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Old 03-10-2002, 09:08 PM
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Talking Alum.heads & HIGH compression

Back 10-15 yrs ago hot street motors w/iron heads were limited to cr.#'s of about 9.4 because 94 octane gas was/is the best you could get at the pump.
Today their are several alum.heads made for every popular motor combo.
With cams being built w/computer techmology,along with these alum.heads & the correct piston materal,I've heard that a high comp-ratio(12.5~14.0 to 1)can be built for STREET use & run on pump gas.
Anyone built such a motor or know of a shop that has ?
The reason I ask"shop" is the parts cost alone on this looks to run $5000+,I don't hav the know how to risk this much $$$
Thanks

All good replys,although I've heard most of it before,all except the Marvel Mystery oil ?
You who replied didn't mention what type eng.you had ?
What !'m wanting to build is a big block Mopar,498 in.or larger.
There are two"Mopar only" shops one in Ill.one in Mich.both well known to the Mopar faithful that are advertizing 12.5 cr.street motors that will run on pump gas.It's not that I don't trust these shops,but I'm in southern Ohio and would like to be closer to where I spend my $$$$.By the way the crate motors go for double the above parts cost,so you can see why personal contact with the builder is important.
Any Mopar guys HELP !!!

[ March 11, 2002: Message edited by: plysat ]</p>

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Old 03-11-2002, 05:37 AM
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I think anything over 11.1 and you are really pushing it for any street motor.
Thanks
DRIFTER
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Old 03-11-2002, 08:46 AM
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Ive never heard of anything that your talking about. I think 10:1 would be the highest i would go. Besides anything above that and you would have to buy either race fuel or octane booster. There is no way you could run pump gas on a street car with 11.5:1 compression.
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Old 03-11-2002, 12:06 PM
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I have 10.9:1 cr now, with alum. heads and a large duration cam and runs fine on 93 pump gas. I hit 6500 rpms often w/o any pinging, with a large cam the valve overlap helps bleed off the compression, but your right 10:1 does make a better street motor but you can run 11:1 run the street w/o race fuel.
Drifter
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Old 03-11-2002, 12:53 PM
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plysat,someones fed you a line of b.s.!10.5 ;1 is about max on 94 octane fuel,and even at that timing will be critical.happy rodding!jimm
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Old 03-11-2002, 05:42 PM
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I have close to what Drifter has,with alum. heads
I'm running 11:5to1 on compression on 93 pump gas.
Try using Marval Mystery Oil in your gas. You can safely run 1 point higher compression with alum. heads and be safe and no ping . Use flat top or even better yet dish pistons for better flame travel.
I just put on a cross ram intake and WOW.
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Old 03-12-2002, 03:59 PM
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11:1 can be done and be streetable but when you start getting around the 12:1 range you will run into trouble in a street motor with out racing fuel or octane booster. With cast iron heads I would not run over 10:1, there is no way you could run 12:1-14:1cr without major problems, also on the dyno the hp per one cr point is not that great, certainly not worth the headache.
Just my opinion
Drifter
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