Injector size?

Achilles · 10-24-06, 09:02 PM

Went and had a dyno run today and found out I'm way too lean. I start out at 12.5 and then leaned out to 13.9 @ 5000 rpm. I have 22# pink tops in now and I thought that would be fine with the new motor...Guess not! The guy at the shop recomended 30#. That seams too big if I only need to drop my air down a couple of points. My intake is a ported stock piece w/ stock runners and my cam is a 210/216...nothing too drastic. But I am running 11:1 comp pistons that might have something to do with sucking so much air. Oh, I also have a Fast Chip too for my application.

Does anyone have any suggestions.

I was thinking more along the lines of 26# - 28#.

vetteboy86 · 10-24-06, 09:24 PM

Were you watching your fuel pressure while you did this? I am running into a problem now similiar to yours. Perhaps you fuel pressure regulator is malfunctioning

Hrtbeat1 · 10-24-06, 10:27 PM

Quote:

Originally Posted by vetteboy86

Were you watching your fuel pressure while you did this?

I was thinking the same thing.

We need more specifics on the "new" motor ... ci, heads, intake.

There is a formula for injector size: (HP x BSFC) / (# injectors x duty cycle) = lb/hr

You have to realistic though or you won't get a good rating.

HP is crank HP
BSFC = Brake Specific Fuel Consumption (.4 ~ .5 for a N/A V8)
duty cycle is the open time for the injector ... normally .8

The 22# "pink tops" you have should be good to over 400 HP depending on the pressure. If you exceed the rated pressure (normally ~43#) the flow rate goes up, so at 50psi they flow something like 25#. There is a formula for that but I can't find it right now.

I've seen Fastchips at work. The car ran good but the scan of the car during driving had things messed up. I worked up a "tune" and got the car running really good. Not knocking them ... they do a good job for not being hands on, but each car is a little different.

Craig If you still have those disks mail them to me and I'll get to work on yours and Justin's tune. My old laptop died and I don't have anyway of reading the scans you sent me. Or you might want to email me some new scans as those are a little old. Oops I forgot about your other chip ... I don't have a way to know what was changed from stock... so I'm gonna be in the dark there, unless we work from your stock chip and the old scan.

Achilles · 10-25-06, 09:23 AM

I have a new BBK afpr & it was set at 47 psi for the first pull and I was super lean...13+.1. Turned up the fp quite a bit higher. I didn't hook up my fp guage because I was trying for a rich condition. But I'm sure I was close to over 50 psi.

The second pull starts out @ 12.5:1 up to 3200 rpm then begins leaning out to 13:1 @ 3500 rpm, finally reaching 13.8 @ 5000 rpm. I always thought the computer would automatically richen the mixture at high rpm. But now I'm thinking it can't keep up with my vacume pump (motor).

So specifically this is what I've got:

350 TPI bored .30 over w/ stock crank & rods

Sealed Power pistons with a final cpr of 11:1

Trick Flow D-port heads (56cc w/ 1.94 small valves)

Crane Cam 210/216 @ .50 - Llift @ 400/454 w/ Crane 1.5 roller rockers

Stock ported base, stock runners, plennum & 48 mm TB w 22# injectors

Stock ignition

TPiS long tubes w/ true 2 1/2" mandrell bent dual exhaust ( no cat)

My net #'s for my first pull under lean conditions were:

278.5 rwhp @ 4,558 rpm

384.4 rwtq @ 3,372 rpm

I won't do another pull until I can get my AFR issue resolved.

Hrtbeat1 · 10-26-06, 05:01 PM

13:1 is still rich compared to stoich, maybe not as rich as you would like. I think you have the right idea adjust the pressure up a bit more. As the vaccuum drops with the higher RPMs the AFPR should also lose some of the vaccuum pull and let the pressure come up to where you set it (with the vaccuum disconnected) One other thing I would check would be the TPS voltage ... make sure you are getting the 5V @ WOT. That is the only way the ECM knows to go into PE (Power Enrich) mode. But you are right is should be able to keep up. What about fuel filter, pump, and fuel level in the tank? After about 10 pulls my level was down far enough that it started breaking up at high RPMs.

With the stock TB, plenum, runners you may be able to squeeze another 500 RPMs but thats about the limit for the TPI. With those numbers it seems the curves look typical .... almost a big X. 320HP at the flywheel is pretty good although I would guess somewhat higher with the 355 and the Trick Flows. The cam is kinda small but I would think it would make around 360 FWHP.

Achilles · 10-26-06, 10:10 PM

I was hoping for 350 -360 hp at the flywheel. Anyway i ordered the 30# injectors and will check to see how they work. I found a site on the forum from past threads on how to determine the proper size injector and based on my figures I should have 28# for my assumed HP. So the 30#'s may work ok.

Achilles · 11-02-06, 11:34 AM

This injector size issue seems to get more and more confusing the more I learn about it...Does that make sense? I've been reading past posts on what size injector everyone is using and the way to determine the right size for your engine application. I also got my accel 30# injectors and read on the back of the box for engines w/ 350 hp @ the crank (which I think I potentially have) and comp. over 9.7:1 ( which I'm @ 11:1), they recomend 26# injectors based on their 85% duty cycle.

Problem is I don't see anyone offering a 26# for the TPI. Its either a 24# or 30#. Also in a old post I see Holley recomends if you calculate a 26# injector for your application and one is not available, choose the 30#. Now if the 30# is too large and I have to decrease my FP to compensate for the large injector, that will hamper my spray patern and hurt performance. But Accel does not recomend the 30# for high compressions over 9.7:1 in my horse power range.

Now something more to consider...My dyno results proved my AFR to be between 12.5 - 13.8 at WOT. I saw in a past post that AFR @ WOT should be 13.1. Ok, I can see I have a lean condition. Since I live at an elevation of 2400-2600 ft., our air is thinner which allows for a richer running condition. My tech advised me not to take my car in areas closer to sea level (Los Angeles) untill I resolve my fuel issues... Makes sense to me. If I'm already lean it would be much worse at sea level. And since this is a track only car, I will be running closer to WOT most of the time.

So, I'm guessing at this point its a crap shoot. I'll try the 30#'s, if they run too rich I'll go to plan (B) and install a Big Mouth & large tubes to try and help balance the AFR.

grumpyvette · 11-02-06, 09:03 PM

just some info
Im running 36 lb injectors on my 383 and they can,t keep up past about 6000rpm where it starts to lean out significantly

stuff you need to understand

http://users.erols.com/srweiss/calcpchg.htm

http://users.erols.com/srweiss/calchpaf.htm

http://www.z31.com/software/injector.pl

http://users.erols.com/srweiss/tableifc.htm

http://www.rbracing-rsr.com/runnertorquecalc.html

http://www.newcovenant.com/speedcraf...runnerarea.htm

http://www.newcovenant.com/speedcraf...ors/intake.htm

Achilles · 11-03-06, 11:07 AM

Thaks Grumpy, that answeres a lot of questions. Based on my assumed HP at the crank, I think I would do better w/ the 26# & with the afpr I can adjust for 27#+ if needed.

I figure the 26# are good up to 390 +/- HP @ a stock fuel pressure setting. Which is plenty for what I'm running

grumpyvette · 11-03-06, 11:47 AM

if you think 27 lbs will do fine for 400 hp, get the 30 lb size, the BSFC: should be around 45%-55% depending on your combo and nitrous use,the CPU will just use the O2 sensor data and cut back the pulse width to compensate, giving you the correct A/F ration, but you won,t need to upgrade injectors again till your up in the 500hp band,trust me, the programing not the injector limits the a/f ratio as long as the injector and fuel supply system can keep up with demand, but the injector quickly becomes a restriction past about 85% pulse width or duty cycle

Achilles · 11-04-06, 10:01 AM

Quote:

Originally Posted by grumpyvette

but the injector quickly becomes a restriction past about 85% pulse width or duty cycle

Are you implying the restriction towards 85% > 80% duty cycle?

I don't have NOS...I have 327 HP @ the crank now with the lean condition and retarded timing (2* BTDC). I'm hoping that once I'm able to richen the AFR that I can advance the timing somewhat and unlock a few more HP. Like I said, I am assuming I can get 350-360 HP without further mods. Realistically, I would be surprised if I get any more HP than that by simply changing the injectors.

I was wondering if there is a formula to determine how much more fuel is needed (cc/min) to richen AFR 1 point. For instance if the AFR is currently 13:1, how many more cc/min is needed to richen AFR to 12:1?

Also, I was concerned about my fuel pump keeping up with the 30#'s. And do I have to worry about washing the cylinder walls? Sounds like if the computer will help to compensate for the large flow injector, it is nothing to worry about.

grapeknutz · 11-04-06, 11:47 AM

Some great info!!! thanks

grumpyvette · 11-04-06, 12:35 PM

first you need to understand the stock programing controlling the corvettes a/f ratio trys to maintain it at 14.7:1 for max mileage and LOW emmissions, MAX power is usually found in the 12.6:1-13.0:1 f/a ratio range, (significantly richer than ideal for EMMISSIONS)

http://www.fordmuscle.com/archives/2...vate/index.php

http://www.innovatemotorsports.com/r...e_tutorial.php

http://www.techedge.com.au/vehicle/wbo2/default.htm

http://www.customefis.com/index.html

http://www.holley.com/TechService/Library.asp

http://www.holley.com/types/Chevrole...FI_Systems.asp

Achilles · 11-05-06, 01:25 AM

[quote=grumpyvette;763798]first you need to understand the stock programing controlling the corvettes a/f ratio trys to maintain it at 14.7:1 for max mileage and LOW emmissions, MAX power is usually found in the 12.6:1-13.0:1 f/a ratio range, (significantly richer than ideal for EMMISSIONS)

Achilles · 11-05-06, 01:33 AM

Quote:

Originally Posted by grumpyvette

first you need to understand the stock programing controlling the corvettes a/f ratio trys to maintain it at 14.7:1 for max mileage and LOW emmissions, MAX power is usually found in the 12.6:1-13.0:1 f/a ratio range, (significantly richer than ideal for EMMISSIONS)

http://www.fordmuscle.com/archives/2...vate/index.php

http://www.innovatemotorsports.com/r...e_tutorial.php

http://www.techedge.com.au/vehicle/wbo2/default.htm

http://www.customefis.com/index.html

http://www.holley.com/TechService/Library.asp

http://www.holley.com/types/Chevrole...FI_Systems.asp

My mistake.... I understand the that part of it. I'm trying to figure out the best way to go about getting it and what is required to get it.

Thanks for the info on the wide band readers. I have been looking at a wide band commander and thinking about getting one to help me with this issue. But they are a bit pricey and I was hoping to narrow down the guess work in the hopes of finding an injector size that fits my application. But maybe the only way to know for sure is to bite the bullet and get the wide band. Basically, I'm just trying to avoid having to buy a slew of different size injectors while trying to find the right combo.