Does octane level matter for power?

There are two types of rating methods, the research and motor methods. The mehtods are quite different. The motor number is more important with regards to how a tractor endine runs; full throttle, low RPMs. This is the downside to Ethanol, sorry farmers, because Ethanol actually increased only the research number. When the two methods are added together and divided by two, you get the overall number.

As far as Exhaust gas temps, it's true that leaner will be hotter. Other things to keep in mind as well are that when spark timing is retarded, EGTs will increase; and when the engine is knocking, they will decrease.

The only reason a higher Octane rating may help is because the blend itself may have a higher BTU rating.

bd

EGT gauges are generally made for aircraft engines. When you go from sea level to a couple of miles up, you need to be able to monitor and change your mixture. The sensors are short, round probes which go in a hole you've drilled in the header pipe and are fastened by hose clamp type devices. They're made for tube steel pipes -- so the idea of putting one on your cast iron tractor exhaust header may cool your interest in installing one.

Your engine may want to run somewhere between 1100 to 1400 degrees. It takes a little experimentation to establish a baseline for a particular motor. Remember -- if you run too rich you only waste gas or foul plugs. If you run too lean, you could waste some engine parts -- exhaust valves are usually the first to go.

Mikey G

Does the octane make that much difference? No, it's down the list a ways...more of a sanitary factor than a real power booster. From my miss spent youth and too much time around a dyno with a Cosworth engine we figured that 104 octane was about optimum for a 10.5:1 engine... but it wasn't nearly as critical as other factors in making power. The way to make big power gains (short of turbo charging) was with better breathing (time on a flow bench shaping the head and manifolds to flow air better, accurate block honing, good rings, etc).

A reliably timed spark at high RPM's was very important -- and even with a popper running 975 RPM it's important. You might get a bigger gain by shimming up the distributor shaft and rotor so it fires at the right time, every time.

The right mixture will make much more significant gains than the octane - that is, setting the carb mixture for the day's factors in temp, humidity and air pressure. We used an Exhaust Gas Temp -EGT - gauge to set the carb jets -- two and three times a day at the track. The heat range and shape of the plugs - and the flame front they produced were also at least as important as octane in the category of things that are easily changed.

I'm also from Indiana, but from the part where we have a race track called Indy. Lots of race track rats running around here, I was once one of them. I used to think pulling 3 g's on a high bank corner with my hair on fire was heaven, but now -- having topped the 50 mark some years ago --putting along at 5 mph on a Johnny Popper is very satisfying. People change, but I don't think the physics of an engine have. Hope some of my long ago gained experience helps you.

Steve