ZF at 700 hp

[tom pritchett]

Re: About to sign on the dotted line

Just a quick question, I have a zf 5 speed in my cav gt 40. Can it be strong enough for the 700 hp out of my 427 hammer motor or should I be looking elsewhere? tom

 

[John_1949]

IMHO you should look for a stronger transmission it you at all going to drive the car hard. I did not work for Ford in the 60's won't work for you now.

 

[Dutton]

Tom,

Just my two cents, but I'd say the ZFQ and the TRT both sound like they have the beef you're looking for. Were I were faced with your 700hp 'problem', I'd have a good long look at the TRT - infinitely adjustable gear ratios and reportedly built to take a lickin.

Like many other racing transmissions it's a dog-box, so be advised (for me, I love the whine associated with those gears and dog rings!).

Do try to keep it under 200 mph,

T.

 

[domtoni]

Tom,

Take a look at the transaxel comparison and multiply newton meters by 0.734, and you wll foot pounds of torque.

Take a good look at Gearfox' units, as they are (I would do this if I was buying a unit):
- in production (for most OEMs this is the most important feature - car makers don't like to take risk with new products)
- has a box that is close to meeting your requirements - I don't think you will find a 1000 ft pound box on the market
- probably gives you more speeds than you really need

Ciao
Dom

 

[tom pritchett]

Guys, I really appreciate your input. I may just have a polished 5 speed for sale soon. I have taken it to the track twice and it came home on a wrecker twice. Not good. The first failure, the outboard cv disentegrated. Luckily the axle didn't flail or hit anything! Whew! The second failure is a broken ring gear in the final drive. I love the power this thing puts out, even with rich 48 ida's, and as much as I want to keep it original, I want to drive it. I will look more into the new zfq and this other tvt. I'll look back at the thread. I know I got that wrong. tom

 

[Russ Noble]

I want to keep it original,

Hmmmm......... How 'original' was 700hp?

Cheers

 

[Keith]

Hmmmm......... How 'original' was 700hp?

Cheers

No good will come of it, I'll tell you....:squint:

"They won't get there any quicker".... (my mum, aged 96)

 

[Jac Mac]

Purely out of interest Tom, it would appear that these parts are breaking at fairly low road speed or in the case of the CV there would have been considerable damage in the surrounding areas. Is it on standing start--- shifting from 1/2-2/3 etc--- or just when the tyres really hook up and the torque curve gets to its peak.

Jac Mac

 

[wanni]

Without dressing the professor,
the power means nearly nothing for the transmission.
The gearbox feels:
1) Torque
2) Grip
3) Weight on the traction axle
4) Weight transfer to the traction axle
This in acceleration and in low gears, then:
5) Torque
6) Aerodynamic resistence
7) Total weight

The ammount of 700 HP is huge if it is at relatively low revs ( 6.000 ), this means that the torque is important, the ratios are long and the transitory time in torque on the gears becomes long and not instantaneous.

Conclusion: If your power gets out at 10.000 revs, never mind for the ZF ( except if the box can not reach those revs ). If you have it lower then 7.000 revs, then look for another, stronger box.

Just a data for evaluation: 2 bearings shafts ( isostatic ) would need about 92-93 mm as center distance. 85 mm are ok with a 3 bearings shafts supporting ( hypostatic ).
Ciao
Wanni

 

[tom pritchett]

This is a 351 cleveland built by PI motorsports bored and stroked to 427 with alot of custom work on cam and heads. 2.08" and 1.64" on valves. Ok I know this is not real original, but the trans is a dead give away from what I have seen. The drive shaft let loose at turn 1 at Pacific Raceways in Seattle area about 140 mph. The cav now has about 525 miles total on it. The ring gear broke at low speed and under alot of torque. I have heard these transmissions really don't like alot of torque and absolutely no wheel spin. Now I know. I suppose that it would be just fine if I kept my foot out of the loud pedal at lower speeds, but there is some kind of mental detatchment from what I should be doing and the adrenaline of the moment when I hear that sweet sound of that engine. That is when I figured I need to just try to make it more bullit proof. I hope that this more information will help! I really appreciate your input alot! tom

 

[tom pritchett]

Also, Wanni, I am running 335 35 17 michelin sport pilot tires with "stock gearing" weighing 2100 lbs total. So I have alot of torque with some good traction. Something has to give. I havn't taken the car to a scale and weigh it for front, rear diferential. I need to do this. I am wondering, what of these other transmissions that are available, is the easiest swap so I won't have to do alot of fabrication? I went to the link you posted and it appears they make several options with some differences. I will need to do some more research. I only want to do this once. thanks again. tom

 

[wanni]

Also, Wanni, I am running 335 35 17 michelin sport pilot tires with "stock gearing" weighing 2100 lbs total. So I have alot of torque with some good traction. Something has to give. I havn't taken the car to a scale and weigh it for front, rear diferential. I need to do this. I am wondering, what of these other transmissions that are available, is the easiest swap so I won't have to do alot of fabrication? I went to the link you posted and it appears they make several options with some differences. I will need to do some more research. I only want to do this once. thanks again. tom

You have around 1.1 as friction coefficient on a good surface
I do not know stock gearing ( too much yankee )
How much your 0-60???Must be over 4 seconds, correct?
With this weight and your torque you shall spin up to 4th gear.
It seams you are braking down for stifness of the system. ( all the shocks are reaching in the gears with the higher possible peak ).
Probably, inserting some elasticity avoiding high peaks, maight be enough to avoid ruptures. Ex: elastic thin drive shafts (34NiCrMo16 fully tremped) can be ok.
Immagine that on the F1, at the green light, the output shafts have already made 1 and half turn before the wheels start to move. Also an imput shft made in the same way will help a lot.
At your disposal for ore answers.
Ciao
Wanni

 

[Scott Calabro]

Tom.. if "you only want to do it once", buy a Hewland LG 500/600 or T44 !!!

Best,
Scott

 

[Russ Noble]

Immagine that on the F1, at the green light, the output shafts have already made 1 and half turn before the wheels start to move.
Ciao
Wanni

That is absolutely fascinating! I would never have imagined that!:burnout:

 

[wanni]

That is absolutely fascinating! I would never have imagined that!:burnout:

More elasticity you introduce in the system, and the impact factor coefficient for the calculation decreases. More it decrease and lighter are the gears.
You would have appreciate how thin and long are the F1 drive shafts.
Those materials have a very high rupture strenght and a low fatigue strenght. It is enough to finish the race, anyway.
The input shaft as well is made in this way and it is quiet long because he should cross the oil tank, helping himself to this target.
Ferrari is now at 11 mm width for the 1st gear - 10 for the 2nd and 8 mm for all the others. Can you immagine.
Ciao
Wanni

 

[tom pritchett]

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

 

[Tom]

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

 

[David Briggs]

Tom, you will be surprised at how much your CAV weighs, mine is about 2800 w/170 lb me and 15 gallons of fuel.
The outer CV on the CAV is a 90 mm Audi unit and will not take 400hp, I am surprised that the ring gear failed before another CV joint, is your ZF new or used?
I (and some other CAV owners) have had problems with the outer CV joint(inner is 110mm 930) and I am in the process of having a pair of custom stubaxles made that will accept the 930 joint and have a free floating axle.

 

[BruceA]

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 ....

 

[Mike Drew]

Re: About to sign on the dotted line

Just a quick question, I have a zf 5 speed in my cav gt 40. Can it be strong enough for the 700 hp out of my 427 hammer motor or should I be looking elsewhere? tom

I only know one guy who routinely breaks his ZF. He has a 750+ hp motor in his dedicated race Pantera, and he just drives the hell out of it. The problem is that he is extremely abusive to the car. I think I've mentioned him before on this site; he is just like Animal, the drummer in the band on The Muppet Show. He just gets the red mist and starts pounding the hell out of the car, and eventually the gearbox goes. On several occasions, Lloyd Butfoy showed me destroyed pieces out of his gearbox, and he's just astounded. This guy has managed to find new and innovative way to break things previously thought unbreakable.

Each year, he races against Dennis Quella, who also has a ZF in his 700+ hp Pantera. Dennis is a sympathetic (although extremely aggressive) driver, and has NEVER had gearbox problems as far as I know. They are both evenly matched on the racetrack, which just shows that you don't need to be abusive to be fast.

Oh, wait, I know of one other person who blew up a ZF. He had a 572-inch stroker in his Pantera, and did side-step-off-the-clutch drag race launches and burnouts, again and again and again, showing it off to dozens and dozens of passengers. After a few months of nonstop abuse, it finally blew apart.

But these are obviously extreme cases. Somebody who drives normally (that is, somebody who takes no special precautions, but has enough mechanical sympathy to not over-rev his engine or lock up his brakes, or bang gears without using the clutch etc.) should be able to make a ZF live forever, even with 700 hp in front of it.

Speaking of which, I have to ask, is the 700 hp of your motor 'advertised' hp, or has your engine builder provided dyno sheets to prove it to you? And what sort of exhaust system was it measured with? Dyno exhaust systems are almost always heavily optimized relative to the exhaust that the motor actually gets to use in the car. My 427 Cobra's motor dropped a full 110 hp when it was run with the standard Cobra sidepipes and headers, versus the dyno exhaust system (I subsequently modified the Cobra exhaust and hopefully got a fair bit of that lost horsepower back, but have no illusions that my motor is making as much power in the car as it is on the dyno).

My point is simply that it's quite likely that even if, in a best-case scenario, your motor does actually generate 700 hp on the dyno, by the time it's installed in the car, choked with an air filter and plugged with an exhaust system, that the power level will be at least a bit lower.