Hey,

I don't like my high EGT, the prob is in the 4th runner of my tubular manifold, very close to the engine port.

I get 800C~ at cruise @ 100kph~ @ 40deg of timing, when I stop to check I can see the manifold+turbine is red hot.

I was running 16afr and then dropped it to 14 just to check, the egt went down a little (700-750C) but was hitting 800C sometimes still...

My idle EGT is 500-600C (normal ?)

When I disconnect the wastgate actuator and run with no boost, I still get the same cruise EGT as before...

Could be the manifold design is the cause and that is that ?

Thanks !

 

nope
it's the way the engine is running

 

Cruise EGT on stock engine is 750-800~ ?

 

nope. yours are high
I'm not sure why, but that's not normal

 

This is my question, if I run 750-800C @ cruise with wastgate actuator disconnected, It leads me to believe the manifold is the cause.

What is a normal cruise egt ?

 

Check timing with timing light.

Check harmonic damper TDC mark with a screwdriver in cylinder 1.

What is your cruising kPa?

My guess is your timing is off.

 

I checked in the past and I will check again np.

What is a normal cruise ignition and EGT ?

I run 40deg~, it lowered my egt from 850+ to 800~
afr 14 took it down to 750~ and 13.5 will run 700-750~

My cruise kpa is I think like any other NA miata... 40-70~

 

Number 1 on the right

3 years old...

 

EGT probes on all 4 cylinders, not turbo, anywhere between 700*C and 820*C during cruise. WOT is actually at ~780*C @12.5-12.9AFR.

 

You blog is very helpful on this, you have really been working on it.

Not that its a central issue, but have you done a coolant reroute? It can only help with hot #4 issues.

Another thing I wonder about is your sequential injection settings. I have never played with it, but from reading your posts there, I wonder about timing your injection when the intake valve is closed as you stated. I would think (people can fry me if appropriate on this) that you want that injector starting its pulse maybe 15 degrees or so before valve opens on the intake stroke, so a big part of the injection is while the valve is open. Spraying with the valve closed seems like it could cause a bit of build up, meaning that your burn is not as efficient/fast, meaning you are burning fuel as it flys out the exhaust side of the head. The WB02 would not necessarily pick up on the diff between fuel burning in the chamber and fuel finishing up its burn in the manifold.

You probably based your settings on what people here have done successfully though no?

 

This is interesting/surprising. This is a tad under 1500F. Doesn't AL get a bit soft at that temp and fairly woobly at 1600F?

 

Aluminum melts at bit over 1,200*F.

Now ponder what the pistons are made of.

 

I'm running injection timing suggested and used here in the forum... what would you suggest to try ? 360deg all the way ?

At cruise the injection timing is at 385-395, I think this is very normal - no ?

Thanks !

 

Just for compare: I have the probe just after the head port on the #4
Idle: never over 500C
Slow cruise (40-50 kpa): 550C
Fast cruise (70-90 kpa): 750C
Wot sixth gear (street): 850C
Wot dyno (4th gear): 940C

 

That's what I would expect to see too. Less on your ex ports at those temps.

 

I am not the guy to ask, I have never messed with sequential in any way. My injector tuning experience comes from frigging with total duty cycle as a % and adjusting the ECUs compensation for dead-time trying to get LTFTs within 5%.....on injector and ECU technology that's 20-30 years behind what we use in these parts nowadays.

My main concern is that if you have fuel injecting while the valve is closed with a short-term low flow/high pressure situation in the intake port, could there be a 'pooling' effect where you have the fuel droplets hitting each other, port walls and even the valve itself, condensing into larger droplets. A larger droplet will take more time to burn. That longer burn time could make for combustion of fuel as the ex. valve opens, which will make for huge EGTs.

Basically, if you do something that might cause the burn to take too long or start too late, you can see really high EGTs.

The thing is, that is all theory.

The really smart idea is to quadruple check your ignition timing, then quadruple check your sequential injection settings, and then see if maybe you have a suspect signal from a CAS that's resulting in some retarded spark or injection occurring at a different time than you think it is.

Or, maybe the temp sensor is not so good.

Known good parts you can switch in would be immensely helpful on this one. Try a different temp probe. Then try a different CAS. Would not be surprising to see the problem figured out by one of those two tests.

 

Thank you for your input, I will start with a new sensor.