Tight lash setting solid flat tappet cam

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mderoy340

mderoy340

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I'm currently running a Comp Cam XS274S SFT at .012/.014 lash RHS iron heads and hughes Al rockers. I set lash cold and have .001 change cold to hot. Comp cams specs the lash setting at .016/.018
When I installed the RHS heads I knew a future cam change was going to be necessary to get the most performance, but I'm thinking of closing the lash a little more to increase duration.
Anyone have real world experience doing this?
What's the tightest lash anyone has run successfully?
 
The big danger would be with too tight exhaust lash. I wouldn't be afraid to try .008 on the intakes, but exhaust i would be carefull. There is some cam and parts flex that changes lash depending on where the lobe is on the base circle. On my race roller with VERY BIG springs with 350 lbs on the seat, the lash swings from a setting of .015 cold to .019+ cold depending on where the lobe is. It is caused by cam flex. Your combo will obviously have a lot less, but it wouldn't hurt to check lash change, and duration change to stay out of trouble. As you get closer to zero lash, the running duration will rise rapidly.
 
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.001-.002 is about normal lash opening on an iron/iron combo and yet and still you have people today telling other people to set cold lash loose with an iron/iron combo.

It was wrong the first time it was suggested and it will be wrong every time it's suggested.

It's nice to see someone actually measuring and keeping track of important **** like this. Most guys ignore the small stuff and the wonder after the beast when the **** fails.


Ok, rant off.


As for cold lash, it's easier to test on the dyno. Well, not exactly cold lash but lash testing in general. You can sneak up on closing the lash. The first .004 or so with a lash that tight to start with is pretty easy. After that, you've got to be very attentive to idle characteristics and power. When you start getting too tight on the exhaust it will almost feel like you are floating the valves. So be cautious and be very attentive. It's pretty easy to see on the dyno, but you can do it if you are careful.

Like anything else, there is a diminishing return. With lash that tight, you are making greater changes in lash as a percentage with small moves than you are with a cam that lashes at say .028 o some nasty valve train crashing lash like that.
 
yellow rose said:
.001-.002 is about normal lash opening on an iron/iron combo and yet and still you have people today telling other people to set cold lash loose with an iron/iron combo.

It was wrong the first time it was suggested and it will be wrong every time it's suggested.

It's nice to see someone actually measuring and keeping track of important **** like this. Most guys ignore the small stuff and the wonder after the beast when the **** fails.


Ok, rant off.


As for cold lash, it's easier to test on the dyno. Well, not exactly cold lash but lash testing in general. You can sneak up on closing the lash. The first .004 or so with a lash that tight to start with is pretty easy. After that, you've got to be very attentive to idle characteristics and power. When you start getting too tight on the exhaust it will almost feel like you are floating the valves. So be cautious and be very attentive. It's pretty easy to see on the dyno, but you can do it if you are careful.

Like anything else, there is a diminishing return. With lash that tight, you are making greater changes in lash as a percentage with small moves than you are with a cam that lashes at say .028 o some nasty valve train crashing lash like that.
Click to expand...
Not sure if you were refering to my post with your rant? I edited and added " cold" after .019 for clarity. Nothing was said about cold to hot lash change. My whole post was about learning what will happen when deviating from the lash settings on the cam card, and also what CAN happen when checking lash in different spots on the base circle. Probably not terribly critical with lower spring pressures, but there will be some change. And if you are pushing the limits,,,,,,
On my race roller the cam grinder said DO NOT go more than .002 in either direction from cam card lash settings. That requires that I am very carefull about how i set lash to stay in spec.
 
You have to excuse yellow rose he smokes a lot of pot! He forgets who he's talking to and when he's talking to them. I myshelf was just mentioning the other day about setting cold Lash at around .019.
Myself if I felt like I had to play with the cam that much and get that close to problems I would probably just do what I just did and change the cam.
And of course me personally I would just call Ken at Oregon cam grinding and ask him what happens when you start messing with the Lash too much. I'm sure he could tell you exactly what would happen.
 
That was a good experience. Going to Oregon cam. Cam's standing on end on the floor that were taller than me! What does that stuff go to?
 
yellow rose said:
Like anything else, there is a diminishing return. With lash that tight, you are making greater changes in lash as a percentage with small moves than you are with a cam that lashes at say .028 o some nasty valve train crashing lash like that.
Click to expand...

YR, Mine called for 28/32 cold. I run it at 24/28 and have never had an issue.

Are you saying you think I could go tighter that that?
 
yellow rose said:
.001-.002 is about normal lash opening on an iron/iron combo and yet and still you have people today telling other people to set cold lash loose with an iron/iron combo.

It was wrong the first time it was suggested and it will be wrong every time it's suggested.

It's nice to see someone actually measuring and keeping track of important **** like this. Most guys ignore the small stuff and the wonder after the beast when the **** fails.


Ok, rant off.


As for cold lash, it's easier to test on the dyno. Well, not exactly cold lash but lash testing in general. You can sneak up on closing the lash. The first .004 or so with a lash that tight to start with is pretty easy. After that, you've got to be very attentive to idle characteristics and power. When you start getting too tight on the exhaust it will almost feel like you are floating the valves. So be cautious and be very attentive. It's pretty easy to see on the dyno, but you can do it if you are careful.

Like anything else, there is a diminishing return. With lash that tight, you are making greater changes in lash as a percentage with small moves than you are with a cam that lashes at say .028 o some nasty valve train crashing lash like that.
Click to expand...
My dyno is 1320 ft. I'll sneak up on the intake lash and see what happens first. I run a GV OD and this cam works well with a 2400 rpm cruise for the 100 mile round trip to get some track times. Thanks for the info.
 
gregsdart said:
Not sure if you were refering to my post with your rant? I edited and added " cold" after .019 for clarity. Nothing was said about cold to hot lash change. My whole post was about learning what will happen when deviating from the lash settings on the cam card, and also what CAN happen when checking lash in different spots on the base circle. Probably not terribly critical with lower spring pressures, but there will be some change. And if you are pushing the limits,,,,,,
On my race roller the cam grinder said DO NOT go more than .002 in either direction from cam card lash settings. That requires that I am very carefull about how i set lash to stay in spec.
Click to expand...


Nope. No rant at you.

It was an all purpose general rant at people who tell other people to set the lash .002-.004 LOOSE cold on an iron/iron engine because they THINK lash gets tighter.

I've never seen lash get tight with heat.

Had nothing to do with you. Don't know why you'd think that, as I didn't even quote you.
 
roccodart440 said:
YR, Mine called for 28/32 cold. I run it at 24/28 and have never had an issue.

Are you saying you think I could go tighter that that?
Click to expand...


Most likely. I'd start at .020-.022 cold and work with it.

There was a long, very long, nasty thread on speed talk about lash and lash ramps and when you catch the lash ramp. It was very interesting.

It was probably a year ago and I'm not sure the whole thread may have been deleted.

The point was on those cams that call for lash that loose have relatively long lash ramps and you can tighten the lash up quite a bit and just catch the lash ramp closer to the base circle.

Damn, I hope I'm saying that correctly, but I think that's close. Cams with lash ramps that are fairly quick (my cam lashes at .014/.016) don't have nearly the room to work with so you have to be real careful moving from what the cam card calls for either way.
 
gregsdart said:
I went .012 and .014 on a .590 mopar bb cam, no problems
Click to expand...


That's what I'm talking about. Those lobes have a lash ramp an mile and a quarter long. You can close up on that thing a bunch and as long as you can tolerate the change in duration and valve opening and closing points you can usually find some power.
 
yellow rose said:
Nope. No rant at you.

It was an all purpose general rant at people who tell other people to set the lash .002-.004 LOOSE cold on an iron/iron engine because they THINK lash gets tighter.

I've never seen lash get tight with heat.

Had nothing to do with you. Don't know why you'd think that, as I didn't even quote you.
Click to expand...
kinda seemed that way, i was the only response so far. No big deal.
 
That lash change on the 590 bb cam was worth a bunch,,,,, iron 906 heads on a 535 cube stroked 440.
 
I've lashed those XS comp lobes as tight as .010 int / exh with no problems that I was aware of. Tight lash will force the lifter to follow the lobe through the entire approach ramp, loose on the other hand will cause the lifter to crash into the flank = toasted lobe.
 
yellow rose said:
Most likely. I'd start at .020-.022 cold and work with it.

The point was on those cams that call for lash that loose have relatively long lash ramps and you can tighten the lash up quite a bit and just catch the lash ramp closer to the base circle.
Click to expand...

It's a MPP cam

I've been running .024/.028 since the day it first fired and was dyno'd. I'll take it down a little further and see how it likes it.
 
yellow rose said:
Nope. No rant at you.

It was an all purpose general rant at people who tell other people to set the lash .002-.004 LOOSE cold on an iron/iron engine because they THINK lash gets tighter.

I've never seen lash get tight with heat.

Had nothing to do with you. Don't know why you'd think that, as I didn't even quote you.
Click to expand...

I've seen lash loosen with heat. On my VW race car for example. And that ran .004/.006 cold.
 
roccodart440 said:
I've seen lash loosen with heat. On my VW race car for example. And that ran .004/.006 cold.
Click to expand...


That's what I was trying to say. Some guys say to set your cold lash loose with an iron head/iron block combo because they say that valve lash on those engines will CLOSE with heat.


I've never seen that.
 
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