Hi all. I own a 2003 JCW, it currently has an intake, full exhaust, aftermarket cooler, 4% crank, 17% SC and a bluefin ECU remap and the car makes a pizzly 15psi of boost.

Heres the interesting part..... I have done the mods in stages, factory boost was about 13psi, then I did exhaust/intake/intercooler/4% crank and boost only rose to 15psi. Then, today, I have added a 17% pulley and the boost is still only hitting 15psi!!! WTF??!! Admittedly, it is making that boost at 3000rpm, which was much better than before, but still I was expecting 18+ psi with these mods.

Any ideas???

Cheers all!

 

With my 17% I'm at 16psi and that is with a head and cam, which lowers boost. When I had 17% and a 2% I was at 18%. Your belt might be slipping, since you now have a smaller pulley. Also check your bypass valve.
Now I just run the 17% with 16psi and my car makes 25whp more than when I had the extra 2 psi. What does the dyno say?

 

17% and hitting 17-18 psi at redline..
check for leak

 

No boost leaks and the belt definately isnt slipping.... in regards to that bypass valve, could that be bleding boost off after a particular boost pressure?? do they work like a turbo actuator??

 

my car hits 21psi with a 17% pulley at full throllte in 1-4.

 

A supercharged car doesn't work like a turbo. If you are making 15psi at 3000rpm, then it should be several psi higher at redline. A supercharger makes max boost at redline, while a turbo can potentially do it in the middle of the rpm band and then hold steady if it is wastegated or VG. If your boost doesn't continue to slowly climb as you rev the engine higher (assuming WOT), then you either have a leak or more likely the belt is slipping.


As for a 17% getting 21psi, what else have you changed vdub???

Scott
90SM

 

Wired the bypas shut last night - presto!! 18psi at redline! feels stronger through the higher revs (even though it pings lightly 5K+), throttle response is heaps better and I now know what u all mean by "yoyo" - because it's gone too!!! Now time for a retune to get rid of that pesky ping!!

Cheers all!! who would hve thought that a 20c zip tie would = 20hp!!

 

Take a hint from Mario about more power with less boost. With that supercharger spinning that fast all you're making is hot air. Don't wire the bypass valve shut. You will regret it.

 

I'm glad you found your boost but call Detroit Tunned and get yourself a $125 bypass valve. You will love it and the car will be safe.
take care
Mario

 

lucky dog (ps, that is a brand of dogfood in Aus!), I can garuntee you my intake temps are not high. With the Alta v2.0 cooler, the intake temps are lower now with the 18psi than they were as a standard car!

I understand that witht the SC spinning so fast the charger and air gets hot, but at the end of the day, with a high quality cooler like Altas, the only thing that will be damaged is the charger as the intake temps are well within safe numbers... Correct me if I am wrong....

Also, even witht he detroit valve on the car, wont it still be making big boost anyway?? I understand that there will be less pressure on the charger on backthrottle with a valve, but I dont quite understand why it would make any difference to the longevity of the engine without the valve?? Again, the only thing it can damage is the charger right??

Please dont get me wrong, I am looking onto that valve already, but my theory is right isnt it??

 

Oh, and "more power less boost" only comes with a ***** load of mods to head/cam etc... that really isnt relavent to a car with a stock head.

 

Wiring the bypass closed means that the supercharger is always loaded.

The heat rejection will be the same at WOT whether the bypass is wired shut as you currently have it, or with a DT bypass and its stronger spring, or stock but working properly. However, when you are at something less than WOT (which is the vast majority of the time for anything but a dedicated race car), the stock or DT bypass reduces the loads on the supercharger. This reduces heat (charge air temperature, and thus in-cylinder temps so oil and coolant temperatures are theoretically impacted but may or may not be measureable), improves fuel economy, reduces wear on the supercharger, and reduces the load on the belt drive system.

Wiring the bypass shut doesn't do the engine any favors, though it was a great troubleshooting technique in the case. There are very sound reasons that BMW spent the extra money to have a supercharger bypass valve on our engines.

While it will take a little more of your time, you really would be better of with a functional bypass. You can remove yours and adjust it to close more completely, replace it with a new one from the dealer (check to make sure the butterfly valve closes and seals the bore relatively well before you accept it) or install a DT bypass valve. The latter is a stock valve that has been adjusted to close fully and also had a slightly stronger spring installed to allow it to close a littler earlier. This latter feature theoretically improves throttle response, but also has a minor impact on fuel economy and intake air temperatures.

Good luck.

Scott
90SM