Silver bullet for Honda GX balancing?

1

So I know I am quite stubborn on the subject, but I would like to find a solution to balance those engines.
As Honda is manufacturing those engine at a industrial grade and scale, I suppose the tolerances on the internals might be small enough to not create differences. If you consider that and the fact you apply the same carburetor setting, I don’t see what could be the element that creates the issues.

My theory is that intake/exhaust are too limiting. Intake is a simple piece of plastic, highly restrictive and I guess it makes a big difference between two seemingly engines. Exhaust is also far too restrictive, because SODI only sells the indoor exhaust on its RT8/RT10 karts. It overheats tons as well.

Would changing both those parts allows for engine to be closer ?

2

So if I understand correctly you are trying to figure out if the variance in the Gx270 is due to a couple specific parts being inadequate to the task? Can one modify the intake and exhaust at all currently? Could you mess around with a few engines to see if they dyno more similarly?

I think you showed me a link to aftermarket stuff to make the gx better (aluminum flywheel etc). Are there any aftermarket intake improvements already out there?

Personally I have been noodling the idea of getting an old gx270 to learn how to rebuild them. But I have no tools and am an imbecile, which is problematic.

Also, this looks cool and makes 20hp and isn’t hugely larger than the 270. I’m guessing there’s a reason it’s not used as a kart engine tho:

IMG_0949

3

I’ve found it to be the opposite. If you create an artificial breathing limit, it tends to bring the engines closer. Although that’s something I prefer to do post carb with a restrictor plate (or just run a smaller carb) rather than in front of it in the form of a choke of sorts.

In the rental scenario you have two challenges. One: getting them close with an amount of blueprinting: popup, compression, valve clearances, carb etc…

The second is keeping them there. This is the really hard part. After some time you can see variances in cam wear, compression, valve seal, ideal valve clearance etc.

4

Those are bicylinder engines weighting around 44kg or 98lbs. Pretty big and 22lbs heavier than the GX390. Could be fun but not really adapted to such use.

Admitting valves and cams clearances are checked often and considering the fleet is used only for competitions and not arrive and drive, it should be fine right ?

My theory was that SODI didn’t put too much work in their base exhaust, so we could see differences in backpressure and overheating, especially considering how fast a track it is.

5

Honda twins have been used in “Super Prokarts” in the UK and Ireland. Pretty quick, probably around KA speeds, with electric kart weight :smiley:

image

https://www.cpracing.co.uk/spro/main.php

Maybe, except there’s the factory recommended clearance for expansion when it’s turning a generator and then there’s what’s actually fastest for each engine. Max lift\minimum clearance is rarely the answer. This variance in ideal clearance can make a measurable difference, as much as 0.2\0.3 HP but finding it is really only practical on a dyno. Also, this ideal clearance can change with time.

The other variable of course is that the chassis can sap power too. Dragging brakes, bent frame, low tire pressures, toe, drivetrain resistance in chain\belt and axle bearings etc, can happen during an event, so checking the fleet before hand only goes so far until some wobbler causes problems.

There’s so many variances between out-of-the box generator engines that only matter when you have competition racing and it’s easy to go down a rabbit hole to equalize them mechanically. You can’t rely on the OEM tolerances and you have no choice to go beyond them. That includes the carbs too because just like the engines, some will work better than others.

Overall this is why I like running larger engines than needed then holding them back with a carb restrictor plate, or a smaller carb. It brings the engines closer together. Smaller carb is preferable because you keep good throttle response.

I think getting rid of the stock intake and exhaust would exacerbate the differences between the engines. But the intake side is easy thing to test. Removing the stock intake\airbox usually warrants a jet change too. I do get what you’re saying about potential heat soak if there’s an exhaust restriction, logging head temps might help with that.

So, in terms of what to do with that particular fleet… the ideal thing would be to gather data to see where they are. IMO the only way to do that reliably is with a dyno. Once you know where they are, then you can decide what changes to make and test to bring the fleet closer together. There are a couple of rental series that have a dyno trackside to “objectively” verify any concerns from drivers. I believe endurance karting do this.

I’m not sure what kind of dyno Chris uses, but it’s possible to make a portable hydraulic hub dyno. Basically remove a wheel from the kart, bolt on the pump to the hub and make some runs. If the curve doesn’t look right, then you can do some logging and digging.

I should note, I know you’re aware of a lot of these things, just documenting them here for readers too. I know a lot of these things might seem very nuanced, but the list is LONG and when you combo a handful of them together you can quickly end up with a dog of a kart.

6

The bent chassis thing is huge. That seems to be the primary driver of fleet disparity that I have seen. However, Tanguy’s fleet is “race only”, I think, ergo less likely to have damage from general public abuse.

7

Yep I understand that. I was careful to say “during the event” as presumably they would be checked prior. Drag in the drivetrain can vary too.

8

It is really frustrating to think that there is not a good solution to this issue. IMO rental karting competition is going to be more and more prevalent, as it is a steady source of income for facilities and it is far cheaper for drivers.

That’s why I think there is a market for a proper rental kart engine and not an off-the-shelf power washer engine.

9

As much as I love burning gasoline, electric karts seem to fit this bill better than anything else.

10

Indeed, but without a breakthrough in the battery technology, it aint gonna happen

11

Briggs 206, Tillotson etc. I think is as close as one can economically get. Essentially you’re oursourcing the blueprinting. Maybe not ideal for the weight of a heavy rental kart, but if you want something that’s intended for parity… Outside that you’re likely moving outside OHV generator stuff and I would imagine the cost gets exponentially higher.

My thought is that economical solutions will have to involve blueprinting of some sort. At the very least, getting a bunch of them on a dyno, picking the ones that are closest to each other and putting the rest aside. Buy 25 or even 30 engines for a fleet of 20 karts for example. Taking that approach clone engines vs genuine Honda GX starts to make more sense. You can end up with a more robust engine with billet rods for around the same cost. Labor is another thing of course.

I think current electric can address this for sprint races in the technology\mechanical sense. But I think you might need to have lots batteries on hand to hot swap depending on power level and length of races… plus the cost is going to be pretty harsh.

The new outdoor K1 track operates karts I think? I’d be curious to know the economics behind it. I think they are importing the raw materials (or at leas the kart) so that perhaps helps with costs.

12

How is the quality of clones against Honda genuines ?

13

:joy::joy::joy::joy: this made me chortle

14

Aaargh. I’m a proponent of electric but… it just doesn’t have the same fizz. At least in the forms I have driven which all have a powerband that abruptly reaches its top end and then you awkwardly toodle alongside the person you should be pulling ahead of since you got to power earlier. But don’t.

So you wave and smile and then pod them off the next corner.

But yes the parity is way better. And the heavy guys do way better.

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