Are there any guidelines for how big a plenum like this should be? I thought with a plenum this big it might cause some slugishness in throttle response, I could very well be wrong.

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The old white brick

A plenum with a 3 1/2" diamenter and 21" long would be just about right. The runners will need to be between 6" to 7" long to clear the exhaust manifolds. And idealy they should be about a 15* upward curve in the runners to gain even more clearance from the exhaust manifolds. This would also move the throttle body up out of the way of the engine fan. A stock Ford 5.0 throttle body will work nicely. Yeah, I started down this path and have decided to try something different. Of course this was with my Dart. An A100 may not have the clearance in the dog house.

3.5 is a little too small, but then again I'm used to dohc 4 cylinder engines that require more airflow per cylinder. my drawing is of a 4" plenum 24 inches long. I'm planning on using a 65mm throttlebody off of a ford zetec motor. It's really similar to the 5.0 throttlebody, and I already have a few laying around because my other vehicle is a ford ZX2 S/R.


I haven't built anything yet. just drafting everything up before I do, so I don't waste a bunch of time making uneeded parts.

NEW REVISION!!
I'm thinking that these might work good for a itb setup also.

A 24" long plenum will but your throttle body into the fan and the rear end will be very close to the firewall. The 4" diameter tube will place the bolt holes for the throttle body flange very close to the outside of the tube.

Nice flange, How are you going to make them?