New 3.3 build completed - need advice


New Member
Sep 9, 2019
Reaction score
Detroit, MI
I recently completed a new build, a 3.2 bored for 10.6 high compression pistons. Other than the pistons and a SHOSource underdrive pulley the motor is basically stock (3.0 cams, stock ECU, stock MAF, etc). I do have an adjustable fuel pressure gauge because I'm running a 255lph fuel pump (not because I needed it for the motor but it was part of my fuel cell). I have other mods that are not yet installed but can do these later, for now I wanted to get the motor back in the and running (+40 cams, larger MAF, ported intake, big bore butterflies).

I started everything up last weekend and things looked good. No leaks, water/oil temps and oil pressures good, idles and revs throughout the range. This motor is being run in an endurance race car so will be ultimately run at high RPM's for extended periods.

A friend who maintains race cars said I needed to get an AFR gauge on it ASAP; he said with the higher compression with stock fuel could lean it out and eventually start melting things due to higher temps. I don't have enough knowledge to know how true this is for my situation. I'll go ahead and install a AFR sensor & gauge but I'm on a stock ECU so can't tune it (and would need help on what to tune anyway).

I'm running the fuel pressure at 39psi based on advice from Josh at SHONut.

I'd appreciate any advice here; I've also posted on the Facebook Gen1 group please excuse the 'double post'.


Last to Know
Supporting Member
Aug 25, 2008
Reaction score
Ontario Canada
There are plenty of cars with higher compression than yours, on the street and doing fine. You need a robust cooling system to help, and high quality fuel helps too.

Your application in some kind of race car application requires the same robust cooling system and fuel. Your knock sensor is a big help as well, and if not overridden, will adjust the timing to protect your engine.

Try it out and see, if you are experiencing detonation and melting engine internals, you will be aware of the situation at an early stage.

More gauges are never a bad idea, but monitoring them is an issue.


SHO Owner
Aug 21, 2003
Reaction score
Portland, OR
A higher flow pump only means more flow returning to the tank by the pressure regulator return line.

Stoichiometry is learned via the oxygen sensors and air measurements obtained from the MAF input.

Non-stock pressure with an adjustable regulator is the only big variable you've introduced, which means the duty cycle required of injectors may be further from the PCM default with a computer reset. Boosting pressure for more fuel at open-loop WOT may be quickly "unlearned".

The amount of air pulled into the cylinder per s-troke isn't affected by piston top. Compression affects the efficiency of the combustion stroke.

Even with intake flow mods and more bore than your 3.0 PCM, you are still "stock" at anything but WOT. The throttle plate sees to that. I don't thing there is concern here or need for anything but premium-only or better fuel to resist detonation. The injectors can flow significantly more than required for NA and run the engine rich at WOT anyway.

edit: censorship is making this forum impossible.


Tyler Durden
Sep 9, 2019
Reaction score
Higher compression is not going to "lean out" an engine, though it may actually require a richer AFR to avoid detonation. Unless your intake tract has been highly modified your MAF should still do a good job of metering the air and keeping AFR on target.
The whole point of "open loop" at WOT is that there are no feedback mechanisms and the ECU doesn't learn or unlearn anything. This is mainly because narrow band 02 sensors are useless at anything besides stoich. Tuning fuel in your case should be really simple. Want lower AFR? bump up the fuel pressure. Want higher AFR? turn it down. BTW I would highly recommend setting your new wideband to display in Lambda instead of AFR and learn to use that now and forever.