Ram Horn Manifolds - Impala Tech
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post #1 of 7 (permalink) Old 02-08-2012, 11:35 PM Thread Starter
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Ram Horn Manifolds

Hi, I was wondering what size ram horn manifolds the '67 327's came with, the 2" or 2.5"? Also, they don't hurt performance much on a pretty much stock daily driver do they? I've heard all different sorts of answers so... just wondering.
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post #2 of 7 (permalink) Old 02-09-2012, 12:10 AM
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The '67 full size cars only had one 327 available, it was the 275hp version and it came with the smaller 2" exhaust manifolds. With a stock daily driver these manifolds will work just fine.
The only 327's that came with the larger 2.5" rams horns were the High Performance 300hp versions but they were not offered in '67.

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post #3 of 7 (permalink) Old 02-09-2012, 09:29 AM
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There is a pretty big difference in size between 2 and 2.5 inch rams horns. At least that is what I see on the rams horns used in 64.




You might also find this dyno chart of interest. This was done on my 327 (bored and stroked to 383). Engine uses stock block, heads, intake and carb as I wanted perfectly stock appearance on the outside. It is interesting that the rams horns (blue) do not cause much performance difference until the RPMs hit the top end. I am not sure how reliable the last point or two of data is, but it seems to show the headers starting to show some real advantage only above 5,400 RPM. Considering how little time a stock engine will spend up there, headers seem like a waste, at least for my engine.

On the other hand, when I had the old 350 based 383 in my car, and upgraded the exhaust and rams horns from 2 inch to 2.5 inch, performance was quite noticeably improved. How much this 383 info applies to a 327 is your guess, but they used the 2.5 manifolds back in the day for a reason





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post #4 of 7 (permalink) Old 02-10-2012, 10:43 PM Thread Starter
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Thanks for the info guys, it helped alot. one last thing, are headers really much louder than the ram horns?
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post #5 of 7 (permalink) Old 02-10-2012, 11:28 PM
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I have never used headers, so I can't make a direct comparison. Most people who run headers are not after 'quiet' I would point out that the thickness of the metal is certainly different between cast iron and steel pipe.



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post #6 of 7 (permalink) Old 02-11-2012, 12:21 AM
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The "noise" associated with headers is not from the thickens of the primary tubes (which is often 14 gauge metal), but from a lack of a muffler and sewer pipes for exhaust tubing.

There are people who port the big 2.5 inch cast iron ram's horn manifolds for class racing under certain rule books that will flow as much exhaust gas as a set of headers, but still not make as much power. This is because headers not only improve the flow rate, but also isolate the exhaust pulses so that one cylinder opening it's exhaust valve can not dump it's higher pressure exhaust gas into an adjacent cylinder that still has it's exhaust valve off the seat (as happens all the time between cylinders 5 and 7).

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post #7 of 7 (permalink) Old 02-12-2012, 10:01 AM
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I was totally surprised when I put headers on my 72 GTO. The car ran better breathed better and was quieter. And I like noise
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