Exhaust Back pressure measurement test

warp2diesel · **Posted:** Sat Apr 18, 2009 10:32 pm

I am going on a trip this coming week that has some up hill runs climbing the river bluffs. I may be towing my trailer, but that is not known yet.
to run the tests, I hooked up an old boost gauge into the exhaust down pipe just behind the turbo to see how much back pressure is against the turbo with a stock system.
If the old boost gauge is not sensitive enough, I will install another gauge or manometer and test.
I plan to install my Magnaflow muffler in a couple weeks, run the tests again and report the results.
Suggestions will be considered.
I will record:
1) RPM
2) MPH
3) EGT
4) Boost
6) Back pressure

Here are photos of the very temporary setup that will be used to take the readings:
Where I tapped in my EGT probe.

Where I originally had my probe, I make lemonade out of lemons.

I installed a steel brake line to dissipate the heat before connecting to the plastic line.

Plastic line connected to steel brake line.

Plastic line routing.

Gauge set on dash, I may extend the line so I can snap the gauges with a camera.

CATCRD · **Posted:** Sat Apr 18, 2009 10:55 pm

I'm interested in the results. Stock cat? Any changes planned to the cat?

warp2diesel · **Posted:** Sat Apr 18, 2009 11:06 pm

My system is stock including the Cat.
I have no plans to gut the cat at this time.
I will cap the steel brake line when I am done testing my Magnaflow.
I will have some 2 1/2" 304 Stainless Steel pipe left over and may take the cat off later or gut it.

honey_don't · **Posted:** Mon Apr 20, 2009 2:04 pm

You could go to a 2.5" hi flow cat and measure before and after on that vs. stock cat independent of the the muffler test. :wink:

http://tdiparts.com/catalog/product_inf ... ts_id=1175

warp2diesel · **Posted:** Tue Apr 21, 2009 9:51 pm

I fought a head wind that had the flag whipping and there were high wind and thunderstorm warnings including some pea sized hail. We had a hitch carrire loaded to 200 pounds, an empty roof rack and provisions loaded to the roof.
When I was going 70MPH (corrected from speedo reading error) with 12psi boost, 2100 RPM, and 950f EGT the gauge on the back pressure stayed at ZERO.
I got it to get off the zero peg when I got over 2100 RPM witht least 10 PSI boost.
At 2250 I got 1PSI of back pressure as long as I had at least 10 PSI boost and EGT around 1000f.
When I passed a slow car I got the back pressure up to 3.5 PSI at 3000RPM, 18PSI boost and 1000f EGT.

Preliminary conclusions: Engine RPM is the one consistent factor in generating readable back pressure.
2100 RPM is the point that I get the gauge needle off the zero point on back pressure.
Stock system in adequate up to 2100 RPM with 10 PSI of boost. Over 2100 RPM the stock system creates back pressure and robs performance.

I will run some more tests and post the results before I install the Stainless Steel Magnaflow.

CATCRD · **Posted:** Tue Apr 21, 2009 10:26 pm

Do you have the F37? Any chip? I remember people seeing up to 25psi stock boost before F37, do you ever see anything that high?

gmctd · **Posted:** Wed Apr 22, 2009 9:45 am

Pull the EGR solenoid connector, run the test again..................

linewarbr · **Posted:** Wed Apr 22, 2009 2:23 pm

Does the SEGR effectively pull the EGR solenoid?

UFO · **Posted:** Wed Apr 22, 2009 2:44 pm

linewarbr wrote:

Does the SEGR effectively pull the EGR solenoid?

Yes. Literally and effectively.

Warp, I had no idea the factory muffler was so restrictive. I would think an Ultraflow would work wonders -- I use a 3" model on my 300whp road racer (turbo 2.8l) and it sings.

warp2diesel · **Posted:** Wed Apr 22, 2009 9:48 pm

My SEGR is waiting for time to test and hook up. I have no chips installed yet. Mine is an 06 so I think it came with f37 done in the factory.
I do use a fuel cooler that keeps the ECM from turning down the power when the fuel gets warm.
When I get back, I will do some heave acceleration and see how that effects the back pressure.

warp2diesel · **Posted:** Sun Apr 26, 2009 11:53 am

I had to tow my tandem axle trailer loaded with brush to the wood dump with a total load of 3500#. I noticed that even with that load, the exhaust back pressure was the same as when I was driving into the strong head wind a few days before.
With the CRD loaded down with weight in the back to have the rubber bumpers kissing the stops driving into a head wind accelerating I was able to obtain 4 PSI back pressure at 3500 RPM.
When I returned home with no head winds and even more weight in the CRD, my exhaust back pressures were 1/2 PSI lower than when I was driving into a head wind.

Preliminary conclusion: RPM is the biggest factor in having Exhaust back pressure, load does make some diffrence, but not as much.

Next plan is to shoot a video of gauges when I accelerate to put it into perspective.

CATCRD · **Posted:** Sun Apr 26, 2009 2:06 pm

Nice work. Did you see what the boost and EGT numbers were during the 4psi backpressure measurement?

If the magnaflow is a straight through design it should have negligible restriction when you install it, and anything left we could chalk up to the cat.

warp2diesel · **Posted:** Sun Apr 26, 2009 6:56 pm

CATCRD wrote:

Nice work. Did you see what the boost and EGT numbers were during the 4psi backpressure measurement?

If the magnaflow is a straight through design it should have negligible restriction when you install it, and anything left we could chalk up to the cat.

I can see light out the other side of my Magnaflow.

Does Photo Bucket support videos, or do I need to U Tube :?:

Having a Exhaust Back Pressure Test on U Tube would make some shake their heads :lol:

Exhaust Back pressure measurement test

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