Alright, let me run this by you guys to make sure my math is not terrible. Three assumptions for what I'm doing with a 6:1 Vortech FMU:

1) The stock injectors are 255cc (true?)
2) The stock fuel pump is adequate enough to supply the fuel for what I'm running (Around 190lph? My concern probably isn't with the pump not supplying enough fuel (190lph pumps can supply fairly big (600cc+ injectors) at normal fuel pressure levels) but whether or not it can supply the pressure. I know several members here have had problems with FMUs - however, they've been using EXTREMELY high pressures (12:1). If I ran 8psi with a 12:1 FMU, I would experience fuel rail pressures around 136psi... not my cup of tea. I'd worry about injector and line health a lot at that level.
3) My math isn't terrible.

Either way, here is the math as far as I remember it.

Fueling a car:

(Estimated horsepower * Brake specific fuel consumption) / (# of injectors / duty cycle (80% standard).

So with that, assuming I put out around 200 brake horsepower, and turboed cars are generally .55 BSFE (regular motors .5), we end up with:

110 / 3.2

34.375 lb injectors needed (360cc).

Now you gotta find out what the stock injectors can flow with higher pressure(assuming 255cc).

Fuel Pressure / Stock Fuel Pressure = New rate of flow. So with a 6:1 @ 8psi, 48psi fuel pressure over stock (43psi) we end up with 91 psi.

91/43 = 2.116(etc)

Gotta take the square root of that.

1.454743(etc) x 255cc

371cc.

So, hypothetically, I should have enough fuel to maintain a stoich fueling (assuming this formula is for getting a car to stoich), possibly running a hair towards lean at higher speeds (don't go that fast, boosting 2nd/3rd gear mainly) and higher rpms (turbo I run is probably going to make the most power at a lower rpm, i.e 5700rpm so not too worried about that).

Does my math fail or does it make sense? LOL.

My math was sex, car runs great. I'll post videos and pictures later in showroom probably.

How do you have it installed? I had mine inline right after the regulator going on to the stock return.

I had two different FMU's and couldn't get them to do anything and that was with the gsx pump (190lph) thats in there right now.

I had a begi and a vortech. With the vortech I tried several discs blindly 6:1 , 8:1, 10:1, 12:1. And nothing helped. I finally borrowed a Wideband from a friend and found it running extrememly lean with the 12:1 plate (as in pegging out the wideband). Said screw it and got some 440's and and smt-6 and didn't look back.

btw, I was running 5 psi. That was waaay back before I got my forge mbc. Are you using a wideband?

Mmm, thats odd. Yea, I've ran it with a wideband that I borrowed, I have a bung in the manifold, but plug it unless I borrow a friend's because I'm cheap lmao.gif . Its a little rich mid rpm (10:1) and leans (12:1) at high rpm, simply because the FMU can't tell RPM, only boost, so obviously its adding the same amount of extra fuel at the same boost at different RPMs.

I'm using a Vortech 6:1, with my turbo @ 8psi.

Mine is installed further down the rail than most have installed it - I have it mounted on the firewall near the TB, and its inline on the return, mounted in on the return kind of near the fuel filter, though obviously not on the feed side of the fuel lines. Vacuum source I'm using is teed from whatever small vacuum line goes from the passenger side of the stock IM through the firewall.

Did you try your FMU with the stock pump? Fuel pump flows (190lph, etc.) are based off 43.5 psi. High flow pumps like Walboros are meant to support higher fuel pressures - a larger flowing fuel pump may not necessarily be able to support higher fuel pressure you want from it. Most stock fuel pumps max out 70-80 psi I believe (which is where I am at around now, my math below was slightly bad in that 8psi in the manifold blocks 8psi of fuel pressure from what I've read, so in reality I'm running ~80psi). I recall a lot of DSMs when I owned one having problems with bumping up fuel pressure on the stock pumps via RRFPRs - perhaps DSM pumps, or especially used DSM pumps, don't support higher fuel pressures well?

If the fuel pump you have doesn't like supporting above 43psi like it is now, when you used 6:1, 8:1, whatever and had no change, the pump simply couldn't handle the request for added fuel pressure.

FMUs and such were never my forte, its a simpler method of adding fuel that I'm trying, so perhaps my thinking is wrong in there somewhere.

EDIT: Had my AF ratios wrong.

may, at the time I didn't think about that. Are you sure the stock pump is 190lph??? If thats the case then I'm not sure why people were switching to the gsx pumps, I did it because I was told the stock pump couldn't keep up over 8 psi and thats where I was headed. Running 12 right now.

Naw, I'd probably guess our stock pump to be around 120, although I have absolutely no clue. Fuel pump sizes vary so much, even among motors. Old Mustang GTs (5.0s) had 90lph stock fuel pumps even with them having similar horsepower to DSMs. So you can't necessarily say, oh, that car has more power that mine so a fuel pump direct replacement from it is going to help support my power. Around in my first post was kinda relative. However, I don't think 2G pumps are 190 either, I recall them being around 120-150 as well as 190lph Walboros were somewhat common upgrades.

(http://www.dsmtuners.com/forums/newb...-pump-lph.html as an example, several other posts as you search around, how people rate them ranges from 120-150).

It'd be nice to get accurate numbers. However, its not often that someone tests the stock LPH on a stock fuel pump, so the information is hard to find. I haven't stumbled across math for finding out how much lph you have to flow to support a certain horsepower, although I'm sure it is out there.

Did some more testing later today, 1st, 2nd, and 3rd gear are fine, A\F ratio wise. However, 4600rpm in 4th gear the fuel starts falling off, so yeah, I think fuel pump is the weak link there. I see a Walboro 190 in my future.

Not like I will be running 100mph that often to where it actually goes lean, so it'll be fine till then.

all I know is I'm running 12 psi pretty rich with it! so it must be keeping up! I think that 190 lph was a rough estimate by someone some time. General consensus was that it flowed more! laugh.gif