Pop N Wood Posted October 7, 2006 Share Posted October 7, 2006 The valvetrain is what makes or breaks forced induction suitability... Bingo. On a standard 2 stroke the intake and exhaust ports are open at the same time. The turbo needs exhaust pressure to work. Build up exhaust pressure and you will also backpressure the intake port. The 2 stroke GM turbo diesel in the nuke plant I worked in had a single exhaust valve at the top of the cylinder and ports at the bottom of the cylinder bores for intakes. Thus the intakes were only open when the piston was near the bottom of it's stroke. The turbo was clutch driven to develop "boost" during start up. I have also heard of opposing piston, 2 stroke diesels that had cranks at the top and bottom of the engine with separate pistons at either end of each cylinder. When the pistons were all the way apart, they unshrouded an intake port at one end and an exhaust port at the other. Thus the pistons themselves worked like valves. These engines also use some type of turbo or supercharger to force air into the cylinders. These small engines CAN BE "SUPERCHARGED" .... That is what I was thinking. Quote Link to comment Share on other sites More sharing options...
24 oz Posted October 7, 2006 Share Posted October 7, 2006 Aren't detroit 2 strokes diesel? and a diesel 2 stroke wont start without a blower because it can't get enough air to start, and the turbo is for more power, or so I've been told. Not sure how accurate this is though. Can someone let me know? Quote Link to comment Share on other sites More sharing options...
Sparks280zt Posted October 7, 2006 Share Posted October 7, 2006 there isn't any supercharged diesels.it's just not effictive. they can't make enough boost. seen people try and they ar not "true" suprechargers they only force air not fuel and air. true as in 6:71 4:71 4:53 etc.. top mount. a blower on a 2 stroke diesel is NOT for proformance! Hmmm you better tell that to Detroit Diesel because they used to make a supercharged diesel... Quote Link to comment Share on other sites More sharing options...
warrenp Posted October 7, 2006 Author Share Posted October 7, 2006 nope! NEVER a supercharged diesel! i'm 100% sure. the blower was to force in and push exhaust out. drtroit 2 strokes have ports on the side of the cylonders to allow this to happin. it was not to add horse power on a 2 stroke detroit. there a gut i believs it PDR "piers diesel reserch" trying to make a supercharged kit for diesels . it works but not well. they say they aare having a hard time trying to get the boost out of it. when a diesel turbo we are boosting up around 40+ psi. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted October 7, 2006 Share Posted October 7, 2006 All of the Detroit Diesels I have worked on are two stroke, supercharged, and sometimes super-turbocharged. Like Pop N Wood said, they have only exhaust valves and no intake valve. When the piston is nearing the bottom of the power stroke (every stroke), the exhaust valve opens, blowing down the cylinder. Near the same time the piston slides past a port or ports in the bottom of the cylinder. Pressurized air from the supercharger (super high boost) enters the cylinder through these ports and pushes the exhaust gasses out the exhaust valve. The piston starts back up the bore, covering the port and the exhaust valve closes. When the piston gets close to TDC, fuel is injected and ignites, pushing the piston back down the bore, starting the cycle all over again. Without the supercharger, it can't run; it requires boost to fill the cylinder and evacuate the exhaust. Some of the V engines, like the 6V71 use a HUGE turbocharger that blows directly into the supercharger inlet. The supercharger then takes in air that is already pressurized to infinity and compresses it by another several atmospheres. PHENOMENAL COSMIC TORQUE. Some of these engines make around 500hp at 1500rpm. That's 1750lb of torque. Quote Link to comment Share on other sites More sharing options...
a6t8vw Posted October 7, 2006 Share Posted October 7, 2006 Ok so the original question "340 Polaris and a ihi RBH5" yes u could make it work, what i would do is convert your carb(s) to throttle bodys only. Remove the reed cages and run a fuel injector(s) with megasquirt. Is there a battery on that polaris? Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted October 7, 2006 Share Posted October 7, 2006 Ok so the original question "340 Polaris and a ihi RBH5" yes u could make it work, what i would do is convert your carb(s) to throttle bodys only. Remove the reed cages and run a fuel injector(s) with megasquirt. Is there a battery on that polaris? That is just it, I don't think you can make it work with a turbo. Don't know anything about that engine but unless it has some type of valves then I don't see how you could get a turbo to work. But a supercharger might work. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted October 7, 2006 Share Posted October 7, 2006 Two strokes depend on the exhaust being "sucked" out by proper tuning of the expansion chamber. Putting a turbo in there and creating back pressure would kill the motor. I have seen Jetski's with superchargers here. Huge power at low boost, but high boost isn't possible because of the crank case seals. I've even seen crank case seals and base gaskets blow out just by adding blocks to the crank to decrease volume, thereby increasing the ram effect into the transfer ports. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted October 7, 2006 Share Posted October 7, 2006 A standard 2 stroke uses the piston travel downward to force the air/fuel/oil mix up the transfer ports into the cylinder. I have and have built several detroit diesel engines, marvelous design IMO. The detroit 2 strokes had up to 4 exhaust valves ala 71 series, and 92 series, I converted my 6-71 from a 2 valve to a 4 valve head. The airbox on these detroits is separate from the crankcase. The turbo was a power adder and the engine kits for a turbo and non turbo are different. Lower compression for the turbo. The expansion chamber is just a round pipe about 12 inches in diameter that runs the length of the motor. I would think that a standard 2 stroke with the crankcase seals maybe doubled would be able to handle moderate boost like aroud 7 psi fine. V8's have the intake and exhaust open at the same time as well, its called valve overlap. They turbocharge fine, but since you can optimize valve timing they can and will work bettter. That's not to say that the two stroke won't work though even with the intake and exhaust ports open at the same time IMO. I always had dreams of a blown 2 stroke v8 like the detroit design 92 series with 2 exhaust valves, but running on gas. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 7, 2006 Share Posted October 7, 2006 That picture I posted earlier IS a turbocharged 2 cycle quad. The turbo is under the seat, so everybody saying it can't be done, there it is right there...I just went to the link a few posts up from that, and clicked on one, I believe it was the carbureted turbo kit link...Now how it works, or how well it works I don't know, but that page was full of different kits and pictures. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted October 7, 2006 Share Posted October 7, 2006 That picture I posted earlier IS a turbocharged 2 cycle quad. The turbo is under the seat, so everybody saying it can't be done, there it is right there...I just went to the link a few posts up from that, and clicked on one, I believe it was the carbureted turbo kit link...Now how it works, or how well it works I don't know, but that page was full of different kits and pictures. Nobody was saying you can't PUT a turbo on a two stroke. They were saying it probably won't work very well. Besides exhaust back pressure, there's also the issue of exhaust energy. When the exhaust hits the expansion chamber, two things happen: 1. It loses velocity shortly after the divergence. 2. It loses a great deal of heat once it enters the divergence. When heat is lost, the gas condenses and there is further pressure drop. Will it work? Sure. Will it work well? Probably not. This may be the example where the supercharger actually works better than the turbo for power production. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted October 7, 2006 Share Posted October 7, 2006 V8's have the intake and exhaust open at the same time as well, its called valve overlap. They turbocharge fine, but since you can optimize valve timing they can and will work bettter. That's not to say that the two stroke won't work though even with the intake and exhaust ports open at the same time IMO. Two stroke engines rely mostly on a low pressure area in the exhaust port to evacuate the spent charge where the four stroke pushes it out with the piston. As the expansion chamber widens (diverges), the gasses further increase speed and pressure drops. This pressure drop actually creates a low pressure area in the port for the exhaust gasses to fill. Adding pressure to this area would be extremely detrimental to engine operation, let alone the negative effect the turbo itself would have on wave reversion back into the chamber and engine. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted October 7, 2006 Share Posted October 7, 2006 Ok so the original question "340 Polaris and a ihi RBH5" yes u could make it work, what i would do is convert your carb(s) to throttle bodys only. Remove the reed cages and run a fuel injector(s) with megasquirt. Is there a battery on that polaris? The reed valve in a two stroke is a one way valve that keeps the air/fuel charge from pumping back out and into the carb when the piston comes down and ensures it goes up the transfer ports and into the cylinder. You can't remove it or the engine won't work. Quote Link to comment Share on other sites More sharing options...
a6t8vw Posted October 7, 2006 Share Posted October 7, 2006 The reed valve in a two stroke is a one way valve that keeps the air/fuel charge from pumping back out and into the carb when the piston comes down and ensures it goes up the transfer ports and into the cylinder. You can't remove it or the engine won't work. it will if the turbo is constantly boosting the crankcase and soon as the piston is all the way on the down stroke the air/fuel will move up the the transfer ports, soon as the the piston moves past the transfer ports the piston seals off the intake... so if you think about it the turbo is trying to keep the reeds open anyway... Quote Link to comment Share on other sites More sharing options...
cheftrd Posted October 8, 2006 Share Posted October 8, 2006 it will if the turbo is constantly boosting the crankcase and soon as the piston is all the way on the down stroke the air/fuel will move up the the transfer ports, soon as the the piston moves past the transfer ports the piston seals off the intake... so if you think about it the turbo is trying to keep the reeds open anyway... Seeing as how the "boosted" pressure in the crank case is the same as it is in the intake tract (the exact same as if it were only ambient pressure), when the piston moves down, pressurizing the crank case, air will move anywhere it can. That means up the transfers and back out the intake, etc. Also, the piston moves down, pressurizing the crank case way before the transfer ports open up at the bottom of the stroke. If the pressure is increasing, and the ports are not open yet, where does the charge go? Back out the intake... ALL two strokes that use piston motion to move the air must use a one way valve because of this, be it a piston valve, rotary valve, or reed valve. The diesel two strokes don't because they use a supercharger to compress the air and the air does not enter the crank case. The only way to do it on a bike is to eliminate the transfer ports and blow the charge directly into the cylinder when the ports open up. To do this, you must have a supercharger or a turbo that makes significant boost on idle. This also leaves you wondering how to lube the bottom end. Quote Link to comment Share on other sites More sharing options...
a6t8vw Posted October 8, 2006 Share Posted October 8, 2006 yeah after i was thinking about it, when the piston is on the downward stroke its building pressure 80% of the stroke till the last 20% (approx) and soon as the top ring clears it gets blasted in swirling atop the piston and pulseing out the exhaust at the same time... Quote Link to comment Share on other sites More sharing options...
warrenp Posted October 9, 2006 Author Share Posted October 9, 2006 A standard 2 stroke uses the piston travel downward to force the air/fuel/oil mix up the transfer ports into the cylinder. I have and have built several detroit diesel engines, marvelous design IMO. The detroit 2 strokes had up to 4 exhaust valves ala 71 series, and 92 series, I converted my 6-71 from a 2 valve to a 4 valve head. The airbox on these detroits is separate from the crankcase. The turbo was a power adder and the engine kits for a turbo and non turbo are different. Lower compression for the turbo. The expansion chamber is just a round pipe about 12 inches in diameter that runs the length of the motor. I would think that a standard 2 stroke with the crankcase seals maybe doubled would be able to handle moderate boost like aroud 7 psi fine. V8's have the intake and exhaust open at the same time as well, its called valve overlap. They turbocharge fine, but since you can optimize valve timing they can and will work bettter. That's not to say that the two stroke won't work though even with the intake and exhaust ports open at the same time IMO. I always had dreams of a blown 2 stroke v8 like the detroit design 92 series with 2 exhaust valves, but running on gas. i believe the 92 series is 4 stroke. a friend of mine ahd on in his boat.over 1000hp! he's soon replacing it with a D-deck 8v92 for more power. Quote Link to comment Share on other sites More sharing options...
bjhines Posted October 10, 2006 Share Posted October 10, 2006 I keep seeing posts that seem to differentiate between "Turbo" and supercharging... You guys have fallen victim to marketing my friends... A turbo is by definition a supercharger in fact it is formally called a turbo-supercharger... It is just the most unsuited for most 2-stroke apllications... Quote Link to comment Share on other sites More sharing options...
warrenp Posted October 11, 2006 Author Share Posted October 11, 2006 I keep seeing posts that seem to differentiate between "Turbo" and supercharging... You guys have fallen victim to marketing my friends... A turbo is by definition a supercharger in fact it is formally called a turbo-supercharger... It is just the most unsuited for most 2-stroke apllications... turbo's are exhats driven we all know this ther are two types of superchargers/ blowers. to me i call a "true" blower the kind that mount on top of your engine with carbs/ or FI. forcing air and fuel. then there are those others that just force are. i refer to them as a belt driven turbo. on an other note i stand corrected! 8v92 is a 2 stroke! i asked my buddy this morning. Quote Link to comment Share on other sites More sharing options...
Alex_V Posted October 11, 2006 Share Posted October 11, 2006 Bjhines is trying to say everything that forces air into the cylinders is a supercharger. We know a supercharger as a belt or eletric motor driven device that pushes air into an engine. We know a turbocharger as a exaust driven device. When both are super chargers, the latter is just a turbo-supercharger. ~Alex Quote Link to comment Share on other sites More sharing options...
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