ICEngineering: Two-Strokes and Electrics

Last kart day of the year, Oct 27 2012!

I'm finally getting around to rebuilding the kart, which has been a spectacular autocross and level-1 fun (fun the whole time) success. The thing's a blast and a workout - driving it helps slow down the other racing, and the physical requirements helps motivate to get stronger. True, I haven't gone wheel-to-wheel in the kart yet, so I'm certainly no real karter...

My kart reflects that a little. I got it used, great deal, great working condition, but it's well-worn. The frame is Trackmagic, a brand known for it's complete lack of support with some odd-sized parts (need to machine a new lower steering column spacer for next season...), and has mismatched knuckles, some welding on it, etc. The engine fires on the first couple compressions but the inside of it was otherwise a mystery on purchase.

So rebuilding the engine was interesting, it was the first time I'd seen what modifications are done to it. The answer is not many...the ports are smoothed, but stock shape and size, transfers are all stock, compression is stock.

As usual, first step is turning working things into piles of gears

Look at all the 2strokes...

Tray 1 of 2. So many parts for such a simple engine!

What's most interesting is the damage found, there's been some fairly impressive detonation history.

Interesting piston damage

I'm still learning what is normal and what is not for this kind of engine and use. For instance, in the head, I think the damage below is actually normal-ish for extended use! Comparing the detonation on the head to the piston, I actually think the piston has been swapped after most of that head damage was done, but the previous owner just kept using the old head... let me know if you think otherwise.

Detonation never looked so evenly distributed

Also detonation around top of cylinder, apparently normal (and some lower in the cylinder?...strange)

I ordered a new piston (fancy Wiseco GP, forged) with rings, and I have a new head...that's it for the cranktrain! It'll go back together with the old cylinder, and the bottom end is good. Looking for a stock ignition now to get rid of some ballast, and maybe will increase compression ratio by machining the cylinder in the summer if I'm feeling comfortable. Only thing keeping the kart engine from reassembly is some transmission small parts still on order...about $100 worth of tiny overpriced washers and bushing which I had damaged the first time I ran the kart...without trans fluid...

I'm slapping it back together because again, the purpose of this thing isn't top-level karting, still just practice and experience. I'd decided to keep this kart and engine going until 4-strokes were legal (expecting 1-2 more years for autocross) and then go in for some nicer stuff. I am looking forward to racing a kart with less oil burning and noxious pollution. It would be nice for my interests in car racing and mountain biking to be less opposed, not to mention becoming less of a giant tool who selfishly contributes to ruining the world by purposely running unbelievably polluting things for fun...

However, now I don't think I'll ever go 4stroke. I think my next kart will be electric. (And yes, I am concerned about battery manufacturing and disposal, jury is still out)

The 86g soft LiPo battery in this costs $7 and is rated to 30amps at 8.4V! Battery technology is truly improving

After taking custody of one of Kenneth's older RC cars needing only a once-over and a battery, I have been impressed by the capability now so easily available. The above battery is essentially rated to 1/3 hp, costs $7, and weighs less than 1/5th of a pound. It's what's called a lithium-polymer battery, a simplified description of its chemistry. These have disadvantages in their volatility though. For application in larger packs, a different chemistry is introduced, LiFe. I don't really know my history, but I understand A123, the highly-government funded company which has gone bankrupt and just been sold to Chinese investors, is primarily responsible for them. Among many different characteristics, they are also very resistant to becoming...overactive after being damaged. You could drive a nail through a LiFe battery pack, and wouldn't expect it to react violently. A LiPo cell would violently burn and burst, and the chemistry we're used to in cell phones and laptops, lithium-ion, would do similar. The LiFe cells are what's used for the current generation electric cars. These are the cells in the Chevy Volt, the Tesla Model S (not the old Elise-based roadster, those were the laptop-type) and also in Zero Motorcycles. Compared to lithium-ion, LiFe also allow for higher discharge rates, similar to LiPoly. This is good for Zero Motorcycles, and good for aftermarket, because it allows power to be achieved through amperage instead of voltage. This is a lot safer to people if anything goes wrong and the electricity tries to short though the user.

Power, Watts, is (volts)x(amps): 1hp is 746W, and that can be achieved with any combination of amps and volts. It's just that with dry clean hands (which have great electrical resistance) under 100V is generally not enough motivation to hurt a person. 300V on the other hand could be much more...fatal.

So we now have the technology in the battery, and the voltage isn't scary. The hardware is available. Additionally, the hardware is available assembled, wired, programmed, and even warrantied! Motorcycles have donated the 2strokes we use in the karts, and now Zero Motorcycles make their electric drivetrains available to anyone.

This is the 2012 stuff. 2013 has much improved battery packaging

After heavily flirting with the idea, I won't be going electric this year. Maybe in another 2. The required components currently cost ~$8800 and the battery to power the 44hp 35lb motor still weighs 85lbs. I'm excited though. I am lucky enough to know electric cars can be seriously fast, and now with the market moving as it is, I expect batteries will rapidly improve in both discharge rate and cost.