Comet 40 Series Max Reliable Horsepower?

#1
I know Comet rates the 40 series at 18 horsepower max, but many people run them far beyond that rating. I see them on built big blocks pushing 30-40 horsepower, Predator 670cc builds which already have 22 horsepower stock, and even on a 60 horsepower Predator 670cc lawn mower. My question is how far past the rating can you reliably go before you start getting belt slip/shredding? Would a 40 series even hold up to a Predator 420cc with a mild cam?
 

chrisr

Active Member
#2
I have a VC460 on a homemade bike that I was overpowering the 40 driven in the low 20s and when I got it into the high 20s the belt slipping and overrunning the 40 driven was really bad (correct clutch alignment and belt length). I ended up going with the Comet 94-c/90d and since have no issues with full throttle take offs. I have the 40 on 8 & 10hp on big mini bikes like in my avatar and it works great off road.
 

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#3
I have a VC460 on a homemade bike that I was overpowering the 40 driven in the low 20s and when I got it into the high 20s the belt slipping and overrunning the 40 driven was really bad (correct clutch alignment and belt length). I ended up going with the Comet 94-c/90d and since have no issues with full throttle take offs. I have the 40 on 8 & 10hp on big mini bikes like in my avatar and it works great off road.
If I do a big block I might be better keeping the stock cam then.
 

MJL

Active Member
#5
I have a VC460 on a homemade bike that I was overpowering the 40 driven in the low 20s and when I got it into the high 20s the belt slipping and overrunning the 40 driven was really bad (correct clutch alignment and belt length). I ended up going with the Comet 94-c/90d and since have no issues with full throttle take offs. I have the 40 on 8 & 10hp on big mini bikes like in my avatar and it works great off road.
Got any videos of your rides?
 
#6
The stock 420 seemed to do fine with the Comet 40 on my homemade but the VC460 makes a lot more power. Should also mention the default 40 driven spring is red for inboard but in my setup I had to use the reverse wound yellow spring for outboard.

https://www.bmikarts.com/Reverse-Wound-Comet-Yellow-Spring-for-40-Series-Driven_p_4381.html
I would be doing essentially a Stage 1 420 but with added safety parts (billet flywheel/rod). Keeping the stock cam. Guessing around 20 horsepower.
 
#8
20 forum horsepower :)

I think you're going to need more ingredients in your recipe to get to that number.
A site called Affordable Go Karts sells a pre-built 420cc engine that's very similar to what I plan, and they have recorded 22 horsepower and 6400 RPM. No idea on torque though. I've also seen GX390s with nothing but a governor removal, air filter, and exhaust (stock carb) produce just shy of 18 horsepower. The stage 1 kits add a decent bit of power and really let the engine breathe.
 
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