A
Anonymous
Guest
I think you really need to understand why you break pistons when you turn the boost up. I think a lot of you believe that it's because the increase in pressure is too much for the engine to cope with. This isn't the case at all. 9 times out of 10 when you kill an otherwise standard engine by running 1.4 bar boost, its because you've run the engine lean which has lead to very serious detonation and / or melted piston crowns.
If you actually inspect a piston that's blown either from failed ring lands or a melted crown, you will see that on the crown itself there are lots of tiny pits. These pits are a classic sign that detonation has been happening for some time.
Standard pistons will not break under high boost if the engine tune is ok, you could happily run 20psi all day long if you don't run lean or knock. It's also worth remembering that forged pistons aren't indestructable either. So if you kill a set of standard pistons and drop some forged ones in without first fixing the problem that caused detonation in the first place, then engine will blow again. Also detonation doesn't just crack pistons, it will bend rods, hammer flat spots in rod bearings and the crank, and it's also what causes head gaskets to blow.
If you want to run 1.4 bar boost then to be safe you will want to run an AFR of around 11.5 - 11.8:1. Standard injectors have enough fuel to safely run 15 - 16psi of boost (at 7300rpm) without maxing them out. They will supply more fuel if you ask them too, but you'll run them around 90 - 100% duty which not only is bad for the injector, but also gives you no safety margin for cold days or boost creep. If you run leaner than 12.5:1 at 1.4 bar boost, your cylinder temps will rise very quickly and the engine will start to detonate, then when that happens its just a matter of time before you break something.
So in short, standard pistons are fine for high boost on a tuned engine and will not fall apart because you've added an extra 10psi pressure on the already extreme pressures of combustion.
Forged pistons are not indestructable, they can just take a little bit more punishment that standard pistons. Fitting these however just means you've move the damage from detonation on to the cylinder walls and rod bearings.
If you actually inspect a piston that's blown either from failed ring lands or a melted crown, you will see that on the crown itself there are lots of tiny pits. These pits are a classic sign that detonation has been happening for some time.
Standard pistons will not break under high boost if the engine tune is ok, you could happily run 20psi all day long if you don't run lean or knock. It's also worth remembering that forged pistons aren't indestructable either. So if you kill a set of standard pistons and drop some forged ones in without first fixing the problem that caused detonation in the first place, then engine will blow again. Also detonation doesn't just crack pistons, it will bend rods, hammer flat spots in rod bearings and the crank, and it's also what causes head gaskets to blow.
If you want to run 1.4 bar boost then to be safe you will want to run an AFR of around 11.5 - 11.8:1. Standard injectors have enough fuel to safely run 15 - 16psi of boost (at 7300rpm) without maxing them out. They will supply more fuel if you ask them too, but you'll run them around 90 - 100% duty which not only is bad for the injector, but also gives you no safety margin for cold days or boost creep. If you run leaner than 12.5:1 at 1.4 bar boost, your cylinder temps will rise very quickly and the engine will start to detonate, then when that happens its just a matter of time before you break something.
So in short, standard pistons are fine for high boost on a tuned engine and will not fall apart because you've added an extra 10psi pressure on the already extreme pressures of combustion.
Forged pistons are not indestructable, they can just take a little bit more punishment that standard pistons. Fitting these however just means you've move the damage from detonation on to the cylinder walls and rod bearings.