FrontEngineDragsters.Org Forum
Technical => Matt Shaff's Engine Shop => Topic started by: Supercat on January 21, 2018, 10:52:46 AM
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What is a good compression ratio for a blown 477 cu.in. alcohol engine?
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What is a good compression ratio for a blown 477 cu.in. alcohol engine?
That is a hard question and I do not profess to know the answer.
What I have heard is there are really two schools of thought.
1) keep the compression relatively low in the engine (9:1) and let the blower do all the work.
2) Let the compression be higher in the engine 11.5:1) and do not push the blower as hard.
My last engine I ran for 5 seasons with an engine that was set up al wrong for a blower (theoretically (11.5:1, long stroke, smallish piston bore) .
My new engine has less compression, shorter stroke and bigger bore.
https://www.youtube.com/watch?v=S0uwfDStmTY&list=PLCygmy1ErMtjruWj0jLgDVB8rH4N18_CI&index=2
Time will tell.
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The new 477 is a 4.500 bore and a short 3.750 stroke.
The heads flow 500+cfm
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It all depends on your tuning window. A high compression blown engine can be finicky, go from safe tune to detonation. I have been anywhere from 10-1 all the way to 11.8-1 on my SBC’s
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Lots of thing add to correct answer. Combustion chamber design,amount of boost are few of them. Our Hemi stuff ran 12 to 13:1. Agree that going on lower side helps tunning window.Plus with blower you can always up drive for more power. IMO 11 or 12 :1 works good. If small chamber heads I would probably go little less and tune to it.
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Our TAD was a roots blown 438 CI Hemi. The most we could get out of it for compression was 11.8/1. It was hard to make any more compression than that due to the combination of the short 3.750 stroke and the piston to head clearance required. The funny car guys back then typically made more compression (around 12.2/1) because they had more stroke to help them out. They were typically 526 CI
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We are at 10.3:1 with our Iron SBC. A 4.133 X 3.48 engine. It has been plenty fast enough and very reliable.
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Thanks for the replies everyone.
We should be around 11:1 from all we are looking at.
I can put a thinner gasket in to raise things up some, if needed later.
Any ideas on a fuel pump size I have a few to chose from.
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Thanks for the replies everyone.
We should be around 11:1 from all we are looking at.
I can put a thinner gasket in to raise things up some, if needed later.
Any ideas on a fuel pump size I have a few to chose from.
What HP are you shooting for?
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We are not trying to hit a certain HP level per say.
We are trying to get the highest level of HP and back things down to a reliable amount knowing we have more if needed.
We are trying to hit 215+ mph.
That is the Buick record. We may run TD if it is allowed?
Haven't looked into if there are any FEDs running in the class in Division1 or Nationally. Anyone know of any?
We will be running the engine at 496 cu.in. with either the 671 or this F3R ProCharger under the body.
Compression ratio of about 10.75
Thanks again for the info.
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FEDS are allowed in TD just have to be self starting meaning you can’t have an external starter
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Thanks Paul.
We are a self start. 16v system , spin it up and hit the Mag.