for the track yet!

[Billy Nees]

Originally Posted by A56

Aubrey, Im using the header to draw the air into the engine, something you might want to consider doing. If you cant spin the engine to 7400 without problem, simply dont do it. Try to make more power in your usable RPM. I myself if I was in your shoes would keep your current lobes, or even go smaller or softer, then build a small set of headers.

Mark Lelchook
F/SA #764

I've been wasting my breath saying the same thing for years. It's nice to see that another header guy is thinking the same way that I do. I don't know just what that says about you though Mark.

[Alan Roehrich]

Aubrey, those flow numbers are not nearly as low as you think. I'm betting if you sent the heads to the right person to have them done, they'd be even better, especially with the right valves. You have enough cylinder head to make good HP at 6800 RPM with a 0.060" over 409, the biggest problem is probably the intake manifold.

For your cylinder head flow, your cam is too big, especially if it has some sort of wildly aggressive lobe on the intake.

Mark is right, the right headers could reduce the need for all that duration on the exhaust, provided you even need that much now.

With good valvetrain control, 0.055" on the intake and 0.075" on the exhaust is plenty of clearance. With the right cam lobes and the right valvetrain, control should not be a problem.

Working with pushrod length will probably solve some of the problem with longer valves. There's no such thing as "ideal" valvetrain geometry in Stock Eliminator for most engines. The restrictions of the class prevent it. We're not anywhere near ideal with the big blocks, yet we have not had a single valvetrain failure in over 5 years. I think 2006 was the last time we had a valvetrain failure of any kind, and the problem was solved with the correct rocker studs.

[Aubrey N Bruneau]

This is GREAT !...
I'm 3 times as confused as I was before ! ! !
HE HEE !!

Facts and numbers

The engine makes about 45 HP more than anybody ever did with even a "resembling Stock" 409 before.
Speed through the traps is at least 4 MPH faster than anybody ever went.
My bottom end is legal... piston/rod weight is dead on, combined combustion chamber volumes of the block and head, are safely within spec.
All that I have done different from everybody else with these things, is a big-azz camshaft, and big-azz headers ! Seriously, when tested... went from an EXCELLENT set of 1 7/8" tube, to my own 2" stepped to 2 1/8". Torque curve moved up, peak torque went up by 17 ft lbs, and the engine made 21 more HP.

The old "torque thinking" just doesn't seem to apply to this short stroke engine. Unrestricted ( for the CID ) carburetor CFM, I believe, is also a reason to pursue the escape of the mid-range torque concept ?
I dunno ?.... other than the intake valve going out of control... this damn thing really works.
So, at the moment anyway... fix what's "broke" ( square cam lobe )... and leave alone, what seems to be a really good "package".

assymetrical cam lobe ?
THAT may be the very compromise that I need !

You guys are amazing... Between the support I get here, and the practically "out of body" experience of attending places like the race in Mission... I'm getting hooked on this REALLY bad !

[Rich Biebel]

assymetrical cam lobe

Opening ramp is different than closing ramp. Rate of lift might be fast open and softer on the closing side.

A symetrical cam has the same opening and closing ramps...

Cam companies tried all kinds of unique designs.

Even going back to my days racing in Jr. Stock around 1970 there were distinctly different cams. We were limited to stock springs and pressures and valve train. Some cams we used could not be run much past 5800 rpm and one would run right up past 6000 with no problem....Stickshift hydraulic cam small block Chevy.

[nickh]

Aubrey could you go to a taller tire to kill some rpm through the traps? Some great feedback on this thread

[Aubrey N Bruneau]

I'm paying attention here... so,
Cams aren't that expensive. I already have a set of good "civilized" headers.
I'll get two cams. One how I "feel" it should be. The other with 10-12 degrees less duration, and run it in the correspondingly somewhat lower RPM range. I have the 4.88's to use in place of my current 5.13's.
For testing purposes, I'll use my current heads.
I'll make that my goal before the end of this season.

Currently, the engine never sees below 4500 RPM on a run.