maximum brake Torque - How does one do this???

[TurboGTi]

As the post says guys .... how do you do this?
I've heard you all speaking of this but how do you do it?

[Richard L]

Maximum brake torque is the the results of a "torque" measures on a "brake" dynometer.

A "brake" dynometer works very similar to a car's braking system, it records the amount of force required to maintain a contact speed of an engine.

"Maximum" just means when the peak force applied before the engine speed begins to drop.

[hotrod]

There also appears to be two commonly used defintions for the term MBT. It may be a regional thing but I've seen two usages that are similar but have slightly different meanings that in some cases are important.

MBT Maximum Brake Torque as Richard mentioned would just be the highest torque your engine can achieve at a given engine rpm. YOu would get this info by putting the car on a dyno and tuning to find the ideal mixture, timing settings to give you the highest possible torque at the rpm of interest.


You will also see MBT used to mean Minimum Best Torque timing.
This deals specifically with ignition timing and how it effects engine torque. If you look at a graph of engine torque and how it changes at a single rpm as you modify ignition advance you will see it rises very quickly at first as you move toward the timing value that gives you Maximum Brake Torque.

You will also notice that as you get very close to that value the torque levels off and the engine torque output does not change much over a range of several degrees of ignition advance. What engineers discovered is that if you dial in the ignition advance that gave the absolute max torque and then pulled back the ignition advance so max torque dropped by only 1% you gave up a very small amount of torque but gained a huge advantage in the safety of the tune, and greatly reduced cylinder pressures and temperatures. This is the Minimum Best Torque timing. It is a very reliable and safe way to tune the engine.

Put the car on the dyno, keep adding advance until you get very little gain for each additional degree of advance, then back off a couple degrees until you just detect a small drop in max torque. This setting will give you some wiggle room for those situations where you peak the tune on the dyno but when you get on the road the car detonates like mad because it is hotter or the loading on the road is much different thant what the engine saw on the dyno.

I always use the term MBT timing to make it clear I am talking about ideal ignition advance.

In practical terms the two usages are essentially the same except with regard to the safety of the tune. If you tune the same engine to Minimum Best Torque, timing you will only be down by about 1% on the best Maximum Brake Torque. you could make if you pushed the engine right to the edge.

On a 400 hp engine you would give up about 4 hp to have a safe tune that was kind to your bearings, head gaskets and pistons.


The NACA studies appear to always use the Minimum Best Torque timing for their standard for ideal ignition timing on the tests.

Hope that helps ?

Larry

[TurboGTi]

I haven't been in here for a while,
This is an awsome post hotrod!