I took the Jag out yesterday evening for a couple runs at the 1/4 mile dragstrip. I had never been, but I was anticipating mid to low 13s. I raced 6 times and 5 out of 6 I hit 13.8 and once hit 14.0. I was disappointed. Any advice guys?

 

The right tires for a dragstrip can make a difference [note I did not say bigger tires...]

 

LSD?
Seems to be the way to go...

 

Post up the slip so we can see all the numbers

 

I'm getting the cat detailed. As soon as I get home I'll post the pics of the slips. Surprisingly they were fairly consistent. I never got over 101 mph

 

A couple questions come to mind.

Did you have traction?

What were your shift points?

Cheers
DD

 

With a 13.8 ET I would've expected more like 104 mph

101 mph sort of suggests a lack of high rpm power, or going thru the lights a less-than-optimal rpm.

Cheers
DD

 

My tires are 285 street tires. I did slip just a little but for the most part they gripped better than I thought.

 

I left it in auto with the traction control off and sport mode on. It was about 80F outside. And it rained as soon as I got there. Only for a bit though. Then it was just cloudy.

 

60ft times aren't bad , just 101 trap speed means it's down on power.

How many miles in the car?

 

Today 78K. Just did the oil change. I kept the hood open between races to try and keep heat soak to minimum. The car has no CEL or issues that I am aware of. Does a few extra pounds in the trunk really make a difference?

 

The old rule of thumb, FWIW, is 100 pounds = .1 second difference

Cheers
DD

 

Ouch. Gas tank was half full. Or actually half empty I had my spare tire. I brought my tools in case I broke something while racing. My cleaning supplies. Fire extinguisher. And subwoofer.

 

Back on the laptop now, and just saw the list of mods in your signature...

The car is definitely down on power, regardless of having a half tank of fuel and some junk in the boot.

 

Here's my last outing to the track

 

What should this car run without the upgrades you've done?

A couple thoughts.....

Sometimes a pulley upgrade creates a more highly heated air charge at sustained full throttle. You may feel a big improvement for 5-8 seconds of full throttle but then the power actually drops off after that.

What are the details on the details on the intake manifold? That is, in what rpm range is it supposed to be most effective? Are you reaching that range? Are you revving way beyond it?

Cheers
DD

 

CAM, that's awesome. I was hoping to get numbers like those.

Doug, there are several pulleys out there. I went with the 6% pulley to play it safe and avoid the extra heat stress. Also, I tried to compensate with cooling mods. Bigger Aux coolant pump. Low temp thermostat, and the porting. Bob explained that the SC porting would not really increase boost much. But allow the SC to move air more efficiently and maintain lower air temp as well as increase the life of the SC. As far as shift points I'm not sure. Whatever sport mode in Drive was shifting at. I didn't use the j-gate.

I never had the car dyno'd or tuned. I have been trying but locals are scared of the "Jaguar software"

 

Well I guess you should start with the basics...

78k miles, and serviced by the book, means it's still on the original sparkplugs. Most likely on the original fuel filter as well.

When did you last change/clean the air filter? Ever cleaned the MAF?

You've got Magnaflow cats, did you put an extension or minicat on the downstream O2 sensors? This is not a good idea as it messes with the fueling, the downstream sensors are also used for fuel trims by the PCM.

What fuel do you run?

The wildcard on your list is the ported supercharger, I have no experience with these but over the years i've become more & more skeptical of modifications that "work" on other cars being applied to Jags...

Have you got some way of monitoring the fuel trims via OBD? Something like the Torque App can be useful to get some numbers from road testing, like fuel trims, MAF rate, fuel pressure, etc...

20" wheels don't help on the 1/4 mile either, but in saying that I run the stock 20x9 Sepangs with 255's, you have staggered wheels, so wider at the rear? (heavier?)

Big wheels rob power, and accelleration. I know several guys down here in Oz who went from 18" to 20" and noticed the cars lost some of their zing, not Jags, but other V8 sedans (Commodores aka Chev SS's)

You don't give your location, where are you man?

 

Thanks for the excellent feedback Cam. I'll try to answer your questions the best I can.

I did my sparkplugs 10,000 miles ago. Replaced them with bosch if I remember correctly. I replaced the fuel filter the same week. That same week I also did the fuel pressure sensor and all the motor mounts and trans mount. I also did the hard fuel line and regulator in October last year.

Air filter is couple months old. Cleaned the MAF a month ago.

I did not put mini cats nor extensions when I installed the high flow cats.

I run nothing but 93 octane fuel.

I have an obd2 scanner that I keep handy. I constantly monitor IATs, coolant temp, fuel trims, 02 sensor readings etc. If anything I might do this more than necessary.

The supercharger porting, I mentioned in the other post mostly contributes efficiency and life to the SC. To be honest the improvement is not significantly noticeable.

The wheels, although wider on the rear (285) believe it or not are much lighter than my old sepangs. I was shocked. The car accelerated quicker after the wheel change.

I am very picky about maintenance and details. I try to ensure the basics are covered.

I just bought an aftermarket warranty in December. Usually I enjoy doing the work myself. But I'll be taking it to the Jag dealer to get a couple bushings replaced and will ask them to look into the loss in power.

I've been itching to dyno tune it. That might tell us what the issue could be. If anything id get power numbers and see how low I am. I live in Tampa Florida. I cant find anyone to tune it here.

 

From what you say, there's nothing that jumps out as a "you should check this"

The car should trap 105mph easy

Try to get some full throttle runs in 2nd (or 3rd if you can) and monitor only the MAF rate, capture the peak in grams/second. Too many parameters being monitored will slow down the refresh rate.

My XJR peaks out around 360 g/s, if you are well below that then the engine isn't breathing right.

There are two forum members in Florida (both in or near Tampa I think) with the SDD diagnostic system, who would be able to flash a tune to your car. I'm running a modified tune in mine now, but had to back it off because the transmission is not up to the extra torque (118'000 miles on it now, it's worn out)

But even without a tune yours should be a 105mph car, like mine was with the stock tune...

The only real difference hardware wise between yours and mine is the ported blower really.

Have you got any pictures of where the downstream O2 sensors on your car were relocated to when the cats were changed?

What are the Short Term Fuel Trims when it's idling at running temp?