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One of the best kept SECRETS
of tuning a racing engine for the BEST OVERALL TORQUE curve is the OPTIMUM
setting of the VALVE LASH !
Why not just use the lash that the camshaft SUPPLIER gave you with the
camshaft. Well, he probably is giving you the lash that he says is the
"BEST"! Of course, he got this lash number by reading some "professors" CAM
BOOK !
In my opinion, ALL these books are WRONG ! His numbers were probably
extracted from previous books and articles he read.
Why not develop YOUR OWN VALVE LASH numbers by actually trying different
lash numbers on your engine dyno or race track testing. I have developed
this method during the past fifty years of testing different camshafts under
actual testing conditions.
Try this method:
1. Set the lash COLD at the specs furnished with the cam. Test and record
ALL the numbers.
2. Tighten the INTAKE only lash .004 thousands (0.1 MM) and see if the
recorded numbers are better (OVERALL) or worse. Use a GRAPH of these numbers
for a better view of overall data.
3. If the numbers are BETTER continue TIGHTENING the lash in .004 increments
and record all the numbers.
4. If the numbers are WORSE LOOSEN the lash in .004 increments and
record all the numbers.
5. Find the BEST OVERALL GRAPH and use this lash to run this same procedure
on the EXHAUST LASH.
6. After finding the best lash for the exhaust, rerun the INTAKE "LASH LOOP"
for any possible improvement.
This LASH LOOP method will also tell you if the engine needs a different
PROFILE on the INTAKE or EXHAUST lobes. A MUCH TIGHTER intake lash indicates
you might request an intake profile with MORE DURATION AT FIFTY THOUSANDS
CAM LIFT. Request at least FOUR or FIVE degrees !
Of course, if the LASH LOOP says more lash was better, you need LESS
DURATION in these same size steps.
I have found the Chevrolet V8 small block mechanical tappet camshaft part
number 3849346 (sometimes referred to as a "30 30 DUNTOV" because the GM
factory says the lash is set at .030 thousands) runs MUCH BETTER at about
.045 thousands lash. |
