Revisit - Glowing Exhaust and Turbo

[cygnusx1]

Cast iron begins to glow around 1150 deg-F.

 

Too much fuel causes combustion to complete in the exhaust. And too little fuel causes a hotter burn. So which will cause higher EGT's?

 

What is an optimal EGT for an L28ET?

 

Thanks, if anyone can add some knowledge.

[Guest Cronic]

Both too ruch, and a too lean condition will cause higher EGT's, this is why they're not great for precise tuning. Combine an EGT with a wideband o2, and you will be alright.

 

A wideband will run you about 400 bucks. The EGT gauge and probe runs about 130 or so.

 

A wideband is an EXCELLENT way to spend 400 bucks.

[Guest Cronic]

There is not a really safe EGT temp to say. However, I like to keep mine under 1500F.

 

My friend max said his regularly hit 1800+F

[yo2001]

EGT is more effected by ignition timing which causes the turbo and manifold to glow. my2 cents

[Pyro]

Ignition timing also adds to the equation.

 

Rich mixture combined with retarded timing really makes cast iron glow.

 

Not sure if lean mixture will increase exhaust temps. However, a lean mixture will cause dentonation which will crack pistons.

 

I haven't researched on this subject, but it seems to me exhaust temps would be lower with a lean mixture. How do you make heat without fuel? Maybe a high oxygen content burn is hotter?

 

Exhaust temps will rise as the turbo is working. Boosting for long durations will increase exhaust no matter how good the fuel ratio is.

[Guest Cronic]

a high oxygen content burn is hotter?

 

You nailed it right there. Yes, ignition timing will effect EGT also, this is how many people tune their ignition timing w/o a dyno.

[cygnusx1]

Thanks guys. Great info. Looks like I need to start scouring cyberspace for a good deal on a wideband setup or time on a dyno or both.

[cygnusx1]

I just want to follow up. I brought my base ign timing from 22 to 27 btdc and the turbo glows MUCH less than before under the same set of driving conditions. I also feel I gained a sh'load of torque from 2K to 4K rpms. I luv it. Idle has also improved. Engine GROWL has improved. She's running like a monzter!

 

Thanks for the tips!!!

[Hugh]

Use a wideband to set the precise A/F ratio. I use the Innovate LM1 - http://www.innovatemotorsports.com

 

Then use the EGT gauge to adjust your timing and put the EGT right where you want it. Advance a little to drop the temp. If you advance too far, the temp will rise again.

[slownrusty]

Things mentioned here, you think are obvious but are definately not! Excellent thread and info!

 

Yasin

[Pyro]

It sounds like your timing mark has moved? Maybe you should check the timing mark position with a piston stop tool.

 

Now you need to lean out the mixture a little. Check fuel pressure first, if it that is ok, tighten up the airflow meter spring.

[cygnusx1]

Hmm, how would that move? The timing pulley is keyed, the scale is bolted to the block and piston one TDC, can't move relative to the keyway on the crank. The only error that can be made is by picking the wrong tooth when sliding the oil pump in. Ultimately that wont matter however as long as timing jives with a timing light and the distributor bolts line up at factory timing.

 

I haven't yet built a Z motor so I may be missing something

 

You are right though, confirming TDC with a tool would not be a bad idea.

[Pyro]

The pulley with the timing marks is rubber mounted around the keyed hub. The rubber gets old and can slip. Plus the pulley is always being twisted because the ac/alt/ water pump is pulling on it along with the spinning/vibration forces from the engine

[cygnusx1]

Oh, I see. Thanks for the tip. It could be the case, the pulley looked good when I painted it and put it on but you never know. It does have 110K on it.