Just another 3.2 Short Stroke

[Henry Schmidt]

About 6 months ago we started an engine for a back dated wide bodied 911.
The engine is as follows.

3.2 Carrera case tumbled and treated with caustic soda to replicate early mag case.
The case has feed mods for extra crank oiling
Shuffle pins
GT3 main and rod bearing with dry film lubricant
Turbo pump
Cross drilled crank
Pauter rods
Racing Iwis chains on a properly fitted intermediate shaft.
Supertec head studs
Mahle factory 98 mm cylinders reconditioned by Millennium and machined for cooper sealing ring by Supertec
10.5:1 JE pistons with tool steel wrist pins, ceramic coating and dry film skirts
3.2 Carrera heads with new valves (51mm X 42.5mm) and guides
Eibach racing springs and Aasco titanium retainers
Intake ports modified for MFI
DC 80 cams with 102 LC , cam are gun drilled for center lube with is fed through the two center cam journals.
Carrera tensioners and Supertec tensioner arms
Supertec reconditioned rockers (DU bushings, reformed threads, surfaced & dry film pads then Cryo treated)

More about the injection later.

[Henry Schmidt]

[TT Oversteer]

Like the case finish. What brand of valves are you using? Can you give us more info on the case mods for crank oiling?

[Henry Schmidt]

Originally Posted by TT Oversteer

Like the case finish. What brand of valves are you using? Can you give us more info on the case mods for crank oiling?

The case is tumbled with medium steel peaces giving it a dark, rough surface (sort of like sand casting) then it is washed in a steam cabinet with mild caustic soda (sort of like Easy Off). If you try Easy Off oven cleaner be careful to apply it evenly and be ready to wash it off when it reaches the color you desire.

The valves are Swiss made InterValve prepped by polishing the stems.

Oil mod simply involves drilling the main bearing feed hole ( 7/32" or 5.5mm) from saddle to the main oil galley to promote increased flow to the #4 main bearing. The grooved and drilled (7/32) # 4 main bearing then transfers the increased oil flow to the #2 and #5 rods bearings through an additional hole in the crank.

[KTL]

Henry,

You went with a basic 3.0L 70.4mm crank for this short stroke project?

Rods are basic Pauter 3.0L or did you choose the lightweight option with the 2 in. journals.

Did you choose to offset bore the small end of the rods to use Carrera style pistons or just use the typical compression height for SC style 98mm JE pistons with the SC crank?

[Henry Schmidt]

Originally Posted by KTL

Henry,

You went with a basic 3.0L 70.4mm crank for this short stroke project?

Yes, It's my engine so cost was a concern.

Originally Posted by KTL

Rods are basic Pauter 3.0L or did you choose the lightweight option with the 2 in. journals.

Stock Pauter 3.0 rods. I just happens to have them in stock.

Originally Posted by KTL

Did you choose to offset bore the small end of the rods to use Carrera style pistons or just use the typical compression height for SC style 98mm JE pistons with the SC crank?

The same response here. We used stock Pauter 3.0 rods because I had them on the self.

Correction: They were actually 2.7 rods. I sent them back to Pauter to have them narrowed for use on the SC crank.

[KTL]

Henry,

Sorry my short questions may have come across the wrong way. Reason I asked about the crank choice wasn't to jab you for using a basic 3.0L crank. I just happened to notice that your list of components didn't state what crank you were using for this application. Didn't mean to imply, "hey what the hey, why aren't you using a Supercrank?"

Reason I asked about the 3.0L lightweight Pauter rods was also to see if you went that route, since I thought you might be building another screamer like the recent 3.1SS thread The shuffle pinning and center lube cams had me thinking you are going for high RPM capability.

Also asked about the rod lengthening via the offset pin bore to see if you wanted to get that better rod length-stroke ratio you've mentioned before, to take advantage of the lighter Carrera JE pistons and again serve the purpose of being easier to achieve high rpms. Was considering doing that for my motor.

Reason I ask the above isn't to critique your build choices. I'm still on the fence with my re-rebuild of the racecar engine to either 3.0 or 3.2SS. Time to _____ or get of the pot and select my rods & pistons since i'm sticking with a 9 bolt 70.4 crank. The previous 3.2SS was a baffling choice of:

std 3.0L crank (no complaint)
typ 3.0L Pauter SC rods but w/bored pin end for 23mm pins (nice rods!)
98mm Mahle Motorsport 9.8:1 carb/MFI Carrera comp height pistons (nice pistons, wrong pin height)
Bored & replated SC cyls (typically not a good idea)
Loooooong deck height of ~2.4mm (why?)
Single plug (odd, considering it uses Electromotive crankfire already- just add another board & plug holes)
Leaded race gas w/46mm Webers

Have no idea why that configuration was built. So, last go-around I made a traditional 3.2SS with "correct" rods (reconditioned Pauters w/new 22mm pin bushes) and new 10.5:1 98mm JE w/SC pin height, added some extra spark plugs. Then I somehow wasted all the bearings (except intermediate shaft- weird) & that took out 1 rod, scoring all of the crank, oil pump, pistons, cylinders, cams, cam housings. Big mess.

Sorry for the interrupt/comparison. Just bouncing around some ideas in my head about where to go with mine & of course you've got some lengthy experience with skinning the 3.2SS cat in various ways.

[Henry Schmidt]

No worries Kevin. No offense taken.
I like the idea of using the GT3 rod configuration on the 3.0 crank.
The extra rod length (130 vs. 127.8 mm)adds to piston dwell and reduces rod angularity (side loading) all of which makes for a spirited engine.

If I had a clean sheet of paper (read mega bucks) the build would generally take a different form but like most everyone else, I have a budget.

A generous budget made the 3.1SS possible and I enjoyed every aspect of that build.
This on the other hand is "Just Another 3.2 Short Stroke"


Cheers

[E Sully]

Henry,
I am curious what is meant by "a properly fitted intermediate shaft."
Regarding the Intervalves. I used them on my '86 3.2 engine. What led to the decision to polish the stems?

[Henry Schmidt]

Originally Posted by E Sully

Henry,
I am curious what is meant by "a properly fitted intermediate shaft."
Regarding the Intervalves. I used them on my '86 3.2 engine. What led to the decision to polish the stems?

The gear on the intermediate shaft should be fitted to the drive gear on the crank.
By fitting I mean: achieving the appropriate backlash. Matching the numbers is close but not always close enough.

The InterValves seem like a very nice product with the exception of the shaft/ stem finish. They seem a little rough so we just polish them with the same tool we use to polish cranks.

[YTNUKLR]

ho hum

why did you increase the valve size, particularly the exhaust? not being critical at all , I am genuinely ignorant of why and curious to know.

cheers

[Henry Schmidt]

Originally Posted by YTNUKLR

ho hum

why did you increase the valve size, particularly the exhaust? not being critical at all , I am genuinely ignorant of why and curious to know.

cheers

Increased flow at all RPM levels. The Carrera head has huge ports. I was trying to bring the ratio of port size to valve diameter in line with what I understand to be optimum about 80%.
I've tried reducing port size with our Venti-port system (with reasonable success) and now we're trying bigger valves.

[Flat6Heaven]

Another beautiful engine... The cleanliness and attention to detail are breathtaking!

I was at the "Alméras Frères" garage yesterday in Montpellier and though they have a great history in Porsche racing, none of their engines look as nice as yours.

Looking forward to seeing the fuel injection setup, as well as the exhaust.

As always, thank you for sharing,
Ben.

[Henry Schmidt]

Well, thank you for the kind words.

Looking forward to seeing the fuel injection setup

Here's a hint on the injection.

[Nickmysta]

Hi Henry - this may be a stupid question, but what are the key benefits or characteristics of short stroke vs. non-short stoke? Does it rev faster, feel any different?

Thanks

[Henry Schmidt]

Originally Posted by Nickmysta

Hi Henry - this may be a stupid question, but what are the key benefits or characteristics of short stroke vs. non-short stoke? Does it rev faster, feel any different?

Thanks

Covering this topic in general will require a semester of classes so I'll just cover the different between 3.2 Carrera and the Short stroke 3.2. The main difference is the relationship between the crank and rods.
In the 911 engine, Porsche found themselves stuck with a dilemma. Because they were a tiny car company, each engine development was an attempt to improve the previous engine changing as little as possible.
That meant every time they made the engine bigger, they compromised something.
In trying to keep the engine's external dimension consistent (to eliminate chassis changes) they were forced to keep the distance from the head to the crank consistent.
That meant every time they increased the stroke they had to shorten the rod (compromise the rod to stroke ration).
Starting with a 2.0, Porsche rod length to stroke ratio was close to 1.97:1 (2:1 being theoretically desirable) . As the engine grew that ration decreased. Finally in the 3.6 it was 1.67:1
The short stroke engine provides longer piston dwell time at & near TDC, which maintains a longer state of compression by keeping the chamber volume small. This has obvious benefits: better combustion, higher cylinder pressure after the first few degrees of rotation past TDC, and higher temperatures within the combustion chamber. This type of engine will produce very good mid to upper RPM torque.
The longer rod will reduce friction within the engine, due to the reduced angle (see illustration) which will place less stress at the thrust surface of the piston during combustion. These specifications work well with numerically high gear ratios and lighter vehicles.
There is also the issue of journal size. The 3.0 journal is smaller 53mm vs 55mm, making the crank lighter and allowing for a larger rod bolt that will still clear the oil pump.
This larger rod bolt increases the reliability of the engine at higher RPMs.
After the 2.0 (906 type), few if any, Porsche factory race engines were ever built using the 55mm, 3.2 Carrera rod journal configuration.
Some version of the 53mm journal was used in the 917, 935, 962, 956, 936 and on.
Even the recent versions of the GT3 uses the longer version of the 3.0 rod .
This rod length to stroke ratio was a major player in the design of the Supertec SuperCrank.

[Henry Schmidt]

A change in direction on my car has me leaning towards a non-ntercooled 3.6 turbo so this engine may be for sale. The custom inject has been sold but I can complete the engine with MFI or PMOs and exhaust or just sell it as a long block.
Let's talk

[Shuie]

That is my dream engine. Awesome!!

[gt3racerich]

What would the expected numbers be on such an engine? (HP,Torque)
Thanks, Rich

[Henry Schmidt]

Here's what it could look like finished with MFI installed, modified stock air filter and heat.




This 3.2 SS had milder cams (mod S), lower compress 9.5:1 and SSI exhaust and made 285 on Fat Performance dyno.