Just wondering how much I can adjust it outside what the card recommends. I wouldn't run any looser, just tighter. The cam card calls for .020" hot lash. Could I try half that, or would that be too tight? I've been wondering lately if I would run a little faster with a bigger cam, and I thought this might be a poor mans way of finding out. Tightening the lash to make it act like a slightly bigger cam just to see how the motor likes it.

Or am I completely in left field and this a bad/dumb idea all together?

 

not enough to gain there to bother, imo. would be fun to mess with on an engine dyno, though.

 

You could try to experiment but 0.020" lash is already considered tight. Typical lash is anywhere from 0.020" - 0.030"

Changing your lash to 0.010" would only gain you that much in lift but would also increase duration slightly as the valves will be opening sooner and closing later. This may cause other issues.

Without putting it on an engine dyno, I doubt you'll notice any changes. You would be better off just getting a different cam grind.

 

Well, maybe it was coincidence, but the car did pick up .5 mph by tightening the lash by .004". That's the only change I made to the car anyways since last time. And the air was worse than last time by a decent amount. Warm and very muggy and the DA was 800 feet higher. Ran the same 60' and same ET as last time. Last time was 111.8 mph and ran 112.3 Friday night. May try tightening it another .004" next time. Only got one run in because everyone was oiling down the track, breaking stuff, and wrecking into the walls. Bad night for racing.

 

too many variables between trips. if you want to measure a difference like that, make the adjustment at the track.

 

x2 of yesterday being a bad day racing, as I posted in the carnage sticky.


If your numbers hold true/average just bby changing the lash, then the cam is definitely not right for the combo. - Lots of big named engine builders/tuners & cam companies have noted, if a lash change makes a noticable difference in performance the cam isn't right for the combo.

 

Ouch! That sucks.

It'll be a few weeks before I get back to the track, but I'm going to leave the lash as is for now and make my first pass the same way to see what happens. Then I'll tighten it up another .004" at the track and see if it improves. At this point now though I won't be buying a new cam for it at all. At least not for a NA motor. I've had a 7.3 turbo laying around for a few weeks and my boss just gave me the go ahead that I could keep it (its the old turbo off a customer truck). Can't find any good data to say how much power it will support on a gas motor, but I did a few rough caculations on cfm flow and it looks like it could support the cfm for my motor at 6300 rpm and 10 pounds of boost and not be maxed. So it may very well work. And for a free turbo, I have to try it.

 

Here's a Car Craft article that did exactly what you're asking. Looks like it depends on your combination.

http://www.carcraft.com/techarticles...ng_valve_lash/