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Message: [QUOTE="TARM, post: 353641, member: 578"] What size are your gates? Original config: 66mm with a 1.0 housing 15lb spring 88mm with a 1.27 housing 15lb spring 66 mm WG output into 88mm turbine. Now here is what I am coming up with for boost and PR numbers based on the info you have provided in this thread. I think your are gating way too much pressure over to the Atmo turbo. Here check out my math in case I am doing something wrong. Now for the actual boost made by each turbo I using standard atmosphere compressor to keep everything simple as well. But I am also using to show how much boost the manifold compressor using the PR with a normal atmosphere pressure at the inlet instead of the compressed air from the Atmo. as that IMO gives a better showing of the work its actually doing like it would as a single. I am adding all this stuff so others can follow that may not know this stuff. But more importantly to make sure I am not making a or multiple bone head mistakes. :D To get PR break down for total and for each turbo: Basic Formula for Pressure Ratio (boost +14.7)/14.7=PR (Not accounting for altitude changes or filter restriction) Formula for Pressure Ratio for each Compressor in a Compound Setup: In compounds the turbos individual PRs are multiplied together to get total PR. So if you have the total you divide it by either one comp individual PRs. The Atmosphere Compressor is the easy one to compute along with the total combined PR. So The total PR divided by Atmosphere gives use what the Manifold Comp PR is. With that we can use the standard PR formula to see what it would be making if inlet was standard atmosphere pressure. This is helpful IMO as most people are use to looking at compressor perf by boost as opposed to PR. Total Manifold Boost: 50psi PR 4.4:1 88mm Boost: 25psi PR 2.7:1 66mm Boost: 9.2 PSI PR 1.63 Inlet boost psi+ standard atmosphere psi multiplied by pressure ratio minus standard atmosphere psi equals total boost. [(25+14.7)*1.63]-14.7=50.1 psi total boost Does this look correct to you as well? Everything seems to mesh. My inexperienced opinion is, I think you have the 66mm not doing enough. The 15psi spring is not much when you consider where the turbo's map shows where it really starts to flow well. My guess is its not getting enough flow to allow the comp to get to its best efficiency islands and it staying to far to the left and bottom of the map as well. If it had more drive energy it would allow the ratio to hit closer to a 1:1 ratio as the comp would be in a more efficient area of its map. Currently if you factor a 15lb spring its 1.5:1 D:B Actually it may be a bit more as that is just cracking open the WG I do not know. Gate size could have an effect. I would go ahead and add boost to both sides with the top regulated of course. Pressure from both sides will help stabilize the valve as I understand it. Move the PR into the 2.0 range. You switched the 88mm WG spring from 15lb down 8lb The result was: No drop in 88mm boost pressure. I could be wrong but to me if you make a spring change to a lower spring and boost for the atmosphere Compressor does not drop this means you are already at the limit of your waste gate or something is not right. It may take a bit longer to reach the boost as its delaying the spool up but it would still reach it. Am I making sense or am I way off here? What size are the two waste gates? Just an FYI as I was digging thru it: I had done some calculations when I was working of how proper turbine flow to compressor flow. If you figure a 130 F inlet temp for a a given PSI to keep a certain weight/volume of air and then increase the air temp to say a exhaust outlet temp of 1600 F. It would take either 3.5 x the pressure to keep the same weight/volume or take 3.5x the vol to hold the same lb of air compared to the inlet. That's a lot of expanding energy flowing thru the turbine side of things. [/QUOTE]