ESE's works engine tuner

[TZ350]

Due to requested fuel amount you need big injectors, big injectors have longer 'deadtime', the time for opening the injector(time from pulse start, to when the injector actually flows any fuel)Example, Bosch '465cc' injectors hav about 0.8ms of deadtime, that is about half of the time you got to inject it in.

Thanks for your tip SwePatrick, I have drawn myself a picture so I can visualize it.

For 12,500 rpm and a duration of 130 deg the transfers are open for 1.73ms (orange area)

The injectors I have are rated at 1ms to open and 0.5ms to close (dead time or at least poorly controlled fuel squirt, dark green area)

The 0-5ms close time can all happen after the transfers have closed. The 1ms can start before port opening.



In initial runs with these injectors I have found the minimin useful pulse width (not including close time) is 1ms, so maybe not much but the start does inject some fuel.

Now the opening time can start before the transfer opens and the close time after so that leaves me a clear 1.5 to 1.7ms of full on injection time.

The start point can be early but it looks as if the timing of the injection end point is going to become critical if we are going to get the bulk of the injection happening towards the end of the transfer event.

Now to work out what the injection pulse width might be.

Base Engine Data

125cc or 0.125 l cylinder capacity
Weight of air at STP 1.275 g/l
Max 13,000 Rpm
120% VE from EngMod2T's delivery ratio simulation.
12:1 air fuel ratio.
Injector 1 is 80 g/min
Injector 2 is 496 g/min (actually two 248 units)
130 deg Transfer duration.

Calculations

Injectors ability
130 / 360 = 0.36 transfers are open 36% of the time.
(80 + 496) * 0.36 = 207 g/min possible while transfers are open.
207 / 60 = 3.45 g/sec.
3.45 / 1000 = 3.45 mg/ms

Fuel Requirements
13,000 * 0.125 = 1625 * 1.2 = 1,950 l/min of air
1,950 * 1.275 = 2,486 g/min of air
2,486 / 12 = 207 g/min of fuel.
207 / 60 = 3.45 g/sec.
3.45 / 1000 = 3.45 mg/ms

Time
13,000 / 60 = 217 rpm/sec
217 * 360 = 78,000 deg/sec
78,000 / 1000 = 78 deg/ms
130 / 78 = 1.7 ms available to deliver 3.45 mg

By luck the Injectors ability to deliver 3.45 mg/sec is just what the engine needs so in theory 1ms of full on injection time is all that is required and there is 1.7 ms available to get it done in.

So in theory I think its possible, but timing is going to be the real challenge.

[Frits Overmars]

Transfers 130 deg duration....130/360 = 0.36 transfers are open 36% of the time.

Seems to me that "transfers are open 36% of the time" is a very generous definition of 'open'.
The transfers need some time to build up a decent open area just like the injectors do.

[TZ350]

Seems to me that "transfers are open 36% of the time" is a very generous definition of 'open'.
The transfers need some time to build up a decent open area just like the injectors do.

Yes true, good point and there will be other issues like the transfer flow stalling when there is insufficient blow down time, so not that straight forward. But not obviously impossible yet, just difficult.

[richban]

Hi Guys

In the constant quest for power on the NSR300's we are developing, We are now using and looking into ram air setups.

We have a proper NSR F3 box that is working well. It is massive. The volume has not been measured but I would guess almost 20 litres. Maybe more.

Frits / Wob I have a couple of questions if you don't mind.
Number one is. How big does it need to be. I can replicate the HRC one for my bike but it does make working on the bike a little bit of a pain. Also its not fully inclosed. It pushes up against the bottom of the tank. And looks like it could leak with vibration and movement of the rider pushing on the tank.

I was thinking of making one the connects to the bell mouths and is fully enclosed with no chance of leaking. But how do I figure out how big to make it?

Is there some rule of thumb that needs to be applied. 300cc / 11500rpm / 85hp = ??? litre box?. From playing around with 4 stroke airboxes / plenums its can really rob power when it is wrong. Usually to small form my experience.

Also i suppose the sooner the positive pressure is there the sooner the power increases. I wonder if this will work on a bucket. Maybe not on a Kart track but it could work on a big tack. Max speed on the bike would be close to 150 160 kph.

Also the intake leading edge on the faring is very important. As has been discovered.

Anyhow, not sure this has been covered lately. Thanks Rich.

[Frits Overmars]

You can hardly make the airbox volume too big; certainly not within the restrictions of a bike.
If you connect the airbox to the bellmouth, the carb hangs out in the open which will create all sorts of complications. Put the whole carb in the airbox.
At 160 kmh you may get about 10 mbar overpressure; that's just one percent of ambient pressure but it is enough to push the fuel down the emulsion tube, unless the pressure in the carb and the pressure in the fuel tank keep up with the airbox pressure. That is why you need a large breather hose between the airbox and the fuel tank (Or a pump. Or injection).
Is an airbox on a bucket worth bothering? Definitely, but not so much because of that 1% ram-air pressure; its main purpose should be to feed cold air to the carb.

[wobbly]

I would have thought 260Km/Hr , Trevs TZ350 was doing 232 at Hampton during the Sheene Challenge.
And Frits is right as usual, the Helmholts resonant frequency of the box vol and the intake length/area means that basically the bigger the box the better it works within
the forcing frequency range of the carb inlets.
The inlet from the front must be a divergent duct, to use the inlet flows decreasing velocity to increase the pressure, along with the velocity pressure of the air at the front of the bike.

[richban]

You can hardly make the airbox volume too big; certainly not within the restrictions of a bike.
If you connect the airbox to the bellmouth, the carb hangs out in the open which will create all sorts of complications. Put the whole carb in the airbox.
At 160 kmh you may get about 10 mbar overpressure; that's just one percent of ambient pressure but it is enough to push the fuel down the emulsion tube, unless the pressure in the carb and the pressure in the fuel tank keep up with the airbox pressure. That is why you need a large breather hose between the airbox and the fuel tank (Or a pump. Or injection).
Is an airbox on a bucket worth bothering? Definitely, but not so much because of that 1% ram-air pressure; its main purpose should be to feed cold air to the carb.

Nice one. Thanks Guys.

The bike running the ram air really starts to pull hard from WOT in 4th to the upper gears. However fast that is. We think its worth 5hp at the top.

Ok so I will replicate Mr hondas design. Nice one on the divergent duct. I was thinking the the other way around, as is so often the case.



Thanks again.

[Neal]

Rich , I use the soft adhesive foam to seal my tank against the air box . You can also put 2 small pieces on either side of the tank where the air box does not sit to help stabilise the tank on the frame . The air box helps , check the breather on the fuel cap ! And seal the cap as tank pressure is lost there

[lodgernz]

Rich, don't forget to also pressurise the float bowl, and block any breathers to it.

[Neal]

The ram air box for the nsr has the carbs inside it so they become pressurised , the breather for the tank gets in closed on the underside of the tank by the air box so all good there too . You just have to jiggle the powervalve cables and all good

[richban]

The ram air box for the nsr has the carbs inside it so they become pressurised , the breather for the tank gets in closed on the underside of the tank by the air box so all good there too . You just have to jiggle the powervalve cables and all good

Yeah quite a good setup. Seams to work really well.

[TZ350]

The transfers need some time to build up a decent open area just like the injectors do.

Graph of Transfer mas flow simulated using EngMod2T.



I see what you mean, not only do the Transfer streams need a little time to get moving they can reverse before the port closes.

Because the engine is making good power here (peak torque 12,250 rpm) my guess is this reversal is because the cylinder is being pressurized by the rising piston and plugging pulse from the pipe.

The horizontal lines represent 1ms at the different rpm.

[Yow Ling]

the streams can also reverse when the port opens. I read here or somewhere the first port to open is the last port to flow, to do with blowdown.

[TZ350]

the streams can also reverse when the port opens. I read here or somewhere the first port to open is the last port to flow, to do with blowdown.

Yes your right and I think residual pressure in the cylinder from insufficient blow down will show up here on the transfer port opening side of the graph.

[F5 Dave]

Perhaps you could reduce the reverse flow at the start of the phase by countering it with a larger pressure in the cases. Perhaps mount a sparkplug in there