Manning

I wasn't merely going on the FSM, which while vaque does clearly state the various differences of subsequent improvements. I was basing my comments on statements from 1) the regional (or national, I can't remember) technical rep from PCNA, 2) the service manager from Fred Baker and 3) our local regions trans tech expert (DanP's brother I think).

Also, when I referred to the S, I meant the TS, not the 944S.

Manning

I want to add also that when they made the comments they were fairly insistent that the myth of the 951 trans being an uber trans was just that, a myth and that there was really nothing to be gained by switching to one. Now maybe I misunderstood the point of their comments and they merely meant that swapping one into an NA gains nothing, but they also stressed that it is launching and hammering through gears that destroys these trannys more so than the added HP and torque of a stock 951 or 951S.

I do want to add also that they commented a few different times that while the 951 diff/R&P was different it was not significant and the real improvement came with the S2.

Oddjob

I don’t want to come across as being argumentative, and I welcome technical discussion on this or any p-car related topic. And I certainly don’t know the full context of the tech session you mention, but I completely disagree with any statement that would imply that a complete n/a transmission is as strong as a Turbo transmission – and I will emphatically state that anyone, regardless of their title/experience, that says otherwise is wrong.

Sure there are certain components that will be of equal strength (case casting, differential side plate, gear carrier forging, end cap/cover, etc), but for the entire combined assembly, the Turbo trans will hold up to a significantly higher engine output than an n/a trans.

I agree that there is absolutely no reason to ever install a 951 trans into an n/a, but its because the taller gearing would be a big detriment to the acceleration characteristics of the much lower powered n/a. And its also not necessary because the additional strength of the turbo trans (R/P) is ridiculously excessive for a 150 bhp car.

And I have heard the argument that n/a R/Ps are strong enough for an n/a, and that failed R/Ps in n/a’s are either due to poor/rough driving technique or a poor rebuild (improperly spaced/shimmed ring and pinion preload and backlash) – I don’t agree or disagree with this.

Gearing-wise, either the S or S2 transmission would be much closer to the final drive gearing of an n/a. So if you really felt it necessary to upgrade an n/a’s transmission to a stronger gearbox, the S2 would be the way to go. Since it is significantly stronger than an n/a, yet the gearing is not dramatically taller.

Otherwise, I cannot infer why they believe the S2 R/P is an improvement over the Turbo trans (?).


Back in the early ‘90s, there was a Panorama tech question regarding S r/p’s being used in turbos. At the time Bruce Anderson and another staff writer stated that there were known S r/p failures in that application, and the there was potentially a Porsche Tech Service Bulletin stating that only the S2 3.875 should be used to replace/upgrade a Turbo (when trying to shorten the final drive), the S 3.889 was not strong enough. Whether or not any actual Porsche TSB existed, I have no idea - I never cared enough to look.

But Turbo guys have been paying big bucks to find S2 transmissions to install for the shorter final drive, for years. If a Turbo wouldn’t break an n/a or S R/P, they would not be paying the extra money for the S2 transmission, since n/a trans’ are half as much and 5 times as available. No way is Fred Baker, or any other p-car shop, successfully installing n/a transmissions in 951s; they will destroy the n/a ring and pinion, and potentially the front pinion bearing.

But regardless of any of that, I have played with a couple turbo R/Ps, and they are big chunks of steel, and have noticeably larger teeth than even the S2. I still have a torn down Turbo trans in my garage, so if anyone wants to take some measurements off an n/a trans (R/P diameters, tooth size, input shaft diameters, pinion bearing size, etc), I would be more than happy to compare to the Turbo parts.

Manning

Well, again, I may have taken their statements out of context. Perhaps they were speaking only in the context of using one in an 8V NA. Regardless, they did reiterate that the turbo trans is not the wonder trans people make it out to be.

I would have to think that is to facilitate final drive, not strength.

Yeah, the issue with the S R&P is pretty well known.

Oddjob

If the tooth sizes were all the same and only the tooth count differed (which would require the diameters of the ring gears to be different - but in reality they are the same), then it would only effect the ratio. But since the ring gears have the same diameter, since the differential housings are all the same part - the tooth size changes with tooth count. So the thicker/larger the tooth is, the stronger it is.

I actually deal with this for my real job as an ME - chain drives, sprockets, gearboxes, etc for industrial processing equipment. Comes down to force acting on the cross-sectional area of the tooth, and material strength is given in lbs/sq-in. So the same force acting on a larger tooth/area generates less stress (psi) in the material.

Manning

Bear with me here:

So, if the ring gears are same diameter, then the tooth size has to change when you add or remove number of teeth. So no matter what, a R&P with a shorter final drive will have smaller teeth, no what around it. Turbo trans R&P may have larger teeth but it is, again, due in large part to its final drive numbers.

And larger does not mean better. For all we know the R&P in the turbo trans could be made of pot metal and the noted improvement to the S2 R&P was as a result of better materials and treatments.

I also thought some of the LS1 swappers have stuck with an NA trans to start with. Are these guy smoking the trannies in short order?

SD Porsche Fan

sh944 also had this done to his 87 951 and has a Vitesse MAF kit. Very fast!!!! He'll probably chime in on this subject.

Also remember that there was a Callaway 944 Turbo that was an early car. Only something like 30 were ever built. There are a few "kits" floating around if you can get your hands on one. You can also try to pm Porsche-O-Phile. He has all the parts for a Callaway conversion and could give you some ideas on intercooler placement. He posts more on the Pelican board these days so you might try him over there.

There are a few turbo'd NAs around. I'm sure you could do a search and turn up some interesting results.

Geo

This is always a humorous discussion.

As for buying a 951 being less expensive in the long run, I guess that depends on too many factors.

1) Condition of the NA 944

2) Condition of the 951

3) Cost of the 951 engine and engine management

4) Who is doing the work

What does a really really nice NA go for today? (not much)

What does a really really nice 951 go for today?

The delta there leaves a lot of room for a cost effective 951 engine and management or better yet, a turbo conversion assuming someone can do the work themselves (as I have done on all my project cars).

PORobinSCHE

okay, i am going to hijack this thread a little. what N/A choices are there for more useable power. 2.7 Litre....is there a 3.0 Litre that will bolt in?

Chris_924s

My guesstimate is.. 951 owners dont do holeshots.

VaSteve

The 951 oil cooler mounted in the stock 951 location will not however. I am mounting one for my n/a track car and had to hollow out the back of the foglight to get it to fit.

Mike C.

I think the feasibility of the turbo engine in an NA is largely dependent on how much you have to spend to get the engine, DME, trans, and all of the other assorted goodies to do the job right. If someone hands you a good turbo parts car for free - why not? Otherwise, it's pretty hard to justify from an economic standpoint.

As for the 951 vs. 944 transaxle - being an ME also, I have to agree that bigger/wider gear teeth will be lower stressed with all else equal. It may have been a long time since any service manager has gotten his nose into a transaxle.... Shot peening 1st and 2nd gear imparts compressive residual stress on the gear teeth surfaces which makes it harder for fatigue cracks to develop. I'm not sure why they never did this to the R&P...

Campeck

too add on.

NO an increase in power doesnt mean your "puny" NA brakes need to be changed to "super" turbo ones...

MM951

I feel the same way. It'd be nice to upgrade the brakes, but up to a certain point you really don't need them.

fwiw, both of my starions had the same size brakes as the n/a , didnt stop as well as my n/a but were plenty more powerful then the n/a. nobody complains about those brakes when owners upgrade to big power levels (300rwhp +)

Campeck

I just laugh when someoen posts that picture of the "what it takes to turbo an na" and then when someone says they want to do it everyoine jumps on them and says! no it willc ost to much. look at all the parts you need. you need brakes, the trailing arms, of course you need the valence becuase the higher hp output will make your car fly, and the turbo badge is needed so your not an NA poser!!!11one!!