Fastest/ most powerful slant six?

Bill Dedman said
I am not sure, RE: the runner-length. Here's what I know...

Both Ryan Peterson Turbo Slant Six 10.74 @ 127 mph 7-19-10 - YouTube

and Tom Wolfe's Turbo charged Slant 6 11.02 @ 120.56 - YouTube

engines make a little over 500 horsepower, each. Ryan's engine has a long-runner Hyper Pak manifold while Tom's has a short-runner aftermarket (Offenhauser or, maybe Edelbrock?) 4 bbl manifold.

Otherwise, the engines are pretty similar.

So, it looks like either manifold worls for a high-horsepower slant 6.

But, I have an online friend who is a consultant to the engineering departments of a couple of the BIG auto manufacturers, and he told me to get rid of the long-runner Aussiespeed manifold I use. He makes his living, giving advice like that to manufacturers, so I tend to believe him when he talks.

When I bought my long-runner nanifold a few years ago, Aussiespeed didn't yet offer a short-runner manifold, so, I bought what they had...

I probably need to exchange it for a short one.

My advice; get a used Clifford manifold off ebay for whatever you can make the deal for; I think it'll work well for you...

What car is this being installed in?

I am thinking the long runner, aka hyper pak manifold, was the new technology of the day and a cheaper way of creating high air flow rather than turbo charging. I have articles and photos where they actually used different lengths of radiator hose to find the optimum length for best air flow - 17" was the final answer. With turbocharging or supercharging I am guessing it wouldn't make much difference since it is forced air, other than perhaps reduce turbulence? It will be interesting to see what your friend says. To answer your last question, plans right now or for it to go into my 1948 Plymouth coupe, but that will be a ways in the future, and who knows what I might find in the meantime?