Hey folks, since the fleabay XJS did not pan out, I've located a 1990 that has a 4 speed GM 700-R4 instead of the stock 3 speed BW. I believe John's cars supplied the kit required for the swap. The original engine overheated, and current seller sourced another V12 (not 350 V8, thank god) and swapped out the tranny at the same time. Stock differential retained.

I'm working on scheduling a test drive, in the meantime any thoughts?

The TH700R4 (aka 700R4 ) gear ratios:
3.059 : 1
1.625 : 1
1.00 : 1
0.696 : 1


Does anyone have the stock BW ratios around for comparison?

 

Only a pre-1978 would have the old BW trans

Anyhow.....

The ratios for the TH400 are something like

2.48
1.58
1.00


This from memory....but I'm sure it's close


Cheers
DD

 

If it works well, it is a very good mod to have, better fuel consumptio, lockup top gear, etc. Just check when you drive it that 1st gear is OK for quick takeoffs, and that top gear is not so tall as to be virtually useless, as the later cars which used this box has lower final drive ratios. Do let us know what it is like.

 

Uh, ok BW was pre-HE, got it.

Thanks guys, I found the comparison ratios and details on John's cars :
Jaguar conversions, swaps, parts, service and advice - from John's Cars in Dallas.

Gear Jag T700
1st 2.48 3.06
2nd 1.48 1.62
Drive 1.00 1.00
Overdrive Dreams .70

So it should have better drive off the line, and better cruising as well in overdrive. Unfortunately not a numbers matching car, plus high miles, I'll drive it and make a decision.

Will post driving impressions

 

21years and still perfect, along with 3.73 rear ratio, gives around 2.60 in overdrive, and

1st gear take off is outstanding!!

 

Test drove it today, feels more peppy off the start, but it's not like a huge difference, more like a mild upgrade. I'd say about 10-15% by seat of pants feel.

Seller is older man with health issues, and wasn't inclined to more than a drive around the block, so couldn't gauge the overdrive

Driver quality car, was red now painted black, with some red traces showing in the engine bay. Driver quality paint, but no rust and in great mechanical condition with new rubber and wiring in the engine bay. I'd prefer a stock car with original paint in better condition that a modest gearing upgrade....

Ron, the 3.73 ratio you speak off, is that an alternative differential or what are we talking about?

 

1st gear would be a bit better. With the 2.88 gears I believe that the overdrive would be questionable unless going a hi speed. It would shift back and forth between 3 and 4 excessively

 

Do you mind me asking why your looking for another XJS? Since getting my XJR-100 I've been contemplating selling mine. Not sure what your budget or distance to look is.

 

The 700R4 with 2.88 has same 1st overall gear as TH400/4L80e with 3.54

 

2.88 rear gear ratio will never be a performance street ratio,, 3.54 is cheap and available but 3.73 rear is the most all around rear gear ratio, but both are good for street performance, in most any type heavy car!

take off is all about torque available at the tires, not the engine(course you gotta start with something).

cubic inches ,no replacement for displacement,(except a pressurized inlet manifold).

 

I currently have a XJ12, looking for a pristine, low miles, pre facelift HE, 89 or later when they came out with the new seats. Oh, MUST be original black paint

 

My bone stock 350 LT1 and 4l60E in my 83 XJ wuzza six pulls the
2.88 gears in it's .70 over driver with ease. And, no hunting. Great
throttle response any time, any where.


Why not If you like the car??? If not, it doesn't matter, one whitt.


Carl

 

mines an 86, original black paint, 80,004 on it but alas it's the pre " new seat" model ( but why would anyone want those annoying seat belts&#128521

 

An oft-mentioned concern over the years with so many 700 swaps into Jags but in reality doesn't seem to materialize.

In any case, if you find occasionally find yourself in a engine load-vs-road speed sour spot where there is excessive hunting....it's almost inevitable.... there's always the option of manually dropping down a notch to eliminate OD.

Cheers
DD

 

I wouldn't too worried with the stock diff. The V12 will motor the car along in OD @ 100km/h no problems. And as Doug said you can always manually drop it back to 3rd.

Not sure on the 700R4 but the 4L60e locks the TC in 3rd.

 

hey carl, i bet my V12 ,with 700R4 will run circles around your chevy powered car!!LOL

with 3.73 ratio no hunting at all, but if i push the pedal to quickly it will shift down, if i floor it it usually goes to 2nd, 1st is for stop light work, altho if i'm under 15mph it just spins the tires and shifts to 2 gear!

not to forget in overdrive ratio is 2.60 to 1, so cruising is perfect!

and to add; 2.88 in overdrive is 1.99 to 1, sorry i have a hard job thinking it has good response unless you shift it down to 3rd,maybe even 2nd gear, while i just motor on my merry way!