Engine Exhaust Port Temp

[CATD8]

Hello! Question..

I have a modified 200cc 4 stroke engine that puts out about 20 hp.

Any guesses at what temperature the exhaust port gets? Thanks

 

[tgus3]

I think its around 320F?
is that dino verified or gestimated

EDIT:been doing some more research and im not sure if that numbers right..
anybody else have an idea?

 

[Tpdingo]

320? Lol. More like 450-500. I know a Briggs motor running at 3600RPM will get to 400-450 without an issue, so I'd imagine 500 is a pretty good ballpark. 320 is probably the low side of what the head is running.

 

[anickode]

I think its around 320F?
is that dino verified or gestimated

Talking about exhaust gas temp at the Port, I assume?

320? Ought to be a lot hotter than that. That's freshly used up fire coming out of there. Should be at least double that, running full throttle at no load (like up on jack stands)

Seeing 1000 to 1200 wouldn't be a surprise to me at wide open throttle, full load, like a sustained top speed run. I've had my header to a dull red glow on my Briggs after a sustained top speed run, which should put EGT between 1100 and 1200

This is assuming proper jetting. A rich engine will run colder EGTs and a lean engine will run hotter.

If you're talking about the head temp, then it will be significantly lower than the EGT. The 500 degree range is about where that should absolutely top out on a lightly modded engine after a sustained high speed run.

 

[CATD8]

is that dino verified or gestimated

Dino-ed It in my imagination

---------- Post added at 07:07 PM ---------- Previous post was at 07:04 PM ----------

Talking about exhaust gas temp at the Port, I assume?



This is assuming proper jetting. A rich engine will run colder EGTs and a lean engine will run hotter.

If you're talking about the head temp, then it will be significantly lower than the EGT. The 500 degree range is about where that should absolutely top out on a lightly modded engine after a sustained high speed run.

Yes Im talking about freshly burn fuel temperature at the port. before it enters the header.

 

[tgus3]

Talking about exhaust gas temp at the Port, I assume?

320? Ought to be a lot hotter than that. That's freshly used up fire coming out of there. Should be at least double that, running full throttle at no load (like up on jack stands)

Seeing 1000 to 1200 wouldn't be a surprise to me at wide open throttle, full load, like a sustained top speed run. I've had my header to a dull red glow on my Briggs after a sustained top speed run, which should put EGT between 1100 and 1200

This is assuming proper jetting. A rich engine will run colder EGTs and a lean engine will run hotter.

If you're talking about the head temp, then it will be significantly lower than the EGT. The 500 degree range is about where that should absolutely top out on a lightly modded engine after a sustained high speed run.

yes i was talking about the port but i knew it was low..thanks for the info

 

[bob58o]

Not sure if it helps but when I pointed the laser thermometer gun thing at the header pipe right at the flange where it attaches to the head - I was getting over 600 degrees F.

Modified Predator 212cc with warmed up engine while idling.

---------- Post added at 08:32 PM ---------- Previous post was at 08:26 PM ----------

This is assuming proper jetting. A rich engine will run colder EGTs and a lean engine will run hotter.

For some reason I thought hottest exhaust temperature is what you should be tuning for. Maybe that is for economic stoich 14.7 AFR?

I thought I've read that going leaner OR richer from that point will cause exhaust temperatures to drop???? It seemed to make sense to me at the time, -but I really don't know???

Here is a picture from interwebbing showing what I think I saw.
And here's another picture to confuse things more.

 

[ezcome-ezgo]

You know, Bob. You Know. Embrace the GAB.

 

[Tpdingo]

Not sure if it helps but when I pointed the laser thermometer gun thing at the header pipe right at the flange where it attaches to the head - I was getting over 600 degrees F.

Modified Predator 212cc with warmed up engine while idling.

---------- Post added at 08:32 PM ---------- Previous post was at 08:26 PM ----------



For some reason I thought hottest exhaust temperature is what you should be tuning for. Maybe that is for economic stoich 14.7 AFR?

I thought I've read that going leaner OR richer from that point will cause exhaust temperatures to drop???? It seemed to make sense to me at the time, -but I really don't know???

Here is a picture from interwebbing showing what I think I saw.
And here's another picture to confuse things more.

No, lean has a lower EGT but the engine itself runs hotter. Look at a acetylene torch. When running the stoich flame, it creates a lot of heat around the torch but the flame is only 1 - 1.5K degrees. Now put it lean to make the blue flame. That flame is hot as **** at the source, maybe 4-5K degrees but around the flame it isn't all that warm, well it is warm but not as warm as stoich. Same applies inside a motor.

It probably also has something to do with the unburnt fuel in a rich mixture extracting heat from the burnt gasses and possibly the air in the lean mixture doing the same for the hot gasses. What do I know? I only took regular chem, not organic chem.

 

[Randy H]

Fun fact. Boost the CR, and the exhaust temp gets lower.

Bust out your slide rule and the appropriate equations and you may find it necessary to decrease the header diameter. Lots of factors to consider.

 

[65ShelbyClone]

For some reason I thought hottest exhaust temperature is what you should be tuning for. Maybe that is for economic stoich 14.7 AFR?

Sort of and not really. EGT isn't really a good target to shoot for. You have to know how a lot of other conditions correlate to a specific engine's EGT before later using EGT to deduce what is going on.

Ideally the engine would be tuned for best output first, then the EGT observed. Preferably all that can be done without knocking and without melting the valve, head, or exhaust.

Ignition timing has a big influence on EGT too. It could be driven over 2000°F just by retarding the timing because the burn hasn't finished when the valve opens. This would also cause power to drop like a rock possibly followed by a dropped valve and cata$trophic engine failure. It's an extreme example of why max EGT shouldn't be the objective. It's more of an obstacle to overcome in reaching best output.

Conversely, advancing the timing will cause EGT to drop and power to go up because more of the burn has finished when the exhaust valve opens. That's good as long as there is adequate octane to prevent pinging. Having said that, there is a point where lots of advance will start to make power drop as the combustion pressure starts to resist the piston moving upward on compression more than it helps push down on the power stroke even if there is no pinging. That trend will continue until parts break.

Very very generally speaking, I would expect a highly-tuned spark ignition engine to have EGTs in the 1300-1500°F range. Diesels should be below that. Turbo gas engines frequently exceed that and factory setups typically have better and more heat-resistant materials on the exhaust side.

 

[itsid]

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