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Choosing an injector and idling it smoothly with speed pro

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G

Guido

Old School
Joined
May 29, 2001
Messages
32
This year I ran 55# siemens with my 406 and vortech supercharger with a speed pro and WB02. I had no problems.

Im in the middle of upgrading to a PT88 turbocharger. I have 406ci, AFR190 heads, 233/226, .529/.523 cam,

im trying to decide if I should go with an #84 or #96.

Has anyone had problems idling injectors that large with only a bakn to bank speed pro
 
How much power will you make with the new combo? Divide your horsepower number by 16 and that should give you a good approximation of what size injector to use.

With a 400+ inch motor I will guess that you will idle an 80-90 lb injector without too much trouble. I've tuned a 4-cylinder with 72 lb injectors and it idled quite well.

Craig
 
Craig, I figure I will be in the 800+hp range. Using that line of thought, the 55# will still work but will be close to max duty cycle. Id like a little bit more saefty factor and know I wont stop here so upgrading to something larger seems logical to me.
 
Based on what you've said....

I think 72's would work fine. If you plan on really going past those #'s (which) that PT-88 is capable of: 83's would work (they're almost good for 1200hp static) @ .55 BSFC. I can't say I'd want to run more injector than that. A bank to bank system with 400+ cubes should be OK with 83's. 96's would be alot of injector, I think you'd run into idling issues without sequential.
 
I'm running some 83's on a 351 and intercooled Paxton setup and have gotten a good idle with the bank to bank system. I think you'll have plenty of cubes to make a similar size work in your setup. I checked your page out ....looks like a real interesting project you've got going...Good Luck!!! Hope it rocks.
 
I've been using 96's on my stock block GN for the past year. They idle like stockers. I wouldn't be afraid of them. The larger injectors with the F.A.S.T will give the system a chance to throw additional fuel if problems arise - fuel pump starting to fail, etc.

Paul Thompson
 
Originally posted by Craig Smith
How much power will you make with the new combo? Divide your horsepower number by 16 and that should give you a good approximation of what size injector to use.

With a 400+ inch motor I will guess that you will idle an 80-90 lb injector without too much trouble. I've tuned a 4-cylinder with 72 lb injectors and it idled quite well.

Craig
Click to expand...

Craig,

When tuning a 4 cylinder motor with big injectors 68 lb & up is it normal for the idle to be running real rich ie 10:1-12:1 a/f? when i try to make the motor run leaner 14:1 the motor dies out. is this because i'm not using an air idle control motor? would an AIC help out in the situation?

Thanks so much, Andy
 
Andy,

I bet your combo is on the edge of working well with a B2B system. Watch your pulsewidth numbers while you are idling - I bet that once you approach 13:1 or leaner you are probably getting around 1.5 mS or so on the injector pulsewidth. I don't think that the "problem" here is that your motor wants to idle rich, I bet it's that when you try to get the motor to a nice, lean idle mixture you are starting to lose good control of the injectors.

Just a theory - maybe I'm off here, but take a look and let me know. I'd be quite interested to know.
 
Craig,

Thanks for the help. So, what you're saying is having the motor run on the rich side with big injectors is something normal? I have no problem with that, its just this whole time I thought i was doing something wrong. Also, sometimes when theres an electrical load, ie. the fan kicking in, or flipping on the lights the motor dies out. Is this because I don't have an air idle control motor hooked up?

TurboMike,

I meant AICM to mean air idle control motor.
 
Andy,

Can you tell me what the serial number of your ECU is? There are different versions of firmware inside ECUs of different ages, and the newest ones have big improvements in the way the ECU responds to changes in battery voltage. If you have an older unit I may have an upgrade for you that will help this out a ton.
 
Craig, if I gave you my S/N, would you be able to tell me as well? I'm having some issues with my B2B system also.
 
Here's my stuff anyways:

Assuming you could tell me, here's the info on my box. It's kinda old too (2 years).

P/N: 30-115010
S/N: 01029 1029
Firmware Rev: B2BEDI_A
Date: 11/30/99 - 2/7/00
 
I think that we Buick system guys have to be careful with comparing our b2b case with the other b2b cases. If I'm not mistaken, we have what amounts to an out of phase sequential basically, in that the ecu doesn't cut the pw in half like on the generic b2b box. In other words it fires each inj once every 720 deg, same a SEFI. So our expeience with large inj is ~ the same as with a sequential. And we don't seem to have much problem with large inj. IME things were much different with a b2b 4 cyl app with 84 lb inj. The config and VE tables and all were much different with the generic b2b box in place, compared to when I put my Buick configured ecu onto it (while the other was being reprogrammed). I ran into similar issues to what SEFi8LOxCivic seems to be having.

TurboTR
 
I idled and tuned a stock GN with 83 lb/hrs. with an old DFI. Drove the car everyday, never had a problem. Anything is almost possible, if you have a good tuner.
 
Todd, you are correct in that the Buick systems only fire the injectors once per combustion cycle, so it is a little different than on a 4 cylinder. This "problem" can be affected by many things - battery voltage, fuel pressure, injector opening time, etc. Some guys may have no problems at all, others may go to hell and back trying to get it to work right. This is true of any combination.

The smaller the motor, and the bigger the injector in that smaller motor, the more prone to idle problems a person will be. This isn't to say that someone fitting this profile WILL have problems, but it should be kept in mind.
 
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