By my calculations, using Garrett's formula (https://www.turbobygarrett.com/turbo...compressor_map), a 300HP goal is obtained via 29.1 lb/min flow at 2.27 pressure ratio. If I map that to my MHI TD04-19T compressor map, using the following data, it shows the TD04-19T is within the efficiency range (I think).
HP Target = 300
AFR = 12
BSFC = .55
CI = 109.8
RPM = 8200
VE = .95
IAT = 130
compressor loss = 2
piping loss = 1

This gives me 300HP at 14.4 on the boost gauge. Sounds about right to me. So, here comes my question...
If this compressor is still within the >70% efficiency range at redline, why does it fall flat on it's face at 7000RPM? Max boost after 7000RPM is about 7psi. (I know it's too small, but why do my calculations show otherwise, or do they?!)
Don't hate too much! I've been out of the tech side of boosting for a few years, just trying to decide on a new compressor and EMS. I wanted to figure this out before I use those calculations to make a major mistake. I'm running a TD04-19T (D series) turbo on a B series Greddy kit, with a few mods in sig. I'm leaning towards the GT3071R for a 350HP goal, daily driver. That should put me closer to the center island of efficiency.
I attached my Excel, in case anyone wants to look at the formula.

 

Garrett goes by crank hp. Which is not the same as wheel hp, also the ve you are using is not very conservative.

try this follow this it may help https://youtu.be/TLXw3UyfmcI

I usually just take the lbs per min times .9 times 10

and that's just a rough guide that does not consider alot of things like elevation pressure losses etc.

3071 is barely overkill for those goals but good if you may want to go fore more power later. I'd probably go a little smaller just for the added spool myself

I'm sure shodan can brake it down much better but I just figured I'd give you a few ideas until then

 

Good info, I didn't realize that. I changed the VE to .9, but it is still in the same general area on the chart.

 

I went ahead and mapped it using the method I posted for you using a 90% VE and 1.8L motor

at 8.4k its a the edge of the map and in a poor efficiency island, this is whats happening to you I believe, if you look at the 6.5k-7K range its in the 70% efficiency area
Basically the turbo is just too small for what you are trying to do, if you look at the more efficient part of the map its at 400 CFM

400CFM divided by 14.27 (to convert to LBS per min) = 28LBS per min times .9 times 10 = 250 (wheel HP)
so based on that anything past 250 HP is generating alot of heat, and thus not as efficient
even at 7.5K its already at the 65% efficiency area. Im not an expert in this but thats the way i self taught myself to map a turbo with the help of youtube. and it pretty much draws out what you have been explaining, its not a perfect science there are lots of other factors, VE, intercooler, and pressure losses to name a few

sorry about the poor colors lol i kinda rushed it but i hope it makes sense to you

 

on a side note you may want to check for boost leaks, My first dyno session I was dropping from 17PSI to 14 after about 6K. The only thing i did was change my manifold and fix some boost leaks and it holds 17 PSI now

 

Wow, thanks for all that! Much appreciated! I've had boost and exhaust leaks, which make it worse, but I never got the 19T to hold 10 psi to redline no matter how sealed up it was. I'll have to run through the video to see where you got the 2.0 pressure ratio. Otherwise, it's about the same as my calculations for CFM.
I'm still unclear about why Garrett's calculations show this is an acceptable compressor, when it is not.

 

It' very clear. That calculator is a basic calculator to get you into the relative family of turbochargers to utilize. It doesn't give all of the variables by way of a formula in order to do that.

If you have to use any of them, the BW Matchbot is a better calculator, and even helps you if one of your variables are off scale. It even uses your gearing ratios to help.
BorgWarner MatchBot

 

Boost value + 14.7 divided by 14.7

I used a value of 1.97

 

Yep. Pretty standard for using @2PR on the adiabatic maps

 

Thanks guys, it is clear now. Part of what I got out of this is not to use Garrett's calculations. The BW MatchBot plotted the points where I expected them to be (@12psi on the gauge, very close to 2k's plots@14). This shows that the compressor is passing the choke line after about 7000RPM, and aligns with my experiences.

 

I wasn't using their online calculator, it's offline I was using their full formula from the link above. Just didn't get the results I expected, where I do with the MatchBot tool. Thx again!

 

I understand it was offline, but it's still a basic turbocharger calculator. It lacks a LOT of the inputs needed. I made my own 10 years ago in excel, and still caught up with Matchbot's current dynamic calculator. I actually feel vindicated now.

 

how did u get it to overlay on your map? or did you do that manually?

 

MS Paint :D