Reverse-flow hot rod engines are fascinatingly bizarre

Increasing performance by reversing the natural order

4w ago

Recently, I learned of a fascinating old trick that some hot-rodders used to get more power out of Ford flathead V8s back in the day, and I can't stop thinking about them. You see, one of the biggest flaws with the Ford flatheads is that the middle two cylinders of each bank share an exhaust port, and that middle exhaust port gets disproportionately hotter than the others. As a result, when you start increasing the performance of the engine, you can reach a point where the middle exhaust port gets hot enough to crack the block, and then your day is ruined.

The solution according to hot-rodders in the 50s? Run the engine backwards (or the same direction, but with a custom camshaft to reverse the intake/exhaust cycle)! Bolt carburetors or injectors where the exhaust manifolds should be and make the exhaust exit where the intake used to be. Now you don't have to worry about the middle port getting too hot, because that's where the nice cool air is entering!

These engines are some of the strangest things I've ever seen and I love that not only does it actually work, but it vastly improves the flathead's thermodynamic efficiency and made these engines quite successful in racing. Of course, it's a bit more complicated than just reversing where air enters and exits. A little bit of machining should be done to make sure the intake-turned-exhaust works properly while keeping the top of the block durable, but that's still better than cracking engine blocks all the time.

Sadly, this neat trick is mostly forgotten now, and I haven't found any videos of surviving cars with reverse-flow flathead V8s. These are some of the only color photos of them I could find, and the one pictured above seems to have been built as a demonstration of what reverse-flow engines can do. It reportedly made 560 hp on the dyno, which is absolutely insane for a Ford flathead V8.

This one was used in a streamliner for the purpose of setting land speed records!

This one was used in a streamliner for the purpose of setting land speed records!

Nowadays, there are still some people who build reverse-flow engines for the sake of novelty, and most of them seem to be built out of small block Chevy V8s.

I particularly like this one, which has one of the tidiest turbocharger setups I've ever seen. They bolted the turbo where the carburetor used to be, and from there the compressed air splits to the carburetors on either side of the engine, and exhaust exits out the hood via a rusty soup can. It's brilliant.

There doesn't appear to be any performance advantage to doing this on an engine that already has the proper number of exhaust ports, but it's still cool that it actually works to do it that way. Looks pretty neat in a hot rod, too.

The one other engine I can think of that would actually benefit from this modification is the Packard V8, which was a pretty neat motor and would've had good performance potential, but suffered from the same problem as the Ford flathead V8 in that it only had six exhaust ports.

To my knowledge, nobody has ever put a reverse-flow Packard V8 in a hot rod before, but now I really want to try that...

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Comments (8)

  • I want to have one of these in a supercar now just to see what they can do.

      1 month ago
  • Well bugger me with a soup spoon. That is so cool. People solving problems with the stuff the have got and some brilliance in their heads.

    Can we have more please?

    Thanks for taking the time

      1 month ago
  • Great article about a forgotten trick, I love it

      1 month ago
  • This was a very creative trick. It cures the flatheads one major flaw.

      1 month ago
  • Oh boy, another thing we thought of in the 50;s will now come back be a big thing and everyone will say wow that's so cool, how did you come up with the idea. Yes I was around in the 50's. Does that make me old? Don't answer that, please.

      1 month ago