Muscle Cars - Chevy vs Ford

[sub006]

Originally Posted by MrPbody

Sub,

Most of the mid-'70s through mid-'80s Jags I worked on had TH400 in them. At least two "Ss" I rebuilt the trans in, at just over 150K miles. I have no idea what the exact year "spread" is, but Jag "pattern" TH400s are "out there". The internals are the same as a Chevy or BOP TH400. The case and converter are "special".

FWIW

Jim

I think you're correct about V12 Jags. If the BW was strained by the Six, no way was it going to live behind a 12! John's Cars recommended Turbo 350s for XJ6s with small blocks but insisted on 400s for Rat engines. But standard XJ6 automatic transmisions were four different Borg Warners over 20 years of production: Models 8, 12, 35 and 65.

If only they'd followed the Rolls-Royce lead and used a 350, it would have been a lot better. And an "aluminium" Powerglide would have lasted forever in that application!

PS: My name's Jim, too

[MrPbody]

Jim,

Never did much with Rolls'. A couple of engines for antiques over the years, one brake job on a '78 (NOT tirvial...). Not impressed for the kind of money they get, but I suppose that's the way of high-end luxury cars, the NAME is more important than the result.

I feel there's no "place" for a 2-speed trans in a luxury car made after WWII... 'glides may be tough, but they sure are barbaric.

I still don't see the "logic" in putting the low-level GM powerplant in such a high level car as a Jag. The original Jag 6s were straight out of aviation, the highest level of technology of the day ('30s). They flipped it "right side up" and added a sump and internal oil pump, and it's bulletproof. The V-12 (5.3) leaves something to be desired, I agree. It should be more powerful than it is, but it is SO SMOOTH and has a nice "flat" torque curve. Just right for a high-end luxury "performance" car. The very heavy "S" is still a decent performer, though nowhere near the E-type. And besides, a little oil under the car gives it "character"... (:-

The modern 3.9 is a pretty lively engine. I believe it's "based" on the 4.6 Ford (or vice-versa).

Fun to discuss these cars. I don't often get to talk to someone as or more (you) knowledgeable than I about them. The local dealership techs won't give me the "time of day" (arrogant, unaware of the "big picture") and most of the independents that work on them are insecure about it. I make them "nervous" because I "ain't from 'round here..."

Jim

[sub006]

To be called more knowledgeable by the Dean of Musclecars is a rush, thank you. But I'm just a civilian who tries to maintain and do light repairs on our motor pool.

I did not mean to denigrate Jag engines, just their choice of American automatics to put behind them! The sixes are straightforward to work on and certainly were refined after 40 years in production.

The way I understand it, the XK engine came from aviation, but indirectly. When planning their postwar sports car and its engine, they looked to the best pre-war sports car. That would be the BMW 328, which, with an aerodynamic body, won many premier races in 1940 including (I think) Le Mans.

Compare pictures of a 1939 328 to a 1949 XK-120. The Jag is the same car, only larger. The twin-kidney Bimmer grille is morphed into a single large oval.

BMW began as a builder of aircraft engines, which it still was doing in the 30's. The XK prototype engine was a four-cylinder copy of the BMW unit. Walter Heynes expanded it to six cylinders, producing the world's fastest production car at the midpoint of the century, with 130 mph capability for only about $3000.

The "lowly" small-block Chevy is significantly lighter, more powerful and delivers better mileage than the XK, when installed in a Jag sedan. I never felt the need to transplant one myself, but I can't blame owners who wanted to free themselves of dependence on the surly dealer techs and independent specialists you have encountered.

I was not seriously suggesting factory installation of Powerglides, just that even that early transmission would have needed NO rebuilds or replacements compared to the Borg Warner units.

In the 1930s, Rolls-Royce bought one new American car each year to tear apart and find out what advances were being made by the world's leading auto-producing country. They chose Buick. Postwar, they tried for almost a decade to build their own automatic transmission and finally gave up. They went back to GM, asking to buy Hydramatics. GM gave them a good deal on warranty returned Hydros, which Rolls would disassemble, blueprint to closer tolerances, and install in their new cars.

In the '70s, my Corvette tech/tuner Dick Guldstrand did a fine side business replacing blown-up Rolls engines with Cadillac 472s. One thing that made it easy was the instant bolt-up compatibility with the "Rolls" Turbo 400!

[MagicRat]

Originally Posted by sub006

Postwar, they tried for almost a decade to build their own automatic transmission and finally gave up. They went back to GM, asking to buy Hydramatics. GM gave them a good deal on warranty returned Hydros, which Rolls would disassemble, blueprint to closer tolerances, and install in their new cars.

And this 'rebuilding' process was not a success. Soon after Rolls started installing THM 400's, they started to experience embarrasing lubrication-related failures on their own THM 400's. Knowing that GM did not have such a problem, they asked GM to look into this. A couple of GM transmission engineers went to the UK to look at their "refinement" process.

It turns out that Rolls thought some of the rough, cast internal parts were unbecoming of Rolls, and were polishing these parts to a smooth finish. GM said the rough cast finish was essential to retain a sufficient film of oil on the parts for lubrication. So the polished part was actually doing harm.
My understanding is that, after that, Rolls left the THM 400 alone.

But they did use an electric servo motor to move the shifter. Therefore, the Rolls gear shift lever was not directly linked to the transmission, it just controlled this servo motor.

As I recall, other high-end makers used the THM 400 too, back in the day, such as Maserati, for their older Quattraportes.

[MrPbody]

I'm no "dean" of anything. But 35 years of "doing it" does help... (:-

I learned something from your history lesson. All goodness!

Yes, 350 is "lowly", but it's the most popular performance engine on the planet for a lot of reasons. IMO, it's NOT because it's "cheap". I think it's "cheap" because it's so popular... Which came first, the chicken or the egg? But at least the Jag owner wouldn't feel COMPLETELY out of place with it, as it will still leave oil spots on the ground... (:- I just grow weary of the "put a small block in it" mentality. As a "Pontiac guy", I've dealt with that most of my life. My solution to making a '55 Chevy run "hard" is to install a 400 Pontiac in it... (:- I remember one in San Bernardino with a TriPower 389 that was the TERROR of the street scene for a while.

Jim