I've been searching for the answer but just to clarify...

If I get forged pistons for my EFI turbo build, custom made is perfered over the 2.2 forged pistons. Right?

Who has the best service and products these days?

It's going to be an E85 fueled engine. If I run 10 to 15 psi of boost, what compression ratio should I strive for with the alcohol?

Any thoughts would be appreciated. Thanks

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About 8.5 to 1 should do. Thamks Ron Parker












Bagels On Juice Im On Boost

Whats the RON of E85 fuel???
We have E10 here, and its worse for fuel economy than 91RON ULP.

It all depends on what rods you use and if you want to do any milling. 2.2 pistons will be about .030" down in the hole with 198 rods, but around .330" down with a 225 rod. Decide on your piston after you decide on your rod.

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After quick search I came up with 104. (sorry it took so long to get back to this subject I was snowed in for a couple days and gone for a couple.)

Your fuel economy concern is the reason I want to do this. Ethanol blends are getting a bad rap because they are being used in engines that have to compromise between the E10 to E85 blends. A purpose built E85 engine can be as efficient as a petrol engine. Or at least that is what I hope to prove .

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From what I have read (please correct me if I am wrong) the 198 rods are getting tougher to find so I just dismissed that idea. A properly prepped 225 rod is plenty strong in many peoples opinions but is up to 15 lbs. of boost too much for them? If I have to buy aftermarket rods I may have to re-think my boost levels.

My main question for you engine guys is if it is worth it, or should I say cost effective, to do some heavy milling and use 2.2's or just order custom pistions to my specs?

And this is where my question on compression ratio comes in. Striaght ethanol like an air fuel ratio of 9:1 where petrol likes 14.7:1 Raising the compression will use more of the ethanol's energy. Do I just do this with boost or a combination of boost and chamber volume?

Thanks for the replies everyone

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With 225 rods 2.2 pistons will be around .325" down the hole. Don't know if you can mill enough to get back to 8-1.

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If you are going to use 225 (6.7") con rods, order custom pistons to whatever compression you want.
Only mill the head and block surfaces enough to clean them-up, dead flat. Leave these surfaces thick to help head gasket sealing.
DD

The E85 forum lists the RON at 129.

I think I am going to re-phrase my question.

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Ok. Let me ask you guys this.

I know that the 8:1 to 9:1 seems to be the normal compression ratio for turbo engines. Alcohol likes much higher ratios in normally asperated form. My question is how do I split the difference? When going down the road (not under boost) E85 is going to need more compression to achieve efficentcy. Under boost this isn't going to be an issue (odds are mileage wont be either ).

Does this question make sence? Because of the fuel used, do I need to up the static compression and lower the boost?

Am I confussed by this whole compression ratio/boost relationship?

Any ideas would be appreciated.

Chris

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