Max valve lift with stock heads [Archive] - El Camino Central Forum : Chevrolet El Camino Forums

: Max valve lift with stock heads


elky-man
03-23-2004, 07:31 PM
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
03-23-2004, 08:55 PM
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.

greasy5thwheel
03-24-2004, 01:23 AM
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.

Mrapii
03-24-2004, 05:39 PM
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.

elky-man
03-24-2004, 09:59 PM
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
03-25-2004, 12:51 AM
ought to be all right with that cam. should make for a fun daily driver. good luck and enjoy.

Mrapii
03-25-2004, 01:25 AM
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.

B McDonald
02-07-2012, 01:09 PM
I have that same engine in my 81 elcam. The issue is with the clearance between the valve guide/seal and the retainer. We checked this clearence and I believe it was not much over .400" with valve fully open. The lift on the stock cam is .383/.401". I had to have the valve guides machined down in order to run a comp cam 268H which has valve lift of .454". You will also have to have your springs checked to see what height they coil bind at and if spring pressure is adequate for the new cam your installing. I installed the complete cam kit, which includes cam, lifters, springs, retainers and locks. I found a cylinder head guy that milled the heads and cut down the guides, installed new seals and did a back cut on the valves and reassembled everthing, all for $168.

steelybill
02-07-2012, 11:31 PM
Getting in the .5" lift area is getting the spring retainers close to the top of the valve guides also. Just another clearance item to be checked with high lift set-ups.
A cam with like .480 lift, with 1.6 ratio rockers for example, could be pushing the limit for clearances,

TrannyMike
02-08-2012, 08:14 AM
I have brand new Vortec heads at the machine shop right now. First of all just because a higher lift than stock is possible doesn't mean it will work out at high RPM's. The stock valve spring pressure may not be enough. 2nd, the stock Vortec retainers to valve stem seals is where the limitation is for lift. I bought high performance springs, retainers and keepers. The retainers are designed to give more clearance at the seals. The springs allow for higher RPM's without floating the valves at high RPM's. I'm having screw in studs installed because the stock pressed in type can pull out with high spring pressures. :beer:

steelybill
02-08-2012, 10:33 PM
What Mike said.........stiffer springs=screw-in studs.

truck
02-09-2012, 12:25 AM
ok sorry to jump in on this . What would the max spring pressure be with pressed in stock studs?