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Author Topic:   Lash v duration
Clevo377
Gearhead

Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000

posted 08-19-2001 05:14 AM     Click Here to See the Profile for Clevo377   Click Here to Email Clevo377     Edit/Delete Message   Reply w/Quote
In general, how many degrees difference in duration does adjusting the lash on a mechanical lifter cam make, and how far can you go?

Paul

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kid vishus
Gearhead

Posts: 6098
From: middle of NC
Registered: Oct 2000

posted 08-19-2001 09:33 AM     Click Here to See the Profile for kid vishus   Click Here to Email kid vishus     Edit/Delete Message   Reply w/Quote
On a solid, I was told .004 or .005 is all you can safely alter them from the crad specs.

I hae tried changing mine before, and the only time it helped at all was when the cam was way wrong for the motor. If the cam is even close to being the right grind, I saw almost no difference.

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camachinist
Gearhead

Posts: 102
From: Fresno,CA,USA
Registered: May 2000

posted 08-19-2001 02:05 PM     Click Here to See the Profile for camachinist   Click Here to Email camachinist     Edit/Delete Message   Reply w/Quote
Clevo377

You can quantify this when degreeing in the cam...

IME, not much duration gain is experienced, certainly not enough to make a noticeable performance gain. As the lifter is on the clearance ramp during the takeup of valve lash, very little lift is effected.

With aluminum heads, I tend to run the lash on my SVO A333 cam at around .023-.025" hot....and likely wouldn't consider tightening it up....or loosening it. There's plenty of other more easily mined routes to increased performance IMO.

Pat

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SteveLaRiviere
Administrator

Posts: 43151
From: Saco, Maine
Registered: May 99

posted 08-19-2001 05:16 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Pat, nice to see you posting again!

------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
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Ford. The closer you look, the better WE look!

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Mike_R
Gearhead

Posts: 176
From: Indianapolis, IN 46237
Registered: Feb 2001

posted 08-19-2001 08:20 PM     Click Here to See the Profile for Mike_R   Click Here to Email Mike_R     Edit/Delete Message   Reply w/Quote
It generally takes a change of about .0015" to .002" to the lash to alter duration by 1 degree. So if you were going from say .028" lash to .020" lash it will add approximately 5 degrees of duration to the cam. Of course this can vary some with different rocker ratios and different lobe agressiveness. I saw a 514 crate engine in an article that picked up about 20 horsepower just by changing the lash from .028" to .020" because it effectively shifted the powerband upward with the longer duration. So you can use it to some degree to adjust your cam, but the best scenario is to find the correct grind on the cam and then run it fairly close to the lash specs recommended by the manufacturer.

What I've done on my current 460 is I bought a cam that was a little bigger than I needed for the 460 because I have future plans to use it in a 513 cubic incher. So I'm running it with the lash on the loose side on the 460 to lower the duration somewhat. Then when I stick it in the 513 I will tighten the lash up to the tight side to increase the duration

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Clevo377
Gearhead

Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000

posted 08-20-2001 07:09 AM     Click Here to See the Profile for Clevo377   Click Here to Email Clevo377     Edit/Delete Message   Reply w/Quote
OK, from what you say it is really most usefull for fine tuning.
Thanks for the replies,
Paul

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