Dual fuel injectors per throttle bore

Yves · Post by **Yves** » Tue Mar 04, 2008 11:22 am

I have ordered my efi-electronical system this weekend, so now i'm tackling the putting together part of it.

Since I will be running ITB's and since i don't really trust the original position of the injector after the throttle blade (t.i. 90Ã‚Â° into the airstream) I would want to fit a second injector in the airhorn so above the throttle and maybe divide the amount of fuel injected between these two injectors.
Is this a good idea at all ?

Secondly : any idea where i could get a fuel rail to mount the injectors outside the manifold ?

Thanks

devastator · Post by **devastator** » Tue Mar 04, 2008 11:38 am

Do you plan to use the original injectors still, or are you looking to replace them all together?

fury fan · Post by **fury fan** » Tue Mar 04, 2008 12:50 pm

Depending on your configuration, this might help, regardless it's just a good site to browse:
http://www.rossmachineracing.com/dualinjassm.html

As for adding an injector:
I'll mention upfront that I have not done an EFI conversion yet but I have done lots of research. I would not recommend adding a 2nd injector just because of the 90Ã‚Â° of the OEM location. The added injectors will be squirting on a throttle blade (similiar to OEM TBI) and that is not ideal either.

With 2 injectors you now have more plumbing, more wiring, and more components -- more items to adjust and tune, especially with ITBs. I'd recommend keeping your system as simple as possible.

devastator · Post by **devastator** » Thu Mar 06, 2008 5:51 am

I agree with Fury Fan on this. Adding an injector only confuses things, unless you need one for added fuel or alky injection on a Turbo'd engine. I'm assuming that's not your situation though, as you are going TBI to start with.

Yves · Post by **Yves** » Thu Mar 06, 2008 10:13 am

Not a turbo and not and TBI either it's a real itb (8)

devastator · Post by **devastator** » Fri Mar 07, 2008 9:07 am

itb?

fury fan · Post by **fury fan** » Fri Mar 07, 2008 10:41 am

Individual Throttle Body (or maybe independent throttle body?)...
Usually suggests motorcycle TBs mounted on a car engine (or on a motorcycle, of course!).

devastator · Post by **devastator** » Fri Mar 07, 2008 11:32 am

Ohhhhhh. Thanks. That makes a lot more sense than any words I attached to those letters.

pstrbrc · Post by **pstrbrc** » Wed Mar 12, 2008 7:10 pm

Just as an aside, an injector upstream of a throttle plate actually reduces the potential flow through that throttle bore significantly. I don't have the numbers in front of me right now, but this would be a really good reason not to put an injector where you're talking about.

chicksdigwagons · Post by **chicksdigwagons** » Wed Mar 19, 2008 1:09 pm

Thats an interesting point that I have never considered...

rug · Post by **rug** » Mon Mar 31, 2008 1:33 pm

I found this in another forum. This guy merges the secondary injectors in the airhorns over 4800 RPM.

/Carl

devastator · Post by **devastator** » Mon Mar 31, 2008 3:23 pm

Interesting. What's he spraying with the second injectors? Alcohol, water, fuel? Just curious.

rug · Post by **rug** » Wed Apr 02, 2008 5:00 am

devastator wrote:Interesting. What's he spraying with the second injectors? Alcohol, water, fuel? Just curious.

Fuel. They start spraying at 4800 rpm and merges out the ones near the head. Found this on www.jenvey.co.uk site:

Where is the best place for the injectors?
Where one injector is to be used per cylinder the best compromise position is immediately downstream of the butterfly. This gains maximum advantage from local turbulence and gives results surprisingly close to the optimum at both ends of the rev-range. This is the recommended position for most applications
For performance at low RPM, economy and low emissions the injector needs to be close to the valve and firing at the back of the valve head. This is the favoured position for production vehicles.
For higher RPM (very approximately 8,000+) the injector needs to be near the intake end of the induction tract to give adequate mixing time and opportunity. The higher the RPM, the further upstream the injector needs to be. As a result, use of speeds above approximately 11,000 RPM may give best results with the injector mounted outside the inlet tract altogether (see our remote injector mounting). It is common to fit both lower and upper injectors in such a system to cover starting and low RPM as well as high speeds.

So he is getting the best of both worlds

And since they do it on F1 cars, it is probably a good way to do it

http://www.youtube.com/watch?v=o_QyUD6V5_I

/Carl

gon · Post by **gon** » Wed Apr 02, 2008 2:12 pm

I'm about to do that as well , I'm just a bit worried with timing ....
since ms only has 2 injector banks , I'm setting the first set in the head with batch fire and the second on the outside of the trompets also as batch .
but i have read somewhere that on the outside each injector has to be fired on the intake stroke of that cylinder or "fuel fog" will appear ......
MS can't do this ....
will the fog just be sucked in the next intake cycle and no harm done ?

what do you think ?

sorry if it is a bit off topic