3 twin throttle bodies in place of a single throttle body on a plenum...

[Walken100]

Ok as I start to look into options for a manifold for my build I ran into a few articles on ITB's (individual throttle bodies). IE one throttle body per runner.

The question is what is the down side? I can't find one but I'm sure it exists.

If I have to make a manifold it could easily be a simple manifold to mount 3 twin throttle bodies. I could change the length of the velocity stacks to tune the intake. There is more to run to ground but what am I missing?

 

[aussie7mains]

Individual runner manifolds and a venturi for each cylinder works really well for NA applications, tuned length can be used in that case, Im unsure of what engine and application your asking about. If your talking about a 300ci six NA, then yes it would work, however tuned length for best torque around mid RPM would be quite long, somewhere around 700mm, could you fit that in? Also for this application you would need no less than 45mm carby, bigger for a race application, costly! If your talking not NA, either turbo of blown, then a tuned runner system is unnecesary and might not lead to best performance. I would suggest you read some of Graham A Bells texts on these subjects, he is IMO the best authority on them. Ive done both and can say that for NA applications individual runner manifolds and 3 twin throat Weber/delorto carbs will give best performance in all driving. A single carby (big holley carby) type thing can be made to work quite well for drag applications, but wont be as tractable on the road. For boosted applications, a log type of manifold works well and is easiest to manage in a vehicle, you will find most boosted engines in cars are like this, including the turbo Barras. I have a manifold like this on my blown crossflow, it works very well, and was relatively easy to make. Ive run 3 delortos on a hot 250-2v and they work really well, even with big cams they can be a daily driver.

 

[Walken100]

Individual runner manifolds and a venturi for each cylinder works really well for NA applications, tuned length can be used in that case, Im unsure of what engine and application your asking about. If your talking about a 300ci six NA, then yes it would work, however tuned length for best torque around mid RPM would be quite long

I kept my question somewhat general because I'm looking for the down side. I'm not reading a downside in your response. My application is NA STRIP/street 300 with peak horsepower around 5500 so I'm looking at about 205mm. I could package much longer but it isn't necessary. I landed on this topic because I need to make an intake. 6 straight tubes with a flange is a wee bit easier than creating a manifold with a plenum. I've got some reading to do both on ITB's and on paralleling throttle bodies.

 

[pmuller9]

The downside is that the twin TBs have a different spacing than the intake ports so that the runners cannot be straight.
You can do single TBs if you use port fuel injection.

However, if you go port fuel injection, the best arrangement is 8" tapered runners going to a large round plenum with a single TB at the end of the plenum.

 

[Walken100]

The downside is that the twin TBs have a different spacing than the intake ports so that the runners cannot be straight.
You can do single TBs if you use port fuel injection.

However, if you go port fuel injection, the best arrangement is 8" tapered runners going to a large round plenum with a single TB at the end of the plenum.

There are options spaced correctly but so far none of them are reasonably priced options.......

The other potential downside I found was using a Map sensor. There are work arounds but it would need to be addressed.

I am going port injection so that is why I was thinking about it.

 

[drag-200stang]

The downside is that the twin TBs have a different spacing than the intake ports so that the runners cannot be straight.
You can do single TBs if you use port fuel injection.

However, if you go port fuel injection, the best arrangement is 8" tapered runners going to a large round plenum with a single TB at the end of the plenum.

This should be the easiest, cheapest and best running/ power.

 

[Walken100]

This should be the easiest, cheapest and best running/ power.

Definitely the cheapest. Not the easiest from a fab stand point and regarding flow, getting the flow right in a plenum isn't a gimme. However it is the cheapest by a long shot. So ITB's are off the table for now.