How do you read a compressor map?

[4sfed4]

Quote:

Originally posted by turbovanman So for those of us without egt, what is an acceptable backpressure reading?????????

EGT was only mentioned becuase it was a convenient port in my manifold to use. You can tap anywhere you like in the exhaust manifold and will probably get similar readings. Ideally, it should be measured right at the turbine inlet at the flange.

As far as what is a "good" backpressure reading, I can only offer what I have measured on my car.

With the stock trubo, I saw 43 psi backpressure for 13 psi boost. Thats terrible. But, thats also why the turbo would spool so fast.

With the TO4E 50 / Stage 3 / 0.63, I saw about 24 psi backpressure with 14 psi boost. When I raised boost to 20 psi, backpressure was 42 psi.

[4sfed4]

Quote:

Originally posted by contraption22 An article in Hot Rod mag last month (which is fully available for free right now on hotrod.com) Recommends that you use a VE of 100% when doing these calculations.

My current (and maybe simplistic) thoughts right now are that we should use VE equal to at least 100% on turbo charged engines. The reality is, to make the numbers "work", the VE will come out much higher than 100% when using the traditional formulas.

[4sfed4]

Quote:

Originally posted by fkatzenb I stayed at a Holiday Inn Express last night. hehehehe

hehehehehehehee.

Very well timed retort!

[Frank]

let me fix a couple of misconceptions.

a guestimated VE is always better then assuming 100% VE because you are closer to real life... unless you cant guestimate very well. :big grin:

also...

turbocharged and really good n/a motors will have a VE greater than 100% only because they are comparing between "achieved equivelent volume and ideal volume". When I say "achieved equivelent volume" is what the volume would be at std temp and pressure.

So on a turbocharged application, the 2.0L of 30psi air @140*F equates to say 3.0L of air at std. temp and pressure. That would equate to 150% VE. That VE will also always be used for fuel calculations. It is also used on all speed density efi systems. THIS IS NOT THE VE USED FOR COMPRESSOR MATCHING.


The VE that my spreedsheet and all compressor map formulas use is a VE that comparing to what you should have to what you have at a constant pressure and temperature. So since we have a turbocharged motor that is not totally efficient in its port and cylinder characteristics we will always have a VE les the 100%.
For example: we would expect a 2.0L of 30psi air @140*F to equate to say a 3.1L of air at std. temp and pressure. The problem is that we only are getting 3.0L of air at std. temp and pressure. That would give us a VE of 96.8%!!!!

I hope that clears things up!

Frank

[contraption22]

This is a spectacular thread. Thanks for all the great info.

[turbovanman]

Quote:

Originally posted by 4sfed4 EGT was only mentioned becuase it was a convenient port in my manifold to use. You can tap anywhere you like in the exhaust manifold and will probably get similar readings. Ideally, it should be measured right at the turbine inlet at the flange. As far as what is a "good" backpressure reading, I can only offer what I have measured on my car. With the stock trubo, I saw 43 psi backpressure for 13 psi boost. Thats terrible. But, thats also why the turbo would spool so fast. With the TO4E 50 / Stage 3 / 0.63, I saw about 24 psi backpressure with 14 psi boost. When I raised boost to 20 psi, backpressure was 42 psi.

So you don't check the backpressure in the exhaust? you say at the turbine inlet or am I reading this wrong? Turbine inlet, is that on the intake side-sorry I am new to turbos and still trying to get the lingo down,

[4sfed4]

Quote:

Originally posted by turbovanman So you don't check the backpressure in the exhaust? you say at the turbine inlet or am I reading this wrong? Turbine inlet, is that on the intake side-sorry I am new to turbos and still trying to get the lingo down,

The turbine inlet is right where the exhaust enters the turbo. Basically its where the turbo bolts onto the exhaust manifold.

So, yes, you would be measuring the backpressure in the exhaust.

I also have measured the backpressure in the exhaust after the turbo. This is a good check to see how restrictive your downpipe and exhaust system is. The backpressures will be cumulative. So, if you see 40 psi in the exhaust manifold before the turbo, thats is the sum of ALL backpressures in the system downstream of that measuring point (i.e. turbo, downpipe, cat, muffler, piping, etc).

In my case, I found that the backpressure in the manifold was due more or less entirely to the turbo itself as the pressure measured in the downpipe right after the turbo was zero. So, there is really nothing to improve in the system downstream from there.

If one were to get really fancy, you could also check the pressure in the exhaust manifold right where it meets the head in each runner. If any of those numbers are higher than what is seen at the turbine inlet, then the manifold is restrictive to some degree.

[Vanquizor]

I guess the real question is what kind of tubing did you run from the manifold to your pressure guage so that it wouldn't incinerate once you were on it..

And also where can I swipe a 'demo' copy of this spreadsheet?

[contraption22]

You can run a coil of copper tubing so it cools before it gets to the gauge.

[turbovanman]

Thats awesome, thanks. Now for my last question, maybe! how did you tap into the turbine housing? Did you drill into the exhaust manifold or the Turbo housing? Thanks again!:big grin:

[Frank]

Quote:

Originally posted by 4sfed4 The turbine inlet is right where the exhaust enters the turbo. Basically its where the turbo bolts onto the exhaust manifold. So, yes, you would be measuring the backpressure in the exhaust. I also have measured the backpressure in the exhaust after the turbo. This is a good check to see how restrictive your downpipe and exhaust system is. The backpressures will be cumulative. So, if you see 40 psi in the exhaust manifold before the turbo, thats is the sum of ALL backpressures in the system downstream of that measuring point (i.e. turbo, downpipe, cat, muffler, piping, etc). In my case, I found that the backpressure in the manifold was due more or less entirely to the turbo itself as the pressure measured in the downpipe right after the turbo was zero. So, there is really nothing to improve in the system downstream from there. If one were to get really fancy, you could also check the pressure in the exhaust manifold right where it meets the head in each runner. If any of those numbers are higher than what is seen at the turbine inlet, then the manifold is restrictive to some degree.

i will be doing something similar to my turbo manifold that I am building. my plan is to use a leaf blower and use two map sensors and some volt meters.

(good thing my friend knows how to weld stainless tubing)

frank

[4sfed4]

Quote:

Originally posted by contraption22 You can run a coil of copper tubing so it cools before it gets to the gauge.

Exactly.

I happened to use some aluminum tubing and a compression type fitting. I ran about 3 feet of this tubing before connecting to some vacuum line that went to the gauge.

[4sfed4]

Quote:

Originally posted by turbovanman Thats awesome, thanks. Now for my last question, maybe! how did you tap into the turbine housing? Did you drill into the exhaust manifold or the Turbo housing? Thanks again!:big grin:

I drilled into the exhaust manifold and not the turbine housing. I already had a tapped hole in the manifold for the EGT, so I just used that instead of making another hole in the turbine housing.

Ideally, the turbine housing is where you would measure. In my case, the turbine housing and where I am measuring in the manifold are only 2" apart or so, thus the difference would be negigible.

[theskeptic]

Here's a good one for the experts:

What about elevation changes in regards to pressure ratios? Since I'm at just over 1 mile elevation, we see around 12 psi of absolute pressure during the summer months. Does this make my formula:

(Boost + 12)/12 = Pressure Ratio

Yes?

Bummer for me, eh. That divide by 12 on the bottom sends my PRs through the roof, yeah?

-Dana

[4sfed4]

Quote:

Originally posted by theskeptic Here's a good one for the experts: What about elevation changes in regards to pressure ratios? Since I'm at just over 1 mile elevation, we see around 12 psi of absolute pressure during the summer months. Does this make my formula: (Boost + 12)/12 = Pressure Ratio Yes? Bummer for me, eh. That divide by 12 on the bottom sends my PRs through the roof, yeah? -Dana

Thats correct! The turbo on your car in Santa Fe, NM will be higher on the pressure ratio axis at the same "boost" pressure as that same turbo on my car in Tarpon Springs, FL (elevation about 10 ft).

Thus, all else equal, the turbo will (generally speaking) have to spin faster to make the same intake manifold "boost".