Xtremejr
Member
Hold my beer and watch this shit.
Posts: 493
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Post by Xtremejr on Dec 6, 2014 18:55:19 GMT -5
So my 425 block with a 400 crank is finished. had new flat top pistons installed, the machinist was curious what heads i was planning on running so i said i was going to use the 400 A heads on the 425 and he said that I will not be able to run pump gas cause of the high compression? Also a new cam from mondello, Int-300 Ex-310, lift intake-480, ex-496. I believe its mondellos part #20-22 cam. Any thoughts on fuel? and or cam selection?
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Deleted
Deleted Member
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Post by Deleted on Dec 6, 2014 19:22:11 GMT -5
I run a 400 with the stock 350 pistons 4.057". Same cam 20-22. Need a little help for octane boost. Running around 32 total advance. Some race gas would wake the engine up. All good.
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Post by mongoose on Dec 8, 2014 8:18:41 GMT -5
Is the machinist able to calculate the compression ratio for you? You can get away with 10.25 to 1 or so with some aluminum heads, but you'll want/need to stay around 9.5-9.7 to 1 with iron heads or you'll have to mess with boosting octane (or retarding timing) to keep from getting detonation.
If you have easy access to a racing gas supply (and you don't mind the cost) then there's no problems. If not, then it becomes a PITA quickly, you drive the car less, then ultimately blow a head gasket and end up changing out the pistons or heads. I know... probably not exactly what you want to hear... but I've gone down the same path in the past.
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Xtremejr
Member
Hold my beer and watch this shit.
Posts: 493
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Post by Xtremejr on Dec 11, 2014 19:45:34 GMT -5
Would I be ok with 50/50 mix? 96+race gas?
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Post by mongoose on Dec 14, 2014 8:05:15 GMT -5
That will still depend on the compression ratio you're building into the engine, which you or the builder should determine. But from what I've read in your thread so far, a blended fuel with a net octane rating of ~96 should be fine, allowing you to set your timing where you want it without detonation. But it's still a really good idea to calculate your compression ratio.
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Xtremejr
Member
Hold my beer and watch this shit.
Posts: 493
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Post by Xtremejr on Dec 14, 2014 19:07:32 GMT -5
if my calculations were right it came out at 11:1
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Post by 64b09 on Dec 14, 2014 19:25:09 GMT -5
I know the gas station on 76th & Lincoln sold race gas, not sure if they still do.
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Post by mongoose on Dec 15, 2014 9:05:51 GMT -5
I've run an 11.5 to 1 455 with iron heads using a 50/50 mix of 93 octane and 100 octane avgas with good results. The composition of today's gas is a bit different, so you may have to make some adjustments on mix, or ignition advance, or jetting, but I think you should be fine if you can put up with the cost and effort to run enough octane to feed your engine.
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