Paxton FMU re-calibration

**Paxtu22** · 11-12-2002, 11:10 PM

Hawk,
I think that you could get away with the 14-1 and the 30's. What is your set up? 24's where not enough for me, I think that 30's would have worked. I run 42's and an Interceptor2.

Eric

**TheHawk05** · 11-13-2002, 12:26 AM

Originally posted by Paxtu22
Hawk,
I think that you could get away with the 14-1 and the 30's. What is your set up? 24's where not enough for me, I think that 30's would have worked. I run 42's and an Interceptor2.

Eric

I'll give it a try anyway. My set up will be stock bottom end, AFR 165cc heads, Edelbrock intake with 70mm TB, 80mm Mass air, E303 type cam, 1 5/58" shorties, 2 1/2" H pipe w/cats. My blower is being shipped with a 30lb FMU and a 255 lph @90psi Walbro pump. As mentioned before I have an Interceptor II. Boost will be kept under 10lbs due to the stock bottom end. If the injectors do end up being too small after tuning with the Interceptor, no biggie. Just get new ones. I'm not worried about it.

**slider_buck** · 11-17-2002, 07:15 AM

i have a kirban regulator on mine and its not boost sensitive. the only one i have found that is boost sensitve is the mallory. i think it was too senstive or something. i blew it the first day having it on, the thing wouldn't hold any pressure at all after seeing full boost so i'm back to my kirban for now.

**TheHawk05** · 11-17-2002, 12:10 PM

Originally posted by slider_buck
i have a kirban regulator on mine and its not boost sensitive. the only one i have found that is boost sensitve is the mallory. i think it was too senstive or something. i blew it the first day having it on, the thing wouldn't hold any pressure at all after seeing full boost so i'm back to my kirban for now.

Someone else mentioned this to me before so I took the liberty of calling Kirban. I spoke with their top tech guy and he assured me that it is boost sensitive. However most people should know that boost sensitve FPR's won't make your fuel pressure go up like an FMU does. He told me the rate of gain is 1:1, so for every pound of boost, the fuel pressure will rise 1 pound over what you have it set at idle. This why you have to step up to such a large injector when ditching the FMU. FMU's allow you go smaller on the injectors because of the huge fuel pressure rise when it comes in so they make the injectors act bigger than what they are. Most fuel injector's flow rates are based off of a pressure setting of 42-45lbs in which case a 30lb injector would be too small for my above mentioned combo. But 30lb injectors will flow more like a 36lb or more when all that fuel pressure ( sometimes up to 90lbs) is pushing on it. The biggest detraction with the FMU however is they generally make the car go rich when it initially comes in to play because the fuel pressure rise is not linear in nature as the fuel pressure rises almost immediately, therefore costing you some power. However if you have a PMS or an Interceptor, you can tune that transition by backing off your fuel injector pulse width. Sometimes FMU's are a necessary evil due to emmissions regulations for some people. I've heard and read about some states being very thorough with emissions inspections and won't pass a car that has larger injectors. A guy running a Novi 1000 with the box stock 5lbs of boost would be able to keep his 19lb/hr injectors with an FMU in place, and therefore avoid those hassles. But most of us aren't going to leave it stock anyway so obviously bigger injectors will be required. IMO for the guy who can't be bothered tuning for maximum power, run an FMU in the setup because most tuners agree it will keep the motor safe as they all tend to make the car go a tad on the rich side . I know that seems silly to most of us as we want the best tune we can get for the most power, but there is a large segment of blower buyers that only care about slapping it on and immediately going out on their test drive and stomping on it so an FMU in most cases will keep those guys out of trouble.

**slider_buck** · 11-18-2002, 07:35 AM

i know i have a kirban on mine and it doesn't raise the fuel pressure at all under boost. i'm seeing 9lbs with my seup and the fuel pressure does not budge at all under boost.