3+ gallons of testing, racing and wear means our equipment actually looks used, not brand new – particularly the OS 2090 pipe.

By Stephen Bess

Welp, I’ve tested the OS B2101 about as thoroughly as I possibly can at this point, and I’ve managed to squeeze nearly a dozen races (with practice, qualifying and mains included) into my testing for the B2101 Speed engine.  After each weekly race, I followed the same maintenance routine – remove the engine/pipe, clean and prep the clutch, disassemble and clean the head, backplate and piston/sleeve.  Carbon buildup on the button and piston head are lightly removed with 0000 steel wool, and everything is then thanked for running properly, cleaned and reassembled.  Yes, I whisper sweet nothings to my engines to keep them happy.  You don’t?

The Speed B2101 performed as well as I expected it would, with only a few issues.  First off, break-in went well – almost too well, considering the heat cycle method I use usually results in an engine that’s still pretty tight until several races worth of run time.  My B2101 broke in very quickly, almost too quickly for my liking, losing its tight mechanical pinch the first day after approximately 5 tanks of fuel–a much different situation compared to the Samurai engine that continued locking at TDC for nearly a gallon of fuel.  I don’t consider this a negative necessarily; manufacturing tolerances of tens to hundreds of a thousandth of an inch make all the difference in piston/sleeve fit.  That my test engine lost that mechanical pinch rather quickly but maintained its strong, well-sealed thump at TDC during testing meant that I wasted less fuel on break-in than I expected I would.  After 3+ gallons of on track torture against guys like Mike Truhe, Jeremy Kortz and other SoCal fast guys, the engine maintains a solid, substantial thump at TDC and idles reliably.

So the B2101’s powerband.  Due to its square-stroke design (identical bore and stroke dimensions), the B2101 is designed to offer a smoother, more controllable power band than its long-stroke sibling, the XZ-B Speed Spec II.  And indeed that’s exactly how the B2101 feels, compared to the XZ-B — smoother, more linear, less explosive low-end, but with a kickass mid-range and top end scream.  This engine spins and spins to the high heavens.  I ran it with a 6.5mm restrictor, Byron Gen2 30%/8% fuel blend, and an OS T-2090 pipe.  I also tested with the ProTek 2060 pipe set, but preferred the 2090’s smoother power and wider tuning window.


OS P3 plugs & Byron Originals 30% fuel keep the B2101 happy.


Speaking of tuning, the only nag I had with the B2101 has been a slight mid-range lean tune during long mains, in part due to our wide temperature shifts here in Southern California.  The engine is not leaking air, as I’ve sealed it with ThreeBond 1211 sealant, and the engine comes off the track dry and clean.  The few problems I’ve had were due to me and my tuning screwdriver.  On the track, the B2101 can fool you into thinking 1-2hrs leaner will be just fine, because the engine revs and revs and seems to love it.  Only after the sun goes down, temps drop and engine has fully warmed up to operating temp will it become apparent that the high speed needle is an hour or two too lean, as the engine will lightly bog in the mid-range and then catch its breath if you back off.  This happened to me twice, and both times the B2101 responded perfectly to a 1-2hr richer turn on the needle.  I also tuned the mid-range needle (spray bar), which is a needle I rarely if ever touch on my VZ-B and XZ-B engines.  Racing against crazy fast locals like Mike Truhe and Jeremy Kortz, I’ve kept the B2101 tuned to kill, so finding that slightly too-lean setting hasn’t been difficult.  Unlike the XZ-B and ProTek Samurai engines, however, the B2101 has been considerably more sensitive to low-end and mid-range needle settings.

I didn’t pop a plug during testing (although I did witness a friend’s radio tray burst into flames in the pits when he charged a lipo on NiMh mode–entertainment points!!!) which consumed over 3-gallons of fuel.  This is impressive and the sign of a proper head clearance from the factory, especially when using the recommended ultra-hot, thin element OS P3 plugs.  Mileage varied for me from track to track, but I consistently had half a tank of fuel remaining after 5-min qualifiers, and pitted often at 9-minutes.  In cold, damp weather like the kind I’ve raced in recently, the B2101 struggles for mileage like all engines.  I’m still finding the engine’s 10-minute sweet spot (a smaller restrictor would help) but due to that mid-range lean bog, I haven’t had an easy time reaching 10-min yet.  Time will tell.


Photo taken after a 20-min main – yes I keep my filters cleaner than this!


So my overall feelings about the B2101 as it compares to the other popular OS engines would go something like this — the B2101 is the middle child.  The Goldilocks of buggy engines.  The best of both worlds, between an XZ-B long stroke and VZ-B short stroke, and would be at home in a buggy or truggy, although its ideal fit would be buggy use.  Having raced the short-stroke Samurai (VZ-B internals) and the XZ-B Spec II quite a bit over the last few months and years, to me the B2101 is most UNLIKE the XZ-B long stroke, and still very similar to the VZ-B short-stroke engine.  If your last engine was an XZ-B stump puller, you will indeed notice a significant difference in the engine’s torque delivery and mid-range with the B2101.  However, I can’t say that the B2101 is that much different from the VZ-B-based engines, even though its square stroke design produces a different power band.  If you have a dialed-in VZ-B or Protek Samurai-type engine, I can’t recommend running out to buy a B2101, because I don’t think you’ll feel THAT much of a difference between the two.  To me, the B2101 is great but just not massively different from the short-stroke VZ-B style engines.  But let’s face it, the B2101 is the current IFMAR World Champion engine, so what the hell do I know?

It comes down to picking the proper weapon for your particular battle.  For me, I’ll run an XZ-B in truggy, and alternate between the B2101 and VZ-B style engines in buggy.  After all of this testing and all of this babbling (if you’re still reading, you get a cookie), I’ve reached the conclusion that any of the available OS Speed engines will do what it’s asked installed into any 1/8-scale vehicle, be it buggy or truggy.  There are fine differences between the platforms.  To the guys at the track who swear that OS’s don’t last, or are too expensive, let them believe that all they want.  They’ll be the ones replacing their entire engine around the time you replace a piston/sleeve.  They’ll be the ones flaming out, while your OS continues to run like a top.  Keep the engine tuned properly, keep it clean and sealed up, keep an eye on the plug element and treat it well with quality nitro fuel, and the B2101 will become one of your favorites.  It’s that good, even if its needle settings are a little more finicky than others in the OS .21 family.

My MP9 TKI3 test mule - raced weekly!

My MP9 TKI3 test mule, fresh off the track.  Thanks to Upgrade RC for the radio box & wing skins.