converting lbs/min to cfm for dyno 2000

[s13sr20chris]

ok, this should be so simple. i have been modeling my sr20det on dyno 2000 and would like to accurately model my t25. nevermind that i cant find a t25 compressor map. i found one for a gt28rs just to see if it gets anywhere close. i need to input FLOW(defined as the "island flow" of highest efficiancy) in cfm. i figure this means the cfm(even though garrett compressor maps give flow in lbs/min) where the efficiency is highest. i also need to input PRESSURE RATIO(defined as the pressure ratio where highest efficiency occurs). then there is intercooler efficiency, turbo efficiency, surge flow(i have no idea where to find this spec), and boost limit. i have searched high and low. i have tried calculating cfm from lbs/min from the garrett compressor maps by dividing by the density of air. i tried it at outside temp/pressure, at turbocharged temp/pressure, and just got some "magic universal" air density figures like .069. i keep coming up with crazy stuff that doesnt work. i have a dyno 2000 dyno graph with some turbo i made up while not knowing what i was doing and all the engine specs accurate(or close). the flow i was using was ranging from 30cfm to 120cfm. it gave me around 275bhp at 13 psi which is about standard among sr owners with the same work done. thats also about what it feels like. i tried some math and heres what happened. the gt28rs is 77% efficient at 2.0 pressure ratio and flowing 25 lbs/min. i convert that to 362 cfm. enter those figs into dyno 2000 and get 200hp. that and my turbo wont even push out the 13psi. the graph for manifold pressure is showing 18psi(subtract atmo of 14.7) which is only around 3psi really. i wont bore you all with the other many things i did, but anything that made sense did not work.

please help.

i know you engineers are prepared for something like this. i also know that a modeling program like this is not gospel. i just want to do it for the heck of it, but i dont want to just enter random turbo specs as the dyno graph ends up being useless.

1)can anyone help me make the conversion to whatever kind of figure that the program is looking for?2)can anyone tell me where to find a real t25 compressor map?3)can anyone explain how to calculate or find surge flow?

thanks and God bless,chris

[s13sr20chris]

there certainly must be someone with an idea...

[Q45tech]

1 CF of air is 0.0807 pounds= 36.61 grams of which 8.49 grams is oxygen at standard temp and pressure [29.92" HG- 0.0 degrees celsius /32F]

Believe it or not everything you need was on the web but http://www.gnttype.org disappeared ------forgot to reup their url? Network Solutions sucked it up maybe they'll be back?

Here is a cache locator but I havent found the .xls spreadsheet to figure what you want:http://216.239.51.104/search?q...hl=en

Like magic:http://www.ffdet.com/tech/turbocalcs.xls - http://www.egr.msu.edu/~remondi2/Car%20 ... ciency.xls

http://www.mygen.com/users/dbr...s.htm

http://www.stealth316.com/2-turboguide.htm

[Q45tech]

Note that many of Mitsubishi's TD turbos are interchangeable with the Garrett T25, so don't be surprised if you see a Mitsubishi turbo on a Dodge or a Nissan.

[s13sr20chris]

wow, i havnt even read all the links yet but thanks. as in-depth as your posts usually are im sure this will be a huge help!thank you very much.

[s13sr20chris]

well i went through all of those great links and found that i was coming pretty close on my calculations. for some reason the program is not trying to work with that. i dont guess that you have experience with that program do you?

[golgo13b]

I'm playing with that program right now. I'm still downloading cam-specs. Try using one of the turbos provided that is similar and changing the numbers it gives you, then save it as a custom turbo.

[golgo13b]

This might help if you find compression maps.