Has anyone tried this, I have a spare fuel rail and injectors lying around and have been toying with the idea for a while. From what I can gather the emerald has the facility to drive the extra injectors and they would only be used at load sites 13-15 and speed sites above 5500rpm, thereby reducing the risk of having fuel dropping out of the airstream.
Is there a benefit of around 5% to be had at the top or is really not worth the effort of extra plumbing and wiring. My thinking is that with the extra 200mm of intake length I have added there should be some benefit.
The extra intake length would give a benefit on low-midrange their own(at the expense of top end), but the dual injectors won’t.
Some time ago somebody (I think it was Steve Butts) experimented with a dual injector setup as you mentioned and there was no benefit.
In hindsight it’s no surprise, if your fuelling is already correct with the single injector, why would you benefit from more fuel?
I’d say you have to look at it logically.
Maybe the injectors you need to run at low and mid range are too small for the top end and the ones that would give a good top end would be too unprecise for the bottom end.
In that case, you’d benefit from both.
Some time ago Ducati started playing with the dual injector far away from the bellmouth on their race bikes successfully, even their road bikes have it now, because they discovered that at high rpm the location of the one that would give good bottom and mid range was too near the valve, and they discovered they got a much better mix when the injector was far away (actually about 10 cm outside of the trumpet ). Probably good for 2-3 horses and better linear delivery somewhere in the range.
My point is that if you’re going to play with it, configure it in such a way that you’ll get the benefit from both.
And once you develop the brackets for outside the trumpets, maybe I can buy a set off you
Good mate of mine who is a Ducati mechanic was around this weekend and he suggested the same, injectors have to be way out of bell mouth to be of any benefit and not hamper air flow at all other times. Have to agree that a real benefit would be had if injectors were so large that they could not fuel very well at the bottom, then you could run smaller injectors and have finer control over fueling. But it is not the case with my current setup, would only be looking at getting some extra power at the top, but it would have to be around 5% to warrant the setup and fabricating involved.
Have a cunning plan for mounting them though which should work quite well and retain the std airbox.
But if your current Air/Fuel ratio is correct, there is nothing to be gained by enrichening the mixture, you’ll lose power then.
And if your injectors are below 95% duty cycle (meaning, not really stressed or staying open most of the time) they can still provide more fuel if needed.
So, in your case, I don’t see how can you have any extra gains
Uldis you’re missing the point of using extra injectors.
Broadly speaking, injectors placed very close to the head are good for low down torque, and those placed a distance from the head are better for top end.
When my induction length was jenveyDTBs+50mm trumpets (~170mm assuming I’ve correctly remembered the length of the DTHs). I tried an extra bank of injectors into the bellmouths. They gave no benefit - identical power curve but more fuel was required. One thing that my not have helped was the angle I was holding the injectors at, somethign like 30 degrees to the TBs is good (IIRC) but in the experiment I was just holding them by hand into the bellmouths, pretty much parrallel to the TBs. So perhaps nto as scientific as it could have been, but I didn’t want to go to the effort of fabricating brackets to hold the fuel rail unless the first test showed at least a hint of benefit (which it didnt’!).
Dave Walker has seen some good gains on different engine types, some using much longer induction - around 10%.
He thinks it may be worth trying again now that I run longer induction, but I’ve not got around to trying yet.
If you have Exige TBs then the induction is already longer than the length which I was running when I tried the above experiment so you may well get benefit.
Thanks for the reply Steve, the idea is to obtain better mixture at the top, I use long extensions so it might be worth a try once the new motor is up and running. Ideal is to haveinjectors designed to be run outside the bell mouth, like they use on the bikes and also to have them firing exactly in the middle of the trumpet. Would have been keen to have given it a go, but no sense in murdering this motor on the dyno while trying to perfect it. I propably would have done the same initially using my old injectors and not seen a gain worth pursuing.
I am sure there are gains to be had, perhaps not huge but when you are trying to get those last few hp out of an engine, propably worth it.
Be aware that over trumpet injectors can create quick favourable conditions for airbox fires to take hold. This isn’t a problem if you are sensible with location / direction and carefully map it but it’s worth being aware of. The other (more minor) thing is that transient fuelling can sometimes be a bit trickier.
At the 200+bhp level a gain of 5% for the price of a set of injectors is very cheap
A friend (Guy Evans) built a 2.3 duratec for his race Elise and took advice from an engine building friend at Cosworth who mentioned it was critical to get the angle of the injectors correct.
Maybe some research into this is worthwhile, perhaps fabricating injector rail mounts to allow for some adjustability.
You may get some even cheaper gains by just playing with trumpet lengths. EG I picked up 7bhp on my engine by swapping from four trumpets of the same length to unequal length ones…and if you’re familiar with bike engines, you’ll probably know that as standard the hedgeabuser uses unequal trumpet lengths.