Horse power drop using early A 273 manifolds

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Syleng1

Syleng1

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I was just thinking, that leads to drinking but that a whole another post.

I cannot find anything but has anyone dyno a 318 in a car with original 318 manifolds and then dropped that 318 in an early A (or just swapped the manifold out) with the power steering clearing manifolds and redyno to see if loss or gain using those manifolds over the stock 318. I know a lot of people swap out a 273 for a 318 and wondered how much (if any) it hindered the engine? Not much beats headers. But if you stick to factory, I just wonder how much it hurts.
thanks. Syleng1
 
If you're swapping in say a stock early to mid-70's 2Bbl 318, you probably won't notice much loss.
 
'73 - '76 A Body manifold

1 5/8" ID exit

20200618_195617.jpg
 
273 said:
Installing Exhaust Headers Into 300hp Crate Engine - Mopar Muscle Magazine

On this 310-320 hp 360 there's barely a difference between 318 manifolds and headers, I highly doubt 273 manifold are that much different than 318's.
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The ports are the same and the outlet diameter is about the same as later manifolds, the problem on the early A manifolds is where the dump flattens out to curl around the steering column. It looks VERY restrictive, much more than the later A manifolds. That's why some real world numbers would be interesting...
I stole this image from dgswinger's for sale ad to illustrate the bottleneck.
92c51fee-b474-4da2-8313-6eca443b7436-jpeg.jpg
 
Which manifolds are you talking about. 273 and 318 manifolds are the same.
 
toolmanmike said:
Which manifolds are you talking about. 273 and 318 manifolds are the same.
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I talking power wise, 318,340,360 manifolds have little difference in hp, can't see 273's be that much difference power wise than a 318, especially on lower powered engine.
 
273 said:
I talking power wise, 318,340,360 manifolds have little difference in hp, can't see 273's be that much difference power wise than a 318, especially on lower powered engine.
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I should have quoted @Syleng1 The 64-68 A and B body RH manifolds are the same number. The 64-66 A body LH manifolds are the same number and the 67-69 LH manifolds are the same. 273 stopped in 69 so they were 318 manifolds from then on.
 
Syleng1 said:
The ones in post #8 Mike. Vs the ones on say a 1974 318 Dart.
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Thanks, I should backread more. :BangHead::BangHead: Between 3 and 4 in the morning when I don't have anything else to do. LOL
 
Professor Fate said:
The ports are the same and the outlet diameter is about the same as later manifolds, the problem on the early A manifolds is where the dump flattens out to curl around the steering column. It looks VERY restrictive, much more than the later A manifolds. That's why some real world numbers would be interesting...
I stole this image from dgswinger's for sale ad to illustrate the bottleneck.
View attachment 1715547988
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going by that magazine there is almost no difference between stock 340 manifolds and Headers be it TTI or hedman shorty headers
 
Interesting stuff people. Looks like I back handed got my answer. I figured a 318 with the early a manifolds would choke off a 318 hp. But after the article I’m guessing not so much. That’s good news.
Thanks for the input.
 
It may not be the 273 rear firing manifolds killing it, but the F'd Y-pipe they used off of them, that kinked 90 was nasty! Then you had this..and that. Although it worked pretty good for a 273. Pics courtesy of @cosgig

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pishta said:
It may not be the 273 rear firing manifolds killing it, but the F'd Y-pipe they used off of them, that kinked 90 was nasty! Then you had this..and that. Although it worked pretty good for a 273. Pics courtesy of @cosgig

.View attachment 1715548095View attachment 1715548096
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Yikes! Lucky for me on my 318 in an early A with the 64-66 wrap around manifolds I have a dual 2-1/2” exhaust. So the manifold is the restriction.
567C7F49-7C58-4EE1-8006-FEC25EB41E98.jpeg
 
pishta said:
It may not be the 273 rear firing manifolds killing it, but the F'd Y-pipe they used off of them, that kinked 90 was nasty! Then you had this..and that. Although it worked pretty good for a 273. Pics courtesy of @cosgig

.View attachment 1715548095View attachment 1715548096
Click to expand...
If that's a NOS or original HP head pipe, there were no mandrel bends back then. That design is very efficient. With that restriction it chokes the passenger side down through the pipe like the drivers side does through the manifold. LOL Even the HP 340 manifolds choke down around the steering column but not as much.
 
I've run 1972 340 heads on my 273 with 64-66 exhaust manifolds. Ran pretty strong with 2 in duals and turbo mufflers. I'm thinking, they are not as bad as everyone makes them out to be on the street.
 
I wouldn’t worry about running the 273 manifolds, it’s only an issue once you start adding a lot of cam overlap then you need long tube headers for scavenging. Difference in manifold hp not worth the worry.
 
273 said:
I wouldn’t worry about running the 273 manifolds, it’s only an issue once you start adding a lot of cam overlap then you need long tube headers for scavenging. Difference in manifold hp not worth the worry.
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really , at that level you are talking maybe 3 0r 4 hp nothing you would feel , at least he has a decent exhaust system not thefactory y pipe
 
Nat said:
really , at that level you are talking maybe 3 0r 4 hp nothing you would feel , at least he has a decent exhaust system not thefactory y pipe
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The factory HP Y is pretty efficient for a mild 273. 2 1/2" outlet to the muffler with a 2 1/4" tailpipe.
 
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