Setting waste-gates/ratios: What's the math?

Somewhere, I thought I've had somewhat in-depth talk about setting my waste-gate via math using drive-pressure, boost, etc. I've searched and can't find anything about such. Ratio, Back-pressure, etc shows nothing.

Can anyone help me by presenting the math to show what the ratios are with given pressure readings?

I need to properly tune my heap.

Thanks guys.

Are you running compound turbos or a single ?

Snedge said:

Are you running compound turbos or a single ?

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Duh, that info would help to start with huh? Sorry about that.

Triples.
Two S362/68 w/12cm undivided exhaust-housings playing into an S362/68 with a divided/waste-gated 14cm exhaust-housing. [The waste-gate has the spacer-plate as well as the machined-dimple cover (for additional gate opening)].

It seems I recall having to first do some math with the primary(s) to come up with their ratio. Perhaps the results was then applied to numbers from the secondary to cypher the overall ratio. . . . . . er something along those lines.
I've got a number of pages in a pile somewhere where I've done the math before. Can't find them.

Thanks again.

For wastegate opening the surface area of the face times the pressure applied to the face minus the forced of the spring holding it closed. I always made a setup to run regulated air to the bottom side of the piston to see what the actual pressure it was to open the spring. Then the rest of it was just using surface area and psi to determine opening. I did something in excel to simplify my life.

AH! I found the thread with the math. Thanks, guys.

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Drive pressure is a product of necessity depending on the boost level you require, my advice would be to avoid exceeding a 2:1 rise in pressure across the secondary compressor.

Still working out some wiring/sensor issues common with an engine replacement that took a phacking year but, initially, things still look good as far as net-boost* to back-pressure ratios go.
- 1.74 to 1.00 @ 2800RPM.
- 1.47 to 1.00 @ 2900RPM.
- 1.14 to 1.00 @ 3000RPM.

* Net-boost is that seen by the head's intake-log (approximately 3psig lost in the charge-air plumbing and IC).