2 stroke engine
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West South Central Moderator
Joined: Oct 2000
Posts: 3,371
From: Kilgore TX 75662
2 stroke engine converted from a 4 stroke?
ok, I couldn't find a thread specifically about this type of engine. I've found a few good websites
http://www.offroadhaven.com/porting%...technology.htm
http://science.howstuffworks.com/two-stroke.htm
http://auto.howstuffworks.com/diesel-two-stroke.htm
Has anybody here ever converted a 4 stroke engine into a 2 stroke? I've got a 305 that I have thought about trying this with.
I'm thinking it would be best to use forced induction with this to NOT presurize the crankcase. This would allow the use of Chevrolet's excellent oiling system to function normally and so that it wouldn't smoke out the tailpipes all the time. A positive displacement supercharger would probably be the best way, but I'm thinking that the coolness factor of twin turbos is hard to beat. I'm wondering if there would be too small of a pressure differential between a pressurized exhaust port and the chamber? There will obviously be a higher pressure in the chamber.
Anyway, to make it a true 2 stroke, then it would need to only use a reed valve. However, I think that with the pressurized air from a blower or turbo that reed valve wouldn't be needed.
Now, here's what I'm thinking. Cut holes in the cylinder walls for the intake and exhaust ports. I'd need to make the intake manifold go to the side ports inside the V, then move the headers down the outside of the block. Then seal a set of valves to the heads and cut off any unwanted material that isn't needed for cooling or bolting the heads to the block.
The problem I see with this is not wanting to pressurize the crankcase... I was just thinking about the old 4 ring pistons that were in the tall deck truck big blocks. I know piston weight is defintiely a bad thing, but it might be needed. I could also use a vacuum pump to help out. Or use a venturi in the exhaust port/header with tubes running from the crank case to help evac?
One thing I can find very little about retaining to 2-strokes is the ring package. These are very important in a 4 stroke, but since a conventional 2-stroke relies on a pressurized crankcase to operate, I don't think it would be near as important. Can anybody shed some light on this subject for me?
I don't know, it's 3am and I'm thinking crazy again
But since this would just be for a drag racing motor and run for maybe a minute at a time, gas mileage isn't a concern. Eventually this car will get a big block, so I'd rather try this with the POS 305 first, then do the same to the big rat 
Just imagine. A twin turbo ~500cid 2-stroke engine running on alcohol
http://www.offroadhaven.com/porting%...technology.htm
In a nut shell it looks like this:
1: Piston moves from BDC to TDC creating a low pressure area in the crankcase.
2: Because of the vacuum in the crankcase fuel/air is sucked in through the carburetor and past the reed valve assembly.
3: Piston moves down from TDC to BDC. Reed valve closes causing the pressure to build in the crankcase.
4: Piston uncovers intake port and pressurized fuel/air rushes into combustion chamber.
5: Piston now moves up from BDC to TDC completing one cycle and starting an other. On its way up it compresses the fuel/air that is in the combustion chamber while at the same time creates a low pressure area in the crankcase. (see step 1)
6: Spark plug fires and ignites the compressed fuel/air in the combustion chamber sending piston back down towards BDC.
7: Piston uncovers exhaust port and allows the burnt fuel/air to escape. Further in its downward travel it uncovers the intake port and fresh fuel/air rushes in and helps to purge the remaining exhaust gasses. (see step 4)
At this point everything starts again at step 1.
1: Piston moves from BDC to TDC creating a low pressure area in the crankcase.
2: Because of the vacuum in the crankcase fuel/air is sucked in through the carburetor and past the reed valve assembly.
3: Piston moves down from TDC to BDC. Reed valve closes causing the pressure to build in the crankcase.
4: Piston uncovers intake port and pressurized fuel/air rushes into combustion chamber.
5: Piston now moves up from BDC to TDC completing one cycle and starting an other. On its way up it compresses the fuel/air that is in the combustion chamber while at the same time creates a low pressure area in the crankcase. (see step 1)
6: Spark plug fires and ignites the compressed fuel/air in the combustion chamber sending piston back down towards BDC.
7: Piston uncovers exhaust port and allows the burnt fuel/air to escape. Further in its downward travel it uncovers the intake port and fresh fuel/air rushes in and helps to purge the remaining exhaust gasses. (see step 4)
At this point everything starts again at step 1.
http://auto.howstuffworks.com/diesel-two-stroke.htm
Has anybody here ever converted a 4 stroke engine into a 2 stroke? I've got a 305 that I have thought about trying this with.
I'm thinking it would be best to use forced induction with this to NOT presurize the crankcase. This would allow the use of Chevrolet's excellent oiling system to function normally and so that it wouldn't smoke out the tailpipes all the time. A positive displacement supercharger would probably be the best way, but I'm thinking that the coolness factor of twin turbos is hard to beat. I'm wondering if there would be too small of a pressure differential between a pressurized exhaust port and the chamber? There will obviously be a higher pressure in the chamber.
Anyway, to make it a true 2 stroke, then it would need to only use a reed valve. However, I think that with the pressurized air from a blower or turbo that reed valve wouldn't be needed.
Now, here's what I'm thinking. Cut holes in the cylinder walls for the intake and exhaust ports. I'd need to make the intake manifold go to the side ports inside the V, then move the headers down the outside of the block. Then seal a set of valves to the heads and cut off any unwanted material that isn't needed for cooling or bolting the heads to the block.
The problem I see with this is not wanting to pressurize the crankcase... I was just thinking about the old 4 ring pistons that were in the tall deck truck big blocks. I know piston weight is defintiely a bad thing, but it might be needed. I could also use a vacuum pump to help out. Or use a venturi in the exhaust port/header with tubes running from the crank case to help evac?
One thing I can find very little about retaining to 2-strokes is the ring package. These are very important in a 4 stroke, but since a conventional 2-stroke relies on a pressurized crankcase to operate, I don't think it would be near as important. Can anybody shed some light on this subject for me?
I don't know, it's 3am and I'm thinking crazy again
But since this would just be for a drag racing motor and run for maybe a minute at a time, gas mileage isn't a concern. Eventually this car will get a big block, so I'd rather try this with the POS 305 first, then do the same to the big rat Just imagine. A twin turbo ~500cid 2-stroke engine running on alcohol
Last edited by AdioSS; Jul 20, 2004 at 07:41 PM.
Registered User
Joined: Feb 2001
Posts: 878
From: Clovis, NM
It sounds like you want to make a dertoit diesel all most, there a big @ss 2 stroke diesel engine they were made in I4, I6, V6 and V8 configureations.
We have a few detroit deisel a few have roots type blowers that put out 1.9psi and another type that has a turbo I guess it runs about 2psi also.
The Detroit diesel doesn't have exhaust ports it has over head exhaust valves and an in block cam, WTF how the F... does that work you might ask?
That engine has intake ports all around the bottem of the cylinder and 4 exhaust valves at the top that work like normal exhaust valves.
As the ports uncover the valves also open and the 2psi pushes the burned up s#1t out the exhaust.
The blower or super replaces the crank case pressure and you keep a wet sump oiling system.
They have huge blocks and big soup can size pistons that have 3 rings at the top and 2 air sealing rings at the bottem.
How would you cool it?
You would have to cut into the water jacket and make the inlets go on to the cylineder that way if you could cool it like a detroit diesel.
YOu would not beable to pressurize the crank case becaues the pistons are moving in and out of the block at the same time.
You would have to use a blower or turbo.
To use the big soup can size pistons you would need long rods so the crank doesn't hit the pistons.
We have a few detroit deisel a few have roots type blowers that put out 1.9psi and another type that has a turbo I guess it runs about 2psi also.
The Detroit diesel doesn't have exhaust ports it has over head exhaust valves and an in block cam, WTF how the F... does that work you might ask?
That engine has intake ports all around the bottem of the cylinder and 4 exhaust valves at the top that work like normal exhaust valves.
As the ports uncover the valves also open and the 2psi pushes the burned up s#1t out the exhaust.
The blower or super replaces the crank case pressure and you keep a wet sump oiling system.
They have huge blocks and big soup can size pistons that have 3 rings at the top and 2 air sealing rings at the bottem.
How would you cool it?
You would have to cut into the water jacket and make the inlets go on to the cylineder that way if you could cool it like a detroit diesel.
YOu would not beable to pressurize the crank case becaues the pistons are moving in and out of the block at the same time.
You would have to use a blower or turbo.
To use the big soup can size pistons you would need long rods so the crank doesn't hit the pistons.
Registered User
Joined: Oct 2000
Posts: 2,915
From: Sacramento
Re: 2 stroke engine
Converting a 4 stroke V8 into a 2 stroke would be quite a trick.
A two stroke cylinder requires its own individual crankcase to contain the incoming fuel/air charge. The V configuration would not be compatible.
Where would your transfer ports (the passages that the fuel/air flows through to get from the crankcase to the intake port)be?
How would you lubricate the main bearings? Generally 2 strokes (at least the ones I'm familiar with) use roller bearings on the crank mains.
Then there's the matter of the big blue cloud that would pour out of your tailpipe...
A two stroke cylinder requires its own individual crankcase to contain the incoming fuel/air charge. The V configuration would not be compatible.
Where would your transfer ports (the passages that the fuel/air flows through to get from the crankcase to the intake port)be?
How would you lubricate the main bearings? Generally 2 strokes (at least the ones I'm familiar with) use roller bearings on the crank mains.
Then there's the matter of the big blue cloud that would pour out of your tailpipe...
Registered User
Joined: Nov 2001
Posts: 2,985
From: In a house by the bay
Re: 2 stroke engine
Just start from scratch and build a 300 ci 2 stroke designed like a .21 cc nitro RC engine (some of these are better than 3hp!). Pull the air in through a carb placed over the crankshaft and let her rip. Should be one loud, economical, 2 stroke. 
-Mindgame
-Mindgame
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Re: 2 stroke engine
Originally Posted by Mindgame
Just start from scratch and build a 300 ci 2 stroke designed like a .21 cc nitro RC engine (some of these are better than 3hp!). Pull the air in through a carb placed over the crankshaft and let her rip. Should be one loud, economical, 2 stroke.
-Mindgame
-Mindgame
Registered User
Joined: Nov 2001
Posts: 2,985
From: In a house by the bay
Re: 2 stroke engine
Yes it is OS... I meant ci.
Funny how all these little motors are sized in ci. But I may have fibbed about the 3 hp, although I think they're around that. There's really no standardized way of testing these engines.
Do know that my little Nova .21 pushes a ~6lb 1/8 scale (Serpent 950R) can/am bodied car to ~80 mph. With the right gearing, I'm sure something short of 100 could be achieved. What a hoot!
-Mindgame
Funny how all these little motors are sized in ci. But I may have fibbed about the 3 hp, although I think they're around that. There's really no standardized way of testing these engines.
Do know that my little Nova .21 pushes a ~6lb 1/8 scale (Serpent 950R) can/am bodied car to ~80 mph. With the right gearing, I'm sure something short of 100 could be achieved. What a hoot!
-Mindgame
Registered User
Joined: Oct 1999
Posts: 356
From: Oakland City, IN
Re: 2 stroke engine
My sons EK4 truck is the most mind numbingly unbelievable things I've ever seen! It is difficult to even conceive that something that small can make that much power. The thing damn near jumps off the ground from a stop. 
You guys figure out this 2-stroke thing, and I'm in like flynt Not much is scarier than the powerband of a two stroke dirt bike or quad racer. Turbo, blower, nitrous, and stoker all rolled into one! 
Damn, I gotta quite thinking about that or I'm gonna need to change my shorts!
Dave C.
You guys figure out this 2-stroke thing, and I'm in like flynt
Not much is scarier than the powerband of a two stroke dirt bike or quad racer. Turbo, blower, nitrous, and stoker all rolled into one! Damn, I gotta quite thinking about that or I'm gonna need to change my shorts!
Dave C.
Registered User
Joined: Sep 2003
Posts: 17
From: Westminster, MA
Re: 2 stroke engine
I may be waay off here but you may be looking at this wrong. Would you just be able to make a cam gear that is the same size as the crank gear and then the valves would cycle every revolution (two strokes). You would need a really custom cam and the intake valve would have to open at BDC and not be open for very long, but you will be boosting it so you won't need it to be open for long. And if I'm right then a regular distributor would work (but it would have to be good for 12k rpm!) because it would be spinning the same speed as the cam and crank. You would probably need huge intake runners because they would need to flow twice what a normal engine needs. You would also probably need it to spid very fast to start up and you would need to be running alot of boost.
If I'm completly wrong please explain why.
If I'm completly wrong please explain why.
Last edited by dave96dcm; Jul 21, 2004 at 06:24 PM.
Thread Starter
West South Central Moderator
Joined: Oct 2000
Posts: 3,371
From: Kilgore TX 75662
Re: 2 stroke engine
Originally Posted by dave96dcm
I may be waay off here but you may be looking at this wrong. Would you just be able to make a cam gear that is the same size as the crank gear and then the valves would cycle every revolution (two strokes). You would need a really custom cam and the intake valve would have to open at BDC and not be open for very long, but you will be boosting it so you won't need it to be open for long. And if I'm right then a regular distributor would work (but it would have to be good for 12k rpm!) because it would be spinning the same speed as the cam and crank. You would probably need huge intake runners because they would need to flow twice what a normal engine needs. You would also probably need it to spid very fast to start up and you would need to be running alot of boost.
If I'm completly wrong please explain why.
If I'm completly wrong please explain why.
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