12s 390
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Senior User
Joined: Mar 2005
Posts: 135
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From: indiana
ive got a question. what if i put a 428 crank in my 390 and kept the same connecting rods and just had the top of pistons shaved would it work. now im just looking into building a high compression engine.
Elder User
Joined: Jun 2001
Posts: 508
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From: Corpus Christi, Texas
Well now your using my idea...lol That is exactly how I built mine. The pistons actual set .004" out of th hole. Check out my gallery their are pics of my engine. I run racing fuel in it at the track. turn the timing down and run 93 octane in it around town.
Elder User
Joined: Jun 2001
Posts: 508
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From: Corpus Christi, Texas
Well their are a couple of ways. First you need to partially assemble your engine crank, cam, timming chain. install number 1 piston no rings. install your head, lifters and rocker assembly, but befoer you install your head you can either tape some feller gauges (roughly .100" or more) to the top of the piston, or put some marking clay on top of the piston. Rotate the engine over and as the valves open, they will leave a impression on the clay, or IF the valves hit the feeler gauges it will lock up the engine. If you us the clay, after the impression is made you will need to remove the head and measure the thickness of the clay. You will want a maxium of a .100", of sufficient clearance espscially on the exhaust valve. But you want also to get the piston as close to the head to get your quench. around .035 to .060. this will help with HP and pre-detenation.
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Post Fiend
Joined: Dec 2003
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From: "Islander"
I bet with piston expansion, rod stretch (steel), wrist pin and rod bearing your at .020" quench at 6,500 rpm's. I ran .028" quench years ago on a punched and poked 401 AMC motor, it had crushed carbon marks on the crown and heads at teardown. I like tight, funny so does the wife.
Last edited by "Beemer Nut"; Dec 4, 2006 at 08:55 PM.
Thread Starter
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Senior User
Joined: Mar 2005
Posts: 135
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From: indiana
i just got a 428 cj crank today and i get my heads 2morrow. polcat i have the same heads u do. i will probably start on the engine next week. im still looking for an intake though. so ill update u guys on my progress.
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Elder User
Joined: Jun 2001
Posts: 508
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From: Corpus Christi, Texas
You can email me anytime for help or suggestions. My buid up took 8 months but is was well worth the wait. Jus tmake sure you do alot of measureing. it will all work out!!! but is should be one nice engine!!!
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
The 390 rods are shorter and stronger than 360 rods.
Unless it's a chug chug build where you won't be jumping on it hard 360 rods will work but beware of piston combinations that will make piston stick up beyond the block.
Unless it's a chug chug build where you won't be jumping on it hard 360 rods will work but beware of piston combinations that will make piston stick up beyond the block.
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