FMU and injectors

[Superv6bird]

I still have the stock injectors in my bird along with a boost-a-pump and fmu. According to these calculations I found on this website listed below, I wouldnt have enough injector with the supercharger on so I ordered up some 36# injectors to install. Is it possible that with the FMU I would not need the bigger injectors, or should I order up hp tuners to tune for the bigger injectors and ditch the fmu?

Assuming 80%
lb/hr = (HP * .5) / (num. injectors * .8)

to solve for hp, you can reverse it :
HP = (lb/hr * num. injectors * 0.8) / 0.5

so, say we take the hp of the 3.4L, that would come out to 160. so we solve to see what size (lb\hr) injectors we need:

lb\hr = (160 * .5) / (6 * .8)
lb\hr = (80) / (4.8)
lb\hr = 16.67


so basically the 17 lb\hr injectors on the 3.4L car are a bit more than actually needed, but not much.

So then we solve for the 3.8L:

lb\hr = (200 * .5) / (6 * .8)
lb\hr = (100) / (4.8)
lb\hr = 20.83


Stock injectors on a 3.8L are 22 lbs/hr.

So now we solve for a modified 300HP3.8L:

lb\hr = (300 * .5) / (6 * .8)
lb\hr = (150) / (4.8)
lb\hr = 31.25


So the injectors on a 3.8 to support 300HP could use the L67 36 lbs/hr.

[Radcat]

http://www.rceng.com/technical.htm

[Mighty Thor]

You probably need to get rid of the FMU and just do injectors. Tune it with the HPtuner.

I got rid of my BAP and went with intank Walbro 255.

[arthansen]

The only problem with getting rid of the FMU and using HP Tuners is that your 1 Bar MAP sensor will not function when in boost. The GTP has a 2 Bar MAP but our PCMs do not support a 2 Bar MAP.

Without the 2 Bar MAP, there is no way to adjust the fueling to account for boost. You will be running very lean unless you can set up a 2 bar MAP.

HP tuners is working on a modified PCM program for our cars to add 2 Bar support. However, they currently only have it for V8s.

I am not a expert on forced induction so I would recomend you check out HPTuners.com and look in the V6 tuning forum. Lots of info there about this. All the FI V6ers are eagerly awaiting the 2 Bar MAP system. Eventually, they will have a 3 Bar setup for boost greater then 15 psi.

Good Luck.

[grayman]

math hurts my head.

[Mighty Thor]

From what I know, it's better to have big injectors rather than having both FMU and injectors. Because having both makes it hard to tune.

[mrbako]

you don't need to tune to the map, using the maf is fine as long as it's scaled or replaced w/ a larger unit and ecu recalibrated.

[John_D.]

You will need to do some sort of tuning with the bigger injectors, or your idle will be WAY too rich...

[kahouna23]

What about upgrading to the Walbro 255, using an FMU, and getting the Transaltor Plus to adjust the a/f and timing? Shouldn't that be enough to support up to 10psi? Anything past 10psi you should upgrade injectors. Right?