It has been a long time since I put the pedal down off the line. Dry pavement and broke traction!. V12 is really an amazing engine!

Anyone ever changed from the TH400 to the 700 4 speed? If so, is it a pain to do?

 

Yup, a V12 in proper tune will easily spin the tires. So many neglected models don't, and people come to think of that sluggish behavior as normal. Definitely needs respect in the rain.

There are a couple of members who have done the 700 conversion. Don't think they have any official acceleration comparison times though, just subjective butt dyno observations.

 

Yeah! i changed to 700R4 16yrs back(HD Corvette trans), been perfect,no problems, BUT i also changed my rear gears, to 3.73 down from 3.07,.

now, much better acceleration, and still have proper gearing in 4th overdrive cruising,(add Quieter at speed)!

 

In proper tune? The 2:88 rear set is what is "sluggish" not the V-12. The car would have tremendously benefited from a different trans configuration and rear gear set...all of which were readily available at the time. Jaguar IMHO blew it with the trans/rear gear combo on the car.

 

I changed my trans to a 700r4 5-6 yrs ago. I am overall happy with it. I bought the John's cars kit. Fit excellent.

 

My stock 89 5.3 with 2.88 would spin the rears off the mark in the dry. Can't wait to see what she will do with the new 3.58's in the rear.........

 

I swapped in a 700R4 as well. its significantly lighter than the old 400, with a lighter and higher stall converter.

 

Yes they did.

No they didn't. :-)

No question that the 400/2.88 combination dulled the performance. And I don't know where the notion came along that the 5.3 V12 was a torque monster. It isn't, at least not to my estimation. I suppose it depends what it's being compared to.

I think, though, that Jaguar was primarily looking to get something remotely resembling "decent" fuel economy out of the car....which they certainly did. And when the HE version came out sales DID pick up for several years so the public was at least reasonably content with the less-than-optimal drivetrain combination.

They could've made different choices but I suspect they blew their financial wad on the HE engine itself. Gotta remember that for a long time Jaguar struggled to merely stay afloat and sell even 10,000 cars/year....and the XJS itself was almost on the chopping block a couple times.

As it stands they ended up milking the car for all it was worth....and got 20 years out of it !

Cheers
DD

 

IMO the stall is the problem. 2k stall is way too low for the top end biased V12 in a moderate ratio (such as 3.56+) and completely ludacris for a sub 3:1 ratio.

needs moar stall.

 

I went to a 2500 stall on mine. Helped quite a bit

Cheers
DD

 

i bet. not only is it gonna compiment the engines power/tq band its also significanty less rotating mass which is gonna help with drivetrain powerloss.

 

for my torque converter, i used a smaller 10" diameter unit(much lighter rotating weight), and it gave me a higher stall along with it, around 2500-2600rpm, that with my 700 and overdrive,have about the best automatic and rear gear combination, for the low torque of the V12 5.3.

and Doug is absolutly correct,5.3s do not have a lot of ft.lbs., people should drive a Big block chevy for a few days, now they got torque, i have owned both types of engines and cars.

i weighed my 400 against the 700 trans , 30 lbs lighter weight for the 700,YUP! GM knows how to do things right, lot of folks forget the 700 has a very low 1st gear ratio 3.12-1, good for acelleration, and a 1st to 2nd shift that is instantanious.

700 is not super strong, but can handle 400-425ft.lbs. with the proper mods to it(not much money to do).

course if you got a 7L and a supercharger,better of with the 4L80 GM trans.

i have been driving a friends ZL1 Camaro 6spd auto, and it is marvelous piece, seems transmissions are moving into a new order! with launch control you can put 600hp to the ground with out wheel spin, the car just damn near lifts the wheels! YIKES.

 

Yes, a higher final ratio will definitely give better take-off, and sportier perf around town and short bursts, but of course it is the cruising ratios which give the ultimate top end without killing your engine.
Years ago, I had MoPars, '70 challenger with 318X4 auto and 3.55's, had nice top end, with sluggish launch, then had a '69 Dart Swinger w/340X4X4sp and 3.91's, wild little beast, but topped out at 118mph.
Just two days ago, I drove my '89XJS approx. 160 kms on real nice 4 lane, and toed it down for the helluvit. Let's say I know that 5000 rpm gives me 210km/hr(128mph) and I was only 1/2 to 3/4 throttle. That felt damn good.

 

i saw a poor running XJS do 140mph. those 2.88's have their purpose.

 

There are *some* driving situations where the TH400/2.88 combination is not-really-a-bad-thing. First gear is good to 60-65mph and 2nd gear to 100-110mph...giving the driver downshift options that usually wouldn't be available with shorter gears and/or the ratios found in most 4-speed autos.

Cheers
DD

 

dont know if this helps the topic, but my 700R4 in overdrive with my 3.73 rear,gives me a final drive ratio of, TADA, 2.60, even better than 2.88s.

i'm guessin anything lower than,say 2.50-1 would have a 5.3 almost luggin, MPG could drop off!

 

I don't have actual figures, but say a 5.3 HE with stock transmission could do 0-60 in high 7s.

What are you 700 guys running?

 

even the 6.0's with 700R4's arent very fast, considering the amount of power they put down.

 

Doug, what did you do to increase the stall to 2500?

 

Called this outfit....

High Performance Automatic Transmissions & Parts - TCIŽ Auto

....and had 'em make one up for me.

Cheers
DD