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Choosing the right turbo size.

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Hi everyone. I'm sizing out a turbo for a 3L 2jz drag application. I've been playing around with Borg Warners matchbot. I'm a little confused about the engine delta pressure. When adjusting the turbine expansion ratio to match different turbines, I'm seeing that I'm getting less Manifold pressure than boost. Does this mean that the turbine is so efficient that it's only taking say 12psi drive pressure to create my desired boost of 25psi? What is the limit for delta pressure? Should I be keeping it closer to a 1:1 ratio?

There's a link to what I'm taking about.


Did you look at the tutorial videos linked at the bottom of the matchbot page? They talk about delta pressure in part 4.

Yes I've watched them all. Just re-watched part 4 and basically all he said is that low delta pressures are good.

The lower your engine pressure delta is the better as far as power is concerned. The downside is you're not providing as much energy to the turbine wheel to drive the turbo so your boost threshold increases. For a drag application with a reasonable compromise between power and response (less of an issue with a 2 step launch control) a ratio of 1:1 is great and if you can end up with EMAP a little lower than IMAP you're doing well.

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