Author Topic: Fuel injection talk here... (Read 23563 times) Tweet

mike45 · « **Reply #50 on:** January 22, 2004, 08:50:00 PM »

Why is Rick still using 10" when his unit pulls 400CFM. Just wondering??

YAG · « **Reply #51 on:** January 23, 2004, 03:02:00 AM »

Has anyone here experimented with small ports?

spdingtkts · « **Reply #52 on:** January 23, 2004, 08:54:00 AM »

I sense a post coming up with "Motoman says....."

DaveO · « **Reply #53 on:** January 23, 2004, 10:31:00 AM »

10" I assume, will ask Bob next time.

Dave

YAG · « **Reply #54 on:** January 23, 2004, 02:39:00 PM »

quote:
Originally posted by spdingtkts:
I sense a post coming up with "Motoman says....."

Heheh... yeah kinda... I have just never heard of doing that with a turbocharged motor. Curious if anyone has.

spdingtkts · « **Reply #55 on:** January 23, 2004, 03:13:00 PM »

Well that is usually how it starts.

Guys start quoting Motoman like he was Rob Muzzy himself come down from the mountain to give a sermon.

If Motoman says it, it must be the way. Funny thing is, who the heck is Motoman?

YAG · « **Reply #56 on:** January 23, 2004, 03:27:00 PM »

Right, I agree with you, and I'm not quoting the guy, and won't either. I'm just curious if it has been done on a turbo bike, and what the end result was, just because I'm curious how different ideas work in different applications, nothing more, nothing less.

Steve A · « **Reply #57 on:** January 23, 2004, 03:29:00 PM »

I don't think it would make any difference on a "pressurized" intake system.

YAG · « **Reply #58 on:** January 23, 2004, 05:38:00 PM »

I was kind of thinking it might rob power because of the port flow velocity... once you get into supersonic, you get a lot of restriction. Thats how pressurization systems work on small planes... it takes the air off the turbo and puts it through a nozzle that will accelerate it to supersonic flow. Once the air reaches supersonic velocities, even a major increase in manifold pressure barely puts any more air through the nozzle because the shock front limits the flow speed.

BusaGeek · « **Reply #61 on:** January 23, 2004, 10:09:00 PM »

Injectors stop working reliably at around 85% duty cycle, so manufacturers keep them under that number. But, the higher the duty cycle, the better cruising characteristics. If an injector were so big that it could fuel the bike at 30% duty cycle, it would have half of the ability to fine tune fuel delivery at small throttle openings as an injector that runs at 60%.

Because of this, injectors are generally sized to run at about 75% duty cycle (maximum ''on'' time) on brand new vehicles. Same for cars, trucks, and bikes.

DarkFalcon · « **Reply #62 on:** January 23, 2004, 10:25:00 PM »

Maybe we are not on the same page. When you said the intake was only open 30% of the time I inferred you were speaking of the % intake time open during the four cycles; so if the intake cam had 250 degrees of duration, the % intake would be 35% or 250/720. If I am correct, then I don't understand the relationship to duty cycle.

BusaGeek · « **Reply #63 on:** January 24, 2004, 09:41:00 AM »

My point is that most of the time the injectors are spraying into relatively stagnant air. The surface finish of the intake tracts won't matter much unless the air is moving.

dakinebusa · « **Reply #64 on:** January 24, 2004, 09:53:00 AM »

From the stuff I have read, where surface finish becomes a factor is in improving fuel vaporization.

Because the injector is spraying into a pulsating flow with all kinds of acoustic reverberations there is a mist in the intake tract during compression and exhaust strokes. It is best for fuel vaporization if this mist evaporates quickly before the droplets can coalesce. This is why race head designers are trying to spray the fuel on the back side of the hot intake valve instead of upstream.

Intake tract surface finish won't affect air flow (within reason) but a very rough surface will give a lot of crevices for fuel to hide in and hang up resulting in poor vaporization and cycle to cycle a/f ratio changes. This leads me to the conclusion that a reasonably smooth surface is best. Mirror polishing is a waste of time but a nice matte finish like a walnut shell blasted one probably is best at minimizing cycle to cycle variations.

That's my story and I'm sticking to it.

spdingtkts · « **Reply #65 on:** January 24, 2004, 10:32:00 AM »

I thought they sprayed the fuel on the valves to keep the valves cool.

dakinebusa · « **Reply #66 on:** January 24, 2004, 11:33:00 PM »

IMO, No.
If the exhaust valve can live you sure don't have to cool the intake.
The downside of using the intake for vaporization is the fuel cracks to carbon resulting in deposits.
Thats what intake valve cleaning additives made from nitrated polyglycol compounds are for.

DaveO · « **Reply #67 on:** January 24, 2004, 11:48:00 PM »

Dakin,

I agree...

Dave

spdingtkts · « **Reply #68 on:** January 24, 2004, 12:36:00 PM »

The purpose of cooling them wasn't for longevity. I remembered reading somewhere that someone had changed the injector location so that it would spray directly on the valve so it would keep the valve cooler for better performance.

I do not remember if it was to keep the valve from heating the intake charge or to improve valve sealing on the seat or whatever.

YAG · « **Reply #69 on:** January 24, 2004, 01:37:00 PM »

What about the reasoning that spraying fuel on something hot = complete fuel vaporization, giving more complete combustion, more power, better fuel economy.

len · « **Reply #70 on:** January 24, 2004, 01:50:00 PM »

you wouldnt want to spray the charge at the valve , because it would heat the charge- thus less dense of a charge going into the chamber. Also valve stem and valve head temps can be controlled by barrier coatings. Dont forget the valve cycle is every other revolution compaired to the injector ON time over 2 revolutions.

dakinebusa · « **Reply #72 on:** January 24, 2004, 07:46:00 PM »

At near full throttle when the injector is close to maxed out it is on nearly continuously.
That's when this fuel vaporization thing gets real important.
Vaporizing the fuel cools the charge a bit which pretty much offsets the volume taken up by fuel vapor.
If fuel economy isn't important then you can get away with all kinds of stuff but even Moto GP engines must get decent milage because of fuel capacity limitations and pit stop considerations.

Low pressure fuel injection is really more like an electronic carburator than high pressure injection.
With high pressure direct injection where you can squirt the fuel in after the valves are closed things change.
Atomization and vaporization aren't much of a problem with high pressure direct injection.
Thats why modern diesels that have to meet smoke regs are going to injection pressures approaching 100,000 psi

THEMOTORHEAD · « **Reply #73 on:** January 24, 2004, 07:57:00 PM »

YA LOOK AT THE HONDA GAS ENGINE WITH DIRECT INJECTION
40-1 MIXTURES

len · « **Reply #74 on:** January 24, 2004, 08:03:00 PM »

busageek, I understand the seq. injection timing on the busa, What I was saying is, the injector pulse length can be as long as two rotations, minus the intake valve open time. The stem of the valve can also be coated up to the valve guide. to retain heat in the stem, untill it can be passed to the valve guide, and on to the head. And some heat will be transferred to the seat. I would find it hard to see any benefit of spraying the fuel at the valve. thats all

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Author Topic: Fuel injection talk here... (Read 23563 times) Tweet

THEMOTORHEAD