torque converter long vs short belt?

#1
So I was looking into buying a new belt for my setup and kinda went down the rabbit hole, what would be pros and cons of short vs longer belt?

my setup came with a 669 belt but I was reading a lot of places recommend a longer 725 belt?

Also stumbled across some people claiming a bit longer belt actually gave them better performance
 

MJL

Active Member
#6
A longer than necessary belt would effectively increase your engagement RPMs and reduce your final drive ratio. Can't see where that would be helpful excapt maybe in a hill climbing competition (providing the longer belt doesn't slip).
 
#7
On my MTD there are 2 different belt lengths that will work. They are very close in length, i chose the slightly longer one.
It just means the engine is like 1/2" farther forward than the shorter belt. I was looking for more room to fab up an intake manifold so that seemed like the better choice.
I have had zero problems with it works like a champ.
ymmv
 
#8
Well, got the "725" belt in, seemed a bit more robust than what I was running, maybe im crazy but seemed a hair thicker, was a bit longer when compared to the 669 but seemed to actually fit snugger almost once installed since it had a bit more width?

Anyways, bike seems to run good, grips better than what was there, I actually was able to hit 40 mph top speed where as my previous was 36 mph although not much a of a difference, probably just need a fresh belt.

I still end up just sitting on the governer at 5k rpm if I drive it on the street. Off road its great.
 

MJL

Active Member
#9
Well, got the "725" belt in, seemed a bit more robust than what I was running, maybe im crazy but seemed a hair thicker, was a bit longer when compared to the 669 but seemed to actually fit snugger almost once installed since it had a bit more width?

Anyways, bike seems to run good, grips better than what was there, I actually was able to hit 40 mph top speed where as my previous was 36 mph although not much a of a difference, probably just need a fresh belt.

I still end up just sitting on the governer at 5k rpm if I drive it on the street. Off road its great.
I'd call the seller of your engine and see if is even capable of of more RPMs with the existing valve springs, under load. You may be hitting valve float. That 5800 rpms may be a "on the stand" measurement used for go kart racing. If it were me, I'd put a billet rod and 22 lb valve springs in it if you want to rev it much past 5k on a regular basis.
 
#10
I'd call the seller of your engine and see if is even capable of of more RPMs with the existing valve springs, under load. You may be hitting valve float. That 5800 rpms may be a "on the stand" measurement used for go kart racing. If it were me, I'd put a billet rod and 22 lb valve springs in it if you want to rev it much past 5k on a regular basis.
Ive got the Ducar 212, seems like its got some decent parts in it and should handle the RPM, but I dont really care much about revving higher, just annoying when it starts to hit the governer cause its kind of invasive, its definitely the governer surging and not valve float, saw some reviews that mentioned how aggressive the governer was with this engine and thats exactly what im feeling
 
#11
Drilled a hole a bit further away on the governer and its letting me rev out to 5300 rpm with no interference but seems to stop about there at 40 mph/5300 rpm

Either way, bike runs great, dont need any more speed
 
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