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-   -   E85 and boost, what compression ratio could I run? (https://www.miataturbo.net/engine-performance-56/e85-boost-what-compression-ratio-could-i-run-90031/)

aidandj 09-06-2017 03:16 PM

run 15:1 and 30psi. For science

18psi 09-06-2017 03:22 PM

I genuinely wonder how high you can go on a dinky BP head before you run into serious issues

aidandj 09-06-2017 03:26 PM

1 Attachment(s)
Try these and let us know

Attachment 231740

patsmx5 09-06-2017 04:04 PM


Originally Posted by 18psi (Post 1437999)
I genuinely wonder how high you can go on a dinky BP head before you run into serious issues

What serious issues would you run into? Lift the head? crack the head?

LOL on the rods!

18psi 09-06-2017 04:35 PM

e85 does knock/detonate with enough craziness thrown at it, so there's that.
and then there are the physical load limits you mentioned

k24madness 09-06-2017 07:51 PM


Originally Posted by patsmx5 (Post 1437995)
Using your calculator, my current setup with 84mm bore, 85mm stroke, 5.233" rods, 9:1 compression, 50* ABDC inlet valve timing, and 40 PSI boost, I get
7.96 dynamic compression ratio
29.62 effective boost compression ratio.

That is already significantly over your 18:1 sane numbers.


If I ran 12:1 and 35 PSI boost:
10.57:1 dynamic compression ratio
35.74:1 effective boost compression ratio.

That's beyond where I would be comfortable. Kudos for boosting "All of it".

At 20 psi you're at 18.77 dynamic with the same above info. Again just my target on race gas or E85 in a highly stressed environment. YMMV. In for results.

patsmx5 09-06-2017 09:44 PM


Originally Posted by 18psi (Post 1438010)
e85 does knock/detonate with enough craziness thrown at it, so there's that.
and then there are the physical load limits you mentioned

Yeah, I think I have octane to spare right now. At least for how I use the car, which is street and drag.



Originally Posted by k24madness (Post 1438057)
That's beyond where I would be comfortable. Kudos for boosting "All of it".

At 20 psi you're at 18.77 dynamic with the same above info. Again just my target on race gas or E85 in a highly stressed environment. YMMV. In for results.

My spring pressure for wastegate is 30 psi.

So if you consider 18:1 safe for track, and I have gotten away with 29.62:1 effective compression ratio, that is quite a difference. Do you think you could run more boost, or more compression on your setup?

LownSlow616 07-14-2018 05:51 PM

I know this thread is about high comp and e85 but there is also some good info about high(er) boost levels and e85. I want to add some timing to my map but a lot of timing tables that Ive found are all for lower boost numbers.
I hit 22psi at ~4700rpm and it tapers up to 25-26psi by 7250. E85, stock 9.5:1 pistons, stock rings, stock head.
My current WOT, full boost timing numbers are highlighted in the picture. Could I safely add 4-5 degrees in all the cells?

https://cimg5.ibsrv.net/gimg/www.mia...daeb1fac9a.png

18psi 07-14-2018 06:30 PM

no such thing as a definitive answer to that. assuming you don't start knocking, and don't stop picking up significant power per degree of timing, you might. I have on several cars in the past


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