Marc sierra

iTrader: (1)

I've seen people talk about peak and held boost pressures. What does it mean exactly? Is the held pressure determined by the ECU through the amalvalve, or is it just the turbo not making the boost at the higher revs?

My car has a bleedvalve instead of the amalvalve, does that mean the peak and held boost pressures are the same, as the ECU cannot control the boost pressure?

Marc sierra

iTrader: (1)

Nobody knows?

J1mbo

iTrader: (1)

Peak and held are both controlled through the ecu and Amal valve,

Boost can fall away at higher revs due to back pressure building up, so with your bleed valve you could be getting a big spike to hold a high amount of boost up top rpm

Is that any use?

Marc sierra

iTrader: (1)

Thanks, yes that is of use!

But isn't the fact that the boost pressure drops at higher rpm due to the fact that the turbo cannot supply enough air anymore, as the engine consumes a lot more air at high rpm. So basically the turbo runs out of puff? That's why fitting a bigger turbo keeps the boost pressures higher at high rpm than a smaller turbo.

But what is the real function of the amalvalve? I know it drops the boost a bit at high rpm, but why does it do that? Is it to protect the turbo from spinning too fast? As the higher boost is no problem for the engine itself, right?

martysmartie

iTrader: (1)

The Amal valve controls the boost pressure, (The same as your bleed valve is doing) more boost is not good for the engine, unless you can fuel for it along with a whole other lot of factors! Without no boost control you would run infiniate boost and so would end up melting your engine as well as damaging the turbo, you can only run as much boost as your setup allows!

Yes as far as I understand a larger turbo will hold boost better at high RPM, whereas smaller turbos tend to tail off and "Run out of puff", but these have the benefit of less lag.

Martin