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Compression of 520 with P51's

17K views 25 replies 15 participants last post by  AZEX2001 
#1 ·
I was told the compression of my 520 with P51's was 13.5:1, but after experiencing some problems with it on the dyno popping through the exhaust between 5,500-700, the dyno operator pulled his Moroso slide calculator out and it says a 520 with 72cc heads should be closer to 15:1 and that the 110 octane fuel is not enough resulting in the popping. We're going to pull my Quickfuel 1150 off tomorrow and try my buddies Quickfuel 1250 tomorrow and see if it pops with it and if it does we're gonna try more octane. Any other ideas on what may be causing the popping?
 
#13 · (Edited)
Problem Solved! The two wires going to the distributor were backwards, swapped them and fixed the popping. With 30 degrees timing it put out 921 hp and 720 tq at 6,200 rpm. Torque peaked at 728 at 6,000 and 899 hp. Do these numbers sound right or do they seem a bit high? I wasn't expecting it to make over 850......
 
#21 ·
What pistons are you running. I want to go 520, been talking with Kaase, but I want a more street freindly 10.5 1. The cam specs he was talking are right up there with yours though, if not the same.

Just wondering what the HP diff would be by dropping the comrpession down. Kaase said it would make over 800?
 
#23 ·
Did you ever figure out your actual compression, 13 or 15?
Either way, using the 25 hp per comp pt, Bob460 and I are still looking at over 800 HP on pump gas using this build with lower compression.

THAT ROCKS. Good on ya. Pesky wires. That multi colored plastic spaghetti scares the crap out of me. I have to re wire the whole car, I can only imaging what will come on, and what wont come on when I push a button:eek:
 
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