iam in the middle of putting my motor together and i need to know what the min. piston to valve clearance is. i e-mailed a couple of people and no one has answered back yet also did a search but could not find a number. info on motor is 396 lt1, srp 12.5:1 pistons with two valve reliefs, ported lt1 heads with 58cc combustion chambers, 2.055 int and 1.56 exh. valves, cam is a solid roller 250/256 .614/.644 lift with 1.6 shaft rockers. any help would be greatly appreciated.

justin

 

.080 minimum intake valve and .100 exhaust when the cam is installed in it's running position (straight up, 4* advanced or whatever). I'd check it with maybe .010 max lash, just to make sure.


If you tell me the stroke and LSA of the cam, I should be able to tell you about where in degrees minimum valve to piston clearance occurs.

 

.080/.100 is standard fare

Check at overlap, 5-15º ATDC for the intake and 5-15º BTDC on the exhaust. Calcs are nice but you still need to do a physical check.
I prefer to do this with lightweight springs and a 1" dial indicator as opposed to the clay method. Also may want to check the cam (degree) before you start.

-Mindgame

 

i checked them with clay lashing the valves .010 i have the following clearance .058 exh. and i have .084 int. this is with no gasket so if i am using fel-pro 1074 which has a compress thickness of .039 this should give me .097 exh. and .123 int. at .010 cold lash, my cam calls for .022 lash which should bring my clearances up to .109 exh. and .135 int. iam not worried about the intake just the exhaust has me a little worried be so close to the min.

 

Jason,
Don't sweat it too much, you're in the 'safe' zone. I've run 7075 aluminum BME rods to .110 piston to exhaust valve clearance, turned 8500 rpm and that engine never showed a sign of impact. Steel rod motors with full round pistons and tight bore to piston clearance have nothing to worry about... I've run plenty of them as tight as .09 on the exhaust without a nick.

-Mindgame

 

you can run some really really tight valve clearances if you have a good stable valve train, after there were about 10K miles on my motor, i overrevved it and had a piston valve collision (due to valve float not the clearance lol) when we took the motor apart, we found that the valves were actually rubbing in the reliefs the whole time!!! this was unnoticeable and didnt make any noise or anything (it was very slight) overtime this would have caused alot of valve wear and some piston wear(we sent the pistons out and had them cut to clear)....but if my valves can touch and not hurt anything then you can run some mean tight clearances

 

thank you very much

 

When I tore my LT-4 down for record this year I found that my valves had been touching the pistons lightly. I put the motor back together and decided to pull it the next week. That was Saturday. On Sunday during first round of eliminations the head came off of one of the valves at 7500 rpm. It took the entire short block with it!


Daren