Comet 40 Series Max Reliable Horsepower?

[SquidBonez]

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?

 

[Denny]

That will depend on how aggressive you get with hearing and tire size.

 

[SquidBonez]

That will depend on how aggressive you get with hearing and tire size.

Right now, I'm thinking 18" tires and a 5.4:1 gear ratio. If I go bigger I'll drop the ratio closer to 6:1. Kind of basing it off the Edge Taipan buggy which calls for a 5.5:1 ratio on 22" tires (which i think is pretty high for such large tires).

 

[madprofessor]

I'm thinking 6:1 would be as tall a gear as you should go right now, on those 18" tires.
If you're already concerned about overpowering that Comet 40, then you want shorter gears to minimize the pull on it.
With that much motor, shaving off some top speed for better holeshot should still leave you plenty of multiple rollover potential on the top end.

 

[SquidBonez]

I'm thinking 6:1 would be as tall a gear as you should go right now, on those 18" tires.
If you're already concerned about overpowering that Comet 40, then you want shorter gears to minimize the pull on it.
With that much motor, shaving off some top speed for better holeshot should still leave you plenty of multiple rollover potential on the top end.

I can always adjust it if need be. Not sure how many RPMs I'll be turning. I got in contact with affordable go karts that sells a pre-built big block that's very similar to the one I'll be building (basically a stage 1 kit with billet internals for added safety, stock cam). They say that engine can turn to 6400 RPM. I was under the assumption I'd be turning around 5500. If that is the case I could lower the gearing. Aiming for 55mph.

 

[Denny]

Manco had a Dingo with that tire size and gear ratio and a tav2 with a 5 horsepower Briggs. It moved just fine (stock) 35 mph top end.

 

[SquidBonez]

Manco had a Dingo with that tire size and gear ratio and a tav2 with a 5 horsepower Briggs. It moved just fine (stock) 35 mph top end.

6:1 you mean? Because I have a Dingo with that exact gearing. I came up with 5.4:1 because big blocks don't rev as high as small blocks but have way more power and torque. The Edge Taipan buggy plans uses a big block and a 40 series, and runs a 5.5:1 ratio on 22" tires. That being the case, I imagine a 5.4:1 ratio with significantly smaller tires would be safe to run. And again, it could always be changed if need be.

 

[madprofessor]

Wondering about that 6,400 rpm's. Hard to imagine that high on stock springs before they float, guessing it would have stiffer ones.
Regardless of how it gets there, hoping that "billet internals" includes a flywheel. Stock cast iron flywheels aren't rated for high rpm's, can explode at high rev and shoot chunks thru housings and people.

 

[SquidBonez]

Yep, 35 pound springs and billet flywheel

Wondering about that 6,400 rpm's. Hard to imagine that high on stock springs before they float, guessing it would have stiffer ones.
Regardless of how it gets there, hoping that "billet internals" includes a flywheel. Stock cast iron flywheels aren't rated for high rpm's, can explode at high rev and shoot chunks thru housings and people.

 

[Denny]

That was the ratio my brothers Dingo had. I had the bigger one with 8 hp Briggs and 22 in tires and 6:1 ratio.