[ChrisS]

FWIW, I'd say yes and yes. As long as the flow rates really are identical at the same fuel pressure then no problem. As it's a closed loop system at idle, any small variations in injector response time (if any) shouldn't be an issue as the ECU can adjust as required. As injector duty cycle increases, any small differences in response time become pretty unimportant for a 'normal' engine. Can't comment on any potential differences in flow vs. battery voltage for the two types though - this data tends to be hard to come by. Probably almost identical but could just possibly be quite different.

Suck it and see - not likely to do any harm.

 

[QuadrifoglioSCG]

FWIW, I'd say yes and yes. As long as the flow rates really are identical at the same fuel pressure then no problem. As it's a closed loop system at idle, any small variations in injector response time (if any) shouldn't be an issue as the ECU can adjust as required. As injector duty cycle increases, any small differences in response time become pretty unimportant for a 'normal' engine. Can't comment on any potential differences in flow vs. battery voltage for the two types though - this data tends to be hard to come by. Probably almost identical but could just possibly be quite different.

Suck it and see - not likely to do any harm.

Fuel pressure in Q4 is 3bar but in Fiat Coupe it is maxed at 2,5bar at pressure regulator...

I'm afraid because there is possibility to burn my ECU, right?

 

[ChrisS]

QF,

Nope - ECU will be fine. The important parameter as far as the ECU is concerned is the injector impedance, which you have confirmed is the same at about 14 ohm. There are basically two types - so-called high impedance at 12-14 Ohm and low impedance around 2 Ohm IIRC. You couldn't use lows in place of highs unless the ECU used PWM drives, which is unlikely. Using highs instead of low might work, but worst case wouldn't involve any damage - it might just run lean (or more likely not at all) as the ECU wouldn't be able to open the injector properly or at all.

So, basically, the injectors you have won't cause any problems to the ECU. The important thing about the flow rates is that they are the same at the same pressure, so you can make a direct comparison. It is possible to recalculate flow for different pressures, but the formula isn't totally accurate. The fact that the Coupe runs a maximum of 2.5 bar and the Q4 3 bar isn't important in this case.

..and I forgot to mention...the 4 nozzle injectors do indeed give better atomisation of the fuel. Most of the superbikes use this type I think.

Hope this helps. I'm no expert, but have picked up some basic knowledge from the people who do know, while fiddling about with aftermarket engine management systems.

Cheers

 

[QuadrifoglioSCG]

thanks chris
things are now clearer to me IW158's are going in

cheers

 

[Humour]

Chris,

in your opinion, do you think this is a worthwhile mod for a NA Twinny, or a waste of space due to lack of forced induction?

Hum

 

[ChrisS]

Well, I wouldn't expect to see any big difference in performance to be honest if you swapped a set of good injectors for another with the same flow rate but better spary pattern. There might be a tiny reduction in consumption and emissions but I doubt it'll make any more power as there are no other mods. I kind of assumed QF had a reason other than performance for doing this - maybe there is a problem with the older injectors?

The only way a change in injector is going to do anything significant for power is if you are running at the limit of what a certain set can provide and you are having to limit boost as a consequence. If a nat asp. motor is running short of injector flow you really are in trouble! All you could do there I suppose is limit revs until you can sort it out.

So, for a nat asp. twinny it would not be worth doing (unless the original injectors were FUBARed)....in which case any injector with the same spec as the originals would do fine to restore the original performance.

Main thing to remember is that the engine only needs as much fuel as it can use...and this is determined by how much air you can get into it. Pouring more fuel in won't do a whole lot for power. Check out the comments about the e-bay special power boost resistors in the back of this months PPC mag!...and check out next months issue as Dave Walker is starting a new series about engine managment. Now there is a real expert with masses of real-world experience.

An example. A car I was involved with recently - twin turbo 12V V6 164 motor. At 12psi of boost, it ran a maximum duty cycle on the injectors of IIRC 92%. Pretty much all the experts will say that much over 85% and you need to look at changing for bigger injectors or upping the fuel pressure. Later development on this motor will mean some bigger injectors than it has now, and ECU boost control. At the moment, it's running simple actuator set boost limiting. Somewhat by chance, it turned out to be almost perfectly 'matched' in terms of boost and available fuel flow. It would have been quite feasible to have had more boost than the injectors could have supplied fuel for (which would have been a problem), or more fuel than it could have used, had the injectors been bigger (which wouldn't be an issue as the mapping would just have opened them for a shorter period).

But don't forget what I said, I'm no expert!! This is just stuff I have picked up from the real experts and I think I have got it straight in my head

Cheers.

 

[QuadrifoglioSCG]

well old ones need cleaning and checking and those IW158 are brand new so i decided to pop them in lower consumption is always welcome but not priority

Chris are you saying that if i lift boost for let's say 0,2bar ECU will add more fuel automaticaly?

 

[ChrisS]

well old ones need cleaning and checking and those IW158 are brand new so i decided to pop them in lower consumption is always welcome but not priority

Chris are you saying that if i lift boost for let's say 0,2bar ECU will add more fuel automaticaly?

A perfect reason to swap them!! Be interested to see if you get any measurable improvment in consumption.

I'd not dare comment on your ECU/engien setup without knowing more (something!) about it.

Winding up the boost is of course the 'simple' way to get more power and is usually the first step. Great long list of caveats though of course...and I'm REALLY no expert on turbo cars - just happened to get involved with one.

I'm sure there are folk out there who can give you a definitive answer on this. If I had to guess, I'd say you'll probably be OK...but don't quote me!! If it was me doing it, I'd make sure I could monitor lambda and maybe EGT while I was doing it I think.

The guy who was mapping the twin-turbo V6 was making sure to put plenty of excess fuel in at higher boost levels to help prevent detontation.

A mate of mine who had a very similar V6 motor melted both turbos, and the exhaust manifolds, by winding up boost beyond the point that his fuel system (injectors and fuel pumps) could handle. The ECU was asking for more but it just wasn't there. I don't remember if he trashed the pistons as well but I'd think he would have been lucky not to. This was on a system that didn't have ECU controlled boost, just a bleed valve, so the ECU had no way to control what was going on.

Take care!

 

[ChrisS]

There is a fascinating thread on turbos etc on the Westfield forum at the moment. Describes perfectly why winding up boost beyond a certain point (set by numerous factors) isn't actually a good idea. It can lead to LESS power and a greater chance of detonation. Also helps to de-bunk all the Max Powa type claims too......

 

[QuadrifoglioSCG]

can you provide me with link to that forum?
thanks

cheers

 

[ChrisS]

Here it is...

http://boardroom.wscc.co.uk/cgi-bin/ikonboard.cgi?;act=ST;f=3;t=33665

It starts to get interesting about half way down page 1.......as soon as people start producing graphs & tables of real data, that's when it gets really good! Some good general principles to be had though.

 

[Jarkko.Männistö]

is the 384cc really the original injector size of 155 Q4 Alfa ?

 

[QuadrifoglioSCG]

is the 384cc really the original injector size of 155 Q4 Alfa ?

yes they are 384cc

Weber IW058 (beige)

 

[Jarkko.Männistö]

thanks.....