ptuomov

Unlikely, given that the whole point is to use a flat/single plane crank.

Ben Allison

sorry, I meant if the goal was to be able to use the 944 pistons (higher compression, slightly larger bore and no sleeving necessary)

I should rephrase. On the 2 valve there are readily available 944 parts to complete a hypothetical conversion to a flat plane crank (there are also 944S2 parts available to facilitate converting a 4 valve engine but they are rarer and more expensive). There is the added benefit of additional performance enhancements from these 944 parts, although there are cheaper ways to accomplish that separate goal.

White Lightnin'

Interesting comparison pics Mike...

I've never really taken an interest in the Italian cars, so flat plane crankshafts are a mystery to me.

Ben Allison

No, on a flat plane crank, 2 cylinders on the same bank are TDC at the same time, but one is about to start intake stroke and the other is about to start power stroke. Firing alternates between banks.

On a traditional cross-plane crank, the "TDC mirror" is on the other bank. Firing does not alternate between banks consistently (two fires on the same bank sometimes). This firing scheme is what reduces scavenging effects on cross-plane V8 engines. It's also what gives it the unique burbling sound.

Besides better exhaust scavenging, the main advantage of a flat plane crank is elimination of the counterweights on the crank.

White Lightnin'

So, to put a flat plane crank in a 928... much more would be involved than just having a crank made:

Something like reprogrammed ignition and injection brains; redesigned camshafts; different timing belt configuration (or use 2 independent belts on redesigned custom gears)?

Sound like H-P's suggestion of just dropping a Ferrari V8 would be cheaper (unless you had 100 other customers to pre-pay for all of the custom work).

Ben Allison

944 cams would work fine (at least on one bank, have to think through to see if it'd work on the other bank or if it would have to be reverse rotation). Firing order could be solved by swapping ignition wires around. Existing belt is OK.

76FJ55

Wouldn't the only necessary parts be crank and cams? You would then just need to rearange your spark plug and injector wires to account for the new firing order.

White Lightnin'

So, at least for the late model engines with the 2 distributors... you would end up with the left bank distributor firing some right bank cylinders (and vice versa)?

For reversing the 944 cams (or the vario-cam 968), you would have to have the drive gears relocated... or simply a custom grind in a mirror-image of the standard lobes?

If the ignition sequence can be easily handled by a simple rerouting of plug wires... what about the chance of doing the same for the fuel injectors. The respective brain boxes will 'think' they are operating a standard 928 engine, but the impulses will be sent to the redesignated targets.

Correct?

hacker-pschorr

IMO if anyone is serious about this project and plans to use stock ECU's.....you are crazy.

I would assume the "goal" of this project would be some serious power, in the excess of 700+hp. The stock ignition system will become a limitation. Might as well toss that in the garbage with the stock crank.

dprantl

Fuel is batch fired, so it doesn't matter if you are using stock LH.

Dan
'91 928GT S/C 475hp/460lb.ft

White Lightnin'

The ECU's would have to be custom mapped of course... perhaps the Shark Tuner II program?

Stock ECU's (but remapped) are still used on race cars... and run the same risk of failure as a street 928, so there shouldn't be a difference.

Or should there?

If your goal is the 700+hp range, then the ultimate weak link would be timing belt stretch at high revs... and the resulting 'interference engine' piston-valve contact.

Has anyone ever tried to devise a 'gear drive' type of replacement for the timing belt?

This would eliminate any belt stretch and eliminate 'tooth-jump'. The only problem would occur if a gear tooth broke off. It would be a lot of work, but I think it could be made as a complete assembly that mounted to the front of the engine.

LT Texan

them's some looooooooooooooooooooooooooooooooooooooooooooooong primaries

ew928

For the ignition stuff, can't a flat plane crank V8 be treated as a pair of twinned 944 motors.

jpitman2

I think the burble comes from the fact that V8s always have 2 adjacent cyls firing in sequence, and if they have symmetrical exhaust manifolds, the pulses from these 2 interfere. In my experience with the BOP-Rover V8, as soon as they went to asymmetric manifolds (rhs 1+2, 3+4, lhs 1+3, 2+4) the burble pretty much disappeared - these were one of the std chebby firing orders - 18436572, with 5 + 7 being the culprits.
Also, re flat plane cranks, which all but one Ferrari V8 used, I doubt that anybody would accuse their engines of being rough running?
Audi race one their V8s in Euro touring car races (or at least they did in not too distant past), and use a flat plane crank in them - they take a stock 2 plane crank, and PRESS IT FLAT. If you read some of the Chebby books , you will find they also do this . Would love to see that press at work!
jp 83 Euro S AT 52k

puyi

For the sound of the V8 with flat plan crank, you seem to refer to ferrari which use it for a long time, but Corvette C6 R and Vantage GT2 use flat plan crank and they sound more like a US V8 than an itlaian one.
I know a worshop that have made several flat plane crank for V8 engine, As I understand, it is machined digitally from a piece of metal. The cost would be large but not as high as you imagine. The 7 to 10 K euros is the goal. I don't know if I will investigate that solution or spend any money to achieve a prototype on that. But I found interesting to have your opinion and experienced on it.

Thank's for all

Puyi