Before I launch into buying a Bighorn I've been reading and learning a lot about turbo boosted direct injected diesel engines (4JB1T mainly) from the many and varied topics on this (awesome) forum.
From what I understand, and lacking any real technical knowledge:
1. The volume of diesel in the cylinder at the time of ignition will burn until all the oxygen is used. Overfuelling beyond this produces sooty black smoke.
2. The volume of burned diesel and therefore energy (and heat) is proportional to the power generated. More burned diesel = more power = more heat.
3. The cylinder pressure from the gaseous expansion of the burned diesel must be far greater than the 17:1 compression of 20psi worth of boost pressure.
4. The temperature of the air at TDC of the compression stroke is what ignites the diesel.
5. The temperature of the compressed air must be greater when running 20psi boost than 10psi, but by how much and is it significant in terms of possible engine damage when the diesel is burned?
6. The factory setting of the 4JB1T is for 10psi boost with a 15psi limiter.
7. The timing of diesel injection also important in using the generated power. Too advanced and there are too many stresses on the internals and mechanical damage will result. Too late and the generated power is less useable due to crank position, leverage/torque, etc.
8. Fuelling is tweaked/increased by boost pressure, but this must be relative.
9. EGTs are good to monitor to prevent piston meltdown. Below 600 degC is good. More air has a cooling effect.
Correct me if I'm wrong but from what I understand as long as there is plenty of oxygen available, it's the fuel volume and timing that determines power and combustion chamber temperature and not so much the boost pressure.
So if the boost pressure is set to 15psi and the fuel is adjusted to just below the over-fuelling point, then the boost is increased to 20psi so there is an excess of air/oxygen and the EGTs are low, would this extra boost really reduce the life expectancy of the engine??
If you haven't fallen asleep or moved on by now then any knowledge and experiences would be great.
I'm considering buying a 4JB1T that's been boosted to 20psi and runs low EGTs, and it's got some great power, but I'd prefer to drop it back to 15psi and not kill it than enjoy it for a short time.
Cheers.