I typically run .87 float and 4 clip position on a black slide in Houston. Lately, I’ve started monitoring head temp and trying to adjust float based on reaching an optimal temp of 385F. To reach this temp, I’ve run up to .89 float which seemed to get the temp in that range for practice but can’t tell temp for longer races. We are not allowed to run sensors for the regional races. I’ve had two engines run well with this approach but go from 98% compression to below 70% (leaky exhaust valve) in less than 10 hours. Below is a pic of one of the heads and the plug. Plug is white and exhaust valve is white. Is it possible the engine is overheating and causing valves to warp prematurely?
Head temps and valve leaks
- Thread starter ad67
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CarlsonMotorsports
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Are you pulling the engine over to TDC on the compression stroke each time you come off the track? Any exhaust leaks?
It's pretty common to bend an exhaust valve (running excessive temps or not.) Not pulling the engine up to TDC is a common cause for bent EX valve.
My suggestion: Do not tune an ohv engine by CHT. By the time that thick cylinder head soaks up combustion temperature to the underside of the spark plug, (enough to hit your limit on your gauge, the damage is already done. On the old flathead, you were dealing with a cylinder head heat sink that measured 1/2" between the combustion chamber and the thermocouple. Not so on an OHV engine with a thick head at the plug.
Tune with lamda on an oxygen sensor for practice if you want, then disconnect it (change pipes/mufflers) prior to racing. You can use EGT also, but I think you'll be happier monitoring 02/lambda.
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Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
35 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
It's pretty common to bend an exhaust valve (running excessive temps or not.) Not pulling the engine up to TDC is a common cause for bent EX valve.
My suggestion: Do not tune an ohv engine by CHT. By the time that thick cylinder head soaks up combustion temperature to the underside of the spark plug, (enough to hit your limit on your gauge, the damage is already done. On the old flathead, you were dealing with a cylinder head heat sink that measured 1/2" between the combustion chamber and the thermocouple. Not so on an OHV engine with a thick head at the plug.
Tune with lamda on an oxygen sensor for practice if you want, then disconnect it (change pipes/mufflers) prior to racing. You can use EGT also, but I think you'll be happier monitoring 02/lambda.
-----
Thanks and God bless,Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
35 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Thanks all.
My driver keeps forgetting to pull to tdc at track exit. Need to have him restore a few 206 heads to help with his memory.
I had thought about lamda but was trying to avoid the hassle of swapping exhausts. Since I understand these engines like to be rich in the middle rpms and lean at the top, what lamda values should I try to hit for optimal combustion?
My driver keeps forgetting to pull to tdc at track exit. Need to have him restore a few 206 heads to help with his memory.
I had thought about lamda but was trying to avoid the hassle of swapping exhausts. Since I understand these engines like to be rich in the middle rpms and lean at the top, what lamda values should I try to hit for optimal combustion?
CarlsonMotorsports
Site Supporter
You can weld a bung into the muffler and just change mufflers. I've placed the O2 sensor behind the muffler with a clamp and got decent readings without too much wash-out from outside air. It would be best to place the sensor inside the muffler though in my opinion.
Lambda of 1 is the stoichiometric air/fuel ratio. A reading higher than 1 is leaner, a reading lower than 1 is richer. 14.7 would be "ideal" stoichiometric, but realistically you'll see mid 12s with a good tune. You can tune the engine on the dyno for peak power, then show up at the track and find out that it'll see those rpms that you tuned to very few times per lap. Typically, you richen it up for smaller/shorter/tighter/more technical courses. Then, of course, different fuels require different tunes, ie not all 89 octane is created equally. Even fuel from the same station can vary from week to week. For sure, if you're going to err one way or the other, err to the side of being rich on mixture.