Max compression ratio (static) for pump gas?

[D K]

Whats the highest anybody has ran on pump gas?
Gen 3 is 12:1 so is 12.5:1 ok? 13:1?
I would like to be able to run E85 for track events and pump gas on the street.

Anybody have experience?

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[D K]

The short answer is yes..
Actually, going up to 12, 12.5 or 13 to one would pretty much indicate that the motor would be built.

The highest I have heard in a roadrace environment has been 15.5:1 and a drag car, 17:1 scr.

Obviously, at that point you are committed ot either ethanolor some pretty good race gas.

I dont know this for sure yet, but everything indicates that this motor loves compression.

Being that 12:1 is already the norm in gen3, I would think 12.5:1 would easily be obtainable and probably 13:1 as well provided that you run a conservative tune.

I would love to see someone with a 13.5:1 motor that has run pump gas.


Just for reference, mylast build was a 2.0L FRS that had 12.5:1 compression that we boosted to 13.5psi and that made 550hp on E85

So I knowit is possible lol

I don’t, but I’d like to ask. Are you building a motor ?

 

[engineermike]

Interesting idea! The stock compression ratio at 12/1 was designed to run on 87 octane with GDI. The gt350 also has 12/1 and PFI but requires premium. You can definitely run higher compression on the 5.0 as long as you commit to premium fuel. Mazda runs 13/1 compression and Ferrari as high as 14/1.

Tuning would be very interesting. The stock GT borderline timing is based on 12/1 and 87 octane. Published data suggests that one compression number requires 5 octane numbers higher, and one octane number per deg of timing. A starting point for 13/1 could actually be very close to stock borderline timing. Other things can be done with cam timing and throttle opening in certain situations if cylinder pressure is too high.

Clearance would have to be watched closely. The stock gt and gt350 pistons have dimples to clear the spark plug electrode, so it’s already very tight in there.

In going to 13/1 compression, you can expect 20-30 ftlb increase and 25-35 hp just from compression. In fact, I believe most of the gen3 gains over gen2 were due to the compression increase.

Also keep in mind that GDI is critical to running these higher compression ratios, so it must be retained and maximized.

 

[4sdvenom]

OP, is your build going to be focused solely on a N/A basis or do you have plans to eventually add boost as well?
Very interested!

Ken

 

[Gogoggansgo]

The most I’ve seen on a coyote was 12:5:1 and that was on hood 93 otherwise knock becomes an issue and you’re not doing anything without corn.

i know a few guys back in the gen 1 days do some 13:1 builds and make big boy power but they had to run corn all the time, and even then they used race e85 at the track

 

[Gogoggansgo]

Interesting idea! The stock compression ratio at 12/1 was designed to run on 87 octane with GDI. The gt350 also has 12/1 and PFI but requires premium. You can definitely run higher compression on the 5.0 as long as you commit to premium fuel. Mazda runs 13/1 compression and Ferrari as high as 14/1.

Tuning would be very interesting. The stock GT borderline timing is based on 12/1 and 87 octane. Published data suggests that one compression number requires 5 octane numbers higher, and one octane number per deg of timing. A starting point for 13/1 could actually be very close to stock borderline timing. Other things can be done with cam timing and throttle opening in certain situations if cylinder pressure is too high.

Clearance would have to be watched closely. The stock gt and gt350 pistons have dimples to clear the spark plug electrode, so it’s already very tight in there.

In going to 13/1 compression, you can expect 20-30 ftlb increase and 25-35 hp just from compression. In fact, I believe most of the gen3 gains over gen2 were due to the compression increase.

Also keep in mind that GDI is critical to running these higher compression ratios, so it must be retained and maximized.

everything you said is 100 percent on point. To the OP also remember that DI cools the combustion chamber down, because of how fine the spray is. This lowers the knock threshold, why do you think DI and turbos are so popular even on crap 87. But there is a limit to this ferrari found out with the 458 speciale, they went with 14:1 compression and recommended using race gas anytime you beat on the car. The reality is the gas quality now isn’t very good and also not consistent at all. Which is why your base tune tends to be so conservative. And the aftermarket can get 10-20whp just by taking up the slack left over

 

[D K]

As of right now, its just a proof of concept phase as I am evaluating both 2.3 with huge boost or 5.0 with normal aspiration.

They both have advantages, but what I really like about the Coyote is the huge average torque over a huge rpm range. That's very attractive in roadracing and it might just be the thing that pushes it over the edge.
I think its possible to get more max power out of the 2.3 than the 5.0 NA, but there are other factors as well. Having an engine that pulls from 3000 to 8500 is a pretty wide power band and somethign that might keep me from having to shift mid turn or somewhere undesireable. Or having some overrun in case I have to go super deep into a brake zone.

A 15.5:1 Coyote is very happy at high rpm and with good fuel, but it starts becoming a law of diminishing returns and I suspect a 13:1 motor might be just what the doctor ordered.

So to answer the original question, the appeal of the Coyote is to keep it an NA motor.

OP, is your build going to be focused solely on a N/A basis or do you have plans to eventually add boost as well?
Very interested!

Ken

 

[D K]

I would like to work with the Gen2 engine with proper liners if at all possible.

I'm not worried if my base tune is super conservative, as long as the E85 tune is real good for track events.

everything you said is 100 percent on point. To the OP also remember that DI cools the combustion chamber down, because of how fine the spray is. This lowers the knock threshold, why do you think DI and turbos are so popular even on crap 87. But there is a limit to this ferrari found out with the 458 speciale, they went with 14:1 compression and recommended using race gas anytime you beat on the car. The reality is the gas quality now isn’t very good and also not consistent at all. Which is why your base tune tends to be so conservative. And the aftermarket can get 10-20whp just by taking up the slack left over

 

[engineermike]

I would like to work with the Gen2 engine with proper liners if at all possible..

If this is gen2 and you want to run pump then I think 12, maybe 12.5 would be the limit. Gdi does a lot for the gen3. You could maybe go higher if you used torque control to limit cylinder pressure or dropped the spark timing way down below 20, but that would ultimately hurt the power.

 

[LSchicago]

Let's not forget running larger cams allows more compression too.

 

[D K]

More compression??

Usually big cams take away compression, not add.

Let's not forget running larger cams allows more compression too.

 

[engineermike]

Let's not forget running larger cams allows more compression too.

You can manipulate stock cam timing to try and reduce cylinder pressure which has the same effect as a bigger cam. It’s just that intentionally reducing cylinder pressure with cam timing is counter to increasing compression to begin with. That could be a tool you could use on pump gas to get by if compression is too high though, much like demanding less torque or retarding spark.

 

[WildHorse]

The stock compression ratio at 12/1 was designed to run on 87 octane with GDI.

Why are 12:1 & 87 octane in the same sentence ? Ya ya Ford did that to sell to the masses to cheap to put premium, which in my opinion is beyond stupid. But whatever. 12:5 / 13 / 14 / to 1 is doable on pump with aluminum heads. And a top notch fuel system. But don't expect a lot of timing out of it.

 

[Idaho2018GTPremium]

EngineerMike is accurate with his account for Gen 3 Coyote w/ DI. Your original post wasn't clear which Gen Coyote you were starting with but it alluded that you were starting with Gen 3 by mentioning the Gen 3. But reading further at post #10, you said you want to build a Gen 2 due to the iron liners. Anyway, a Gen 2 doesn't have DI, which will lower the compression ratio threshold. I honestly don't know what the limit for a Gen 2 would be without DI cooling the process down inside the combustion chambers. If I were you I'd certainly talk to engine builders like MMR (Modular Motorsports Racing) who have very high performance Coyote builds.

I'll add that for Mazda to achieve high compression ratio (sykactive G is 14:1 in some markets- 13:1 in the US), aside from DI, Mazda specially designed the 4-2-1 exhaust header manifold so that the hot exhaust gasses leaving one cylinder didn't make their way back into a cylinder downstream that is closing the exhaust valve and starting the intake stroke, helping keep cylinder temperatures down. They also have a specially designed piston that uses a bowl that adds some neat features like flame control and shortens the combustion process time. They also use Multi-hole injection, rather than just one DI location within each cylinder.

 

[engineermike]

Why are 12:1 & 87 octane in the same sentence ? Ya ya Ford did that to sell to the masses to cheap to put premium, which in my opinion is beyond stupid. But whatever. 12:5 / 13 / 14 / to 1 is doable on pump with aluminum heads. And a top notch fuel system. But don't expect a lot of timing out of it.

Are you saying Ford is stupid to design a car that runs on 87, or the masses are stupid for putting 87 in a car that’s designed to run safely on it?

Mazda seems to think that 13/1 and 87 are compatible. They actually are, depending on how you control it. Optimal for best power? Maybe not, but it can be completely safe if controlled properly.

The stock GT spark timing curves barely command 20 deg of spark timing when mbt is around 30. If you run good gas it can get up to 27 or so with knock advance. At 13/1 and 93 I would expect low 20’s.

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