Optimal Valve Lash

[roccodart440]

My MPP cam states .028 intake and .032 exhaust cold lash.

Now keep in mind that would be with an iron head. I run aluminum.

currently I run .024 and .028 for lash. My engine builder said this is safe. He felt .028 and .032 was excessive unnecessary lash.



I'm wondering what you guys run or recommend. I'd also like to know how much variation can be achieved and what is optimal for performance.

Last, why do some cams have such tight lash while others like mine have so much?

 

[67Dart273]

I don't know does the builder have any basis for this? He's a master cam designer?, LOL and knows better than the company who designed and built the cam? Excuse my usual cynicism, but that's what comes to mind.

 

[IQ52]

Is your .024/.028 lash setting hot or cold? If cold, you are probably at .030/.034 hot. The optimal lash will be determined by varying the lash and making a test run to see what the engine wants. I generally loosen the lash no more than .004" and tighten the lash no more than .008". So the cold iron settings would be .020-.032 intake and .028-.036 exhaust. Aluminum heads would be around .014-.026 and .022-.030 cold. I've tightened the lash more than .008" but you start running into increase overlap and some poor low end running.

If the engine runs better with tighter lash, you might could use a bigger cam. If it runs better with looser lash the cam might be too big. Try the intake and exhaust separately to see if it wants more or less duration on the intake or exhaust. It could take a couple of days to sort out the valve lash.

 

[Marcohotrod]

the moparperf cams are kinda old school-more lash. my comp cam says .022"/.022" hot. like IQ said-u can play with lash, but not too much cuz lobe ramps are designed to last with lash within a sensible range. if u want the cam a little larger, and the lifters hitting it a little less harsh, go less lash. set it cold, and measure again hot! then u will know what is up with your combo

 

[moper]

I don't know does the builder have any basis for this? He's a master cam designer?, LOL and knows better than the company who designed and built the cam? Excuse my usual cynicism, but that's what comes to mind.

The cam designer determines a spec. In the case of MP I've always found the factory recommended lash was too lose. It's been a while since I ran MP but in the past mine liked about .006" tighter than what MP wanted. Some modern stuff likes a tighter lash due to the take up ramps and lobe designs.
That beign said the engine materials and actual engine build may mandate changes from that recommended spec. I usually set mine on the lose side to get things up to temp. With iron i'll reset them hot. With aluminum I run it to get it to temp, then reset one head hot, run it again to reheat eveything, and reset the other head. Once that's done you can mess with the lash on back to back pulls (or runs) to see what it likes. But also as IQ hinted at - if you have to go too far you probably missed a little on the cam choice.

 

[roccodart440]

I don't know does the builder have any basis for this? He's a master cam designer?, LOL and knows better than the company who designed and built the cam? Excuse my usual cynicism, but that's what comes to mind.

I didn't ask for a basis from him but i'll take what IQ52 has to say over your cynicism any day. by the way, IQ52 is currently building the top end of my new fire breather.

Is your .024/.028 lash setting hot or cold? If cold, you are probably at .030/.034 hot. The optimal lash will be determined by varying the lash and making a test run to see what the engine wants. I generally loosen the lash no more than .004" and tighten the lash no more than .008". So the cold iron settings would be .020-.032 intake and .028-.036 exhaust. Aluminum heads would be around .014-.026 and .022-.030 cold. I've tightened the lash more than .008" but you start running into increase overlap and some poor low end running.


If the engine runs better with tighter lash, you might could use a bigger cam. If it runs better with looser lash the cam might be too big. Try the intake and exhaust separately to see if it wants more or less duration on the intake or exhaust. It could take a couple of days to sort out the valve lash.

Cold IQ, I always set lash cold. Sounds like I'm within your range with the .024/.028 cold. Just on the looser end. I'd have to try this at the track or on a dyno. I'm not noticing any major changes when I tighten down the cold lash from say low .030's to mid .020's. Just less noise.

The cam designer determines a spec. In the case of MP I've always found the factory recommended lash was too lose. It's been a while since I ran MP but in the past mine liked about .006" tighter than what MP wanted. .

This is right about where my local guy Boyd Motorworks set it. He wanted .004 tighter after some dyno time.

 

[RustyRatRod]

The cam designer determines a spec. In the case of MP I've always found the factory recommended lash was too lose. It's been a while since I ran MP but in the past mine liked about .006" tighter than what MP wanted. Some modern stuff likes a tighter lash due to the take up ramps and lobe designs.
That beign said the engine materials and actual engine build may mandate changes from that recommended spec. I usually set mine on the lose side to get things up to temp. With iron i'll reset them hot. With aluminum I run it to get it to temp, then reset one head hot, run it again to reheat eveything, and reset the other head. Once that's done you can mess with the lash on back to back pulls (or runs) to see what it likes. But also as IQ hinted at - if you have to go too far you probably missed a little on the cam choice.

All of that makes perfect sense since the MP cams generally mapped smaller than advertised.

 

[67Dart273]

Cold IQ, I always set lash cold. Sounds l.


Aren't most modern cams specced HOT?

 

[roccodart440]

Cold IQ, I always set lash cold. Sounds l.


Aren't most modern cams specced HOT?

I don't know. I don't have a modern cam.

Edit: If the cam didn't specify hot or cold on the cam card i'd make a phone call before setting them lash.

 

[AndyF]

One thing I learned by working with a cam designer is that the lash value is determined by the ramp design. So the lash is determined by the ramp that the designer uses. I also found out that the lash spec depends on the rocker arm ratio. So if you have a cam that is speced at 0.020 lash with 1.50 rocker arms then you need to open it up to 0.023 if you put 1.70 rocker arms on there. I didn't know that before.

 

[gumper]

I've been in this same battle with that loose lash for years. It's 28/32 hot, I set my iron block/aluminum heads at 23/27 and it's right on spec when hot. 28/32 sounds really loose, but I've been running that for 8 years. Tighter gained me nothing. Cam design is such a voodoo art I've learned to just roll with what they recommend. It's definitely and old fashioned cam design, but it works pretty good.