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Why no EFI 2 strokes?
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Nonetheless my feelings won't be hurt and if this is a duplicate by all means delete the thread.
The Shop
with the way the rules are messed up the way they are now. i doubt theres a lot of $ getting poured into R&D so they can gain 2% improvement while a 250T still has to race against a 450F
Four strokes are outselling two strokes and are both heavier and more expensive... if only marginally.
The potential gains of a two stroke with DFI, a linear power curve and clean running, perfect throttling are what interests me... It's not like they're 4 thousand cheaper and 30 pounds lighter.
The facts are that an injection system (fuel injection would be easiest, direct injection is more tricky) should be just as cheap as a carburetor, easier to maintain, more power, just as reliable and won't be heavier. And if it is heavier, the extra weight will be offset by the extra power.
Athena (the guys who sponsor Red Bull KTM, produce gaskets and stuff) have already done DIRECT injection on a 2 stroke 125cc supermoto: https://www.youtube.com/watch?v=5gVeqix2Yc4. There are fuel injection conversion kits for 2 stroke scooters and I believe Serco had an EFI 2 stroke bike on show recently.
Nonetheless, if KTM or Gas Gas (or whoever) did sell enduro or trail bike EFI 2 strokes, people would just swap the fuel delivery systems over to a dirt bike equivalent (so a 250 EXC to a 250 SX). For the average person it is too difficult to convert their own bikes and the expense, time and uncertainty is too high.
Two strokes really require direct injection to squirt the fuel in the cylinder head during the compression stroke. These require a lot of injection pressure, whereas a regular throttle body injection system just uses the vacuum of the engine itself.
MXA has a point in that it really does create enough added cost and complexity to negate the benefits to the consumer. We love two strokes because they're simple and easy to work on. They wouldn't be with a DI system.
THE WHOLE PURPOSE OF A 2STROKE IS LIGHTNESS AND SIMPLICITY.
Pit Row
People seem to think that 'Direct Injection' with 'in head' injectors is the only way. Orbitals almost universally used stratified injection is not the only way to do it.
Set ups like the Athena, Ossa, Sherco AND Hondas ( go looking , Honda had quite a few patents / drawings out on EFI and 'in barrel side' injectors - all long since timed out) that make use of the existing flow / scavenging patterns within a 2ts cases / barrels, are much more logical. No high pressures, using flow patterns as 'blocking' ( or trapping valves / power valves) is the real way forward. I think at least one of the Outboard manufacturers use simpler, non 'in head', low pressure injection systems.
The Euro regs that come into force for 2017 will bring in various manufacturers solutions. Well, at least the ones that want to sell bikes that are road registerable - where the Big sales figures come from.
A reverse cylinder throttle body Honda drawing - was supposed to be for an ATV application:
The engine bay of one of one of the EXP 400s - 5th outright in the 95(?) Dakar, against the 780 twins and even larger bikes:
Another Honda throttle body injector engine:
A Honda 'on barrel' injector set up:
The Athena set up - with one of the great 2t geniuses of all time in the background:
KTM seems to have gotten elec start down to a science but for a pure MX machine I don't think I need elec start. Off road absolutely but given the economy of scale if I "have to" have
Until regulations force change I like my two strokes like I like most things......traditional old school.
Hondas blocking isnt doing a good job then is it?
In a fairly rated power output comparison, an EFI four stroke and a DFI two stroke, the favour likely heads back to the two stroke... It'll still be lighter, engine is still simpler and now the rideability, fueling and usability all goes up to equal the four stroke.
in my opinion, that will give us the answer on if we will ever see it on MX bikes.
KTM has publicly stated that their DI/EFI system is ready but they will only use it when they are forced to, and even then, I'm sure it will be on enduro bikes first.
MXA nailed it for sure. I wish they would explain the technical details in the next article to support it, so maybe, everyone can understand how a 2 stroke DI engine works.
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