I'm am a soon to be 2005 XKR owner...should pick up car this week!

After a test drive this weekend I had a few questions about the acceleration and manual shifting. I haven't really driven these cars enough to experiment with different driving styles.

It seems to me you have to mash the accelerator then wait a few long seconds to kick in supercharger. Is that just a characteristic of a supercharger to wait patiently as the power is conjured from the beast within? Or is there a way to drive these to feel the torque sooner without violently mashing the accelerator to strongly get up to speed.

Also, there seems to be lags while manually shifting. If I pull down to a gear it seems to take a second or two to change, when the transmission is ready to change, not me. What situations do most of you use the manual shifting for if this is the case. My newer model japanese car will shift on demand using the manual shifter.

I'm also confused because I thought there were 6 speeds in a 2005 model but I believe the gate plate shows gears 2-5 printed.

Again, I have only test driven these cars a limited amount of times so I'm not too familiar with it's driving characteristics...I may have not driven it in the manner she desires. The car has very low mileage and it is in top mechanical and physical shape, it could have been just me

 

I just purchased an XKR about 2 months ago. The "J-gate" shifter is fun, but it's no manual. It's not meant for you to start, shift to 3, shift to 4...and so on. Whatever speed it's in is the speed that the XKR won't surpass (it's an "upper bound" shift limit), but the tranny will automatically shift in between.

1. All supercharged (and turbo) vehicles have this "lag", since these power adders deliver more air (and HP) through spinning up, they thus need to be in higher rpm's to kick in. That's normal. Trick is to keep the RPM's around this sweet spot (function of speed vs. RPM - more on that in a bit).

If you're driving with a bit more "spirit" click the "sport" button in (this raises your shift points, letting you pull through more of the rpm range), leaving the car more so in the performance RPM range. I also turn off the "traction control" for a bit more fun out of the hole

In the city, I leave the shifter in "3". This means the jag automatically shifts between 1, 2, and then 3, but stays in 3. In 3rd I cruise around the speed limit but just under 3k rpm's, which is higher than if I let it shift into 4, this keeps it just at the beginning of the "sweet spot" so when you step on it then the supercharger instantly kicks in. If, by contrast, you cruise around in higher gears, then in the city the car will shift all through the gears and try to cruise as close to idle as possible to be the most fuel efficient, and as a result you won't be in the "sweet zone", if that makes sense.

2. The reason why you don't have a gear "6" (or on my 2002 xkr, gear "5", is that that's the "D" gear. So when you're on the highway you throw it into "D" auto, which includes the highest gear.

On a side note, the xkr's shifter is actually quite useful on downshifting, I find it quite more responsive, and smooth then trying to manually shift it up. Again, I usually set it in "3" and can cruise down hills with minimal use of brakes, just like with a manual.

Overall:
- Turn on the sport button, turn off trac control for more spirited driving
- When starting from a light, don't have it sitting at 2 and then try shifting up. Rather, select the gear for how fast you think you'll be going. For me, that's "3" in the city, or "4" eyeing "D" if entering the highway.
- Feel free to downshift going through slower turns, or even downshift to 2 when coming to a stop. Then once stopped throw it back into the "higher" gear limit.

Hope that helps, have fun!

 

Great reply, thanks! I knew I was failing to understand the use of the manual mode somehow. Makes sense and seems really useful in that way.

Using sport mode, no traction control, manual mode and the automatic speed limiter I can't get in trouble right?! Fast starts, no speeding.

 

Good post , I appreciate your detailed reply

 

A couple of more observations. First, this is the first automatic trans car where there was not a selection for the very first gear (lowest you can choose is 2). Second, in downshifting other automatic cars I have owned, I would always notice the downshift much more, particularly in my last car which was a 1995 Corvette. The second you manually shifted to a lower numbered gear, you felt the effect. I had assumed that the reason that this was not the case for the XKR was that this is a much lower compression engine so you do not get as much engine brake effect (but I could be wrong).

Finally, make sure your throttle cable is adjusted correctly (there should be a a bunch of posts on this). If the cable gets too much slack than it will not be opening the throttle plate fully but this should be a simple 5 minute adjustment.

Happy driving!


Doug

 

I also think, that I experimented with the '2' j-gate selection, and when in sport mode, the car starts in 1st. (as you can feel it shift) When not in sport, no 1st. Am I imagining things like that little leprechaun on my printer over there?

 

Yeah, the car starts in second unless it's in sport mode (or you floor the throttle). The J-gate selector merely restricts the maximum gear the 'box will select, so if you select 3 it'll happily use 1, 2 and 3 as it sees fit. Great for engine braking (as noted earlier) but not so good to try to force the car to use specific gears when accelerating. Of course, the 'box senses the throttle position and holds the gear longer if you're driving "enthusiastically".

 

The lag is not the same with a supercharger that is directly coupled to the crankshaft and thus spins at the speed dictated by the engine rpm as a turbo powered by exhaust. That lag is the same as a non supercharged engine, throttle plate opens, fuel is injected and then spark ignites it. Small lag time. A turbo is powered by exhaust gases, but first the engine has to rev up to make more gases, then the turbo spins up and starts to deliver pressure. That does take time and is called turbo lag. Mazda has shortened turbo lag by using multiple, different sized turbos at the same time.

 

Yes, but the supercharger also experiences a similar lag, but it's much shorter. The supercharger doesn't develop max pressure until the engine spools up to a higher RPM range. It might only take half a second, but there's still that delay. If you want max power on tap at any moment, you have to drive around using the J-gate to keep the RPMs up around 4500 or so, which is rather hard to do from a standing start. If our cars had a clutch it would be easier. I don't know about you, but I'm not going to put it in neutral, rev it up to 4500, and then pop it into "D". That's just not going to happen in my car .

That's why they say there's no replacement for displacement.

 

No, Rev, the proper way is to left-foot brake, run the revs up to ~1800 RPM to preload the torque converter, then simultaneously let off the brake and mash the gas pedal. Then watch the tires go up in smoke because they aren't sticky enough...

 

I have no perceivable throttle or transmission lag on my 05. The only time I'll get transmission shift lag is if I'm playing lead foot and release the throttle after hard acceleration, then it stays in the current gear for a few seconds between 2-4k rpm until it shifts normally. This is in sport mode though.

My XK8 on the other hand, does have a brief throttle lag.