Briggs Blue Slide - Advice on Tuning?

Any advice on the following with the blue slide (Canada Junior Lite). We’re introducing it this year in our club in the west:

  1. What color spring combo to use on the Hilliard Flame?
  2. Is there generally any advantage to hit the rev limiter, or do we want to be under the limiter (like with the red slide, where you normally target 5800-5900 rpm)?


I had given this some thought over the winter as my daughter was going to Jr Lite (though she grew so much we ended up putting her in Jr this year). One of the things I always struggled with was gearing. Everyone always says gear for the powerband, but many seem to forget that gears multiply torque output; it’s not just about the number on the dyno plot - final output to the wheels is determined by gearing. Therefore, my feeling is that, depending on the drop in power output up top, you might still put more torque to the wheels past the powerband with a smaller rear sprocket than dropping down 1-3 teeth in the rear to stay in the powerband. It depends on the severity of the drop and how long you’ll be sitting above the peak power output.

So many factors can affect gearing choice and whether/when to hit the rev limiter. For instance, if your kid is fast and pushing upfront with the lead group and constantly in the draft, you’ll want to gear lower so they have the top-end to stay with the train. But if they fall off the draft, it might be harder to keep up on their own.

If your kid is still learning and making mistakes or struggles to maintain momentum through the corners, then a higher gear will probably help, even if they are bouncing off the rev-limiter near the end of the straight. They’ll make the difference up and then some in the short sections and out of the corners. Elevation also plays a big role (not sure if your track has elevation). If you’re bouncing off the revs coming into an uphill turn (e.g. turn 2 at Mosport), the engine is likely going to fall down into its powerband up the hill and have a gearing advantage over lower geared competitors. If you have faster sweepers that exit onto a straight, then you can get away with being geared a bit lower, especially if you’re pushing into a draft.

Another consideration is whether the track is twisty and technical with perhaps one biggish straight. In that case, you may want to sacrifice being able to accelerate down the last 85-90% of the straight for more punch in the corners and make up the difference with exit speed. Having the extra power coming out of the corners can create more passing opportunities too or help with fending off another driver.

So I guess the answer is, it depends. :slight_smile: I’ve only been wrenching on my kid’s kart for a year and a half (Cadet to Junior), but my recommendation is to gear to hit about 6000-6100rpm for a blue slide. I don’t know what the drop off is for a blue-slide but, on the gold-slide, I find I’m pushing my kid’s engine to the rev limiter more and more. Jr Lite is 35lbs less so more aggressive gearing might not be quite as critical but, depending on the track, weather conditions, driving, etc, don’t be afraid to be on the rev limiter.