Tuning an apex primary

[Chudwick]

Hello. I built a rzr xp4 out with an apex engine and electronics. It came out awesome and is stupid fast. Right now it’s running about 4k rpms to do 10-12 mph and it’s rough on the ears. It was engaging at 4k so I bought a couple primary springs from Yamaha and got it to engage at 2500 so I got it moving in the right direction. I messed around with some secondary springs yesterday hoping to get the rpms to be a little lower in between 10-20 mph but had no luck. Is it possible to achieve what I’m looking for by changing the primary weights ?

 

[Srxspec]

What are you using for a secondary setup? Stock Apex?

 

[maim]

you could try my primary clutch set up as it will crawl at less than 5mph where as stock clutching wants to be doing 15 mph in the sled.

my set up is drag n flies with the heel having 3 grams of weight in it with the black spring (if memory serves). it does loose some top end but the gain in bottom end/crawling was worth it.

 

[Chudwick]

What are you using for a secondary setup? Stock Apex?

I’m using a stm tuner secondary.

 

[Chudwick]

you could try my primary clutch set up as it will crawl at less than 5mph where as stock clutching wants to be doing 15 mph in the sled.

my set up is drag n flies with the heel having 3 grams of weight in it with the black spring (if memory serves). it does loose some top end but the gain in bottom end/crawling was worth it.

I’m not too concerned about top end to be honest. I haven’t had the chance to get it wide open but I’m thinking this thing will do over 100mph and I don’t need to go that fast. I’d like to bring the wife and kids out but it’s really loud when just slow cruising and they won’t like it. I added a custom exhaust which definitely helped out but lowering the RPM’s at low speeds would really do the trick.

I was hoping to do it with just the springs because they’re super easy to swap out so if I wanted to go out and raise hell it would be just a couple bolts to change it back but I’ve tried all options I could come up with and none of them worked.

 

[74Nitro]

What are the identification marks on the weights and what diameter are the rollers?

 

[maim]

with smaller rollers, putting more weight into the heel/lowest hole should help.