Author Topic: YZ 250 EFI  (Read 54643 times)

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Offline Jeram

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Re: YZ 250 EFI
« Reply #255 on: September 02, 2013, 06:36:06 PM »
20% less fuel burn this weekend. It depends on the type of usage, at lower speeds ( tighter track ) there is a larger benefit, more top end running = less fuel saving. I would imagine top out both bikes would be similar fuel consumption ( similar power ). Now it's getting exciting, every time out on the EFI bike is a little better as we change settings slightly. This weekend we got the raspy original feel back ( like my standard bike ) but we soon tuned that back out! It's much better / faster to ride with the smooth program installed. We even had a 250F rider have a go on the bike, he was quite shocked at how it went, it was hard to pry him off the bike after that. 

With this torquey, tractable powerband, would it be possible to increase the revability of the 250 two stroke? Most are typically the midrange monsters as we know, but how about revving them out to their redline? And possible a slightly shorter stroke/bigger bore design to increase said redline?

MX seems to be the exception to the two stroke bore/stroke rule of thumb.

square bore/stroke is almost always optimal except for in moto-cross.

I always wonder why the didnt build the optimal 68x68mm 250-2T and then achieve the required bottom end/mid range/top end balance with pipe design and porting....

I am sure there is a very valid reason and it likely has nothing to do with HP, but more likely about usability and traction... and even more likely; laptimes.....

I always thought it was a traction issue. Whats the standard bore/stroke of the 250t offroad motor? 66.4x74 or something? 6mm off the stroke compensated for by a 1.6mm increase in bore, wouldn't that mean an increased turnover speed? 250 2ts struggle for traction in alot of places as they are, I always just put it down to a turnover speed too quick for the dirt. Four strokes can get away with it because they deliver a power stroke half as often.

72


Offline Stusmoke

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Re: YZ 250 EFI
« Reply #256 on: September 02, 2013, 06:45:16 PM »
I thought that had too many fours in it.... My bad.
See you in Hell or Motocross Des Nations, whichever I get to first.

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Offline SachsGS

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Re: YZ 250 EFI
« Reply #257 on: September 02, 2013, 09:45:24 PM »
It was Maico that pioneered the 72 mm stroke.

Offline bearorso

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Re: YZ 250 EFI
« Reply #258 on: September 03, 2013, 01:32:45 AM »
And then you get the various 2t Trials Bike Engines - most of which are quite oversquare.

Yet, they are Torque / soft(er) power oriented.

Optimal bore and stroke - it depends on a designers particular 'bent'. And each and every bloody one would argue furiously for their 'optimal' ratio.

Maico 250s, for a few decades, have had the 67 / 70 bore and stroke. My 320s had 76 x 70. When they had 72 stroke, and abandoned it, I have no idea. They may have 'pioneered' it, but they  sure didn't stick with it.

Maicos fabled 490 /500 engines, were never a square design - both being a slightly oversquare engine. I think the one '500' that I know of, with a 'square' engine, is the KX500, at 84 x 84. Though, I'd not be surprised to be informed of other '500s' that are square engines.

 Open Class 2t MXers, had such a surfiet of power and torque for their times, they were bouncing around with inumerable bore stroke ratios, when they were common.

4ts keep going for more and more revs, for getting their HP. So, more and more oversquare.

The 2t design, is so interweaved within itself  - bore / stroke / crankcase volume / porting as making up the whole induction, and exhaust cycles, as to be incredibly varied in how it's done.

Someone coming out with "this is optimum", I just think of as one who has picked his 'favourite' - or, is subscribing to their particular worship of  a designer / brand / model.

There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI, as the fuel component of the charge, will be less dependent on the 'whole engine' concept.

I think, for quite some time, the Evinrude E tech outboards have been based on a fairly oversquare ratio. It seems to be 96mm x 76mm for the V6s, and 91 x 66 with the V4s and inline engines. Of course, these engines are used in a much different context.


Offline Stusmoke

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Re: YZ 250 EFI
« Reply #259 on: September 03, 2013, 07:47:11 AM »
And then you get the various 2t Trials Bike Engines - most of which are quite oversquare.

Yet, they are Torque / soft(er) power oriented.

Optimal bore and stroke - it depends on a designers particular 'bent'. And each and every bloody one would argue furiously for their 'optimal' ratio.

Maico 250s, for a few decades, have had the 67 / 70 bore and stroke. My 320s had 76 x 70. When they had 72 stroke, and abandoned it, I have no idea. They may have 'pioneered' it, but they  sure didn't stick with it.

Maicos fabled 490 /500 engines, were never a square design - both being a slightly oversquare engine. I think the one '500' that I know of, with a 'square' engine, is the KX500, at 84 x 84. Though, I'd not be surprised to be informed of other '500s' that are square engines.

 Open Class 2t MXers, had such a surfiet of power and torque for their times, they were bouncing around with inumerable bore stroke ratios, when they were common.

4ts keep going for more and more revs, for getting their HP. So, more and more oversquare.

The 2t design, is so interweaved within itself  - bore / stroke / crankcase volume / porting as making up the whole induction, and exhaust cycles, as to be incredibly varied in how it's done.

Someone coming out with "this is optimum", I just think of as one who has picked his 'favourite' - or, is subscribing to their particular worship of  a designer / brand / model.

There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI, as the fuel component of the charge, will be less dependent on the 'whole engine' concept.

I think, for quite some time, the Evinrude E tech outboards have been based on a fairly oversquare ratio. It seems to be 96mm x 76mm for the V6s, and 91 x 66 with the V4s and inline engines. Of course, these engines are used in a much different context.



I hadn't considered the crankcase volume and pressure implications of a motors bore/stroke but it makes sense. Like you said, using an electronic injection method, direct or not, turns it into a whole nother board game. If this rumoured 2014 DI 250 two stroke turns out to be true it will be interesting to see where things go.
See you in Hell or Motocross Des Nations, whichever I get to first.

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Offline Uniflow

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Re: YZ 250 EFI
« Reply #260 on: September 03, 2013, 05:20:05 PM »


Wayne Blackwood, right, with his YZ250EFI and some other guy hanging around we couldn't get rid of!


Offline Jeram

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Re: YZ 250 EFI
« Reply #261 on: September 03, 2013, 06:06:05 PM »

There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI, as the fuel component of the charge, will be less dependent on the 'whole engine' concept.

I disagree with the idea that a DFI two stroke would require an over-square engine configuration. Its still a two stroke, it still relies on crank case induction and exhaust scavenging, just like almost all other DFI two strokes (with boats being the exception).

However a DFI trapping valve two stroke would probably make good use of a short stroke as it does not need the long stroke for additional exhaust time area.

Offline bearorso

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Re: YZ 250 EFI
« Reply #262 on: September 05, 2013, 03:04:27 PM »

There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI, as the fuel component of the charge, will be less dependent on the 'whole engine' concept.

I disagree with the idea that a DFI two stroke would require an over-square engine configuration. Its still a two stroke, it still relies on crank case induction and exhaust scavenging, just like almost all other DFI two strokes (with boats being the exception).

However a DFI trapping valve two stroke would probably make good use of a short stroke as it does not need the long stroke for additional exhaust time area.


Disagree all you want young fellow.

As I wrote "There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI". Therefore, there will be disagreements.

I don't believe there is a need for 2ts in Motorcycles to go that route - chasing revs to get HP, as naturally aspirated 4ts do. That's through my own, perhaps 'old timers' viewpoint, on what I want from a 2t.

2ts can keep relatively long strokes, whilst doing battle with 4ts.  Simple maths / time calculations show that 4ts "big bang advantage", so to speak, is gradually being negated by the revs they must go for, for power to compete against a 2t, at least for now. Though, Moto 3 rules (well, the max. bore rule of 81mm - shared with Moto 3 - is a somewhat of a 'control' in Moto GP) , are keeping a cap on revs.

But, as I wrote, there have been, and will remain to be, quite a varied opinion on what bore / stroke ratio is 'optimum'.

One Engineers "Optimum", will be anothers "Dud".

I gave the Evinrude dimensions as an example of what has been done, with a certain, pretty successful application of DFI  2 strokes.

I'll have to have a squizz at what the 2t Snowmobiles tend to use. It may be comparable to the
Outboards, as they may be more of a 'steady state' engine than a Motorcycle Engine ( but, I'd think, less so than an Outboard) would be. It, of course, may not be comparable, at all.

Offline Jeram

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Re: YZ 250 EFI
« Reply #263 on: September 05, 2013, 03:55:43 PM »

There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI, as the fuel component of the charge, will be less dependent on the 'whole engine' concept.

I disagree with the idea that a DFI two stroke would require an over-square engine configuration. Its still a two stroke, it still relies on crank case induction and exhaust scavenging, just like almost all other DFI two strokes (with boats being the exception).

However a DFI trapping valve two stroke would probably make good use of a short stroke as it does not need the long stroke for additional exhaust time area.


Disagree all you want young fellow.

As I wrote "There is quite some arguement that 2ts will go to more oversquare engines, especially with such techs as DFI". Therefore, there will be disagreements.

I don't believe there is a need for 2ts in Motorcycles to go that route - chasing revs to get HP, as naturally aspirated 4ts do. That's through my own, perhaps 'old timers' viewpoint, on what I want from a 2t.

2ts can keep relatively long strokes, whilst doing battle with 4ts.  Simple maths / time calculations show that 4ts "big bang advantage", so to speak, is gradually being negated by the revs they must go for, for power to compete against a 2t, at least for now. Though, Moto 3 rules (well, the max. bore rule of 81mm - shared with Moto 3 - is a somewhat of a 'control' in Moto GP) , are keeping a cap on revs.

But, as I wrote, there have been, and will remain to be, quite a varied opinion on what bore / stroke ratio is 'optimum'.

One Engineers "Optimum", will be anothers "Dud".

I gave the Evinrude dimensions as an example of what has been done, with a certain, pretty successful application of DFI  2 strokes.

I'll have to have a squizz at what the 2t Snowmobiles tend to use. It may be comparable to the
Outboards, as they may be more of a 'steady state' engine than a Motorcycle Engine ( but, I'd think, less so than an Outboard) would be. It, of course, may not be comparable, at all.

The 2T snowmobiles have a large bore/short stroke configuration, but the main point is that the bore/stroke rations did not change when the bikes went from carbied to EFI and then to DFI. The DFI two strokes did not alter their bore/stroke ration when they swapped from carbied to DFI either.

The bore/stroke rations remained constant because gas flow dynamics and power characteristics do not care how and when the fuel enters the engine, only that its there and dispersed in time for ignition to occur ;)

So therefore I can only assume, and rightly so, that the bore/stroke will stay constant for two stroke motorcycles regardless of the fuel delivery type.

Offline citabjockey

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Re: YZ 250 EFI
« Reply #264 on: September 05, 2013, 10:11:28 PM »
I would think EFI (and DFI) would give engineers more freedom to work with other engine parameters. If a really oversquare piston would be prone to hot spots and pinging at specific throttle settings and RPM ranges it may be easier to compensate with the computers than it would be on a carb. So one would expect EFI/DFI engines to push the envelope in this regard (ratios further away from 1.0 than we are use to seeing). Maybe.
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Offline georgemicra

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Re: YZ 250 EFI
« Reply #265 on: September 19, 2013, 06:33:10 AM »
It might be possible to set up the ecu as a virtual V engine and use 3 injectors (2 transfer and 1 intake port) and run the 2 from one driver of say right side of V engine and the intake injector from another driver of the left side of virtual V setup. Then you have to play with the V degrees in order to adjust the injector groups timing.  :D
« Last Edit: September 19, 2013, 06:34:42 AM by georgemicra »

Offline Uniflow

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Re: YZ 250 EFI
« Reply #266 on: September 19, 2013, 10:50:50 AM »
I thought I was using an Ignitech EFI ( ordered through Wobbly ) but it appears they might be no more! Wobbly's ordered is now five months old and no news. Not even contact from Emails. They have taken the money for the order. Unfortunate as it seemed like it might have been a good unit.
We will stick to the LINK ecu at the moment, we now have total control over injection timing.

This is totally off subject but my own YZ now has a Rekluse clutch in it, with a left handle bar rear brake. Foot brake is totally gone ( for old people with a worn out right hip ). It's a bit like a mountain bike with both leavers on the handle bars operating front and rear brake. Much better entry to the corner control. 
« Last Edit: September 19, 2013, 12:59:30 PM by Uniflow »

Offline Jeram

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Re: YZ 250 EFI
« Reply #267 on: September 19, 2013, 01:14:07 PM »
I thought I was using an Ignitech EFI ( ordered through Wobbly ) but it appears they might be no more! Wobbly's ordered is now five months old and no news. Not even contact from Emails. They have taken the money for the order. Unfortunate as it seemed like it might have been a good unit.
We will stick to the LINK ecu at the moment, we now have total control over injection timing.

This is totally off subject but my own YZ now has a Rekluse clutch in it, with a left handle bar rear brake. Foot brake is totally gone ( for old people with a worn out right hip ). It's a bit like a mountain bike with both leavers on the handle bars operating front and rear brake. Much better entry to the corner control.

That's very disappointing!

Ignitechs quality was lacking in a big way over the last 2 years, I've had numerous faults and very poor customer support. So its not suprising that theyve gone belly up. (I dont know whether they have or not, but what your saying doesnt sound good)



Offline georgemicra

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Re: YZ 250 EFI
« Reply #268 on: September 19, 2013, 07:15:38 PM »
There is a new brand to me that makes an ecu with many features and good price. I tried to send a message to uniflow but is seems that there is a problem and I cannot send a message.

Offline lauterbacher

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Re: YZ 250 EFI
« Reply #269 on: September 19, 2013, 08:33:22 PM »
Post your link for him on the Board.it can't be any worse thing than people saying come and check out my bike porn.