It depends on the dyno of course but a 1% margin of error would be horrific 
I spent a few hours with a builder who specializes in 206’s. That’s the only thing he will run on the dyno. It was definitely repeatable to within a tenth of a HP and claims a resolution down to 1/1000.
I think we did about 30 pulls over three hours. A/B testing most changes.
He was floating around USPKS at MCCC. I even saw a few High Rev stickers on karts. Maybe @XanderClements can add more details there.
That’s amazing but if it’s a eddy current dyno or even an inertia dyno ok. I tried to find info on resolution and repeatedly but couldn’t find.
Just for comparison, its better than the best tire pressure gauge.
This was an inertia dyno. Here’s more info on the visit
Saw that one right after reading this thread and had to chuckle out loud…
For what to do with a less powerful engine: you advertise it as a school / practice engine, include a dyno sheet, and sell it at a discount.
I just read this whole thread. Damn. Y’all are fired up.
Here’s the reality that I think is getting lost in this discussion where you all are way way way down in the root system of the weeds:
-racers are their own worst enemies. The karting gods descended from heaven and gave us an engine package that basically saved grassroots performance karting for about 10 years. And lo, as is time honored tradition, we (racers) have found a way to screw it up. The same thing happened Rotax, with KT-100, and many other engines before that. There will always be someone with more money and more time and more “throw stuff at it and see what sticks” than you.
-People are twisting cams. It’s not a rumor, it’s a fact. How much difference it’s making is debatable. It isn’t “legal,” but it’s not “illegal” either. Until Briggs makes a quantifiable line in the sand rather than a “range” the “cheating” will continue. This is only 1 of a handful of things builders are doing.
Regardless, .8 hp, .4 hp, or 17 hp it isn’t just one* thing that separates those that win from those that don’t universally. Kart setup, practice, and knowing what to change and how to change it is what wins more races than big horsepower.
The dyno cell is a great tool, but it isn’t the real world. You still have to cut your apex right. A fast motor won’t overcome an overstuck kart.
Lastly, you could have a .4 higher horsepower engine out of the box, but if you don’t care for the motor properly that advantage will go away quickly. A lot of performance is gained or lost by preventative maintenance and simple attention to detail.
Update on this from PRI:
Spoke directly to the Briggs folks at their booth, asked about the cam question:
-Their engine developer / engineer was dismissive of advantages, and said that all people are doing by twisting is damaging the cams. He had a pretty wordy explanation for this, but I can’t say I followed all of it nor felt like there was a lot of really deep insight despite a pretty lengthy explanation. That could be me not understanding, or him giving me a political type answer.
-They also had an assembler there who commented that twisting of the cam interferes with the compression release mechanism, which leads to making it impossible to start the engine.
Regardless, it seems that from Briggs’ perspective they view the rules loopholes competitors perceive as an experience of the vocal minority, and not representative of a larger systemic issue.
I did ask about rules updates for ‘24 and they both claimed they didn’t know what specifically would be updated, but that something would be put out in January.
Not totally buying this. You can still start a 206 with a failed decomp. It’s not impossible by any stretch of the imagination. A pain in the arm? Sure. But totally doable.
Have to say I’m disappointed with that statement.
I heard a few things from a few vendors that I was pretty disappointed in, or surprised. Most at PRI were not karting, and it isn’t about naming names.
Like all of us, I don’t know everything, but I’ve done this racing thing long enough to know when I think* I’m hearing facts vs when I’m hearing speculation or deflection.
In fairness to them, it’s not common in any application or industry to tell customers there’s an issue until after you resolve it - and I frankly don’t know how to solve it (have ideas but not an engineer nor claim to be one).
I just thanked them for their time, smiled and walked off slightly shaking my head.
100% false statement. Yea, you can break the compression release. No, these engines don’t have enough compression to make it impossible to start. You just roll it to the top of compression and yank her good.
I’m just reporting what they said 
The largest discussion this off season has been block height.
Meaning what some call ‘pop up?’ Or am I not understanding the term?
We’ve still got people decking blocks for max popup if the piston isn’t already out of the hole far enough and it’s starting to become more common again.
Gotcha.
I had heard that the tooling at Briggs was used in such a way that it was easy to visually see if the block had been decked post-Briggs but it sounds like I’ve got more to learn.
I do recall one fairly large event I was at several years ago where a driver in the Junior categories was caught with a decked engine that still complied with its ‘smart seal’ numbers. I never understand exactly how tech determined that it was incorrect, but after watching that driver yard everyone else by a straightaway at a draft heavy track it also didn’t surprise me.
Racers are our own worst enemies.
I’d love to see dyno numbers for these optimizations. Sure, the dyno has its limitations, but it’s still about the most repeatable tool for this.
From the rule book:
Deck gasket surface finish is not a tech item. Piston pop up can be .0035” maximum. Piston pop-up to be checked with flat bar in center of piston
parallel to piston pin and then again checked 90 degrees to piston pin. Push piston down to take up rod play.
Is that does with feele blades or a dial gauge?
