burndog

Sequential Injection Timing RE: Megasquirt 3X application

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Here's a good one for you all to noodle on...

 

Has anyone here accurately established the optimum injector timing / degree's for Opening Before Top Dead Center? This is one of the final fine tuning adjustments I would like to complete prior to my Dyno Testing. I have read many theories on injector opening 10Degrees Before Top Dead Center or 10 Degree After Intake Valve closes.

 

The application is a Megasquirt 3X EFI Forced Induction M10 with let's call it a stock cam profile. So, 1) At what degree does the intake valve open before top dead center on a stock cam? 2) From a forced induction perspective where would you recommend the injector start before top dead center of the stock cam profile?

 

This is beyond my experience / capabilities of calculating on my own and looking for and direct experiences or better yet help in figuring / calculating this.

 

Thoughts? Recommendations? Experiences?

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1 hour ago, burndog said:

10Degrees Before Top Dead Center or 10 Degree After Intake Valve closes.

You are gonna need a lot more than 10 deg BTDC because the intake valve has been closed for more than 150 degrees at that time.  Look at the book, it shows when the valve closes.  Your end of injection should occur some degrees before BDC intake stroke.  Beginning is just what it is depending on the PW injection, so all the fuel gets in or the fuel has to wait for the next cycle.  You should be thinking and talking in terms of 720 degrees if it is on sequential fuel.

Haltech says this about the importance of the injection timing:

http://forums.haltech.com/viewtopic.php?f=23&t=12892&p=44723#p44723

Edited by jimk

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You mean 10 degrees BTDC on the intake stroke, I imagine...

 

I think you may end up discovering that this is sorta like what color brake caliper

paint makes you stop fastest- yes, there is some difference, (probably mostly around idle and low throttle transition)

but when all's said and done, at WOT at 6000 rpm, the injector's open for 600 degrees crank anyways, so it's a bit arbitrary.

Me, I'd start with the injector firing at .050" of valve lift on intake, and see what happened.

But I bet that's not the best answer at over about 30% of max hp....

 

But then, I'm a batch kinda guy at heart...

 

t

 

Edited by TobyB

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I was not working on a forced induction engine but did not find a huge difference playing with injector timing on my engine (336 cam and 48mm intake valves, ITB's) I tried as early as BDC (the start of the Exhaust stroke) and as late as 10 deg BTDC intake stroke.  On the dyno I did not see any difference but there "MIGHT" be some advantage one way or the other in drivability I just have not played with it in the car.  The old Lucas timed injection we use on race cars are timed to squirt fuel starting at TDC on the intake stroke and I have seen them set up all over the place and have never found a big difference except for at idle (and these are full tilt race engines like BRM 1.5 liter V8 F1 engines all the way to 8 liter Big Block Chevrolet Can AM engines and they don't idle worth a damn under any circumstance so I'm not sure that is really a difference. 

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2 hours ago, TobyB said:

You mean 10 degrees BTDC on the intake stroke, I imagine...

 

I think you may end up discovering that this is sorta like what color brake caliper

paint makes you stop fastest- yes, there is some difference, (probably mostly around idle and low throttle transition)

but when all's said and done, at WOT at 6000 rpm, the injector's open for 600 degrees crank anyways, so it's a bit arbitrary.

Me, I'd start with the injector firing at .050" of valve lift on intake, and see what happened.

But I bet that's not the best answer at over about 30% of max hp....

 

But then, I'm a batch kinda guy at heart...

 

t

 

Thanks Jim and Toby!

 

Yes I meant BTDC on the intake stroke as the point I would want to time my injector opening from. I originally had this set up running batch and it ran ok, but I knew there was more, there's always more ;) Now, I am running sequential ignition and injection and it pulls like a freight train even with the advanced tuning parameters, like injection timing not optimized.

 

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45 minutes ago, Preyupy said:

I was not working on a forced induction engine but did not find a huge difference playing with injector timing on my engine (336 cam and 48mm intake valves, ITB's) I tried as early as BDC (the start of the Exhaust stroke) and as late as 10 deg BTDC intake stroke.  On the dyno I did not see any difference but there "MIGHT" be some advantage one way or the other in drivability I just have not played with it in the car.  The old Lucas timed injection we use on race cars are timed to squirt fuel starting at TDC on the intake stroke and I have seen them set up all over the place and have never found a big difference except for at idle (and these are full tilt race engines like BRM 1.5 liter V8 F1 engines all the way to 8 liter Big Block Chevrolet Can AM engines and they don't idle worth a damn under any circumstance so I'm not sure that is really a difference. 

Thanks Preyuppy,

 

Maybe I am just a lucky SOB. The car idles with just a slight lope when hot, drivability is very smooth and the boost powerband pulls from 3400 to 6500RPM. Maybe I should just run it and determine what the tuner says from there.

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As a turbo engine you should not have a ton of valve overlap, getting them to idle well is much easier.  I'm sure your tuner will have some input about the injection timing.  Have fun.

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