I took my XJR to the dyno today, just to see the figures before installing the lower pulley from Powerhouse, and the results were a bit disappointing: 332hp/442Nm (calculated from rwhp with 17% drivetrain loss). Two runs with identical results using 4th gear.

There are no other signs of a problem, no error codes, revs nicely up to the limiter, mpg is normal, does not overheat, plugs & filters done about 4000ml ago... sadly we didn't have obd2 logging during the dyno. Any ideas? Something that obd2 logging would show?

The car is going to the shop (jag specialist) tomorrow for a tensioner job (just in case, no symptoms) and lower pulley installation, will see what they think...

 

Just curious,

I'll ask the questions that were asked of me:
What type of dyno
correction type and correction factor
environmental conditions, barometric pressure
What year XJR

The answers to these questions may help get a faster response when someone who knows better than me reads this


Your adding a 4 lb pulley? Are you planning on doing anything to enhance cooling the soon to be higher IATs?

p.s. If you have a smart phone, I suggest you download the speedview app which will allow accurate in car live recording of 0-60 and 1/4 mile times. having these before and after performance numbers (while subject to lots of other variables) may also prove useful in determining actual gains from mods.

 

looks like he is using a dynomite which is known to really have low numbers so theres one thing to keep in mind.

what mods do you currently have if any and conditions would be nice to know as well I couldnt really read the sheet to well because of glare what was the numbers at the wheels?? If Im reading correctly its looking like it made 284 to the wheels and if my calculations are correct then this would give you the 332 number at 17%. what was the torque at the wheels cus it looks good and flat

 

Take off the throttle body and clean the egr, egr hose, and egr mount hole. Had the same problem, because my was totally clogged with carbon. After vaaavooooom! and adjust the throttle cable.

 

+1 on checking and adjusting the throttle cable

 

If torque and hp are scaled the same (which is does on the print), torque and hp should cross at 5252 rpm. So something is wrong in the calculations used.

Edit: Sorry, only now notice it is nm, so the drawing is correct, so will wait for all the details.

 

AFAIK the dyno was a Dynomite, uses a single drum. Correction type was DIN, not sure what the factor was... 16C (61F) / 1001hPa (29.6inHg). The XJR is MY2000.

I think the uncorrected numbers at the wheels on the first run (which was almost identical) were 270hp and 366Nm (270lb/ft).

I did a couple of standing starts today with Dynolicious on my iPhone, and the best I got for 0-100km/h (62mph) was 6.9sec and 1/4 mile in 14.84sec @ 102.9mph. Lots of problems with traction though... road surface was very rough and somewhat damp.

Throttle cable has been adjusted, and the only mod is a BMC drop in air filter.

Interestingly the guys at the shop were certain that there is nothing wrong those figures. I'll check the egr system when I get the car back.

 

What would be interesting is of course the a/f ratio, and another test would be the actual boost. Pending the outcome more can be tested.

Tire pressure also plays a big role, although not 30rwhp...

 

Can I get the a/f ratio from obd2? How about boost... MAP reading minus 14.7psi?

 

No you can't get a good reading for the a/f ratio (didn't they measure that on the dyno?), therefore you need an WDS/IDS. You don't have a boost sensor, but usually a dyno shop should have a external boost reader which you than need to attach.
Does the MAP value change between idle and driving? -14.7 isn’t right, so either you don't get data and your software is just displaying something, or there is something wrong.

 

I finally took a drive with ProScan connected yesterday. MAP value does change between idle and driving, and measures 13psi at WOT. And I noticed that absolute throttle position is at 93% when I floor it, so I'm guessing I need to re-check that throttle cable...

The bigger lower pulley is now installed together with latest generation tensioners (secondary & primary). Old plastic ones had absolutely no cracks at 77k miles, but at least I don't have to worry about them any more... The pulley makes a noticeable difference in the midrange, and the supercharger whine comes up way below 3000rpm now. I hope the difference is there in the dyno too, will see in couple of weeks, I'm off to Germany (and Nordschleife) for a holiday trip tomorrow. I did one 0-100km/h (62mph) run with Dynolicious iPhone app, and got 5.9sec with a rather poor start, so I'm not really worried anything being terribly wrong with the car.

 

The throttle opening position is not completely controlled by the throttle cable. There is also a drive by wire component. What you need to do is adjust the throttle cable, then train the ECM.

Apparently the training procedure is: key on, engine not running, press throttle to floor five times, key off. That lets the ECM know where the 100 percent position is on the cable, and it will then be able to position the butterfly properly when the cable is in that position.

 

The vacuum you have measured is 14.5-13=1.5 psi (or 103 millibar). To get a good reading best you do a run in 3rd gear, and watch only this value. You will see that the higher the rpm gets the lower your psi reading gets as the vacuum increases.

 

Interesting to know about the training procedure for the TB I was always told to just turn ignition on and let it cycle but makes more sense this way will give it a try

 

That part only lets the ECM decide on what the optimal idle position of the butterly should be. The training part is at the opposite end of the spectrum, ie WOT.

If you consider that at idle position when the ECM has been reset, the ECM still does not know what the cable travel is on any specific car, then it starts to make sense. You are only showing the ECM where the cable ends when the pedal is nailed to the floor.

Once the ECM knows where the two end points are for a particular cable, it knows where all the points are in between the two end points.

 

Does that only work immediately after a hard reset?

 

No idea.

However, it is probably effective at any time.