[JSH]

Originally Posted by Megahurtz

I mean the exhaust valve temp being cooled by ethanol evaporation by spraying when the exhaust valve is still partially open. I'm not sug.

My son manages a German company that designs and supplies all F1 inlet and some exhaust valves, and all MotoGP valves, and he thought that spraying the exhaust valve could be a net positive and the valve shouldn't suffer. Given that both jurisdictions run titanium aluminide valves, his opinion should be tempered for our engines.

[Evansa22]

Originally Posted by Megahurtz

no PID for that, I mean the exhaust valve temp being cooled by ethanol evaporation by spraying when the exhaust valve is still partially open. I'm not suggesting this is correct or good or accurate. It's just a thought I had about I wonder if it actually does anything or is beneficial. I also wondered if it cooled the cats a little too. I have NO working theory or proof of this thought.

SOI at 400-440 is VERY bad on DI. You're literally dumping raw fuel into the exhaust stroke and probably at some point at WOT you will have a continuous flame from the exhaust tips as the hot exhaust mixed with raw fuel hit oxygen rich air.


360-380 SOI is fine. 160-180 EOI is fine. Fit the spray window in where you minimize spraying fuel out of the exhaust port and minimize spraying too far into the compression stroke.

I'm sure you've seen this but the factory tune definitely dumps fuel into exhaust, up to I think around 385* SOI when COT engages. A few different sources recommend SOI around exhaust valve closing like you're saying. Usually pushing SOI further before EVC to keep EOI around 180*, my tuner says above 150* is ok. Interested in your theory about exhaust valve cooling, possibly why factory tune does it, but usually I've seen it correlate with COT turning on. Completely agree with the statement the dyno tells the tale, just like with a few aspects of tuning. It's all about what makes the engine happy and each one will have small variances at a minimum.

JSH, Get that bad boy on a dyno with a competent tuner so you can document your testing for us

[Joshinator99]

Originally Posted by Evansa22

I'm sure you've seen this but the factory tune definitely dumps fuel into exhaust, up to I think around 385* SOI when COT engages. A few different sources recommend SOI around exhaust valve closing like you're saying. Usually pushing SOI further before EVO to keep EOI around 180*, my tuner says above 150* is ok. Interested in your theory about exhaust valve cooling, possibly why factory tune does it, but usually I've seen it correlate with COT turning on. Completely agree with the statement the dyno tells the tale, just like with a few aspects of tuning. It's all about what makes the engine happy and each one will have small variances at a minimum.

JSH, Get that bad boy on a dyno with a competent tuner so you can document your testing for us

Factory tune richens the mixture during COT to get the exhaust temps down, which in turn protects the cats. That’s all.

[Evansa22]

Originally Posted by Joshinator99

Factory tune richens the mixture during COT to get the exhaust temps down, which in turn protects the cats. That’s all.

10-4, thought they could've possibly hidden the exhaust valve cooling effect as it makes sense I guess if the exhaust is getting hot, the valve itself is probably getting hot as well. Megahurtz comments got me thinking, so maybe I'm just trying to give gm engineers more credit than is due haha

[Joshinator99]

Originally Posted by Evansa22

10-4, thought they could've possibly hidden the exhaust valve cooling effect as it makes sense I guess if the exhaust is getting hot, the valve itself is probably getting hot as well. Megahurtz comments got me thinking, so maybe I'm just trying to give gm engineers more credit than is due haha

Yeah, they definitely didn’t get that deep into it lol! Think about it this way: exhaust valve cooling could be beneficial at times other than COT conditions, but the enrichment only happens during COT operation…. Heck, the ‘19 LT5 had port injection and was only used for COT operation! Crazy.

TLDR, take that credit back haha

[Megahurtz]

Your thoughts about COT pulling SOI back to where the exhaust valve is still open are exactly what got me thinking about the theory that it would actually cool the exhaust valve down and even the cats. The effect of the fuel or especially ethanol evaporating on the way past the hot exhaust valve and cats would have a cooling effect.

I have nothing to support this as its more of a theory but I'm sure GM Engineers and some engine builders likely know. But there is really no need for COT it if you're running ethanol and high flow cats. Then it becomes that you would be backing up SOI to support a longer spray window before it sprays too far into the combustion stroke. But if you have the fuel system and don't need to cool the cats or exhaust valves, and are not spraying too far into the compression stroke, then why waste fuel out of the exhaust valve by backing SOI up to 380+? Would make more sense to start injecting close to TDC.

[JSH]

Originally Posted by Megahurtz

I'm sure GM Engineers and some engine builders likely know.

I guarantee you GM knows, and it wouldn't surprise me if they were to say, just let the ECU handle it.

[Evansa22]

Originally Posted by Megahurtz

Your thoughts about COT pulling SOI back to where the exhaust valve is still open are exactly what got me thinking about the theory that it would actually cool the exhaust valve down and even the cats. The effect of the fuel or especially ethanol evaporating on the way past the hot exhaust valve and cats would have a cooling effect.

I have nothing to support this as its more of a theory but I'm sure GM Engineers and some engine builders likely know. But there is really no need for COT it if you're running ethanol and high flow cats. Then it becomes that you would be backing up SOI to support a longer spray window before it sprays too far into the combustion stroke. But if you have the fuel system and don't need to cool the cats or exhaust valves, and are not spraying too far into the compression stroke, then why waste fuel out of the exhaust valve by backing SOI up to 380+? Would make more sense to start injecting close to TDC.

Now let me ask you this and sorry if this is getting off topic.... do you think COT taxes the fuel system more and will you gain some headroom if cats were removed and COT is disabled? In my mind it stands to reason but feel I may be thinking incorrectly.

[Joshinator99]

Originally Posted by Evansa22

Now let me ask you this and sorry if this is getting off topic.... do you think COT taxes the fuel system more and will you gain some headroom if cats were removed and COT is disabled? In my mind it stands to reason but feel I may be thinking incorrectly.

COT absolutely taxes the fuel system. That’s literally the only reason the LT5 has port injection…! When you tune these cars virtually everybody turns COT off for that process…so when that is turned back in (to protect the cats), you don’t necessarily have all the fueling you need anymore unless the tuner specifically checked the fueling data logs during COT operation.

[Megahurtz]

Originally Posted by Evansa22

Now let me ask you this and sorry if this is getting off topic.... do you think COT taxes the fuel system more and will you gain some headroom if cats were removed and COT is disabled? In my mind it stands to reason but feel I may be thinking incorrectly.

Yes and yes

[6spdhyperblue]

From my research e85 has a similar egt as e10. I’d be happy if your findings disprove that. Being able to Advance the timing by running e85 will reduce egt some.

There is a table for max COT enrichment by ethanol percentage. So if you’re running e85 or e50 and don’t have additional fueling headroom for COT, you may at e10, you can then have it be active for atleast that case

[Evansa22]

Originally Posted by Joshinator99

COT absolutely taxes the fuel system. That’s literally the only reason the LT5 has port injection…! When you tune these cars virtually everybody turns COT off for that process…so when that is turned back in (to protect the cats), you don’t necessarily have all the fueling you need anymore unless the tuner specifically checked the fueling data logs during COT operation.

Originally Posted by Megahurtz

Yes and yes

Right on, thanks for the info