CR suggestions for turbo E85
CR suggestions for turbo E85 I am looking for compression ratio suggestions for my build. I have a Gen 4 aluminum block 5.3 and going to do a forged rod/piston combo with new bearings etc.. It will be a turbo set up with A2A intercooler on E85 and ran with Holley HP EFI. Also, 243 heads. I’d like it to handle 20-25 psi. I was thinking 10:1 but the machine shop that I took my engine to acted like that was too high. Any input or suggestions are appreciated.
Last edited by ZachJ03; May 2, 2020 at 12:58 AM.
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How much boost do you plan to "throw" at it? What rpm will it be run at? Do you have a competent tuner to define timing strategy? Do you expect to reach MBT at boost > 20psi?
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From: SOFLO
9.5 - 10.5 static on a street car sounds about right.
Do yourself a favor and google the topic. There are several articles and videos reference the subject that provide a good explanation of the effects of increasing static compression ratio vs. boost pressure. More static compression is not always a good thing.
Do yourself a favor and google the topic. There are several articles and videos reference the subject that provide a good explanation of the effects of increasing static compression ratio vs. boost pressure. More static compression is not always a good thing.
13:1 static with 30psi on E85 is definitely not street car territory which got my attention. I'm sure there's more too this story but like always there are plenty of people on here that pop off remarks but doesn't answer the questions.
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Sorry OP to derail earlier. Is this a street car? Wheel hp goal? Depending on goals, planned rpm and cam specs, will ultimately dictate where to spec static compression. Did your machine shop talk about/ask these things? If not, may not be the ideal place to work with. Either way, 5.3, e85, street car and max 7500rpm, I would run at least 10, target 11-1. This will generate good cylinder pressure and temperature when out of boost. Get up to temp quickly and safe with good tune. Lower SCR is more forgiving (wide tuning window especially with e85) with timing, etc. with boost >15+ psi.
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Jakson ran 12.5:1 on his destroked 6.0 with about as much boost. His build is on here in detail.
Static compression means very little. Dynamic compression matters more.
Bikes like the R1 have 13:1 compression ratio and run fine in 91 octane. Don't get scared by big numbers.
Shoot for somewhere around 9.5 to 10.0 and let the boost do the work, you will have a MUCH larger tuning window and turbos love higher pressure ratios anyways. Plus your big limitation is keeping the heads on the block no matter what fuel you are running, and while E85 is good its also not very forgiving at the limits like any alcohol based fuel.
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Shoot for somewhere around 9.5 to 10.0 and let the boost do the work, you will have a MUCH larger tuning window and turbos love higher pressure ratios anyways. Plus your big limitation is keeping the heads on the block no matter what fuel you are running, and while E85 is good its also not very forgiving at the limits like any alcohol based fuel.
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Not really. The difference in 9.5:1 and 10.5:1 is generally 3-4% of NA power. If you have a 400whp NA motor thats 16whp.....now add 30 psi, thats 48whp difference total. That's about 2 psi of boost lol. You end up with a larger tuning window at the lower compression. Doing it over again I would have dropped my CR by half a point or so to widen the tuning window for pump gas. That said E seems to not care about boost or CR anyways
I disagree so much with the 3-4% especially with power adder cars. No one figures in how much better higher compression spools, how much easier it is to make boost on the transbrake, etc, etc. Sure the gains may seems small but figure guys are spending thousand of dollars on intakes or other items that might gain 20horsepower. The more power you make the harder it is to make more so why leave power on the table.
Oh, and I already accounted for the power gains with boost. You can't make more than double NA power at 1 bar of boost. 4% of NA power is doubled at 1 bar. I accounted for 2 bar of boost PLUS the gain of NA power.