I find that if I need to rest, putting on a racing vid of mine pits me right to sleep. There’s something very calming about 4-stroke kart engines gently putt-putting along.
However, aren’t 4 strokes pretty standard in dirt bike world? Are there versions that sound angry?
Well my vintage MX bike is loud 1974 BSA b50mx, 570cc.
That’s proper growly!
Someone post a loud 4-stroke kart engine.
The Biland always sounded pretty cool. Reminds me a bit of a V4 dirt midget engine.
Believe it or not, 4 strokes can be harder to please neighbors with because their lower frequency sound travels further.
That makes proper racecar-like noises, relatively!
Yes, unfortunately, and the noise from 4-strokes booming across valleys killed half of America’s motocross tracks. CRF/YZF/RM-F/KX-F/SX-F 250 and 450 are all obnoxiously loud and the low-frequency noise carries much better than a two-stroke, with the added “bonus” that effective silencing is both heavy and restrictive.
So why is it we don’t have angry 4 stroke karting? Maybe the dirt folk? Oval racing aint quiet.
Because they blow up, big time, and cost a fortune when they do!
A four-stroke engine’s maximum gasflow is limited by RPM, a two-stroke engine’s maximum RPM is limited by gasflow.
Karting is dominated by a small band of Italian 2-stroke manufacturers. Rotax also have no interest in developing a 4-stroke lump for karting. So when the FIA announced 4-stroke basically it never really happened because of the push back. dirtbikes ont he other hand are dominanted by the likes of Honda. And Honda never liked 2-strokes. The move to 4-stroke has not been a success for the average dirtbiker
When we’re talking small capacity engines 2-stroke just have 4-stroke licked. For some reason people accept that 4/ can have double the capacity, but when it’s equal up until around 250cc, nothing comes close to a 2-stroke.
Also, you have to imagine the development war would be atrocious with 4-strokes. In both spec and multi-make. The low power stuff isn’t so bad, but once you’re over 15hp and big guns come out to play.
I was there racing mx when it went 4stroke and I remember at the time there was a lot of push back from riders, in fact a lot of us just stuck to riding aging 2strokes for quite a while. However when the 450 4strokes became superior to the 250 2strokes it was game over.
Also I remember being out cycling a few miles away from Milestone mx track in Riverside and you could hear the bikes easily.
This is the sound from my KTM350 for reference if anyone is interested.
My 350 - YouTube
Two strokes lend themselves to karts so well that theres little to no industry support for a move to 4t.
There was a push around the time of the KF classes where vortex and others worked on some high performance 4t, but they never saw the light of day.
There’s a kind of inflection point with the 4t that once you cross the 15HP threshold, you have to move to more complex valvetrain and/or a heavier package with larger displacement where the 2t starts to looks pretty good again. Some of the other 4t benefits like easier (or basically no) jetting changes also go away when you start making 80+HP per L of displacement.
Also as some said, if you blow up a 4v OHC engine it gets REAL expensive REAL fast. In a shifter setup, that’s pretty easy to do if you bump down two gears vs just one. While a sprag clutch stops that, it’s also another expense that’s close to $1000 at times. In a 2t, it’s hard to hurt it from overrevving, you can spin it 16k and it probably won’t care…
Wankel rotary engines are well suited to karting in many ways. while there’s maintenance to be done (apex deals of course), they are mechanically super simple and the power output per LB of engine weight is potent.
So basically they make tremendously good sense in the 5-15hp range. Once you start going for bigger power output, the engine becomes more complicated and has more failures, if I’m understanding.
Why is it that the Honda gx’s and similar have such a gentle, rolly sound? When we first started, Nick called the Briggs he was on the putt-putt kart, because that’s what it sounded like. Apt description.
You want loud? Skip to 15:00 on this one: Drag Mini
Should never have had 240 extra cc to play with in the first place.
Alan do you have anything in your archive on the four strokes Vortex and others developed just after FA\FSA etc were cancelled?
that’s about it on Vortex.
Suter were furious with the FIA iirc.