Did some loging today with Torque Pro ( 08 XKR 1.5psi pulley)
Highest boost I have ever seen was at 11.6
what is surprising to me that max boost of 11psi is developed at only 4200RPM
Wow, so at 6200rpm I should be pushing much more, so is the boost control valves kicking in or is the supercharger running out of efficiency? I suspect that its the boost control that is limiting my max boost..
Why isnt tuner able to open this up , or what am I missing in this picture?


Any ideas gents?

 

Check the sites that sell the pulley upgrades, they will tell you that these mods provide most power increase in the midrange , so your figures are correct

 

Fitting a smaller pulley on the supercharger is going to push it past it's peak efficiency at higher rpms. So it's not surprising that you get peak boost in the midrange and not in the top end. That's just the nature of the Eaton M-series...

The 2008 XKR test car we have makes 13.2psi with a stock pulley on the supercharger, however this is with a free-flowing exhaust, some changes to the VVT phasing and the torque limiters all lifted in the tune.

There is no "boost control" in the AJ40 engine management, only a torque limitation based on airflow & engine rpm, if this limit is passed then the engine will be throttled back, which has a consequence of reducing manifold boost pressure.

I don't know why your tuner isn't able to address this, maybe you need a better tuner?

 

Cambo Im not sure on the accuracy of the Torque Pro as I believe it goes by the map sensor. I had a shop with a more professional tool hooked up and they told me 14.6 was the highest boost recorded in the logs, which sounds right with the 1.5psi pulley. So im figuring that Torque pro shows the correct boost curves, but is just a little off on the numbers. Either way max boost is at 4200rpm , if its is at 14.6psi,, is the supercharged maxed out at this point?

 

Yes, it's maxxed out.

When Jag sized the pulleys on these engines they already had the blower spinning past it's peak efficiency in the top end, adding a pulley or pulley's just makes that worse.

You do get gains in the low-mid range, but in some cases you will lose a little power in the top end.

 

I made the decision to go to a smaller pulley (1.5) based on hundred's of threads on GM & Ford forums from users and tuners swearing by the smaller pulley, in fact some of the tuners have noted increasing the boost to as much as 20psi. I wish there was a way to go back to the OE sized pulley to do more dyno runs.

 

Hindsight is a bitch... I put the smallest possible pulley on my XJR (supposedly 3psi) and i really wish I hadn't now...

The whole idea of pulley's on Jags goes back to the 4.0L on the X308/X100, there they did make a positive gain, but on the 4.2's they were already in the sweet spot from the factory...

It's again a different story on the 5.0L cars since they run a TVS which doesn't fall off a cliff in the same way as a M-Series...