3.2ss CR 9.8:1 vs 10.5:1

[breaqnaway]

Hi,
I've been reading up on the different rebuild options for my 1981 911sc with EFI. The goal is to for a fun and reliable street car/ auto-x and a few DE's a year.

The plan so far is a 3.2 short stroke. From what I have read, there is a pretty big increase in price for the build by increasing the compression from 9.8:1 -> 10.5:1 (Max-Moritz single plug -> double plug with lots of piston options.

What are the pro's going with the higher compression twin plug set up? How much is the HP and torque improved? More reliable than the Max Moritz single plug? Better options for cams...even for a street car? Seems like the only real "con" is the increase in price.

Thanks in advance.

[ChrisBennet]

I can't answer all your questions but I can give you a subjective data point:

I have a 3.4 twin plug 10.5:1 compression motor and it is revs much quicker than a stock 3.2 and has a nice "bark" to it when shifting at high RPM's.

That said, it's a lot of money and effort for not a lot of HP gain. I estimate I got another ~25-30HP for all that work but I enjoyed building it.

[wayner]

I wanted to go from 9.5:1. Up to 10.5:1 twin plug on my 3.0
I also wanted to go from 3.0 to 3.2

Here was my thought process:

1) are my cylinders good? If so splurge for new high compression 3.0 pistons and twin plug ( since I have a 73, and it is in RSR trim, so twin plug seems right.

2) if my cylinders were bad, I'd make that my priority and if I was buying new ones anyway, why not 3.2?

Ideally I wanted both, but with the Canadian dollar, I couldn't justify the cost of new jugs. Pistons were relatively cheap in comparison, as was labour to twin plug.

[mreid]

If head labor is all you worry about for twin plug, you are missing the real cost - ignition. Easily another $2k depending on desires.

I have a 10.5:1 twin plug 3.2ss in my 904. Cam selection is your next big decision. Higher lift/overlap cams lower your dynamic compression (real compression). I'm running DC 80 cams and it really screams above 4,500 rpm. With the low weight of my car, the slightly lower low end torque is not noticeable. This is the perfect engine for my car and how I want to drive it. Build the engine for your particular car and desired driving style, not to engine specs.

[Trackrash]

It really boils down to money. I would love to have a 3,2 SS with a distributor based twin plug 10 to 1 CR motor.

The reality is, since I had good nikisil cylinders in my SC based motor, I chose to stay 3,0 with new pistons and cams.

New pistons, $1k, new cams, $1k.

New cylinders, $2k, 12 plug distributor $2K. Plus machining the heads, wires, second CDI etc.

The good news is, when I win the lotto, I can change over to the twin plug set-up.

[breaqnaway]

Thanks for all the insight. In regards to cams/goals of the engine, this car will primarily be for street and autox with a modest increase in redline. Right now, I'm leaning towards using something like gt2-102 cams for some low end grunt but still fun to rev out.

Sounds like twin plugging opens pretty nice. Leaning towards putting off the rebuild a year and then springing for the 3.2ss 10.5 twin plug cams.....

[breaqnaway]

Thanks everyone for the good insight. In regards to the goals of the rebuild, the plan is for a primarily street/ autox with a wide power band but still fun to rev out. Planning on something like GT2-102 cams.

Sounds like twin plug and higher compression is something a lot of folks have been happy with. Maybe out of the rebuild for another year and then spring for the 3.2ss 10.5:1...the problems is that seems to be getting into 3.6 swap territory...

[Jeff Alton]

Twin plug high compression motors with a good cam are a great deal of fun and can make fantastic power. Induction and exhaust also play a role here...

Yes, building a high performance twin plug motor approaches 3.6 cost. But what is you need to rebuild that 3.6? The 3.6 are not plug and play and have some costs associated with installation and making it all work as well.

Cheers

[Mick_D]

I understand that the 3.6 heads also are a bit more fragile than the 3.2 heads. Something about a ceramic sleeve in the 3.6 that's not replaceable, vs a steel sleeve that's replaceable in the 3.2 heads. Not really sure of the details.

[wayner]

I am fundamentally against engine swaps from newer cars.

I remember when the hot setup was to get a 7R case to build on.
The lightest strongest magnesium engines and transmissions

I am willing to accept a stronger aluminum 3.0 as a starting point to keep costs down, and that's where the 3.0 bumped to 3.2 makes a lot of sense to me. Good amount of torque but the ability to scream like a banshee up top!

Oh, and still,keeping as much weight out of the back of the car as possible ( none of those heavy modern intake setups).


...But, over the last decade, that style of hotrodding has fallen out of favour as the younger crowd subscribes to what I call the the camero or mustang go big block mentality. more power but more weight.

Seems to me a really nice light high revving 2.4 bumped to 2.7 in the low 200hp range, or a 3.0 bumped to 3.2 in the 300ish hp range just seemed right for these cars, none of the pounds of wiring and even more pounds of intake castings that those big heavy 3.6 lumps come with.The newer bigger engines really change the character of the car in the wrong direction for my taste. My friend commented that my Max moritz styled 9.5:1 peaky "cammed" 3.0 engine had more low end torque than his stock T, so I didn't give up anything in drivability around town.

But now I have it up to 10.5:1 with new pistons and ignition system,

And, if I'm being honest, the main reason that my 3.0 has twin plug?

Because growing up I learned that any proper hot rod 911 was twin plugged. It just has to be
Twin plug engines are special and exotic

CONVERSATION:
Q - What has it got in it
A- A 3 litre bumped up to 3.2
Q- Oh. that must go?

Q - What has it got in it
A- A high compression 3.0 litre twin plugged engine
Q- WOW!!!! Can you open the lid so that I can see it?

[ChrisBennet]

Originally Posted by breaqnaway

Thanks everyone for the good insight. In regards to the goals of the rebuild, the plan is for a primarily street/ autox with a wide power band but still fun to rev out. Planning on something like GT2-102 cams.

Sounds like twin plug and higher compression is something a lot of folks have been happy with. Maybe out of the rebuild for another year and then spring for the 3.2ss 10.5:1...the problems is that seems to be getting into 3.6 swap territory...

3.6 have lots of other costs associated with a swap above and beyond the motor. What I don't often seen factored into the swap cost is that the 964 3.6's [and probably the 993, I don't know] need a top end rebuild if they haven't had one since new. I don't know if its valve guide material or all that heat or a combination of the two. And then of course there is the leak fixing... Long story short, a 3.6 swap is a rebuild+swap, not a swap instead of a rebuild.

That said, I think a 3.6 swap is the way to go if funds permit.