Exhaust Gas Temperature

[Brad Potter]

Has anyone ever tetsted exhaust gas temp in relation to cam timing. Does the EGT getter hotter with the cam advanced or retarded?

[Adger Smith]

Advanced cam opens the ex valve earlier. If it is still hot in the chamber that earlier opening will usually let hotter gases into the ex pipe. Try retarding the timing and watch the ex gas temp go up, but don't try advancing the timing until the EGT cools down. You will end up with melted/broken parts in the cylinder/engine. There are quite a few variables that affect ex temps. I know I'll get some flack for this statement, but there is no "one" ideal ex gas temp for every engine combination. There will be an ideal temp for "each" engine combination that is tuned correctly. The engine will tell you what it is. I get a smug smile when someone tells me they can tune by just ex gas temp. It helps to know them and plot the changes, but EGT isn't what makes a tune up correct.

[Billy Nees]

Amen!

[Dave Turner]

Originally Posted by Billy Nees

Amen!

Pastor Nees!!!....fans of innuendo enjoy!

[Charles Rainey]

As I get to play on my dyno quite often, I have learned a lot. In the early day, EGT's was all we had and we learned to tune with them and read spark plugs. But most know that EGT reading are on a bell curve. You can be reading on the up side or reading on the down side. You must determine which side of the bell curve you are on. With the advent of the O2 sensor, we got yet another tool to work with along with the EGT. Then we got to learn about BSFC. All 3 of these together will let u tune the engine pretty doggone close right off the dyno and just like was stated, every engine will be different. The swirl effect in every engine has its on characteristics and the amount of Octane you run will affect the curves. You most certainly indeed can add too much octane and slow the burn cycle down too much. Most (not always) of the time you want the octane to be matched as closely as you can to your optimum burn time. I have actually had the octane so high, that I continued the burn thru the header and the EGT temp was extremely high. We try to match the engine as closely as I can get it to O2 sensor readings AND BSFC. I then look at EGT numbers and try to get close to that on the track, but I also try to have at least one O2 on each side to keep me on the honest side. O2's are funny, as they get warn and used up with lead fuel, their cycle time goes down, so dont keep yourself feeling too happy about not spending $40. Keep new ones too make sure of your numbers.
Oops did I just open myself up for scrutiny> Yep sorry my $.000002.
charles

[Dave Turner]

Originally Posted by Adger Smith

Advanced cam opens the ex valve earlier. If it is still hot in the chamber that earlier opening will usually let hotter gases into the ex pipe. Try retarding the timing and watch the ex gas temp go up, but don't try advancing the timing until the EGT cools down. You will end up with melted/broken parts in the cylinder/engine. There are quite a few variables that affect ex temps. I know I'll get some flack for this statement, but there is no "one" ideal ex gas temp for every engine combination. There will be an ideal temp for "each" engine combination that is tuned correctly. The engine will tell you what it is. I get a smug smile when someone tells me they can tune by just ex gas temp. It helps to know them and plot the changes, but EGT isn't what makes a tune up correct.

Tried to respond to your PM Adger, but the inbox is full!!

[Adger Smith]

OK, cleaned it out...

[bill dedman]

If "too much octane" slows burn time, then what about E 85, which supposedly has a LOT of octane (because it's alcohol. mainly?)

Anybody have any comparative figures for E 85, compared to 110 octane gas? (burn rate)

[Jim Wahl]

Originally Posted by Adger Smith

Advanced cam opens the ex valve earlier. If it is still hot in the chamber that earlier opening will usually let hotter gases into the ex pipe. Try retarding the timing and watch the ex gas temp go up, but don't try advancing the timing until the EGT cools down. You will end up with melted/broken parts in the cylinder/engine. There are quite a few variables that affect ex temps. I know I'll get some flack for this statement, but there is no "one" ideal ex gas temp for every engine combination. There will be an ideal temp for "each" engine combination that is tuned correctly. The engine will tell you what it is. I get a smug smile when someone tells me they can tune by just ex gas temp. It helps to know them and plot the changes, but EGT isn't what makes a tune up correct.

Especially important in a turbo engine! Jim

.

[Charles Rainey]

Originally Posted by bill dedman

If "too much octane" slows burn time, then what about E 85, which supposedly has a LOT of octane (because it's alcohol. mainly?)

Anybody have any comparative figures for E 85, compared to 110 octane gas? (burn rate)

Bill
You are not comparing apples to apples. You are comparing apples to oranges. If you use that train of thought, then look at Methanol or even better lets look at Nitro or even look at the pure Methane (My Wife)gas that some people put out HeHaw. All these fuels have totally different burn characteristics. Yes I have played with E85 and I only use it where they say I have to use pump gas and even then if I can get by with it. You really better check each batch of E85 you purchase as it is all over the place and you better not run it on the razor edge and then purchase more fuel and not check it. Weve seen E85 or E80. I guess, what I am saying try it on the dyno first so you can monitor it. I had a customer jet for E85 and he took the top ring right out of the engine and then he called me. wished he had called me B4. There is Et in fuel, but do it smartly. Some engines burn towards the exhaust valve, some dont. How much quench area you have will make a difference. I personally want a small quench are (read the piston number on the head).Oh also on E85, you better watch the carb for deposits and other changes you may not like.
charles