Another underdrive/harmonic balancer pulley question
Last edited by UnVMySS; Oct 23, 2013 at 06:56 PM.
The Best V8 Stories One Small Block at Time
that's what I did, 2 trips to autozone.. finally nailed it dead on
Got mine that way
Those deals are still around if you know what to look for, but I try not to buy used stuff from people anymore.. I got burned twice this last year
started with a stock pulley on a cammed motor.....went to an SLP and gained a couple of HP from the pulley change..
Later when I switched to my 408 I reused the SLP Underdrive Pulley.... when we went to the dyno my engine was falling off unusually early for the size of cam I have...
at the time it was a 248/252 on a 108 ICL...it was done by 6100 rpm and falling off quickly...quicker than expected by the cam builder and by myself.
from tuning hundreds and hundreds of cars I knew it should be more like 7000-7200 with that cam
we looked at everything...springs, valves, pushrods, lifters.....nothing made a difference...
I was stumped...but an engineer buddy of mine thought it may be harmonic vibration related.....being caused by the damper....or not being controlled by the damper
after a thorough discussion and talking to him about his racing experiences...I thought it was worth a shot and worth the piece of mind anyways since I was going to make more power with a power adder and I wanted to prepare for a dry sump or a vacuum pump anyways...
I bought a Full size ATI pulley/Hub combo with a Gilmer(HTD) belt drive on it to prepare for the vacuum pump
across the entire RPM Range(starting about 3000 rpm) I picked up 5-10 HP..... and my RPM carried out to 7400 rpm as expected...
all that issue(on my setup) was caused by an SLP underdrive pulley
so I gained power over the SLP Underdrive pulley by switching to the ATI, and I gained stability that allowed me to hold my power out to higher rpms.





