Engine M44/07 150hp, M44/05 163hp??

[944year83]

Can I change piston rings without doing anything to the aluminum block? Has anyone done this?

[Tom]

Can I change piston rings without doing anything to the aluminum block? Has anyone done this?

Some people have been able to 're-ring' existing pistons/blocks with success, but there is a risk that the new rings won't seat well -- leading to poor compression, high oil use, smoking, etc.

Why do you want to do that?

[Oringojin]

Can I change piston rings without doing anything to the aluminum block? Has anyone done this?

I understand, now. You're thinking of replacing the pistons in the 924S engine before having it installed in your 944. As you said the 924S has only 70 000 kilometers, it should be in good condition with fairly fresh bores, so fitting new rings to the 10:1 pistons and installing them ought to work fine. It will be a total strip down of the motor, so, you should probably replace all of the seals and the rod bearings in any case, since that won't add much to the bill, and you'll get a fresh, leak free motor. If the old rod bearings don't show signs of scratches, you can probably skip replacing the main bearings and the balance shaft bearings.

It will be a lot of labor time, so if you're paying someone to do it, you will have to ask yourself if the 10-13hp gain will be worth the money. If you're doing the work yourself, it could be a fun project, though. You could also look into other power upgrades, like a camshaft, more modern ignition, AFM delete, ECU, injectors etc. but then, all of that wise advice about keeping things stock go out the window...

[944year83]

Correct

[944year83]

https://ibb.co/Vc70T8Kn

[Petethepug]

Consider a non evasive inspection of the cylinders and valves. The numbers don’t lie.

https://qbh-borescope.com/how-to-check- ... -head-off/

These motors are prone to rod bearing failure. Especially at #2 from oil starvation. The previous owner(s) of my 968 did them at 80k a decade ago. The motor’s had almost 150 clicks since then on original rings and a RS barn rebuilt head.

The head was done close to the rod bearing service from head gasket failure. I’d do the rod bearing, spec the oil pump and only crack open the head based upon info above.

[Oringojin]

Back on the road, I see! Congratulations! 200kph at 4600rpm seems a little odd, though. Either your speedo is optimistic, your tach reading low, or you've got smaller diameter wheels...first gen speedos read off the front wheel spindle, and mine has always read quite fast compared to my gps, like 15kph too fast at 160kph running stock tires and wheels.

[944er]

200kph at 4600rpm seems a little odd, though.

Looks about 7-8 KPH fast to me, which could be from tire wear. Speedometers are required to read at or above actual speed, including with new tires.

gearing.png (1.36 MiB) Viewed 206 times

[Oringojin]

According to that chart the speed/rpm isn't too strange at all. Reading over by 7-8kph is perfectly normal.

I was going by a spreadsheet I made a little while ago just doin' the math to compare different ratios in preparation for a transaxle swap, as well as my own experience with my 924S. I've almost never cruised at 200kph, but my usual highway speed was in the 160-180 range, and my engine was turning in the 4500-4800rpm range at those speeds. That's why I've swapped in an 01E 6 speed.

The photo looks more in line with the ratios of a Turbo AOR box.

Capture d'écran 2026-05-12 110647.png (88.36 KiB) Viewed 192 times

[944year83]

205/50/17
255/40/17