Gday guys,

Basically as the title states, looking to get more info in regards to the relationship between ignition timing and Exhaust gas temperatures. From what i have gathered thus far it seems in petrol engines most people only refer to exhaust gas temperatures for cylinder power balancing.

However currently in my situation i have a engine setup that is very sensitive to ignition timing and have to keep my ignition timing values very low to avoid detonation. As the lower ignition timing values go the hotter exhaust gas temperatures gets - this makes me worry about the condition of my head and exhaust valve components.

I currently have a K-type thermo-couple mounted in the collector of my exhaust manifold. Yes i do realise this isnt exactly ideal as there would be some heat loss between the exhaust port and where my probe is.

My main question is Generally speaking what sort of exhaust gas temperatures can honda heads usually take? would it make any difference to heat tolerance if i had nitrate coated stainless exhaust valves & bronze guides? or would this simple prolong the inevitable ?
I only ask as i want to be able to judge how low i can tune my ignition timing before it becomes detrimental.

Also what sort of heat difference would there be between the actual egt at the exhaust ports and the heat i would be measuring in the collector of a ram-horn manifold ? General figure like 10% 25% etc ?

Cheers guys

 

I am most familiar with the '80s era turbo Chrysler products. We try to keep EGTs below 1600 F (not sure what that equates to in Celsius).

Mike

 

If you're worried about high egt's maybe you could run inconel exhaust valves. But not having the thermocoupler close to the exhaust ports is gonna skew it. Has the car been to the dyno to optimize ignition timing? What exactly are the reasons behind the low advance?

 

I don't know the offset numbers, but you do lose energy (heat) the closer to the collector you get. That is lost as radiant energy. The goal is to keep the probe about 1-1.5 inches from the exit of the head. You'll find a good mix of air there.

Bronze guides are a little more forgiving in high rpm and high seat pressure applications. Same with bronze\beryllium valve seats. That's the real reason why people use them.

EGT is dependant on fuel types as well.
What kind of gas (petrol) are you using and what's the RON value?
What's the compression ratio of the motor?

 

Thanks for the feedback so far guys.

Just useing pump fuel 98 octane. CR - 8.9:1

As i only have one thermocouple, if i were to mount on a single exhaust running is there any cylinder preferable ?

 

There are a few things that confuse me here....

Is this a force inducted motor? I'm assuming it is by you posting in the FI section....

In a Honda, typically, the highest egt cylinder by default is going to be #3 unless you trim it out with individual cylinder tuning.

 

Yes mate this is a turbo setup. Running hondata s300. is there any specific reason as to why #3 usually has the highest egts?

 

Mostly because of flow characteristics in the intake manifolds.

 

^ cheers mate. Anyone got any figures about what temperatures are / not safe ?

 

any more info guys?