Besides using a trial and error approach, how can a particular turbo's efficiency range be determined/found? I have a SPA5000 turbo on my Rev-up. Any info would be nice.

 

I've spent a bunch of time trying to research this topic, but there's nothing that I've found.

 

Look it up on the manufacturers website

 

I tried. SPA is a Brazilian company, and I don't read Spanish well. haha. There is very little info on them, that I've been able to find. None the less, I'm not really asking the specs, but at what PSI / rpm range this turbo would be most affected on my g35? It's apparently similar to Garrett gt30

 

It is too small for the VQ35 engine, as the largest turbine housing for it is a T3 .63a/r. If you have two of them, then it will work, otherwise don't bother.

 

I gained over 75rwhp and 100rwtq @ max 8psi. The previous owner gained 95rwhp and 110rwtq using same turbo, different add-ons. But my question is 'how can you find out the PSI that starts to inversely effect performance?'

 

Exactly. IIRC, people with larger housings can gain over 150whp. I think your best bet is to learn how to read compressor curves. I haven't looked into it myself, but I think that the Garrett Honeywell website has tutorials that you can struggle through to get an idea of how to read the curves and (I'd imagine) size a turbo effectively for your application.

 

Thank you for the helpful information. I am running on a dynojet currently 340rwhp/340rwtq on a dynojet 224 at approx sea level on a 100degree very high humidity day. I understand that I would have much more hp/tq with a bigger turbo, but I also was have a decent setup for what it is, custom fabricated. I may upgrade the turbo and rebuild the engine, in time.

 

The manufacturer is who tests the turbo when they design it and build a compressor map off of that. I'm not sure if there are any companies that you could send a turbo to and have them build a compressor map from that. That is the only way to see what the efficiency range is unless you just keep cranking up the boost and watching intake temps rise but then you don't know if it's too small of an intercooler or the turbo is out of boost.

 

Very good points. Thank you Jeff.

 

very simple, use an exhaust backpressure sensor.

you go over 1.5:1, your turbo is past its efficiency.

 

Would the # be constant throughout the rpm band? Ex: 1.4:1

 

Rich...the big manufacturers don't do this, and you expect a DIY guy to do it? 2:1 is the point where you have to consider turbo or turbine upgrades.

No, it would rise with RPM. Should look something like this:

http://i137.photobucket.com/albums/q...BUILD/EBP2.jpg

 

he asked, and thats probably the easiest way that isnt guessing.

2:1 is pretty high, well outside efficiency.

On a single turbo kit its super easy to do, or any kit that isnt installed yet.

If i have to pull my motor again, I'm going to put the bungs on my manifolds.

 

Mr. Bell says 2:1, and I have seen the cars still making power at that, so maybe it is one of those topics that can be debated/beaten. Either way it is a good start.

I made an adapter so that it can be used in the place of an O2 sensor (once the sensor is removed. Works well, and you don't need an extra hole in the exhaust.

 

Oh, nice chart. Makes sense now. What if that same setup was running 8psi? would that make the back pressure still 20 (2.5:1)...or would it be more like 8psi boost & 14 psi ebp = 1:1.75 ?

 

ya, hal used sasha's back pressure test port on my car. You have to run it with no exhaust on due to the backpressure of the exhaust. I thought the housing on mine was way too small due to backpressure but it turned out the exhaust was the issue. A 6765 turbo definitely wasn't out of steam with only 463hp. Put an exhaust cutout on and everything was fine.

IATs will rocket up pretty high once the turbo is out of steam as well. As you turn up the boost the power will stay the same. All of those measures combined would give you a little idea of how hard you can push the turbo.

 

Makes sense. Thank you.