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Message: [QUOTE="Powerstroke Cowboy, post: 879497, member: 610"] Here is a S480 Comp map.[ATTACH=full]124679[/ATTACH] Here is a S475 comp map. [ATTACH=full]124680[/ATTACH] I could not find a map for the S482 or the S488. This is one reason I love Garrett turbos!! They have one for every turbo I love it! As you can see by the maps the S475 moves about 80 LB/MIN @25 PSI The S480 move about 85 LB/MIN @25 PSI. Now the S475 moves about 91 LB/MIN @30 PSI and the S480 moves about 100 LB/MIN @30 PSI. The S475 moves about 102 LB/MIN @50 PSI the S480 moves about 115 LB/MIN @ 50 psi. From that they do not look that much different. In till you get into the upper range. Now with that said. Why would you want the S475 as a atmo charger?? @ 25 PSI it flowing less the a single S366 would at full song. And the S366 can spool fast set up right. I feel like you really would not be gaining a thing You might even loose power with the S475 as a atmo. If you ask all the guys that run compounds on the 7.3 and used them (like Charles) you will find most of them say Go with at least a 88mm inducer for the atmo. Why?? So you get the flow and volume needed when running lower boost. The S475 does not have the flow or volume needed to move enough air when only being run in the 25 to 30 PSI range. Even as a single at 50 PSI it would be nip and tuck with 250/200. It still would not clean them up. How will it do it in a compound setup @25 PSI flowing about 20 LB/MIN less? In the Gasser world that can equate to about 200 less HP not sure about the diesel world BUT it would not be as drastic of a loss. Ok The S475 feeding a S300 something (does not really matter because teh flow the engine will see is from the S475 anyway. The S300 is there just to get boost started and compress the air more.) Lets say the S475 is (On the gauge) @25 PSI and lets say we are @ sea level with 14.7 atmo pressure. That means the S300 will be fed 39.7 PSI Now lets say the S300 is @ 20 PSI (on the gauge) That would mean you will see on the gauge 59.7 PSI at the manifold. Now the engine would really be seeing 74.4 PSI of boost. you just would not see it on the gauge. And all you would have would be in the 80 LB/MIN range with 59.7 PSI on the gauge. That is not enough air to support 450 hp @3000 RPMs It would be smoke. I am not really sure how to put it this stuff on paper. In order to get the Volume of air flow needed you would to run 50 PSI on the atmo. And that would put by gauge right @ 84.7, actual pressure would be 99.4 BUT if you speed the S300 up to keep them in a closer ratio to 30 PSI you would see 104.7 on the gauge and 119.4 actual. Hence the reason you need a Bigger atmo to keep pressure down but still got the Volume of air needed. if all you were looking for was Density all you would need to do is get a S300 something and run high boost to get the air density. Yes air density play a big part on a turbo setup BUT without the VOLUME to go with it you have nothing. Hope this makes sense. ON EDIT: I apologize if my math is wrong!! That is something I do not like posting on open forum! AND I am sure I did not use the correct math to get the pressure ratio. To be honest it feels like I laid my head on the chopping block! WITHOUT being blindfolded!! [/QUOTE]