I Have the Mina Pulley for my 2005 XKR and the factory pulley is about the same size....

Anyone have the same thing.. Small Pulley on 2005 Jaguar XKR?

 

Hey Donny,

I have the pulley installed on my XJR, which I would assume used the same factory pulley as the XKR.

The Mina pulley is smaller, but only very slightly. The biggest difference I noticed was the weight of the factory pulley compared to the Mina pulley, which is significantly lighter.

Here is a link to my thread about the pulley/install:

https://www.jaguarforums.com/forum/s...ad.php?t=13206

I hope the information in that thread is helpful to you. I ended up getting 340rwhp on a Dynojet. Here is a link to that dyno video:

http://www.youtube.com/watch?v=YOi_e4Fd2HA

I can say that after installing the pulley, the car didn't feel any different, however, doing pulls up deserted roads near my house proved that the pulley did do something. Passing certain areas, my speeds were a couple of MPH higher. I also did a few drag races (from a 45 roll) against a few friends and found that I pulled about a car and a half more than I used to. I understand that there are infinite variables to my "testing" but I am convinced the pulley did something. Especially because the factory car dynos around 315~rwhp.

Have you installed the pulley yet and if so, what are your thoughts?

 

Shame you didn't do a before dyno, as I would believe a stock car in good condition would pull about 330-340 rwhp. The older 4.0 cars pull about 310-315 rwhp. The latter is on dynos that also puts a load on the drums to give a more realistic figure, was this also the case on the dyno you used?

The biggest gains with just a pulley change are in the lower rpm area, as you move the power curve more to the front if you see what I mean. Top end power might be different, as by spinning the sc faster you also generate more heat which will hurt your top end. I think you also see this in the dyno done, after your 3rd gear, the power collapses in 4th (or was it 4th to 5th?). This is due to the extra heat that builds up, and the ECU is probably reacting accordingly to avoid detonations.

Do you know what your boost pressure was before and after the pulley change?

Andre.

 

Andre,

Out of the 5 pulls I did, the power drop off in 4th only occured on that sheet which, unfortunately, was the printout that was given to me. Of the other runs, power stayed consistent between 335-340rwhp between 3rd and 4th gears. This was a little odd to me considering 3rd has a much higher ratio than 4th (which is closest to 1:1) but in the other runs, the power curve was the exact same. Could this be because of the type of dyno I was on? The last run, which is the sheet I received, had a significant power drop in fourth.

I guess this could be explained by heat soak as the dyno operator shut my car off between each pull...and I assume R owner know how hot those intercoolers become when the car is shut off. What is even worse is that they take forever to cool down once they are heated up. To answer your question, the pulley I have installed is quoted to give an extra 1.5lbs of boost.

You know, I have heard mixed things about how much power the 4.2's should put down. There was a thread on the S-Type forum not too long ago of an STR doing a baseline and a pull with a modified intake, 2.5lb pulley, and custom exhaust. The baseline was only 290 something I believe and after all the mods, the car put down 330rwhp or so. So I guess the power figures differ from every type of dyno.

I want to go back to that dyno and perform a couple of pulls to see if there is any difference. When I made that video, the oil was old and worn and the car hadn't been rung out. I now have a fresh change of oil and an axle-back and it would be interesting to see if I gained (or lost) and power.

-Pat

 

Dyno types are important to know when comparing figures, also if a load has been placed on the drums (good systems use an Eddy current system). Of course there is more, and without knowing all conditions a comparison has a wide margin of error.

Here is an example on how heat soak works. Try to measure a 0 to 60 speed, then do a separate 60 to 120 and last but not least a 0 to 120. You will see that the latter takes longer then adding up the individual times. Anyhow all SC owners should know by now how susceptible the SC cars are to heat soak.

It is so important to do first a base line, otherwise you will never know if a change truly did have an effect or that it masks something that is not right.

Have seen some values from the states for a stock 4.2 Stype to make about 340 rwhp, and I also have a dyno done on a Stype I know on a Dyno I know, and also that one made in stock trim 337 rwhp. This fits with some 4.0 cars that have been in the 310 range.

Then I have my serious doubts about the 20% drive train loss on these type of dynos, I think a more conservative figure would be 15%. So a stock 310 rwhp becomes than 365 BHP, and 340 becomes 400 BHP, interestingly close to advertised figures isn’t it ;-) ? Maybe 17% might be a real figure; anyhow, I only look to rwhp.

Regarding the boost, the advertiser may claim it adds 1.5 lbs, but it would have been more important to know what your stock boost was. Then you know if that one was right, and you will know what it actually has added.

Appreciate that you post your experiences, whish more would do it, and best with a stock (before) dyno first, will be very learn full for many.

Andre.