Stocker Cam Lobe Profile ?

[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.

[Alan Roehrich]

That's a bit too much drop between gears. It needs to stay up above 5000.

I'd expect to use a 5.14 with your combination, I think you'll find the 4.88 won't run well. Consider that most run a 5.00 or 5.14 with a 396 or 427, both of which have 0.250" more stroke.

The secret to going fast is average HP between around 5200 and 7400, and having it recover really well from the shift. You cannot give up average HP to get peak HP, or it will not recover from the shift.

Call Tim, see if he has the lobes to grind you a cam with between 254 and 258 in the intake, and 266 to 268 on the exhaust, between 108 and 110 LSA, 109 LSA, in at 107 is probably a nice compromise. If you can't tighten up your RPM drop, you really need to look at a 107 LSA, in at 105. It may not make great peak numbers, it might not look great on the dyno. But on the dyno, it does not have to recover from the shift, in the car, it does, and if it drops below 5000, it's probably way below peak torque, and won't recover well.

The modern big block lobes will be stable to 8000 RPM, provided you have 250 on the seat, and 525 open, you need a spring rate around 525-550 per inch. You cannot control that big intake valve with anything less. If you're not running at least a 7/16" x 0.125" wall pushrod, it will never work. The pushrod will be a secondary spring, and make everything surge and bounce, even with a gentle lobe.

For a single step header, I'd expect to see something similar to an 1-7/8" to 2", with 16"-17" long steps, for a total of a 32"-34" primary, and a collector about 16"-18" long, merge style, tapering from 3" to 4". If you went for 2 steps, split the 2" section into a 2" and a 2-1/8" section, each about 8" long. That's a real simple merge, you could do more if you wanted.

[Aubrey N Bruneau]

On the gear change, of course it doesn't drop to 4500. Transmission has only a 2.83 first gear, so in terms of modern drag racing stick shift... it's almost a close ratio.
I know... not enough first gear for a 3640 pound car.
Also, these engines have a nortoriously long torque curve... never a lot, but very flat. A wider spread in gears would be better. Peak torque is at 4600-4800... still within 5 ft pounds at 5400 RPM. More gear spread would allow the engine to fall back into the real "thick" of the torque.
Simple math, if I lower the RPM range of the engine, I have to go taller gear ratio in order to retain trap speed.

Alan, I don't know WHAT you are using for a spring, but I've studied the hell out of this, and I can't find a single spring that will get near those figures. Also, in these engines, there's no room for a 7/16" pushrod ( the "pinch" in the intake port, adjacent to the pushrod hole, is already paper thin ). Can't be done. I have 3/8" Manton.
Also, header tube length under about 42", with a merge collector... ? Impossible, period. Chassis will not allow it. My headers are about 33"-34" long.16" total collector length.

maybe it's just destined to remain a slug ? ! ! !

[Pvt Parts]

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


You'd better be making peak torque no higher than 4300 rpm.

200 rpm above peak torque is the basement. If you drop below that it won't recover.

[Alan Roehrich]

You might get by with a 3/8" x 0.125" wall. Consider a dual taper, Trend has a dual taper 3/8" - 7/16" pushrod, it's 3/8" on the ends, and 7/16" in the middle. Trend will measure for you to see if they can make something work.

You do not have to run a single spring any more. They opened the spring rule up.

Not sure what you mean about the headers. If your headers are 33-34" long, with a 16" long collector, that's about what I was suggesting, length wise. A merge collector will fit where a plain collector will.