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Thu Jun 04, 2009 1:01 pm

Hello-

Since it's not uncomon to welded/regrind cranks to increase their stroke, why couldn't one de-stroke a Porsche 356 A or B crank so it would work in a 36HP VW case? While the cost of the core/machine work wouldn't be inexpensive, it seems like an affordable way to build a reliable 36HP crank.

Thanks,

Paul

Thu Jun 04, 2009 5:26 pm

Like this one? Std 36hp mains,72mm stroke,36hp rods on this one.Works quite well............

Fri Jun 05, 2009 12:57 am

Or use a preA crank.
Not easy to find admittedy!

Fri Jun 05, 2009 1:51 am

gimmesomeshelter wrote: Hello-

Since it's not uncomon to welded/regrind cranks to increase their stroke, why couldn't one de-stroke a Porsche 356 A or B crank so it would work in a 36HP VW case? While the cost of the core/machine work wouldn't be inexpensive, it seems like an affordable way to build a reliable 36HP crank.

Thanks,

Paul

Is not the 356A/B crank usable if you do some clearance work on the case?
I seem to recall reading posts of people using 74mm Porsche cranks.

Anders

Fri Jun 05, 2009 10:38 am

Scat will grind you just about any crank you need, and its brand new, not welded up.

Tue Aug 25, 2009 12:53 pm

swanlakers wrote: Scat will grind you just about any crank you need, and its brand new...

They have 74mm stroke Porsche mains/Porsche rod journals in stock, ready to ship! Only $1995!

Kona Flemmimg in Idaho has a Chinese version of the same crank for about $900.

I'd like to hear from anyone who is making serious power with either of these...

Tue Aug 25, 2009 5:53 pm

Hello-

I obtained a Scat crank last year. Unfortunately, I'm still collecting parts.

According to Desktop Dyno, by 80mm * 74mm engine, with Okrasa heads will produce 65HP. :wink:

I was speaking to my machinist, and he's building an old speed engine using Denzel heads. He anticipates that he'll be able to get ~110
HP once he's done.

Paul

PS. Scat cranks are now 2200.

Tue Aug 25, 2009 7:00 pm

Call Jose at DPR Machine in Santa Ana. He's got tons of cranks, access to hard to find items, and can to special machining to any crank.

DPR Machine Shop, Inc.
2121 Susan Street Unit B
Santa Ana, CA 92704
800 517-5659 Toll Free
714 979-7441 tel
714 979-7442 fax
[email protected]

Tell him Derek from Speedwerks sent you so he knows his sponsorship is coming back to him. Thanks. Derek

Thu Aug 27, 2009 9:24 am

KMW wrote:
Is not the 356A/B crank usable if you do some clearance work on the case?
I seem to recall reading posts of people using 74mm Porsche cranks.
Anders

I have looked pretty closely at using a Porsche crank in a 36hp vw case, it's very possible, but no 'one size fits all' answer. I'll explain what I have learned, maybe others can chime in with what they have found.

I am no Porsche expert, but I am pretty sure there's early stroker (but non-counterweighted) 356 crank that is a drop-into a 36hp case. Just about all the others need case machining, certainly case clearencing, crank journal grinding, bearing fitting, and the like. For me, I gave up on the non-counterweighted option.

In the aftermarket, Okrasa and Bud Whitfeild (maybe others too) made drop-in 36hp stroker cranks. The 36hp Okrasa strokers come up 4 sale once in a great while, but a word of caution, buy any expensive crank from someone with a return policy, in case it doesn't pass magnaflux and is cracked. By the way, Bud once told me if I ever came across one of his old cast iron 36hp stroker cranks (I saw one on Samba 4 sale a few years ago), "don't pay much for it because all I would have is an interesting door stop, even if it was NOS!" He said "yea, it was one of my failures" as he laughed, "they all cracked or broke. What was I thinking, casting a 3-main bearing crank?..." he said :oops: (RIP Bud)

I digress... I've looked at a very used 912-356 crank and a 36hp VW crank side by side, dial calipers in hand... I am almost certain the 356 cranks were available in 74mm stroke both with and wo/counterweights, maybe in 69mm stroke non-couterweighted, too. I am a firm believer that if you want more performance, you want more rpms. You start by adding couterweights to the crank, better rods, oiling system for a strong bottom end, and go from there. If it's a stocker, I wouldn't bother with Porsche cranks and different rods and all that stuff.

My counterweighted 912 or late 356 (or whatever it is) Porsche crank has 55mm mains (like a type 1 vw has) and relatively narrow 53mm rod journals, and a 74mm stroke. My oem 36hp VW has 50mm mains and 50mm rod journals, 64mm stroke.

I have seen Porsche 912-356 rods w/53mm journals fit into 36hp vw engine cases, on a 74mm stroke crank.

The rod caps are indeed close, but do clear the cam lobes. With a bigger stroke and longer rod than a 36hp, you need to space the barrels out or use pistons with a shorter compression height (what's referred to as comp. height is the piston pin-to-piston crown dimension). This is so common in building any type 1 engine with a any stroke but 69mm (anything but stock), so it's not to be feared, isn't rocket science.

The mains are another animal... If you use a late 356-912 crank, you need to make changes, and have choices. It seems to me the strongest way to go, would be to have Rimco bore the case main tunnel to accept the Porsche main bearings (I think the center 2 main bearing saddles need to be bored... Matt Kinney?) I say strongest, since much of any crank's strength relies on the amount of overlap you have between the rod journals and the main journals. Said another way, you want the largest main and rod journals, for the most overlap, and the shortest sroke for the greatest strength. The case against boring the case for Porsche mains is that Porsche 356-912 main bearings cost $400/set, were as 36hp VW main bearings cost about 1/10th that price!! The other way to go is to have your Porsche crank's main journals ground down to to 50mm (36hp vw diameter), and use $40 bearings. You'd still likely align bore the case at Rimco, but for an inexpensive oversize 36hp vw bearing. Do you need the strength? I don't know, how much power and how high an rpm are you trying to attain?

Increase stroke, grind Porsche crank mains down to 50mm, grind the rod journals down to 50.8mm and wider to accomodate 2" Buick-Chevy rod size, 50mm stoke 36hp size, and you make everything incrementally less strong.

Thu Aug 27, 2009 10:24 am

Tom: What about using the 55mm Type 1 main bearings ?

Thu Aug 27, 2009 10:52 am

Unkl Ian wrote: Tom: What about using the 55mm Type 1 main bearings ?

I would have to look again, but I think on top of being larger OD, Type 1 mains and Porsche mains are different width. If it were easy, I'd think 356 engine builders would do whatever it took to not use $400 main bearing sets

Going waaaaay out there for a moment....

It's common to buy Type 1 race cranks with larger Type 4 main journals (the center main, or all three). You fit a tanged BMW rod bearing to your un-cut, standard bore, Type 1 case saddles. You use this much thinner steel backed, adapter bearing that fits the Type 4 VW crank journal(s), within your type 1 case.

Now, is the same type of mix-n-match thing possible with an OEM 36hp vw case and Porsche crank?

Well, rod bearings are only availble in standard OD's, no oversized outside diameters, so the case would have to be un-cut never align bored (almost unlikely unless a guy has a NOS 36hp case he's using). A guy would have to research this to see if such a savior bearing were avaialbe from some engine...

Thu Aug 27, 2009 1:37 pm

I have a Porsche 74mm, 50mm main jounals, non counterweigthed crank in my 1620 okrasa. The engine puts out 81 hp @ 3900 rpm. The 36hp motor is not built for high rpm so using non counterweight crank is good enough I think. Its easy to do the clerance work, some minutes with an air file and you are ready :lol:

Thu Aug 27, 2009 3:23 pm

very good to know... Do you have any idea what the Porsche designation for this crank is? 356 Pre-A, 356A, ??

"The 36hp motor is not built for high rpm so using non counterweight crank is good enough I think..."

Yea, that's what they say about the lowley type 1 1600cc powerpalnt... yet I have a 88mm stroke crank in T1 VW case that routinely gets shifted at 8100rpm :wink:

Thu Aug 27, 2009 6:51 pm

Welding and grinding the crank would probably wipe out any cost savings.

Tom Simon wrote: Unkl Ian wrote: Tom: What about using the 55mm Type 1 main bearings ?

If it were easy, I'd think 356 engine builders would do whatever it took to not use $400 main bearing sets

Sat Aug 29, 2009 8:21 pm

Tom Simon wrote: yet I have a 88mm stroke crank in T1 VW case that routinely gets shifted at 8100rpm :wink: I know this is a bit off topic for the vintage forum, but do you have any other specs for that engine? I love high RPM air cooleds.

Sat Aug 29, 2009 8:38 pm

Bengt H wrote:
The 36hp motor is not built for high rpm
so using non counterweight crank is good enough

Besides the cylinder heads and cam, what limits the rpm ?

Sun Aug 30, 2009 12:47 pm

Unkl Ian wrote: Bengt H wrote:
The 36hp motor is not built for high rpm
so using non counterweight crank is good enough

Besides the cylinder heads and cam, what limits the rpm ?

The lifters design is no good for hi rpm, Porsche realiced that already in -55 and VW a litle later

Sun Aug 30, 2009 12:54 pm

What RPM are we talking about? Tom Bruch runs a many of his 36hp race motors at 6,000 with mostly if not all stock parts.

Sun Aug 30, 2009 4:25 pm

Shorrock wrote: What RPM are we talking about?

I'm thinking much higher.

7500 minimum, to start

Sun Aug 30, 2009 4:26 pm

Bengt H wrote:

The lifters design is no good for hi rpm,
Porsche realiced that already in -55 and VW a litle later

Good point.

I've got at least two solutions to try.