I know, I know-- Test one thing at a time. I'm just speculating at this point. #1 on the to-do is my new converter, #2 will (or might not be if I improve enough with the converter, if I do at all) tires, and #3 lash games.

My cam is spec'd 287/291 @ .020 256/260 @ .050 .643 lift 112 LSA.

It has been my opinion since the cam was selected is that it is a schooch too big.
When I talked to my cam guy the other day, I asked him about lashing it (looser?) at like .020 I .022 E instead of .016 I .022 E.
He said the maximum he feels comfortable playing around with is .004 on the cam, and only .002 if I am going to lash (tighter?) at like .014 .016.
Is there any way I can speculate what the actual "advertised/lashed" duration of my cam is when I set the lash at .016/.018?
Would it be harder on my valvetrain to lash it at .020/.022?
As I see it, this would in effect make it a "smaller" cam, which I think might be worth testing out if I am not seeing 119 or 120 with some more traditional tuning and the converter.
Because it didn't really occur to me that my 287/291 @ .020 advertised is not really a 287/291 as the engine sees it, because I am lashing it (tighter?-- sorry, I get the terms confused) at .016/.018
Also, I have a question about ICL, I have been always a bit fuzzy on what this does to the engine.
Comp recommended that the cam be installed at a 108 ICL, but my cam installer put it in at 104.75 ICL.
What did this do?

So is my as-the-engine sees it duration really something like 290/294 or whatever, because of where it is lashed?

Matt

MadMarv,

I generally don't touch Comp Cams questions with the proverbial 10-ft pole, but here are some general thoughts on actual duration vrs valve lash.
When the lash is set at .016/.018 on a big block, the ramp height is right around .010". I am using .01066667" right now, for .016" with a SBC 1.5:1. The valve train deflection means the valve moves off the seat enough(about .001") to claim airflow is started, and I call .015"=.016" valve opening-lift.
There is AT LEAST 4° difference between .020" and this valve opening number, perhaps more, depending upon valve/cam velocities. All my designs are unsymmetrical, so the closing sides have more duration on them than the opening sides. I do not know how unsymmetrical the Comp Cams are, I only know that the timing numbers they publish on their web site are SYMMETRICAL.
My guess is that if you assumed 4° to 6° more duration at valve lift-off, you would be right.

UDHarold

Thanks Harold. If it makes you feel any better, I argued with the guy to put one of your 287/295 solid rollers in, but he kept saying no.
Next engine is going with one of yours none of my cam builds has ever sounded as mean as your HR4 I had a few years ago.

matt

In my opinion, messing with lash affects duration at lower lifts more than duration at higher lifts. You can fine tune your overlap area somewhat and your IVC somewhat, but it won't make a large difference in flow overall.

I spent a mess of time degreeing and playing with my Comp 294s with different lash settings and rocker ratios . . . I'll email you the spreadsheet I made that kind of lays out the results. I don't know how to post it here or I would for everyone to see.

thanks Eric.. I broke two wheelstuds today and it took me 6 hours to remove them (including getting the car back to my house after borrowing a jack and retightening the 3 wheelstuds I had remaining, good thing I broke down about 1/2 mile walk from where I used to work, didn't even have my cell phone on me, I had just left the wheel alignment shop). The knurls were fused to the darn axle. I cut, drilled, hacksawed and finally tapped out with a punch the studs. Killed about 6 drill bits, had to drive to home depot for more (those bits were junk-- wore out quicker than the ones I had been using for 10 years).
I'll appreciate the data. Its been a nightmare day, and I didn't get anything done I expected to.


Matt