I don’t, but I’d like to ask. Are you building a motor ?
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 overInteresting 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.
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
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
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.I would like to work with the Gen2 engine with proper liners if at all possible..
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.Let's not forget running larger cams allows more compression too.
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.The stock compression ratio at 12/1 was designed to run on 87 octane with GDI.
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?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.