Injector sizing info from Accel

[John_D.]

Here is a good link with some really useful information on injector sizing.

http://www.mrgasket.com/accelpdf/Injector.pdf

It also includes a formula for calculating modified flow rates with modified fuel pressure.

I'm in the process of trying balancing injector sizes with fuel pressure and maft tweaks... To hit good o2 numbers like I want, both when n/a and with nitrous, using fuel pressure mods (instead of maft) to push the nitrous o2 numbers.


hmmm, running the formula, says a 300hp v6 needs 29-35 lb injectors, at 85% duty cycle....

hmmm #2, maybe that's not so far off... My dry 85 shot, which would be a 285hp v6 (not including intake or exhaust mods), with a fuel pressure difference from 44psi to 60psi, sees the 21.6 injectors should start flowing like 26lb injectors, and I'm still lean.

[ June 25, 2002: Message edited by: John_D. ]</p>

[FirebirdGT]

This stuff has been in the Technical Database for a long time.

[John_D.]

Ok, you got me on the formula for calculating an injector size on a standard pressure rating... [img]smile.gif[/img]

I don't think you got me on a calculation for determining flow rates on non-standard pressures... ;)
Unless I just didn't find it in the database.

The one that says New_Flow =
sqrt(New_Pressure/Old_Pressure)* Old_Flow

[FirebirdGT]

<blockquote>quote:</font><hr>Originally posted by John_D.:
Ok, you got me on the formula for calculating an injector size on a standard pressure rating... [img]smile.gif[/img]

I don't think you got me on a calculation for determining flow rates on non-standard pressures... ;)
Unless I just didn't find it in the database.

The one that says New_Flow =
sqrt(New_Pressure/Old_Pressure)* Old_Flow<hr></blockquote>

It's there - it is a link to a calculator.

[John_D.]

Ok, right again...

It's too hard to find though. Somebody would have to know that modified sizing for injectors would be under engine specs. Then find formulas/calculations down below the specs, then go there and realize that what looks like a heading for a section in formulas/calculations is also a link to another site...

So technically it's there, but not sure how "there" it really is, for someone who is looking and doesn't already know about it.

Maybe I'm just slow...

Anyway, I played with the calculator, it's pretty cool. :D

[FirebirdGT]

This is a good advertisement for everyone to read the Technical Database. It is FULL of info. It's like a technical archive, we've added to it as we or members find items of interest.

I'll also add this site as a link, since it actually has stock injector sizes listed. It is CONFIRMED the stock 3800 injector is 19 lbs/hr.

[ June 25, 2002: Message edited by: FirebirdGT ]</p>

[John_D.]

FirebirdGT, just wanted to take a second to say thanks, for setting up and maintaining the Technical Database information. It's probably a thankless job at times... It helps a lot. The first thing I did when I found this site back in January was print off a bunch of the information from there, read it, highlight sections, make notes in the margins, and read it some more.

[FirebirdGT]

<blockquote>quote:</font><hr>Originally posted by John_D.:
FirebirdGT, just wanted to take a second to say thanks, for setting up and maintaining the Technical Database information. It's probably a thankless job at times... It helps a lot. The first thing I did when I found this site back in January was print off a bunch of the information from there, read it, highlight sections, make notes in the margins, and read it some more.<hr></blockquote>

Thanks, after all the Technical Database and Modification Encyclopedia were what started www.firebirdv6.com in the first place. [img]smile.gif[/img]

[Ironman24]

<blockquote>quote:</font><hr>Originally posted by FirebirdGT:
I'll also add this site as a link, since it actually has stock injector sizes listed. It is CONFIRMED the stock 3800 injector is 19 lbs/hr.
<hr></blockquote>

I think Keith just had the stock injectors flow tested and they came out at 22 lbs/hr. Better confirm with him tho.

[Magnus]

I didn't get #'s... but I flowed my injectors vs a 24 lb injector.. mine were just a pinch under it.

It's realy a huge mess if you ask me.. psi's and all.. I don't even want to think about injectors right now. *sigh*

[John_D.]

I know what you mean. I can't get o2's to hold steady across the board with the nos running...

I'll run .9's for 5 seconds, then average .3's (with lows in the .1's) for the next 3 seconds, then get back up in the .8's.

Haven't determined yet if its a problem with not being able to deliver enough fuel to the injectors, or pulse widths maxing out, or what yet...

I don't think it's fuel volume, because I'm holding pressure (60psi) throughout the entire process.

The dropoff happens right after a shift, when the maf rate drops (maybe dropping below wot recognition on the maft?) It comes back up eventually, after the rpms come back up. The maf numbers bounce up and down for the duration, instead of steadily climbing.

But I wouldn't think it's pulse width either, since the lower rpms should demand less fuel? And the lower rpms allow more off time between pulses... But the lower rpms right after a shift are the problem area.

So I'm stuck too. Boost-a-pump is on the way. Maybe 24lb accels later. Gotta be careful not to get too far off the track though.

Maybe spraying before the screen and before the maf sensor is adding to the problem. I need to relocate the nozzle to the tb, after the maf and see if that tightens up the maf readings and the o2's. :(

(And where in the heck do you find a tap to thread the throttle body for the nozzle?? I've looked everywhere for one. It was supposed to come with the kit, but didn't.)

[ June 27, 2002: Message edited by: John_D. ]</p>

[Ironman24]

The boost a pump should help you a lot. Have you thought about converting to a wet kit?

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Ironman24:
The boost a pump should help you a lot. Have you thought about converting to a wet kit?<hr></blockquote>

I have come to understand the advantages of a wet kit over the past few days, that's for sure... Trying to get the stock injectors to suddenly start flowing more, on demand, in a consistent manner, is a pain.
[img]smile.gif[/img]

The dry kit was an interim thing, while waiting for the supercharger. I'll back the shot way down when I get the s/c on. In the meantime, I was trying to get all I could out of the nos, without going too far... :D

So I'll probably not convert over. Unless I was to decide not to s/c after all. But I want that extra hp on demand at any time, without having to worry about a bottle running out, or having to go spend $40-$50 for my next "fix" for the need for speed.

I think the tb porting is a big part of what zapped me. It's been a struggle cleaning up the na readings as it is. I may try the '99 maf sensor like Magnus just finished doing. He says it cleaned up his maf readings a lot.

But first, I'm going to spray after the maf instead of before, and see what that does. The nozzle is up in the silencer, pointing toward the tb but not a straight shot. So I'm thinking I'm getting some eddy's or some kind of turbulence as the spray bounces off the bellows in that tube between the silencer and the tb. Which would be causing the weird maf readings. For instance, going from 19.8 to 15.4, 18.7, and 16.2, while accelerating in the same gear. Normally the maf readings steadily increase.

Re-aligning the nozzle yesterday did reduce the delay from activation to the time it starts pulling. There was nearly a 3 second gap before, now it's between 1-2 seconds before it starts pulling.

[Magnus]

John, your MAF readings fluctuate because of the PORTED TB... your MAF just kinda hangs there now.. its in a completely different environment than what it was designed for..

You need to either go back to a stock TB or use a 99+ MAF sensor.

[pgriffith]

your going to spray after the MAF with your Nos dry kit?