24# inj.'s, 190lph.......how much boost?

**mygt8a4re** · 03-24-2003, 08:58 PM

im curious how far i can upgrade on my 24# injectors & 190lph fuel pump? can i see 8psi safely? im sure ill upgrade these down the road, im just curious what i can see safely now.........
what kind of gains can i expect from just a 7" crank pulley?

thanx!

**slider_buck** · 03-25-2003, 12:01 AM

i'm running 9lbs with my novi on FMS 24lb injectors and a Walbro 255 pump. i don't have an FMU and my fuel pressure is set to 41 with the vaccum on. i haven't had it dynoed but i did pull a plug during a wide-open run and it didn't look like i was running lean at all. just my .02

**5150 LX** · 03-25-2003, 09:00 AM

I ran 24#'s w/ a 190 in-tank and still ran the FMU with about 7#'s of boost, I will say that the car ran pretty rich once into boost. I never tried running it w/o the FMU though.

**5150 LX** · 03-25-2003, 09:02 AM

BTW, I have stepped up to 42's & a Walbro 255 Hi-press. in-tank in anticipation of the coming 331 & 12-15 #'s of boost

**mygt8a4re** · 03-25-2003, 12:58 PM

sweet, thanx guys, thats what i needed to hear........

**mygt8a4re** · 03-25-2003, 05:15 PM

well, while im here & you guys are such a big help..........what fuel pressure do you recommend at base boost (5-6psi)? what do you set your base timing at? should i gap the plugs around .030-.035?

im just trying to cover all the bases..........
thanx!

**mygt8a4re** · 03-25-2003, 05:20 PM

5150lx, whats the remedy to running so rich at full boost? can you calibrate the FMU to think you have different size injectors to help alieve some of that fuel at full boost. i know its better to be safe but do you think the FMU calibrated to 24's is overkill?

thanx..........

**5150 LX** · 03-25-2003, 05:44 PM

As far as I know the FMU supplied by Paxton is not adjustable, on some vortec FMU's you can adjust the ratio by replacing an inner disk within the FMU. The FMU is widely seen as a "band-aid", the best alternative is to have a fuel system to support the desired boost levels & then taylor the fuel curve with a custom chip or tuner.

**mygt8a4re** · 03-25-2003, 05:54 PM

wow, so the same FMU is used in all kits? this seems as though it would be horrible at low boost levels, as im sure it was designed to add enough fuel for large amounts of boost well over entry level........can you adjust the FP to counteract the massive amounts of fuel at full boost?............im sure down the road i will get a custom chip burned but there has to be a good way to tune with the FMU or it wouldnt be so popular right?

**RydeOn** · 03-26-2003, 04:18 AM

The FMU is boost dependant, which means that for every PSI of boost, an according amount of fuel is added.

**mygt8a4re** · 03-26-2003, 05:20 PM

thanx ryde on, i realize that the FMU adds fuel per a particualr increase in boost, i was just wondering if there were some way to eliminate the amount of fuel when at full boost since the FMU's are non adjustable! this seems kind of nuts since some people run different size injectors, wouldnt this effect the amount fo fuel the FMU makes available per psi of boost? it seems it would be better to have smaller injectors at the entry boost levels with an FMU. if the injectors were bigger the amount of fuel added would be rediculous at base boost!!...............ok, im just getting my thoughts out, want to make sure i have this all down before the install....thanx!

**Texas89LX** · 03-27-2003, 02:06 AM

youd at least want a 1:1 FMU so your injectors act right and dont flow less when there is boost going on.....
but i could be wrong....

**mygt8a4re** · 03-27-2003, 12:46 PM

1:1? I think it should be more like 14 or 16:1 right? i think a 1:1 ratio would detonate pretty bad, might as well not run the FMU!
but im new to this so who knows, im only going off what i have already researched............

**fanglemeister** · 03-27-2003, 05:37 PM

1:1 fuel rise happens at the fuel pressure regulator if you keep the vacuum line connected. If you haven't ordered a blower kit yet, you can request a certain FMU ratio and Paxton will send that out with your kit. I ordered mine for use with 30# injectors, but going to run it with no FMU for starters.

There is a trick to trimming the amount of boost the FMU sees, called a bleeder valve. This in turn limits the amount of fuel presure increase. The bleeder valve is simply a little screw valve you would normally see controlling the amount of air going to a fish tank filter for instance. As you open this inline valve, it lets boost bleed off.