speedrider
New Member
we wouldn't have to have a piston custom made, just find one that is bigger and fits, i did this on a golf cart. but on the cylinder, finding one with a thicker wall would be a good thing
Phil_McCracken
Member
Yeah Andy about rod length, the rod ratio determines the piston dwell at TDC, will slow piston velocity slightly, will also slightly delay peak piston velocity and will reduce piston acceleration/deceleration.
If the crank rotates 10 degrees, then a very short rod will be at a greater angle than if the rod is very long. since the rod doesn't change length then some of the pistons downwards motion will be a result of this phenomenon, so the longer the rod, the longer the "dwell" and the longer the dwell the more complete combustion, higher cylinder pressure and more torque, the rod length is limited by block deck height, piston height and so on.
Hence 6 inch rods in chevs, a standard 350 with 5.7 rod and 3.48 stroke has a rod ratio of 1.64:1 and a rod angularity of 17.774°, which is not real good, change to 6 inch rod and you get RR of 1.72 and RA of 16.858°. which is better, but you have to change the pin height so the piston doesn't stick out the deck.
The only problem trying to get more capacity out of the HT is you don't use all the crank stroke available to start with, usable stroke is from the top of the exhaust port to the top of the barrel, it doesn't start compression till the ports are closed, lowering the roof of the exhaust port would gain you some capacity but also retards exhaust timing so there would be no gain.
The only real option is cylinder size, I have done some searching and there is heaps of lawnmowers, brush cutters etc with 49, 50, 51 ,52 mm cylinders, eg husqvarna has a 50mm piston with rings for 60 bucks US.
But there's the issue of cylinder thickness and also pin height.
If the crank rotates 10 degrees, then a very short rod will be at a greater angle than if the rod is very long. since the rod doesn't change length then some of the pistons downwards motion will be a result of this phenomenon, so the longer the rod, the longer the "dwell" and the longer the dwell the more complete combustion, higher cylinder pressure and more torque, the rod length is limited by block deck height, piston height and so on.
Hence 6 inch rods in chevs, a standard 350 with 5.7 rod and 3.48 stroke has a rod ratio of 1.64:1 and a rod angularity of 17.774°, which is not real good, change to 6 inch rod and you get RR of 1.72 and RA of 16.858°. which is better, but you have to change the pin height so the piston doesn't stick out the deck.
The only problem trying to get more capacity out of the HT is you don't use all the crank stroke available to start with, usable stroke is from the top of the exhaust port to the top of the barrel, it doesn't start compression till the ports are closed, lowering the roof of the exhaust port would gain you some capacity but also retards exhaust timing so there would be no gain.
The only real option is cylinder size, I have done some searching and there is heaps of lawnmowers, brush cutters etc with 49, 50, 51 ,52 mm cylinders, eg husqvarna has a 50mm piston with rings for 60 bucks US.
But there's the issue of cylinder thickness and also pin height.
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A
andyinchville1
Guest
HI Phil,
Thanks for the great info....with all this new info...maybe the cheapest and best option
would be to find an existing cylinder head and piston that will for the HT block and machine a rod to work?.... Of course finding a head to work as a direct replacement would probably be a little much to ask for....it would probably require some tinkering... Well the search is on! ;-)
Andrew
Thanks for the great info....with all this new info...maybe the cheapest and best option
would be to find an existing cylinder head and piston that will for the HT block and machine a rod to work?.... Of course finding a head to work as a direct replacement would probably be a little much to ask for....it would probably require some tinkering... Well the search is on! ;-)
Andrew
runslikeapenguin
Member
- Local time
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- Aug 8, 2008
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my advice would be to contact a machine shop with a CNC machine and get a quote on a cylinder. after that hit the internet and local bike shops and get a good idea on the 2 stroke aftermarket, i know there are still alot of fanboys out there building 2 stroke racing bikes. and see what you can get piston wise, make sure to get measurements on wrist pin sizes and what not. shimming the cylinder will just lower your compression and the flip side fly cutting the head will increase your compression, so your idea will not yield any more CC's but has potential to boost compression. you could shim your cylinder and find a little turbo 
J
JemmaUK
Guest
umm.. why are we looking at more swept volume?
Minx engine - 1592cc - 7.1:1 compression - 59hp
Sceptre engine - 1592cc - 9.5:1 compression - 85hp
That is an identical motor - the only changes is one has a high compression head and the other doesnt - everything else is the same.
We dont need a bigger engine with all the fitment problems that would entail - what we need is simply a cylinder/piston etc configured for a compression ratio of about 9:1 instead of 6.5/7:1.
If I take my tanaka motor @ 32cc on 9:1 compression it produces 1.6 hp peak output. Double the displacement to 64cc and you would be looking at 3.2 hp and all that would require is a compression increase on the already available HTs.
Re the idiot rider problem - you will always have them - just like you have the people who ride home in the dark with no lights and then wonder why they get hit by cars. I dont think it will make much difference if you put them on a 2.2hp HT or a 220hp superbike - they're still gonna have the idiot gene *sigh*
Jemma xx
Minx engine - 1592cc - 7.1:1 compression - 59hp
Sceptre engine - 1592cc - 9.5:1 compression - 85hp
That is an identical motor - the only changes is one has a high compression head and the other doesnt - everything else is the same.
We dont need a bigger engine with all the fitment problems that would entail - what we need is simply a cylinder/piston etc configured for a compression ratio of about 9:1 instead of 6.5/7:1.
If I take my tanaka motor @ 32cc on 9:1 compression it produces 1.6 hp peak output. Double the displacement to 64cc and you would be looking at 3.2 hp and all that would require is a compression increase on the already available HTs.
Re the idiot rider problem - you will always have them - just like you have the people who ride home in the dark with no lights and then wonder why they get hit by cars. I dont think it will make much difference if you put them on a 2.2hp HT or a 220hp superbike - they're still gonna have the idiot gene *sigh*
Jemma xx
Zev0
Member
Amen to that Jemma.
biketec
Member
I agree
Is all you would need to do to make more power out of any engine is deck the lid, and if you want to go further start with polishing ( really just debur the ports ) mirror them if you want. Then when your comfortable try to raise and lower ports, maybe open them up a bit, the better she breathes the better she goes. Look into a carb at a bike shop make some jets get a new cdi that will burn holes in your piston look into lubes IDK sky's the limit but theres no real need for such radical mods.Not to be a whiner but my bikes do just fine I love every last one no matter what they do granted powers fun but its a bike not a GSX R but I do hear ya the more the merrier leave the ccs to the factory and leave the hp tunes and tweeks to us the users.Good luck in your quest !
Is all you would need to do to make more power out of any engine is deck the lid, and if you want to go further start with polishing ( really just debur the ports ) mirror them if you want. Then when your comfortable try to raise and lower ports, maybe open them up a bit, the better she breathes the better she goes. Look into a carb at a bike shop make some jets get a new cdi that will burn holes in your piston look into lubes IDK sky's the limit but theres no real need for such radical mods.Not to be a whiner but my bikes do just fine I love every last one no matter what they do granted powers fun but its a bike not a GSX R but I do hear ya the more the merrier leave the ccs to the factory and leave the hp tunes and tweeks to us the users.Good luck in your quest !
D
dave1490
Guest
a longer rod would allow higher rpm,s aswell,because of less back and forth motion.you dont see many{if any} 383 small block chev,s made with 400 rod,s.also you have grind down the oil pan rail,s to clear the rod bolt,s.with the longer arm.i milled 50 thou off my head{$60 at a shop}and it realy helped.sell milled heads.but i understand what you mean{thier no substute for cubic inches}.it,s the basis and all other mod,s just emphsize it.
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runslikeapenguin
Member
- Local time
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no, a longer rod will only decrease the deck height and increase the compression, but with a 2 stroke in turn changes the 2 stroke port duration. so to keep everything with the engine the same and to avoid problems with the fuel you would have to shim the bottom of the cylinder which would negate the effects of the new rod.
and you do realize the 383 stroker kits come with a crank as well.
M
mnbiker
Guest
After some thinking, the orignal posters idea would work, it would bring the piston up further createing a smaller expansion chamber thus creating more compresssion/power. However, increacing rod length is not really a good way to go about it, your better off using liquid gasket sealer for the head gasket and milling the head down some.
