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E85 and boost, what compression ratio could I run?

Old 09-06-2017, 04:16 PM
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run 15:1 and 30psi. For science
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Old 09-06-2017, 04:22 PM
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I genuinely wonder how high you can go on a dinky BP head before you run into serious issues
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Old 09-06-2017, 04:26 PM
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Try these and let us know


Last edited by aidandj; 09-06-2017 at 04:44 PM.
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Old 09-06-2017, 05:04 PM
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Originally Posted by 18psi View Post
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!
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Old 09-06-2017, 05:35 PM
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e85 does knock/detonate with enough craziness thrown at it, so there's that.
and then there are the physical load limits you mentioned
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Old 09-06-2017, 08:51 PM
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Originally Posted by patsmx5 View Post
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.
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Old 09-06-2017, 10:44 PM
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Originally Posted by 18psi View Post
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 View Post
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?
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Old 07-14-2018, 06:51 PM
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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?

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Old 07-14-2018, 07:30 PM
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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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