Increasing compression?

[DickH]

I'm putting together an NA gen 3 and due to scratches on a couple cylinder bores I'm going to sleeve the motor and go with larger pistons. I am thinking about bumping the compression when I order new pistons. I am not finding much online from people bumping compression but it seems like it should be reasonable to run 13:1, maybe 13.5:1 with larger NA cams.

I'm wondering if anyone knows of an example of a higher compression coyote like this and if it's worth the added hassle for another 10-20 hp from compression.

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[NGOT8R]

You can also increase compression by running a thinner head gasket and/or decking the cylinder heads.

 

[engineermike]

12/1 was chosen with 87 octane in mind. I believe you could run 13/1 as long as you commit to 91 octane or higher, even in stock cams. Tuning it could be very interesting! It would pick up about 15 hp plus torque across the board.

 

[Grimreaper]

I wonder how much the knock frequency might change with a larger bore unless going with std size pistons.

OP you said larger pistons? Why not std size if sleeving?

 

[DickH]

You can also increase compression by running a thinner head gasket and/or decking the cylinder heads.

I won't be able to gain the compression I'm talking about by doing any of that.

12/1 was chosen with 87 octane in mind. I believe you could run 13/1 as long as you commit to 91 octane or higher, even in stock cams. Tuning it could be very interesting! It would pick up about 15 hp plus torque across the board.

I'm debating e85 or premium +methanol at WOT.

I wonder how much the knock frequency might change with a larger bore unless going with std size pistons.

OP you said larger pistons? Why not std size if sleeving?

I might as well go with a larger bore and pick up some extra power If I'm going to go through the hassle of sleeving the block.

 

[Andy13186]

Dont make your car require meth, e85 only

 

[engineermike]

93 alone would allow 13/1 or more. With meth or E the sky is the limit.

 

[DickH]

Dont make your car require meth, e85 only

I'd feel better about using meth at WOT for safety than needing to worry about an e85 source. I'm not opposed to going with e85, I just haven't looked into how available it is locally. On my end, the added complexity of meth is a drawback that I'm not sure is better or worse than the potential variation in e85. If I bump the compression I will surely do one or the other, I just don't know if the added hassle of either would outweigh whatever extra power I'd gain from the compression.

 

[NGOT8R]

If you’re bumping up compression and want to be extra safe, race fuel, E85 or meth injection would be a requirement IMO. My brother went through this a while ago with his Sean Hyland built 98 Cobra motor. He had to run 110 octane in it and the fuel bill was ridiculous. He would spend $250 in a weekend on fuel whenever he took the car out to play. If he wasn’t running 110, all he could do was literally cruise the car (no heavy throttle at all). He is currently in the process of converting the car over to E85 now to simplify things in the fuel department. You may end up having to order fuel by the drum or pail if E85 or race fuel is unavailable at the pump in your area.

 

[CJJon]

No, not worth it.

 

[engineermike]

You can run 13/1 on 91 and 13.5 on 93. It won’t be optimum, but it will run fine and strong if tuned properly. E85 or meth will just allow MBT timing for even more power. The Gen 3 gdi system lets you get away with more.

 

[olaosunt]

I'm putting together an NA gen 3 and due to scratches on a couple cylinder bores I'm going to sleeve the motor and go with larger pistons. I am thinking about bumping the compression when I order new pistons. I am not finding much online from people bumping compression but it seems like it should be reasonable to run 13:1, maybe 13.5:1 with larger NA cams.

I'm wondering if anyone knows of an example of a higher compression coyote like this and if it's worth the added hassle for another 10-20 hp from compression.

Here you go .
https://www.racepagesdigital.com/th...pure-evil-fox-mustang-coupe-destroys-records/

 

[EFI]

My brother went through this a while ago with his Sean Hyland built 98 Cobra motor.

You can't compare a 23 year old engine to today's stuff when it comes to compression.

Back then, 12:1 compression was unheard of for pump gas. Today that engine can run on 87 just fine. Advances in fueling and computer technology allows more compression to be ran.

OP, I wouldn't be afraid to run 13:1 on 93 with a proper tune. If going 13.5:1 I would run at least some sort of flex tune in the E40-E50 range.

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