anyone experience this effect of injecting on intake stroke ?

[Warp Speed]

55 deg ABDC is when "some" OEMs start injection.
That's when the intake valves are closed.
Injecting onto the back of a closed intake valve helps with vaporisation which improves combustion and reduces emissions.
It keeps the valve cooler and the fuel hotter.


Why would you want to do it any other way?

That's a better question?

Performance!

[Orr89rocz]

55 deg ABDC is when "some" OEMs start injection.
That's when the intake valves are closed.
Injecting onto the back of a closed intake valve helps with vaporisation which improves combustion and reduces emissions.
It keeps the valve cooler and the fuel hotter.

Why would you want to do it any other way?
That's a better question?

Performance!

For idle and low throttle tho? It kinda makes sense for idle and low throttle since air speed is slow there. For higher rpm then yes i would think you would start injecting abit later

Holley efi has a injector timing table in it. A lot of guys do report better idle and off idle driving characteristics when they inject fuel either on closed intake valve or just after or around the exhaust valve closing. Then as load increases and rpms increase, the injection event moves closer to bdc of the intake stroke.

Holleys default was end injection point to be bdc of intake stroke. It seems to work ok there as well but you get some more fuel gas smell in the exhaust.

[Warp Speed]

55 deg ABDC is when "some" OEMs start injection.
That's when the intake valves are closed.
Injecting onto the back of a closed intake valve helps with vaporisation which improves combustion and reduces emissions.
It keeps the valve cooler and the fuel hotter.

Why would you want to do it any other way?
That's a better question?

Performance!

For idle and low throttle tho? It kinda makes sense for idle and low throttle since air speed is slow there. For higher rpm then yes i would think you would start injecting abit later

Holley efi has a injector timing table in it. A lot of guys do report better idle and off idle driving characteristics when they inject fuel either on closed intake valve or just after or around the exhaust valve closing. Then as load increases and rpms increase, the injection event moves closer to bdc of the intake stroke.

Holleys default was end injection point to be bdc of intake stroke. It seems to work ok there as well but you get some more fuel gas smell in the exhaust.

Maybe not, but this is " SPEED TALK", not 'MINI VAN TALK!" LOL

[swampbuggy]

a classic Warpspeed remark, AGREE. Mark H.

[Belgian1979]

Only two things I can think of that would be able to explain this would be that due to the fuel vaporizing while being drawn into the cylinder would decrease it's temperature and increase it's density and therefor it would have a higher VE or on the other end would be that during overlap a certain amount would indeed go out of the exhaust. The last I would assume less of a possibility as you would have the same thing going on when you do inject on a closed valve. Even more so, as timing right now is set to exactly TDC on the intake stroke, so part of the overlap effect is already lost.

[Orr89rocz]

What does idle vacuum do now with this change in injection point

[mk e]

A big factor here must be injector capacity. Even the most radical of intake cams won't keep the valve open for much more than ~ 40% of the cycle, whereas conventional injector sizing typically targets a max duty cycle of as much as 85%. Under those conditions the fuel cannot all be injected through an open valve.

Mine are sized for about 35% max duty cyle to allow all the fuel to be injected into the noving air stream....but I've not gotten to the point of playing with it, the testing to date has been low power injecting against a closed intake.

[Belgian1979]

What does idle vacuum do now with this change in injection point

Nothing seemingly. But with the ITB setup it's not a smooth signal either and that in itself has an effect on the FPR which has an effect on how rich it runs and ultimately on vacuum also....difficult to see what causes what here.

I recently changed from an in manifold vacuum chamber to a separate log for the map and another for the iac, pcv and brakes. That already gave an improvement of my previous average of 68-70 kPA to 60-63 kPa but that doesn't mean that any changed on the vacuum of an individual cylinder as those are only averages.
I also tried to measure individual map signal. It's very noisy but seemingly going to a minimum of ca. 55 kPa and a high of 70-80 kPa.

[Belgian1979]

A big factor here must be injector capacity. Even the most radical of intake cams won't keep the valve open for much more than ~ 40% of the cycle, whereas conventional injector sizing typically targets a max duty cycle of as much as 85%. Under those conditions the fuel cannot all be injected through an open valve.

Mine are sized for about 35% max duty cyle to allow all the fuel to be injected into the noving air stream....but I've not gotten to the point of playing with it, the testing to date has been low power injecting against a closed intake.

Mark, you should try it. Injecting onto a closed valve quiets it down.

[mk e]

Mine are sized for about 35% max duty cyle to allow all the fuel to be injected into the noving air stream....but I've not gotten to the point of playing with it, the testing to date has been low power injecting against a closed intake.

Mark, you should try it. Injecting onto a closed valve quiets it down.

When my valve seat issue is fixed I'll try it and let you know.

[adam728]

Like RednGold86Z's experience, at idle and low rpm/loads injecting on a closed valve has always been best for stability and emissions. As loads and rpm increase injection typically moves closer to intake valve opening, but I can't recall any engines I've worked with that showed any benefit of getting even the tail end of injection to occur when the valve is open.

[Belgian1979]

Like RednGold86Z's experience, at idle and low rpm/loads injecting on a closed valve has always been best for stability and emissions. As loads and rpm increase injection typically moves closer to intake valve opening, but I can't recall any engines I've worked with that showed any benefit of getting even the tail end of injection to occur when the valve is open.

Thanks. I didn't say to performance was better. I don't know if that is the case. It was just louder.

[Belgian1979]

FWIW, I just set the injection timing to 540° before TDC on the power stroke but it caused intake backfiring.

[hoffman900]

Here is how Honda did it with their Formula One engines about a decade ago. See Figure 3.

Development of High-Pressure Fuel Supply System for Formula One Engine : www.f1-forecast.com/pdf/F1-Files/Honda/F1-SP2_15e.pdf

[nitro2]

It only takes X amount of power to idle an engine, and "X" is not very big.

When every combustion cycle is decent and there is little cycle to cycle variability, the exhaust will be smooth and quiet like a sewing machine.

As the idle cycle to cycle variability is increased on an engine (by any number of mechanisms - more overlap, poor fuel mixing, variable fuel mixing, variable injection quantity, variable exhaust residual, etc. etc. ) the idle necessarily becomes louder.

The required power to idle is the same for both scenarios, but in the latter you have some strong cycles, some weak cycles and some normal cycles, some early cycles and some late cycles all happening in rapid succession as the engine is running i.e. rough running. When the cycle to cycle variation is small, you just have normal cycles, no extra loud cycles.

The strong cycles and/or late cycles are what you hear. If the strong cycles are also late going off, then that makes it even louder.

Personally I like lots of cycle to cycle variation at idle because it sounds cool (though that's not a thing everyone likes), but then as little cycle to cycle variation as possible at WOT because it makes the most power at WOT that way.