I've already addressed the "R" topic.
The "air duct" should have 25% more area than the throttle body, and rather abruptly make the transition into the thrittle body with an "ideal" inlet radius which will net zero loss. The formula for designing the radius is R/D=.5, where R is the theoretical radius you're seeking, and D is the diameter of the throttle body. Using this formula's radius combined with the 25% increase in area in front of the throttle body allows the lower velocity air flow in the inlet "tube" to exert considerable pressure on the throttle body which is highly desirable from a power standpoint.
All these "little" things add up, and once again, as T.O.O. would say: It's not any one thing that makes a winning engine, it's the best series of compromises one can assemble, and all the "details" add up and generally make the difference between the winner and the loser. Why do you think T.O.O.'s including the air cleaner, duct, throttle body, injector rail, injectors, and even the header in these kits? It's so people won't say "I'll wait to do this or that", and then get upset because the car doesn't run the way it's supposed to.
Posted by T.O.O. on May 14, 1998 at 21:40:31:
In Reply to: Hey T.O.O. posted by body on May 14, 1998 at 21:08:04:
If your planning on going with the blower kit, do not buy an ECU or
any other electronic devices...they come with the kit. The Kamikaze header
is also part of the kit, and it's almost 20 hp above any of the competition.
As for NOS....Never touch the stuff.
For your inlet tube use a constant 3" ID tube, and build a radiused connection for the throttle body as I described the other evening. Use the formula R/D=.5 , where D is the diameter of the max.ID of the throttle body, should give you a theoretical entry radius of about 1.3". So if you make a drawing of the side view of the throttle body, the ID is 2.90", now set a compass to 1.3" and place the point 1.3" away from the TB and swing an arc. Repeat for the other side, and you'll see the correct shape or radius to build.
Posted by alloy_625 on May 15, 1998 at 16:37:19:
You've mentioned the design rules for the inlet horn to the throttle body, but what sort of guidelines should one follow in intercooled turbo applications. Should post-compressor pipes be small diameter to keep velocity up and feed the throttle body directly, or should the pipe be sized up as it would be for a "large" NA application with a reducing horn at the throttle body? Also, what do you think of horns in intake plenums, and how does one determine the spacing from the lip to the wall?
Posted by T.O.O. on May 15, 1998 at 19:44:10:
In Reply to: T.O.O. - Inlet Horns posted by body on May 15, 1998 at 16:37:19:
On our turbo engines, we do keep the velocities relatively high prior
to reashing the throttle body. The type throttle body is a factor here,
as is driving application. If the engine is going to be run continuously
at full throttle, and you have either a butterfly, or slide throttle, the
velocity can remain high, and then after passing through the throttle body
you want to slow it by expansion in the plenum. If part throttle performance
is a concern, such as a road course as opposed to an oval or drag application,
we expand the area about 30% when package space allows. This slows the
flow and lessens vectoring by the butterfly or slide, and the amount of
turbulence is greatly reduced in the plenum chamber.
Regardless of application ( n/a, Turbo, Blower, etc.) the plenum needs to supply each intake runner with the same amount of air (distribution), and the air, even under pressure should represent a smooth "atmosphere" for feeding the ports.
We stopped using air horns in plenums back in the early '80's, and the same "ideal radius formula" is what works best. It will automatically dictate the space from the entry to the inside plenum wall. They'll look like half donuts around each runner entry.
One other note on manifold design, and this is universal. If you assume that the manifold runner is an extention of the intake port, you will idealy want the distance from runner entry to valve seat to be equal on all "sides". So if you measure the length of the "roof" of the port/runner, it shouls equal the measurement taken on the "floor" and "short turn radius". The rational here is one of surface friction and corresponding boundary layer thickness and speed. If the distances are "different", the air fuel mixture will shear in the port, and the increased random turbulence will not only cause flow rates and mixture homogenity to suffer, but the pumping losses go way up, further decreasing productive output.
Intake manifolds and their relationship to the port is, and probably always will be a sort of "dark art form", and perfect examples of the importance is the fact that all competitive ProStock cars run a sheet metal "shroud" around the plenum / runner area so it can't be observed even from the exterior. I will leave you with this: All the cars now running our head / manifold / piston / cam packages have the exterior visable because we simply do it all internally and use a "generic" exterior, and this is not simply for drag racing, but all the various arenas we work in.