Measuring pre-turbine backpressure

[fspGTD]

Knowing the pre-turbine backpressure would be useful as it would indicate the efficiency of the turbocharger and exhaust system.

I'm thinking that the exhaust manifold could be drilled and tapped and a small stainless pipe tap fitting could be inserted.  Coming out of it would be a small diameter, rigidly supported stainless hardline extending long enough to slow the transfer of heat from the exhaust manifold (I'm thinking a few inches, or maybe even a foot or two.)  Stainless seems suitable as it can take the high temps near the exhaust manifold while also being good at limiting the transfer of heat.  Could be a simple compression fitting at the end or some sort of flared end fitting.  Then at a point that is far enough away (and cool enough,) it could transition to a flexible line like is used off the intake manifold for measuring boost pressure - IE: rubber or plastic, and from there leading into a boost gauge.

In fact, by swapping the source that an existing boost gauge is connected to, it could function as a pre-turbine backpressure gauge.  And it could be swapped back quickly or even have a switch somewhere to toggle the pressure source.  Has anyone tried measuring this before?

One could even install a similar fitting post-turbine, to measure backpressure (and judge effectiveness) of the exhaust system.

[vwmike]

I don't know anyone who has done this, but I do know that I probably don't want to know what the backpressure is  

There is no way I'm upping the turbine size. It already takes days to spool.....part of that is probably the crappy stock exhaust (which I will solve as soon as I can find all of the parts to one of my oil coolers and get the Rabbit mobile and out of the garage for now).

[Maarten]

Your talking about the pressure inside the exhaustmanifold right?

Maybe you could use a TDI (or US AAZ) exhaustmanifold with the EGR pipe, thats a good start to fix an adapter on for the pressuregauge.

Altough I think the pressure in the manifold is higher than a normal boostmeter can take (ie. 3 bar) and a 2nd prob will be the debri of particles that could clog the meter.

[Master ACiD]

id be scared to see what the pressure inside the manifold is. on some of those tiny little turbos they look like somthing for which you would affix to a 5hp briggs and stratton.

[Audi80]

Itīs a good way to measure turbo sizing. Exhaust manifold pressure should be less than boost, but normally it isnīt. A little over boost isnīt bad, but if you have twice the boost, itīs bad. And it could easily be reached with small stock turbos...
I have used a ~1.5 feet copper tube and rubber hose connected to industrial pressure meter.

[vwmike]

As far as I've understood, very few vehicles create more boost than they do backpressure. That is usually left to things like F1 cars.

[2383 GTD]

I tried this years ago before I moved from the stock turbo to something larger.  I found that the pressure ratio was about 2:1, turbine to compressor, which was far from optimal.  As mentioned, F1 cars , when they still used turbos, could very easily have a ratio of <1:1.  We would all like to strive for at least 1:1, which is very difficult to do, and still be streetable.  VGT turbos solve this.

When I did upgrade the turbo, I did it in 2 iterations, with the preturbine pressure decreasing each time, until I achieved something close to 1.3:1.  Each time the turbo size was increased, the power increased as well, and the preturbine pressure decreased.

After the EGT was known and safe, I simply removed the thermocouple, found a suitable fitting, and attached a simple copper pipe, about a foot in length to a rubber hose fitted to a 60 psi pressure gauge.  I think I used a flare fitting in fact made of standard brass.  Cheap and easy.

I will also check the preturbine pressure, and report back with the K29 that is on the car now, which should be quite low.  Again, the power has increased tremendously.  More on that in another thread  :twisted:

[fspGTD]

Great to hear it can be done!  I'll take readings on my Garrett 1.6lTD turbo, and then will compare against what the K24 shows after I get that swapped on.