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The December issue of Hotrod, page 154 has a very favorable report on TPIS's 75x90mm throttle body mounted on an LS6 intake with a huge #15 cam. On a Superflow engine dyno the combo made a 32 hp gain, and there is gain all across the spectrum.
It appears that the LS6 intake manifold has a far better design than the new LS2.
I've known Myron Cottrell, owner of TPIS for over 45 years now. Naturally, I favor his products. Myron has an '04 CTS-V and installed this oval tb on it. It gained 18 rwhp to 382 rwhp - TPIS headers and cats, stock exhaust and stock intake.
I visited TPIS this last September, and tried the oval tb on my '05. It is a magnifcent improvement. No flat spots anywhere and increased power everywhere, BUT, there was an anoying intake chrip/whistle at low to moderate throttle transition. We spent a full day locating the noise. It is at throttle shaft edge of the intake. We could not eliminate the noise. It was barely tolerable on Myron's '04, and intolerable on my '05. We don't know why the difference between these two Cadillacs, but the end result is that Myron won't sell them for CTS-Vs with stock cams. Stock cams have high idle vacuum, which increases intake velocity at low rpms. More velocity = more noise. He has had no complaints from buyers who have larger cams.
I did leave
Chaska, MN with a ported stock tb. This increased power also, but more in the area of 8-9 rwhp.
The good news is that TPIS is now working on a method to adapt the 90mm circular tb to our LS6 intakes. Stay tuned.
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