Why is 3 inch better?
The exhaust is a greater challenge than the intake because a lot more is happening than simply allowing air to get in easy.
With the exhaust you have heat and turbulence.
What drives the turbine is pressure and heat differential ......
In basic terms more heat and pressure before the turbine and less heat and less pressure after the turbine are what drive the turbine. The greater the difference the more efficient the turbo becomes.
One of the reasons the .86 A/R housings were not showing top end gains was because the downpipes were too small and pressure differential was getting worse because the exhaust was not growing after the turbine.
Internal wastegates cause a lot of turbulence when the wastegate opens and blows air across the turbine wheel opening. Separating the wastegate is HUGE because of the reduction in turbulence.
With exhaust you want gentle changes or you create turbulence.
The new 3 inch expansion downpipes are very detailed to try and make the turbo as efficient as possible.
The air coming out of the turbo is very turbulent and HOT, it is still expanding as the exhaust leaves the turbo. The new downpipes design is establishing direction of flow and expanding gradually allowing the exhaust to seek out a cooler lower pressure area.
The old style split downpipes have a collector for the exhaust coming off the turbo wheel and the wastegate to merge.....This merge is causing some turbulence and causing the rasp that is herd when you do not use resonators with that style downpipe.
The new downpipes have the wastegate coming back in at full 3 inch and point the wastegate gas straight down the test pipe so it does not cause turbulence and these downpipes have no rasp at all.
We have also increased the size of the pipe where the 02 sensor goes to 2.25"
On the older parts the 02 sensor was sitting in a 2 inch pipe on the 5 bolts and a 1 3/4" pipe on the 4 bolts.
I have been and I am still working on making these pipes more cost effective to build, but I am still struggling with that part of the project and is the main reason I had not put them on our web site.
We have been selling these pipes quietly since the beginning of the year with a fairly large back log of orders the whole time. We are still not caught up with the orders, but we are getting a better handle on it.
Here are some of the dyno charts and also some feedback from a TT.net member that installed them in another part of the country.I will Start with TT.net member WXY (Mike Homer's Stock turbo car)
Mike's car was our highest dyno stock turbo car already with the old parts and I figured if we could squeak more power from his already high powered set up with the little stock turbos and manifolds it would really show if the new design has anything to offer.
One more quick note........
Stock turbos with stock precats can only make about 17 PSI no matter what you do because of the turbulence and restriction.
Stock turbos with split down pipes can make about 20 to 21 PSI.
Here is Mikes Stock turbo Dyno with 3" expansion downpipes and it is making 24 PSI.
*Note that it was only on 104 octane and at this power level you can see it needed more octane and was detonating at this power level. With C-16 this would be a much smoother power band.
For fun here is the Mike's dyno showing single pop to dual pop and then adding 3 inch.
 Here is email I received from TT.NET Member Maglito after installing the 3 inch parts on his car.
He has Sport 700 turbos with the .64 housing and he went from HKS open downpipes with china downpipes and I think it was Stillen cat back to our full 3 inch.
From Anthony........ " before 460-465rwhp@15psi"
" After 532-537rwhp@18.5 " "only change is exhaust (using waste gate springs only no boost controller
even connected)."
.
"So the back pressure freed up 3.5 psi on the wastegates...they were set to
open @17psi...." Maglito has these dyno charts. Next is Sebs dyno before and after with all of our old best 2.5" exhaust to the new 3 inch exhaust with the only change being exhaust on the same day on the same dyno.
What we did on this dyno test was run the car at 21 PSI on both tests to show the gain at the same boost level. In order to do this we had to turn down the gain on the boost controller quite a bit ;-)
 We are making full 3 inch systems for the guys wanting all they can get out of the package.
We found most of the gains come from the downpipe test pipe area where it is hottest and needs the most room.....
As the exhaust goes back and cools it seems not to need as much room as it condenses.
We make both full 3 inch test pipes and also 3 inch test pipes that cone back down to 2.5" so that one can see most of the gains and keep there old 2.5" cat backs.
We did a test on my car going from full 3 inch to coning back to a 2.5" catback system and I kept all the early gains of going 3 inch and only lost 13 RWHP after 6000 RPM with coning back down to 2.5".
The cars do feel faster with 3 inch catbacks, but the dyno shows some of it must be the sensation of the sound!
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3 inch parts.............. - 
21:01:18 07/26/07
