stroker

[sj762]

i need some input i was thinking of useing a 760 with a 4mm stroke would this work out as to a 61x big bore as your adding 2mm to the power stroke witch would be like lowering the ports 2mm has anyone done this or know if this combo will work thanks

 

[Pro-pulsion]

760 with a 4mm stroke

Do you mean a 760 with a 74mm stroke? A Kawi 650 has a bore of 76mm and stroke of 70. Or do you mean you want to add a 4mm spacer to change the port timing? Also if you raise or lower your ports or cylinders, the stroke will still be the same, you will just be changing the volume in the combustion chambers, the squish, and the port heights. The power stroke is only the description for the down stroke after combustion. If anyone has an idea of what you're referring to I'm interested to get a better understanding. Plus it will help me figure out what to do with a SJ in the future when I can manage to get one.

 

[Freakrider]

he is talking about putting a 4mm stroker crank in his 760 motor, will it improve exhaust port timing by 2mm for low end hit ?

 

[Pro-pulsion]

Ooohhhh...a craaannnkk lol. Well, I'm not sure since I have no experience with changing out a perfectly good crank for another but it will cover the ports for a longer period of time. In a way I can kinda see it as being an alternative to power valves and changing how much exhaust leaves right away. That's all power valves do, limit the amount of exhaust leaving on low end to help improve the punch.

I think it should work, but I would do a lot of research on it before going ahead with it. I assume that if you put the longer stroke on there and keep the stock heads the compression is going to be super high. I think every .5mm is equal to 0.020" so he's going to raise the stroke by 0.160"...that's huge. The squish will practically be NIL lol and if he doesn't drift the plugs out of the head they'll drive through the pistons. Any idea of how close I am on this theory to anyone else? Is there more to it than just dropping in a longer stroke crank as mentioned or do you just drop it in and go?

 

[#ZERO]

A 4mm stroker crank will increase the piston travel 2mm in both directions and will increase the dwell time at BDC which will raise the port timing & duration.

You would be better off using a 61X cylinder with big bore sleeves with even lower port timing or an after market cylinder built for a stroker setup.

 

[SUPERTUNE]

Ooohhhh...a craaannnkk lol. Well, I'm not sure since I have no experience with changing out a perfectly good crank for another but it will cover the ports for a longer period of time. In a way I can kinda see it as being an alternative to power valves and changing how much exhaust leaves right away. That's all power valves do, limit the amount of exhaust leaving on low end to help improve the punch.

I think it should work, but I would do a lot of research on it before going ahead with it. I assume that if you put the longer stroke on there and keep the stock heads the compression is going to be super high. I think every .5mm is equal to 0.020" so he's going to raise the stroke by 0.160"...that's huge. The squish will practically be NIL lol and if he doesn't drift the plugs out of the head they'll drive through the pistons. Any idea of how close I am on this theory to anyone else? Is there more to it than just dropping in a longer stroke crank as mentioned or do you just drop it in and go?

A +4mm stroker crank means the connecting rod crankpin is moved out from the centerline 2mm.
This means the piston will travel +2mm farther up and 2mm farther down and that equals a 4mm total added stroke.
With that said... the piston will be .080 thousandths higher with a 4mm stroker crank installed if using the same length rod.

Using a stroker crankshaft starts at the point of the engine build, you must design the engine around the stroker crankshaft first for a freestyle/freeride powerband.
If using a stock cylinder you should re-sleeve the cylinder with special sleeves that change the port locations to keep the bottom end hit very strong, if you don't, the engine will run like a top end race engine with weaker than stock bottom end power and way stronger on the top end.

 

[sj762]

thanks for info chuck its always better to hear from people how know than gust throw parts at it and hope it works thanks again

 

[jetski9010]

A +4mm stroker crank means the connecting rod crankpin is moved out from the centerline 2mm.
This means the piston will travel +2mm farther up and 2mm farther down and that equals a 4mm total added stroke.
With that said... the piston will be .080 thousandths higher with a 4mm stroker crank installed if using the same length rod.

Using a stroker crankshaft starts at the point of the engine build, you must design the engine around the stroker crankshaft first for a freestyle/freeride powerband.
If using a stock cylinder you should re-sleeve the cylinder with special sleeves that change the port locations to keep the bottom end hit very strong, if you don't, the engine will run like a top end race engine with weaker than stock bottom end power and way stronger on the top end.

If you are building a stoker with your stock 61x or 62t cylinders and sleeves can you help fine tune were you want your ports at with a base cylinder spacer?

 

[SUPERTUNE]

If you are building a stoker with your stock 61x or 62t cylinders and sleeves can you help fine tune were you want your ports at with a base cylinder spacer?

No, A spacer makes porting even more radical for freestyle/freeride.

 

[jetski9010]

A +4mm stroker crank means the connecting rod crankpin is moved out from the centerline 2mm.
This means the piston will travel +2mm farther up and 2mm farther down and that equals a 4mm total added stroke.
With that said... the piston will be .080 thousandths higher with a 4mm stroker crank installed if using the same length rod.

Using a stroker crankshaft starts at the point of the engine build, you must design the engine around the stroker crankshaft first for a freestyle/freeride powerband.
If using a stock cylinder you should re-sleeve the cylinder with special sleeves that change the port locations to keep the bottom end hit very strong, if you don't, the engine will run like a top end race engine with weaker than stock bottom end power and way stronger on the top end.

If you resleeve the stock cylinders with custom sleeved do you just move the exhaust port down 2mm? Do you then have to reshape the exhaust port to match the cylinders are can you have an uneven larger lip on the top from moving the exhaust window down?