Has any one had any experience with a Holley 177 Supercharger. I was thinking of running one at about 7psi on 9.1:1 comp. ratio. Cocacolakidd.

 

I have it's little brother (the 142) on my 383. It works pretty well, athough I can't generate the boost of the larger blower (I currently run only 5 PSI and I'm one pulley set away from being maxed out). Even at only 5-6 PSI I will HIGHLY recommend you get the compression down a lot lower than that. Even at only 5-6 PSI I would keep it around 8.5:1 and err lower, not higher.

I currently run 8.7:1 (actual measured compression, not an estimate) with aluminum heads and I still can't crank the spark advance up as far as I'd like to get maximum power out of it without detonation on pump 92-93 octane. I currently run only 26* of total advance on the street, 28* when racing. Anything above that and there are obvious signs of detonation- car slows down and some of the plugs get coated with aluminum dust being blown off the pistons from detonation. No, you can't HEAR the detonation over the blower, but it's definitely happening.

This is my 2nd engine with the 142 on top (that I've had in my own car, anyway) and one of the hardest things I've had to get used to is that 9:1 is still a LOT of compression for a roots-blown engine on pump gas. Maybe the centrifugal guys can get away with it (due to more efficient blowers, possibly intercooling, and the fact their boost builds gradually with RPM). A roots blower ain't like that. ALL the boost is there RIGHT NOW, as soon as you boot the throttle, and it's heated up more than through a centrifugal unit. Don't let the dismal compression ratio I suggest let you believe the bottom end power will get mushy- believe me, it won't. It'll make bottom end torque by the bagfull.

My current combo would run faster if I was to lower the compression down to maybe 8.0-8.5 and then turn up the timing a little (at least up to maybe 30-32*) even with NO other changes. This is true of any engine- you'll always make more power with lower compression but full spark advance than you will with too much compression and dialing the timing back to keep out of detonation.

Stay conservative on the compression and work up the spark advance SLOWLY, checking at every step along the way.

 

FYI even with all of the stuff i have DfI, Intercooler, centrifical, race gas. I have never been past 25* timing.

 

Bigtime- you've got mail. I've been working on exactly that compression vs. timing issue for the last few months. I'd love to hear your experience on that subject.

 

Damon, email me bigtimeauto@verizon.net I hate PM's on this board.