CIS power build q's & comments

[78SCRSMAN]

This is in response to the "Extracting power from a CIS rebuild" article found in the tech info center articles:

Hi,
I used to be into H2O cooled VW's and had a CIS car... I'm wondering if a lorger bore air sensor plate can be used on these cars as we did with the VW's. Perhaps a GTI sensor would work with the Porsche system? Also it seems, if need be, you could alter the fuel pressure by adding or subtratcting the shimms in the fuel pressure regulator to get some added power or fuel. One question I have about this article is: Is it wise or OK to reuse the OE jugs with new JE pistons assuming they are within spec? Also, is it neccessary to use JE pistons when using the 964 cams or can you use Mahle 9.3:1 pistons with this setup? Did the 1980-83 cars made for the US market have the 9.3:1 PC's? If so, why did they have the same 180 HP figure? Any answers or comments would be helpfull.

The article claims 230-240 HP with the cams, increased CR and back dated exhaust... seems like a bargain!
Also, if the 80-83 cars already had the 9.3:1 CR then all you need are the cams and exhaust. (assuming the mahle pistons can be used with the 964 cams)
Thanks
Derek

[mca]

I think those HP claims are a bit liberal. I think the range is more like 200 - 225HP.

Keep in mind that the earlier SCs (pre 80s) had larger intakes despite having slightly lower compression.

I used 9.5 JEs with my Mahle cylinders. Shouldn't be a problem if cylinders are within spec.

[78SCRSMAN]

Originally Posted by mca

Keep in mind that the earlier SCs (pre 80s) had larger intakes despite having slightly lower compression.

Do you mean intake valves, runners, air sensor plate or something else?
I'm assuming you're saying mods to the induction aren't necessary.

How did you like the upped compression and did you use the 964 cams with it?

My car will weigh in @ 2300lbs. or so. I'm thinking 220hp will be plenty of fun?

Thanks,
Derek

[mca]

Originally Posted by 78SCRSMAN

Do you mean intake valves, runners, air sensor plate or something else?
I'm assuming you're saying mods to the induction aren't necessary.

How did you like the upped compression and did you use the 964 cams with it?

My car will weigh in @ 2300lbs. or so. I'm thinking 220hp will be plenty of fun?

Thanks,
Derek

Yea, the ports are larger on the earlier SCs.

I have 9.5 JEs, 964 cams, SSIs (backdated everything) and a Dansk sport muffler (not the high end $800 one ... the $500 dollar one). Cash got tight towards the end of the rebuild! Also, I don't run my 02 sensor and I have my AFR set at 3.5 CO which is on the richer side.

I love the way my car feels. Last year I hit the dyno with it just after the rebuild and got less than stellar numbers - 185ish. This was before I was able to tune it and I expect that I am seeing 200ish right now. My car weighs 2745 lbs. I am starting to shed some weight though - just pulled the a/c .

A buddy did the dyno on the same day with the same mods on an early SC. His numbers were around 220 I believe. His car now has around 25k miles on it.

Also my cam timing is advanced some. Next time I have the engine out I may dial it back some - to 1.26mm.

At 2300lbs and 220HP you will have A LOT of fun!

There is one particular area of uncertainty though. I don't know what my ignition timing should be. If you look at the Bentley it shows different numbers for the 78-79 and the 80-83 (less advance). I can't get a straight answer as to what my full advance should be. So I set it conservatively according to the 80-83 specs (which I believe is based on 87 octane). I think I could get another 10HP out of my engine if I advanced it some ... or had the dizzy recurved.

[78SCRSMAN]

I have a factory manual that covers the 78-83 US spec SC and the timing is as follows:

78-79: 5deg +/- 2deg BTDC@950RPM hose connected
26deg +/- 2deg DTDC@6000RPM hose disconnected

80-83: 5deg +/- 2deg BTDC@950RPM hose disconnected
21deg +/- 3deg BTDC@6000RPM hose disconnected

Engine should be at normal temp... duh!

Since you have increased the CR, maybe try the 80-83 specs as a starter. I assume they were being a bit conservative due to the low quality/octane fuel we had at the time (not that it's much better now)

Hope this helps a bit.
Derek

[78SCRSMAN]

Originally Posted by 78SCRSMAN

Since you have increased the CR, maybe try the 80-83 specs as a starter. I assume they were being a bit conservative due to the low quality/octane fuel we had at the time (not that it's much better now)

Never mind, after reading a bit, it looks like they were looking for better emissions... CR remained the same from 78-83.

I would sure like to know what you come up with on this. I assume you have the later dist curve so a bit more advance would be nice. With 9.5:1, you should be able to look at the 3.2 advance curve to get a better idea?

[mca]

Originally Posted by 78scrsman

cr remained the same from 78-83.

78-80 = 8.5:1 (HP is 172 for US)
81-83 = 9.3:1 (HP is 180 for US)

This is according to Bentley on page 100-1

[78SCRSMAN]

Well that's what I thought... my manual is from Bentley Publishing and says 8.5:1 CR for all years and 175HP on the same page as yours... nice. I think yours is the correct one. I hope the important things are right on mine.