930/02 3.0 as a base for short stroke engine?

[91133]

Have just bought a '77 Carrera 3.0 motor complete but in need of a tear down and considering it as the base for a short stroke 'mainly' (*ahem*) street motor.

Looking for thoughts on that as a concept and also suggestions and experiences...

I already have on a shelf a complete early S MFI system (005 pump) and am happy to go 10:1 or higher compression and twin plug.

Discuss

Cheers,
Mark

PS If a Carrera 3.0 owner out there is looking for an original engine - more than happy to trade as I have no emotional connection to this particular motor. S/N is 66702XX

[Henry Schmidt]

The short stroke 2.8 (I'm guessing that's your thought) is a very cool engine if your plan is to rev the engine (8000 or higher). That's it's only claim to fame unless you're trying to fit in a racing classification.
I've built many and the issues are creating compression without creating a super heavy piston and filling the cylinders.
They (SS2.8) are bullet proof and sound great.
Tuning the MFI will also be a challenge but a good pump builder can point you in the right direction. Trial and error is generally the order of the day.
The best use of this great little combination is a high revving turbo but with a turbo, revving seems counter-productive.

[Walt Fricke]

It's special property is that you can run the 66mm crank (9 bolt flywheel). Can't do that with the later SC cases, and with the earlier cases (especially the 2.0 sand cast aluminum cases) you can't put in 95mm cylinders, or 98mm cylinders, and you can't use 3.0 or 3.2 heads.

Otherwise, all I think it might do is let you run the 9 bolt 70.4 crank. Those might be less expensive? Or a guy might have one left over from a 2.7 or 2.4 to start with.

[Henry Schmidt]

Originally Posted by Walt Fricke

It's special property is that you can run the 66mm crank (9 bolt flywheel). Can't do that with the later SC cases, and with the earlier cases (especially the 2.0 sand cast aluminum cases) you can't put in 95mm cylinders, or 98mm cylinders, and you can't use 3.0 or 3.2 heads.

Otherwise, all I think it might do is let you run the 9 bolt 70.4 crank. Those might be less expensive? Or a guy might have one left over from a 2.7 or 2.4 to start with.

I'm guessing you meant to say "6 bolt 66mm crank". Same with the 6 bolt 70.4mm reference.

You can run 95 mm cylinders on a sand cast case but it requires very special cylinders.
SC heads are without a doubt a bonus as long as you can make compress.

[biopsea]

you mention "mostly" street. a few thoughts. the 2.8 ss is a great track engine. will rev forever. however, must be less fun on the street with very little low end torque. also, as these cases are relatively hard to locate, it may make more sense to sell to an owner of a c3 and build your hot rod using a more common block. just my thoughts.

[91133]

Originally Posted by biopsea

...also, as these cases are relatively hard to locate, it may make more sense to sell to an owner of a c3 and build your hot rod using a more common block. just my thoughts.

Well, I did put that thought in there as a postscript - if you know anyone, more than happy to talk. It's a compete motor although someone has swapped the fan out for an 11 blade.
Cheers,
Mark

[9elf]

Hi Mark.

Can you put 98mm P & C's in these engines and make the 3.2SS?

Craig.

[Henry Schmidt]

Originally Posted by 9elf

Hi Mark.

Can you put 98mm P & C's in these engines and make the 3.2SS?

Craig.

You can but it doesn't make any sense. To make a SS 3.2 with this case you need a 70.4 crank and that leaves you with a 2.4/2.7 crank. These cranks flex at high RPM so they are less desirable than a 3.0 (70.4, 9 bolt) crank. If the goal is a SS 3.2, it is better to start with a 78 or later 930 case and that case is considerably easier to source.

[Henry Schmidt]

There is the option of using an RSR crank but bring your wallet.
Of course if the goal is to rev 8000+ with a 6 bolt 70.4 crank there is the option of running a Supertec SuperCrank. The new design of the crank prevent flexing and that reduces the harmonic vibration that accompanies the 2.4/2.7 crank. This vibration is the major cause of failure in the crank and flywheel of the 2.4/2.7 crank.
Supertec also makes a 66 mm 9 bolt crank making it possible to build the SS 2.8 using a late 930 case. In fact with our crank you can build a SS 2.8 using a 993 engine base.

Now you start talking about building crazy short stroke like 66 x 102or 105 mm which will build a 3.3 or 3.5 SS capable of 9000 RPM. This starts to look like 4 valve territory.

[Matt Monson]

Gorgeous crank.

[9elf]

Thanks Henry.......... and whoa! Nice crank.

[91133]

That IS a pretty nice looking crank…. price?

[Trackrash]

Is it possible to fit an SC crank in a mag case? Assuming the case is bored out to accept the larger SC main bearings?

That crank is a work of art.

[Henry Schmidt]

Originally Posted by Trackrash

Is it possible to fit an SC crank in a mag case? Assuming the case is bored out to accept the larger SC main bearings?

Because all 911 engines are very similar, almost anything is possible.
There is really no cost effective way to put an SC crank in a mag case and no good reason to so [unless the goal is to build the lightest 9 bolt engine possible].
Remember that because of the 9 bolt configuration of the SC crank the flywheel area of the case will have to be modified.

[Trackrash]

I was thinking that it might be a way to save a mag case that needed to be line bored.
I guess the nine bolt flywheel flange, as you pointed out, makes it unrealistic.

[Walt Fricke]

Yeah, the #1 journal area of the 9 bolt cases is quite a bit larger, because the #1 bearing part of those cranks was enlarged so 9 bolts on a larger bolt circle could be used (smaller bolts, too, to help locate them farther from the crank centerline). The earlier cases were not cast to allow that, so the welding and machine work to modify a mag case (which is generally not favored for high HP output due to inherent weakness and degradation over time) would doubtless be very costly - money which could better be spent in improving the power per liter of an aluminum cased motor. Or purchasing one of Henry's cranks.

Those Supertec custom cranks--- require dreams of winning the lottery. And a 9,000 rpm 3.3 SS, wow. Porsche concluded it couldn't deal with heat issues, or something, when it came to making a 4 valve air cooled motor. I have heard rumors that others have figured out how to do that. Not sure if there is any truth to it. Porsche had to go to water cooling at least the heads to crack that nut.