Injector size vs HP = pressure math needed

**EagleMark** · 07-23-2011

If you guys are so good at that how about one that gives new injector ms setting for increased presure?

**gregs78cam** · 07-23-2011

Originally Posted by EagleMark

If you guys are so good at that how about one that gives new injector ms setting for increased presure?

Do you mean injector pulsewidth? That is what I rely on the PCM to figure out. From looking at some of the adders for AE and PE, I am pretty sure that it calculates it in microseconds instead of milliseconds though.

If you mean injector latency due to increased pressure, there are way too many injector specific varibles to be able to make up a blanket calculation for.

**EagleMark** · 07-23-2011

Wasn't sure what to call it, seems like differant ECM have differant names.

I'm working on a 440 Mpoar bored .030 over and undersized cam. It was an origanal six pack engine.

Using the spreadsheet I come up to 15 PSI. not a big differance to the 13PSI stock. Any ideas if I should change this to start?

**gregs78cam** · 07-23-2011

If the expected hp output is a little more than the engine those injectors originally came in, then sure, I would set the FP to 15 and go from there. It's really just a starting point anyways from my experience. With that small of an increase latency won't really change any measurable amount either.

**EagleMark** · 12-04-2011

Just another Injector sizing program...

**lightning-jr** · 12-14-2011

This is a calculator I find quick & helpful,

http://www.gtsparkplugs.com/InjectorSizeCalc.html

An easy overall fuel requirement formula is HP*BSFC=lbs per hr.

Another calc I really like was posted on Sean's site,

**JeepsAndGuns** · 12-14-2011

One of the biggest things I have had trouble with, is how do you figure out injector size and pulsewidth when you have no idea how many HP your engine is making?

**EagleMark** · 12-14-2011

Stock engines should be close to whatever the EFI conversion equivilent is. 304 AMC = 305 Chevy. Add a part and they usually tell you the increase, change a cam and they do give specs. It's all to get close, then tune!

It was wrong to change BPW just to try and add fuel. I tested it and it failed. So I did a lot of reading and came to same conclusion I did long ago when starting a tuning project on a built engine.

1. First you have to know approx HP engine will acheive.

2. Then need to have injectors and pressure to meet that HP number.

3. BPW or BPC is specific for injector size-CID- Fuel Pressure.

If you have enough fuel to cover WOT high RPM of built engine then the BPW or BPC should stay the way you calculated it. Then work on idle

**EagleMark** · 03-18-2012

Originally Posted by JeepsAndGuns

One of the biggest things I have had trouble with, is how do you figure out injector size and pulsewidth when you have no idea how many HP your engine is making?

I found an online calculater that should get you close if you know your cam specs or have a proven engine build crate motor you should know exactly.

http://www.bgsoflex.com/roughhp.html

**JeepsAndGuns** · 03-18-2012

Intresting link. Have no idea what my compression is either...lol. Stock I think was 8.8, minus 20thou, mabey 9 now?
I put in 409 cid (since its 40 over) and 9 compression, it says 301 at 4500.
My cam is the comp cams XE256H