yooperbanshee Posted October 21, 2009 Report Share Posted October 21, 2009 I'm doing a rebuild on my banshee, I'm looking at bumping up to a 4mm stroker crank. I'm finding Short Rod Cranks and Long Rod Cranks. Is their an advantage to either one? Does the Long Rod Crank take a special type of piston? Thanks for the help in advance, Quote Link to comment Share on other sites More sharing options...
JMADD Posted October 21, 2009 Report Share Posted October 21, 2009 I'm doing a rebuild on my banshee, I'm looking at bumping up to a 4mm stroker crank. I'm finding Short Rod Cranks and Long Rod Cranks. Is their an advantage to either one? Does the Long Rod Crank take a special type of piston? Thanks for the help in advance, The longer rod is easier on the piston skirts and crank bearings. The long rod piston is the Wiseco 795 series (if I remember correctly) and has the wrist pin higher to allow for the longer rod. Quote Link to comment Share on other sites More sharing options...
JMADD Posted October 21, 2009 Report Share Posted October 21, 2009 Oh yeah, you'll have to either run a spacer plate at the bottom of the cylinders or have your head cut (or custom domes) to allow for the + 4 mm stroke. The maximize the potential of the longer stroke, you'll need to get it ported. Your port timings will be way off if not. Quote Link to comment Share on other sites More sharing options...
STINKYDELUXE Posted October 23, 2009 Report Share Posted October 23, 2009 I believe Long rods make more power because they end up have less of an angle to the crank which gives it better leverage Quote Link to comment Share on other sites More sharing options...
crustydemon Posted October 23, 2009 Report Share Posted October 23, 2009 I highly recommend a long rod crank, the ladies just love mine. Quote Link to comment Share on other sites More sharing options...
slacker1bob Posted October 23, 2009 Report Share Posted October 23, 2009 I believe Long rods make more power because they end up have less of an angle to the crank which gives it better leverage Power increase is pretty minimal, if any at all, but its more about high rpm reliability. You can safely run higher rpms and for longer duration than a short rod do to the better angel and less stresses Quote Link to comment Share on other sites More sharing options...
dajogejr Posted October 23, 2009 Report Share Posted October 23, 2009 I've yet to see anything concrete (via dyno pulls or track ETs) to state one setup delivers more power than others. As said, a longer rod lessens the angle throughout the stroke and puts less stress on the rotating assembly, in other words...your crank doesn't want to push the piston through the wall of the cylinder quite as bad with less angle. In theory only, a short rod crank might rev quicker due to less mass...but again, that's only my theory...I've never read a dyno pull or seen that proven at the track. Quote Link to comment Share on other sites More sharing options...
Burt Reynolds Posted October 23, 2009 Report Share Posted October 23, 2009 I would go with a 4mil long rod and use wiseco 795's I would stay away from using a spacer plate,milling the head or domes is better,it wont increase your crankcase volume. Porting is essential though,or your wasting your money imo. The only advantages i could see with a short rod is being able to use stock wiseco piston's so there are more overbore sizes available. But i went with a long rod and cut head and im very happy Quote Link to comment Share on other sites More sharing options...
No Limit Powersports Posted October 23, 2009 Report Share Posted October 23, 2009 Oh yeah, you'll have to either run a spacer plate at the bottom of the cylinders or have your head cut (or custom domes) to allow for the + 4 mm stroke. The maximize the potential of the longer stroke, you'll need to get it ported. Your port timings will be way off if not. You do not have to run a spacer plate with a long rod crank just the 795 pistons but you are correct if you do a 4mm stroker and +5mm rod which is most common you have to run the 795 to compensate for the longer rod and a spacer or a cut dome to allow for the additional stroke, assuming were talking about stock cylinders. I've yet to see anything concrete (via dyno pulls or track ETs) to state one setup delivers more power than others. As said, a longer rod lessens the angle throughout the stroke and puts less stress on the rotating assembly, in other words...your crank doesn't want to push the piston through the wall of the cylinder quite as bad with less angle. In theory only, a short rod crank might rev quicker due to less mass...but again, that's only my theory...I've never read a dyno pull or seen that proven at the track. Lets also keep in mind that a longer rod will dwell at tdc and bdc longer than a shorter rod. So the shorter rod will actually allow the ports to be open longer than a long rod motor will. The longer rod motor will put less of a angle on the piston at a given degree of rotation so less drag. So whats better long rod/short rod... well thats the ford/chevy/dodge question. Its all really prefrence. Some people have a hard time with the short rod/long rod comparison. Here is a little animation of it in action where you can actually see the difference. Now apply it to 2 strokes where are valves are in the cylinder and one can see some real advantages/disadvantages of both. Long Rod/Short Rod comparison I would go with a 4mil long rod and use wiseco 795's I would stay away from using a spacer plate,milling the head or domes is better,it wont increase your crankcase volume. Porting is essential though,or your wasting your money imo. The only advantages i could see with a short rod is being able to use stock wiseco piston's so there are more overbore sizes available. But i went with a long rod and cut head and im very happy Agreed, additional stroke cannot be fully taken advantage of unless the ports are corrected. Quote Link to comment Share on other sites More sharing options...
shanYE west Posted October 23, 2009 Report Share Posted October 23, 2009 Long rods do have less rod angle wich lets the assemble spin more freely and less stress on cylinder walls.. Thus creating a potential increase in upper RPM performance.. But.. Longer rods do have more dwell time at TDC and BDC. I've heard from some builders that actually prefer the short rods. saying they make the power faster over a long rod. As Dave said.. I've yet to see any proof of the increased power of a long rod over a short. Quote Link to comment Share on other sites More sharing options...
RILS Posted October 23, 2009 Report Share Posted October 23, 2009 When I built my 4mill cub I had this conversation with Dan Hull at a&s. I allready had the shortrod crank and didnt want to buy new domes to run 68mm unless there was enough difference to justify it. I was told by him the long rod was making a little better torque curve but the short rod would rev faster and make a little more hp on the dyno. I ended up with a 65mm cub and the short rod crank and dont have any complaints. If you plan on going to a bigbore in the future the bb pistons are easier to come by for the longrod crank, last time I looked you had to go with vitos or wsm for a bb and shortrod. I had a 68mm cub at one time but sold it in favor of the 65mm mainly because of piston availbilty with the shortrod crank I couldnt tell any difference in the power. Quote Link to comment Share on other sites More sharing options...
4strokekilla1987 Posted October 24, 2009 Report Share Posted October 24, 2009 Long rods do have less rod angle wich lets the assemble spin more freely and less stress on cylinder walls.. Thus creating a potential increase in upper RPM performance.. But.. Longer rods do have more dwell time at TDC and BDC. I've heard from some builders that actually prefer the short rods. saying they make the power faster over a long rod. As Dave said.. I've yet to see any proof of the increased power of a long rod over a short. i too heard the same i went ahead with the 5mil short rod, when i get my bike back which should hopefuly be next week i will let you guys know how it goes, i also did hear (not from my builder from someone else) that the long rod are good for torque which imo is good for you guys that ride dunes Quote Link to comment Share on other sites More sharing options...
yooperbanshee Posted October 24, 2009 Author Report Share Posted October 24, 2009 Thank you very much for the input. The animation was good to see! I really don't want to port the cylinders so I'll probably go with the short rod crank. I'm thinking that a long rod with porting may be a little much for the riding I do. I mostly ride trails in the upper peninsula of MI. No dunes here. I'm curious what might be the best set up with the short rod would be. The cylinders I have will have to be rebored, they are currently at 20 over. Quote Link to comment Share on other sites More sharing options...
alf44 Posted October 24, 2009 Report Share Posted October 24, 2009 Thank you very much for the input. The animation was good to see! I really don't want to port the cylinders so I'll probably go with the short rod crank. I'm thinking that a long rod with porting may be a little much for the riding I do. I mostly ride trails in the upper peninsula of MI. No dunes here. I'm curious what might be the best set up with the short rod would be. The cylinders I have will have to be rebored, they are currently at 20 over. Why would you not port it. For trail riding you will get the most gain from a good trail/dune port job. Seems too me your kinda going backwards hear. A good port job and advanced timing should be done before diciding too stroke it! IMO. Am I wrong here guys? 1 Quote Link to comment Share on other sites More sharing options...
shanYE west Posted October 24, 2009 Report Share Posted October 24, 2009 Lets also keep in mind that a longer rod will dwell at tdc and bdc longer than a shorter rod. So the shorter rod will actually allow the ports to be open longer than a long rod motor will. The longer rod motor will put less of a angle on the piston at a given degree of rotation so less drag. So whats better long rod/short rod... well thats the ford/chevy/dodge question. Its all really prefrence. Some people have a hard time with the short rod/long rod comparison. Here is a little animation of it in action where you can actually see the difference. Now apply it to 2 strokes where are valves are in the cylinder and one can see some real advantages/disadvantages of both. Long Rod/Short Rod comparison That animation was great! sometimes a picture IS worth a thousand words.. lol VERY good info! Quote Link to comment Share on other sites More sharing options...
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