I realize this subject has been broached many times in the past, however, a lot of these posts are ten, twelve, even 15 years old, and the posters are no longer even active. I’m hoping there might be newer or updated information. Let me begin by saying that I have an SPF Mark1, which is scheduled to arrive on December 7th. The engine is a stroked 351W, 8 stack Borla, which has been dynoed at 571hp and 542 ft. lbs. of torque. The shop I have committed to has/had both Quaife and RBT transaxles available. I use the terms RBT and ZF interchangeably. Are they one and the same? Then I understand that Quaife basically did an upgrade/strengthening modification years ago, sponsored by a member here, that is referred to as a ZFQ. My understanding is this ZFQ is capable of handling approximately 100 ft. lbs. more torque than the ZF/RBT. Yet, today a gentleman on the Superformance Owners Group posted of ”a massive failure” of his freshly rebuilt differential and ZFQ, on the first hot lap of a track day. I had selected the RBT for installation in my car. Am I making a terrible mistake? Are these two transaxles interchangeable in an SPF Mark1 with no modification? Or would I be better off looking at something else, say a Mendeola, Graziano, etc. The car will be almost completely street driven. All constructive opinions are appreciated.
Transaxle Dilemma
- Thread starter DB Clutch
- Start date
My view is from the perspective of being a Pantera owner with a ZF dash 2 5 speed which was completely redone by Roy Butfoy (Lloyd's dad). While my motor has no where near the power or torque of yours, WHERE on earth will you ever apply that much power on the street? Living in Southern California, it is impossible to drive faster than about 90 mph without getting locked up or killing yourself. So unless you plan to cruise the streets dumping the clutch all day long, I do not know why a properly built RBT would not be the right choice for your car. OBTW, there are other members on this site that rebuild ZFs and have outstanding reputations for their work so if you are stuck and can't get your box rebuilt for your car they might be able to help. There are also numerous Panteras running around with in excess of 500 HP and I have never heard of a ZF failure in 30 years of ownership and following the marque. The guy that trashed his box that you speak of has gone through MULTIPLE boxes and his car is used hard on the track. Apples and Oranges Bart.
Julian
Lifetime Supporter
For clarity the Quaife ZFQ is not an upgraded/strengthened ZF, it is a proprietary transaxle of the same dimensions as a ZF that uses Porsche internals and came about primarily due to scarcity / lead time of a new RBT ZF. I have heard of numerous other ZFQ failures, what I don't know is whether any of those failures are in the new improved ZFQ that Quaife is now manufacturing. I also saw the Facebook post of the SPF owner's ZFQ that literally split in two and with a failure of that nature I suspect something else is amiss, especially if it is a multiple recurrence. Most people overlook indexing the transaxle / bellhousing to the block and any misalignment puts additional stress on any transaxle.
In a street driven GT40 a ZF is going to be period correct ad handle what you can throw at it. If your new SPF is destined to be a vintage race car or regular track weapon with 14" wide slick tires then Ron McCall has good experience with upgrades to the ZF to address any weak spots. Ron has a race Pantera and drives it hard regularly, I too have a race Pantera putting out ~725HP through a ZF.
In a street driven GT40 a ZF is going to be period correct ad handle what you can throw at it. If your new SPF is destined to be a vintage race car or regular track weapon with 14" wide slick tires then Ron McCall has good experience with upgrades to the ZF to address any weak spots. Ron has a race Pantera and drives it hard regularly, I too have a race Pantera putting out ~725HP through a ZF.
I failed to mention in my original inquiry that my car is the wide body version with 10” rear wheels. I suspect that this should be a little easier on the transaxle.
Ian Anderson
Lifetime Supporter
Are you going to run as original with the rubber donuts on the driveshafts or CV at both ends.
the rubber eases shocks in the drive train, the C V not so much.
in their day the tracks did not have the lumpy kerbs that current tracks have and the shock loading from those with hard track use will not help any mechanicals. Keep it on the black stuff and be sympathetic to what is happening.
Ian
the rubber eases shocks in the drive train, the C V not so much.
in their day the tracks did not have the lumpy kerbs that current tracks have and the shock loading from those with hard track use will not help any mechanicals. Keep it on the black stuff and be sympathetic to what is happening.
Ian
If you are almost entirely using your SPF for street use either an RBT or ZFQ will be fine. I did break RBT 4th gears twice in my SPF with similar engine to yours on track days. Failure occurred after 10 track days each time. I was running slick tires. I believe Ron McCall has a stronger 4th gear set for track use. With street use my RBT has been fine over 35,000 miles otherwise.
Re the Quaife ZFQ, I seem to remember that the casing splits were propagated at the case bolt bosses. Basically, the bosses' bolt surfaces were machined flat right down to the edge/interface of the boss and the case, which created a big stress riser. Subsequent revision was supposed to have the boss bolt surface standing off from the casing - whether that fixed the problem, I don't know.
Howard Jones
Supporter
If you try to break it you will. If you try not to break it you won't.
Neither of these transaxles was intended to be "race driven" on race tires at that power level. However, relatively legal driving on street tires and like you will pay for it yourself will be OK......maybe. Why not reduce the power by a hundred HP or so instead...........you'll save some motor money also.
Neither of these transaxles was intended to be "race driven" on race tires at that power level. However, relatively legal driving on street tires and like you will pay for it yourself will be OK......maybe. Why not reduce the power by a hundred HP or so instead...........you'll save some motor money also.
Neil
Supporter
Horsepower doesn't break transaxles- torque does.
Howard Jones
Supporter
Well................................. I would agree that applying a large amount of torque to a power train that is stationary as in a clutch dump (or adding a large amount of torque to a gearbox rotating assembly ready in motion) as in leaving the ground and landing with full power applied, is the real cause of load stress and thus breakage..................but...................
No HP no torque.
An engine that makes its torque peak at a low RPM is sorta like the two examples CANAM big block would be an example. Whereas a high RPM torque peak tends to be more forgiving on the power train. A Cosworth DFX turbo INDY car motor would be an example of this one. Both have about 800-900 HP max.
Torque (in foot-pounds) = hp X RPM/5252 So.......... to our stated example
571HP @ 5000 rpms = 543 lb/ft (existing motor)
471HP @ 5000 rpms = 448 lb/ft (with a reduction of 100HP)
Note: guessed on torque peak rpms
More on this here:
IMHO the leading causes of transaxle failure are clutch dumps, downshifts without any attempt to match revs, and loss and reattachment of traction.
A relatively low-power capable transaxle can live a long life, even with a lot of power, if it is shown mechanical sympathy That's Mario Andretti's term.
No HP no torque.
An engine that makes its torque peak at a low RPM is sorta like the two examples CANAM big block would be an example. Whereas a high RPM torque peak tends to be more forgiving on the power train. A Cosworth DFX turbo INDY car motor would be an example of this one. Both have about 800-900 HP max.
Torque (in foot-pounds) = hp X RPM/5252 So.......... to our stated example
571HP @ 5000 rpms = 543 lb/ft (existing motor)
471HP @ 5000 rpms = 448 lb/ft (with a reduction of 100HP)
Note: guessed on torque peak rpms
IMHO the leading causes of transaxle failure are clutch dumps, downshifts without any attempt to match revs, and loss and reattachment of traction.
A relatively low-power capable transaxle can live a long life, even with a lot of power, if it is shown mechanical sympathy That's Mario Andretti's term.
Obviously the final decision on which engine to chose was mine. I went with this build because Doug at Prestige said that this was the one most GT40 builders were going with. This is in no way saying he forced me to buy this engine. I had really wanted to stay around 500 hp and a little less torque. But now that I have this engine, what would be involved in lowering the horsepower and torque? Is it just a matter of remapping the ECU, feeding it a little less fuel? Or would it require a cam change to either shorten duration or lift? I believe it was in one of the Carroll Smith Tune to Win/Race books were he stated “horsepower sells engines, torque wins races.”
ZFQ low gear is 2.5? to 1 and 2nd is 1.6 to 1, so you say you have 543 ft lb @engine= 1357 ft lb for low gear and 860 ft lb for second, doubt even your ~12" tires will harness that, but gives you a better idea of what you are subjecting the transaxle to, learn to treat the TA with some respect.
Neil
Supporter
We ran an LG600 transaxle in Bob Peckham's M8C and he had two BBC built by George Bolthoff ; one dyno'ed at 666 BHP and the spare engine dyno'ed at 665 BHP. At this moderate power level we sometimes saw the ring & pinion part company to the detriment of the side cases. These engines were built by Bolthoff for reliability & longevity so their torque was really outstanding but at a moderate RPM.
Appreciate your response. If your able to keep your ZF together with 725HP, and significantly more torque and wider/grippier tires, it gives me more reassurance
that with a little prudence my ZF should deliver a reasonably long life.
Ron McCall
Supporter
Bart,
Is the shop actually able to provide the transaxle that you choose? Meaning..do they actually have it in stock? Both of these ( RBT and ZFQ)
have been famously difficult to attain in recent years.
BTW, My race car makes 720hp and 650 lb/ft and is only used for track use. It does have some expensive upgrades ( 300m input shaft,M1 case,straigh cut 4th gear oil cooler with external pump) but it handles the power well. MY street car makes 570hp and has been driven hard for
over 20 years without one single issue from the ZF. And both are in the 2800# range. A GT40 should be considerably less than that.
Ron
Is the shop actually able to provide the transaxle that you choose? Meaning..do they actually have it in stock? Both of these ( RBT and ZFQ)
have been famously difficult to attain in recent years.
BTW, My race car makes 720hp and 650 lb/ft and is only used for track use. It does have some expensive upgrades ( 300m input shaft,M1 case,straigh cut 4th gear oil cooler with external pump) but it handles the power well. MY street car makes 570hp and has been driven hard for
over 20 years without one single issue from the ZF. And both are in the 2800# range. A GT40 should be considerably less than that.
Ron
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Ron,
Yes, the shop that I committed to had both the ZF and Quaife in stock. This was back in April. I was given my choice between the two as long as I was willing to place my deposit to hold it.
From experience my engine was built 566bhp, 540ft/lb, it destroyed the ZFQ 3 times. I had the engine rebuilt to match the Gelscoe 302, 495 bhp 420 ft/lb. Even with careful heel and toe etc the synchros need serviced every year. This year I had the gearbox serviced, then the CV carrier bearing fell apart and blew the diff. The diff was rebuilt then the case broke in half. Olthoff Racing have had a lot of experience in both RBT and ZFQ with a lot of problems. I’m waiting to see what to do.
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I have a 427FE & Quaife QBE62G in my GT40. The Dyno registered 715 HP. After 1,000+ miles I have had no problem. BUT..... I run street tires (Avon). I do not do burnouts. When I track it, I will not hit the curbs at the apex of the corners. I do not hesitate to get on it though. You can drive fast and take care of the car at the same time. If you do this you will have no problem with either transaxle. Just my opinion.... It is free so you won't get anything less than what you paid for it.
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