This is a text i managed to get from a very old post of the previous D-series.org forum.I saved it right away into a text file like i do with everything i find
.What i learned true the years is that in most cases you can get better results with a B16a1 (58mm) or B16a2 (60mm) throttle body onto your D16z6 or D16y8 intake manifold.Liveforphysics wrote:
When WOT, we must look at the TB as the entry to the plenum. The plenum volume must be sized correctly to work with the engine/cam/IM combo for an engine to function as a system to raise VE.The entry to the plenum needs to act like a 1-way valve to capture pulses from being lost out the intake tube. Too large of a TB, and you cause increased intake tube reversion and lower IM pressure due to lost pressure waves.
Things to remember, the smaller the plenum, the larger the TB that engine could have and still function, the larger the plenum, the smaller that TB needs to be to still function.
So, how big should your plenum be? Depends nearly all on cam profile.Can you loose power from larger TBs? Absolutely. Power and response can easily be lost. The ability to dynamically change RPM during acceleration can be hurt quite badly by both too large of TB and/or too large of intake pipeing diameter.Very very few d-series are/would benifit from a larger TB. I don't belive ANY d-series can make use of an H-series TB, and this would always be looseing power on that engine at all RPM points, UNLESS this engine had some excessively tiny plenum with very very excessive cam duration. At that point, the TB would be a band-aid for the incorrectly sized plenum, effectively shifting the plenum volume into the intake piping, but simotaniously reducing its ability to capture return pulse energy.Does your D-series need a larger TB? No. Do SOME d-series need a larger TB? Yes... but very rareDoes any D-series need an H-series TB? For NA applications, this will only be slowing you down.
BTW- NEVER NEVER port match a TB to the IM. Never ever ever! The IM needs to have a hole at least 4mm larger than the hole in the TB, and with a harsh step.
If you have sensitive MAP monitering equipment, you can actually see the drop in average plenum pressure at WOT after port matching or worse, putting a radius on the connection point.
With a properly sized TB for the plenum, and a harsh step in the right place, you can see as much a +0.25psi(gauge) of boost from the effective capture of return pulses. Go with a monster and or portmatched/radius setup and watch your plenum pressure always stay below 0psi(gauge).
Best Wishes,
-Luke
I hope somebody collects the post I make here... I'm not going to post the same info twice.
Keep in mind you need to have that anti reversion step of at least 4mm.So in case of a 60mm tb you'll need to enlarge the stock intake manifold opening to 64mm.
With most aftermarket manifolds like Skunk2 ,Edelbrock or Blox you'll be better of with a Stock Tb ,especially on a D14.Or maybe a B16a1 (58mm) Tb if you're going to seriously build your engine.
a lot of guys believe in the bigger tb's .I haven't got to actually dyno testing this,but i know what kind of guy Liveforphisics is and i know he doesn't BS about anything and is very very experienced.