Cherry Picking Short Blocks

JJ/Flash,

What is marginal in your opinion? A tenth of a hp? To think they are all exactly the same is silly. Yes, they are close, but equal? No. When a guy can afford that last tenth, wouldn't he be a fool to not try to find it?
Based on extensive dyno AND track testing, I can say .10 is marginal. I have seen karts with .3 less win big over those with more. Handling trumps HP and with 5 dyno pulls an engine will vary by .10 pretty easily. People who talk about chasing .001 are people who don't really know what makes a difference at the track and are usually chasing ghosts with greenbacks. That said, I do everything I can to get the best performing motor I can for peace of mind and the personal challenge. However, I am not losing sleep when one motor is .2 more than another. I also find almost every 206 I work with is within .2 of each other. I don't do anywhere near the numbers as Brian, Jimbo, or Baker, but I have tested dozens (getting close to hundreds) of 206's and that is the window I find. I have also tested everyone of these guys engines and find they are usually in that window as well.

Right on JJ!
 
When they make the "APP" available let me know but the last time i asked well you know.
 
With the Yamaha KT, cherry picking is especially fruitful. There are some things that can be overcome, like getting the bore straight (unlike the Briggs) and 90° to the crank. Some other things are a little harder, like crank run out. Pin center, to crank shaft center, measurements are notoriously off. Someone with the means, can buy a lot of crank halfs, measure crankshaft centers to pin centers and match them up. A crankshaft with no run out is always better than one with run out. The cast in cylinder liner is also a problem. Mr. Burris (Mike's dad) once told me about a time when he and Mike Culver blue printed 10 new KT's. One was especially bad and nothing they did could fix it. Burris told me he took the bad engines barrel and cut it in half, vertically, right through the exhaust port. He found a big cavity in the aluminum casting right above the exhaust port in the liner. Mystery solved! I have personally dynod a lot of blew printed KT's and have found a wide variance in the peak, and overall, horsepower. One of those, which registered the highest EGT I had seen, also made the most horsepower of all the KT's I tested on my dyno. I attributed this to a good fit on the liner. Conclusion; there are a few exceptional KT's, a lot of okay KT's, and a few really bad KT's. Sad to say, I know of no way to overcome this problem. Unless Briggs & Stratton is working with a .0001" tolerance, I'm sure they have the same problem.
 
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