7M-GE compression increase?

[redshift]

Hello! Wondering if anyone has bumped the compression on a GE motor to get a little more power out of it? There seems to be a ton of piston to valve clearance. Just wondering if there's any reason the head couldn't be decked to bring the compression up to, let's say, 10.5 to 1, or as high as you could bump it and stay on 93 octane. Figure the compression bump could get 10-20hp perhaps. Anyone have any experience with that?

 

[Asterix]

I have, but sorta not on purpose. My head and deck have lost about 1mm over 3 BHGs and I'm still running the stock gasket thickness. (Though it's an MLS gasket now.) My car has never seen a dynomometer, so I have no idea about how much more power it has. I've used mid-grade 89 gas after my 2nd BHG where my head lost the most material.

I'd be careful of the combustion chamber shape, which I think will get significantly worse once you take off much more than 1mm. Someone more knowledgeable than I am will have to chime in about that.

The ECU adjusts timing based on knock, so I suspect at some point as you increase the compression ratio you may actually lose power, even with 93 octane gas. Overall, I don't think it's a straight-forward problem.

 

[Bru]

Going from 9.1 to 10.5 would net you about 3 hp starting from 200. Compression ratio horsepower calculator.
You really don't want to take anything off the head or block more than is necessary to avoid timing or sealing issues. As it is the 7M is a non-interference engine. You might get a few horsepower with a HKS cat back exhaust system for about $600, but is it really worth it? Probably the most effective approach would be nitrous oxide, but I have no experience with that. The GE engine doesn't have a oil squirter cooling on the back of the pistons like a GTE does. Nitrous generates a lot of heat and stress on the engine. The MK3 chassis weighs 3,600 pounds, so you would need at least 360 hp to get it to a nimble 10 pounds per horsepower ratio. The stock GE has 200 hp and the GTE has 230. These cars are more about sport touring than racing. I'm content just looking good going down the street. It's hard to compete with modern cars that are lighter, have 8 cylinders, or variable valve timing. Engine swap is an option, but it's expensive and 2JZ engines are difficult to find these days.

 

[redshift]

I have, but sorta not on purpose. My head and deck have lost about 1mm over 3 BHGs and I'm still running the stock gasket thickness. (Though it's an MLS gasket now.) My car has never seen a dynomometer, so I have no idea about how much more power it has. I've used mid-grade 89 gas after my 2nd BHG where my head lost the most material.

I'd be careful of the combustion chamber shape, which I think will get significantly worse once you take off much more than 1mm. Someone more knowledgeable than I am will have to chime in about that.

The ECU adjusts timing based on knock, so I suspect at some point as you increase the compression ratio you may actually lose power, even with 93 octane gas. Overall, I don't think it's a straight-forward problem.

Good info! Thanks.

 

[redshift]

Going from 9.1 to 10.5 would net you about 3 hp starting from 200. Compression ratio horsepower calculator.
You really don't want to take anything off the head or block more than is necessary to avoid timing or sealing issues. As it is the 7M is a non-interference engine. You might get a few horsepower with a HKS cat back exhaust system for about $600, but is it really worth it? Probably the most effective approach would be nitrous oxide, but I have no experience with that. The GE engine doesn't have a oil squirter cooling on the back of the pistons like a GTE does. Nitrous generates a lot of heat and stress on the engine. The MK3 chassis weighs 3,600 pounds, so you would need at least 360 hp to get it to a nimble 10 pounds per horsepower ratio. The stock GE has 200 hp and the GTE has 230. These cars are more about sport touring than racing. I'm content just looking good going down the street. It's hard to compete with modern cars that are lighter, have 8 cylinders, or variable valve timing. Engine swap is an option, but it's expensive and 2JZ engines are difficult to find these days.

Yeah, that's absolutely not worth it, if that calculator is right. I've actually got a 2JZ-GE vvti that was originally intended for this car. My 87 car though, is near perfect and I just want to drive it, so I picked up a good GE motor and W-58 to go back in it. I have a 90 Turbo 5sp also, and an 86.5 that will now receive the 2JZ. Plenty of other opportunity for making power, so I'm not too worried about the 87. I just thought if there were a few simple things I could do to get a few more HPs out of it, why not?

 

[redshift]

 

[Asterix]

The one best thing I did to my GE to improve drivability was a 2.5" free-flowing exhaust. It may have added some power at the top end, but it also made the engine happier from 1800-3000rpm, where you drive most. Plus, it sounds really sweet.

If your top end is apart, gasket match all the intake parts. It certainly helps a little.

 

[redshift]

The one best thing I did to my GE to improve drivability was a 2.5" free-flowing exhaust. It may have added some power at the top end, but it also made the engine happier from 1800-3000rpm, where you drive most. Plus, it sounds really sweet.

If your top end is apart, gasket match all the intake parts. It certainly helps a little.

Odd, I replied, but the reply is gone. Anyway, I'm sure I'll get exhaust for it. I didn't have exhaust at all, but when we pulled the W-58 out of my 86.5 car, it was nearly perfect. I reckon I'll use that for now. Good tip, though. I'll definitely gasket match it. By the way, I sure wish someone still made a header for the NA cars.

 

[redshift]

Here's my 87 car, by the way.

 

[Nick M]

Changing to the later camshaft that was also used in the Cressida will increase the dynamic compression. It is why some thought they had better power with "NA cams", even though it was not a continuous run of the 7MGE.

Yes, decking it raises it some. I burned a cheap gasket by doing that and tightening the AFM plate a little.

 

[Asterix]

The block decking does/should do very little since you typically only need to take off a few thousandths of an inch, just enough to get rid of the gouges made by the crappy stock gasket that squirms around and chews up the deck. More material comes off the head because the gasket chews deeper into the soft aluminum.

Playing with the AFM spring is just asking for trouble.

 

[redshift]

Changing to the later camshaft that was also used in the Cressida will increase the dynamic compression. It is why some thought they had better power with "NA cams", even though it was not a continuous run of the 7MGE.

Yes, decking it raises it some. I burned a cheap gasket by doing that and tightening the AFM plate a little.

Intake or exhaust? What years? Did the Cressida, in fact, have higher compression and more power?