After reading through the gas vs. Alcohol thread I have a few questions about down nozzle injection systems for those that have experience. The only two areas that this injection system is common is in sprint cars and NA pulling applications, why is this? What are the advantages/disadvantages? If it's a better system why isn't it more common in other racing applications? I've been a puller my whole racing career and it's been around forever, I know people spend a lot of time and money to modify heads to build this system what's the reason behind this? I know most systems run 16 injectors, they run 8 up top to cool the intake charge and then 8 pointing at the back of the intake valve? Just wondering what I'm missing out on by running gas carburetors?
Half Breed
Like all mechanical injection systems, it's good at idle and good at WOT.... anything in between those 2 is not so good.
It makes power on methanol because it gets most of the fuel charge out of the air flow for 95% of the port length.
Will
It makes power on methanol because it gets most of the fuel charge out of the air flow for 95% of the port length.
Will
The most basic answer is-for a one man show like me-it's 1000 times easier washing the car after the races if the injection doesn't have baked on mud covering the whole thing. The dirt & dust goes to that condensation like a magnet, and then cooks in place after you shut off the engine!
I have to disagree with this statement. From my experience they are actually a little more drivable than a carbureted engine that is build for upperend horsepower. I think the reason behind this is it is forcing the fuel in rather than relying on vacuum to pull fuel in.
The whole reason for the question is there has to be a reason people are spending so much time and money to modify heads to use this type of injection, but when I ask for the reasons I never seem to get an answer.
from my understanding it makes more tq due to the cooler air charge you can run more timing thus making more tq, it may not pick up any hp but youll pick up tq every time, this is why a lot of boosted cars run it even when theres a weight penalty because you can make the same hp but youll make big time tq gains in a boosted app.
You guys must have been driving some really fucked up carburetors.
There is no way a constant flow mechanical injections system, that has basically 3 fixed circuits can match the driveability of a properly set up carburetor. At part throttle you stuck with how much fuel which ever spool is in the barrel valve can meter.... You have 3 fixed fuel flow settings.... now way that works as well as something that has literally millions of possible meterings according to vacuum and air flow demand/signal.
I've improved a number of injections that were "ON/OFF" types.... Mostly guys with old used Sprint Car injection stuff using on gasser type street car builds..... They can set up to drive decently - even very acceptable for many things, but seriously they can not match a properly set up carb in this area. Even with high speed lean outs and other intermedieate bypasses there just isn't the same amount of flexibility to adapt to different driving conditions.
Put an AFR logger on one of your perfect driving systems sometime and you'll find out thers lots of holes.
Will
There is no way a constant flow mechanical injections system, that has basically 3 fixed circuits can match the driveability of a properly set up carburetor. At part throttle you stuck with how much fuel which ever spool is in the barrel valve can meter.... You have 3 fixed fuel flow settings.... now way that works as well as something that has literally millions of possible meterings according to vacuum and air flow demand/signal.
I've improved a number of injections that were "ON/OFF" types.... Mostly guys with old used Sprint Car injection stuff using on gasser type street car builds..... They can set up to drive decently - even very acceptable for many things, but seriously they can not match a properly set up carb in this area. Even with high speed lean outs and other intermedieate bypasses there just isn't the same amount of flexibility to adapt to different driving conditions.
Put an AFR logger on one of your perfect driving systems sometime and you'll find out thers lots of holes.
Will
Someone can correct me if I'm wrong, but I always looked at it like cam timing. Was under the impression down nozzles shifted the dyno graphs left a few hundred rpm and up nozzles shifted the graphs right a few hundred rpm. 16 nozzles somewhere in the middle.
Having said that, it seems like the few real high dollar 410 sprint cars I've seen lately are turning more rpms but are also moving away from up nozzles or 16 nozzles. So figure that out...
Having said that, it seems like the few real high dollar 410 sprint cars I've seen lately are turning more rpms but are also moving away from up nozzles or 16 nozzles. So figure that out...
As for the extra TQ or power from down nozzels....
The airflow through the port is not laden with having to carry any fuel until right above the valve..... There is less resistance in the port because 100% air is lighter than dragging the AF mixture through it. There is less heat because the fuel is injected right at the valve instead of being carried thru the induction system where it picks up residual heat from the cyl heads and inducted heat from the friction of the AF mixture traveling through the induction system.
As for why Sprint cars run them. Because it's rock simple, reliable, light weight and is capable of making the power they need.
Just my thoughts on it.
Will
The airflow through the port is not laden with having to carry any fuel until right above the valve..... There is less resistance in the port because 100% air is lighter than dragging the AF mixture through it. There is less heat because the fuel is injected right at the valve instead of being carried thru the induction system where it picks up residual heat from the cyl heads and inducted heat from the friction of the AF mixture traveling through the induction system.
As for why Sprint cars run them. Because it's rock simple, reliable, light weight and is capable of making the power they need.
Just my thoughts on it.
Will
A sprintcar engine builder told me it was for quicker throttle response, less distance for the fuel to travel when the throttle is snapped open coming on to the straight.
Nozzle height changes the power curve. Different injector and intake setups for different tracks. Sprints and supers can run from a 1/4 mile track to a 3/4 mile track. Sometimes even a mile.
After hearing what each of you has to say about this subject it doesn't seam this setup is worth the time, effort, and money (minus the sprint car thing as the heads are already made to take the down nozzles). How much torque are we talking about gaining (I know this is a loaded question), but lets say percentage wise, 5%? I know on some of these high end pulling builds people are paying $15-18K for one of these systems, I'd need to gain a bunch to justify that...
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