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Octane and Fuel

Introduction to Engine Tuning

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Discussion and questions related to the course Introduction to Engine Tuning

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Hi everyone. I have a question. What about power limits that an engine has? For example, not sure but a 5efte Toyota engine with stock internals can make 280whp with 95 Oct. here are 93,95 and 97 options for fuels, can I add more boost and timing if I´m not having knock? (With E-85) or should I respect the 280whp?

Knock is definitely an engine killer, but you also need to take into consideration the strength and fatigue of the part themselves, like the connecting rods for example. With better fuel, you would be able to probably push the power figure over that without knock, but you could have a rod fail.

You need to be careful while chasing a WHP number, because every dynos read different and even the atmospheric condition, your strapping technique, will make that number vary.

Finally you need to take into consideration how the car will be driven. You could also be limited by the oiling system or cooling system if you try to make a track car from a street car with no supporting mods.

As Francis said, you REALLY have to consider the mechanical limits of the engine, and HOW that power level is reached. This is a function of torque (~cylinder pressure) and rpm - increasing either, or both, will increase power.

By that I mean there are two main causes of engine failure - compressive loads (cylinder pressure) which can cause bent rods, piston land or crown failure, or head gasket failure. This may also cause clutch slip, if it was marginal. This is something to bear in mind with forced induction engines.

The second it tensile failure, where an increase in rpm means the piston is 'pulling' harder on the connecting rod, rod bolts, gudgeon (AKA wrist or piston) pin, piston boss, etc. It will often require an increase in oil pressure, too, to counter the increased centrifugal force at the mains.

With some engines, one may be able to juggle the balance with a bit more cylinder pressure and rpm to get more than either on it's own. If you do decide to do something, do some research on what others have been doing, and where the weaknesses of that specific engine lie.

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