Lets talk tuning (KiDo Tunes)

[alexeiwoody]

Very good description

It's been 10 years since I studied that sh!t and though't I'd forgotten everything.
I'm amazed it's all in there somewhere

I'm impressed as well. Thanks for that

Is anyone able to confirm the 1 psi back pressure or..?

[Robbks]

you'll need one of these
exhaust pressure gauge to measure it accurately

[alexeiwoody]

you'll need one of these
exhaust pressure gauge to measure it accurately

Kewl, thanks. Looks the cats will have to go, to get that extra bit of accuracy

[Robbks]

you'll need one of these
exhaust pressure gauge to measure it accurately

Kewl, thanks. Looks the cats will have to go, to get that extra bit of accuracy

No need to ditch them,
just replace with 100CPI high-flow versions

[KiDo_Tuning]

Very good description

It's been 10 years since I studied that sh!t and though't I'd forgotten everything.
I'm amazed it's all in there somewhere

I'm impressed as well. Thanks for that

Is anyone able to confirm the 1 psi back pressure or..?

Do not confuse post turbine dump pipe to exhaust tip back pressure with the back pressure generated between the exhaust ports and the exhaust turbine. Think about how much exhaust manifold pressure is in there to push the WG flap open

In my tunes, I open drop the WG duty cycle after peak power is made to open the valve and improve VE

[alexeiwoody]

you'll need one of these
exhaust pressure gauge to measure it accurately

Kewl, thanks. Looks the cats will have to go, to get that extra bit of accuracy

No need to ditch them,
just replace with 100CPI high-flow versions

I was joking, but theoretically ditching them would be a fair bit cheaper and you get an extra 1kw over the 100cel...

[Robbks]

the stock H6 cat's are very restrictive items. and no doubt the turbones aren't that good either.

IN both cars they are also in a position where the exhaust gasses are still extremely hot and NEED to be able to flow with as little restriction as possible.
So you would see reasonable flow gains from ditching the stock cat (400CPI i believe) for some 100 or 200 CPI units.
Much more gain than swapping out rear mufflers or centre pipes, especially in boosted applications

[jay.ritchie]

the stock H6 cat's are very restrictive items. and no doubt the turbones aren't that good either.

IN both cars they are also in a position where the exhaust gasses are still extremely hot and NEED to be able to flow with as little restriction as possible.
So you would see reasonable flow gains from ditching the stock cat (400CPI i believe) for some 100 or 200 CPI units.
Much more gain than swapping out rear mufflers or centre pipes, especially in boosted applications

It seems there is a lot of debate about the quality of the stock cats on the forum, some reputable members say they're of a high quality and swapping to high flow cats is a waste, and some say they're really restrictive.
How is an exhaust amateur like myself meant to decide!

[Robbks]

While I'd agree they are high quality compared with cheap sh!t like Xforce and other no-name, non-compliant cats.
If you spend good money on good quality cats that actually meet EPA standards (Metalcat or Redback) then you'll have both flow and longevity

[alexeiwoody]

the stock H6 cat's are very restrictive items. and no doubt the turbones aren't that good either.

IN both cars they are also in a position where the exhaust gasses are still extremely hot and NEED to be able to flow with as little restriction as possible.
So you would see reasonable flow gains from ditching the stock cat (400CPI i believe) for some 100 or 200 CPI units.
Much more gain than swapping out rear mufflers or centre pipes, especially in boosted applications

It seems there is a lot of debate about the quality of the stock cats on the forum, some reputable members say they're of a high quality and swapping to high flow cats is a waste, and some say they're really restrictive.
How is an exhaust amateur like myself meant to decide!

They may be of high quality, however being stock cats they will be fairly restrictive. If they're around 400cel and you switch to 100cel, you're effectively flowing a free flowing exhaust.

With the 400cel, they hold back the exhaust quite a bit, as it's a 'tighter' squeeze for the gas to get through than the 100cel.

High quality cats do cost some coin.

Position of the cat, as Rob mentioned before will affect restriction as well, so if it's a free flowing exhaust you're after, you may want to move the first cat as far down the dump as possible.

Getting a free flowing exhaust can damage response. Not cats themselves per say, but if you go say full 3" tbe with aftermarket muffs. Some find the std muffs will net you better throttle response. Depends if you do city driving or not, this may be something worth noting

[alexeiwoody]

Oops double post

[bigBADbenny]

The summation in Cobbs zorst guide https://cobbtuning.zendesk.com/hc/en-us ... ust-Design was that on a big zorst the muffs were the best place for a restriction if any... but that in general the "stealthback = better response" etc... is a myth, specifically in regards to turbo cars...
It's great for mitigation of noise though!

And I'd love to test the theory at the next dyno day, since I kept my modded WRX STi sedan quads and now have TCP quads as well

[Robbks]

the problem is, back to back comparisons are difficult to do,
if you change the flow characteristics of the intake or exhaust, you change the power-band of the engine. (pipe length tuning, back-presures, gas velocity, etc, etc) and it all effects relative VE of the engine.
so swapping parts without retuning achieves nothing, and re-tuning is optimising a lot of different parameters to suit the current setup. you'll have gains somewhere but losses somewhere else.
Peak power vs Width of power-band (area under the curve) are all changed.
Depends what the car is being used for too.
I've seen guys drop bigger turbo's on for more power for faster 1/4 mile times. The cars actually got slower as they lost that wide power-band and dropped acceleration after gear-changes
but stick an auto box in it with high stall converter, then the engine never gets under 5000rpm and just sits at the higher peak power area.

i've gone off on a tangent to illustrate the point.

[bigBADbenny]

Yes... and no.
My current tune works well enough with big or little muffs, so why not measure the difference just for fun.

Eg reset ecu, drive 20K mixed, dyno it, then swap muffs, reset ecu, drive 20K mixed, dyno it.

Just to see if the seat-of-pants actually works, or if the difference is down to subjective input, mainly more noise sounds/feels faster.

[alexeiwoody]

Yes... and no.
My current tune works well enough with big or little muffs, so why not measure the difference just for fun.

Eg reset ecu, drive 20K mixed, dyno it, then swap muffs, reset ecu, drive 20K mixed, dyno it.

Just to see if the seat-of-pants actually works, or if the difference is down to subjective input, mainly more noise sounds/feels faster.

Some of us have the varex muffs installed. Not sure what Justin found, but I've noticed the car tends to feel more responsive with them closed. Of course this could be attributed to the noise being absent while your car is accelerating as normal - ie. feels like you haven't even revved up yet - as the engine is still quiet, but car is already pulling along.

I'm a supporter of the theory that muffs don't make a "noticeable" difference, but I've been told MSR says smaller muffs give him better response. That guy is usually right But with the massive noise change, good luck noticing a tiny response improvement!