Ruuning Without a Balance Belt...

[zcacogp]

Yes - sideways vibration at half the engine speed. It's proportional to the mass of the crankshaft, hence a big 4-pot has more of a problem than a small 4-pot. Usually, you can ignore it on a smaller engine, but when it gets to the size of the sort of thing that is bolted into a 944, you need to do something about it.

3-cyl engines are naturally very nicely balanced. 5-pots aren't, they have a multitude of vibratory forces acting in a lot of directions, but they are all fairly small and hence aren't a problem. 6's are like 3's, and fairly well balanced naturally.


Oli.

 

[Mike_Dawson]

Ah, I know a bit about this, single cylinder = huge vibration, twin = slightly less, even in two up two down mode, 120' triple is quite smooth but still finger tingling secondary vibration at higher revs. 180' triple is an animal (Jota!) that smooths out at higher revs, a straight four is smooth at low revs but high revs = some secondary vibration, up to approx 2200cc, above which the 4 cylinder vibration is very noticeable. 5 cylinder? Must be naturally out of balance. Straight 6 is smoooooth, V6 has rough edges. I'm sure that a V8 is the smallest number of cylinders in natural balance, followed by a V12.

Just thought I'd mention that!

 

[Fen]

OT!

Although I've never driven a 12 I have to say a 6 is my favourite configuration be it flat, vee or straight. As well as smoothness, to my ear sixes sound lovely right through the rev range; better than a V8 which woofles nicely at low revs but just becomes noise further up or a V12 which sounds like a bluebottle.

 

[edh]

Sixes sound great - I loved the noise of my Cologne V6 The 944 would have been so much more dramatic with a decent sounding engine.

I'm rather partial to the CGT V10 - it sounded amazing at Le Mans.

 

[Alpine]

My Jag is a straight 6, one of the last they made. Sounds lovely. The later ones were V8s but they had reliability issues.

 

[andygrey]

The only engine configurations that are completly free from 1st and 2nd orders and moments (read 'vibration') are straight 6's, flat 6's, (not V's), and flat and V12's.
The worst offender is a V4 (remember those 60's and 70's Fords?) with a straight 4 being pretty benign apart from some trouble in the 'Free forces of the 2nd order' department (I'm reading from the Bosch Automotive Handbook BTW!).
But anyway, I woudn't reccomend disabling the balance shaft.

 

[Neil Haughey]

Controversial maybe but I have often thought that if I had to rebuild my S2 engine I wouldn't bother and fit an Alfa V6 instead. Just imagine the sound....it would be glorious and 250+ hp easily available. ISTR the Alfa V6 is much lighter and of course being a V6 of the same capacity is likely to be much more compact hence improving the vehicles handling by reducing the weight in front of the front axle.

In fact I am surprised someone hasn't done it by now, take the best parts of an Alfa and a front engined Porsche sounds like the perfect car to me.

 

[Fen]

I had a 3.0 V6 Alfa once and it sounded marvellous. It did look quite a compact engine as well. That said while I'd happily drop a Chevy V8 into my 944 I wouldn't sully it with an Italian engine []. More seriously while I think the 944 4-banger is utterly forgettable I don't see the point going to the trouble of replacing it with something that only tunes to 250bhp.

 

[zcacogp]

.... not to mention the huge issues with actually fitting it, I'd imagine. Engine mounts and bolting it up to the torque tube would both be a nightmare, I'd have thought, as the Alfa engine comes from a totally different stable to the Porsche unit.

And that's before you have started to think about actually making it run. Italian electrics, anyone? []

It's a nice idea Neil, but I'd have thought the acres of pain required to make it work would simply make it not worthwhile.


Oli.

 

[Mike_Dawson]

The key issue with engine transplant is; will it fit in the engine bay without moving the bulkhead, beating the inner wings and deforming the bonnet? The rest is solveable. Although anything fits within reason (detuned Merlin into SD1 springs to mind). Never really thought about swapping the Porsche engine, what would the purists say? Why buy a Porsche and then fit another manufacturer's powerplant? If it's easy 4 pot horsepower, then F*rd Duratec must be worth a look, although the embarrassment factor might be significant. Duratec is quite a tall engine though.

 

[andygrey]

I saw an article in a magazine a few years ago about an American tuning shop who were transplanting a small block Chevy V8 into a 308...
I guess that a useful angine transplant into a 944 would probably be a BMW straight 6. They are pretty compact, tunable and silky smooth.

 

[Fen]

ORIGINAL: Mike_Dawson

The key issue with engine transplant is; will it fit in the engine bay without moving the bulkhead, beating the inner wings and deforming the bonnet? The rest is solveable. Although anything fits within reason (detuned Merlin into SD1 springs to mind). Never really thought about swapping the Porsche engine, what would the purists say? Why buy a Porsche and then fit another manufacturer's powerplant? If it's easy 4 pot horsepower, then F*rd Duratec must be worth a look, although the embarrassment factor might be significant. Duratec is quite a tall engine though.

A main attraction for me is to upset the purists. I can't abide all the Porsche "up themselves" brigade; it's metal and plastic.

I also see absolutely no point replacing the engine with something that isn't significantly more powerful than can be achieved with the original lump. It's an anodyne 4-banger, but it doesn't have any particularly nasty vices (especially in 8v form) so why go through the heartache of fitting something that isn't meant to be in there only to see the same sort of putput you can have from a Turbo with mild mods?

Off the back of the recent dyno day I'm actually starting to think even the Turbo isn't all that tunable and I'd suggest if your target is much beyond 350bhp you might be better with something else. Sure you can go further with the original engine but the law of diminishing returns seems to step up a gear around that level (possibly really more like 330-340bhp in fact) so it starts to really cost, it can get unreliable and you can start having to sacrifice low down quite significantly to gain higher up.

To my mind nothing beats the Chevy V8 option as it is compact, weighs roughly the same as the Turbo's engine plus its boost appendages and pretty much starts around the 350bhp mark (with more torque than the Turbo makes) and goes up steeply in output from there. There's also a wealth of experience fitting them to LHD 944s which goes a long way to helping with a RHD conversion.

With hindsight I wish I'd binned the Turbo engine rather than rebuild it and try to tune it. I'd probably have spent a similar amount as I have now but would have a running car making more power than all the others on the forum, rather than a land glider and a bill for another engine after it lunched itself.

 

[Mike_Dawson]

Duratec can offer 260 reasonably reliable bhp, but no V8 rumble. Chevy V8 is compact? When did that happen [][]? If upsetting the purists is of no import, I suggest turbo-hayabusa power with a sequential box, positioning will probably need some juggling to maintain 50/50 weight distribution. But is the 944 the best starting point?

 

[TTM]

The Chevy V8 is not only more compact, it is lighter.
Only (minor ?) drawback is the brake booster must be removed to leave some room to the left bank of cylinders.

 

[Fen]

So a Turbo with a decent wastegate and chips is ahead of the full-house Duratec.

I haven't driven a bike-engined car, but I had in mind that the 944 might be a bit heavy to go that route which is purely an assumption based on never having seen bike engines in anything but kit cars.

Is the 944 the best base? Possibly not, but it's a better base than anything the Chevy V8 (which is very compact for a 5.7 / 6 / 7 litre engine) came in. Actually we've discussed the 944 (and I guess 924 and 968) series a bit recently and there isn't a lot to compare with it for price, practicality, handling and build. It's not the best at anything, but it scores quite high across all 4. The Audi S2 was the closest I think we came, but it has a heavier nose and 4wd.

 

[Mike_Dawson]

Chevy V8 is more compact than a Duratec or a Hayabusa? Really?

So a Turbo with a decent wastegate and chips is ahead of the full-house Duratec.

Evidence please. Although I have no wish to defend Fraud's products, having suffered them for years. 260 bhp Duratec is not "full house".

I haven't driven a bike-engined car

Forget the origins, it's an engine, it might need a few revs to get thing going, but the gearing deals with that, a 'bike clutch is designed for operation by a couple of fingers, so it's on/off, sequential shift is a plus.

Best base comment referred to using bike engine power, 944 is (probably) too civilised to benefit from a Suzuki engine, but it's worth a thought if offending the purists is important.

 

[944 man]

A bike engine in a 944 or anything else that weights 1,300 kilogrammes (but a vehicle equipped with a torque tube and rear transaxle particularly) is going to go like a turd. It is a ridiculous suggestion.

 

[sawood12]

Bike engines don't produce the torque. Sure they can produce high power but at the end of the day it's Torque that matters and by spinning the engine faster you can make whatever HP you want but with no torque. I think the best engine to fit in a 944 is the 5 cylinder Volvo engine that Ford pinched for the Focus ST. Makes great power and there is something about a 5 cylinder engine. The Audi one is way too heavy to put in a 944 - they are heavier than the Audi 4.2 ltr v8's.

It seems that 350 - 400 bhp is the best you can expect from a 2.5ltr 944 engine without going for ultra high boost pressures, special fuels, water injection etc. The best thing to do with a 944 engine is to bore it out and sleeve it to 3.2 ltrs. I think we've yet to hear from someone go to town on one of those - though I think there is one guy working on it. I reckon at 32psi they will be a pretty unforgettable engine - they certainly make an unforgettable sound.

 

[Mike_Dawson]

A bike engine in a 944 or anything else that weights 1,300 kilogrammes (but a vehicle equipped with a torque tube and rear transaxle particularly) is going to go like a turd. It is a ridiculous suggestion.

Why? It's an engine, it might have different power characteristics, but it's an engine. Only two things to consider, bhp and weight. And a bike engine is the first step to a sub-1000kgs 944. Rear transaxle and torque tube are mere incidentals.

Bike engines don't produce the torque.

Nonsense. Bike engines produce torque in exactly the same way as any other engine. it might be higher up the rpm range, but a gearbox deals with that. If performance is priority, then - if mass is identical - the car producing 300bhp will accelerate more quickly than a car with 200 bhp, simple physics. Forget engine torque, it's an irrelevance if performance is the priority.

 

[944 man]

"Forget engine torque..."? Mike, with the greatest of respect, this thread was started because I wanted to hear about peoples experiences (or knowledgeable opinions) about running a 2.5l car without a balance belt: not to listen to foolish prattle about bike engined 944s with sequential gearboxes.