CrackHeadMel

iTrader: (2)

Ive been reading about intake and exhaust tunning latley and have a question that none of the books covered

Do you calulate intake runner lengh differently for a turbocharged car as opposed to a normaly asperaited car?

rotarygod

iTrader: (1)

No. The same rules still apply regardless of what pressure is in the manifold. The turbo does not push air through the manifold. It still behaves the same in terms of flow. It's only a pressure change and you'll see this in smal amounts based on weather conditions. Some people say to use a shorter intake manifold with a turbo as the turbo does do all the work. However, if you look at dyno charts of short intakes on turbo cars vs longer ones you can see that the powerband will still shift upwards with shorter runners. Undrivable dyno queen Supras are good example of this. There are many different ways to do it. That's the nice thing about boost.

CrackHeadMel

iTrader: (2)

Ok, i wasnt sure if the pressure wave would be affected by the compressor side of a turbocharger

How does one calulate pipe diameter for an intercooler? Is there a forumla i havent seen? or should i just come up with an avarage area for each layer in the core multiplied by the # of layers

ronbros3

It seems tho, the size of the plenum has a lot to do with useable power and torque.

silvr94r2

iTrader: (3)

This is very true. It also has to do with the transition into the runners from the plenum. Actually everything about the intake mani design effects flow. We rotated the throttlebody and picked up and lost cfm depending on which way it was rotated. We also picked up and lost with throttlebody angle. It's a very tricky thing to get right but using a flow bench can help quite a bit.

rotarygod

iTrader: (1)

The size of the plenum is important. Like the runner length it's size also effects the powerband. Typically a larger plenum will help make more power but throttle response will get slower. A smaller plenum will help make throttle response better but total power will decrease. It's really a weird thing. Both of these statements are only true to a point of course. Throttlebody location as was mentioned above can make a big difference. The key to it though is to allow air to flow evenly to each intake runner. You don't want a plenum with the throttlebody on the front. This causes uneven air distribution and it can be up to 20% different between front and rear runners. That's potentially dangerous if you are running under boost as your a/f ratio readings out the exhaust could be averages while one rotor is rich and the other is lean. See a problem with that and tuning near the edge? Boom! And you may think your a/f was good the whole time.

The first thing I'd do if I were you is to read alot on the subject. The more you read, the more you realize there is even more to read and learn still. It's actually a very involved subject and everything has a good side and a bad side. It is all about making the right combination of compromises for your application. You can probably guess pretty good on a decent design if you use common sense. It is through actual testing and sometimes experimentation of known theories that will allow you to take it to the last few percent. You can get most of the way guessing. It's always those last few percent that take the most effort and knowledge. Here's one thing to think about a little bit. Heat affects tuning length as it affects the speed of sound. How much does your intake temperature change with a turbo? Now ask yourself if you actually tune it to work best with boost pressures and temperatures or without. It gets pretty intricate.

karism

Thanks for explaining it so nicely Rotarygod.Very informative indeed!
karis