LT 1 350 valve to piston clearance
 

What is minumun valve to piston clearance? i have .100 on intake and .60 on exhaust. I am a little nervous about exhaust side. Is it legal to cut the exhaust valve pocket on the piston just a little? nhra stocker

Re: LT 1 350 valve to piston clearance
 

Is that checked with checker springs or the regular springs?

Re: LT 1 350 valve to piston clearance
 

I do not think so.
265 55 Chevys sure wish they can notch their flat pistons to get some valve tolerance.

D

Re: LT 1 350 valve to piston clearance
 

Having raced 265" '55 & '56 Chevies, we damn sure flycut our flat top pistons for valve-to-Piston clearance. Mine was down 4 times by NHRA, three national records & once was protested, passed every time.

Re: LT 1 350 valve to piston clearance
 

No, it is not legal to cut the valve reliefs on pistons in NHRA Stock Eliminator.

I would probably consider 0.060" piston to valve clearance on the exhaust to be the minimum safe clearance, if it was properly checked to begin with, and you have very good valvetrain control.

Re: LT 1 350 valve to piston clearance
 

Ed, we are talking STOCK eliminator.....Alan is correct. I might add just watch yourself in the water....

Re: LT 1 350 valve to piston clearance
 

I apologize. The Stock rules are different enough from when I ran Stock with that '56, I should have kept quite. About all he can do legaly is move the cam.

I don't get the remark about water?

Re: LT 1 350 valve to piston clearance
 

I think he is referring to don't let it get away from you on a burnout. People tend to over rev a car in the water box.

As for vtp like Alan said above .060 .065 exh would be as tight as I've ever ran and it was okay for me. The intake is more forgiving. if I were you I'd advance the cam and get yourself some more exh clearance and less int in my opinion if you are worried about it .

Good luck with it.

Re: LT 1 350 valve to piston clearance
 

Need to use a rev limiter in the water. I run .040" on the intake side a lot, have run .035" and they never touched. Had clean intake pockets. No carbon. I've never run less than .065" on the Ex side. Right now, mine has .040" & .070". Nothing touches.

Re: LT 1 350 valve to piston clearance
 

Curious. Why more Clearance on the Intake vs Exhaust. ?

Re: LT 1 350 valve to piston clearance
 

This^

Re: LT 1 350 valve to piston clearance
 

Hi Asking these questions I would assume your a newbie to stock. As Alan said did you check it the right way? In my younger years I might have run it with .060 but with the cost of everything today I wouldn't risk it. There are several ways to pick up that little clearance you need. I know it sucks but I would take the heads off and have a good machine shop cut .010 off the back of the valve. If possible move the cam a couple of degree's. What head gasket are you using? Have one custom made .05 larger but tighter on the bore so you don't loose compression. They don't cost that much. Good luck BP

Re: LT 1 350 valve to piston clearance
 

No need to apologize Ed, not only do we look forward to it ..but we all appreciate your input. You are a lucky man to have raced in the junior stock era and still be more than competitive in today's Super Stock eliminator. In the Don McElroy era, he would bolt a dummy head on the motor and with the assistance of a BFH he would hammer the valve into the piston.

Re: LT 1 350 valve to piston clearance
 

I ran .050 on exhaust side in my 350/255. Keep burnout to 5500 or less and never had anything touch, at .040 they do.

Re: LT 1 350 valve to piston clearance
 

It was with checker spring. I have since used my regular spring and it reads .080 with everything just like i am going to run it in the motor.I am new to stock. I raced super gas for years. Just dont know how far you guys push the envelope in stock eliminator.

Re: LT 1 350 valve to piston clearance
 

[QUOTE=B Parker;523488]Hi Asking these questions I would assume your a newbie to stock. As Alan said did you check it the right way? In my younger years I might have run it with .060 but with the cost of everything today I wouldn't risk it. There are several ways to pick up that little clearance you need. I know it sucks but I would take the heads off and have a good machine shop cut .010 off the back of the valve. If possible move the cam a couple of degree's. What head gasket are you using? Have one custom made .05 larger but tighter on the bore so you don't loose compression. They don't cost that much. Good luck BP[/QUOTE ] All of those suggestions are very easy to do. thanks for your input

Re: LT 1 350 valve to piston clearance
 

I agree with the above post about giving extra clearance, being on the safe side. I know from recent personal experience flirting with "too close" just cost me about $9,000.00 and set me back a season.

Re: LT 1 350 valve to piston clearance
 

I figured it would pick up some clearance with regular springs. .080 is quite adequate.

Re: LT 1 350 valve to piston clearance
 

Check your PM.

Re: LT 1 350 valve to piston clearance
 

Dan,

The exhaust valve runs much hotter than the intake and expands more.

Roland

Re: LT 1 350 valve to piston clearance
 

Should be more clearance on the exhaust than on the intake. Observe the relationship of the valve action in comparison to the rotation of the engine during the cycle. The piston is closest to the intake valve as the piston is approaching TDC and the valve is closing, so any contact will "push" the valve closed and/or the clearance will increase rapidly. For the exhaust valve action, the opposite is true. The piston is closest to the exhaust valve as the piston is approaching TDC and the valve is opening. The camshaft will push the valve into the piston and potential damage is greater.


There are other factors like what causes valve float, etc., but the above is generally true.

Re: LT 1 350 valve to piston clearance
 

The exhaust valve and the piston are moving toward each other at the closest point.
Intake Side, the piston and valve are moving the same direction. You can run them closer.

Re: LT 1 350 valve to piston clearance
 

The piston is chasing the exhaust as it's closing, if it's a little tardy it gets smacked. The intake is chasing the piston as it's heading down, if the valvetrain is tight you can run .010" on the intake and it'll never hit.

Re: LT 1 350 valve to piston clearance
 

Re: LT 1 350 valve to piston clearance
 

I agree with this. I've ran em so tight that at zero lash on the intake, the motor would not turn over by hand. Set the valves, and turn 10,000 with no problems. The exhaust, high 70's is as close as I've ever dared. And you'd better have good springs.