Why do "performance" cams with greater lift/duration specify greater valve lash? Is it a performance gain, or durability, longevity gain?

I just recently received the cam specs for my engine from the PO. It shows valve clearance should be set at:

.013N
.015X

This just seems really loose! Is this for very high rpm?

The engine is a 75 2.0 with 44IDF's, Euro P/C's, Mallory dizzy & CD, and has Iskendarian cam, lifters, pushrods & springs.

I just recently had some headwork done and replaced the valves. Should I use the above specs instead of .006/.008?

1. Since you are producing more heat, the expansion of components is greater.

2. Since the opening and closing ramps, lift, etc are more severe, the lash is opened up.

3. Yes, it is normal - On our full-race cams we were setting 0.018 +/- 0.002

So I presume the valves will be VERY noisy when cold, but subside somewhat once they become warm?

Should I plan on adjusting the valves more frequently than 3k?

Any other considerations?

They are gonna make more noise. Adjustment intervals will be trial and error - you might start by checking them at 1000 mile intervals and see how they hold adjustment.

Thanks Ron.

I'm doing them now.

That lash is way too much!

What material are your pushrods made of?? Are they steel or aluminum?

If they are stock, or aluminum set those valves to .006 on the intake and exhaust when cold.

If they are steel set them to ZERO LASH when cold!! Isky must be high giving settings like that! Thats insane!

As the engine heats up steel pushrods stay the same length and the engine grows around them creating lash- more than enough lash.

BTW, valves should only need to be set every 6K miles, not every 3K. Only hot running engines need the valves set that often

I thought you were fishing!

I'm leaving in the mornin'......

Thanks for your viewpoint Jake.

They "looked" like steel when they were out (very smooth bright chrome looking ends - but very light. I should have put a magnet on them. The cam, lifters, pushrods & springs are Isky.

It seems like a radical setting to me - I set them and they are REALLY loud, even when the engine warmed up.

Just for clarification, I will get the catalogue that gives those specs, scan it and post it here. Maybe something can be learned from this.

Any other opinions?