150+ hiding hp. 3b engine

[prj]

If you want to make power, then T3 0.82.
And red hot manifold is due to insufficient timing or too lean mixture or a combination of both.

[JariP]

Isn't it more likely to be filthy rich than too lean if the manifold is red hot when cruising on low load? And/or very late timing. With motronic if the idle switch is not working it keeps dumping fuel on overrun and it can get the manifold red hot too, is it the same thing with vems?

Overall with the spoolup problems it sounds more like cam/ignition timing problem.

[prj]

Isn't it more likely to be filthy rich than too lean if the manifold is red hot when cruising on low load?

No. Richer mixture lowers EGT and does not raise it. Engine tuning 101.
Late timing is a likely culprit.

Unless of course the car uses a vapor fuel, such as LPG. But I believe it is not.

[norheim]

timing and mixture should be ok.

I turned over the head today and put it on the bench. filled it up with water
aand there is many leaky exhaust valves..

Maybe i found the fault.? or?

[JariP]

No. Richer mixture lowers EGT and does not raise it. Engine tuning 101.

It's not that simple. On low load cruise the aim is lambda 1 or bit leaner, right? Going leaner from lambda 1 the heat release starts to go down quite soon lowering the egt's too. And on the other direction rich enough can raise the egt's. Those things will probably not happen on the "good" tune AFR range, but you don't need to go too far off to get there.

[adam g]

timing and mixture should be ok.

I turned over the head today and put it on the bench. filled it up with water
aand there is many leaky exhaust valves..

Maybe i found the fault.? or?

I think you found the cause of low compression.

[Rocco]

timing and mixture should be ok.

I turned over the head today and put it on the bench. filled it up with water
aand there is many leaky exhaust valves..

Maybe i found the fault.? or?

glad to know that you might discover your headache

[quattro84]

timing and mixture should be ok.

I turned over the head today and put it on the bench. filled it up with water
aand there is many leaky exhaust valves..

Maybe i found the fault.? or?

Yes, you did.
Because the exhaust valves did not seal under combustion, the pressure got lost and the hot gasses escaped making your exhaust temps run high, and because of that energy spillage it was not making the obtainable torque.

Same happens with burned exhaust valves.

[quattro84]

It's not that simple. On low load cruise the aim is lambda 1 or bit leaner, right? Going leaner from lambda 1 the heat release starts to go down quite soon lowering the egt's too. And on the other direction rich enough can raise the egt's. Those things will probably not happen on the "good" tune AFR range, but you don't need to go too far off to get there.

You need vast amounts of energy to vapourize the fuel (it dissipates the combustion chamber heat, put some isopropanol alcohol on your hand and feel it co cold) and there is no source to oxidize the HC's to create temperature until it reaches your oxi cat and that'll melt it / kill the O2 sensor once you heat it.

[prj]

It's not that simple. On low load cruise the aim is lambda 1 or bit leaner, right? Going leaner from lambda 1 the heat release starts to go down quite soon lowering the egt's too.

Yes, it does. EGT peak is at stoich.

And on the other direction rich enough can raise the egt's. Those things will probably not happen on the "good" tune AFR range, but you don't need to go too far off to get there.

And this is completely wrong, but you can see that on the graph that was posted before me.

My point is, there is no higher EGT peak than running stoich, so mixture at cruising speed has nothing to do with a red hot manifold. Timing does though.
As I said again - unless a vapor fuel is used, EGT keeps doing down until the mixture is so rich it can't burn anymore.

More than that - this is also why otto engines with EGT feedback that run on non-vapor fuels use PID controllers for controlling EGT by enriching the mixture until EGT is on target.

[JariP]

Yes, I have to admit that rich side comment went the wrong way, too little sleep time this week. But I'm still saying with bad enough tune you can see adding fuel raise the egt's but it's more about combination of timing and afr, not the afr's alone. For example way too little timing so the egt's are sky high already and add more fuel in there and see what happens. With good tune it most likely never happens, but it may sometimes help to know it can happen when you are trouble shooting or trying to figure out what went wrong. Just saying leaner - always raises egt's, richer - always lowers egt's simplifies things alot and can lead to wrong way sometimes.

[prj]

Yes, I have to admit that rich side comment went the wrong way, too little sleep time this week. But I'm still saying with bad enough tune you can see adding fuel raise the egt's but it's more about combination of timing and afr, not the afr's alone.

Adding fuel will lower EGT.

For example way too little timing so the egt's are sky high already and add more fuel in there and see what happens.

The EGT will go down.

Just saying leaner - always raises egt's, richer - always lowers egt's simplifies things alot and can lead to wrong way sometimes.

It is 100% correct when you are richer than stoich. If you go leaner than stoich (which most cars don't due to emissions) then yes, EGT will drop off as well.

All this goes out of the window when using a vapor fuel such as LPG unless you inject that directly into the cylinder in liquid form.
But for gasoline and many other liquid fuels what I have said is correct.

[quattro84]

And all if this goes out of the window if one uses direct injection in combination with multi pulse events.
That makes it possible to extend your heat release with multiple small injection portions to keep the fire burning being inside and outside the cylinder until exhaust valve completely closes or oxigen content is too low. This will make all your AFR readings go bad, and without measuring rest HC's in the gasses & indicated cylinder pressure it is impossible to judge.

The plot i posted before showing the relation between AFR & temperature does differ under DI multipulse conditions.

Can make some screenshots from work if one is interested