FMU question

dstanggt50 · Nov 5, 2005

Just had a quick question, I just recently recieved my Vortech S-trim, and as I was going over the instrucitons, it stated for the fmu has 2 settings, one for 19lb injectors and the other for 24lb injectors. When I downloaded the instructions before I bought it, it said to only modify the fmu if you have a cobra, but the instructions that came w/the kit say to modify the fmu if its a cobra or for vehicle equipped w/24lb injectors. I was thinkin just leave it the way it is to run a little richer to be on the safe side, or do you recommend modifying the fmu because of my 24lb inj. Also, any other general tips would be appreciated.

95cobradude · Nov 5, 2005

my fmu is still sittting in the box because it aint worth the headache involved. just get bigger injectors, and like an 80mm mass air meter and a custom chip burned.

94GTLaserRC · Nov 5, 2005

It says "only Cobra" because they assume youre using it on a stock 19# injector GT. The fact that it's a cobra has nothing to do with it.

What Calibration is the FMU that came with it (4:1, 8:1, etc)?

RC

dstanggt50 · Nov 5, 2005

94GTLaserRC said:
It says "only Cobra" because they assume youre using it on a stock 19# injector GT. The fact that it's a cobra has nothing to do with it.

What Calibration is the FMU that came with it (4:1, 8:1, etc)?

RC

The parts list says its 12:1. With the ring spacer it says 10:1. Any opions on which I should run???

95cobradude · Nov 5, 2005

it should give specific instructions on how to set it up for the cobra but i think u should ditch the fmu, get bigger injectors, a good adjustable fuel pressure regulator, and a good air flow meter calibrated for the injectors.

a50sn95 · Nov 5, 2005

You run the one for the injectors you have.
Since you have a GT, and not a Cobra, those insturctions don't apply to you.
If you have 24's in a GT, you need an 8:1 disc....
http://www.superchargersonline.com/product_listing_2M.asp?Cat2=fmu_cal_disk
Me, I pulled it off as soon as I got comfortable with my Tweecer...
(And 36's weren't big enough. Had to go 42's.....)

dstanggt50 · Nov 6, 2005

a50sn95 said:
You run the one for the injectors you have.
Since you have a GT, and not a Cobra, those insturctions don't apply to you.
If you have 24's in a GT, you need an 8:1 disc....
http://www.superchargersonline.com/product_listing_2M.asp?Cat2=fmu_cal_disk
Me, I pulled it off as soon as I got comfortable with my Tweecer...
(And 36's weren't big enough. Had to go 42's.....)

So your saying to not follow those instructions, but if I need the 8:1 calibration, wouldn't my car run better modifying the fmu to be the 10:1, instead of the standard 12:1?

And I definately will get a tune later ( or thinkin about the tweecer) but I drained all of my funds into getting the s-trim. Just lookin for this temporarily,

final5-0 · Nov 6, 2005

You need to use the 12:1 with those tiny 19's.

As your inj size goes up the disk ratio goes down.
See how that works?

If you use the 10:1 disk you will get less fuel

Grady

94GTLaserRC · Nov 6, 2005

dstanggt50 said:
The parts list says its 12:1. With the ring spacer it says 10:1. Any opions on which I should run???

I ran an 8:1 with stock heads and 30# injectors. The FMU had a boost bleeder valve (it lets out boost to retain less fuel, in essence making it about 7:1) and I ran Pig Rich. You "may be" ok with an 8:1, but I would just put the FMU on the way it is, and worry about the rest during tuning.
RC

dstanggt50 · Nov 6, 2005

final5-0 said:
You need to use the 12:1 with those tiny 19's.

As your inj size goes up the disk ratio goes down.
See how that works?

If you use the 10:1 disk you will get less fuel

Grady

I have the 24lb inj already on the car, thats why I was thinkin go ahead and put the 10:1 spacer on, but it sounds like its recommended to leave it the way it is, guess it would be safer that way.

Thanks everyone.

final5-0 · Nov 6, 2005

dstanggt50 said:
I have the 24lb inj already on the car, thats why I was thinkin go ahead and put the 10:1 spacer on, but it sounds like its recommended to leave it the way it is, guess it would be safer that way.

Thanks everyone.

Sorry ... My bad

I did not see you were running 24's the first time around.

The 12 will give more fuel than the 10 never the less and that is a known.

Dennis said he would run an 8 with 24's yet RC said he would run an 8 with 30's.

The safe thing to do is start with the 12 and see how it turns out. If it is too fat you can always move to the 10 to lean it out a bit.

Grady

94GTLaserRC · Nov 7, 2005

final5-0 said:
Sorry ... My bad
Dennis said he would run an 8 with 24's yet RC said he would run an 8 with 30's.
Grady

I said "I RAN" an 8:1 with 30's and was pig rich (also had a T-rex AND 255 in-tank pump. If Dennis ran fine with 24's and 8:1, I believe it.

But yeah, start one higher than you think, and check the tune from there.

RC

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