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Chris · Joined: 10 Dec 2002 Posts: 62

To let everyone know what I am doing, I am restoring (and modifying) a 1981 931 to as close to show room condition as possible.

I am in the process of stripping the engine bay right now. I am cleaning EVERYTHING. Powder coating all of the brackets, putting all new hoses in (and steel braiding them), polishing all the aluminum, cleaning all the components, chroming the alternator, A/C Compressor, etc) to make the engine bay look as new as possible.

HOWEVER, I want to rebuild a motor in the mean time becasue I may just go ahead & pull the engine out since I want to repaint the engine bay black (since I am going to be painting the car black eventually). I have a 1980 931 motor sitting in storage, and I know there is a difference in the pistons, but I am wondering if the block is the same. I am also wondering if the lower compression pistons from the 1980 car would be better to use since I am going to be adding an intercooler after I get it all back together? I have heard that a lower compression engine is more beneficial if you are running an intercooler.

I got about half of the motor components removed today, and should have the rest of it torn out by the weekend, so I am wondering what everyone would suggest as far as going ahead & pulling the motor out, or rebuilding the 1980 motor with the lower compression pistons that I have in storage?

Here is a picture of what I got out this afternoon....

http://www.stuttgartparthaus.com/gallery/P7130011.JPG

Any help would be appreciated....

Chris · Joined: 10 Dec 2002 Posts: 62

Here is a picture of some of the components that I have already had chromed & powder coated.

http://www.stuttgartparthaus.com/gallery/Components.JPG

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

looks like a good start on cleaning up the engine bay. a lot of hoses are molded into funny shapes though, are you just going to replace them with factory rubber?

from what i've read, using something like 8.5:1 on a turbo engine is just about optimal. then you've got decent off-boost response. if you go with low compression and lots of boost then your power band is going to be much higher (maybe something like 3-6500 rpm) and it's going to drive like an NA with a race cam. so it depends if you want to build a race or street car. the GT racecars were running low compression and lost of boost to get their big HP numbers, just to give you a comparison.

what is your HP goal? the Carrera GT's put out 210, if you're running an intercooled setup then you can get the same and could probably squeeze out a little more by making things work a little more efficiently (front mount IC should be more effecient, you could also play with some ignition retard electronics, etc.).

if you're going to do a color change then you definately need to pull the motor out to spray the engine bay. why not just rebuild the later motor why you've got it out? you never know, you may need to bore and replace pistons anyway and the only alternative seems to be the JE's. then you can use any CR you like.

as with any project looking for HP numbers you need to start with an engine and turbo rebuild (actually i am doing that right now). after the $1500-2500+ bill for that i would see what's leftover for color changes/ powder coating/ etc.

good luck
-nick

Lizard · Posted: Tue Jul 15, 2003 2:29 am Post subject:

if I remember correctly the blocks are the same from 80-82 but the pistons and cr did change, in 80 they were 7.5:1 and in 81, and 82 they were 8.5:1, your best option is to get an 80 turbo (bigger compressor) and run the 8.5:1 pistons, unless you are going to be pushing ALOT of boost then stay with the 7.5:1 pistons
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3 928s,

924 turbo · Posted: Tue Jul 15, 2003 10:01 am Post subject:

Lizard · Posted: Tue Jul 15, 2003 10:56 am Post subject:

Thanx for the correction Jon
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3 928s,