Tunnel ram Tuesday!!!...
I’m sure you know on these intakes the top wall curves/pinches down more than the floor. By welding I can match the head port and basically remove that curve and blend it into the top. Hoping that is the right move. I will also have the larger top to try, I measured that street top and it’s actually only 173 cubic inches. This motor will be a 418 with 13.3 compression. Wonder if the larger top is better move for my application. I will shift around 6700 but runner length on these are perfect for that
The only way to know for sure is to test it.
As a general rule, those big bread box tops were used because about the biggest carb you could get back then was not much over 625 CFM. The bigger plenum wants smaller carbs.
As carbs got bigger, the plenum volume went down, within reason.
The other issue is on the dyno the engine will want more and more and more plenum volume and it will keep making more power. The problem is you will hit a point where even though you made more power on the dyno, the car is slower at the track.
So getting a good balance of plenum volume and carb size requires some dyno testing and then verifying that at the track.
And I suspect that is so because of the way a water brake dyno measures torque. The dyno allows the engine to RPM at a constant rate, whatever that is. Some use 300 rpm/sec, some use 600 rpm/sec and others use multiple rates on the engine. But whatever that rate is, it’s probably not going to be the rpm acceleration the engine sees in the car at the track.
I have somewhere copies of dyno testing between a water brake dyno and an inertia dyno. The results were what looked good on the WB looked bad on the inertia dyno, and what looked bad on the WB looked good on the inertia dyno. Both were crank dyno’s.
The upshot is in the car, the manifold that was the best on the WB was slowest in the car and the manifold that was the best on the inertia dyno was fastest in the car.
In fact, the curves were the exact inverse of each other.
That doesn’t mean the WB dyno is useless or inaccurate. It just means as end users we have to know the limits of the tools we use.
