Two stroke turbo

Hey guys, I know it's been discussed time and time again but apparently there actually is something to the turbo on a two stroke. 4 strokes lose some power due to the valve system and restricted exhaust, netting usually at most around 100% extra power, depending on the size of the turbo.

However the argument against two strokes and a turbo is it'll blow air right through the chamber. Would make sense, even without the turbo though it blows your intake charge straight through, at least it would if it werent for the backpressure in your exhaust. Also the pressurized oil and lag from the size.

However what if I proposed to you that you CAN actually turbo a 2-stroke, and it nets between 2-4x the power? No, it wont blow through as much as you think. The turbo, being dependent on the exhaust pressures, also introduces its own backpressure. Being that two strokes love backpressure, this is a gain, not a loss, and the fact that it spins makes it adjustable too. From what I can make out, you jet up when you increase your compression to counter the blow through from the extra pressure anyway, which would mean your expansion chamber length would be different, which the turbo literally naturally adjusts for. The faster exhaust comes out, the more the turbo is going to pump in, and start the process again, more compression, bigger bang, more pressure meets restriction, turbo spins faster, so on...

This may not have been tried on our HT's yet but it has been done on drag snowmobiles, outboard motors and scooters, all two strokers. The gain is huge on a two stroke in general but because our motors have such tiny intakes, breathing is an issue, a turbo would overcome that. I imagine we could net 3x the power currently available in our motors via a turbo, provided we can cool them and get oil flow in the turbo. I'd say drill a hole in the crank case and run it to the turbo to share oil but having gasoline mixed in and knowing the temps turbos can reach, that'd be an inherently bad idea. There is a 40mm turbo available for $1000 or a china clone for $450, from what I recall it does have a sealed bearing system (dont quote me on this), perhaps may be worth a shot.

I know I'll definitely be looking into it, however as we all know, reliability will most likely be an issue, so perhaps a race-only motor.

yeah. Apparently a turbo on a two stroke has commonly doubled, even sometimes a bit more than tripled the power output. there's a 23HP NA motor I really like (the kreidler motor) but that has so much power he had to use a motorcycle rear tire. We would probably have to resort to the same tactic, but the problem is gearing. 15hp would tear through our power band rather quickly and make a ride rather anticlimactic, even on a 26T. It would rip apart a shift kit more than effortlessly. We would have to come up with some kind of transmission, either geared or a ridiculous reduction.

dmb said:

i'd like to see how they deal with the crank case boost and the porting mod's. i mean its hard enough keeping seals in n/a motors. then what to do with the reeds? what would they do? its always pressurised, more boost on the seals. maybe a rotary valve motor where you can block the intake from 100% boost? it sure does look cool thou. nothing sounds better than multi cylinder angry 2 strokes, but singles are annoying.

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I was thinking about reeds too, I dont think you'd need em with a turbo, but you could still reed port though. My thinking is reeds increase compression by not allowing the intake charge back out the intake tract, and forcing it into the cylinder on the downstroke. With a turbo, the pressure would keep trying to ram air into the case, and prevent charge escape anyway, reeds would only restrict the intake at this point, though that may help backpressure by slowing the turbo down a bit, so I'm not entirely sure.

As for the seals, I've never had an issue with them, and I've run a stupid amount of lower case compression before (my new cylinder had ports that were too low for my rod. I didnt check it, and discovered at BDC only half the transfer was open, it wouldn't have run at all if it werent for the reeds).

And as for the sound, I've found more compression gives you a gruntier sound. using the cylinder described above, my bike sounded almost like a small 4-stroke motorcycle... just... next to no power. Apparently a longer exhaust can also give the bike a more throaty sound. Mine sounded as described with an uncapped stock exhaust.

well you can get some pretty small turbos, smallest I've seen is 40mm but the one posted in the pic above looks smaller. Only issue I can think of really is the oil for the bearings. I am worried about the heat though, the turbo would have to go beside the engine, rather than in front or behind, meaning you're going to have a ridiculously hot turbine even closer to your leg, not to mention on the off chance it grenades, means instant sterilization, or worse.

Sure, we could build something with a bigger, stronger motor, as mentioned in the first post 23hp 50cc engines do exist, those who thought morinis had ridiculous amounts of power, the kreidler doubles it. But, the sheer fun and exploration of making a china girl go thousands of kilometers without breaking down OR produce ridiculous amounts of power (as far as I've heard, we cant do both ) makes it worth it. To my knowledge noone's been able to power an EFI long enough for touring, as pricey as it is, it may be fun to do. But I'm more about power., but as stated I have no idea how we would do any sort of drive train. I was thinking about a custom wheel, I dont think that'll be an issue, I'm just curious how we'd gear it so you'd make good use of the turbo. After all, running 0-40mph in 3 seconds would be exhilarating, but only really great if you can go much, much faster.

Update: So I've figured out the costs and the setup. It'll cost me a bit over $700 to do just the motor, but it should work.
Turbo kit: $350 CAD
Oil Pump: $75 CAD
Oil Cooler: $120 CAD
12v Mini-Gen Max: $50 USD
12v Charger: $30
22mm Mikuni carb: $122 CAD
Custom Exhaust & Plumbing: $70
Balance the crank (or get a dax lower), find a better piston, reed port (but not use reeds), and a custom long frame (chopper style perhaps, I want it to be usable as a bicycle... a heavy bike, but a bike) with a small motorcycle tire (bicycle spokes would never last). I'm aiming for a top speed of around 11,000 RPM and jet rich.
11k RPM and a 20T sprocket (if I can find one that small) should net me 103mph, I estimate the time to reach that speed on a turbo motor (producing anywhere between 15-30hp) would be around 8 seconds. Total cost? probably around $1200 (I got connections ). The look on people's faces when you rip past them on a bicycle would be priceless.

Here's hoping it works, should be a sweet birthday present (early october, expect it )

bairdco said:

You could use worksman wheels with their 11g spokes. they're super strong. I've got a buddy using one on the front of a triumph chopper.

Tire-wise, Coker makes repop 26" motorcycle tires for vintage builds, but they ain't cheap.

You could also use an 18" motorcycle wheel. There's 80/90/18 tires that you could squeeze into a bike...

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Like I said I'll be building a custom frame, most likely chopper style, their low center of gravity and length should help (I'm afraid if I hit the throttle it'll just flip). I can make the rear forks wide to accomodate a real motorcycle wheel, question is if I can find one 26" or 24". I thought about using mags but I hear they're pretty fragile. Never thought of workman, if they got the strong tires, I'll have a look. I imagine they dont have to be too strong, after all there comes a point the wheel will just spin, and with so little weight it should come pretty soon. Most motorcycles run 150+hp so a motorcycle tire gives me a huge amount of play room, however the weight is a concern.

it's a small turbo, shouldnt produce much boost at all. I'm looking into motorcycle generators to run either off the chain or off some kind of belt system to run both an EFI system (3A) and the oil pump (1A). I found pretty small alternators that one of my spare chain sprockets could fit that produces 12v @ 42A, but if I run it off the bike chain then of course the issue is it would only work if the bike's moving (which wont be an issue with a battery), and I couldnt idle long or else oil will stop flowing, and the turbo grenades. I may attempt to weld some kind of belt drive onto the small bevel gear (it's either iron or steel, I see rust on the bastard) and mount the alternator in the front of the motor, but I'm still looking for something smaller. I mean if an alternator the size of my fist can produce 42A, and I only need ~4A, then in theory a tiny, tiny coil should do the job just fine.

24V @ 5A @ 2750 RPM, 2.5" diameter, 8mm shaft, that should work wonderfully!
http://www.ebay.ca/itm/Electric-Sco...her_Vehicle_Parts&hash=item53f811c230&vxp=mtr

maniac57 said:

Electric powered turbo?
Sounds too good to be true. Never seen a single working example, even a racing total-loss setup, so I doubt it will work.
Good out of the box brainstorming though. Keep it up!

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Nono, the turbo is an ordinary turbo, I need the electricity to run an oil pump to prevent the turbo from overheating or siezing/grenading. The alternator idea was so I could run the EFI kit as well so when the turbo hits max boost, I'm not running stupidly lean. Hot air + an already lean mix would easily spell disaster for an HT so I'm trying to cover my bases. the turbo alone can be run with the 12v mini gen as the oil pump only requires ~1A of power (mini gen produces 1.5A), but the EFI is asking for 3A, then again that's alot of junk I gotta find a place for on the bike so I may not go that route and just jet rich. One of my friends used an industrial blower fan from a pizza oven as a turbo once and it worked pretty effectively (though not as powerful as a real turbo), but the reason a turbo is so effective on a 2-stroke is the backpressure it creates to create the extra power, creates even more power on a 2-stroke, whereas a 4-stroke gets robbed. An electric blower wouldn't restrict exhaust flow and then we'd see the blowthrough everyone mentions.

I'd also have to get a ridiculously small sprocket, 15-30hp 0-60kph (my top speed currently) would take about 2.5 seconds, but I'm trying to think of alternative ways to gear waaayyy lower, 27 is the smallest I'm aware of, but that would still give me a top speed of 80, while it'd be fast, hitting top speed in 3 seconds would be... lame... if only I had knowledge of how transmissions work on motorcycles and a mill, a custom wide ratio 3-5 speed transmission would be godly. and using a jackshaft is outta the question for... obvious reasons.