Quote:
Originally Posted by Rick Parker
I believe Cushman Motorsports has the correct linkage pieces to allow the single link to work. The arms have to be shorter on one bank than the other because of how they are clocked. Something similar to this was on the GT40's??
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You're trying to rotate two shafts at exactly the same rate. If one arm is shorter than the other, that will never happen, no matter how they are clocked. The throttle arms must be exactly the same length from the center line of the throttle shaft to the pivot point of the actuating rod.
Take a look at a progressive throttle linkage - like for two 4 barrel carbs on a common plenum manifold. You make them progressive by changing the pivot points so they are not equal. If you set up 4 Webers (or EFI throttle bodies) like that on an IR manifold, it will never run right. Your balance will only be correct at idle.
You do have to pay attention to how they are clocked. You are changing a linear motion tgo a rotational motion. Both pivot points need to move through the same arc in relation to the actuating rod. Ideally, at 50% throttle opening, you should be able to draw a line through the center of the cross shaft and intersect the center of both throttle shafts. That doesn't always work, but as long as each pivot point is at the same point in the arc at the same time, it works.
I found that using off the shelf identical Inglese arms worked perfectly. With those arms and a double-D shaft, each arm has 4 mounting choices. That gives you 16 possible combinations. Only one of the 16 will work.
I had mine set up like this for years, and it was well balanced at all throttle openings.
I'v been working with my 8 stack EFI system for quite a few years now. One thing I learned early on was how important proper linkage set up really is. It has to be right, and it has to be very precise. If this basic step is not done the balance will never be correct, and no amount of tuning will ever get it to run the way it should. This is a tedious, time consuming, and often frustrating step; but it is vitally important you're going to get it right.
I found it was a lot easier to do this with the intake manifold assembled on the bench, rather than under the hood. Much easier to make measurements and adjustments that way. I also ended up making a few parts myself. I could have ordered a lot of them from Inglese, but that costs a lot more, and takes a lot more time. To get a new rod sent out takes at least a week. I can make one in about 30 minutes. And if it's not right, I can just make another one.