ViRuS

Upgraded fuel pump and 720cc secondaries on the way and should be here next week. My fuel system is stock on my 87' TII and running 8psi. I would like to know how much boost I can run before I need to change out the stock computer. I can't imagine that the cpu will know injectors have changed, so will it even get more fuel. And how will the mixture be, what about the air flow? Im not sure what I should do. Could I run over 10 psi, without running lean or rich or something like that? Should I get an F-con or s-afc? But these also won't work as well as the stand alone will they?( much more control with the stand alone) Please any help would be great. If its as simple as yes, I can run 10psi maybe 12psi with no detonation and no mix problems then I will be very happy

But I have a feeling it wont.

Oh, I wanna keep my car safe. I know more boost will cut engine life, but If I need a stand alone, I wont up the boost till I get it. I dont wanna loose engines left and right. I want to do it the right way. Thanx again for any help you can offer.

dvls-7

What do you already have in terms of mods? For the stock ecu you will need the fcd. The s-afc works good if your on a budget it does give some control. For fuel, this is my setup.....3rdgen fp, aeromotive fpr, 680cc secondarys. I ran 9-13psi all the time and when i dynoed my a/f was mid 11s all the way across. If you get the 720s then i would suggest getting the s-afc cause with those you will run rich.
Also you might want to look into some form of protective coating for your bumper as this is likely to happen.......

ViRuS

I have a walbro 255 Hp fp, 720cc are going in. I have a fcd already.(8psi) You think I can even out the mixture with S-afc? Whats an fpr? (Fuel pressure regulator?) Do I need one of those?Thanx for all your help.

I do that already but not as big cause of the duals

NZConvertible

If you don't get an S-AFC or similar you'll end up with very rich mixtures that'll cost you power and give you terrible fuel consumption. You shouldn't be running much past 10psi on the stock turbo anyway, in which case the bigger injectors aren't necessary, only the fuel pump.

ERAUMAZDA

10 psi is pushing it on the sotck turbo.....buy a Fuel controller

ViRuS

But arnt the stock 550cc injectors at max duty (over 85%) at 10psi. I thought the stock turbo was good for at least 12psi? OK so the S-afc would be better to get for the bigger injectors or should I not even drop them in at 10psi? Or would I run better with some type of piggy back and the 720cc? Thanx for all your help guys.

Scott 89t2

do you have any other mods? exhuast? intake etc?

pushing past 8psi on the stock intake / TID / precats is not smart. you are just causing alot more pressure and heat in the engine. as well as not making much more power if any.

only put your pump in for now. then buy yourself a downpipe / mide pipe. and and intake. and see where your boost is. don't go over 10-11 on the stock injectors. now stick your injectors in. and put the boost up to 12psi or so.

you are really gona want a S-afc as you will run too rich off boost and while cruising. and maybe still too rich at WOT losing power.

NZConvertible

Actully, 10psi is considered the safe limit and is run by many people with no probs.
Nope, it's the pump that needs replacing well before the injectors. If you keep the stock turbo and run it at sensible levels, you do not need to upgrade the injectors. They can flow enough for ~300hp if they have the correct pressure and control.
The S-AFC is a good idea even if you don't upgrade the injectors because you can effectively tune the ECU to your mods.

ViRuS

I have a full HKS turbo back, 2.5' Dp, Mp, 2' catback
Bonez Intake
Racing Beat FCD
HKS Boost controller

So you think just the fuel pump would be a good idea?

So Since I have the injectors should I drop them in anyway and tune the s-afc to that? Or should I just leave them out and run the stocks inj. and the better pump for the 10 psi. I would have more options with the S-afc and the 720cc's though wouldnt I?

I can run well over that amount of boost but I didnt want to and never have run more than 8psi on the stock fuel pump and injectors. I have replaced the secondaries once before. (while running 8psi)

So the stock ecu will send more fuel on 720cc. I was hoping that maybe they would just work at a lower duty cycle, like 70% or something and not have the injectors working so hard. Thanx again!

NZConvertible

Definitely put the pump in, that's not optional.
Have you car dyno'd to check what the mixtures are with the boost you want to run. If they're fine then you don't need the injectors. There are downsides to installing larger secondaries (like the stumble at changeover that the S-AFC is not sophisticated enough to smooth out) so they should only be put in if the stock injectors aren't enough (unlikely).
Are you planning a turbo upgrade soon? If not you don't need the injectors. You can always put them in later. If you can afford it get the S-AFC now. It'll let you tune the mixtures to suit the mods you have and the boost you're running. You'll probably find you'll be able to safely lean out some areas and gain power as a result.
It doesn't work like that. The ECU has no idea what size the injectors are so it will continue to operate as before. This means those 720's will be injecting 30% more fuel than the stock 550's.

Also, duty cycle is not fixed, it constantly varies. Injector pulsewidth is determined by rpm, airflow, coolant temp, etc; and duty cycle is that pulsewidth divided by the engine cycle duration.

ViRuS

I'll drop the pump in then and hold off on installing the injectors. The car will be on the dyno on the 24th of this month. So I'll see how the mixture is. Thanx for all your help.

ViRuS

How does the F-con compare to the S-afc? Would that get the job done?

liquidferrum

Dvls-7 do you have any cats, and how do you not get pulled over for shooting flames