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91 Ford Bronco Bigblock Prerunner
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Discussion Starter · #1 ·
Thanks to you guys I've learned a ton... I think I've gotten close but need a few pointers on quench and compression ratio eventually cam.
79 block bored .040 over so 4.40 bore 3.85 stroke 72cc scj heads 15cc forged dish pistons I should be at 9.9 to 1 and sounds like I'm close to goal of 10 to 1 since I want to run pump fuel however from what I understand stock its .04 under deck ? So is it worth decking .020 off to get better quench in so doing bumps me to 10.3 compression still safe for 93 octane? This is going in a 91 longtravel bronco 4.56 gears c6 ( stall TBD) 35 inch tires mostly offroad hillclimbing sand drag toy but streetable. Thanks in advance
 

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Iron CJ or SCJ A's?
Which pistons are you running?

Ideally no more than 10 thou in the hole at TDC.

HP and RPM requirements will dictate best static c/r.








Scotty J. "AKA" The "Mad Porter"
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Ported BBF iron head specialist & Aluminum heads from all sources.
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See our products in the Vendor for sale section
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91 Ford Bronco Bigblock Prerunner
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Discussion Starter · #3 · (Edited)
Scotty! You're the man who has led me this far we spoke the other day on the phone about my build that was headed in the wrong direction and now Ive revised... I have an email out to you anyway can I buy these parts from you or set me up with whatever you think. I'd at least like these heads touched up by you. Right now the parts list is Scj aluminum heads and Ic517.040 15 cc dish pistons. Shooting for 550 + hp 6000RPM possible with this setup?
 

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Did you measure piston to deck height or is 0.040" value calculated?
Ideally you want 0 or a few thou, so quench is head gasket thickness.
 

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Remember deck clearance is also part of piston to valve clearance. Lessening deck clearance will close that up some.
 

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91 Ford Bronco Bigblock Prerunner
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Discussion Starter · #6 ·
Did you measure piston to deck height or is 0.040" value calculated?
Ideally you want 0 or a few thou, so quench is head gasket thickness.
.040 was calculated... now with better calculation with new pistons its .020 I did not figure right for different piston height. Now it's 10.4 :1
 
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