Injector size vs HP = pressure math needed

[EagleMark]

Anyone know the math to figure how much pressure you would need from 2 TBI injectors flowed at 83.8 PPH in a approxamately 350 HP engine?

Before I start tuning this engine I want to make sure I can get enough fuel for it.

[gregs78cam]

Info that I used:

http://www.dynamicefi.com/TBI_Fueling.php

[gregs78cam]

Or I figure about 14.372 psi.

I made a simple spreadsheet for this purpose but I can't upload it. what should I change the extension to that is allowed?

[EagleMark]

Tell me the extension and it shall be done! Something like that could be added here and the library.

I did the math on RBobs EBL site and came up with 14.4 PSI. So we have an 18 pound spring and a TPI pump so Good To Go! :jfj:

Truck never ran to full potentail and has some knock, seems to be right side bank. O2 is in left. But this time I am adding WB to right side bank. May switch in the end to get readings from other side, just to see?

Just put the TPI Pump in and have not tried it. Had an adjustable regulater set at a good solid 14.5 but then saw some decline around 3000 RPM.

Also injectors were somthing on one side, I forget, but the other injector had NO markings? So I had a set of BBC injectors, the 80 PPH ones and serviced and the bench flow was 83.8 each. I will install these then probably set presure at 15 to give a little room for test flow and actual flow. Record some data and see how it does. Get to try out my Wide Band Too! :jfj:

[gregs78cam]

.ods or .xlsx

[EagleMark]

You should be able to upload that now. I opened up a lot of files, extensions and sizes so really everything is allowed.

[gregs78cam]

Updated, fixed a few issues.

[EagleMark]

Nice! :wtg:

Just tried it and used stock flow of 80 and came out with 15.05 needed. So I had a fairly accurate guess! :scare:

[EagleMark]

Of course I am probably underestimating the HP. It's a 440 Mopar origanal six pack motor but now four barrell intake and a BBC TBI. Cam was mild too to get ratings of off idle or 1000 RPM power band start for an off road truck.

[gregs78cam]

Error found, will replace when fixed.

[dave w]

Updated spreadsheet and made a little more user friendly.
I downloaded the new file as an excel file. Anyway, I couldn't figure it out. Maybe because of the excel thing?

[gregs78cam]

HHHMMMMM. Well I use OpenOffice and sometimes there is a format issue. I will download it at work and try it with Excel. If it doesn't work I will just re-do it in XL.

[gregs78cam]

Error found, fixed in first reply.

[gregs78cam]

Error found, fixed in first reply.

[dave w]

Sorry, I opened it in Excel, and everything looked right, but the formulas didn't work. So I went in and made it work. Here ya go.

Working now,

Thanks,
dave w

[EagleMark]

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

[gregs78cam]

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]

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]

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]

Just another Injector sizing program...

[lightning-jr]

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]

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]

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 (http://shop.ebay.com/i.html?_nkw=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]

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]

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