Need help on what compression ratio to go

Jonathan

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buying a brand new shortblock from mmr but dont know what compression ratio to go.
Looking to go full e85 on a ported eaton with ported heads from mmr. if anyone can give me some tips on what would be the best route id highy appreciate it thanks
 

Jonathan

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What about if for whatever reason I cant pump e85. Here in California its hard to come around e85 stations from the city im from, what would be the best C/R for running 91 octane and e85 if that makes sense
 

01yellercobra

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So are you planning on running E85 part time or full time? That makes a difference.

IMO....if it's going to be on 91 90% of the time run a 9:1 compression. If it's going to be on E85 most of the time with 91 on rare occasions you can't find it then run 10:1 and have a conservative tune written for 91.
 

Black02GT

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My $.02 don't waste time with an Eaton on a built engine. Especially thinking of running high CR on pump you'll be adding a lot of heat to get your money's worth out of that engine. Plus ported heads (and cams?) You're looking to flow big on the top end where the Eaton drops off. I have what you're thinking of building (10.6:1, heads, cams) and even my 2.3 TVS feel undersized for what the engine can flow.

Also, maybe if you're local MMR might be better but my experience was a nightmare on a build a few years ago. Got like 1500 miles out of my long block before it put a rod through the block. Even during the build hard to get a hold of anyone who knew my engine was even there. Just don't seem to want to build 4.6s anymore.
 

01yellercobra

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My $.02 don't waste time with an Eaton on a built engine. Especially thinking of running high CR on pump you'll be adding a lot of heat to get your money's worth out of that engine. Plus ported heads (and cams?) You're looking to flow big on the top end where the Eaton drops off. I have what you're thinking of building (10.6:1, heads, cams) and even my 2.3 TVS feel undersized for what the engine can flow.

Also, maybe if you're local MMR might be better but my experience was a nightmare on a build a few years ago. Got like 1500 miles out of my long block before it put a rod through the block. Even during the build hard to get a hold of anyone who knew my engine was even there. Just don't seem to want to build 4.6s anymore.
The eaton might be a budget thing. Local guy ran an eaton on a fully built engine. He needed to save up for the Whipple after dumping a chunk of change on the engine. Was kind of interesting though as a eaton pullied for 12-14psi only made 8psi on his engine.

I wouldn't trust MMR to rebuild a lawnmower engine. They have good parts, but unless you're a race team I wouldn't let them assemble anything.
 

RainyP71

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Subbed. Op, im trying to do a somewhat similar engine. Sticking to a mild build, with a long block combo to handle 600hp with ease and reliability, but starting out N/A, then swapping a stock pullied eaton I have once I have the time to modify the car to run the heat exchanger and intercooler. After that's running I'll start on my all out Aluminator build. Was flirting with between 10 or 11:1 with e85 as it's available around here, but have not looked at the math yet to see if everything will be in a safe range. Im sure people with more e85 expertise can chime in, but anecdotally everyone with an engine built for e85 SEEMS to say you are wasting your money if you don't go at LEAST 10:1, some (Ed, the man) saying you should be closer to 13:1 than 10:1 in a full race application with high ethanol content fuels. I have attached a great article which should help you out that I have been chipping at slowly. No matter what you choose, there will be tradeoffs. Knowing exactly what you want, and what choices net what pros and cons is what is important to your engines performance, but more importantly the value you perceive from your hard work. If you bench race a combo in your head, do all the math, and all your calculations come into a range you are comfortable with, then I don't think you'll be unhappy.

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xblitzkriegx

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Solid advice given here. Use a blower that covers your power goals and give yourself room to grow.

I'll add that's it's always going to be easier to add boost or timing than it is to remove compression.
 

Black02GT

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Subbed. Op, im trying to do a somewhat similar engine. Sticking to a mild build, with a long block combo to handle 600hp with ease and reliability, but starting out N/A, then swapping a stock pullied eaton I have once I have the time to modify the car to run the heat exchanger and intercooler. After that's running I'll start on my all out Aluminator build. Was flirting with between 10 or 11:1 with e85 as it's available around here, but have not looked at the math yet to see if everything will be in a safe range. Im sure people with more e85 expertise can chime in, but anecdotally everyone with an engine built for e85 SEEMS to say you are wasting your money if you don't go at LEAST 10:1, some (Ed, the man) saying you should be closer to 13:1 than 10:1 in a full race application with high ethanol content fuels. I have attached a great article which should help you out that I have been chipping at slowly. No matter what you choose, there will be tradeoffs. Knowing exactly what you want, and what choices net what pros and cons is what is important to your engines performance, but more importantly the value you perceive from your hard work. If you bench race a combo in your head, do all the math, and all your calculations come into a range you are comfortable with, then I don't think you'll be unhappy.

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FWIW 10.6:1 is where I landed with a set of flat tops. I don't know how much more you can go without going domed which I wouldn't do myself. Dont know if I'd run pump e85 on 13:1.

Other things to think about are the cams you run. That will change dynamic compression so the statuc CR numbers get skewed a little for what you're ultimately shooting for.
 

98 Saleen Cobra

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Run 10-11:1. Have a tune written for no boost or wot for 91. Basically a tune to get you to the e85 station or cruising around. Pretty easy.
 

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