Long Stroke rebuilt engine - help?

[CamsPorsche]

Hi Folks,

I've just purchased my first "vintage" 911 (1980 911 Carrera) that has a 3.2L Carrera motor and 915 transmission.

The old receipt given with the motor shows that in 2012 a shop performed a compression test on engine and #3 cylinder showed as 30 psi. They removed, disassembled and cleaned engine, replaced all head studs and sent heads, rods, pistons and cylinders out to machine shop.

List of items replaced were pistons (JE), Rings, Studs, Gasket kit, Valve Guide, exhaust valve, clutch disc, ignition points, spark plugs, etc.

However, on the receipt it says in handwriting "Long Stroke 3.2, Pointed Heads and G80 Cams, 280hp estimated" and total bill amounted to $10k.

I've searched around and there's limited information on Long Stroke 3.2 motors. From what I gather the long stroke provides more low end torque, less rpms to get to the power and less top end speed...correct?

Is there anything else I should know about a long stroke 3.2 engine?

While the motor is out right now is there anything you can suggest that I look at before putting it back into the car?

Former owner said that when the engine was mated to a carb setup it felt great up to 4000rpms but then "fell flat". He figured it was a carb issue. The car will be put back together with the Carrera intake system.

Suggestions?

[ChrisBennet]

I'm a little confused as to what you have but here are some data points that might help you sort it out.
911SC: 1978-1983 3.0L motor, 95mm bore.
911 Carrera 1984-89 3.2L motor, 95 mm bore
If you increase the bore of a 3.0SC to 98mm, you get a 3.2 "short stroke"
I guess, you could call a stock 3.2L motor a "long stroke" but I've not heard it referred to that way.
Hope that helps.

[darrin]

shoot us a pic of your engine? wondering whether he swapped (can one?) a 3.2 crank and proper pistons/rods into a SC engine? Want to see from pic whether your engine "looks" like a CIS SC engine or a Motrionic carrera engine

[prschmn]

Interesting. Not exactly a stock engine I just hope those "points" weren't
expensive but maybe they were-very hard to find.

[Henry Schmidt]

Originally Posted by prschmn

Interesting. Not exactly a stock engine I just hope those "points" weren't
expensive but maybe they were-very hard to find.

Although "points" caught me by surprise the mention of "carbs" may be a clue.
The stock 3.2 Carrera engine has a distributor ignition triggered by the DME.
If carbs are installed you lose the DME. Although it's not very sophisticated, I have seen people convert a 2.7 (points) distributor to fill the void.

[prschmn]

A good one Dr Schmidt-----
I failed to read past the 3. with "points"

[KTL]

Along the lines of what Chris mentioned, the long (standard) stroke 3.2 is different from a short stroke 3.2 (95mm bore increased to 98mm) by the crank stroke. The standard 3.2 engine has a 74.4mm stroke crankshaft that is used in the 3.2 Carrera and 3.3L 930. The short stroke 3.2 typically uses the SC crankshaft which has a 70.4mm stroke. Hence the reason for saying long vs. short.

The mention of the engine falling flat at 4000 rpm sounds backwards. GE80 cams are rather high lift, long duration cams with a reduced intake-exhaust lobe separation angle. I believe they're sort of peaky and have weak low end power and don't start to come on power until you pass 4000 rpm. I also think you might have misread (or it's poor handwriting) that the heads are "pointed." It probably means ported heads.

Given what specs you shared about the engine's build components, I don't know that the Carrera intake system will serve the engine all that well. Those cams make power well beyond 6000 rpm but the Carrera intake hits a hard wall at 6200. You'll definitely need to get the engine on a dyno and sort out the fuel & ignition mapping of the DME ECU to get any sort of benefit from those JE pistons, GE80 cams, and ported heads.

[Henry Schmidt]

Originally Posted by KTL

Along the lines of what Chris mentioned, the long (standard) stroke 3.2 is different from a short stroke 3.2 (95mm bore increased to 98mm) by the crank stroke. The standard 3.2 engine has a 74.4mm stroke crankshaft that is used in the 3.2 Carrera and 3.3L 930. The short stroke 3.2 typically uses the SC crankshaft which has a 70.4mm stroke. Hence the reason for saying long vs. short.

The mention of the engine falling flat at 4000 rpm sounds backwards. GE80 cams are rather high lift, long duration cams with a reduced intake-exhaust lobe separation angle. I believe they're sort of peaky and have weak low end power and don't start to come on power until you pass 4000 rpm. I also think you might have misread (or it's poor handwriting) that the heads are "pointed." It probably means ported heads.

Given what specs you shared about the engine's build components, I don't know that the Carrera intake system will serve the engine all that well. Those cams make power well beyond 6000 rpm but the Carrera intake hits a hard wall at 6200. You'll definitely need to get the engine on a dyno and sort out the fuel & ignition mapping of the DME ECU to get any sort of benefit from those JE pistons, GE80 cams, and ported heads.

I agree with most of what you posted but I'm confused about the "Carrera intake hits a hard wall at 6200" ?
We used the stock Carrera intake on one of our 4.0 engines. We reduced the intake port on the 964 heads to 40mm (VentiPort), used a Motec ECU and that engine pulled all the way to 7200.
It made so much torque that it broke a Mindeola transmission designed for 550 ft/lb of torque. It broke the gear box twice.

[KTL]

Nearly all the dyno plots i've seen for stock-like engines with the Carrera intake, which is similar to what's described here (basic bolt-ons and also the occasional 3.4 upsize) by the original poster, hit that approximate rpm range and the power starts to drop off pretty fast afterwards. Here's some various 3.2 based engines to substantiate that belief. The last one is a 3.4 before and after with twin plugging and some different cams






Although I suspect with these GE80 cams, the power drop off would occur a bit higher in the rpm range and be less prominent of a downward slope further out in the rpm axis. Exhaust type would play a factor here as well.

So you are absolutely right "hits a wall" was a poor choice of words. Thanks for the correction to my broad mis-statement. I should have said something like "starts to fall off?"

Your comprehensive build, as in a complete package with complementary modifications and testing, obviously shows that it takes more than a mix and match collection of parts to make it all work out well. It would appear your engine plan had low end torque in mind? That said, I don't think the Carrera intake is the one to go with if high rpm power is what one desires. Seems like the later intakes with their variable runner lengths, or good old individual throttle bodies, would be the way to keep on climbing 7000+

[Tippy]

Good data. Surprised the "cammed" engine fell off. You might be on to something

At the basic level of intake design, is runner length and effects on RPM.

To your point, long runners are generally for low end torque and short for high RPM HP. Hence why ITB's are the bees knees for high RPM power (and no common plenum of course)

[CamsPorsche]

Hi Guys,

Thanks for the replies and I've just read the responses. I'm new to engine terminology and learning as I go but yes, they are ported heads and G80 cam that was installed.

The exhaust ports measured at 41mm whereas the SSI heat exchangers matched to it measured out at 1-3/8" which means there's some step there. I'm now selling those thin flange SSI heat exchangers so that we can find something more suitable to allow the engine to breathe such that I find a 1-5/8" header with heat exchangers. Any suggestions?

The engine is a euro spec 84-89 Carrera engine that has 3.2 heads. The car previously ran with a carb setup (46 IDA's) so it will be returned to a carb setup (bought car without carbs).

Pic of engine:

[stownsen914]

You're right that those heat exchangers will choke the engine. And some 46 mm carbs should help it make some nice power up to at least 7000 RPM with GE80's and ported heads.

I didn't see any mention of the intended use for this engine. With carbs and GE80's, it will make a really nice track engine. Not so great for a daily driver, but maybe sporty street driving.

To the point about falling flat at 4000 RPM, it must have been a tuning issue. Those cams on a carb'd engine would just start to come alive between 4000 and 5000 RPM. If your mechanic has experience tuning performance 911 motors, he will know how to set up the carbs. Or call Richard at PMO for a jetting recommendation if you are not sure where to start.

Scott

[m42racer]

Originally Posted by Henry Schmidt

I agree with most of what you posted but I'm confused about the "Carrera intake hits a hard wall at 6200" ?
We used the stock Carrera intake on one of our 4.0 engines. We reduced the intake port on the 964 heads to 40mm (VentiPort), used a Motec ECU and that engine pulled all the way to 7200.
It made so much torque that it broke a Mindeola transmission designed for 550 ft/lb of torque. It broke the gear box twice.

If that post doesn't confuse you nothing will.

You have to take each part of this engine and see if it is designed to run at the RPM's you desire and if the engine will make power up there.

What do the heads flow? Are they port restricted or valve restricted? What does the Intake flow when attached to the heads? The Exhaust will be factor, but not as much as you expect. If the Intake doesn't flow, the exhaust will not be a life saver.

If G80 Cams are fitted, but are they G80 Cams? Have you had them checked. What is the LSA? What was the valve timing? Was the Intake CL way advanced?

The choice of cam has to be based upon the ability of the Intake to flow enough air to support the valve timing the cam gives. You need to make sure the Intake and Exhaust flow numbers are at a % of one another to support the Cam. LSA and timing numbers can be modified and still use the G80 profiles.

The engine use and the engines pumping ability need to be known here. Guess work will put you where you are now with a lot of unknowns and people saying what they have and done. Forget what they say and have done, (a lot can be taken for internet power) do your due diligence and work with what you have and what your engine does.

BTW, a stock Carrera Intake will not flow enough air and will choke itself due to TB size and runner size to make power up high.