Max valve lift with stock heads

elky-man · Posted: Tue Mar 23, 2004 8:31 pm Post subject: Max valve lift with stock heads

Does anyone know approximately how much valve lift can be used with bone stock chevy small block heads?

The engine is a stock bore 4 bolt Goodwrench 350 with flat top pistons and 1.5:1 ratio rocker arms. The heads are casting number 33417369.

Is the maximum lift limited mainly by valve spring coil bind or rocker arm slot length or push rod clearance?

ElkyPete · Posted: Tue Mar 23, 2004 9:55 pm Post subject:

I would say maximum valve lift is a function of the valve clearances @ TDC and the springs. What you don't want of course is the valve coming in contact with the piston. Bone stock Chevrolet, nothing special heads, maximum lift is under .5" I can't say exactly how much I suppose some of it does depend on the head casting but then if they're old heads then that number will change from new specs. Now Vortec heads are capable of .5" and with a little better springs much more. They flow better than any other Chevy Stock head except maybe the fast burn.

But basically you're limited to under .5" lift and roughly 6000 RPMs. A good trick for stock heads to add a little better HP is to replace all the Intake rockers with 1.6:1 rockers. It takes you to the edge of the valve lift for stock heads but it helps pack a fuller charge in the cylinder, which gives up more Hp.
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greasy5thwheel · Posted: Wed Mar 24, 2004 2:23 am Post subject:

basically it is determined by coil bind, piston to valve clearance at all points not just top dead center, and rocker arm geometry. more lift does not always equate to improved performance however as it and duration have more to do with performance. very basic explanation and i do mean basic, as i am not a cam expert and every application is different. do not allow yourself to fall for the old trap of if a little is good then more is better. more variables than just the cam to determine what you need and desire out of your particular combination. elky pete is right on the vortec heads being the best "production" heads chevy ever mass produced but in stock form they experience coil bind at around .480 on the lift. scoggins dickey reworks them and you can achieve over .500 on lift but they are more money that way than stock. hope this helps as some production heads do not flow air/fuel very well and all the lift in the world will not help even though they will not get into coil bind at lifts exceding .600 at the valve. 1.6 to 1 ratio rocker arms allow more gross valve lift over 1.5 to 1 ratio but if applied on the wrong heads will result in pulled rocker studs, especially pin-in, coil bind, and even valve float at reduced rpm's. any questions about a specific cam or head combination shoot me a pm and i will try to help the best i am able. hope this helps.
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Mrapii · Posted: Wed Mar 24, 2004 6:39 pm Post subject:

Greasyfifthwheel is correct. Unless you have some wild high compression domed piston and a very high lift cam you are not likely to run into valve/piston top interence even at valve lifts of over .500". For street performance small block Chevys .550 valve lift is a practical limit. Coil bind, retainer/valve seal interference and pushrod/hole slot clearance are the things you should watch out for.
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elky-man · Posted: Wed Mar 24, 2004 10:59 pm Post subject:

Thanks to ElkyPete, greasy5thwheel and Mrapii. Excellent information.

The cam I am running now is an Edelbrock Performer with 204/214 dergees duration @0.050" with 0.420"/0.442" lift intake/exhaust.

The cam I want to go to is a 224/234 degree @0.050" with lift int/exh of 0.465"/0.488".

The torque converter is a B&M unit that with the 204/214 cam is giving a stall spped of about 2100 rpm. The rear gear might be a bit low for the new cam as it is only a 3.42:1.

greasy5thwheel · Posted: Thu Mar 25, 2004 1:51 am Post subject:

ought to be all right with that cam. should make for a fun daily driver. good luck and enjoy.
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Mrapii · Posted: Thu Mar 25, 2004 2:25 am Post subject:

That cam is probably as hot as you would want for a daily driven street performance small block Chevy. You're going to have a lumpy idle and low manifold vacumn, but if you can live wuth that, go for it.
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1979 El Camino\r\n1955 Chevrolet Del Ray\r\n1962 Corvette\r\n1966 Corvette Coupe