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Last Post 19 Nov 2015 01:03 PM by  Scoob
KT100 or Briggs World Formula
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New Member
New Member

06 Nov 2015 10:39 AM
    I'm new to autocross but have fixed up an older kart for my son to compete in the FJB class. He raced in two events in 2015 and did OK. He certainly has some improvement to do with driving skills but at the same time I feel his Kart isn't competitive. The rules allow clone engines in his class so we installed a Harbor Freight Predator engine. What I didn't realize at the time is the power difference from on engine to the other in his class. The rules don't allow any modifications other than removing the governor. His engine is probably 7 HP with the governor removed while some of the other engines are 12 to 15 HP. We will be building a new Kart (probably fixing up another used one) over the winter and what I'm trying to resolve is what engine use. I have been told by one person the top engine is the Briggs World Formula (12 to 15 HP) but have read a lot saying the Yamaha KT100 is in the same power range. If anyone has experience with the two engines I would like to hear the pros and cons with regards to autocross. I don't mind a 2 stroke, I grew up racing motocross and have a 125 shifter kart now. I like the simplicity of the 2 stroke but If the KT100 has a measurable disadvantage to the World Formula then I would probably go with the World Formula. One nice thing about the KT100 is they are readily available used, Karts with a world formula don't seem that easy to find and are about twice the price.
    Basic Member
    Basic Member

    19 Nov 2015 01:03 PM
    Sorry for the late reply - hopefully you've asked elsewhere and gotten better responses. I'll share what we've gone through and where we see SCCA going. My son started with the JC kart and Comer C50 his first year, then moved to a Comer K80 in JB the next year. Talk about under-powered and finicky. We switched mid-season to the KT100 and once I figured out the little carb, it ran great for a few years. By this time I had joined the KAC and learned that the SEB was pushing us to adopt the World Formula as a spec motor for the JB and JA classes. The karting parents didn't like that idea, but the SEB didn't want to let it go, so a compromise of sorts was adopted: make the World Formula a favored motor by weight differences between it and every other motor. It quickly became clear to most karting parents that the WF was the chosen motor under this scheme and satisfied the SEB by performing an almost wholesale switch to the WF over a few years.

    While I resisted the switch initially, we did go to the WF a few years ago and I can honestly say that we both couldn't be happier. Once we worked out the kinks in the tuning and got his corner-balancing better, it's been a great switch. The motor weights 2x the KT100 and with smaller kids like my son balancing the kart can be challenging. But it's as close to a "set it and forget it" motor you'll find - very little adjustment and tuning is required to get it in its broad sweet spot. And no more external starter to worry about charging and carrying.

    While we are adjusting weights again, the WF is still going to be favored to make it the de facto standard. I don't see that changing.
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