Valve length
 

Hello guys

I've got a question. Why do the 93-95 models have a shorter valve length in comparison to the 90-92 MY (4.04" vs 4.06")? Is there a special reason behind?

Re: Valve length
 

Yes, lifter compression spec was revised to place lifter plunger travel closer to mid range.

Re: Valve length
 

Thank you Jerry.
So it means when you use for example regrounded stage 2 cams in 93-95 engines you can run into the problem to get not enough lifter pre-load.

Re: Valve length
 

That is exactly what happens. Depending on how radical the regrind is, even more material is removed from the base circle diameter, and even early/longer valves are not tall enough & lash caps are needed.

Re: Valve length
 

The valves I have from two sets of later style heads all the intakes measure 4.018"+- however, the exhaust valves from one set measure 4.057"+-and the other set 4.070"+-
The extra length appears to be above the stem retainer groove.
How do the valves from earlier heads measure?

Re: Valve length
 

I measured by a 1990 head the with stock cams and lifters the lifter pre-load and got 0.097". With stage 1 cams the pre-load drop to 0.051"and with stage 2 to 0.025". To make the lifters work properly a minimum pre-load of 0.040-0.070" is required otherwise you can loose valve opening duration and get a noisy valve train. The situation become worse with the shorter 93-95 MY valves.

Re: Valve length
 

I measured 107 90~92 Exhaust Valves awhile back. Overall height is 4.070 +- 0.003".

I have only had a few new late style valves, so never measured enough to get a good number.

It looks like the 4.057" valves were probably correct late style for the head, but the 4.070" were most likely early length installed in late style heads. Kind off like the carry over early transmission into some of the 1993 cars.

I came to the same conclusion that the difference is above the retainer key groove.

Re: Valve length
 

Your experience with the different cams sounds right with my thinking too. If you're going to get real nit-picky, the exhaust valve stem height should be set about 0.010" less lifter compression to account for thermal growth.

Total lifter travel is pretty darn close to 0.124". Setting stem height to pre-load or compress the lifter, right in the middle of the travel range @ 0.062" will work well for both intake & exhaust valves.