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A switch for a throttle and yank off the brakes, wire the powervalve open and your good
Early 2 strokes had one airbox sensor that read everything that Bob wrote, minus the 02 sensor(Not needed really) but you need a water temp sensor also because a hot or cold engine runs different.
2 strokes run electronic , mechanical or even exhaust pressure power valves, that are totally separate from the EFI system.
This is the complete power valve system for a 2 stroke, Carbed or EFI. This is the entire system.
The Shop
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
Luxon 4-Post Bar Mounts
$189.95 - $239.95
Most are both open and closed loop now.
Then we can jet down to the station from the hills, fill up and go without having to carry a small bottle of oil on long rides. Not that it was really hard pouring a few ounces of oil into the tank, but its just added convenience.
Maybe with all this they can offer a 3 year engine warranty like other shit!
Im sorry you cant grasp some basic concepts Ive laid out, these are well understood by two stroke builders and developers of any merrit.
Two strokes revolve around the pipe, without out they make no power. The pipe works off resonance tuning utilizing the pressure wave created by the exhaust gasses leaving the port. A powervalve's function is NOT to increases the time of expansion on the piston which people still say, rather its design is to delay the pressure pulse timing to trick the pipe into acting longer for the bike. aka a low rpm pipe is longer a high rpm pipe is shorter when you dont have a powervalve. resonance and pipe design is why two strokes have a shorter power window than four strokes. innovations in powervalves, servo controlled pipes that vary length, electronic solonoid powerjets and variable compression heads were all attemps to broaden power width.
But why or how do those work?
Sound speed and exhaust port opening time are two critical tuning components to a two stroke.
Sadly sound speed isnt constant like light speed, it varies with local gas temperature, thus an engine producing more hp (heat) will in general have an average pipe temperature that is hotter than an engine producing less hp. Load time will also vary the pipe temp, short loads less heat, long loads more avg pipe temp, its a simple concept. hold a torch on a metal part of a set size for 1 second it gets x hot, hold same torch on same part for 10 seconds it gets hotter.
measured egt near the piston is the same, but if you measured egt all along the pipe to the tail cone just before stinger the temperatures will vary with load time.
Guess what, more compression lowers egt - lower sound speed, lower rpm tuning
guess what, richer fueling settings lower egt
Guess what, longer pipes work at lower rpm, shorter at higher, adjusting the pipe on the fly allowed an engine more breadth of power
By varying the compresion ratio on the fly engineers were attempting to boost power at low rpm, then be at optimum ratio for peak power for no detonAtion then lower comp past peak for more egt and more over rev.
electronic powerjets supply ADDITIONAL fuel than is optimum at lower rpms up to torque peak to lower the egt to make the pipe work better. then they switch OFF around peak power to supply less than optimum fuel to supply extra egt to extend the pipes range past peak power. The aprilia gp 125 that won everything for years after year innovated with a special powerjet that could vary fuel delivery vs rpm and optimize the exact fuel needed to maximize pipe/combustion. this was a keihin part on a del orto carb, that keihin wont sell to this day.
header length and taper in gp racing evolved to what is considered short headers percentage wise to exhaust length along with multistage tapering, and as cylinders evolved to where transfer directional stream control was improved via optimized short side turn designs and tunnel volume optimization along with roof angle changes, pipes began to get bigger and bigger in diameter. Prior to cylinder improvements too large a pipe lost power because it sucked the fresh charge straight out of the exhuast referred to as "short circuiting"
once cylinder improved you could suck harder and trap the charge within the cylinder.
Now, why does it matter for efi? If the pipe temp varies it alters how well its timed for suction and stuffing of the cylinder. If you suck the cases more empty on a cycle, the next time reeds open there will be more suction to the carb. A carb senses this immediately.. its a delta pressure/velocity sensing device.
efi would normally do this measurement with a maf sensor... easy.
But it aint. two strokes experience terrible reversion at various rpms... maf sensors measure forwards or backwards flow all the same.
reeds do NOT close when they should. In fact on some engines they close WAY past tdc almost near exhaust port opening and are reverse flowing this whole time. It sounds crazy... how could a check valve reverse flow. But the do..
there is so much more to it than ive laid out. Im tired of being berrated by someone who doesnt have a clue about two stroke engine dynamics. Get a clue, come back and solve the headaches a efi faces on a two stroke... make lots of money.
Efi will have some advantages, but in pure racing usage for elite level riders, carbs proved to be far superior in predictability usability ON ATWO STROKE. Four strokes efi is a godsend.
Nothing worse than a gp 500cc two stroke leaned over a 100mph at steady throttle in a controlled slide, pipe temp changes over the corner, efi system doesnt keep up and goes momentarily lean or rich, changes both power output and future cycle pipe temp.. and rider gets spit on his ass. yes it happened plenty of times in efis plights into gps on two strokes.
I can't imagine any EFI having to deal with the oil in the fuel as well. The inconsistencies in viscosity would be almost impossible to overcome in a regular efi system, let alone a high pressure DI system. The fuel pump would probably like it though.
Reed valves close the door. Thats why case reed engines have to have Reed valves. To close the door to the carb or throttle bodies, otherwise all the intake charge would be in the airbox.
We aren't talking about old piston port engines engines either. Thats why true piston port engines are virtually non existant anymore.
I'm guessing that this guy doesn't even realize that most throttle bodies on todays 2 stroke systems don't even integrate an injector anymore.
Every race snowmobile since the late 80's.
just go and watch a super slow-mo video of a single cylinder air cooled motor running. everything you think you know about physics and materials will be challenged.
here's the deal. you don't as much as you think you do. you know what you've read on the internet and magazines. i mean for christ's sake, your trying to tell a guy how a reed valve works. The same guy who just told you the entire dynamic fundamentals of expansion chambers. To think he doesn't know how a reed valve works in ignorant.
2 with turbos and one with Carbon bottle full of NO2. And even one Turd(IMO) 4 stroke with a turbo timbersled.
I'm pretty sure I've built more engines than he is old. In fact, I'm turboing a built 860 twin tonight.
Reed valve is a closed door. With a case reed engine, without reeds all the intake and reverse exhaust pulse would end up in the airbox.
Even with a cylinder port reed valve, the whole function of the reed valves is to trap the intake charge and prevent blowback into the carb or throttle body.
Pit Row
I don't really remember any EFI factory race sleds in the 80's unless they were experimental. I'm not saying there were't, but I just can't picture them. Outside of factory teams, no one used EFI, that much I know. There was definitely no commercially available EFI sysems in the late 80's for snowmobiles. How would you even tune it? from your laptop? haha. I know that Arctic Cat and Polaris race teams ran carbs all throughout the 90's and into the 2000's, even though they both sold EFI sleds starting in the early 90's.
With reed valves, that carb or throttle body is supposed to be sealed from any back pulse from the pipe through the crank case. That is what the design is intended.
Also, thats what boost bottles were supposed to catch and trap. Boost bottle intakes are open to blowback and not blocked by the Reeds.
Either way on piston port only engines with simple EFI, they run extremely crisp and maybe they just arent all that affected by blowback since those airboxes were always wet.
Savvy?
do know what harmonics are? I assume you do. Then you would know that things act very strange at certain harmonic frequencies, and interplay between the mass and inertia of the vibrating part.
seriously, go watch super, super slo-mo x-ray videos of different things and engines, like v-twins and singles and stuff. it defies your own logic almost. watch a cylinder jiggle around like jello, or a connecting rod bend and bounce back every single stroke. It will give you a new perspective in relation to materials and their properties.
i mean, you're having trouble imagining a reed fluttering around, lost in it's own harmonic cadence. At very high speeds even the lightest of materials can generate huge amounts of inertia. That inertia can say, for a brief period, hold a reed petal open past TDC, even against primary compression pressure. valves aren't supposed to float either...but they do.
I also agree with him that there aren't any real "on track" performance gains with EFI, which is a lot of his argument.
But, I do think that modern EFI is great, and other than cost, has no real downsides outside of anything but pro racing.
with that said, i would not be surprised if the 2018 Factory KTM/Husky Team 2-strokes were using carbs instead of the new EFI.
Outboards, sleds, etc all usually have far more power especially on top.
I can run a 52 mm throttle body with no loss of low end.
Outboards even post their HP numbers and the EFI Vs Carbed models was usually about 20 more.
So again, you're wrong. Here are the stated ratings for some simple outboards.
Merc 2.4 Carb HP 245 @7500
Merc 2.4 EFI HP 260 @7500
Merc 2.4 EFI Offshore 260 @7500
Merc 2.5 Carb HP 260 @7800
Merc 2.5 EFI HP 280 @7800
Merc 2.5 EFI Offshore HP 280 @7800
Merc 2.5 EFI Offshore Race HP 280 @8000
Merc 2.5 EFI Drag HP 300 @9000
1992 Polaris Indy 500 EFI was stated to have 5 HP more than the carbed model, so 2.5 HP each side. And those ran 44mm throttle bodies stock.
Racing outboards (drag racing) only started using DFI when Mercury started using it in the latter 2000's. I know this from going to races and checking out engines. Oh, and building a V8 two stroke with a bunch of nitrous with 8 two barrel carbs.
Know your facts before you spew lies on the interwebs
If you could sit back and read what people think you may learn something. Just because you have a bunch of two strokes means nothing....You are a prime example of this.
To be fair you are wrong with your outboard comparisons there. The Merc EFI's ran different heads and intakes compared to the carbureted versions....and the early versions of outboard EFI technology started in the mid 90's and they were not very good....In either the power or efficiency department.
Racing outboards (drag racing) only started using DFI when Mercury started using it in the latter 2000's. I know this from going to races and checking out engines. Oh, and building a V8 two stroke with a bunch of nitrous with 8 two barrel carbs.
Know your facts before you spew lies on the interwebs
If you could sit back and read what people think you may learn something. Just because you have a bunch of two strokes means nothing....You are a prime example of this.
Well, you are wrong. If my specs are wrong, then Mercury lied all these years, and 2.4 EFis were called 260s, and 2.5 Offshores are still called 280's.
The EFI intake was a simple horn. Because of the EFI. The carbed models had a box with a 6 hole intake for the carbs, which most added velocity stacks and tossed the box.
The heads are the same. The blocks are the same. The whole thing is the same on the race outboards. Including the relieved exhaust.
And you are also wrong about the drag racing.
The Merc 2.5 EFI Drag was introduced in the mid 90s as a SS, to follow the 2.5 EFi and EFI offshores with the standard length.
I know because I have 2 hanging on the ass end of my boat. And there were 2 hanging on the ass end of the boat before that, and 2 2.5 Offshores on the boat prior to that one.
So I may know a little bit. And you don't buy them from the fishing boat place.
And none of the 2.5 series was DFI. It is just plain jane EFI with an ECU and then in 1995 maybe they went to a digital ECU even before the new Alien Cowls.
Do you want to talk about modding up 2.5's for 450 HP, I'm game, because that's my summer passion. You couldnt buy these at the Merc dealer.
Efi is coming you like it or not and i like the thing that we have 2 strokes after euro4.
Don't you?
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