Auto or Manual

[melhookv12]

Thinking of putting a V8 supercharged engine in my XJS for track use/ as a race car.

Speaking to a supplier for flywheel and clutch assembly. He suggested using the auto box instead of a manual. The SUPERCHARGED v8 used a 5 speed Mercedes box. The box is very strong. He suggested putting a PCS TCM 2000 to control the gearbox. With the option of flappy paddles for gear changes.

Any suggestions positives and negatives.

Thanks ph

[anonymous-user]

The only significant negative is that the rotational inertia of the torque convertor dulls engine response and makes it difficult to calibrate the box for fast shifts. However, the S/C JAG V8 is a bit of a lazy old hector, and isn't very rev happy (wide flat torque curve biased to low rpm) and has high inertia itself, so in reality it's not an engine you're going to be rapidly throwing gears at anyway.


Big advantage is being able to left foot brake and keep your hands on the wheel during shifts etc


You may need to look closely at the cooling requirements for the box under sustained high rpm / load operation, but with a custom controller you can ramp up the system pressure and trade smoothness for durability! (ie run with much less clutch slip.

One left field option i looked at a while ago for such a project was to replace the torque convertor with an 'automated' conventional dry clutch, as it's really only going to be used to get going and too stop!

[stevieturbo]

melhookv12 said:

Thinking of putting a V8 supercharged engine in my XJS for track use/ as a race car.

Speaking to a supplier for flywheel and clutch assembly. He suggested using the auto box instead of a manual. The SUPERCHARGED v8 used a 5 speed Mercedes box. The box is very strong. He suggested putting a PCS TCM 2000 to control the gearbox. With the option of flappy paddles for gear changes.

Any suggestions positives and negatives.

Thanks ph

what others say is largely irrelevant.

What do YOU prefer ?

For track/race....I can just see it being rare for sloppy auto to be a preferred choice unless the driver has some physical limitations.

But some prefer autos, some prefer manuals. There is no right or wrong.

[nsa]

I drove a Porsche 996 at Palmersport that was a torque converter auto with a flappy paddle conversion. They ran a few around 2007 that did thousands of hard track miles. There is a thread here somewhere about the cars.

I drove that car at (my) 10/10ths and using the paddles in manual mode I couldn't tell it from the more sophisticated sequential boxes we have now. I remember in hairpin corners you could stamp hard on the brake pedal and pull the paddle shift to get into the correct gear, without having to dance around on the pedals double declutching when braking. I don't think it tried to unsettle itself by changing gear in longer corners either.

I have a manual track car but I recently bought a 996 Tiptronic and intend to track it. I think the biggest downside will be that people will forever be asking why you didn't go for a manual box, unless you are very quick in it, in which case they will probably keep quiet! I bet 95% of people would be faster in a properly prepared track car with an auto box but to suggest that is heresy.

You mentioned a Mercedes auto box. If it's the same one that goes in the 996 Turbo, according to Google they can handle 500lb torque easily, and from my own research the Mercedes computer has many adaptive maps compared to my ZF unit, which has only five.

Edited by nsa on Friday 8th April 15:47

[melhookv12]

nsa. Its called a 722.6 gearbox. Fitted in various mercs v12 twin turbo, AMG. Super charged Jags, my E270 diesel !!

There are 2 types. One that handles more power.
I have read that people are using these with 600bhp Jags. With a few mods to solenoids.

There's an American company that do a TCM and wiring, gear indicator and paddles.

There is also a Danish guy who has developed his own controller. Very clever guy by the looks of it. No association but he has some videos on his site.

https://ofgear.dk/index.html

Like you say the new generation of autos are very clever. Keep both hands on the wheel and left foot brake.

[anonymous-user]

Physically controlling an old autobox isn't difficult, as it's just a load of hydraulic valves oeprated by electrical solenoids. The TRICKY bit is controlling it well!

Managing the slip, in near real time across the clutches is difficult, as the friction characteristic of those clutches changes with many factors (wear, temperature, etc). Modern autoboxes use adaptive friction compensation to achieve smooth shifting.

Luckily #becauseracecar you can worry a LOT less about smoothness! And the good news, is that short sharp shifts, that feel awful actually are good for the clutches (because they slip for less time), assuming something else doesn't break from the inertial shock loads!

So, get an aftermarket controller, ramp up the system pressure and bang the shifts home! You might want to get a spare box for when it all inevitably goes wrong and bits come spitting out the bottom of the box..... ;-)