bigsapper

Now that I'm laid up, I get to thinking about stuff, such as the throttle body placement.

I'm assuming, since the introduction of the LS1 in the C5 Corvette, that the front position was done more for accommodating a low profile for hood clearance.

It seems to me, the optimal placement for performance would be centered over the top of the engine.

Does it just not matter or is the front location the optimal position, maybe for other reasons?

bigsapper

Nothing? No opinions? Shocking!

bigsapper

Wow; no response at all? Guess I'll go ask on yellowbullet.

rrsperry

Ok, here goes.

The throttle body, (single throttle plate) controls how much air goes into the engine. The MAF measures the amount of air. If you have it on top of the engine, the hood has to be higher to allow for the plenum.

It's the only place that it fits, and not have it contribute to throttle response problems.

(that's my guess...)

davepl

OP, you're thinking of a naturally aspirated motor, and if you recall where carbs used to sit, that's where they sat.

But for us there are two more important variables:
- Where is the blower inlet
- Where is the blower discharge

Ideally you'd want the blower discharger centralized, like you envisioned the throttle body, and then the throttle body a the blower inlet.

A roots blower discharges at the front (pumps air back to front) and that's why you see Top Fuel dragsters with "set back" blowers, so that the rear discharge is centralized:




So in the picture above, you can see the whole blower has been set back so that the discharge is centralized. In this case if you were allowed only a single TB you'd likely have it at the back top of the blower case.

bigsapper

You're correct, I am thinking NA. I am NA.

What got me thinking about this is aftermarket intakes. When you have something like the Holley hi-rise or custom sheet metal intakes, why leave the TB at the front. It seems it would be better positioned at the top.

0G1Pro

TB Placement since I've been called into this discussion lol


Ok tb placement is a game to play. Building intake manifolds in general is a huge game of tug of war. There is no such thing as a perfect intake manifold. A intake manifold to a 4 cycle engine is what a expansion chamber is to a 2 cycle engine... It is only good for what it is specially designed to do and only makes power in that zone that it is designed to make the power.

This doesn't mean that you cant make power with a intake that isn't right for the car, it just means that instead of running at 100% efficiency you might be 90% or even 70%. AT the same time though it is not always possible to get to 100% and when factoring in other variables such as boost, no2, cost, etc sometimes you have to sacrifice in areas to make up in others.

With all of that said, from a general standpoint;
For equal air distribution a carb style tb placed equal runner length manifold will have the best air distribution in a naturally aspirated setup for a single throttlebody
HOWEVER this doesn't make it the right intake for the job.... Equal air distribution only means equal afs across the board and with proper engine cooling should result in equal cylinder temps. Clyd temps and afs are not what make power for the engine though...

How to make power for an engine with intake manifold tuning.

Go stand out on a mountain and yell hello
you hear the echo
echo 1 is loudest and strongest
echo 2 is weaker
3 is almost non existent...

This is the soundwave reverberation effect. This happens inside of an intake manifold. The reverb is between the back of the valve that is closed and the plenum.

In intake manifold tuning we use this sound wave to force the air in the combustion chamber at a given point. This point is determined by the needs of the setup and many other variables calculate out to determine when to time it.

The biggest things to calculate are cross sectional area because sound and air travels at different velocities through different sized areas. Next is length. Then intake cam duration and desired peak trq rpm for which we are aiming to time the air into the combustion chamber.

What this has to do with tb entrance is basically the runner length determine your powerband of the engine and the size of the plenum will help determine how long you can hold your peak trq. Holding the peak trq can come at a cost of lessened velocity inside the plenum which will transfer over to lower rpm power (wahh I lost 10trq down low....)

Now when we try and get numbers right so we can have a nice powerband for the given application and hold peak trq as long as we can so that powerband will not just drop off is where we get the different shapes of the manifold. Yes you want consistent air to each clyd as much as possible but understand there is no 100% perfect here...
I like to utilize a tumble effect for air entering a plenum. If you notice I aim my tb upwards every so slightly and several inches infront of the first runner. By doing this I'm able to have a large sized plenum, a long runner, fit it all under the hood and keep air flows withing a very tight % of each other. I aim the tb at the roof of the plenum between the front runners. When we do this the air goes in from the tb and hits the plenum roof, when this happens like water hitting the wall it fans out and fairly equally distributes to the rest of all the runners. If we were to aim the air straight down the plenum it would hit the back wall and then fill from the rear forward. I try to fill all runners at the same time.