Setting waste-gates/ratios: What's the math? - Competition Diesel.Com

BC847 · 02-25-2021, 02:52 PM

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.

*Snedge* · 02-25-2021, 03:37 PM

Are you running compound turbos or a single ?

BC847 · 02-25-2021, 03:56 PM

Quote:

Originally Posted by Snedge

Are you running compound turbos or a single ?

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.

zstroken · 02-25-2021, 04:05 PM

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.

BC847 · 02-25-2021, 04:17 PM

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

Tuning Twins - Competition Diesel.Com - Bringing The BEST Together

*Smokem* · 02-25-2021, 05:55 PM

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.

BC847 · 02-27-2021, 11:54 AM

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).

02-25-2021, 02:52 PM	#1
BC847 Name: BC847 Title: Too Much Time Status: Not Here Join Date: May 2006 Member`s Gallery Posts: 851	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. __________________ Original owner of a VE fueled 1993 W250 ClubCab. Silencer ring MIA, str8 pipe with 10" exhaust tip, 250psi boost gauge, ghost-lights 'n truck-nutz. K&N air filter next (if my grades are good enoufh).

02-25-2021, 04:05 PM	#4
zstroken Name: zstroken Title: For $$$ your name here Status: Not Here Join Date: Sep 2006 Location: Western Michigan(by the lake) Member`s Gallery Posts: 23,151	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. __________________ 2008 4x4 Megacab, 68RFE 97 Dodge gone.... 24V P-Pump Mafia member #1(retired) Thanks to Mumau Diesel, Goerend Transmission, Northeast Diesel Service!

02-25-2021, 04:17 PM	#5
BC847 Name: BC847 Title: Too Much Time Status: Not Here Join Date: May 2006 Member`s Gallery Posts: 851	AH! I found the thread with the math. Thanks, guys. Tuning Twins - Competition Diesel.Com - Bringing The BEST Together __________________ Original owner of a VE fueled 1993 W250 ClubCab. Silencer ring MIA, str8 pipe with 10" exhaust tip, 250psi boost gauge, ghost-lights 'n truck-nutz. K&N air filter next (if my grades are good enoufh). Last edited by BC847; 02-25-2021 at 04:20 PM.

02-25-2021, 05:55 PM	#6
Smokem Name: Smokem Title: Turbler Status: Not Here Join Date: May 2006 Location: Iowa Member`s Gallery Posts: 5,565	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. __________________ Infinite Performance

02-27-2021, 11:54 AM	#7
BC847 Name: BC847 Title: Too Much Time Status: Not Here Join Date: May 2006 Member`s Gallery Posts: 851	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). __________________ Original owner of a VE fueled 1993 W250 ClubCab. Silencer ring MIA, str8 pipe with 10" exhaust tip, 250psi boost gauge, ghost-lights 'n truck-nutz. K&N air filter next (if my grades are good enoufh).

02-25-2021, 03:37 PM	#2
Snedge Name: Snedge Title: Comp Diesel Sponsor Status: Not Here Join Date: Sep 2006 Location: Western Pa. Member`s Gallery Posts: 18,859	Are you running compound turbos or a single ?