Kana

Ok so i have an LS that im building for boost. I have an Edelbrock Victor X intake manifold and i was lookin into a big throttle body.

Now the question is, is there a such thing as over kill for a throttle body? Im looking at a 70mm or a 74mm. I know a big one will help but i dont know if a huge one will kill power. Let me know what u think.


Sean

D.Nick

I was always under the assumption that a bigger throttle body means nothing if you can't push all of the air that you bring into the intake out. So you need a decent sized exhaust to push it out. Bigger isn't always better. I think you should be fine with the 70mm. 74mm is overkill IMO.

BAD4DR

If you are building a N/A motor, then it would be far more critical not to go too big. You need enough air to make the power, but too much size, and you kill velocity on a N/A motor.

For a pressurized Turbo application, basically, there's almost no such thing as overkill. Larger will improve throttle response and horsepower. This is due to the pressurized nature of the intake tract, and the fact that it has more to do with how much air you can flow, as the turbo will generate both the intake and exhaust velocities.

DoC-JoneS

what is the port size on the edelbrock manifold? if it's a 70mm opening 74mm won't help too much. use that as your guide as you won't be able to push much more than the port size will allow.

Kana

Not sure on the size of the port.

Fabrik8

You can go too large, but (velocity excepted) the only thing that usually happens is a loss of resolution. You are controlling the flow into the engine with the throttle plate, and ideally the throttle size should roughly match the amount of airflow that the engine can take in at max load and RPM. If you go larger than that, you'll reach that max flow point before the throttle is open all the way, so you won't be using the whole range of throttle travel.
For example, if you go 50% oversize, you'll reach max flow a lot sooner so the proper size, so you won't have to open the throttle plate nearly as much to make the engine happy. Now you're just wasting every degree of throttle plate travel and wasting the associated gas pedal range too. So now full throttle might be 3" of pedal travel instead of 4" of pedal travel, so you have less resolution for the same engine control range.

Back on the topic of velocity, you shouldn't go any bigger than you need to. If you go too small, you'll choke off flow because a given volume of air is moving too fast, and if you go too large that same volume of air will be moving too slow. This is a problem in boosted and naturally aspirated engines, velocity matters regardless of what pressure the air is compressed to. It just matters less with boosted engines because the air will get forced in no matter what. But you will have better efficiency and therefore will make more power with a boosted engine if the throttle body is sized correctly. And, you'll have better performance off-boost as well.

DoC-JoneS

this folks is the main point of any TB/IM/Head porting, boring, oversizing message. honda engines LOVE high velocity air ports. go too big and they'll get lazy and counterproductive. boost lessens this tendency but doesn't negate it.

Jarrod

Damn that Fabrik8 guy.

Kana

So 70mm or 74mm. My goal is atleast 400whp, if that helps.

DoC-JoneS

if you've got the right turbo the 70mm should be fine. just remember about that manifold.