Designing a good NA intake manifold?

**spetz** · 05-09-2006 10:14 PM

What are some key aspects to a good NA intake manifold?

At this stage, I am thinking slightly bigger runners, about 4-5cm shorter than factory.
Bigger plenum with two throttle bodies on each side of the plenum (48mm each)

What are ram tubes? What do they do exactly?

Anything else to look out for/ask to make?

**chef_32** · 05-09-2006 10:48 PM

yeah runner length is key, but it must be matched to the desired engine rpm, diameter should probably be slightly larger then overal port diameter. Plenum volum is usually meant to be something like 3-5 tims the engine displacement depending on how much damping and response you want.

why do you think you would need 2 throttle bodies??

**fatboyz39** · 05-09-2006 10:53 PM

why don't you just go ITB?

**spetz** · 05-09-2006 11:42 PM

Well it will be run only by a piggyback ECU, so I doubt that would be ok with ITB?

2 TB is better than one
And if I am making a custom plenum may as well go 2 smaller rather than 1 larger

**panda[cRx]** · 06-09-2006 01:34 PM

i really dont think the gains will be worth it man. but props for trying something different.

let us know how it goes when its done

**barefootbonzai** · 06-09-2006 01:52 PM

it's strange that you wanna invest time into making a new intake when you're only willing to run piggy back ecu. Really doesn't make any sense at all.

**saxman** · 06-09-2006 01:55 PM

I wouldnt' worry as much abotu two throttle bodies, as I would about a center mounted throttle body that'll allow symetric flow to all four runners. Proper runner length is key, and a good airhorn design at the plenum. Plenum volume is based more on individual cylinder displacement.

If you're going to be going down the route of multiple throttle bodies, don't stop with two, go with itbs

whatever you do, you're going to want a real ecu set up to tune the motor with.

**spetz** · 06-09-2006 02:39 PM

Unfortunately the ECU is from a couple of years back and at this stage I don't have the money to upgrade it

I do plan on getting a full standalone IF I end up doing cams, which I plan to

Does anyone know exactly what ram/velocity tubes are? Apparently they speed up the air and are good for NA's

With a center mounted TB, wouldn't the middle runners get more air than the side ones?

I would go ITB, but I don't think there is any way to tune them with just piggyback is there?
And really I am already stretching the budget quite a bit (engine has been rebuilt, ported heads etc)

**sivic** · 06-09-2006 04:14 PM

Originally Posted by spetz

With a center mounted TB, wouldn't the middle runners get more air than the side ones?

then wouldnt that be the case with 2 TB on either side of the IM except the outer runners would get more air than the middle ones?
although it is ideal to have each cylinder having equal access to airflow source, such is the point of ITB's, its not a massive issue for engines which are still fairly mild. think about a stock setup and the distances each runner is away from the TB. no real problems

**spetz** · 06-09-2006 06:31 PM

What if then, it uses a single larger TB, and the plenum is design in such a way that at the other side of the TB the plenum is smaller therefore air goes quicker to the end runners, and the side with the TB is larger so it goes slower to the runners. Would this even it out?

Is there, realistically, any benefit of twin over single TB?
My understanding was with 2 smaller TB's the air velocity is kept higher with the same rate of volume goine in which = more power/torque

Anyone can explain ram/velocity tubes?

**saxman** · 06-09-2006 07:38 PM

having the plenum like that is rather typical for that exact reason... it doesn't work as well as a center mounted, symetrical design, however.

With two throttle bodies going into a single plenum, you're going to have MAJOR air turbulence issues.

A velocity stack is basically a the taper into the runner that's designed to increase velocity and prevent turbulence into the intakes. If you're going as far as making your own intake manifold, this is a very important feature to have. The air horn section needs to be properly designed(the specs for this should be readily available) and the runner length needs to be tuned to specific rpm ranges for valve reversion and all that fun jazz.