E85 turbo engine, which pistons 8.8:1 or 10.6?
 

So as mentined above, I´m going to install forged stuff in my block. Rods will be ebaystuff and arp headbolts and acl race bearings. I´m running with E85 fuel and I´m thinking what compression ratio to choose? 10.6:1 ratio might help with spool and performance below boost area.

Thoughts, experience...

if full time e85 definitely the higher compression

Yes, I´m using E85 all the time. Anyone else tried with higher compression & e85 & turbo?

Yes, its great. Nothing bad to say

Sold. Cheers!

I would go 11:1, but be forewarned that you will be restricted to E85 use with no exceptions. You cannot do a pump gas tune later on unless you decide to remove the turbo.

One curious question, if on 11:1 CR, and by the off chance that one had to put in pump gas, is it possible to set up the ECU/boost controller to dial down the boost to >5PSI and be safe from knock/det?

You would need 2 maps, and would be REQUIRED to wire that wastegate open.

Dann

I vote 13:1 why not.

Pump gas. If you have an EMS with a flex fuel sensor and timing/fuel trim OR alternate maps, you can pull this off. It will really complicate things though and you might even still knock at 0psi.

This is not a honda s2000. So yes pump gas will not work.

What about the addition of a meth and water injection setup? With fuel flex sensor and dual maps?

n n n

NO. I thought you were going E85 100% of the time????

Sure with water/meth AND a fuel flex sensor AND dual maps you could run pump and boost with high compression pistons.

But

Do you actually know how to tune? You had better know how to tune or have a deep pockets and a great tuner to keep your engine from blowing up. Also, a WI system with failsafes will cost you around $400.

I run water/meth and pump and if I could run E85 all the time, I would throw the stupid WI system in the trash.

I bet you it still won't work.

These motors sometimes knock bone stock on 91oct. If that doesn't give you an idea of how bad it is then I don't know what will.

They also consistently knock on 89 octane. My stock 99 audibly detonated. Crackle crackle. :drool:

No.

I don't know miata's like I know DSMs and Evo's, but in the "other" world we've been going bigger and bigger with compression ratios on pump and E85. Its not uncommon to see 10:1 or greater running over 25psi on 92oct. Now there's a huge apple to walnuts comparison here and Evo's have great heads, but why doesn't tuning for MBT with high compression and med to high boost work on the miata's as well?

What's a walnut? A faogr lik you?

Tuning for MBT with high compression works like shit because you are fagora

Because in addition to having inferior flowing heads, we also had nearly non-existant knock detection, meaning most tune these cars "by ear".

Now that more EMS' are offering advanced knock detection, we can finally make some progress in the right direction....Like the rest of the world has over 5 years ago.

I choose 9.5:1 supertechs to my E85 engine and now kind a regret that i didn’t get 11:1. At Dyno max torque was around 20deg BTDC (@200kpa). We tried to everything between 20-28deg BTDC but torque was the same. It isn’t knock limited by any means

You need moar boost, not timing.