Decided against 347......

Daggar · Sep 22, 2005

An FMU is used to ramp up fuel pressure under boost for injectors that are not large enough to supply ample volume. In a nut shell, an FMU is a bandaind fix for inadequate fuel injectors. larger injectors and a custom tune give much more of a precise control over the fuel curve. Optimum spray patterns for fuel injectors are at stock pressures. Ramping fuel pressure up to compensate for that smaller injector, makes those injector less efficient. Ramp the pressure up enough, and you run the risk of that injector locking itself open. Another potential risk with an FMU is the possibiilty of developing a hole or tear in the diaphram. Absolutely the worse thing that can happen to you. Imagine stepping on the gas, going into full boost, then discovering all too late that the FMU diaphram was damaged and you did not get the fuel you were supposed to. BANG! Game over. I've not heard of the latter happening all that often but it has happened. When it does though... there's no coming back from it.

stangbear427 · Sep 22, 2005

OK, that is the opposite extreme from my situation. I was told I'd need an FMU because I have no use for an A1000 pump, 10AN lines and 5/8" rails on this engine, and an FMU would "babysit" my over-zealous fuel system since that much isn't needed. Supposedly, without it, I'll have idle problems in hot weather, etc, with this monster system on my mild 302- and I don't feel like spending a couple hundred on an FMU so I haven't installed it all yet. I want to have everything I'll need already in before the new engine though; so here I sit, and Aeromotive takes up half my shed.
OH- 24# injectors are being used, if it makes a difference.

tjm73 · Sep 22, 2005

I think a 3.25 stroke 302 is the best balence of all things (in a factory block anyway).

5.02GO · Sep 22, 2005

Myke86GT said:
I ran a blown 331 with no FMU, 42# injectors,with 10#'s of boost on a stock computer(A9P), to a best of 11.19. A chip or tuning probably would of helped, but didn't want to mess with anything at the time. I did have a ignition box and a boost timing retard box though. I ran 40#'s of fuel pressure and and took out about 1 to 1.5* of timing per pound of boost just to be safe. Just make sure you have decent fuel pump(s). I ran 255HP intank and T-rex inline.

A chip and dyno tune would of been nice bt I didn't want to spend $700+ at the time. The one problem I did have was a start up, the car would idle uo for a second or two when I 1st cranked it up.

Thanks for the info myke. You have basically what i am wanting. What mass air sensor do you use? If i do this, i may end up with a granetelli. I have a BTM 6 by MSD. I dont use it anymore cause it quit working. I run 8* timing on the street. On 93 gas, i have no detonation. Or atleast i cant hear it. I will detonate on 89 though. I have reason to believe that i MAY have a blown head gasket now anyway.

So you didnt have any issues with idle? Issues going beyond 2000? Extreme rich?

Thanks again myke

5spd GT · Sep 22, 2005

A dyno tune with a chip by a professional is probably the most optimum way to tune a supercharged engine effectively.

That would be me choice if I had that option in my area for sure.

Grn92LX · Sep 22, 2005

stangbear427 said:
:OT: sorry:
Am I to understand that a PMS will do the job of an FMU? (what's so bad about FMU's?) I have a complete Aeromotive fuel system from tank to rails waiting to go in, the only part I don't have is an FMU and this system is a huge overkill for my current combo so I thought I needed one. Before this engine blows and the big one goes in, I'll be adding an Anderson PMS and Eugo... any thoughts?

The pms will do it the right way, instead of forcing returned fuel back through the injector spiking the pressure, the pms (or any tuning device) will keep the injector open longer/shorter depending where you need the fuel.

I would not use the afm wideband because it won't datalog unless you're buying the interacq software and have a lap top. If you do not have a lap top to use, get the wideband I have, innovate motorsport LM 1. If you do have a lap top, just get any good wideband that datalogs. I like my wideband except for the fact that its a little bulky. Its a VERY important tuning tool so the bulkiness doesn't bother me much.

Fyi, I don't think fmu's are too expensive.

stangbear427 · Sep 23, 2005

I do have a laptop. Hadn't thought about datalogging though, I guess I just figured I'd run it with Ricks basic tune, and have Ed Curtis or someone else close to me mess with it if I had problems. I do think PMS's are too expensive, but that won't stop me from getting one. It may sound dumb, but I like the idea of dropping another grand into a PMS (which I will need for other reasons) a lot better than a couple hundred on an FMU to make my "complete" fuel system work. IMO, it should have come with it if it's that important. Adding it onto a $1600 fuel system makes the FMU price seem excessive to me, for (in my case) arguable results. I will need the PMS for the next engine though, so if it'll get me out of this jam now, more the better.

TC93 · Sep 23, 2005

5.02GO said:
Thanks for the info myke. You have basically what i am wanting. What mass air sensor do you use? If i do this, i may end up with a granetelli. I have a BTM 6 by MSD. I dont use it anymore cause it quit working. I run 8* timing on the street. On 93 gas, i have no detonation. Or atleast i cant hear it. I will detonate on 89 though. I have reason to believe that i MAY have a blown head gasket now anyway.

So you didnt have any issues with idle? Issues going beyond 2000? Extreme rich?

Thanks again myke

I ran a Pro-M 75 mm. I kept my base timing a 10* with the retard box taking out per pound of boost. I always ran 93 or 94 octane in it. But if you don't plan on a chip or tuning device. At the very least use a BTM or the Crane set-up to take timing out under boost. Before adding the retard unit I had use to detonate allot even on 93 octane.

It was little rich at idle, but didn't really hav an idling issue. 98% of the time it rock steady at 950 where I st it at.

5.02GO · Sep 23, 2005

Myke86GT said:
I ran a Pro-M 75 mm. I kept my base timing a 10* with the retard box taking out per pound of boost. I always ran 93 or 94 octane in it. But if you don't plan on a chip or tuning device. At the very least use a BTM or the Crane set-up to take timing out under boost. Before adding the retard unit I had use to detonate allot even on 93 octane.

It was little rich at idle, but didn't really hav an idling issue. 98% of the time it rock steady at 950 where I st it at.

Cool.

I may end up with a stroker after all.

Thanks again myke

5.02GO · Sep 23, 2005

What about running 36's?

TC93 · Sep 23, 2005

5.02GO said:
What about running 36's?

Maybe on a stock motor, but with a stroker I wouldn't run 36's without an FMU..

Rick 91GT · Sep 24, 2005

We made 425/465 to the tires on a 331ci blower combo (ported iron Gt-40's, ported Cobra intakes, A-trim) with 36# inj @ 37psi base it was at 68% duty cycle, so it can be done.

I will say if I have my choice I always go with 42# injectors.....

stangbear427 · Sep 24, 2005

Better to be underworking big ones than overworking little ones... not that "underworking" and "blower" really fit in the same sentance...

Rick 91GT · Sep 25, 2005

stangbear427 said:
not that "underworking" and "blower" really fit in the same sentance...

aint that the truth

Decided against 347......

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