Injector location: in head or ITB?

[JohnCh]

I'm curious if anyone with ITBs has experimented with injector placement? V1 of my Duratec utilized stock internals and cams. At the time, the recommendation was to leave the injectors in the stock factory location in the head. Apparently the fuel spraying on the back of the hot valves promotes lower emissions and better idle/low speed drivability.

 

V3 of the engine has far more aggressive cams with an 8000+ rpm redline. I'm wondering if moving the injectors out to the ports in the ITBs is a better compromise with the current internals? From what I've read, at higher rpm, the extra distance gives the air and fuel more time to atomize, creating a better mixture that burns better, and hence, develops more power. As seen in the photo below, the difference between the two location is about 4 inches.

 

 

The benefits of each location make sense to me, but it's the quantity of difference I'd like to better understand. If it's another 4-5hp at the top end with marginal difference to the low end, then I might give it a try, but if it's 1-2 hp and idle becomes noticeably less happy in traffic, then there's no point. The change will require removing the plugs in the ITBs (I have a feeling that will be a PITA), buying new plugs for the head, a new fuel rail, and doing a little replumbing, so not a quick, simple update.

 

Thanks,

John

[fastg]

I could not find much information but I did find this video, a more extrema movement but little gain. The guy has some interesting videos on velocity stack length changes.

 

[JohnCh]

Thanks for the link, it's a shame he was comparing TB mounts to shower mounts rather than in head, but that one portion of the video showing the fuel spraying down the intake from the shower mount really highlighted the potential improvement at low rpm if the injector is in the head and hitting the hot valve. Jenvey claims that mounting in the TB below the butterfly is the best compromise for a modified engine. If this was a simple switch, I'd just try it.

 

Slightly off topic, but if you are like me and interested in velocity stack length and design, definitely check out this guy's other videos. Very interesting stuff.

 

Thanks,

John

[fastg]

The guy has some very interesting posts, this one about AFR is great.

 

[CarlB]

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. If you look at some of the drag race dyno comparisons between the long runner carburetor manifolds (tunnel ram) and fuel injection with the injectors mounted low and the back of the valve. Typically the carburetors make more power but the fuel injection has a better power curve. They do not show how well the carburetors control the fuel curve, but I would speculate the fuel injections advantage is in the fuel curve.

[repsna]

Doing fast road only having built 3 engines, Plenum, Roller Barrel, ITB, head injectors are simplier and for usual reving with fast road I think it makes no difference

[JohnCh]

Thanks Repsna, did you run the injectors in either the Roller Barrel or ITB before settling on the head mount?

 

Thanks,

John

[repsna]

on the TBs only for a very short time and after discussion with the engine builder and rolling road mapping professional I decided for the head installation and I am fine. I am not racing. I usually ride for several hrs and rev between 2000 - 4000 when overtaking harsh 6000. Consumption wise my driving style of +- 10l/100km (23 Miles/Gallons). Always teh same be it the 2.1 or 2.5 Duratec with 250 hp or the 2.4 with 260 hp.

[JohnCh]

Thanks. From what I've read, the effect from mounting in the TB is most pronounced over 7000rpm. Not sure if that's accurate, but my engine does rev to 8000+, so if true, there may be benefit for my installation. Did you notice any degradation to idle, low rpm running, or throttle response when the injectors were mounted in the TB?

 

Thanks,

John

[repsna]

cant recall, it was 5 years ago but I remember this was a point from the mapping specialist and one of my considerations. Low RPM was form me more relevant than above 7000

 

BRGDS Hanns Per

 

I still have the fuel rail

[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.

Edited December 22, 2020 by hoefi

[fastg]

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

 

 

Move those injectors:)

 

Graham