EGT

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Trickey
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EGT

Post by Trickey »

Hi all
I have just installed a EGT gauge on my sons grass kart that is running a 87 kdx200 engine. we have had a lot of problems
with piston damage (see engine questions thread in air cooled) hoping EGT can tell us if we getting too hot and he can back off before its toasted.

What should we set the warning for max EGT temp for??

Thanks Shane.
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adam728
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EGT

Post by adam728 »

You are not going to like this answer.


It depends.



Depends on the distance of the EGT thermocouple from the piston edge
Depends on the depth the thermocouple is installed into the pipe
Depends on the fuel used
Depends on the porting/pipe/tuning and rpm being ran
Depends how much raw air/fuel is entering the headpipe before the return wave stuffs it back into the cylinder
Depends how much of that raw air/fuel remains in the pipe after the exhaust port has closed
Depends on spark timing


I'll argue that numbers our there on the internet are only good for the particular engine/application they are talking about. A Banshee running trails might survive 680C, same setup in the dunes might want to peak at 600C.

Factor in different engines, intended usages, etc and you might see one setup that melts pistons at 580C, and another survive spurts of 700+.


At work we simply use EGT for reference. I've seen one setup (4 stroke) where we must have been right next to the tip of a flame cone out the exhaust port. Moving the theremocouple in or out maybe 2mm changed EGT 60 degF.
Trickey
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Re: EGT

Post by Trickey »

Thanks for the reply.
Any answer helps as far as im concerned.

This engine is ported a little and running on 100 octane fuel.
Im guessing that the usage would be similar to running in dunes. mainly high rpm not much low rpm work.

Just looking for a ballpark and was thinking around 600c.
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adam728
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Re: EGT

Post by adam728 »

FYI
I threw some thoughts in your other thread
Trickey
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Re: EGT

Post by Trickey »

Thanks.
Got it all up and running yesterday so we could run it in before race day today.
More bad news after 15 min running lost spark!! Looks like the Cdi has quit.
On closer inspection the cdi has been repaired in the past so im on the look out for a replacement now.
Anyone got any source for a cdi for 87 model.
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Jaguar
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Re: EGT

Post by Jaguar »

I sell adjustable replacement CDIs for the KDX. http://www.dragonfly75.com/moto/KDXCDI.html

For me the best method concerning engine heat is looking at the underside of the top of the piston. If it's black then you are running too hot. Factors affecting engine heat:
Ignition timing
jetting
compression
gasoline octane
Performance CDI -- KDX motocross mods -- the SR KDX -- expansion chamber analysis---> http://www.dragonfly75.com/moto/
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fuzzy
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Re: EGT

Post by fuzzy »

In general you want the highest EGT you can get (EGT close to piston). If you start rich, then lean out, the EGT will climb until it peaks, then drop again. Right before that peak is what you want. The factors Adam noted are true also. The EGT/range could change depending on conditions and load. My rule above is really 'what should me EGT be right now?' and that's the highest you can get. It's hard to test with a float/bowl carb where rejetting is necessary, but you'll know your engine with practice. We used them religiously with karts, but used diaphragm carbs with twist-adjust needles you could turn on the fly, and watch the EGT change(big weedeater carb)....also air cooled engines. The peak EGT would change some later in the race where the CHT/entire engine became hotter.
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
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