Driver 11 verses 12 question

W5R said:
That part isnt making sense to me....if you ran 11/69 with the stocker 208cc, you should be needing more gear not less gear, for the big bore stroker, since the big bore stroker is going to make more power and at a higher rpm, with a higher peak torque than the stock engine did. What rpm do you have the clutch engaging at and what is your target rpm on the track, how big is the track, and what air pressure are you using?

A big bore Honda stroker should be making peak torque around 4400-5000rpm, maybe more or less depending on the cam and rest of the build, i would not have the clutch engaging anywhere less than 4500 if it is a true open honda big bore stroker. I had one of these engines last year that was 3" bore .175 stroker with a .356 cam and it was making peak torque around 5000rpm, turning 9500rpm on the small tracks.
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I guess im not understanding your explanation but it maybe im explaining it wrong.
So if you go out and your turning 9500 at the end of the straightaway and you want to drop top rpm to 9000 why wouldnt you take gear off (meaning higher gear)?
 
dirttrax said:
I know there are pages on pages debating the driver verses final ratio debate.
What I'm wondering is if I keep the same overall ratio will going from a 11 to a 12 driver help with a kart spinning as bad maybe not shock the tires? Or will it be no different? Thanks
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here is a chart showing the "chordal" action of chain over a sprocket. I think basically it just shows you how much the chain has to bend over a certain size sprocket. I don't know exactly what it means, but if the chain has to bend less, less chordal action, maybe that's good.
 
dirttrax said:
I guess im not understanding your explanation but it maybe im explaining it wrong.
So if you go out and your turning 9500 at the end of the straightaway and you want to drop top rpm to 9000 why wouldnt you take gear off (meaning higher gear)?
Click to expand...

I think you did misunderstand what I said. You would take gear off to drop rpms. I'm saying the big engine is going to need more gear than a stock engine will usually need. With a mild predator at our tracks I normally use a 14-60's gear, but for my open stroker animal, I use a 12-60's gear...does that make sense? The predator turns 7000rpm at most, the animal turns 9500-10k, which is the reason for higher gearing for the bigger engine.
 
Engine size is not what determines RPM.
Typically smaller engines need too turn more RPM In order to make the same power.
4stroke : cam timing, valve size and induction tract are what dictate​ the power band.
The exhaust would play a role as well.
 
Sorry for the late reply guys. We finally got around to race. I measured the track at 480ft in the center of the main groove. I went from a 11/65 to a 12/68 and the rpm dropped from 9500+ to 9000 I then went to a 12/66 to bring rpms down a little more and we wound up turning 8700 in the feature. There was 60 karts that timed in and we were turned the fastest lap time and lead every lap of the heat and feature. To me the gear changed def helped it hook better and was crazy fast yet still pulled really hard off the turn. Thanks
 
dirttrax said:
I guess im not understanding your explanation but it maybe im explaining it wrong.
So if you go out and your turning 9500 at the end of the straightaway and you want to drop top rpm to 9000 why wouldnt you take gear off (meaning higher gear)?
Click to expand...

If you are wanting less rpm, why not go up one tooth on the driver and leave the rear gear the same, and you will get the rpm drop you want? I always use the biggest driver gear i can get by with and get the rpms i want to see. The .356 cam you have will work well at 9000-9500, they are still pulling hard at 9500 when the rest of the engine is set up properly. I always end up with 1-2 teeth smaller on the driver with my open engines than i do with the stock engines, on the same track. So if i were using 12-68 on a mild stock engine and turning say 6800 rpm, i would want at least an 11-68 on the big engine, if not more, because the bigger engine will not only turn more rpm, but it will be making power at the higher rpm also....the smaller engine may turn 6800-7000rpm, but whether or not it is still making power there is another question, and is not very likely that it will be
 
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