Shanes 3.2 SS - Recommendations and Advice
 

I decided to do this after much consultation and conspiring with several experts. So let me thank Gunter, Jon, Ron, Tom, Tom and Tom, Don, and Troy.

Update from this thread:

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/521313-wtb-3-2-ss-pistons-cylinders-can-someone-bump-am-2.html#post5158741

http://forums.pelicanparts.com/Porsche-911-technical-forum/519227-my-first-full-engine-drop-how-i-spent-new-years-eve-78sc-3-0l-2.html

I have ordered Cylinders and Pistons from EBS (after the third time I changed my mind) I am going with 98mm 9.5:1 Pistons. (Arrived)

I have ordered a new spring kit. (Arrived)

Ordered billet cam shafts from Dougherty Racing Cams. (Got em)

I have a single plug MSD and coil.

I have PMO 46 carburetors:

Venturies: 38
Main: 160
Air: 190
Idle: 55
Idle Air: 130
Emul: F11

I have SSI and M&K 2 in 2 out muffler.

Shane - John Dougherty's site gives an overview of can's and can'ts of grinding - read the NOTES below the specs for the porsche cam profiles

Dougherty Racing Cams

Call John and he will spec a cam for you.

Hello,
I am also in the process, of upgrading my 82SC 3L to a 3.2ss.
Last year, my choice was to go: 98mm P/C, 78-79 CIS, and 964 cams.
After reading comments on this site about the 964 cams with a similar setup,(a dog below 5000 rpm, power comes on after....) I changed my mind, this was not what I wanted for my application. I am looking for power to come on at 3500rpm or so, up to 5500rpm.
I am now using cams from John Dougherty, the GT2-104 and going with PMO's 46mm.
Search this forum, for opinions on 3.2ss with 964 cams.
Regards
Pierre

Here is a WOT dyno run on my original NA rebuild 3.2ss with 964 cams and EFI. The seat of the pants sensation is "on cam" just below 4000 rpm. You can see that peak torque is actually 4800 rpm but horsepower is rising almost linearly the whole time. This is wheel hp and torque.

http://forums.pelicanparts.com/uploa...1265414148.jpg

Thanks Pierre what is the CR on the pistons?

I just changed my order with EBS and will be getting the 10.5:1 CR 98mm pistons and am looking for cam options now.

I am using 98mm 10.5:1 CR JE Pistons and Replated Cylinders for 3.2 liter displacement.

I have large intake ports, 46mm PMO Carburators and SSI with 2 out exhaust, MSD Single plug.

Shane

Hello Shane,

I am using Mahle cylinders and RSR pistons @ 9.5/1 compression.
Ported 3L heads, PMO's 46mm, electronic ignition, SSI, Dansk 2 in 1 out.
You should talk to John Dougherty about the GT2-104 cams for your application.

Regards
Pierre

Ok, I talked with John, he recommended the GT2-108 for my set up, I'll have to go with new billets, and probably new springs and retainers.

Steve,

Thanks for posting, was that the right cam for you? I want the cam to come on sooner, lower.

Shane

Hello Shane,

Yes, this cams choice is appopriate for me. I want the power in the lower band ( start @ 3500 rpm).
This is a street car used. I dont plan to race or rev the engine above 6500/7000 rpm,(rev limiter).
Next spring, I will let every one on this forum, know, the results and impressions on my rebuilt
3.2ss with GT2-104 cams.

Regards

I think you do give up a little on the low end but the pull above 4000rpm was exhilarating, almost turbo like.

Shane

10.5 CR with single plug will require that you run race gas to avoid detonation.

CR above 9.5 requires twin plug if you plan on using pump gas.

sjf911/Steve,
What EFI system were you using?
Those are pretty nice numbers and a nice flat torque curve...

A very enjoyable thread..... I am looking forward to seeing the results.

It's Megasquirt, MS-II v2.88. Beware the slippery slope of horsepower addiction.

Tom,

I told my mechanic this and he said it wont be an issue with my carbs, he has built quite a few motors and says I can control detonation with timing. Also the final CR will be lowered by shimming the bases. We have 92 octane here. I am going to call him and double check to make sure he understood me clearly.

Is there a formula that determines or a process that explains at which CR detonation will occur or is it just a best guess?

My order wont ship from EBS until Tuesday, I am sure I can change it if I have too. Troy has been great I all-ready changed my order once from the 9.5:1.

Thanks, Shane

Hi Shane,

I am planning to build a 3.2ss as well for my car.....I have not found anyone (including highly regarded posche engine builders) that reccomends anything over 10:1 CR on pump gas without twin plug.....I would not go high comp. with out twin plugs.

I think the results can be really, really bad.

Kevin

I built a high compression motor once and figured I'd set back the timing to compensate. I always had to be cautious about what brand gas I was using. On a subsequent rebuild, I lowered the compression and ended up with better performance from full timing advance on any brand high octane.

Another one of John's cams to consider is the DC24. The torque comes on at the same point as the GT2 cam, but makes peak HP another 300 rpm higher up around 6700.

Hi Shane,

IMHO I would get the proper crompression single plug and run normal timing. I cannot see how you will get increased performance with limiting the timing. You will only gain approx. 1% HP increase with the bump in compression IF timing was the same. Limiting the timing will probably net you LESS hp than running proper timing and the 9.5/1

http://forums.pelicanparts.com/uploa...1265578319.jpg

Detonation is a function of a plethora of conditions.
compression ratio (dynamic compression being key)
combustion chamber configuration
piston dome configuration
ignition timing
Octane
head temperature
altitude
fuel : air ratio
intake charge temperature.
With a perfect balance you can achieve max performance.
But we all know "perfect" is rarely achieved.
Some of the conditions above can be manipulated but compression is one we have ultimate control over when building an engine but no control over once assembled.
I always error to the safe side when it comes to compression because so many other conditions are out of our control.

Final Answer 9.5:1 CR
 

Thanks for getting me straight. I was on the edge.

I am going with 9.5:1 CR 98mm Pistons.

I am getting cams and spings from John Dougherty.

Good choice. Enjoy your short stroke!