Engine Rebuild Options/3.2SS Questions

[arbita1]

If you had an impending rebuild in your future and you wanted to keep the stock (MY 83) CIS and also knew that you would need to replace pistons/cylinders because they are alumisil, and you already have SSI's, would you do a...

1. Stock Rebuild (maybe using a 964 cam instead).

2. Upgrade from 9.5CR to Euro 9.8CR by finding some EURO pistons (also w/ 964 cam)

or

3. 3.2 SS Rebuild (and if this option...which pistons would you use, and would it be an issue using the 83 CIS)

[docrodg]

I would consider the intended use, fuel issues with higher compression, and tuning. Considering the performance the engine already has it would probably remain stock with no modifications for regular driving except the SSI. Less mess to deal with. I am not sure if the 964 cam is OK with CIS or if there is too much airflow vibration for the sensor. Certainly some of our more knowledgeable Pelicanites can chime in on that.

Us NY folks have good luck when it comes to inspections tho... no smog check! As long as it is stock-looking and you don't take it to a knowledgable inspector you can get anything to pass on a 911!

[arbita1]

Originally Posted by docrodg

I would consider the intended use, fuel issues with higher compression, and tuning. Considering the performance the engine already has it would probably remain stock with no modifications for regular driving except the SSI. Less mess to deal with. I am not sure if the 964 cam is OK with CIS or if there is too much airflow vibration for the sensor. Certainly some of our more knowledgeable Pelicanites can chime in on that.

Us NY folks have good luck when it comes to inspections tho... no smog check! As long as it is stock-looking and you don't take it to a knowledgable inspector you can get anything to pass on a 911!

The 964 cam is a good choice for CIS 3.0. So I know that works.

If I didn't have to replace the pistons/cylinders due to the alumisil, it would be a no brainer stock rebuild (to keep costs down). But once you have to do that, the cost increase to up the compression and/or the displacement is not much more.

[psalt]

Matt,

This is simply a matter of cost, more displacement is better, look what the factory did one year after your car. Mahle pistons/cylinders are best, but you will pay $2000 more for the O/S Motorsport set. The original CR for a US 83 SC is 9.3 not 9.5, 1/2 point of compression is around +4 hp, the other 20 hp for the EURO version came from other differences.

[Head416]

#3 ftw!

[kerthunk]

I went with the 3.2SS w/ 964 cams option on my '79. I also ran with the CIS after a thorough refreshing (new injectors and such). I had to crank up the mix to get the AFRs into the ballpark and it would still be lean at the top end of the RPMs. If I tried to fatten up the mix more to compensate for the lean top end, then the injectors would start leaking. Seems like my CIS simply was not designed to provide the amount of fuel that the 3.2 displacement needed. I ended up moving to 46mm PMOs. Another issue with the 3.2SS is that you can't get the compression up very high (above 9.5:1) without dual plugging, unless you are ok with not using pump gas. My engine runs fantastic now, but in all honesty it was more money than I really wanted to spend on the engine.

If you are determined to keep the CIS, then I would suggest that you probably just bump up to the 964 cams and stick with 3.0 P+C with 9.8:1 compression. Just my 2 cents anyway.

[arbita1]

Originally Posted by kerthunk

I went with the 3.2SS w/ 964 cams option on my '79. I also ran with the CIS after a thorough refreshing (new injectors and such). I had to crank up the mix to get the AFRs into the ballpark and it would still be lean at the top end of the RPMs. If I tried to fatten up the mix more to compensate for the lean top end, then the injectors would start leaking. Seems like my CIS simply was not designed to provide the amount of fuel that the 3.2 displacement needed. I ended up moving to 46mm PMOs. Another issue with the 3.2SS is that you can't get the compression up very high (above 9.5:1) without dual plugging, unless you are ok with not using pump gas. My engine runs fantastic now, but in all honesty it was more money than I really wanted to spend on the engine.

If you are determined to keep the CIS, then I would suggest that you probably just bump up to the 964 cams and stick with 3.0 P+C with 9.8:1 compression. Just my 2 cents anyway.

Thanks for that honest assessment.

[jamesjedi]

A very good article by Wayne Dempsey on CIS 911;

Pelican Technical Article: Extracting Power from CIS 911s...

[Head416]

Just to throw this out there: I've got a 3.2ss conversion running CIS with 91 octane pump gas (California), 10:1 compression according to the build sheet and single plugged. I'm no CIS expert, so I can't give you AFR numbers, but I can tell you that the car feels strong all the way to 6k rpm, with a perceived peak in power a little before that, maybe at 5.5k.

[jamesjedi]

Short stroke build can be a little expensive. Although 3.0 and 3.2 cylinders are interchangeable, the 3.2 cylinder is recommended for the 3.2SS.

If you go to Engine Builders Supply (Porsche Racing Parts : Engine Performance Parts : Brake Parts : Used Porsche 356 : 911 : 912 : 914 : 944 : Porsche Boxster Parts : EBS Racing Inc.) you will see their 3.2 SS P and C's. They charge $222.75 per cylinder to replate for a 3.2SS. The pistons are just over $1000 for the set.

Another option, is to purchase The 95 mm JE piston's, with a 9.5 c/r, and source within spec 3.0/3.2 cylinders. I bought a set of cylinders for $300.

Make sure that they are checked before you buy. The previous set of P's and C's I bought were given to a metal recycler.

[1979911sc]

If you need to replace pistons and cylinders with brand new then why not get 98mm's in a wedge shaped dome for the build and probably about the same money as 95mm? As others have said I would definitely not go over 9.5 in 98mm especially with the trend in reduced octanes and lower quality fuel at pumps. Finding a good set of used of 98mm p/c will not be easy and could be questionable replates. If you find a good set of used original mahles p/c in 95mm use em. However I have heard the 9.8:1 cast mahle piston fails more often and would just use the stock 9.3:1 for highest reliability. Next budget choice for maybe an extra hp or 2 in 95mm would be JE's 9.5:1 or whatever you want and then if you want cis dome pistons for around $1500 a set, Rothsport makes 9.8:1 forged cis pistons in 95mm. I am in the same boat as you with the cis rebuild except I have some good used 95mm mahles and believe I am gonna use the web cams 20/21 profile. The cis 98mm build vs 95mm should make close to 15 more hp more and with some more torque too which would be nice too. Also might want some head work done. Really depends on how much cash you wanna throw at it which I am finding out adds up real quick on each little conversion and yields relatively small performance gains. Either choice with cis choice would be good and damn reliable though

[arbita1]

One thing ive noticed is that 98mm pistons are not really available for cis. Unless you spend $5000 and get the Mahle Motorsport ones. At least that I can find.

[jamesjedi]

98 mm pistons are available from EBS and Pelican for about $1000. I believe EBS can make a CIS dome piston.

I talked with Don at EBS about power loss from using the flat topped piston vs. the CIS dome, he was not sure about the exact amount of power difference. Perhaps, someone else knows?

The 98mm piston from 3.2 engine cannot be used with the 3.0 crank, unless the connecting rods are modified.