Has anyone measured an FD's exhaust backpressure? If so what did you find out and how did you do the measurement? Any comparisons before and after modifications?

Found this web site, http://www.jdsdiagnostic.com/faqs.html for a commercial test setup. Their page lists the following general statement:

 

I don't think measuring the backpressure in the exhaust system is a very quick and easy thing to do. With the stock cats its probably not the best I can tell you that much.

P.S. the whole 'lose of power thing' is basically any stock exhaust system. This is why you gain that power back when you replace the system. We gain a lot of HP replacing the stock system, if that answers your question

 

So you are talking about post exhaust turbine back pressure right?

I think a comparison of pressure differentials regarding the exhaust turbine sides would be interesting.

 

.S. the whole 'lose of power thing' is basically any stock exhaust system. This is why you gain that power back when you replace the system. We gain a lot of HP replacing the stock system, if that answers your question

Then you get people saying there is no reason to go to over 4" tube size.

I think there is meaningful data to be had- especially regarding spool rates.

 

On another car, I made a fitting from an old spark plug, then used 1/8 copper tubing coiled into a pigtail to dissipate heat. Put this in 02 sensor hole in dp, and hosed up a gage to the copper tubing. Worked well for post turbo back pressure in piping/muff's ( but not on an fd).

 

I was thinking of threading a nipple into the exhaust manifold then hooking it up to a boost gauge to see how much backpressure the turbine manifolds are creating.....havent done it yet though. I was also wondering if anyone had ever tried it

STEPHEN

 

The data would also be usefull for those of us consider a MP with a restrictor plate.

 

Well the O2 sensor bung with a nipple trick works, well, just use hose that can stand the heat, and do 1-3 runs at WOT max, or you'll melt the rubber off... and it'll be a pain to remove. I've seen my own exhaust system read as high as 12 PSI backpressure with Clogged Pre-cat and after DP 8PSI with clogged main cat... 3-6psi seems to be good / normal with stock exhaust...

The trick is to have 2 Boost gauges 1 For Backpressure and one for Boost, so you can see where things really blow ?? (Or Don't) as the case may be...

-DC

 

Knowing the amount of turbo manifold backpressure per rpm would also guide one in how much exhaust overlap to port for for the powerband they want, I imagine.

 

I measured at the 02 sensor with a clogged main cat - and it read over 10 PSI. I never tested after that with a good system. The cat was clogged, the test helped point to this and then when the cat was replaced it made a big difference.

replaceing the 02 sensor is a big enough pain that I lost interest in testing normal condidtions, but I would assume it would only be a couple of pounds.

 

DCrosby - I was thinking of the same approach that you describe,
Noticed that your signature doesn't say anything about an aftermarket ECU, so when you temporarily replaced the O2 sensor with your modified bung, did this cause any big problems? Maybe just an error code to clear out when finished?

 

If I remember right the 02 sensor isn't used at WOT? It goes into a closed loop mode I believe.

 

I finally got around to testing my 7's exhaust backpressure and thought I'd share the results:

1995 PEP w/86K one-owner miles.
RX7 Store's SS DP.
OEM Cat.

Backpressure measured @ DP's O2 bung w/O2 disconnected completely during testing. Used old OEM O2 sensor that I cut-down and knocked out the center. This was attached to a length of silicon hose w/out any clamp and I 'adapted' the other end to so that I could connect to the hose from my Defi mechanical vac/boost gauge; so I couldn't measure boost while testing backpressure. I'm @ ~1,300 ft above sea level.

W/OEM cat-back - 1/2 psig @ cruse, climbing up to 11-1/2 to 12psig @ WOT and 5-6K RPM and above.
W/M2 Single Tip SS - <1/2 psig @ cruse, up to 8 psig @ WOT and 5-6K RPM; held steady at this 8 psig all the way to redline.

Damn, looks like a clogged CAT, too...can you say high flow cat?

PS - when I got the old cat-back off I found that it was starting to leak along the muffler's top seam. Had multiple long black streaks where it had leaked. You can't see this seam while the muffler is installed. Guess 8 years and 86K miles is a little too long for the OEM cat-back. It never sounded good anyway!