[DeTomaso] Final Drive Gear Question

[MikeLDrew at aol.com]

In a message dated 6/23/12 10 11 29, michaelsavga at gmail.com writes:


> Here are the facts:
> 
> Two Panteras
> 
> Both with 335/35/17 rear tire wheel combos.
> 
> 1) One believed to have a stock geared ZF Turns 3,000 rpms at a GPS
> measured 70 mph.
> 
> 2) The other with a questionable/unknown final drive geared ZF turns 2,100
> rpms at a GPS mrasured 70 mph.
> 
> A) does car #1 seem about "right" in relation to all other Panteras?
> 
>>>Yes.   70 mph is about 3000 rpm in most cars.
> 
> >B) what replacement final drive R&P ratio would account for the 900 rpm
> reduction in engine rpms.
> 
>>>That's a huge jump.   The real question is, what's the rpm delta in 4th 
gear?

If the two cars turn the same rpm at the same speed in 4th gear, then the 
unknown gearbox car has a 4.22 ring and pinion and a taller 5th gear.   If 
they turn different rpm, then the unknown gearbox car has a different ring and 
pinion, but it might ALSO have a taller 5th gear.


> 
> >C) If #2 does indeed have a replacement R&P ratio of X, what would the
> theoretical top speed of Car #2 at 6,000 rpms.
> 
>>>That's simple math (which is NOT so simple for me--I SUCK at math!).   
But I can figure this out.

If it turns 70 mph at 2100 rpm, that's 30 rpm per 1 mph.   So 6000 rpm 
divided by 30 rpm per mph, equals 200 mph.

Your tall-gearbox car either has a very tall ring and pinion, or a tall R&P 
plus taller 5th gear. 

4th gear will tell all.

I'll send you a ZF gearbox calculator spreadsheet that you can play around 
with.

Mike