Thats relatively easy, however, most people never put a pressure sensor on their meth system, and its impossible to determine flow without knowing the pressure.

 

Very nice write up sir.

 

This might be a dumb question but I'm going to ask. Injector data in the tune is based off of a certain base psi. Like stock injector data is figured with a 58psi base pressure. When you change the base pressure to something lower, wouldn't your injector data be off? Or is the difference so small that you don't worry about it?

 

Yes it will be off slightly, but not enough to worry about IMO.

 

Okay that is what I was expecting. Thanks!

 

Furthermore, its my personal opinion too much weight is put into injector data when you have properly sized injectors. Let me explain. Most of the non-linearity of injector behavior happens at very low pulse widths, so characterization is most important here. Unless you have an engine with extraordinary high specific output (ie, a 1.4L honda engine making 800hp), your injectors will most likely never go into that non-linear region. This is determined by the fueling requirements of idle vs max power rpm. This is especially true with a vacuum-referenced regulator. As long as the main flow rate vs pressure table is correct and the other tables are somewhat close, it will be fine. If your battery is good, voltage will not drop much during cranking, so that voltage offset table should only use a limited range. The min pulse width table should almost never be needed (unless very high specific power).

 

Hey Richard,

I was looking through some old threads and found this one. His BSFC assumption is a lot lower than yours, but even so, the math (esp. post 3) is worth taking a look at. I've gone a lot higher in rwhp with twin walbros and some meth than your chart predicts as possible.

 

There are 2 big things in his post...one obviously he assumes a much lower BSFC. I came to my assumption based on my fuel flow while on the dyno, ie, calibrated to my specific truck. Maybe we have all been assuming too low of one all along...
Secondly, which is related to the first, he is assuming crank horsepower, not wheel. You could account for this by assuming a higher BSFC, which is more similar to my example.

My chart seems to think a single walbro will tap out around 500-550 rwhp, which is about where every agrees they are maxed. Im curious what you had yours to, but also keep in mind the meth counts as fuel too.

 

I missed that in your chart I didn't look at the thread again today, but had it in my mind that you were predicting much lower for the 255 (like in the 400s).

 

so an a1000 with 40 psi and a 160 lb injector at that psi will support?

so according to your sheet i need 1136 lb/hr pump and the a1000 does 800 at that psi at 13.5 v

Time for an upgrade

the 11104 pump should get me there at 1200 at same rating...