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Injection angle

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When you don't have access to a Dyno to determine the best injection angle, is there a way to rough it in by road test or is there a rule of thumb based on the camshaft/engine design/whatever to have a rough guess of where to set this


Here's a good webinar on the subject if you haven't check it yet: https://www.hpacademy.com/previous-webinars/061-optimising-injection-timing/

One of the effect of having optimal injection timing is that you will have a richer lambda without changing the injector pulsewidth. You can easily have a good idea of the optimal timing while idling, then you can drive the car at a steady RPM and steady load, change the injection timing and see the effect on the AFR or fuel trims. Obviously it's more difficult to do on the road than on a dyno, and the effect on the lambda can be subtle, but it's worth a try!

In trying to learn more about this, I recognize I have kind of a peculiar setup. Large V8 using ITB's with the injectors above the throttle blades. I can't spray on the back of the valve, the throttle blade is in the way.

In my research (thanks, Google), I ran across an article with a similar situation. Idle Fueling and ITB's

Yea, it's a Nissan L6 inline but the system is very similar. He's using TWM (manufacturer) DCOE's. TWM was the predecessor of the Borla units and the main designer(Gary Polled) spent many years with them prior to passing away. The design(injection-wise) and the DCOE is very similar to my 48IDA models.

As I read thru this and try to learn more, some of the lights are beginning to come on. I have yet to read and understand the Ford SAE paper but I may have found some answers. I've begun to play with some of my settings and will report back

If you're looking for reading material for that night you can't sleep, try: "The Effects of Port Fuel Injection Timing . . ."

Would be interested in anyone's review and comments of both the post and the SAE paper

My initial tests are showing only a slight improvement when injecting with valve open. It appears to be sensitive to how much vapor vs raw fuel is sucked in. Still playing with this trying to figure out what works better.

Does anyone have any suggestions on how to use the Histogram part of MegalogViewer on how to map this for a more informed analysis? The software is new to me. I am seeing some good possibilities but it's way above my current paygrade as to how to use.



I'm back with some new thoughts. As I play with this and study what Google can serve up, the link about the ITB's opened some new thoughts.

I think you're aware, my system uses TWM designed, Borla-produced throttle bodies that look like Weber 48IDA's. The injector is above the throttle plates and actually sprays onto the throttle plate where it then drips/evaporates/gets sucked into the air stream and down into the cylinder. There is no way the spray ever hits the back of the valve or onto a port wall.

The link above made me realize the airflow into the cylinder is what is going to be the biggest factor in getting fuel to atomize or sucked in. With the camshaft I am using, the intake valve is open from 371 degrees to 129 degrees. With the valve closed, there is no airflow and any fuel sprayed ends up on the throttle blade and maybe dripping into the port. It will see some engine heat, but not like being sprayed onto the back of a hot valve. With that in mind, I am thinking the fuel spray needs to be while the air is moving - ie, when the valve is open. Using my valve timing and the injector open time ( I am using between 4-12 ms, I came up with a chart to calculate the fuel angle.

I am thinking that I want the fueling done by about 150 degrees at the latest. Depending on where I am on the fuel table, that has the valve open and sucking air while the injector is spraying. I figured the last few degrees are going to be lower on the chart due to the cylinder being filled and the piston beginning to slow down. Not having a dyno, it is difficult to prove my theories. And with it now around 30degreesF (-1C), it's not a lot of fun to be driving an open cockpit car at 70mph to try and test it out.

Does any of this make sense or have I gone over to the dark side?

Look at injection angle from a standpoint of view to quench out the last couple of percents in regards to fuel economy (emissions) and engine running smoothness.

A steady state load bearing dynamometer is mandatory for all areas, only exception being idle.

Without having optimised a setup as yours, my guess is that the gains will be small, if any.


As usual I like your thought process.

While a dyno would be helpful, you can still make changes and observe lambda result in terms of richness, trying to smooth the lambda trace by making injection timing changes and testing.

Have you watched the system at work by eye at idle, or while someone perhaps holds the engine at 3000 RPM by applying a little throttle, while you apply that injection timing change?


Your comment kind of got me back on focus.

I've been working on a fixture to hold the throttle at a given position. I needed it for checking/tuning the airflow on my ITB's. It's impossible to do it trying to hold a position with your foot or hand. Hadn't even thought to use it to hold the engine at a given RPM so as to see the effect of other setting changes.

Back to the bench to finish my fixture. Thanks for the idea.

Does the thought of treating the injection process like a carburetor - dealing with the airflow and ignoring trying to vaporize fuel on the back of a valve. The only way it's going to get there is if it runs down the wall and happens to get there.

Sounds good, or if you've ever considered converting your assembly to drive by wire, now might be the time. That makes this sort of thing a snap since you can command whatever angle you want easily...after you do all the install work of course. :)

it's been difficult to get my head wrapped around all this. To try and illustrate the events and injection timing, I used a graphic that Andre has used on a couple of his webinars, then added some color bars that scaled to the graphic.

The Graphic (attached) shows the valve events based on crankshaft degrees. To that, I add

Red: The area in which the spark event will occur. The difference is the number of degrees advanced. I am using 10-45 (I have some higher advance levels in the cruise/no load ranges)

Green: The length of my injection opening and when the event starts and stops. Length is from converting opening millisecs to crankshaft degrees. This gives me a visual representation of when the injector is open and how it relates to the valve position.

Hoping you guys will look over my shoulder and offer any comments. I figured to stop the injection by 180 degrees, believing the airflow would essentially be stopped by this point as the piston is moving back up. Is this a correct assumption?

The Blue area is where the piston is beginning its travel back up and the valve is still open. Is this the area that causes reversion?

Since the injectors are spraying onto the throttle blades, I figured to treat it as if it were a carbureted/manifold-type installation where you rely on the airflow to vaporize/suck the fuel in.

Does this make sense or have I gotten it all wrong?

Attached Files

You can buy adjustable clutch travel stops, to prevent over-centering with diaphram clutches, and one might be adaptable for your application.


I was about to accuse you of nipping at the adult beverages, what do clutches have to do with Injection Angle?

But then I thought through it, re-read your message, and searched Google for an "adjustable clutch travel stop". After seeing the pictures, I'll look further into these. Not sure they'll work directly but the concept maybe could be adapted to a custom piece.



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