just searching through about TB's.. Since you made it a point to specify NA when referring to 70mm being too big for our 1.8L cars, does that same rule apply to boosted applications? Say, a mildly boosted b18b with about 250whp? This is under the assumption that you're running a skunk2 IM?MichaelDelaney on Sep/20/02 said:If you went 70 mm on both intake and plate side, that will be too big for most all motor 1.8L NA engine packages out there.
2L is a different story. you can get away with 66-68 mm.krayzielilsmoki on Aug/31/06 said:So the people that are using the 68-70mm throttle bodies with matching size intake manifold opening on the 2.0L n/a hondas, they are all wrong or is it ok for that size motor. I have seen alot of 2.0L engines making close to 250whp using these big throttle bodies
Excellent piece of information. Thanks for the thorough reply. As for "posting" in the performance forum, I just ran a search about TB's and found that thread. It was useful, but I still had a question about FI setups. I think starting a new thread asking that question would have yielded "please search" as responses.MichaelDelaney on Aug/31/06 said:the idea here is that the bore can slow flow speed down. if you go too big on an NA motor...which fills the cylinder passively unlike boost,
you have to read the articles here to understand the idea of "flow volume" vs. "flow speed" (click) .
once you understand that, you then sort out WHY we say 70mm will kill part throttle driveability on an all motor car because although it delivers more flow volume, the flow speed to fill the plenum is torched and the acceleration is much less. With boost you aren't limited by flow speed because essentially you are pushing in at a high flow speed from the start. What you are more concerned with in FI is cavitation at the plenum-TB opening as shown. That's when going too big can begin to hurt your flow into the IM runners.
But you don't have to worry about that.
The performance forum here on TI is an all motor forum. We have a separate FI forum. Why the nitrous guys and turbo guys post here is beyond me. I always have to move the threads over to FI forum.
As I said before over and over: the TB isn't your choke point. It's easier to change than an IM, or doing cams/headporting which are the real choke points and so people do the easy way out and focus on it for the wrong reasons - affordability and expedience.