Compression and Octane

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.

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.

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?

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.

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.

I've been running 12:1 and 93 octane forever with no issues. Plenty of street and track miles.

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.

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.

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 ,

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.

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.