128SL Coupé winter project

It may also be to create a cooler mixture since the fuel has more time to expand than a port injector near the intake valve.
I believe you're right. Cool the intake charge. I wonder if it would be possible to have two sets of injectors? One set in the ordinary position, and the other in the location shown for use as the throttle position is increased?
 
I believe you're right. Cool the intake charge. I wonder if it would be possible to have two sets of injectors? One set in the ordinary position, and the other in the location shown for use as the throttle position is increased?
A number of motorcycles use that strategy
 
I agree about the cooler charge temp. On that TV show with engine dyno testing they looked into it a bit. However they are "carbureted American V8 engine" guys, so it was a little different. In their case they compared a multiport injection system (one injector at each intake runner near the head) vs single point injection (injectors at the throttle body on top of a tall V8 intake manifold). The charge temps were lower with the higher injectors, with their rationale being it gave more time for the fuel to cool the air. And the peak HP was slightly higher as a result. Not a great test but the concept has merit.

F1 engines used to do it that way:
bcb149be98cf4cce217829dc28411809.jpg

 
I believe you're right. Cool the intake charge. I wonder if it would be possible to have two sets of injectors? One set in the ordinary position, and the other in the location shown for use as the throttle position is increased?
There was an interesting episode of EngineMasters where they were comparing different intake systems and were able to quantify that the systems that had more length between where the fuel was delivered and the intake valve produced more power due to a cooler charge. Evidently, the belief that carbs may produce more power than port injection may be rooted in this phenomena. I suppose the old throttle body injection systems would behave more like a carb. This approach may be great for getting a cooler intake charge but throttle response would suffer a bit due to the longer path.
 
There was an interesting episode of EngineMasters where they were comparing different intake systems and were able to quantify that the systems that had more length between where the fuel was delivered and the intake valve produced more power due to a cooler charge. Evidently, the belief that carbs may produce more power than port injection may be rooted in this phenomena. I suppose the old throttle body injection systems would behave more like a carb. This approach may be great for getting a cooler intake charge but throttle response would suffer a bit due to the longer path.
I may be mistaken but I believe @TonyK mounted his injectors over a bell mouth opening to the runner inside a plenum. Hopefully he will wander by amidst his springtime housework and clarify this (or dispel my assumption/perception).
 
This video gives a excellent illustration why locating the injectors at the outward ends of the air horns is not good for a vehicle driven at anything less than constant WOT. And the dyno testing performed here is a better comparison of the two injector locations (near the intake valves vs far away) than the TV show ("Engine Masters") did on a V8...at least for our purposes on a import 4 cyl engine.
 
This video gives a excellent illustration why locating the injectors at the outward ends of the air horns is not good for a vehicle driven at anything less than constant WOT. And the dyno testing performed here is a better comparison of the two injector locations (near the intake valves vs far away) than the TV show ("Engine Masters") did on a V8...at least for our purposes on a import 4 cyl engine.
You are correct, testing on a V8 doesn't necessarily translate to an inline 4 very well. I would love to see the show do some I4s, but I'm not holding my breath :(

I love seeing vids like this, especially the views down the individual runner. The setup was also pretty simple, just remove the fuel rail from it's normal location and mount it at the bell-mouth. :) I was surprised that it seemed the injectors did a poor job of atomizing the fuel though. Lots of fuel droplets, less fuel vaporization. I wonder if different injectors, and/or higher pressures, and/or longer runners, would have produced better results?

I still believe injecting the fuel at the bell-mouth will cool the intake charge which will result in more power, if tuned correctly. I wonder if the test above measured AFRs, and, if necessary, corrected for them in the injector in the bell-mouth test? If the intake charge was cooled significantly, more fuel would be required. If no additional fuel was added, as in change the tune, I would think the power outputs would be very similar between the two tests (and that's what we saw.).

I would love to see a test that measures the cooling effect of race gas, E85, and pure alky injected at the bell-mouth :p.

I think it should be relatively simple to add another set of injectors in the "normal" location to handle idle and part throttle. Then, once the throttle is opened up enough to produce some vacuum at the bell-mouth, fire the (high pressure) bell-mouth injectors too. That should produce a bit of a kick! To complicate things further - inject pure alky at the bell-mouth and race gas in the "normal" injector position. :D

Maybe I should write Engine Masters with the suggestion? Who knows, they are getting a little stagnant, and they did a an I6 before... (I would even offer up a test engine ;).)
 
You are correct, testing on a V8 doesn't necessarily translate to an inline 4 very well. I would love to see the show do some I4s, but I'm not holding my breath :(

I love seeing vids like this, especially the views down the individual runner. The setup was also pretty simple, just remove the fuel rail from it's normal location and mount it at the bell-mouth. :) I was surprised that it seemed the injectors did a poor job of atomizing the fuel though. Lots of fuel droplets, less fuel vaporization. I wonder if different injectors, and/or higher pressures, and/or longer runners, would have produced better results?

I still believe injecting the fuel at the bell-mouth will cool the intake charge which will result in more power, if tuned correctly. I wonder if the test above measured AFRs, and, if necessary, corrected for them in the injector in the bell-mouth test? If the intake charge was cooled significantly, more fuel would be required. If no additional fuel was added, as in change the tune, I would think the power outputs would be very similar between the two tests (and that's what we saw.).

I would love to see a test that measures the cooling effect of race gas, E85, and pure alky injected at the bell-mouth :p.

I think it should be relatively simple to add another set of injectors in the "normal" location to handle idle and part throttle. Then, once the throttle is opened up enough to produce some vacuum at the bell-mouth, fire the (high pressure) bell-mouth injectors too. That should produce a bit of a kick! To complicate things further - inject pure alky at the bell-mouth and race gas in the "normal" injector position. :D

Maybe I should write Engine Masters with the suggestion? Who knows, they are getting a little stagnant, and they did a an I6 before... (I would even offer up a test engine ;).)
I agree that video does not cover all possibilities regarding the tune, types of injectors, etc. So there is likely more to be gained with further development. The same guy also has several other interesting videos testing lots of aspects, like air box design, intake runner length, etc. Typically I do not like YouTube; for every decent video there are thousands with idiots yacking about nothing just to hear the sound of their own voice. I happened on the one above and then saw a couple of his others.

Those "Engine Masters" guys did one episode on various fuels and they measured intake temp differences. The results were exactly what you would expect.
 
Back
Top