When Making an FFIM, what do you do about volume???

[85celicasupra]

I know some people here have made their own FFIM, or the couple of people who design/make/ and sell them,

my question for you is when you were doing it, how did you go about determining the volume of the plenum?
did you just try to get as close as you could to stock, is bigger better? what about smaller???

cause I am almost done making my custom one for my custom 5mgte in my mk2 and was wondering this to help me make my decision on mounting the TB...


Any help is appreciated...

 

[carfreek]

Hi Scott. For a boosted app, volume isnt as important. Smaller is probably better, lessvolume=less lag. Remember, you will be driving around off boost most of the time, so if you size same as stock, you should retain some of the cylinder filling characteristics of stock engine.

 

[85celicasupra]

cool...thats what I figured.
I wanted to get off boost driveability close to stock with it.

 

[sethron71]

All depends on your horsepower goals! All of my long runner manifolds are just a bit bigger then the stock volume. But my tapered ones are much larger and for higher horsepower apps where good flow and large volume are a must for big boost at high RPMs.

Hope this helps
Seth

 

[85celicasupra]

that helps alot...

Im not making this for a monster horsepower beast...
just looking to clean up the engine bay, less boost lag, and keeping the custom/one off parts adding to my build.

My intake runners are the same length as stock (cut them off stock mani) and the plenum is as close to the same size as possible.

 

[IJ.]

Turn it up to 11 Dude!!!

On a serious note I experimented with volumes ranging from 2.5 litres to 7.5 and found it changes how the boost hits, smaller volume = hard and fast larger is slower and more gentle.

 

[85celicasupra]

Well being close to stock size , it should be about right in the middle...
Im just about done with the manifold now...well at least the main part.

I have to do a throttle body (of which I dont know what Im gonna use...probably any large one from the junkyard.) And then just the smaller vacuum provisions and such.

 

[jimi87-t]

my question for you is when you were doing it, how did you go about determining the volume of the plenum?

First I found what the stock one was by covering all the openings, such as the TB, ISC, etc openings with sheets of gasket material (example: put the gasket material between the TB and plenum and bolt it down).

Then filled the plenum with water up to where the runners meet the plenum, it has to be off the car of course .

Then I poured the water into a clear 2" inside dia tube. Measured how high the water was and then calculated the volume.

I don't remember how much it was but I then added some where around 10% when I designed my FFIM.

 

[85celicasupra]

Another thing, when making the spot for the ISC...does it have to have the little cup thing inside or can it just be a hole straight into the manifold?