? about boost

[xp800]

I have this pulley installed on the roush charger and i am only getting 5 to 6 lbs of boost . I was wondering if you may have any ideas of why i am not getting more than that . I had it tuned with this pulley , and have everything that a roush car would have come with . Injectors , plugs , tune and that pulley . any input would be great . below is what is stated it can do , but i am no where near that figure

SFPH now introduces the all new Roush Supercharger Pulleys for all 2006 to Current Roush Mustang Supercharged Vehicles.

Expect 3.5 to 4 psi more boost at wide open throttle, for a total of 9.5 to 10 psi, versus the stock 3.25" stock pulley that comes on all Roush Supercharged Mustangs that only produces 6 psi at wide open throttle. These Pulleys are made from 6061 T6 Billet Aluminum and are Keyed to the "Exact Factory Specifications" as the stock supercharger pull

 

[Rangersfan]

I think that they are being a little hopeful with that boost figure based on a 2.8 pulley. The stock one is a 2.93, so it's not that big of a drop from stock. How are you getting your boost figure, from a dyno readout or from a guage?

 

[xp800]

I am using a boost gauge that is in the car .

 

[Hawgman]

Well, I am not famililar with the Roush pulley sizes, but I agree with SteedaSteve on a .13" pulley difference making that much more boost. Hell, with the Saleens you get about a pound per .1" decrease in size. For a .13" to make a 5lb difference is quite a jump. But as I said, I don't know squat about the Roush pulley sizes, including what is actually stock.

What is your exhaust setup? The better flow you have in exhaust the less boost pressure you are going to see. Also, do you have any belt slippage? That would cause a decrease in boost.

 

[marcspaz]

I don't have a SC on this car yet, but in general, what I have found with regard to manufacturer claims is that they are rearly true for "real world" applications. They through out numbers that range anywhere from complete BS to under under perfect laboratory conditions after 7 months of dialing in the tuning on that one specific piece.

I agree with Steve. At 2.93 to 2.8, .13 is not going to increase the rpms of the props enough to up your boost 35%. I would be surprised if you got 1 full psi. Did you have a 2.9 or a 3.5? It sounds like you are where you should be for a puly change of .13

 

[xp800]

I am running a mac axle back w/ a pypes offroad hpipe . I am not sure about belt slippage , really no way to tell is there. Also the car is pulling 22lbs of vac at idle , if that helps .

 

[Hawgman]

well....technically it is inches of vaccuum, not pounds. But reguardless, 22 is around the expected number.

Their are plenty of ways to tell if the belt is slipping. Most obvious is look for dust. You can also tell by sound.

 

[xp800]

does running a real free flow exhaust gonna limit the boost as well.

 

[don_w]

does running a real free flow exhaust gonna limit the boost as well.

I don't see any drop in boost running LTs and wide open cutouts. It doesn't get much more free flowing that than.