APEXi S-AFC - Beginner Tuning - How To Set It Up [Archive]

EvolvedDSM

01-26-2004, 02:36 AM

EGT info in response to the following question:
How long can I spend in this 900*C+ territory? I've read lots of conflicting stories - such as "it's ok to cross the 1/4 at 900, or don't ever pass 900, or you can spend a few seconds past 900."

Think of it like sticking our hand in the oven at 600 degrees. You can do it for a little while, longer if you are brave. It doesn't really do you any good, but to settle a bet you'd do it for a lot longer than you otherwise would. If you are over 900c, you are not making any more power than if you were right at 900c. But you are living on the edge for no particular reason. Don't do it if at all possible, but if you got big brass balls feel free to push the limits.

If you run too lean, you will get uncontrolled and uneven ignition. The flame front travels too fast and collides with the piston on it's way up. It's like beating on the piston with a hammer. You are also beating on the more fragile ring lands (little shelves where the rings sit on) and also beating on the bearings. The knock sensor picks up these hammering sounds long before they do damage and before you can ever hear them.

The ECU will retard timing when the knock noise gets beyond a set level. By lighting the air/fuel mix a little later, it wont hit the piston on the way up. The later ignition means that less heat is converted into energy pushing the piston down and the heat goes out the exhaust valve. This heats up the EGT sensor and you see it in the cabin.

High EGTs are a result of retarded timing which is a result of knock. A little knock and you see a little rise in EGTs. No big deal, still, no reason to be there. 1000c EGTs, lots of knock. At some point you would get more knock than the ECU can save you from. That is when you blow off little pieces of the spark plugs. You will have either a missing ground electrode and possibly pieces of the ceramic insulator missing. Not the end of the world but pieces of spark plug going out the yellow hot exhaust valve are never good. Colder running spark plugs help guard against this.

More violent detonation will blow out the head gasket by distorting the metal sealing ring around the cylinder. Next you will blow off little pieces of the piston and the cylinder head. If your plugs survived enough to get this going you will see specs of aluminum on the plugs.

So guys do a metal head gasket that will withstand this force. Cool. Now you will break the ring lands off the pistons. You start with a little hair line crack and it gets worse. Hot gasses slowly cut away at the piston if you keep driving. So for more insurance you get stronger pistons. Cool. Now you can hammer away in the combustion chamber. But you still have a soft metal bearing at the rod to the crankshaft. Pull your head off and start beating on the top of your #1 J&E piston. How many hammer blows before you mash the bearing to the crank? Now there is a big oil gap and you loose oiling at the bearing. The bearing welds it's self to the crank, the pounding and slapping stretches the rod bolts. Now the rod nuts are lose. One of them eventually falls off and the rod is desperately hanging onto the crank with one bolt. The one bolt gives up and the crankshaft keeps turning and the rod is just hanging there with a stupid look on it's face. The crank comes around and drop kicks the rod for an out of the block home run. Several pieces of shrapnel cut through the oil pan, you break the balance shafts which kill the oil pump.

Choose your weak point/fuse wisely.

Different cars, different ECUs, different octanes, different boost levels, different EGT sensors will all read a little different. The 900c sweet spot is about 85% absolute. On just about every 1G with a TMO datalogger, just when the logger guy in the passenger seat is seeing and reacting to a knock count of 30+, the driver is lifting off the gas because he is seeing 900c+. Back up the EGT reading with O2 sensor voltage, reading your plugs, dumb luck and seat of the pants experience.