Injector location: in head or ITB?

[JohnCh]

Thanks repsna.

Some very sophisticated race engines run two injectors per cylinder to gain a little top end advantage from having a injector mounted high in the manifold.

CarlB, somehow I missed your earlier reply. I didn't want to muddy this conversation from the outset by bringing up that option, but it is something I'm considering and was the impetus for my initial post. If people with real world experience had said they found a benefit at the top end from moving the injector to the TB, but there was a noticeable change to the drivability around town, then I was planning to go the dual injector route. Yes, it would be overkill for my setup, but sometimes I like overkill. Also, there is a chance I may have a new engine loom made, so I this could be done as part of that process.

Thanks,
John

[Bent Wrench]

Another thing happens when fuel is introduced up stream, it changes the weight of the air, this also effectively changes the tuned length of the runner

[JohnCh]

Thanks, I hadn't considered the increase mass for that 4" column of air and how that could impact pulse tuning. Without doing the math (any volunteers?) it doesn't seem like it would alter the effective length of the runner a significant amount. By any chance have you played around with this on a dyno and have any numbers you could share?

Thanks,
John

[Bent Wrench]

The way I saw it done was on a constant flow injection setup.
They ran a spring loaded check valve that opened up when the RPM got high enough (fuel pressure high enough)
The check valve supplied injectors located at the mouth of the stacks.
So they did nothing until the RPM drove the fuel pressure high enough then sprayed in the top of the stacks.
With electronics you can do it lots of different ways.



The gold cylinder is the check valve and it is tee'd into the main fuel feed The 4 hoses go into the air filter for the upstream nozzles.
That is a custom built slide throttle valve.

[CarlB]

I think there are a couple of things going on. The weight is a issue, but the bigger issue is vaporizing the fuel. The fuel has to vaporize to burn. I would also say I wouldn't think it would be worth the effort. The benefit is at high RPM.

[hoefi]

I am running a set of Jenveys with the injectors in the TBs. Biggest problem is large change in air fuel ratio as the TBs get heat soaked. It would idle at 14:1 and lean out to 18:1 when it's heat soaked. Had to run closed loop to stabilize idle and low throttle opening driving. If I had injector bosses in the manifold close to the head, I would prefer to run my injectors there, unless it's a dedicated race motor.

[JohnCh]

I haven't come across that issue before in my research. Is it possible the lean running is due to the engine ingesting hot air, rather than injector location?

Thanks,
John

[papak]

My fueling inconsistencies pretty much went away when I fabricated a cold air intake (ahead of the radiator through a foam filter). Intake air temp becomes much less of an issue.

[hoefi]

I haven't come across that issue before in my research. Is it possible the lean running is due to the engine ingesting hot air, rather than injector location?

Thanks,
John

Unless the owner is doing the tuning himself, review the data log, and actually report the findings on public forums, observation like this is not easily available. If the tuner turns on the closed-loop and have enough enrichment, the driver might not notice any difficulties in idle or driving.

I tuned my own engine when I switched to the Jenveys and I installed an A/F ratio on the dash for observation and data log. I typically run open loop on my other race cars because of leaded racing fuel. So for this street motor, I tried opened loop in an attempt to get the fuel map dialled in as close to optimal as possible. When I ran it on the streets in traffic, I noticed the large swing in AF ratio from heat soak. It would take a bit of running time with more throttle with less, or no traffic, to drop the temperature of the TB enough to get the idle AF ratio back to normal. Running closed lop with high enough enrichment would overcome the problem. But since it typically always goes lean right after dropped throttle, closed loop would dump a bunch of fuel in when it's not really needed. If the injectors are inside the head, the AF ratio swing is a lot less drastic and that's why stock set up from the factory usually place them close to the head. I reckon if I could move my injectors to the stock location, I could get away with no more than 5-10% enrichment with a good base fuel map. Probably slightly better fuel milage and better emission as a result. Part of the over-rich problem during dropped throttle could be tuned out if the fuel injection controller has a deceleration fuel cut feature, but it will depend on how sophisticated the software is, and the willingness of the tuner in spending the time in perfecting it.

[fastg]

I stumbled across this video on YouTube and remembered this post. I little talkative but a lot of information.

https://www.youtube.com/watch?v=dQZXqbgQyTY

Move those injectors

Graham