CAE86 ITB Build

[float_6969]

Anybody with the motor in the car should be able to give that measurement. Unfortunately, mine is NOT in the car, or I'd get it for you.

[GTSRolla34]

This version would extend out 3.5" from the face of the lower manifold. Then the ITBs would stack atop that. I'll have to measure the ITBs this weekend...I think they are 3-4" long. So I'm going to estimate a plenum would start at about 7"from the face of the lower manifold...that seems a bit far. I'll rework the adapter and see if I can shorten in by 1.5". I think the issue then would be how to fasten it to the lower manifold.



I still have to edit the flange for the ITBs. It's one solid piece now, but may end up being 4 individual flanges. The thickness of the walls for the connection between the flanges is at 1/4" right now.

[float_6969]

The only issue I have with this is that you're giving up a lot of flow using the lower manifold. there is a OBVIOUS reduction in port size from the head to the upper manifold. I would guess in the order of 15-20% smaller. IDK what the ID of the ITB's that you're using are, but if they're bigger than the outlet of the lower manifold, this design is going to have an inherit restriction there.

[ragenasian]

This would however make it universal between 4 port and 8 port head users right? Lower mani is the only difference between the two if I remember correctly.

[float_6969]

That is true. The upper manifold (or plenum as the UK guys call it) is the same between the 4 port and later 8 port's.

[GTSRolla34]

Correct, this makes the piece a universal fit, but creates a port issue. About the best I could do is design the ITB side with enough material to allow serious porting potential for any body's individual needs. The issue with making something that isn't restrictive and has a smooth transition is there needs to be distance to create the transition. Otherwise it's too sharp. Using the stock lower manifold puts the universal adapter far enough from the head that it needs to be compact as possible. Otherwise the ITBs stick out so far that a plenum would have to be very narrow, or the velocity stacks would have to curve 90* up or down to allow placement of a larger plenum. Again, I can give an accurate measurement for shock tower clearance from the face of the ITBs if I can get a measurement from the lower manifold to the shock tower.

Here is an image of the lower manifold ports and the ITB ports. The inner diameter of the holes is close to those on the ITBs, but not exact...I don't have them sitting in front of me. I do know that the silvertop ITBs are 42mm and the blacktops are 45mm (but not a true circle). The bore in the drawings are just under the blacktop itb size.



So the issue is trying to create a smooth transition in what I'm assuming to be a very limited space considering that the ITBs still need to be sandwiched in somehow.