Short stroke 3.2

[dd74]

What are the principles of short stroking a 3.2? What I mean is increasing the displacement of a 3.0 to a 3.2. Has anyone done this? Has anyone retained the CIS after doing this, and if so, what cams do you run with this set up?

Thanks.

[trak ratt]

I think Mickey Thomson summed it up nicely “the only substitution for cubic inches is rectangular dollars”. A short stroke 3.2 is generally a big bore SC. There has been a lot of posts about how to increase power in the SC & this is certainly a good one, especially if you are looking at a top end rebuild anyway. The couple I’ve seen kept the CIS. I understand that the meager increase in displacement nets a disproportionately higher increase in HP & torque. Though I haven’t seen any dyno tests I understand that combined w/SSIs, a 2 in 2 out muffler and a K&N you could see as much as 230 HP. I wonder if there would be even more HP using the early SC CIS (bigger runners) & different cams? If heard the 964 cams increase the top end HP & are still compatible w/CIS? I bet the same pistons in a 3.2 would be interesting too.

[CamB]

As described, a short stroke 3.2 is an SC case and crank with 98mm (up from 95mm) pistons and cylinders. I know of two methods people have used to do this conversion:

1) Andial sell 98mm Mahle pistons and cylinders with a 22mm wrist pin (to suit SC rods) for either CIS (around 9.5-9.7:1 compression ratio) or carbs/MFI and higher lift cams than CIS compatible ones (in 9.5 or 10.5 c/r - the latter requiring twin plug too). See their advert in Excellence. Cost is about $3000 including rings

2) Buy JE pistons and have your 3.0 cylinders bored out from 95mm to 98mm. They then need replating if they are Nikasil, I guess? I think EBS Racing offers this service (both selling pistons and replating cylinders), and I think it is closer to $2000. I think there is also the option to bore and sleeve with steel (which doesn't last as long as stock Nikasil).

Mahle are better (says me - 'cause that's what I bought). The pistons and cylinders have a more closely matched expansion rate so the clearance is closer when cold and thus the engine is quiet while warming up (no piston slap).

You shouldn't expect more than 6.5% extra power (all other things being equal) as the increase is from 2994cc to 3164cc (I think). However, I am told it revs more freely as it is "over-square" and engines like this LIKE revs. It probably then feels faster. Although I have a conversion, I can't comment cause I haven't really driven it, and I have no before to compare to.

[ChrisBennet]

I'll pretty much 2nd what CamB said except for a couple of points. 1) You can't bore out the 3.0 (95mm) cylinders to 98mm because of the groove at the top.
2) I've run 98mm JE's in my 3.4 without any piston slap noise. I think that the tolerance/noise thing might have been true a few years ago though.
-Chris

[kepperly]

CHRIS,
COULD YOU ELABORATE ON YOUR 3.4? IS IT A 3.2 W/ 100MM P&C'S.
THANKS KEITH

[ChrisBennet]

Originally posted by kepperly
CHRIS,
COULD YOU ELABORATE ON YOUR 3.4? IS IT A 3.2 W/ 100MM P&C'S.
THANKS KEITH

Hey Keith,
No need to SHOUT. My engine is a 3.2 Motronic converted to 3.4 with 98mm bored and renic'd cylinders with JE pistons. JanusCole inquired about EBS 3.0->3.2 conversion and was told that the SC cylinders weren't suitable cores.
-Chris

[HawgRyder]

Has anyone tried hard-chroming the cylinders?
I know that all air-cooled aircraft engines use this for longevity.
I think they also use ductile iron or cast iron rings with this.
ALso....perhaps teflon buttons on the pistons to keep the pistons straight in the bores...makes the rings last a lot longer and cuts down on friction (heat).
Bob

[CamB]

Hmmm, now I am shooting my mouth off in two threads I better check what I remember... I think the Alusil cylinder bit is mandatory.

okay what is the word on the displacement increase for 3.0 SC

JE Pistons

This also reminded me that my mechanic showed me how Mahle had made my brand new 98mm p&c set by starting with a 95mm cylinder and boring it out (presumably before plating). It still has the 95mm part number, I think.



Also, the JE pistons in my case were probably 5+ years old and they were in SC cylinders which were in spec but still worn 0.001", which my mechanic told me contributed to the problem.

[CamB]

I have found the pictures I took and one has the part number - I was told the "95" refers to 95mm, but they have been bored out to 98mm.

[curlesw]

Sorry to ask such a basic question...but what is a twin plug and why is it needed as described above? Thanks in advance.

Wayne C
rookie in a 83 SC

[ChrisBennet]

Originally posted by curlesw
Sorry to ask such a basic question...but what is a twin plug and why is it needed as described above? Thanks in advance.

Wayne C
rookie in a 83 SC

Ideally, the plug would be situated in the center of the combustion chamber dome but because of the 911's large valves there isn't room to do this so the plug is on one side of the chamber. A downside to this arrangement is a greater tendency to prematurely detonate (ping). Larger bores tend to make this worse. Adding a second plug addresses this problem.

In this picture the original plug hole is on the right and the 2nd plug hole is on the left.

-Chris

[curlesw]

So now there are 2 spark plugs which ignite at the same time...correct? And with it goes a second distributor and other electrical equipment? Or do you re-use the existing equipment?

Thanks.

Wayne C.
...still learning in a 83 SC

[CamB]

Twin plug comes 3 ways - they all fire simultaneously:

1. Ordinary distributor modified to RSR cap and rotor (12 plug leads). Cap and rotor very expensive ($1200). Will also need a second Bosch/Permatune capacitive discharge box (or twin MSDs or equivalent)



2. 964 distributor modified to fit your engine - twin distributor caps and rotors with innards joined by a cogged belt. Distributor not too expensive but must have crank gear, points and advance mechanism added from original distributor. Cheaper, but not much. Ditto #1 on additional CD box or 2x MSDs



3. Crank fired ignition such as Electromotive, which has a little cogged wheel on the crank pulley which is "read" by a sensor. This signal goes into 1 (for single plug) or 2 (for dual plug) coil packs which have the facility to set advance. Slightly more expensive, but CD box etc not needed

Can't find a pic of two plug.. this'll do - double all the pink and black bits...:



A much better description is available at:

www.rennsportsystems.com/~porsche/
How reliable is a built 2.7L?

[Wrecked944]

"JanusCole inquired about EBS 3.0->3.2 conversion and was told that the SC cylinders weren't suitable cores"

"This also reminded me that my mechanic showed me how Mahle had made my brand new 98mm p&c set by starting with a 95mm cylinder and boring it out (presumably before plating). It still has the 95mm part number, I think. "

These two contradictory facts have been troubling me for a couple of months. Are there any experts who know the real score? True, Chris is correct. I asked EBS about reboring my cylinders and they said it would not work. But the reason I asked EBS in the first place was that I'd read in various places that it was a common practice. And I don't have anywhere near enough knowledge to form an intelligent opinion on this. Is there anyone who has actually had it done or who knows the details?

Thanks,

[ChrisBennet]

Originally posted by JanusCole
"JanusCole inquired about EBS 3.0->3.2 conversion and was told that the SC cylinders weren't suitable cores"

"This also reminded me that my mechanic showed me how Mahle had made my brand new 98mm p&c set by starting with a 95mm cylinder and boring it out (presumably before plating). It still has the 95mm part number, I think. "

These two contradictory facts have been troubling me for a couple of months. Are there any experts who know the real score? True, Chris is correct. I asked EBS about reboring my cylinders and they said it would not work. But the reason I asked EBS in the first place was that I'd read in various places that it was a common practice. And I don't have anywhere near enough knowledge to form an intelligent opinion on this. Is there anyone who has actually had it done or who knows the details?

Thanks,

This makes sense if you drop the sealing ring and the groove for it when you go from 95 to 98mm cylinders. Carrera's don't have the sealing ring so it must not be absolutely necessary. Mahle would simply bore the original casting out to 98mm and omit the groove. They wouldn't necessarily even have to re-bore, just bore it 98mm the first time.
I wonder if 97mm Turbo cylinders say "97" on them?
-Chris

[CBRacerX]

I had one of these 3.2 short stroke engines for years. Excellent runner and 8K RPM all day long. Mine was stock ignition, GE40 Cams, Early Heater Boxes, Sport Muffler and 46IDA Webers. Based on the Max Moritz P&C kit.

Absolutely fantastic engine. Torque curve was awesome!

I'd buy one again in a heartbeat. Getting the last one required me to buy the entire car it was running in (an ugly, beat, brown 78 SC) but it was worth it!

Chris
http://www.christianbrown.com

[curlesw]

CamB, thanks for taking the time to educate me on this topic.

v/r
Wayne C.

[RLJ]

When I built my 3.2 short stroke I had not planned to add cubic inches. My cylinders were Alusil so rather than buy new/used 95mm cylinders I had mine BORED and SLEAVED to 98mm. I was going to buy new J-E pistons anyway so the price between 95mm and 98 mm was cheap.

The cylinder is bored out to say 100mm and a 2mm ( or so) special spun cast iron sleave was machined and pressed in to the cylinder. Been doing this for years.

Randy Jones
1971 911

[surflvr911sc]

I'm planning a rebuild next year on my 3.0 and this looks like it might be a nice road to take. What is the projected cost of doing this?

[Wrecked944]

"I'm planning a rebuild next year on my 3.0 and this looks like it might be a nice road to take. What is the projected cost of doing this?"

Me too !! And where can we get the 95mm -> 98mm cylinder conversion done? Obviously, I've already tried EBS and they shot me down.

Thanks,