Fuel Pressure For Gti6 Injectors In A Xu9j4

[VisaGTi16v 1]

My 1.9 Mi16 XU9J4 is currently putting out 170 ish with its flowed, ported head with Piper cams so the standard injectors are pretty much at their limit bearing in mind they are old and I havent had them out for cleaning in 5 years. I have some good GTi6 injectors which I was thinking of swapping but am aware due to their higher flow rate, the engine will massively over fuel.

 

Mi16 Injectors 214cc/min @ 3 bar (standard rate with stock pressure regulator?)

GTi6 Injectors 265cc/min @ 3 bar

 

So if the GTi6 injectors ran at say 2.6 bar, that would give 230cc/min. Would that sound about the right ball park figures or 2.55 bar giving 225cc/min

 

I presume its simple to do that with an adjustable fuel pressure regulator fitted but is that all that would be needed? It would just run fractionally richer than normal so it shouldnt need anything doing ecu related?

 

cheers

 

Darren

[DrSarty 90 1 Cars]

I can't wait for the 'answer' (you could read: opinion) on this one for two reasons:

 

{i} you may be the first person EVER to buy and fit an adjustable FPR and turn it down from std

 

and (seriously)

 

{ii} for my 2.2 hybrid, I have been assured that the std pump and FPR (on the GTI6 rail admittedly) will be fine for my set-up running complete GTI6 inlet including injectors, and I suspect producing 'a tad' over 200bhp.

 

Plus secretly I'm a geek, and find the whole subject - which is probably as simple as hell and your calculations are bang-on - fascinating

 

Edited January 27, 2008 by DrSarty

[VisaGTi16v 1]

Oh dear it has just occured to me that changing the pressure wouldnt change the flow rate at all so no need for anyone to answer

 

As I am only 170 bhp ish or a bit more the GTi6 injectors are no use to me as I cannot change the ecu to sort the fueling and money would be far better spent on new suspension than a programmable ecu for a bit more power. I will look into finding some that actually flow 225 ish then increase the fuel pressure slightly

 

cheers

[petert 588]

Oh dear it has just occured to me that changing the pressure wouldnt change the flow rate at all so no need for anyone to answer

 

Yes it will. The flow rate is proportional to the square root of the pressure.

 

eg

 

36 psi: sq. root = 6

25 psi: sq. root = 5

 

6/5 = 1.2 (or 20%)

[Sandy 191]

Be careful relying on the quoted flow rates, in reality the GTi6 injectors provide the equivalent fueling of around 300cc/min at 3 bar in my experience. They aren't really practical for a swap. The 0280155216 injectors from the later 406's work well and are 209cc/min.

 

Rich- I have often used 2.5 bar regs as "downgrades" on twin injector set ups, to move the duty switching point down.

[DrSarty 90 1 Cars]

Rich- I have often used 2.5 bar regs as "downgrades" on twin injector set ups, to move the duty switching point down.

 

Very clever stuff.

[VisaGTi16v 1]

Ta Peter/Sandy although confused a bit more heh but no need for me to understand, will just listen to what you say

 

Sandy: So those ones you mention should be ok for my Mi16 giving only a little bit more fuel so not running over rich whilst not being at their limit duty cycle wise all the time? Why is that though if they are 209cc and the mi16 ones are 214cc? Would you recommend bumping up the fuel pressure slightly with them or leaving it as it is

 

cheers