Can I machine my 3.6 pistons to get 8:1 CR

[matty74]

is it safe to machine my 3.6 pistons to get 8:1 CR on my 3.6 build?

[David]

No, the crown on a stock 3.6 piston is probably not as thick a turbo piston to begin with.

[mamut]

Ruf did it on their 964 RCT's, I don't see why he can't.,they machined the top of the piston crowns in order to drop the compression on them,
cheers.

[matty74]

hoping someone who has done it chimes in

[turbo nut]

I have seen it done a few times with no issues. Thermal coating the piston tops may not be a bad idea after there cut.

[Arnoud]

There are 100mm(3.6l)pistons where the crown is solid and there are ones that aren't.I would invest in turbo-specific pistons.

[TurboKraft]

Having done this, I'd suggest you don't machine them and instead buy new pistons.

After 9.0:1 CR it gets pretty thin. And thermal coating the crown only helps so much.

It's thickest above the pin bosses, 90deg from the valve reliefs. You can take out a lot of material there. But note how the inside of the piston is pocketed under the valve reliefs -- not a lot of material there to take away, and leaving it leaves a really poor shape for a piston crown. Not combustion-friendly. If you try to machine a really low dome on them, like Turbo 3.6 but 8:1, don't expect them to last long term.

I've got several sets of take-out pistons from client engines built at other tuner shops, plus some of my own early engine experiments. Not pretty. All motors ended up getting replacement pistons or pistons & cylinders.

Just my $0.02 having been there, done that.

[911st]

Good info Chris!

[matty74]

thanks for the info guys a great help