Valve lash settings

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Running more or less lash on the exhaust profile is okay because the ramp rate is so slow in comparrison to the intake ramp. Running more lash on the intake can break parts because the point at which the cam contacts the tappet the cam will be going much faster than it would be at the prescribed lash setting.

The top lines are velocity, the bottom line is the lift curve. I drew lines to show you how much velocity there is at each lift point. This is an intake profile with two different styles of lash ramps. Our design is the dark blue.

Red line is .010" lash
yellow line is .015"
white line is .020"

Running .020" here is dangerous. The velocity is 3X what it is at .010". Running a tighter lash on the intake as you can see will gain you little if any extra area. Running tighter lash does increase lift by the amount the lash was decreased by. It also opens the valves sooner but, this varies based on how the ramp is shaped, as well increases duration a small amount across the entire profile. I would not play with different lash settings much on the intake too much. On the opening and closing of the intake if you ran .020" the velocity is 3x what it should be when the valve is opening and closing, this will hammer and snap your tappets to little pieces.

On the exhaust, decreasing lash can open the exhaust valve sooner which will make a larger pressure pulse hit the chargers. This creates better spool, more boost and at max power it creates more drive pressure. This is why on performance cams with large exhaust profiles, you need an external gate to control excessive drive pressure. Large duration exhausts usually have more overlap so high drive pressure really kicks your butt.

Increasing lash on the exhaust will make the lash be taken up in a point with less velocity. Less velocity, less noise. More lash, more velocity much greater valve noise.
 
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Good tread

Opening the lash will normally make more power but like I said it is harder on the valvetrain. A duramax runs a big lifter with a big wheel on the bottom, it's not a problem. By opening the lash you open the valve faster at the start of the opening ramp on the lobe. The intensity rate at the valve will go up. I hope this helps to explain it better. For the guy who went to school at SAM ask Judd what way he would go when trying to get everything out of a car while qualifying a Pro Stock or Hot Street motor. Jeff
 
Stingpuller said:
Opening the lash will normally make more power but like I said it is harder on the valvetrain. A duramax runs a big lifter with a big wheel on the bottom, it's not a problem. By opening the lash you open the valve faster at the start of the opening ramp on the lobe. The intensity rate at the valve will go up. I hope this helps to explain it better. For the guy who went to school at SAM ask Judd what way he would go when trying to get everything out of a car while qualifying a Pro Stock or Hot Street motor. Jeff
Click to expand...

Lol I never attended SAM, but spent hours upon hours on the phone with Erik who built the longblock for my previous 434 ls motor.
 
.008/.018 on my hamilton 181/210. Noticed about a 100rpm better spoolup vs .010/.020.
 
Hamilton Cams said:
Running more or less lash on the exhaust profile is okay because the ramp rate is so slow in comparrison to the intake ramp. Running more lash on the intake can break parts because the point at which the cam contacts the tappet the cam will be going much faster than it would be at the prescribed lash setting.

The top lines are velocity, the bottom line is the lift curve. I drew lines to show you how much velocity there is at each lift point. This is an intake profile with two different styles of lash ramps. Our design is the dark blue.

Red line is .010" lash
yellow line is .015"
white line is .020"

Running .020" here is dangerous. The velocity is 3X what it is at .010". Running a tighter lash on the intake as you can see will gain you little if any extra area. Running tighter lash does increase lift by the amount the lash was decreased by. It also opens the valves sooner but, this varies based on how the ramp is shaped, as well increases duration a small amount across the entire profile. I would not play with different lash settings much on the intake too much. On the opening and closing of the intake if you ran .020" the velocity is 3x what it should be when the valve is opening and closing, this will hammer and snap your tappets to little pieces.

On the exhaust, decreasing lash can open the exhaust valve sooner which will make a larger pressure pulse hit the chargers. This creates better spool, more boost and at max power it creates more drive pressure. This is why on performance cams with large exhaust profiles, you need an external gate to control excessive drive pressure. Large duration exhausts usually have more overlap so high drive pressure really kicks your butt.

decreasing lash on the exhaust will make the lash be taken up at a point with less velocity. Less velocity, less noise. More lash, more velocity much greater valve noise.
Click to expand...

Sorry it should have been decreasing the lash on the last paragraph not increasing...fixed it.

On the duramax grinds, that will only gain you power if you have a slow ramp you are doing t on, and it wil lonly work with a bigger than factory grind, not on a stock grind. If you already have designed very fast acceleration into the cam, you will be at a point where velocity is too great if you loosen lash and you will wipe a lobe or damage a lifter.
 
depends on the profile, on some .020" might no be very high velocity at all on some .010" is crazy velocity. In general though, yes.

If you look at -30 degrees the velocity stays almost the same for around 12 degrees on the opening ramp, so you do have some leeway. on some profiles the lash ramp is only a few degrees and then velocity goes through the roof. Of all four event, intake opening usually has the most velocity. Too much lash there is where you will break something.
 
In general, lash ramps exist in solid valve trains (flat tappet or roller) and are there for a reason so the idea of running super loose lash to accelerate the valve faster upon lifting seems like a very odd and awful idea to me. Why not simply get a lobe with the ramp meant for the taking up of the lash than turning into ultra agressive if that is what you want? Loosening the lash may give you some power if you have too much cam and need to shrink the duration etc. but other than that I don't see the benefit and from what I gathered neither did Erik K.
 
If you grab a 6 pack of your choice beverage and sit and think about it, it is pretty simple. If a guy with my mental capacity can figure them out you guys will be rocket scientists, well some of you anyway.
 
Lash

I didn't mean it was the thing to do for everyone. It's not something that should be done by most people. I was simple stating that it would make more power and it does. I would always tell someone to get the correct cam for what they are doing with there setup. Sorry to rock the boat, carry on. Jeff
 
If you have the piston to valve clearance, 10 and 10 works great, been running it for years!

Jim
 
I was told years ago with these higher lift cams and various duraton's to set at 8/10 hot . ?????????? :blahblah1:
 
Jim I'm thinking of trying 8/10 on a stock internal with a 181/210 cam I should be alright? Or is that cutting it close?
 
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