Pulse width and ignition timing question.

MrMazda92 · Post by **MrMazda92** » November 13th, 2012, 12:52 am

I've been bouncing an idea around for a while now, and haven't been able to find my answer to my question anywhere so far. It may sound weird, but try to bear with me...

I'm thinking about ignition timing, and exactly how far I could advance the timing safely running premium fuel(My engine will be a KLG4, so on 9.5:1 static CR), my intake air temp should also be reasonably low due to thermo spacers, isolated Intake Manifold from heads, and fully insulated intake piping from foglight hole to throttle body. I'm also hoping to install a shroud that directs hot air from the radiator off to the side, and out a vent in the hood.

Anyways, back to my question...

What benefit might be seen from running larger injectors(say Millenia, for example), and drastically narrowing the pulse-width(time the injector actually stays open), while dumping the same amount of fuel as the stock injectors?
Simply put, spraying the same amount of fuel in less time, due to the larger injectors.

I'm also toying with the(possibly silly) idea of insulating the fuel rails themselves from the cylinder heads.
This is all for the purpose of reducing the risks of pre-detonation, and hopefully allowing an extra degree or 2 of ignition advance.

I haven't seen all of these concepts applied together before, and I don't recall ever seeing the injector idea being applied anywhere. I may be flat crazy, but the idea of keeping the fuel itself cooler, and keeping it away from the hot combustion chamber as long as possible, should help to reduce those risks.

What does everybody think?

fowljesse · Post by **fowljesse** » November 15th, 2012, 2:09 pm

I'll repeat what I said at the meet, just to get more feedback.
I read that you can put the K8 pintles on the bigger injectors for better atomization. I don't know if there would be restriction in higher rpm.
Another benefit I was considering is injector opening time at high rpm. I have been thinking about going with sequential injection for better low end, and fuel economy. The injector can not get the fuel sprayed in, during the time the intake valve is open, but could get more in, the bigger it is. Maybe there is a cam/ injector combo that could achieve this, but it would be for race only, I'm sure. I don't think it would be a big deal to start the spray while the valve is closed, and end end just in time to have the tail end of the mixture suck in. It would take some careful tuning! I imagine you'd have less x-tau than alternate-fire.

Now, for pre-ignition, or knock, some things you can do are; polish the combustion chambers and piston tops, get cooler range spark plugs, and in extreme cases, make water injection.

In my opinion, you don't need to push the timing far enough to need injection of any kind, and pushing it that far on a daily driver is inviting trouble. Once your build is done, dyno tune it with a margin of safety, on race gas for one map, and have another map for daily driving. Mirror polishing any of the internal aluminum is a good idea, in general.

fowljesse · Post by **fowljesse** » November 15th, 2012, 2:20 pm

If you're in there to polish the CCs, you can make the atomizing dimples just below the injectors, too.
Here are a couple other thoughts on fuel atomization;
I used to run Acetone for about 5 years (2.5oz per 10 gal). I gained 2-3 mpg the entire time. I just forgot to do it after a while, since I'm not allowed to pump my gas. It works by reducing the surface tension of the gas for better atomization. I did a thread about it here a long time ago.
Also, I have considered actually warming the fuel, for the same purpose. I don't think it would affect the combustion temp, but should atomize better. In fact, I have learned a bit from sites dedicated to fuel economy, and this is one of the things that has been done successfully. One guy wrapped a copper fuel line around his coolant hose. Of course you would have to be careful about it.
With MegaSquirt, you can get away with a lot more of these things, since you can control more.

crazycanadian · Post by **crazycanadian** » November 16th, 2012, 1:52 am

There is a lot of debate that could be had over all this...I'll keep my opinion simple... Blake you are over thinking everything... stick to the KISS principal... Do a lot more research on how things work in general..

Jessie, KL's from the factory run sequential fuel injection...

fowljesse · Post by **fowljesse** » November 16th, 2012, 8:39 pm

crazycanadian, I would like to read your opinion, and thoughts about all of this, even if it goes off topic.
I think he's overthinking it, too, but what the heck? Everyone needs a hobby

I love overthinking stuff. It keeps me from thinking about murder, and that's where innovation comes from..

Daninski · Post by **Daninski** » November 16th, 2012, 10:32 pm

Running fuel lines through an ice can is old school. Alcohol injection is probably the best way to lower temps prior to ignition.

fowljesse · Post by **fowljesse** » November 17th, 2012, 12:50 am

Yeah, we used to make the gas cold to increase volume. I try to buy my gas at night when it's cooler, so I get more gas per volume.

crazycanadian · Post by **crazycanadian** » November 17th, 2012, 2:45 am

fowljesse wrote:crazycanadian, I would like to read your opinion, and thoughts about all of this, even if it goes off topic.
I think he's overthinking it, too, but what the heck? Everyone needs a hobby
I love overthinking stuff. It keeps me from thinking about murder, and that's where innovation comes from..

All right Jessie, I`ll put my 2 cents in... I am the kind of person who much prefers to push things until they brake, pull it apart and find out why it broke before I go stepping out side the box..

First off the KL`s stock have sequential fuel injection with the factory ECU.. I am not sure how you are running yours with your mega squirt...

Fuel atomization can be a very complicated thing.. There are a number of variables that affect it.. duty cycle is not one of the major factors... 90% of us aftermarket tuners will benefit more from maxing out on tuning with stock set ups then we will trying to chase the 1 or 2 hp gains by going out side the box and getting overly complicated...

Be realistic about what you are building the car for and how the motor is going to be run... injectors that are running at 90 - 95% duty cycle at peek power and rpm are never going to hurt a motor thats in a daily driver... They aren`t going to hurt it if the car sees the odd drag run either.. In that case the motor wont spend enough time maxing out the injectors to become a problem...

Spark timing.. This is a really interesting subject.. Lots of information goes around talking about EGTs, octane ratings, compression ratios... At the end of the day there is lot of room in a stock motor to advance timing... manufactures are limited to what they can do for emissions reasons.. remember higher octane gas doesn`t mean more power... The goal in making power is to have complete combustion occuring when the piston is just cresting over TDC... High octane = slower burn time... slower burn time = more timing needed to make up for the slower burn time... Higher octane does resist preignition from high cylinder temps though... This is where tuning becomes so critical and the true balancing act of it all comes into play...

MrMazda92 · Post by **MrMazda92** » November 17th, 2012, 4:39 am

I'm all for a little overthinking as well.

I don't need a pat on the back for every idea that pops into my head, and I'm perfectly fine with constructive criticism.

That's why we're all hear, right? To learn what works and what doesn't.

The idea was something I hadn't seen elsewhere, and there is probably a good reason for that, but I figured I'd ask anyways, and see what you guys thought of it. Turns out, it led to some interesting posts and information I hadn't considered before.

With larger, domed pistons, and an increased static CR, I figured this idea would possibly apply as well. Keeping the fuel out of the combustion chamber as long as possible, and then getting it in and out faster. I figured more in less time would be a good fit, but who knows?

fowljesse · Post by **fowljesse** » November 17th, 2012, 3:38 pm

Thanks, crazy

What about pushing the fuel pressure, so it takes a smaller pulse width to get it in there? I assume that it would atomize better with higher pressure, too.
Unfortunately, MegaSquirt doesn't do sequential squirts. It has only 2 outputs for firing the injectors. It's a step back, in that regard. Since it was actually developed for a once carburated V8, it was a huge step up. There are people working on it, but they claim it's not really worth it. I really was sequential firing for my next project; An 80+mpg Metro, or Swift.
I figure that, if our ECU was designed for sequential, it must have some benefit for this engine, and just maybe, with the right setup, it could put all the fuel in, without x-tau (fuel sticking to the pre-combustion chamber area)

Currently, I'm engineering an intake that will be very simple, and great, which started with over-engineering, and then paring down, which is how I do everything.

I would love to be able to afford to test things to failure. I would learn a lot!

crazycanadian · Post by **crazycanadian** » November 17th, 2012, 7:39 pm

fowljesse wrote:I would love to be able to afford to test things to failure. I would learn a lot!

Thats why I stick with junk yard builds... Keeps things cheap...

You can up the fuel pressure.. It will help get more fuel in with less pulse width.. It will help a little with atomization... But like everything there is a limit... At some point your injectors wont be able to close properly or seal properly while closed...

fowljesse · Post by **fowljesse** » November 17th, 2012, 8:02 pm

Would you please blow one up for me?

crazycanadian · Post by **crazycanadian** » November 17th, 2012, 10:41 pm

fowljesse wrote:Would you please blow one up for me?

Eventually...

I am keeping an eye out for an M90 from a thunder bird...

MrMazda92 · Post by **MrMazda92** » November 18th, 2012, 12:08 am

crazycanadian wrote: You can up the fuel pressure.. It will help get more fuel in with less pulse width.. It will help a little with atomization... But like everything there is a limit... At some point your injectors wont be able to close properly or seal properly while closed...

I'm confused out of my mind here.

Wouldn't a good compromise be using my suggestion about Millenia S injectors, and maintaining stock(or slightly higher) Fuel pressure? They wouldn't be anywhere near maxed out, and that would avoid the necessity of increasing fuel pressure, if I'm not mistaken?

crazycanadian · Post by **crazycanadian** » November 18th, 2012, 12:55 am

MrMazda92 wrote:I'm confused out of my mind here. Wouldn't a good compromise be using my suggestion about Millenia S injectors, and maintaining stock(or slightly higher) Fuel pressure? They wouldn't be anywhere near maxed out, and that would avoid the necessity of increasing fuel pressure, if I'm not mistaken?

Higher fuel pressure = more fuel... so bringing down the pulse width on larger injectors but running higher fuel pressure will get you no where...

Stock injectors in a stock application are no where close to maxed out on a KL... It will take more then a bolt ons cams and a port job to max out stock fuel injectors...

My origonal comment was staying stock was your better option and focus more on your tuning... you will have less troubles and gain more...

MX-3.com

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