ZF at 700 hp

[tom pritchett]

HI Mike! I have not had this car dyno'ed as of yet. I am an instructor for the porsche club and I have had the opportunity of driving alot of diferent cars on the track with alot of different horse power ratings such as 500 hp vipers etc... I have not doubted the 700 hp as advertised by the individual that I bought the car from or the builder that I interviewed from PI Motorsports in orange county which also built the ZF and installed the whole package into the car. The company that represents, builds and sells the ZF in the US is a sister company of PI Motorsports and shares the same building. I thought that I had a really good combination because of the builder of the engine and the transmission. I have no delusions that the transmission problem is because of operator error. That darn loud pedal. I am looking for solutions to a problem that exist because of my loud pedal problem related to broken parts. The obvious solution is to put throttle stops on the ida's, but there is a certain fun factor that I don't necessarely want deminished. There has been alot of great help from the members of this forum and I am very greatful for the ample knowledge found here. If I can just put in a new ring and pinion gear set in the ZF and it will hold together, what a wonderful world, but the general consensus is that it just won't. What to do. I have taken my porsche of 350 hp to the track on a regular basis for 5 years with never an incident or broken part. Knock on wood. I would like to have more time at the track with the CAV GT 40.

Now Bruce. I was not aware there were two different styles of the ZF. I will go and look tonight for any distinguishing markings to see what exactly I have. Thanks for the heads up! tom

 

[wanni]

Wanni,

Sorry to be an idiot about this, but what does it mean when you talk about isostatic bearings vs. hypostatic bearings?

The elasticity you mentioned in drivetrains is fascinating, and makes a lot of sense.

Thanks,

Tom

Not bearings but shafts
An isostatic shaft has ust 2 bearings and the line connecting both is straight.
Hypostatic means there are 3 or more bearings for supporting that shaft.
Even being extremely precise the line will be as a snake giving pre tensioning to the shafts if the bearings play is not sufficient, generating vibrations and premature wear.
The machining of the holes holding the supports MUST be accurate as for a cranckshaft.
I hope it is now clear.
Wanni

 

[wanni]

Let me add a bit here. I understand (correct me if Im wrong), but the ZF transaxle was produced in different strength variations. The 5DS25/0 (4-bolt) was the weakest of the series, being the 7-bolt 2DS25/2 the strongest.??

Now, elasticity. I would say that Ferrari use the 'twistability' of the axles to compensate for the 'shock' to the driveline, as the engine/gearbox is solid mounted to the rest of the car. And as pointed out, a somewhat flexible input shaft will help as well.
I have a rather long input shaft that I made and decided not to 'waste' it down rather to leave it solid at 1 inch all the way along its length to the first input bearing, (so as to help eliminate shaft flex from gear mesh vs power issues). So to give me the 'shock absorber' on the driveline, I'll use a sprung centre clutch plate and somewhat flexible engine/trans mounts.
... works for me ....

I do not understand exactly what you are meanning with those words, but I feel you miss some points.
The elasticity that I am trying to explaine is the capability of the shaft to have a great torsion before breaking.
Of course that as long as it is possible to have it and as much torsion the shaft will do without breaking and cutting the impact torque peaks.
Example:
WHY the Saleen S7 does not destroy the RBT box by having a huge torque and tyre grip? It has an entry shaft long about 600 or 700 mm. Check the car and you will confirm that the box is nearly 1 meter away from the engine.
The RBT in this specific case will have a structural rupture for fatigue and not for impact shock. Billy Tally, the Saleen designer is not stupid at all.
The springs on the clutches are too easly fully compressed.
This means that they damp for 8-10° only and they give back the impact as soon as they are compressed. The torsional shaft has an infinite torsion angle before the rupture.
I hope it is now clear how that concept works.
Ciao
Wanni
PS I ttach a drawing of my box.
You will see that the primary shaft is cutted in 2 parts. The external one is torsional and the internal one is rigid.

 

[wanni]

Wanni, you are a wealth of information. I love to watch f1 and follow it as time allows. I had no idea that the drive shafts were made out of any kind of elastomer. This may be the most simple solution that I am facing. I can only imagine that this will be a total custom set up for the drive shafts. I will see what I can get locally and put something together. The 34nicrmo16 looks to be metal for my uneducated eye. I see nickel chrome molly. Of course I am probably wrong. My 0-60 has not been timed and because of the current situation of the transmission, I don't dare try as of yet. tom

It is a steel which has a huge torsionality when it is fully tremped.
34NiCrMo16 is the chimical compound. The commercial name in Italy is TPR1. Every country call the steels in a different way.

I want to be clear that is ust a concept or a mode in designing transmissions.
Do not take it like the law and do not try your own to build such a parts without the support of an engineer, pls.
Those infos are ust for your knowledge and that' s it. Do not play with those parameters alone.
Ciao
Wanni

 

[Mesa]

Wanni,
My Ferrari 360 transaxle has a two piece input shaft. Is it this way for the same reason your transaxle has a two piece shaft?

Very interesting observations you bring to the forum - 8mm gears in an F1 gearbox !!!!! How does THAT work? I don't really expect an answer.

 

[wanni]

Wanni,
My Ferrari 360 transaxle has a two piece input shaft. Is it this way for the same reason your transaxle has a two piece shaft?

Very interesting observations you bring to the forum - 8mm gears in an F1 gearbox !!!!! How does THAT work? I don't really expect an answer.

It is very difficult to cook such a long shaft and keep it straight, also there might be some assembly issues.
I do not know exactly why GTG is cutting in 2 pieces the primary shaft, because i do not know the material they are using.
I do cut for:
elasticity adding
simplicity in building a new shaft for a new client
easiness in keeping straight the shaft after heat treatment.
I do not GTG strategies.
Regards
Wanni

 

[Iain]

Tom, If you are serious about using your horse power and torque on the track then I think you should be looking at a Hewland VGC, the rateing was the only one that came close to the requrements that we have for our track car. We now have one installed in the car and have the solution to the bell housing issue, if you need any more details or info please feel free to send a message, Iain

 

[Ian Clark]

Hi Tom,

Great question and what a wealth of info it's produced. My observation in driving big cube CAVs is that there is no problem with the ZF.

However as has been pointed out breakage can occur due to abuse (or exess adrenaline) or shock impact. There's another thread running about CV joint failures also with good information.

IMHO your fear of dynamiting the RBT is unfounded. The ability of other boxes to live under huge torque reversals that occur in stock CAVs on the track is not guarenteed.

What I do know is that there are improvements to be made in controling the rear tire contact patch before you'll get anywhere near the real capabilities of the chassis.

CAV Canada has released a new uprights, front and rear, that dramatically reduce the rate of camber climb, increases rear anti squat, corrects front ackerman geometry, eliminates binding and are stronger parts. This is all designed to create the most contact area possible on the tires throught the usable suspension travel. Please see the CAV Talk section for more info.

Its fair to say that, and this applies to all cars, if you're not in control of the contact patch on a race track then bad things can happen. Driveline components break, handling is unpredictable or nervous, braking is long, corner exits are slow and that's without throwing in the kitty litter or a guardrail.

Being an instructor for the Porsche club qualifies you as a competent driver and Porsche definately has their cars figured out, at a cost of untold millions of dollars and decades of racing. Wonderful cars...

I'd be interested to hear your observations about the handling of your CAV GT vs other high performance cars you've driven on the track?

Worries over possible gearbox failures, brake sizes, tires, shock valving etc cannot be adressed until the chassis is hooked up. Sticky tires and big brakes won't compensate for less than optimum suspension and wheel control, might even aggravate it.

Cheers

 

[tom pritchett]

Ian, the car can be a handful to drive. I have had it to the track twice and broke it two times. The most successful event of the two was about a total of 40 minutes at speed. I have been at the track so many times with the porsche that I am very comfortable with it and can do anything with it. Having the GT 40 out, knowing that it can hurt me really bad, I started slowly in to the corners and slowly increased the speed. I wanted to know if this car would either have under or oversteer. I really wanted to get a feel for the car before pushing it too hard. Before I broke the outboard cv, I didn't get the front to push or the rear to come out at all. I was up to about 7/10ths of my porsche which is a 91 C4 with about 350 hp. The C4 has a tendandcy to push where C2's don't. I'll get back to the track after I finnish my wife's dream home and my dream garage. Hopefully that will be in 2 months. My Porsche mechanic saw a kit GT 40 with a Porsche G 50 trans in it and called me about putting it in instead of the ZF. My decision is not yet made up with which direction I will take. I will say that the CAV GT 40 is the quickest car that I have driven and I am careful and humbled by it. It is also pretty raw. Alot of new car drivers that I have at the track are driving their new carrera, camen, etc... and are looking at how they may perform, but these new cars, with all of their new driver aids, almost drive themselves. Maybe that is one great draw this car has for me. It becomes all driver. I'll post more as more comes to bare. tom

 

[tom pritchett]

Iain, I have not heard of this hewland transmission. Please tell me more. How much fabrication will be done to install it from the ZF? Where is it produced and how much does it cost? thanks tom