Smartcarb SC2 - auto air density compensation & improved fuel atomization

How in the world could EFI cost that much for a single cylinder karting engine?

You’d need one injector, a small fuel pump, EGT sensor, crank sensor, throttle, COP, small battery, and a computer. You can build a port injection EFI system for a V8 for much less than that. Complete TBI off the shelf kits are well under $1k.

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The hardware itself isn’t the issue. I would attribute the added cost chiefly to firmware R&D for fuel mapping for the application & redesigns needed to incorporate it, & also perhaps sales & marketing hype. If a carburetor costs ~$700, I would expect EFI integration to be at least as much.

The thing is, TM already makes EFI 2 stroke MX bikes, so it wouldn’t be a stretch for them to pursue it & apply for CIK homologation for their KZ line. But whatever the costs, they would naturally roll into it. The nexus issue is would be is it financially worth pursuing?

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EFI on a tuned pipe two stoke still not at a level that could be used in karting IMO. KTM struggle with it as it is in Motocross. Latest version has three injectors (one in each transfer port, one in TB), crankcase pressure sensor and then all the rest. The other challenge is preventing\discouraging cheating of the system via software and/or hardware.

I’ll circle back with a BOM for the EFI system I have for the four stroke shifter with approx costs. It’s not far off $400 in parts. Not including dev for a custom ECU that’s non-flashable.

Interestingly KTM in previous years had been using a TPI (transfer port injection) system for their 2 stroke models where the injectors were mounted right in the transfer ports. Now it appears they’ve gone to a more traditional throttle body. From what i’ve read it’s been a praised change. It would have to be a spec EFI system that each manufacturer of KZ would utilize for cost reasons.

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It’s a combo of TPI and TB. They were experimenting with two injectors in each transfer port as well… two of off the pipe/low load and the additional pair for when you hit the piiiiiipe.

Spec ECU for KZ could be interesting. The pain is the need for a charging system the fuel pump. Even the smallest of pumps, with PWM controlled draw a decent amount of power… So the system would have to be total loss (Don’t forget to charge it) or add a generator… I don’t like either option really. Total loss is not user friendly and generator strikes me as something people would fool with to gain fractions of a HP.

Mechanical fuel pump (Still EFI\ECU fuel control) is another option… Well in theory, I have not found an existing pump that’s small enough… would probably have to be a ground-up design.

Researching the new KTM it sounded (and looked) like the TPI injectors were gone completely and there was just a throttle body with multiple injectors. I have to imagine you could use a similar generator setup as the KTM’s. A slightly different tank design would be required, but a drop in pump would theoretically be able to fit through a port the size of most of the fuel caps.

Anything specific on the negatives?

One thing I’d like on a shifter is a bigger carburetor. A road-racing 125 motorcycle used to use a 39mm, and so did Formula C.

Makes sense for RR, but the 30mm is probably more sprint friendly.

The SC seems like a plug-in alternative to EFI, minus the implementation hassles of the latter. If karting wants to be more “green”, this seems like a logical option.

Bigger isn’t always better, you gain volume on top end sure but you lose air velocity on the partial throttle which can be a bad thing for usable power.

I thought it was a hybrid, but I could be wrong… There’s certainly fuel pumps small enough to drop into a kart tank, that would flow enough, I’m just not sure how I feel about running the pressurized line from the tank to the engine and running the power line to the pump in the tank.

Curious on people’s thoughts on that from a safety perspective?

You really need that good transition control of the 30mm when the track grips up though. It’s one of the key advantages KZ had over the mod motos along with less compression braking.

I would think EFI on a 2-stroke, at least for road racing, would be easier compared to motorcross or sprint. That use case is nearly all WOT or off-throttle, with only a little part-throttle for the occasional turns. Not a lot of bouncing on/off/on throttle action to manage.

I agree that sprint would be more difficult (start with road and then move that way), but that is what open-source EFI (e.g. Megatunix on MegaSquirt) is all about. Other than physical cheating by alternate fuel type or bore/stroke modifications, EFI controls should be open.

IF it were to be done on a KZ by the CIK/FIA (unlikely) I would think the hardware portion would be spec, just like the dellorto is the spec carb. With this I would imagine spec pump, throttle body, injector, and control unit. However, let the mapping be open.

I’m sure there are lower-flow EFI pumps that take a lot less power. An AEM 340lph (total overkill) shows about 12amps at 13.vdc. A small 4s3p 21700 battery could easily power that for an hour. Essentially a tool battery.

Sorry for screwing up this thread. :slight_smile:

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I’d personally have no issue with it as long as the lines are run inside well-secured conduit for those worst-case crashes. It’s relatively low pressure (3-4 bar usually) and certainly low voltage. A manual STOP kill switch for safety (JIC) in addition to automated pump-off due to rollover, high-impact, or engine stoppage (normal automotive OEM stuff) should be sufficient.

All good. Seems to illustrate some of the potential, comparative advantages of this carburetor.

The bigger carb was faster, it was just harder to drive and suited the rotary shifter more than the reed.

I guess it depends what we’re comparing… I’m comparing mod moto vs KZ.

My intended application/discussion for the SC is KZ.

Yes, it seems some were either too lean or too rich…they could not fine the sweet spot.