[fastsvo]

Hey guys,

Recently I had an S-trim installed on my car and wanted to get everyone's opinion on my dyno charts and user experience.

Ok here it goes.

Vehicle: 1991 Mustang GT

Engine: V1-Strim with stock pulley setup (3.33”) on a stock 57k mile shortblock. Stock heads, 1.7 rockers, GT40 Intake, 70MM Throttle Body, UPR PowerPipe, JBA shorty headers, BBK 2 ½” catted h-pipe, stock tail pipes with 2 chamber flowmasters

Drivetrain: FMS Alloy driveshaft; 3:73 gears w/ Auburn differential.

Electronics: SCT BA-2400 MAF (the plastic Granatelli unit) with custom Diablo (black chip) tune.

Fuel: 42# injectors, GSS-340 hi pressure 255 in-tank pump with a Vortech T-rex as well.

Dyno: 351RWHP on a DynaPack Dyno
A/F Ratio = 10.8
Timing @ 18*
Injector Duty Cycle = 70%
Boost = 11.5 psi

Overall I am pretty happy with the results. Part throttle acceleration feels like a stock car, but when you smash your foot on the throttle, it really picks up and goes. It’s not as snappy from part throttle for example, compared to my SVO when it goes into boost, but this car will roast the tires in 1st and 2nd gear.

My biggest concern is fuel consumption. It’s bad, even when driven conservatively and on the highway, I am seeing anywhere from 10-14mpg, which leads me to believe it’s running way to rich. I understand the tuner went the conservative route (which I am ok with), but I can smell fuel during a cold start up, at idle and in decel acceleration.

Isn’t the A/F ratio a little too rich here? Where do you guys usually like to see it at? Could the larger than needed injectors be a factor here?
What are your opinions on the timing? Too low or just right given stock iron heads and shitty California gas?

Ok I’ll stop with the long post and look forward to everyone’s input and of course, thanks in advance!

[1slo5.0]

Those are good numbers for a stock engine. The fuel consumption is not right though. There is definitely a problem somewhere. The injectors could be a factor. They are on the big side for your set up. I used those same injectors at well over 500rwhp on a blower engine. 36lbers would be plenty for your set up. Do you have a boost retard or is the timing locked out at 18 degrees? I bought a car with an S-trim kit on it and it was retarded for fuel economy but they had some stupidly low amount of timing in it and had the boost retard at zero. I set the timing at 16 degrees with the spout out and set the boost retard at just a hair over 1 degree. The car picked up a ton of horsepower, drove better and fuel economy went up 4 mpg on the highway. Is your A/F ratio 10.8 all the time or under full boost or what? If its 10.8 all the time, that will have alot to do with your fuel consumption.

As far as boost not coming on right away, that is the life of a centrifigul supercharger. The boost increases with rpm. They are kind of doggy down low until they get spinning.

[fastsvo]

The timing is locked and controlled by the chip. This car has no BTM or FMU.

In regards to the 10.8 AF, I believe that is just my WOT AF ratio, but I have no idea what I am getting during cruise.

It's good to know that I was right on about centrifugal superchargers - I just had never driven one before.

Thanks

[1slo5.0]

Originally Posted by fastsvo The timing is locked and controlled by the chip. This car has no BTM or FMU. In regards to the 10.8 AF, I believe that is just my WOT AF ratio, but I have no idea what I am getting during cruise. It's good to know that I was right on about centrifugal superchargers - I just had never driven one before. Thanks

I'm curious to know what the timing does when you rev the engine and driving around with no boost. If you have no BTM, how does the computer know when the engine is seeing boost? I bet the timing is just locked out and not controlled by anything. I'd also be curious to know what your idle, cruising and part throttle A/F ratios are. Sounds like they didn't give you much information. You might want to go somewhere else. There is no reason why you can see over 20 mpg on the highway with that set up.

[grnstang]

i thought 11.5-11.8 was a better A/F ratio on a boosted application.

[flattusmaximus78]

Thats way to rich for wot. You should be 11.5 to 12.0 depending on how comfortable you are with your tuner. My car did 10.6 afrs on the dyno and made 345. It was on a mustang dyno, and the belt was slipping. But Im wondering the same thing. My timing must have been locked out on the chip. We didn't touch it at all. I'm at 10 degrees base.

Get a aem wideband for about 200 bucks and see were your afrs are at during cruising speeds. That may be the issue. Even at 10.6 wot it wouldn't kill your gas milage like you say unless u have a lead foot. My car gets that roughly but I have idle issues were it floats in neutral and sits between 10.9 and 11.0000 ish

On a dyno jet my car should be around 390 or 400 or so with my mods even at 10's afr. I'm curious as to what timing could have done for me.

[1slo5.0]

I don't know, I think in the 10s is where a boosted car needs to be because the fuel demand is so much higher than a naturally aspirated car, but I'm no expert on boosted applications. My n/a cars have been in the 12s at WOT.

[flattusmaximus78]

Everyone I know with a boosted car mustang or not usually wants 11.5 across the board wot. Like I said some people aren't to confortable with it. But it's generally safe. My dad has an 06 gt with a paxton and it does 11.5 at wot and has been like this for a year. 10's is just to rich for me. persoanlly.

[ryans88gt]

11.5 to 12 for 15 PSI and under is pretty good. 12 is getting to where you'd better be dead nuts on the timing side of things or you better have some intercooling or methanol.

10.5 is too rich for sure, but very safe. Probably only giving up 20-25 hp.

You should easily be getting 20 mpg, so something is up with the tune job.

[grnstang]

yup have your tuner lean it out a tad