You guys think 30lbs injectors would be overkill or just right for my setup??

The folks over at TPIS think 24lbs are plenty, but I've seen a lot of mixed opinions on this board..

-- Joe

 

24# should do just fine, do you have an AFPR? Since you're blown you may need to recalibrate the PROM as well.

 

Yeah, I have an AFPR but with the vortech, it max's out the rail pressure. I think it blocks off the return line under boost.
Not very controlled.

So you think the 30#'s will cause problems? I'm running 22lbs right now.

-- Joe

 

I have a similar setup (different heads, no supercharger, same cam) and I threw 30# injectors on the car because the 22#'ers were close to or were maxing out. The pulse width is a little on the low side at idle, but everything seems ok.

 

i need 30# injectors for my engine.. so unless u have #'s like mine.. im sure 24's would be fine. my 26 lbs i use now r maxed out at 62 psi and thats STILL not enough fuel.. so the 30's r on their way :lala:

 

#30s are fine. #24s will be too small. IMHO

 

Madmax,

When you say the pulse width was a little low, what do you mean? Does it run rich at idle? did you have to make any prom adjustments??

-- Joe

 

Well the pulse width is running right on the border of what the ecm says is the lowest pulse width it will run, on mine I think it was 1.49ms and any lower and it just defaults to 1.49 (as I understand it) so I just changed that value. Didnt seem to run rich, but I never had it on a sniffer either. o2 values looked ok. I'm no longer even close to maxing out the injectors, it's sitting in a pretty comfortable zone, leaves me room to change the engine and use more fuel later

 

I would buy 30# injectors for your combo...I say that because TPIS uses smaller injectors with high FP to make it work.

The best deal for the $$$ is 30# SVO injectors and run them at 45 or so psi FP. Especially if you can burn your own chips.

It will give you an option to expand later on to more HP...

HTH,

 

Yeah?? This guy wants to semm me some 30# SVO injectors.. I just don't wanna put 'em in, find out I run slower, or run soo rich that my rings dissapear.

So change the injector constants to 1.49ms. Now what about when boost kicks in and the vortech FMU kicks in, think it will run too rich?? Can I change stuff up there?

-- Joe

 

You don't change the injector constant to 1.49ms. Thats the 'open time' of the injectors at idle. Thats the limiting factor in how big of an injector you run and stay streetable. The injector constant changes wit hthe injector size, and is a number like you are familiar with, expressed in lbs/hour. And yes you need to change this number in the PROM basically ANY time you change injectors.

As for the FMU, i'm not familiar with all models, but as i understand it, it shoud be adjustable. Like you said above, it works by restricting fuel in the return line from the normal FPR. As far as i know they are adjustable in that it will add X psi of fuel for every Y psi of pressure in the manifold. The ratio of X / Y (gain) should be adjustable. With larger injectors you will need proportionally less gain. For more on how people deal with this i'd post a question (or even better, try a search) on the power adder board to the effect of "How much less gain do i need in my FMU when moving to 30lb injectors"

 

Ed,

thanks for the reply. I think I understand a little better now. I'm not really sure that I even need to chaneg my injectors. Keep in mind, I'm running a stock prom. But having the FMU makes things a little more tricky than most applications I guess.. agree?

-- Joe

 

Thats why i say ask onthe power adder board, i'm sure there are a few folks over there who have actually tuned with an FMU before. While i understand how it works, i can't say for sure exactly how much adjustment you'd need to make it work 'right'. And when i don't know thw answer, i prefer to defer to people that do.

In the grand scheme of things though it's probably a good idea to move up in injectors as well as get started in PROM burning. You'll never get the most out of your set-up until you get into the PROM. Once in there you can dial the timing cuve in to work effectively with boost without getting yourself into knock. There are probably some other games you can play in there too on a MAF computer since you're using an FMU

 

Hi Ed,

Yeah I'm totally at the point of ready to start burning proms.. I'm running 110mph trap speeds, and roughly 12.7's or so in 96 degree F weather.. I figure with some good tuning, and maybe a way to cool the air down I could knock off .5..

I appreciate the response.. I've searched a few posts. looks like a few guys running the 30# just ripped out the FMU. But I also noticed they wern't running MAF. Will keep looking..

Anyone else with any experience, please jump in if you will.

-- Joe

 

One such trick i just thought of that would kinda let yu get rid of the FMU with MAF would be playing with the PE fuel adder. It's a simple number that varies with RPM that tells the ECM how much extra fuel to dump at WOT. I'd bet that if done right you could duplicate what the FMU dies in a more accurate fashion using that instead.

Just an idea, like i said i've never tuned a boosted car so don't go listening to me and blowing your engine up. But there is a lot to be found in there i'm sure if you talk to the rigt people.

 

Hi Ed,

I hear ya.. I guess the scary part is the fact that i'm considering throwing eitehr water, or N20 injection into the mix.. Mainly just to cool the hot air charge down.. I wonder hwo thats gonna effect things.

-- Joe

 

You have several paths, some of which are better then others.

Just to use some easy numbers,
if you have 20#/hr in a stock engine, and it makes 200 HP, and then you modify the engine to make 300 HP you'll want to use 30#/hr injectors. there are some formulas for figuring out injector sizes but they are more accurate when using aftermarket ecms. With the properly sized injectors, then you can work on getting the prom right.

The FMU is just a somewhat cost effective way to get things close enough to run.

If you want to stick with the FMU then a Bst Sensing timing retard would be in order. If you rely on the oem knock sensor, it takes too much timing out to make sure the engine stays out of detonation. If you see 6d retard, the engine prolly would do fine with 4d actually less timing.

You can add a S/C easily, getting the tune of it Correct takes time effort and money.

On other option is going SD, but that gets into even more work.

 

Hey Grumpy,

I'm running a MSD BTM. I pull out a degree of timing for each pound of boost. I'm only running 8 degrees initially anyway, and I'm sure the spark curve on a stock 165 is nothing to brag about..

I've considered speed density, but from what I've read even the basic SD harness/ecm isn't that great with forced induction, I've heard of the (749 I think it is) hack to repin and use a different map sensor, but that sounds more like a big winter project than a "lets see if we can go a little faster every weekend" during race season.

-- Joe

 

umm.. u dont need 30# injectors if u make 300 hp... if that was true id need like 52 # injectors. for 300 hp u prob only need 24's.. and im sure thats more then enough.

 

he was just using those numbers for the ease of math / proportions. Grumpy is quite aware that you don't need 30lb injectors to make 300hp.