Better charge cooling by moving injectors?

[ShadowFromHell]

Lately I've really been wanting to build a V8 turbo car but the budget won't allow it so I just read lots of build threads and drool lol.

But I've noticed something. The guys running blow through carbs, especially the guys running E85 are able to get away without a IC at much higher boost levels then the EFI guys. The theory is that since the fuel hangs out in the runners much longer then a EFI setup. That allows the fuel to pull way more heat out of the charge. This has been proven with data logging. Even the guys running pump gas get this same effect, just not as drastic.

So this got me thinking, if a guy moved his injectors to the plenum side of the runner instead of the head side could we see similar gains? Or at least some sort of gain over the traditional right at the head injector placement? Anyone know why injectors are always placed right at the head? I'm not the smartest guy and there are plenty of guys who have been messing with turbo cars much longer then me and that makes me think there is a reason I haven't seen anyone do this.

Thoughts guys?

[jonnymopar]

While I don't know for sure, my thought was always low-speed efficiency and here's why: when the engine is revving higher, there's more air velocity to carry that fuel in. At lower revs, you don't have as much air movement to carry the fuel into the combustion chamber, so not only are the injectors located near the head, they're also angled toward the port as much as possible.

I'd love to know if that's actually why.

[c2xejk]

I believe F1 cars had the injector at the top of the runner. I have seen video of the injector spraying into a carbon fiber intake trumpet.

Much of the placement of injectors is more about emissions than power. With the injector close to the head, there is less lag for the pulse of fuel entering the cylinder.

Worth noting that moving to direct injection has allowed many turbo cars to get away with 87 octane fuel.

[Force Fed Mopar]

Couple of the Engine Masters challenge engines have used injector placement waaay up the runners, some at the top of a tunnel ram type intake.

Besides having more time to cool the charge, it also has more time to mix with the air, giving a more complete atomization.

[going4speed]

Injector timing would need to change to account for fuel transit time though right?

[GLHNSLHT2]

Wet intakes flow worse than dry intakes. Get a better intercooler vs moving the injector. As far as F1 engines go when you're talking about 20k+rpms and an idle of 5k rpms you really need to have a whole hell of a lot of fuel and you don't have time to turn injectors on and off so you just turn them on and let them flow.

[jonnymopar]

Worth noting that moving to direct injection has allowed many turbo cars to get away with 87 octane fuel.

Kia Optima: 274hp out of a factory-tuned 2.0L partially thanks to this.

[contraption22]

Kia Optima: 274hp out of a factory-tuned 2.0L partially thanks to this.

Agreed. Mom's Ford Ecoboost has high compression on top of boost. When the fuel is injected into the combustion chamber at just the right moment, there is no worry about preignition. However, it's still better to have a cooler intake charge to get the most oxygen into the CC.

[c2xejk]

Injector timing would need to change to account for fuel transit time though right?

Yes, especially if you are doing complicated things to meet modern emissions...

Wet intakes flow worse than dry intakes. Get a better intercooler vs moving the injector.

??? Wet intakes do need to account for fuel volume displacing air volume, but I am not sure why they would flow worse. The design needs to deal with fuel not falling out of suspension and make sure that all cylinders are being properly fueled, but that doesn't necessarily mean they flow worse.

As far as F1 engines go when you're talking about 20k+rpms and an idle of 5k rpms you really need to have a whole hell of a lot of fuel and you don't have time to turn injectors on and off so you just turn them on and let them flow.

They still need to control the fueling of the engine, so they can't just turn them on without a secondary method of controlling fueling. My point is that they did fuel them way up top and likely did it for performance reasons...

[johnl]

Most high-performance fuel injected motorcycle engines use a shower injector that is placed high in the air box above the intake trumpets and which is switched on as the engine rises toward maximum power.

I imagine that the sole purpose of that design is to cool the intake charge. I say that because they don't need that 5th shower injector to add fuel, they already could add that extra fuel by way of the existing four injectors

So, yes I agree that moving the injectors farther up the port would enhance cooling the intake charge but I have ask, why not just add a 5th injector, instead? After all, Gus Mahon did it