Compression of 520 with P51's - 460 Ford Forum
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post #1 of 26 (permalink) Old 03-01-2012, 05:54 PM Thread Starter
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Compression of 520 with P51's

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?
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post #2 of 26 (permalink) Old 03-01-2012, 06:51 PM
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I'm showing 13.09:1.

As for the popping, I'm thinking timing and/or plug gap.

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post #3 of 26 (permalink) Old 03-01-2012, 07:25 PM Thread Starter
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Timing is at 30 right now, I'll have recheck the gaps, any suggestion on the gaps?
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post #4 of 26 (permalink) Old 03-02-2012, 08:25 AM
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popping

What type fuel were you running ?
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post #5 of 26 (permalink) Old 03-02-2012, 12:12 PM Thread Starter
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110 octane
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post #6 of 26 (permalink) Old 03-02-2012, 12:18 PM Thread Starter
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Changed carbs and it's still popping thru the exhaust at 5,700 rpm. The plugs are gapped at .030
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post #7 of 26 (permalink) Old 03-02-2012, 05:19 PM
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If you're running flattops, zero deck and HGs in the ~.040" thick range, static compression shouldn't be much more than 13:1. Something in the ignition system is playing foul. What's the ignition system made up of?
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post #8 of 26 (permalink) Old 03-02-2012, 05:34 PM Thread Starter
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An MSD Digital 7, an MSD HVC coil, and a locked out MSD distributor.
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post #9 of 26 (permalink) Old 03-02-2012, 06:06 PM
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try different plug wires, think i had this problem once, had one bad wire with brand new set, put an old set on and away we went
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post #10 of 26 (permalink) Old 03-02-2012, 11:50 PM
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An MSD Digital 7, an MSD HVC coil, and a locked out MSD distributor.
Did you try Fuel with more octane?

Later Mark.
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post #11 of 26 (permalink) Old 03-03-2012, 08:13 AM Thread Starter
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I'm going over this morning with a new set of plugs, wires, MSD box, and 120 octane fuel.
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post #12 of 26 (permalink) Old 03-03-2012, 09:22 AM
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Quote:
Originally Posted by juiced520 View Post
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?
http://www.dvorakmachine.com/Calc_staticCR.shtml
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post #13 of 26 (permalink) Old 03-03-2012, 03:08 PM Thread Starter
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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......

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post #14 of 26 (permalink) Old 03-03-2012, 05:09 PM
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Congrats! That's really impressive! did you try different timing settings to see if you could get any more out of it?

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post #15 of 26 (permalink) Old 03-03-2012, 05:16 PM
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Quote:
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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......
Very nice numbers with your build, there was a build by a guy on here with 572ci...p-51...and more comp than you and made 934hp!!!!...........you should be happy
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