GTT Exhaust Back Pressure - Measuring& Results

[roland2003]

Hi Guys, we have now made a suitable probe with thermal decoupling to enable us to check positive pressure within the exhaust system. all tests results will be at WOT using -17% SC pulley at 6500rpm. There are 2 places we can connect the guage these are
(1) Before the cat which will measure the overall back pressure of the cat (not the manifold primaries though) PLUS the 'cat back system'
(2) After the cat, measuring just the back pressure building up in the 'cat back system'.
-Initial tests will be connected at ' 2'

We want to test;-
1) Complete stock system
2) Stock system with GTT 'Re-Route Pipe' (deletes one of the two silencers)
3) JCW System
4) As many aftermarket systems as possible.

The tests are NOT comparing build quality,fit,sound,appearance but only back pressure.
High back pressure here will almost certainly be losing power,causing excess heat at the exhaust valves & compromising fuel economy. It is quite difficult to design a non restrictive system for the Mini that isnt too noisy. Small diameter pipes,tight bends, more silencers coupled with restrictive silencer materials, all shut out noise ,but build up back pressure under full bore as a consequence. Also any deliberate or accidental mega restriction 'out of view' will show up big time. By this I mean things like weld that almost fills the bore ,mega mis-alighnment between two tubes within the silencer, or excess flattening of the pipe ends within the silencer. All these are a good way to 'shut the damn thing up a bit ' without redesigning from scratch. -It can happen..
Best Regards Roland GT Tuning

Cat -Back 'System' Results So Far, (check back regularly as will add every result as we get it).Remember the LOWER the reading the better!

SCORPION .........+3.5psi
STOCK................+2.5psi (' 03 car)
GT TUNING 'RE-ROUTE PIPE' (combined with 'stock' system) ..........+1.75psi ('03 car)
JCW ...................+3.75psi
Miltek..................+1.25psi

[obehave]

If possible Roland you may want to test the much discussed straight through design.

Sounds like good stuff

[roland2003]

obe . Do you mean going straight down the middle of the car,with one 'resonator' type silencer?

Dan. Cheers, yes we do servicing.
Regards Roland Gt Tuning

[wibbly]

And the winner is.....

[roland2003]

This testing (unlike the quick change over air filter test) will take time. We will need to use more than one car ,as Im not changing the whole exhaust system over 6 times or more . I will try and do a couple of tests in the next couple of days. As we get results I'll post them up.
Regards Roland

[Perm]

Roland,

I know you have a vested interest in all of this but I think it is great that you are willing to do such "impartial" open testing of your products vs the competion in such a scientific way.


Great work.

Cheers

Perm

[roland2003]

Cheers perm, TBH I 'could' fudge the results if I realy wanted to,but long term you're only cheating yourself. I'm happy to repeat 'easy to do' tests with a panel of scruteneers if needed. With this test we dont make (or even sell at the moment) a cat back system for the MCS, if we do find one that gives good results we may stock it, likewise if they are all poor we may design our own,but there are no immediate plans at present.The 'Re- Route' pipe we do is not 'competing ' with other systems directly here anyway as is a quarter of the price,If it out performs the systems ,great ,if its better than stock thats still a good product with a market place. We have not done this type of testing on exhausts before so the results will be news to me as much as anyone else.
Regards Roland GT Tuning

[obehave]

Quote: Originally Posted by roland2003

obe . Do you mean going straight down the middle of the car,with one 'resonator' type silencer?

Dan. Cheers, yes we do servicing.
Regards Roland Gt Tuning

Yes. There's much debate as to it's effectiveness.
Not an easy task for you I'm sure but it would be nice info for the Extreme exhaust pursuers

[BlackFerret]

i just realised you managed all this testing between customers, fittings, postings and eating and sleeping????

how exactly?!?!?!

[ThreeAlarmChiliRed]

Quote: Originally Posted by roland2003

This testing (unlike the quick change over air filter test) will take time. We will need to use more than one car ,as Im not changing the whole exhaust system over 6 times or more . I will try and do a couple of tests in the next couple of days. As we get results I'll post them up.
Regards Roland

WARNING: Unsolicited test engineer advice ahead!

Using more than one car may introduce some unknown variables -- engine condition, oil brand and viscosity (hey, oil companies and brand fanatics claim it makes a difference), car weight and tire size (affect the engine loading) -- as might weather conditions. I haven't done any thermodynamics in years, and I've never tested exhaust systems, so I can't give you specifics right now, but I believe that one possible way to mitigate these differences would be to measure the total energy of the exhaust flow and normalize the pre-cat energy conditions. That is, adjust the cat-back conditions to a single pre-cat condition giving you apples and apples. You can measure the fluid energy by measuring temperature and flow rate at the two positions along with the pressure. Basically you would be doing the same thing as determining which cat-back system has the least back-pressure, except you would be determining the "back-energy."

Sorry, it's a disease.

[ThreeAlarmChiliRed]

By the way, great idea!

[roland2003]

There will always be very very small differences made by some of the variables you mention. The important thing is we use WOT at same revs /gear/ same pulley size and put the probe in the same place. At the end of the tests we can do another test which involves putting the actual system tested onto another car on a different day with different brand oil & tyres of a different make & aspect ratio to compare the pressure reading. I believe reading will be identical (or as near as makes no odds).
Regards Roland GT Tuning

[Root Ginger]

As always, Roland has come up with another way of getting some solid measurements that don't use a dyno. Why are none of the other manufacturers doing things like this?

Roland you are the man I look forward to the results especially a Milltek as this is what I'm considering swapping my Quicksilver exhaust for.

[ThreeAlarmChiliRed]

Swapping the system to different cars would help.

How do you do WOT at same revs and gear? WOT will eventually take you to redline in the lower gears. Are you looking at transient back-pressure or steady-state?

[roland2003]

RESULTS !!

Ok weve just been out ,and did the FIRST test,as I say all tests at this stage are using probe after the cat so measures pressure build up in the 'cat back system' only. When we move the probe forward to before the cat I expect the results to be even worse

1) Scorpion 'cat back system' .................... +3.5 psi


That to me seems pretty awful, and more than I expected. However we havn't got any others tested yet to compare. It might be a good result (compared to those yet to be tested). Ultimatly I wouldnt be happy +3.5 psi and would endeavor to find (or produce) something that would better it by some margin.
BTW Tests were repeated in second third & forth gear, no difference in reading . As the revs rise you can see the boost guage needle slowly increasing in reading (as expected). The +3.5psi occurs at 6500rpm,at which point we then change gear.
Regards Roland GT Tuning