I have a similar setup: 355 with ATI P600B @ 9 psi, 1.6RR's, CC305H, 8.5 compression, MMS tune, M6, 3.73's and Borla xhaust with stock manifolds. I average 150/tank city so about 9 with moderate/heavy driving. I have no surging concerning the bypass valve and a relatively tame ride unless I step on it! Then its what you would expect. this is with cheep 300 A A 275/40/17 and stock suspension with eibach pro spring all the way around.

 

Do you use an FMU or did you get bigger injectors and a tune. Do you think using an FMU is the best way to go?

Thanks again this good info although a little painful(9mpg?).

 

I get 250- 260 miles out of a tank of gas combined city/highway up to 95 mph,
pushing up to 5 psi of boost under 5000 rpm a few times and 2 or 3 psi a lot.
So I'm getting almost 18 mpg overall.

 

Well Im just amazed

Ive got a tune from Morgan Motorsports and 42# injectors. I need to retune bc the car was from CA. Im worried about the elevation change here in Vegas.

 

Thats about the same mileage I was getting.

 

Wow nice tune. Is your tune mail order. Do you use an fmu or bigger injectors? I've been told that if you use the fmu you can lose a blower belt and still limp home.

Thanks

 

That really doesnt have anything to do with it. Just make sure the MAF is routed to the pressure side if you want to drive with no belt. Other than that the car should be fine with/without the FMU.

 

I threw a belt when I first installed the S/C.
My MAF is before the S/C head.
The car ran fine except no boost.
Luckily unlike most stuff on our cars the belt
was easy to get to and change.

 

 

I'm averaging 18.5 - 20MPG per tank. Which includes at least one or two good blasts down the highway.

383 c.i., ATI-P1SC 8psi, LT4 heads/intake CC304 (baby cam), M6, 3.73's, 138,000 miles, good tune.

 

I thought if you lost a belt with a computer programmed for boost with no FMU it would be pig rich at higher rpm.


On the other hand if you use an FMU it only increases fuel flow while under boost.

Thanks for your input.

 

Only at the point in which you max out your MAF which would probalby be between 5000-6000rpms with a P1SC. Hopefully if you lose your blower belt your not going to be doing too many 5000-6000rpm blasts down the road especially if all you want to do is 'limp home'

 

The FMU increases the fuel pressure but drains it off under normal conditions.
As soon as it sees boost it stops recirculation and the extra fuel pressure you need is right there at the engine instead of having to wait a moment for it to come from the back of the car.

 

I remember nothing but BAD gas mileage with my supercharger, but that probably had something to do with my desire to push the pedal throught the floorboards. But thinking back I did notice a small decrease in normal driving mileage( which rarely ever happened) which I would think comes from parasitic drag, much like an a/c compressor, but with much less effect upon mileage. Just my .02 cents.

 

OK I understand now. Your fuel tables dont get rich until real high in the RPM and like you said it happens when the MAF is maxed out. Even if that happened you could probably unhook the MAF and go speed density.

Next question is could I take off the belt and hook up my old induction system and run the engine on long trips without the supercharger and without changing the tune?