Senior LO206

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larsenracing16

Member
Just purchased a brand new LO206 for adult class. I ran the motor thru a break in procedure. Supposedly where I got the motor from they set the valves and carb for me. After multiple cycles, I ran the motor to the rev limiter. My mychron says 5750rpm. Is that normal? Or is there something I should look at adjusting to get the rpm closer to the 6-6100?
 
The number you are seeing is just where your mychron happened to catch the rpm as the rev limiter slowed the engine. Probably with no load on it.
I'm not sure what the sample rate of the gauge is, but the engine can fire 6050 times per minute, or more than 100 times per second.
The rev limiter is not an exact thing either.

Plus or minus 150 rpm would be as close as can be expected.
Probably to the minus side for safety.

Take it to the track and check it after running it on a long straight against the limiter.

Banging the limiter on the stand is a great way to shorten the life of your engine
 
Been involved in racing for over 20 years, I know hitting full throttle on stand is a bad thing. But the limiter is checked at the local tracks on the stand to make sure, so it has to be tested.
 
Every "legal" 206 engine that I have ever tested on the dyno (under load) has come up with 6040 or 6050 rpm max.
Free revving the engine can yield different results (and often does in tech.) That is why a variance is allowed in the rule book.
Are you watching the tach while holding the engine at peak rpm, or looking at the max rpm on replay (or better yet download?)
You'll notice the rpm drop (sometimes dramatically) when the engine hits the coil rev limiter. I've seen them drop just a few hundred rpm or as much as thousands of rpm. This happens so quickly, that it is insignificant to lap times. We're talking milliseconds.

Another thing to consider is that when an engine is dyno'd at your engine builder, it is most often tuned to his elevation and atmospheric conditions (then normalized) to make comparisons. The builder can make assumptions based on your track's elevation and typical air density as far as tuning goes, but generally speaking, they're all tuned to max power wherever the dyno is located. Now, if that engine is shipped from say Linden to Denver, the tune will obviously be different (Denver necessitating a leaner carb tune.) If the engine is shipped and handled roughly at all, the float drop tab can become bent and/or the inlet needle become stuck. This usually results in the carb running full rich and not turning as much rpm. Float height and drop are easy to check and change if necessary. We've got a video on our Youtube channel if that helps.


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Carlson Racing Engines
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I’ve seen this. then one guy rev the motor slowly on the stand to 6050 rpm. Instead of holding it wide open.
 
What can you gear this motor for a 1/4 mile track for a senior 206 heavy class to run 6000-6100 rpms and what rpms to engagement of a stringer clutch with what color springs?
 
Best call the club or track to get a recommended starting gear.

The gearing depends entirely on the combination of turns and straights at the track. Someone on the forum here might also know what the ratio is for your track.
 
larsenracing16 said:
My mychron says 5750rpm. Is that normal
Click to expand...
Assuming you’re on track for this measurement, it does sound low. This could be due to factors such as

A new driver not getting enough exit speed before the straight.

Chassis setup causing binding on the exit of turns, causing slower exit speed.

A gear that’s simply too tall for the track.

Engine that’s down of power for any of the typical reasons.

The limiter cuts the ignition briefly, that confuses the mychron somewhat and throws the exact reading off, but 5700 is definitely low.
 
Something to think about too, the rev limiter on the 206 is controlled by the coil so its cutting the spark. My mychron goes crazy when this happens so I kind of ignore the actual RPM value. As long as you're somewhere around 6k, you're good.
 
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