valve lash

[hotrod1994]

does the valve lash of a cam effect the performance of it

i foud a cheaper cam with the specs as as the comp cam i was looking at but the lash on it is .026 intake .028 exhaust and the comp cam is .20 on the intake and .022 on the exhaust

what difference will this make? if any?

thanks -logan

[TheRabbit]

I've never run as much lash as mfg says to use. I only ran .015 on my little BBC.

[roadkill2]

does the valve lash of a cam effect the performance of it

what difference will this make? if any?

thanks -logan

Depends on a bunch of things . . Tighter valve lash settings will lengthen duration (everybody knows that) but it also has to do with the lifters you use, the pushrod length and installed height . . Hot running expansion is the main reason for establishing a "General" valve lash setting and each engineer figures his own tolerances . . easiest way is warm it up and then measure what you have left . . work within those, being careful not to preload your cam/follower(lifter) or valve stem . . Probably ought to stay outside of .010+ . . both sides . . or . . just go with the instructions until you have the balls to screw with it and risk a slight misunderstanding . .

One opinion . . . .

[TheYellaBrick]

:D :D :D :D
"risk a slight misunderstanding"
I LIKE that term !
A kinder gentler way of saying "Catastrophic engine failure"
:cry: :cry: :cry: :cry: :cry: :cry: :cry: :cry: :cry:

[olds48]

Cam companies have their reasons for establishing certain lashes for certain lobe profiles. We don't know why,but they do. And they are not going to do anything to make their cams make LESS power. That's their reputation on the line. You can loosen lash for less duration in the hopes for more bottom end power. Or tighten it up for more duration like stated before,for topend.But the effects are usually minimal,especially for the risk you are taking. Why did they specify that particular lash????....who knows,just go by it and you'll have one less worry.

But you asked "why" they were different,not if you can change the lash. Looser lash cams typically have a more aggressive lobe profile.Like faster opening ramps.

[hotrod1994]

ok thanks guys

[sbu]

does the valve lash of a cam effect the performance of it

i foud a cheaper cam with the specs as as the comp cam i was looking at but the lash on it is .026 intake .028 exhaust and the comp cam is .20 on the intake and .022 on the exhaust

what difference will this make? if any?

thanks -logan Yes the lash does make a difference, the tight lash will normally take away some of the low end performance, the tighter lash fools the motor into thinking the cam is bigger. Usually the lash will grow about 10 to 15thousandths. I never set lash out, only check hot and the if any are off , I change. Iam not the smartest in the world but have been drag racing and building motors both big and small block 500 inch SB and 815 BB, I am 67 and have been doing this for 48 years. So lash does matter, go by the cam card, it is a starting point and then play around with the valves lash, tighter about 5 thousandth and see if the motor slows down then loosen and see what happens, what ever change you make should show up in your 60ft times first. Hope this helps

[hotrod1994]

ok so i should set the lash warm it up and check again and readjust if needed?

[markdunlap]

When I am initially set valve lash cold on an aluminum headed, iron block engine,
I take the cam builders hot specs and go .004" loose cold. When the engine is fully up to temperature and heat soaked for a little while, I recheck the lash and see what the difference from spec is. I correct it to spec.

I use the difference I saw warm to change the cold setting. Next time I check it hot again to see if it is right.

I don't vary hot lash from spec except to see if it is faster with .004" less or more lash seperately on the intake and then the exhaust.. Then I go back to spec. If I want to go faster, I go back to the cam guy and tell him the results and have a different cam ground for that combination.

On an iron head/block, I go .004" tighter cold and recheck hot.

[hotrod1994]

ok thnaks

[markdunlap]

Don't do what I said, do what I meant on the valve lash.

It's .004" tighter for aluminum heads and .004" looser for iron heads.

Sorry about that, I was still asleep, I guess.

[roadkill2]

Mark's pretty close . .

We have a preliminary cold setting of about +.005 over . . Then, once well warmed, set to cam specs. I can't remember what the cooled setting was (it's written down, 'cause old guys can't remember shit) and we refer back to that as long as we don't change anything in the valve train . .

We also check the hot lash after the third run on qualifying day or before first round of eliminations, just because . . you can tell a lot about your engine's condition by running the valves after a couple (or more) hard passes . .

[hotrod1994]

ok thanks for the correction guys