Compression Ratio Help!

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tdstuart

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For my car I do. If you are mostly using E85 I would not. I run mine pretty hard on gas and do what I can to prevent pre ignition and detonation.

If you really are going to use E85 then 12 to 1 is fine. But when you do use 91 baby it.
Sounds good, I think I can manage that.

 

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Maybe a 180+, but I think I will wait till I am able to upgrade the cooling. I got the motor too hot last time, and don’t want to do that again.

The 176 was on e85 if I remember correctly. And ya I would like to cc the motor but I don’t have the heads :(
Flex tune ?

What’s the hold up with the heads ?
 
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Flex tune ?

What’s the hold up with the heads ?
The heads have taken like 2+ months lmao. Getting a quote took a month.

And it was probably on a dedicated e85 tune at the time although I may have been running a flex fuel tune as I ran the flex tune a lot.
 

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I'd take a look at how you've enjoyed it for the last 12 months and then what were your planned mods for the immediate future (3-6 months ahead). If you are honestly about to boost it, build it for that. But if there's any real delay ( 1 year or more) before you slap a blower on, I'd build for NA. Life happens, things change. Especially if being used for daily duty or even partial daily duty.

How much is really gained power wise 12:1 vs 11:1? Has there ever been a real dyno comparison/time slips?

My own gen2 setup was limited to very similar timing numbers as k4 mentioned. 24 it 25 degrees on pump 93 was all she would take consistently na. Can't imagine what 12:1 would want.

11:1 and na or boost gets my vote. Tried and true. Maybe bit of ring gap added for comfort/ long pulls.

Thank you guys for posting all the math/calcs. Great reference for those of us that don't have as much experience
 
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I'd take a look at how you've enjoyed it for the last 12 months and then what were your planned mods for the immediate future (3-6 months ahead). If you are honestly about to boost it, build it for that. But if there's any real delay ( 1 year or more) before you slap a blower on, I'd build for NA. Life happens, things change. Especially if being used for daily duty or even partial daily duty.

How much is really gained power wise 12:1 vs 11:1? Has there ever been a real dyno comparison/time slips?

My own gen2 setup was limited to very similar timing numbers as k4 mentioned. 24 it 25 degrees on pump 93 was all she would take consistently na. Can't imagine what 12:1 would want.

11:1 and na or boost gets my vote. Tried and true. Maybe bit of ring gap added for comfort/ long pulls.

Thank you guys for posting all the math/calcs. Great reference for those of us that don't have as much experience
Good points. No idea how much hp I would gain from 11:1 e85 vs 12:1 e85. It just sounds cooler lmao.

I am a broke college student and my GF wants to get an apartment next year. So I will probably be broke for the foreseeable future. If I can afford boost I will get boost but I doubt I will be able to boost for awhile. Plus my trans has like 110k miles on it so I’m sure it will go soon. It’s why I want to lean on N/A. I could always pull the heads off and put a thicker gasket in to drop the CR back down to 11 (if I go to 12 now).
 
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Google;
3-4% per one full point.
Literally just typing that out, but you beat me to it.

Thats anywhere from 15-20whp if I assume I will make around 500whp with 11:1. Thats pretty good.
 
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The gt350 has a compression ratio of 12:1 with no direct injection.
 

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The link just basically says the same about how much power I should expect, right?
Yes and no. The 11 to 1 coyote is octane limited with 93 octane fuel. I get 24 degrees of timing. We don't have 91 so I can't log it.

If I up the compression and have to reduce the timing I won't get the 5% increase in power at WOT. I might get 2% or I might lose 3%.
 

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The gt350 has a compression ratio of 12:1 with no direct injection.
It also runs cam timing that bleeds off cylinder pressure.

I'm still studying the differences to try and understand why Ford did things the way they did.

So far it looks like they used cam timing to lower dynamic compression enough to be able to run enough spark timing to make the car livable on the street.

Ask any gt350 owner and they will complain about the lack of torque below 5000 RPM. Exactly opposite of what one would expect from higher compression.

The OP or WOT cam timing is also completely different from what any other coyote runs. In the tune the duration is the same as a gen 2.

I think if Ford had kept the Voodoo it would have got DI and a huge bump in power.
 
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It also runs cam timing that bleeds off cylinder pressure.

I'm still studying the differences to try and understand why Ford did things the way they did.

So far it looks like they used cam timing to lower dynamic compression enough to be able to run enough spark timing to make the car livable on the street.

Ask any gt350 owner and they will complain about the lack of torque below 5000 RPM. Exactly opposite of what one would expect from higher compression.

The OP or WOT cam timing is also completely different from what any other coyote runs. In the tune the duration is the same as a gen 2.

I think if Ford had kept the Voodoo it would have got DI and a huge bump in power.
So I think 12:1 will be perfectly fine. The pump gas tune may have to have slightly retarded timing but it shouldn't be that big of an issue. I should gain around 15hp on e85 with 12:1 compared to 11:1.

Also wanted to reference this:
https://www.mustang6g.com/forums/threads/max-compression-ratio-static-for-pump-gas.150641/

I read through it all and lots of good talk there but nothing conclusive.

I think that since the gt350 runs 12:1 I should be fine.
 

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For my car I do. If you are mostly using E85 I would not. I run mine pretty hard on gas and do what I can to prevent pre ignition and detonation.

If you really are going to use E85 then 12 to 1 is fine. But when you do use 91 baby it.
This
 

 
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