Turbo now or later

[johncmng]

I'm in the process of rebuilding my 3.2 motor. Can I install high or low compression (I forget which one for turbo motor) piston and run it without a turbo/supercharger? Will there be any harm, power loss or power increase? Should I do it all at the same time or can I do it little by little?

[RarlyL8]

Lower compression pistons will reduce your power output until the turbocharger is added. It will also allow you to run regular unleaded fuel. I can't see how that would harm anything. I would assume the stock motronic would not be thrown off. You should be able to run a turbo compression motor with out the turbo and associated plumbing until you are ready to finish the project.

[kenikh]

The car's performance would be dramatically affected, but yes, you could do it and compensate somewhat with ignition timing, while using regular gas. Would you go with a 7.5:1 CR?

[johncmng]

Thanks guys! Man this is the best forum =)

[johncmng]

Ooops! What is the highest CR would you recommend?

[kenikh]

It depends on what you want to accomplish. You can typically make more top end HP with a lower static CR because you can run more boost, but your performance off boost will suffer. It is essentially a compromise between off-line performance and top end (sound familiar?).

The lower the static CR of the motor, the more you can boost it, thus giving more latitude for increasing the dynamic CR (on boost). The higher your static CR is, the more torque you'll have off boost, but a higher static CR limits the boost you can run by moving the starting point for the final dynamic CR number upward.

It is more complex than this in practice, but this is the basic understanding I have gleaned from this board.

[BReyes]

7.5 CR. Have you discussed with your machinist/builder, the benefits of twin plug upgrade?

Good luck!

Regards,

[JeremyD]

The route I **was** going to take was with JE's - 9.8 to one 3.4 (98mm) - extrude hone - hot cam - when it came time to boost - pull the JE's and mill the top to lower the compression to 8.0 or so to one - then boost.

[id911T]

Perhaps it's a throwback from my watercooled VW experience, but I tend toward higher CR's and less boost for street applications. For the water Vdubs, 8.5 was pretty good for a street turbo. It allowed reasonable boost, decent off boost snap, and pretty good fuel economy. And, at the track when more power was needed, race fuel could be used and the boost turned up a bit. Since our aircooled engines are a little bit more sensitive, I'd say between 7.5-8, closer to 8 though.

[RarlyL8]

I vote 8.0:1
With a large intercooler you could possibly run 1.0 bar boost.

[Wayne 962]

Read the section on turbocharging in my Engine Rebuild Book - I explain in detail what you need to look out for when considering this path...

-Wayne