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Old 06-01-2020, 11:55 AM   #1
Chris_AAFord
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Default Rear exit manifolds for flathead 39 Ford

Hi Fordbarn,

Does anyone know of a good exhaust manifold thatís a rear exit that will fit a 39 ford standard? My current manifold dumps in front of the steering box and Iím looking for something that will be easier to run a dual exhaust.

Thanks,
Chris
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Old 06-01-2020, 12:10 PM   #2
tubman
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Default Re: Rear exit manifolds for flathead 39 Ford

Fenton cast iron headers is all I can think of. I also think one of the parts vendors (Carpenter?) used to make a repop 8BA police manifold,but I don't think they are available anymore. You could look around for one (or maybe even an original?) though.
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Old 06-01-2020, 12:34 PM   #3
Chris_AAFord
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Default Re: Rear exit manifolds for flathead 39 Ford

Thanks, let me look around for the police manifolds.
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Old 06-01-2020, 12:44 PM   #4
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Default Re: Rear exit manifolds for flathead 39 Ford

Bob Drake Have them.

https://www.bobdrake.com/FordItem.aspx?Item=HR-9431
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Old 06-01-2020, 12:58 PM   #5
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Default Re: Rear exit manifolds for flathead 39 Ford

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That part is listed for 49 - 59 cars. Would they work on a '39. They will fit the engine, but will they work with the earlier steering box and frame?
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Old 06-01-2020, 01:05 PM   #6
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Default Re: Rear exit manifolds for flathead 39 Ford

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That part is listed for 49 - 59 cars. Would they work on a '39. They will fit the engine, but will they work with the earlier steering box and frame?
Well the 8BA is a 49-53 Engine.
I have not used one in a 39 but think will be good candidate.
maybe some know better.
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Old 06-01-2020, 02:15 PM   #7
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Default Re: Rear exit manifolds for flathead 39 Ford

Will isn't this interesting!

From Drake's site:

"These manifolds are the single most effective way to increase horsepower through vastly improved exhaust flow, because the key is changing the stock single-exhaust to dual-exhaust."
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Old 06-01-2020, 02:31 PM   #8
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Default Re: Rear exit manifolds for flathead 39 Ford

I have a lot to learn. Why to do you scoff at Drakes statement? Doesn't dual exhaust improve delivered horsepower?
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Old 06-01-2020, 02:42 PM   #9
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Default Re: Rear exit manifolds for flathead 39 Ford

I have an original "police" exhaust manifold and the exhaust pipe flange is definitely bigger but as far as increasing HP by it self is questionable, exhaust gas flow better YES so maybe better throttle response and cooling
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Old 06-01-2020, 02:54 PM   #10
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Default Re: Rear exit manifolds for flathead 39 Ford

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I have a lot to learn. Why to do you scoff at Drakes statement? Doesn't dual exhaust improve delivered horsepower?
By the time the exhaust pulse makes it down from the top of the block through those snaky little passages (with the two center cylinders fighting each other), there's not much you can do to help it get better.

Duals do sound better, though.
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Old 06-01-2020, 03:02 PM   #11
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Default Re: Rear exit manifolds for flathead 39 Ford

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I have a lot to learn. Why to do you scoff at Drakes statement? Doesn't dual exhaust improve delivered horsepower?



From what I've read, the intake tract on a flathead is the limiting factor in gaining horsepower, not the exhaust. Dual exhaust sure sounds a lot better, though!
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Old 06-01-2020, 03:20 PM   #12
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Default Re: Rear exit manifolds for flathead 39 Ford

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I have a lot to learn. Why to do you scoff at Drakes statement? Doesn't dual exhaust improve delivered horsepower?
Dyno tests show minimal hp gains with exhaust modifications on semi-stock engines. The Drake statement is "...the single most effective way to increase horsepower...". That is a false statement. I like headers on a flathead, I like the look, I like the sound, but it is NOT the single most effective way to increase horsepower, not even close.
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Old 06-01-2020, 03:20 PM   #13
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Default Re: Rear exit manifolds for flathead 39 Ford

According to the old magazines

Dual exhaust 10 hp
Dual carbs 10-15 hp
High Compression heads 10-15 hp

All is bolton ;-)
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Old 06-01-2020, 03:21 PM   #14
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Default Re: Rear exit manifolds for flathead 39 Ford

AA Ford needs to buy JWL's book to know why he should spend his money elsewhere on his project.


R
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Old 06-01-2020, 03:22 PM   #15
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Default Re: Rear exit manifolds for flathead 39 Ford

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Originally Posted by JSeery View Post
Dyno tests show minimal hp gains with exhaust modifications on semi-stock engines. The Drake statement is "...the single most effective way to increase horsepower...". That is a false statement. I like headers on a flathead, I like the look, I like the sound, but it is NOT the single most effective way to increase horsepower, not even close.
What is the single most effective way then?
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Old 06-01-2020, 03:23 PM   #16
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Default Re: Rear exit manifolds for flathead 39 Ford

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What is the single most effective way then?
Compression ratio. Milling the heads. JWL calms almost no HP gains with his dyno test. Flatheads suffer from low compression not exhaust flow.

I'm a big dual exhaust fan, but got to realistic about the expected results.
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Old 06-01-2020, 03:54 PM   #17
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Default Re: Rear exit manifolds for flathead 39 Ford

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AA Ford needs to buy JWL's book to know why he should spend his money elsewhere on his project.


R
Or you should read my post...my question has nothing to do with performance.
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Old 06-01-2020, 04:06 PM   #18
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Default Re: Rear exit manifolds for flathead 39 Ford

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Originally Posted by Mr 42 View Post
According to the old magazines

Dual exhaust 10 hp
Dual carbs 10-15 hp
High Compression heads 10-15 hp

All is bolton ;-)
That says it all. When we were kids, we'd go through the J.C. Whitney catalog and add up the horsepower gains advertised for each part. We all knew that if we had enough money, we could make a 175 HP flathead easily.
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Old 06-01-2020, 04:32 PM   #19
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Default Re: Rear exit manifolds for flathead 39 Ford

I wonder if back in the day the muffler was a restriction so the police manifold would give you 2 mufflers on the car. Police needed to be quiet. Seems like it would be a lot of engineering, must have made a bit of difference.
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Old 06-01-2020, 04:52 PM   #20
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Default Re: Rear exit manifolds for flathead 39 Ford

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What is the single most effective way then?
Cubic inches, which if the heads remain the same, brings added compression ration as well.
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