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Compression and Octane #2573134
11/02/18 06:06 PM
11/02/18 06:06 PM
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Michigan
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Kiddart Offline OP
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Kiddart  Offline OP
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Dumb question but I am putting together a 2004 5.7L with stock heads and I want to know what is the highest Compression I can go and still maintain using 93/94 octane gas. I want to stay away from the 110 octane due to it being $7.99 per gallon.

help and I am grateful for all answers. I am back to learning all over again.


Last edited by Kid-Dart; 11/02/18 06:07 PM.

Thank you
Kiddart
Re: Compression and Octane [Re: Kiddart] #2573191
11/02/18 08:14 PM
11/02/18 08:14 PM
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Kalispell Mt.
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HotRodDave Offline
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Plastic intake still?

If yes then at least 11 to 1. The 6.4 is about there with 205 thermostat and a lean emissions friendly mix and you know they put a little room to spare in it. Probably be silly to go under 11.5, these things are very octane tolerant.

Aluminum intakes heat the air a bunch and will probably take 1 to 1/2 point less compression.


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Re: Compression and Octane [Re: Kiddart] #2573357
11/03/18 10:38 AM
11/03/18 10:38 AM
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Kiddart Offline OP
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Hi hotrod,

I will be using the new Prefix Cascar intake. So I feel 10.1 or 11.1 I can still run premium gas? that would be awesome. it does have the stock chamber head. I will plan on getting the compression up.

anyone else like to weigh in?

Last edited by Kid-Dart; 11/03/18 10:39 AM.

Thank you
Kiddart
Re: Compression and Octane [Re: Kiddart] #2573486
11/03/18 03:23 PM
11/03/18 03:23 PM
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Kalispell Mt.
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HotRodDave Offline
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On my engine build I would shoot for 11 to 1 then or maybe a hair less but not more. I would focus on things like a tight quench and getting as cool air to it as possible and with an ignition curve made for the modern hemi motor instead of a 1950s design wedge it should be fine.


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Re: Compression and Octane [Re: HotRodDave] #2579861
11/18/18 03:06 PM
11/18/18 03:06 PM
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Taxes & Virus's R-US, NY
Dragula Offline
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12:1....And maybe a little more 12.4:1 or so. Tune up has to be right on though. Hemi's can tolerate a lot more compression than other engines. And with twin plugs per cylinder, the G3 is the best.

If I find a block for my heads, I am going 13:1 with the thinnest head gaskets I can get and go from there.

Last edited by Dragula; 11/18/18 03:07 PM.

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Re: Compression and Octane [Re: Kiddart] #2579899
11/18/18 05:57 PM
11/18/18 05:57 PM
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Smyrna, South Carolina
STEFF Offline
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I've been running 12:1 and 93 octane forever with no issues. Plenty of street and track miles.

Re: Compression and Octane [Re: Kiddart] #2579962
11/18/18 08:50 PM
11/18/18 08:50 PM
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Rust Belt, SW PA
Silver70 Offline
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Lots of people put the eagle heads on the earlier engines and that puts them around 12 to 1. If using a stock ecu, just need a tune.


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Re: Compression and Octane [Re: Kiddart] #2580107
11/19/18 09:04 AM
11/19/18 09:04 AM
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Australia
aus370 Offline
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Cam selection has influence on what your dynamic compression ratio ends up at : that's what a smart guy told me ; anyway It's worth looking into.



Re: Compression and Octane [Re: Kiddart] #2580110
11/19/18 09:48 AM
11/19/18 09:48 AM
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Trumbauersville PA
ric3xrt Offline
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FWIW, the 428 in my 2014 Ram is 12.6 to 1 static with the Eagle head and I run a comp cams"270"
Duration @ .050" Intake: 222
Duration @ .050" Exhaust: 230
Valve Lift Intake: 0.615
Valve Lift Exhaust: 0.609
Lobe Sep. Angle: 115

93oct......A good tune is a must ,


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Re: Compression and Octane [Re: Kiddart] #2580133
11/19/18 11:41 AM
11/19/18 11:41 AM
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Michigan
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Kiddart Offline OP
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this is lots of good info here. right now I have no issue filling up with 93 octane. the price of that sure beats race fuel. I really don't want to go over 11 to 1 right now because I may boost later. at that point I will change the slugs(pistons) and get right back to 9 to 1 and use some boost. that's way down the road. for now I want miles on this car to pay for the investment.


Thank you
Kiddart
Re: Compression and Octane [Re: Kiddart] #2598265
12/29/18 07:22 AM
12/29/18 07:22 AM
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Charleston
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sixpackgut Offline
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I think about this alot and with the low spark lead on timming i am wondering if its possible to run well into the 13s with some tight lobes


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Re: Compression and Octane [Re: sixpackgut] #2598315
12/29/18 12:02 PM
12/29/18 12:02 PM
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Trumbauersville PA
ric3xrt Offline
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Originally Posted By sixpackgut
I think about this alot and with the low spark lead on timming i am wondering if its possible to run well into the 13s with some tight lobes


I think it's possible.


Truth has no agenda, but those with an agenda make their own truth.
Some of us are so open minded they only see their View









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