ignorant
ignorant SuperDork
7/17/08 7:27 p.m.

give me a reason any reason... why this is better than direct injection or manifold injection..

http://www.youtube.com/watch?v=GsKNbsDqEPs&feature=related

The only one I can think of is bragging rights...

Seems super ineffecient to have these as your mains. I guess a holdover from the 70's?

neon4891
neon4891 HalfDork
7/17/08 10:58 p.m.

looks like an over-glorified TBI

Strizzo
Strizzo Dork
7/17/08 11:34 p.m.

well, if i could find the pictures from my trip to the bmw assembly plant in south carolina, i'd show you that thats how they did it on the bmw f1 car in 2006, so i'd imagine its worth some ponies

fiat22turbo
fiat22turbo GRM+ Memberand SuperDork
7/18/08 12:27 a.m.

Depending on the spray pattern, it could help get more fuel suspended in the air. Also using them to inject nitrous oxide, methanol, ethanol, water or a mix of the above could help depending on the application.

After looking at the video, those are similar to the ones used in my Fiat (only they are suspended in mid-air)

One of the sets of DCOE throttle bodies I have has two sets of injector bosses, so it isn't unheard of to use multiple sets of injectors and I've read about suspending the injectors above the throttle plate.

ignorant
ignorant SuperDork
7/18/08 6:41 a.m.
fiat22turbo wrote: I've read about suspending the injectors above the throttle plate.

I've seen it..

I don't know why anyone would want to take a step back the evolutionary chain..

RobL
RobL New Reader
7/18/08 7:04 a.m.
ignorant wrote: give me a reason any reason... why this is better than direct injection or manifold injection.. Seems super ineffecient to have these as your mains. I guess a holdover from the 70's?

They are not the mains, the engine would not run with the throttle plates closed.

The why you do this is so that you can use smaller injectors as your mains. Smaller injectors are more easily tuned and are more efficient at lower duty cycles. A 100cc injector at 25% duty cycle has a better spray pattern and consistency than a 500cc at 5%. Once the mains reach some threshold, the secondaries come on and fill the fuel gap.

This is just a little more extreme example of this because of the independent throttle bodies. You need one secondary injector per plate. Usually the secondaries are placed somewhere upstream in the intake.

ignorant
ignorant SuperDork
7/18/08 7:44 a.m.
RobL wrote:
ignorant wrote: give me a reason any reason... why this is better than direct injection or manifold injection.. Seems super ineffecient to have these as your mains. I guess a holdover from the 70's?
They are not the mains, the engine would not run with the throttle plates closed. The why you do this is so that you can use smaller injectors as your mains. Smaller injectors are more easily tuned and are more efficient at lower duty cycles. A 100cc injector at 25% duty cycle has a better spray pattern and consistency than a 500cc at 5%. Once the mains reach some threshold, the secondaries come on and fill the fuel gap. This is just a little more extreme example of this because of the independent throttle bodies. You need one secondary injector per plate. Usually the secondaries are placed somewhere upstream in the intake.

Ok using them as secondaries makes sense... But a plate hanging out in the middle of the air, spraying effectively into open space...

Try to get that through scrutineering.

njansenv
njansenv New Reader
7/18/08 7:48 a.m.

Year's ago, I read an article about this: someone ran a test on an ITB Honda motor with injectors 'in space' and then in the more traditional spot. With the injectors a few inches from the runner opening, significant power was gained. Theory was that the fuel provided significant cooling of the intake charge by evaporation. Ever see a carb ice up on a warm day? Similiar theory, I believe.

Nathan

Dr. Hess
Dr. Hess SuperDork
7/18/08 8:55 a.m.

Billzilla says that stand off injectors work better at high RPM. Look for it on his site: www.billzilla.org. He has (or had) a pic of a F1 Renault or something set up like that.

Esprit SE's have 2 extra injectors mounted up before the airbox, after the chargecooler. The come on with more boost.

MadScientistMatt
MadScientistMatt HalfDork
7/18/08 9:41 a.m.

Yep, they're a second stage of injector that only kicks in at full throttle and high RPM. The idea is to run smaller primary injectors for better control at idle. There isn't much room for the second injectors near the port, but they only fire when airflow is high enough that vaporization is not an issue.

dan_efi
dan_efi New Reader
7/18/08 4:23 p.m.
njansenv wrote: Year's ago, I read an article about this: someone ran a test on an ITB Honda motor with injectors 'in space' and then in the more traditional spot. With the injectors a few inches from the runner opening, significant power was gained. Theory was that the fuel provided significant cooling of the intake charge by evaporation. Ever see a carb ice up on a warm day? Similiar theory, I believe. Nathan

Search Bisimoto on either hondatech or even google. I haven't actually seen the article, but I did meet and talk to Bisi in Pomona October 2007. Asked him about the setup, he explained exactly what you just said. Cool guy.

z31maniac
z31maniac HalfDork
7/18/08 7:01 p.m.

Nearly every sportbike made uses two banks of injectors, with the upper bank coming on at high rpm. As well as some even using variable-length velocity stacks.

ImpishSprite
ImpishSprite New Reader
7/18/08 7:29 p.m.

They aren't hanging out in Free Space, the injectors are ranged to be in the Crux of the Intake Aircharge's flow point.

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