3.1SC to Turbo Rebuild - Piston Choice?

[mikedsilva]

My car is currently running a "3.1" SC based motor.
The previous owner (many years ago) rebuilt it with 97mm turbo barrels and Max Moritz style pistons at a compression ratio of 9.5-9.8 (sorry, I cannot be sure). Iin it's CIS form, the car drove well and made decent torque using SSi headers.

Recently I converted it to using a small Turbo and aftermarket EFI and it runs well, but I plan to rebuild it because the motor needs the heads rebuilt.

I'm looking for a little guidance for direction on my build. (If I need to order pistons, it looks like I need a big head start as I have a set on order through Carrillo and it's already been 4+months with nothing to show.....)

The goal is NOT to build a 500hp monster. The gearbox will remain a 915 at this point and it's a road car only. It will be driven with care and no burnouts!

I'd like to see 350rwhp safely and would imagine that should keep me happy for a long time to come (my budget precludes me from 930 trans or G50 swaps etc).

If my pistons and barrels measure within spec, is it "ok" to re-ring and reuse them with this compression ratio?
While it is apart, I could have the heads twin plugged - would this help to safeguard me against detonation?

From reading these posts, I get the impression that lowering compression is mainly done to safely run higher boost.

Sure, I could run a 3.6 crank, 98mm barrels and pistons, different cams, etc etc but I feel that's creating a motor that is going to be mostly unusable in this car...

[Jeff Alton]

Mike,

Will the rebuild include an intercooler? Will you add knock sensing to the ECU? The 97 bore with 70.4 stroke may create a delay as well getting pistons. The SC cam will work well enough for sure. Twin plug will help with the CR of the current pistons, and help overall regardless of CR. We can chat on messenger as well.

[mikedsilva]

Originally Posted by Jeff Alton

Mike,

Will the rebuild include an intercooler? Will you add knock sensing to the ECU? The 97 bore with 70.4 stroke may create a delay as well getting pistons. The SC cam will work well enough for sure. Twin plug will help with the CR of the current pistons, and help overall regardless of CR. We can chat on messenger as well.

hey Jeff
yes, there is currently a single knock sensor fitted on the case and there will be an intercooler added for sure.

If I had to change bore, I have another set of std 95mm SC cylinders or could get a set of carrera barrels bored out to 98mm.

But if 350ish hp is achievable with twin plug, SC cams, headers and existing pistons and barrels, then it might be worth leaving the combination as is?

[Henry Schmidt]

Sounds like a nice project.
On a side note: 911SCL
The factory produced a limited number of 3.1 upgrade engines.
They were built just like you describe.
3.3 Turbo 97mm half fin cylinders and Mahle Max Moritz (wedge head) pistons.
The case was generally stamped with 3.1 directly below the designation stamp.

[mikedsilva]

Originally Posted by Henry Schmidt

Sounds like a nice project.
On a side note: 911SCL
The factory produced a limited number of 3.1 upgrade engines.
They were built just like you describe.
3.3 Turbo 97mm half fin cylinders and Mahle Max Moritz (wedge head) pistons.
The case was generally stamped with 3.1 directly below the designation stamp.

This engine isn't one of those.. but when it was done back in the early 90's. I guess they wanted to copy the factory offering.
Do you recall the claimed compression ratio of this option?

[ToySnakePMC]

Public Notice: For those unaware and want to watch Mike assemble and comment on his personal project, please look for his YouTube channel. It’s very good! That is all. Patrick

[mikedsilva]

Originally Posted by ToySnakePMC

Public Notice: For those unaware and want to watch Mike assemble and comment on his personal project, please look for his YouTube channel. It’s very good! That is all. Patrick

Thanks for that.. and don't forget to give the vids a like to help them get noticed a little more

https://www.youtube.com/playlist?list=PL33XrsdrT6VOkbWiZb8hCuhPfcYZbBQUr

[Henry Schmidt]

9.5:1
Here's a nice article on the 911 SC-L.

https://www.excellence-mag.com/issues/180/articles/point-one

[Jeff Alton]

Originally Posted by mikedsilva

hey Jeff
yes, there is currently a single knock sensor fitted on the case and there will be an intercooler added for sure.

If I had to change bore, I have another set of std 95mm SC cylinders or could get a set of carrera barrels bored out to 98mm.

But if 350ish hp is achievable with twin plug, SC cams, headers and existing pistons and barrels, then it might be worth leaving the combination as is?

If P/C set in spec, good to re use. With kock sensing and EFI you are good.

Cheers

[Classic 911]

Interesting build.

[Jeff Alton]

Mike,

My messeger app seems to have $hit the bed. Lets continue via email or whatsapp.

Jeff@turn3autosport.com or 1-604-313-3494