Hello, I was wondering if any one is running GSL-SE 680cc injectors in their T2? can you run them in your primary with out running to rich, or having a idle problem? I came across some and picked them up. I have a 87 T2 (early model) stock computer and just your basic upgrades, also is the Walboro 255lph the best fuel pump to run for more fuel? thanks

 

Plenty of people run uprated injectors, but no, you can't just throw them in. You need a fuel computer to tune them or you'll just run stupidly rich. Also if you're only doing two then you'd put them in the secondary position, not primary.
The stock 550cc/min injectors can support ~300hp as long as fuel pressure is maintained. If you're not near that (sounds like you aren't), then there's really no need to change injectors. Definitely upgrade the fuel pump if you plan more mods. The fuel pump runs out of capacity before the injectors do.

 

That pump is a damn good one. I have the HP model and my car is running dog rich right now. I need to get the haltech in and actually lean the thing out.

 

I was lead to believe the reason for upgrading to 680cc's (GSL-SE's) in your secondaries was to mechanically trick the computer into delivering more fuel if ur running more then stock boost, just to be safe about things and prevent ur motor from leaning out. If you're still running stock boost there's no need for them.

 

Are sure about that? where did you get your # from? I have heard 250-260, which seems more reasonable.

 

I think hes basing that on BSFC and other factors which show the injectors have a max capacity of 320hp at 100% cycle. If you factor in 80% duty cycle that hp figure becomes approx. 250.

 

Yes the 550's may be able to run up to 300hp but how high a boost
are they safe running to with the stock computer even with
the upgraded fuel pump the stock computer never
runs that high a duty cycle.
I think the idea of the 680 cc secondaries would give
the extra fuel needed without changing the stock computer.
they might run rich when they first come on line, but once
higher boost levels and higher rpm are reached, this is
where you would see the larger injectors help? now a safc would help
with the rich condition to start with but is it needed?

matt

 

This is a really crude method of doing this, that'll result in overly rich mixtures and a drop in power as a result. Higher boost means higher airflow, which is measured by the AFM and compensated for by the ECU up to a point. But before you reach the point where the ECU can't keep up, the fuel pump runs out of capacity. High boost lean-outs on stock fuel systems are the fault of the pump, not the injectors. If you throw bigger injectors in with a standard pump, you're still going to run out of fuel because the pump can't keep up.
Once you have the pump, a fuel computer is a really good idea, so you can tune the rich factory mixtures for a bit more power. Doing this on a dyno means you can see what areas this can be done in safely and which can't. You need a lot of boost to reach 300hp on the stock turbo, far too much in fact. So if you're still using the stock turbo, it's unlikely you need to touch the injectors.
If you still really think you need to change them, spend the money on a dyno run to see what the mixtures actually are, instead of just assuming they're lean and over-fuelling your engine.

 

Many tuners use a figure of 8cc/min of fuel per kW of power as a safe guide. Note that that's the actual amount of fuel required to be injected.
If an injector is rated at 550cc/min @ 35psi (stock TII), then it will flow enough fuel for 550/8 = 69kW (~92hp) if and only if it has 35psi behind it. So four of them held fully open could flow enough fuel for 369hp. 80% duty cycle is considered a safe maximum, so 295hp is their safe limit.
Fuel rail pressure is what's vital here. If your pump cannot maintain pressure, fuel flow will drop no matter how big the injectors are.