10.9 compression + Boost + Pump 93 (Could use some guidance)

lietuvis91 · May 8, 2026

So I went on a bit of an impulsive splurge over last black Friday for my 1995 GT and ended up with some parts that probably don't work all that well together.

Here's what I've got:
Ford Racing 363 shortblock
Canfield 195 heads with a 58cc combustion chamber
Procharger P1x kit with an upgraded 3 core intercooler

Some of you probably already noticed that shortblock and the heads leave me with rather high compression. 10:9-1 to be exact.

If my goal is to run 93 octane, how much boost do you think I can safely get away with. The Kit I ordered with a pulley for 8lbs on my 302, which I guess will get me a little less boost on the 363. The pulley is a cheap fix, so not too worried about that.

At this point I can:
1) Build it and run low boost
2) splurge on new heads with 68-72cc chambers

I know E85 is the answer here, but I don't want to switch to E85. It's too hard to find and goes stale quickly compared to non ethanol 93.

If anyone's boosted something with this compression, would be great to hear your story.

All thoughts welcome and appreciated.

MICHAEL PENDRISS · May 12, 2026

6-8psi with proper cooling and reasonable timing/good tune, would be my suggestion. Carb offers a bit more room over fuel injection due to cooling of fuel, not much but a bit.

lietuvis91 · May 12, 2026

MICHAEL PENDRISS said:
6-8psi with proper cooling and reasonable timing/good tune, would be my suggestion. Carb offers a bit more room over fuel injection due to cooling of fuel, not much but a bit.

Very interesting... So you do think compression that high will still be workable with 6-8lbs on pump 93, so long as timing and all is dialed in appropriately? That really would be awesome. I purposely upgraded the intercooler to give me the best chances with this setup and I'm not looking for stupid power, just good street drivability and a little more go than just a stroker by itself. So maybe I can make this work pretty well for my goals. I guess I need to talk to a tuner or two and see if they'd be willing to tune a setup like this.

Just want to make sure it'll make sense before I put it all together. Definitely appreciate your input, bud.

MICHAEL PENDRISS · May 12, 2026

You can wait for other members to chime in but yes I would think so, if you added methanol that would be another safeguard. Make sure to go to a reputable tuner and start low and work your way up, they would have the most insight as to how the detonation is controlled...Also what fuel system is being used, spark plugs will most likely need to be a range colder and gapped for boost along with a ignition system that is in good working order.

96blak54 · May 14, 2026

Yes 10.9 static compression forced induced is a bit high and into a discomfort zone for 91 octane. In your compression mathematics did you include piston deck height and head gasket thickness/volume? If possible, add a small dish to the pistons by chucking into a lathe and dish out .010" or .020". Also thicker head gaskets will help to reduce static compression. Check the piston deck height, you may find your pistons are down below the deck, which will reduce compression too. Be sure to include those details into your math.

The availability of E85 or E98 ethanol in a 55gallon drum is dag near everywhere these days. After you get the car up and running and you want some comfort, figure out what ratio to cut some E85 into a fuel blend specific for your car. It could be as simple as 1gallon E85 to a 9gallon tank of 91 octane too boost octane 1.5 point making it 94.5octane.

Id suggest narrowing down the math, adjusting compression by headgasket thickness and piston dish

Snorky · May 14, 2026

96blak54 said:
Yes 10.9 static compression forced induced is a bit high and into a discomfort zone for 91 octane. In your compression mathematics did you include piston deck height and head gasket thickness/volume? If possible, add a small dish to the pistons by chucking into a lathe and dish out .010" or .020". Also thicker head gaskets will help to reduce static compression. Check the piston deck height, you may find your pistons are down below the deck, which will reduce compression too. Be sure to include those details into your math.

The availability of E85 or E98 ethanol in a 55gallon drum is dag near everywhere these days. After you get the car up and running and you want some comfort, figure out what ratio to cut some E85 into a fuel blend specific for your car. It could be as simple as 1gallon E85 to a 9gallon tank of 91 octane too boost octane 1.5 point making it 94.5octane.

Id suggest narrowing down the math, adjusting compression by headgasket thickness and piston dish

Could a carefully selected cam reduce the dynamic compression? Possibly making the static work as the lord intended?

lietuvis91 · May 14, 2026

96blak54 said:
Yes 10.9 static compression forced induced is a bit high and into a discomfort zone for 91 octane. In your compression mathematics did you include piston deck height and head gasket thickness/volume? If possible, add a small dish to the pistons by chucking into a lathe and dish out .010" or .020". Also thicker head gaskets will help to reduce static compression. Check the piston deck height, you may find your pistons are down below the deck, which will reduce compression too. Be sure to include those details into your math.

The availability of E85 or E98 ethanol in a 55gallon drum is dag near everywhere these days. After you get the car up and running and you want some comfort, figure out what ratio to cut some E85 into a fuel blend specific for your car. It could be as simple as 1gallon E85 to a 9gallon tank of 91 octane too boost octane 1.5 point making it 94.5octane.

Id suggest narrowing down the math, adjusting compression by headgasket thickness and piston dish

Appreciate the good thoughts there. I did factor in gasket and piston placement, so i'm pretty sure I got that number pretty close to right. I didn't want to go down the path of messing with e85, but it might become inevitable with these parts.

What would you say the benefit would be of mixing 91 with e85 vs running straight e85? I feel like if I'm signing up for e85 at all, then maybe I just run straight e85 to maximize the potential of this combo.

96blak54 · May 15, 2026

Premium gas vs E85 is a night and day difference when used in an an engine built for E85. Long story short about the 18.1 compression engine I built (intended for E85) I first started the engine on premium gas just to see where the point of intolerance was. Hoping some operation rpm was possible. The engine would idle and rev, but once to temperature the idle would run off erratic to high idle and temps would keep climbing. I drained the tank, dumped fresh E85 in and got the engine running again.....no other changes. The idle was perfect, rev was super snappy, engine sounded link something of a nitro dragster and now engine temps stayed cold and struggled to get to a normal operating temp of 190-200. Im sure a simple thermostat swap would have helped, but I was eager to get the car tuned. Got it tuned, drove great, engine was not tame and sort of scary touchy. If i remember correctly, the forged pistons I used to achieve that compression ratio were made for a propane drag car that I purchased used from Shelby America. I was having oil consumption because I modified the 2nd oil ring groove to accept a standard modular ring with the dimensions for standard groove from standard pistons. In short the piston crown wouldnt grow enough to push the ring against the cylinder walls due to very low in cylinder temps. So I ditched the 18.1 pistons in favor of stock flat tops that brought the compression down to 13.1.