Ross, you should become a teacher or something :y:

lol, i wouldn't mind it if there wasn't so much red tape nowadays with teaching - i'll stick to finance for the time being :hug:

for sure - the gti6 injectors are rated at 265cc but Sandy has measured them as equivalent to around 300cc ish. As a result of this I'll use a mid point for the workings (283cc) and do it at 3Bar fuel pressure. He did note that they have a nice spray pattern.

Boost
283cc = (Max BHP x 5.6) / 4
which gives Max bhp = 202hp

BUT ideally at that BHP, you'd have 350cc injectors at 80%duty cycle

NA
283cc = (Max BHP x 4.6) / 4
which gives max bhp = 246bhp

BUT ideally at that BHP, you'd have 350cc injectors at 80%duty cycle

Desired Injector sizes will change depending on your injection type - sequential etc too

You really don't want a large conical spray pattern if your using a 8v head. Your afr will be all over the place as fuel collects on the port walls and de-atomises.
The reason carbs are so unpredictable

also some 172/182 injectors are not what stated... had my test and cleaned and was only 244cc!!! :S

what would they be at 3.5 bar for boost, its what ive got in mine at the min so need to know how far they can go before there know good

Injector Static Flow = ((theoretical flow (from above formula)) x 100) / (Number of injectors per cylinder x Desired Duty Cycle)

and then plug the injector static flow back into my equations above for NA and boost.

just bookmarking.

I'm with Andysaxouk, we watched them test some "283" cc injectors and they were found massively wanting

Andy

very complicated to spec injectors exactly --apart from the fact that different companies test their injectors with different viscosity fluids --which will make a big difference in what the quoted size is .

the formulae quoted above must always be taken as a guide --not gospel ,the way your head burns the fuel --ie how it scavenges will make a differnce as will alot of other things ,and once you start adding accel fuelling in as well ,and how rich you want to run the engine --it all makes it a bit hard to use any formulae as gospel ..
rasing fuel pressure will also have a big effect not only on flow but of the atomisation ,especially at low engine powers. clio 182 --does notsuprise me at all that the injectors are not as big as some think --
smaller they can run the better it will be for emissions at low rpms .changing from 3 bar to a 4.5 bar reg will usually give you another 12-15% --but again this is only a rough guide

On an NA clio they are usually swapped out when venturing past 200bhp, so that is a good indication of their limit.

and that will not be at high rpm --duration window gets smaller as rpm increases

Sorry to pull this up John, but I'm rather interested in the the effect of increasing the fuel pressure in terms of increasing efficiency - as I'm guessing there would be better atomisation with increasing exit velocity (through an increase in fuel pressure). My worry is that it will run rich in open loop conditions (idle is my biggest concern for MOT emission regs). You mention 'will usually give you another 12-15%', is that power I'm assuming?

I've got standard injectors, and the usual intake and and exhaust modifications so I know that increasing the fuel pressure would be overkill in my case if I'm pursuing hp although I'm not thinking of it increasing it to even 4 bar - is it viable or am I barking up the wrong tree?

Cheers,

Ads

In regards to increased fuel pressure and atomization this is an interesting read on the effects in an inlet manifold

http://pdfserve.informaworld.com/57444__778649592.pdf

If a little brain ache inducing!

link doesn't work dude!

a std ecu is in closed loop control at most times except for certain conditions decided by the ecu designer ,
std vts ecu is in closed loop at everything but fullthrottle up to around 4k ,after that it is open loop from around 70% --these are not exact figures -but your worry about raising fuel pressure and mot is unfounded ,the std ecu is adpative and will correct quite happily when using a 4.5 bar reg ,but yes it will make it richer on WOT.
I,m not sure what you are trying to achieve ,but if by effiency you mean economy ,then there is a lot more to it than making car run lean .
a stand alone ecu with full w/band will allow yopu to decide where it is controlled and allow you to decide at what lambda level you run at at any given throttle /load setting .
economy + emission are not the same lambda level for cruise --

too deep a subject for a full reply

Thanks John,

ok so (and there is a sale in it for you depending on what you say but I'd like your honest opinion), based on what you're saying, a 4.5 bar fpr on my engine, standard internals, induction kit and lower restriction exhaust, will be fine - but what about 70%-T to WO-T how rich are we talking? too rich and kill the top end? or is there top end power gains to be had? Although it's not my priority (see below).


You're correct about my desire to improve the economy when I was referring to efficiency. but I wasn't referring to running the car leaner at part throttle or any other running condition. I'm referring to better atomisation of the fuel, through a higher fuel exit velocity at the injector that would occur with a higher fuel pressure.

So essentially I'm after a better burn from a fixed amount of fuel - which would be the case if we're at part throttle, closed loop, but comparing a standard fpr (3 bar isn't it?) to a 4.5 fpr. The system with the 4.5 FP will have a shorter injector pulse duration - which means the fuel has to exit the injector with a higher velocity to ensure the correct mass flow (to maintain the ECU's required AFR).

If the gains are negligible, or there is something I've overlooked which means it'll scupper ecomony then don't worry. If the gains are minimal but there are gains to be had, then I'm interested.

Thanks!

Ads

you can get gains but not by using std ecu +narrow band --you are stuck with the preset lambda values .
std ecu runs WOT too rich to be honest -
it is quite normal for customers to remark on the better economy after having fitted t/bodies --when cruising back home --thats because we have better control of fuelling than the std ecu .
you can run 16-1 or 17-1 on LIGHT cruise ,but NOX levels rise --thats why 14.7 is lambda 1 and what std cars are set to--for emission regs

cheers man I'll have a read of it now :)

Thanks again John, really appreciate your thoughts. So you're saying even with the standard FPR and ECU that the AFR is still too rich at WOT? blimey.

Yeah I forgot about the rising NOx for leaner conditions! There's a graph somewhere showing the variation of HC's, COx, NOx with AFR which is interesting. Ta!