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I am putting my 496 together and am ending up with 8.5:1, I was hoping for 9 or a little higher, as I want to run on pump gas.
My question is, what kind of power difference am I looking at to bump it a point. I realize that CR is a very basic ingredient and is only but one factor of many.
Here is what I am running:
496 (4.31x4.25)
Ported Dart Iron Eagle heads
Comp Cams XE274 (230/236 @ .050 and 110 lobe sep)
Dart Manifold
EMI Exhaust
Is taking the trouble to boost the compression a little worth it?
Thanks all.
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Here's a basic idea. 496 inches...6500 rpm...hp possible.
8.5 = 482 hp
9.0 = 511 hp
9.5 = 539 hp
10 = 568 hp
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Fiat seems pretty close there. From the looks of it, a little, no, not worth it. A lot, maybe.
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Hey Fiat,
How did you come up with those #s, interesting. Can you give me the same #'s on a 305
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Here's a great article on power vs compression ratio. It will answer your question in more detail but using thier chart it looks like you'll lose ~1.75% or about ~9hp out of 500hp possible. The article author, David Vizard, is pretty darn sharp and has a bunch of books out.
Don't sweat it and enjoy being able to burn 87 octane!
Compression vs Power (http://www.popularhotrodding.com/tec...power_squeeze/)
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Hey Fiat,
How did you come up with those #s, interesting. Can you give me the same #'s on a 305
Camshaft design software using 100% volumetric efficiency and sea level elevation. I chose 6500 rpm as just a number as I have no idea of the mans application.
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Had I had time, I was going to put something together on DD and then vary comp ratio, and likely get results close to yours Fiat.
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Hmmmm, thanks for all the info. I certainly won't be running 6500 rpm, up to about 5500 for me...I don't think my King Cobra would like too much more!!!
So, the next question is...what CR do you think I can get away with on pump gas, don't care if its premium or not, I just don't want to run Trick or VP (been there done that)
At 6500 the trouble is absolutely worth it but not so sure at 5500 max. And actually its not so much the cost, it's time...another week w/o my motor :220v:
Damn, not even 500hp from this thing on your program huh FIAT48...that kinda sucks
Thanks again to all that replied
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Remember those numbers are only possible if:
#1. You turned 6500 rpm
#2. Your engine had 100% volumteric efficiency
#3. Where you were running the engine was at 0 elevation, 60 degrees temperature and 0% humidity. Rare day indeed. Most days have less air available so less hp available.
5500 rpm at 8 to 1 = 384.5 hp
8.5 = 408 hp
9 = 432 hp
9.5 = 456.5 hp
10 = 480.5 hp
Sorry I do not know what compression you can get away with on pump gas. Would guess maybe 9 to 1. Depends on camshaft also.
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Ya I know!!!!! Not likely :)
Oh well, I decided to take the puss way out and just leave it. The boat was fun and pretty fast to me (definately fast enough to get me introuble in rough water) before with a tired stock 454.
So I guess I shouldn't be concerned with #'s because I know there is going to be a considerable difference between the new and the old. In addition I longevity is very important. So with all that I am leaving it.
Thanks for all the responses.
