Long-Tube Intake Manifold

[Admiral]

Has anyone here experimented with a long-tube intake manifold on the flathead V8, something akin to Chrysler’s Ram Induction engine of the 1960s? I’m toying with the idea of fabricating something similar. Every time I look at a stock sidevalve V8 intake I cringe because of the ridiculously convoluted path the air and fuel must follow before finally entering the cylinders.



What I’m most interested in here is maximizing torque production rather than pushing for more top-end horsepower, playing to the flathead’s strengths as a choked-down, low-RPM workhorse, not a high-winding screamer.

Like the Chrysler design, I was thinking of incorporating intake runners that are as long as practically possible (i.e. ones that will still fit in an engine compartment) and of a reasonably small diameter to keep air velocity high. I like the idea of doing this with a single carburetor, but plumbing all of that in an “over-under” configuration like the stock intake would be a packaging nightmare, therefore a dual-carb setup would probably be best, just like the Mopar configuration.



I’ve managed to find one photo of an intake that’s similar in concept to what I want to experiment with (attached to this post) but it incorporates four carburetors, which I think is gross overkill from both fueling and complexity standpoints.

[donald1950]

quite interesting. to me i believe i would use something like the Chrysler concept and one carb on each side and with the carbs sitting sideways on the plenum box like the Chrysler, not front to back like what is shown on the 4 carb set up......

[Ggmac]

I thought about nearly the same using side draft Webers , the small ones for the VW. Just one for each side .
Side drafts would keep it low and the Chinese copy is only $120 each .

[revkev6]

i've done the math, I think you need something like 20-24" from the back side of the valve to the opening of the tube to get the best "bang for your buck" from the tuned intake pulses. there's a guy on a facebook group who is making up a flathead manifold that's EFI and looks like stack injection with a hat on top. i'm very interested to see how his project turns out.

[Ronnieroadster]

Overall it couldn't hurt but remember two things first the design ends up becoming four two cylinder engines with the four carb set up as an example since theres no balance system between the ports. Second the lack of heat in the runners will cause some issues until heat gets into the runners. If your able to get the tuning to work with these issues you might have something. Good Luck

[revkev6]

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Originally Posted by Ronnieroadster

Overall it couldn't hurt but remember two things first the design ends up becoming four two cylinder engines with the four carb set up as an example since theres no balance system between the ports. Second the lack of heat in the runners will cause some issues until heat gets into the runners. If your able to get the tuning to work with these issues you might have something. Good Luck

not quite old school, but still interesting. it's single plane long runner. heat in the runners may still be an issue though.

[Talkwrench]

I bet it would run like a pig until everything was hot ..

[JSeery]

You would be hard pressed to come up with something to try on a flathead that hasn't been attempted many time before!

[Ol' Ron]

The man to talk to is Flat 32, He's built several of them, even has a nice casting of one.

[Tinker]

Im sure there are better samples and more precise ways to do things. Always great to see new ideas, never say never.

for me these two designs are pretty good. I'd run them. cool thread look forward to more posts.

[Tinker]

if going for efficiency wouldn't something like this be better? I don't know.



or https://www.jalopyjournal.com/forum/...thread.338475/

but we might all be here like... you have to replace your computer fuel ignition box... or you could just run a carburetor.

[revkev6]

Originally Posted by Talkwrench

I bet it would run like a pig until everything was hot ..

actually, when you look at that setup because there is no fuel running through the long tubes manifold temp wouldn't matter. it's got fuel injectors right at the base of the intake into the block. you won't have fuel falling out of suspension due to a cold, long intake runner.

Originally Posted by Tinker

if going for efficiency wouldn't something like this be better? I don't know.



or https://www.jalopyjournal.com/forum/...thread.338475/

but we might all be here like... you have to replace your computer fuel ignition box... or you could just run a carburetor.

I posted up a thread on the hamb about long runner flathead manifolds not too long ago. basically calculating out the optimum length for an intake manifold is the same idea as making up a set of scavenger headers. the theory goes that when the valve closes there is a shock wave produced because the air and fuel mixture has mass and its moving into the cylinder, the valve closing stops the flow. that shock wave creates a pulse of air that runs back and forth in your intake tube. when that shock wave hits the open plenum it bounces back into the runner. this happens extremely fast. I don't remember the exact calculations but with a 20-24" long runner a flathead will get either the 3rd or 4th pulse at around 4500 rpm. the more pulses you catch at your higher RPM the more you get them at lower RPM. so the longer the tube the more times you catch a pulse pushing the air back in the cylinder. it's kinda like a "free" supercharger effect. takes time and tuning though to find the perfect length. calculations only get you close.


btw, there's lots of COOL setups in the EFI thread you posted.

[Tim Ayers]

Like Ron said, try to get in touch with Flat 32. He made his manifold using long tube runners. He showed me his prototype and it was pretty cool that for the mock model he used pool noodles to get the idea down for his model.

From what I understand, it ran pretty well. IIRC, Bored & Stroked & JWL own intakes that Flat 32 made, so maybe they'll chime in on this as well. The carbs ran on top, but the runners where of a long tube design. I believe he also designed the top to be removable and different carbs set-ups could be used.

[revkev6]

tim, are you talking about the intake that JWL ran in his book?? that was pretty cool. not only long runner but it also was 180 degree instead of single plane.

[Tim Ayers]

Originally Posted by revkev6

tim, are you talking about the intake that JWL ran in his book?? that was pretty cool. not only long runner but it also was 180 degree instead of single plane.

I'm not sure if it's the same one JWL used in his book. Flat 32 is friends with both JWL and B&S. I thought they each have one of Flat 32's intakes with the long tube runners.

[revkev6]

this is the same type of intake that JWL put on his dyno in his book. think it's the one you are talking about?

[Pete]

While this is not a V8, the principal is the same.
This is a B engine I did about 15 years ago. The runners were about 14 inches long and the carb was a 650 Holley. This manifold lowered the torque peak from
4500 to 4100. It cut the lap times .1 of a second over the Hilborn injectors.
Not much on looks what with the carb sitting above the hood.

[Pete]

...

[revkev6]

Pretty sweet banger. What did it run? 4500 rom for peak torque is a screamer!

[Pete]

Originally Posted by revkev6

Pretty sweet banger. What did it run? 4500 rom for peak torque is a screamer!

It ran in a vintage circle track car. Mostly on 1/4 and 1/2 mile dirt tracks.
It was the top car in the 4 banger class for several years.
Turned 6200.
This engine or it's clone (I don't remember) won the Antique Nationals 2 years in a row in the 4 cylinder top fuel dragster class.