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Old 01-12-2022, 05:42 PM
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justincampbell justincampbell is offline
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Default Exhaust Difference - '73 Formula

I have been looking at new stock exhaust systems for my '73 Formula 400 and see 2 different options. Most exhaust I see is listed as either "70-'74 Ram Air" or '70-'74 Except Ram Air".
What is the difference?
It seems like the application is not entirely accurate as I was under the impression that the only difference by '73 was the air cleaner.
Even though my car has the Ram Air(air cleaner) option, am I to assume the exhaust I want is the one listed for non ram air?

Also, are the classic industries, classic exhaust, or any of the other lower priced options acceptable?
Gardner was recommended to me. But they were expensive even before things went completely bonkers.
FYI - It must be stock style exhaust. Every 2nd gen I hear that isn't OEM style exhaust just sounds wrong to me.

It will be a while before I need exhaust. But, no heat in the garage and a hatred of working barehanded in the cold means winter is pretty much just for research and parts acquisition here in Iowa.

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  #2  
Old 01-12-2022, 11:31 PM
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I believe they are distinguishing between the exhaust manifolds and their outlet point.
1970 Ram Air III and IV, along with 71-74 round port cars, had a unique exhaust manifold outlet point, that required different headpipes.

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Old 01-13-2022, 01:09 AM
Ramairnacho Ramairnacho is offline
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Quote:
Originally Posted by justincampbell View Post
I have been looking at new stock exhaust systems for my '73 Formula 400 and see 2 different options. Most exhaust I see is listed as either "70-'74 Ram Air" or '70-'74 Except Ram Air".
What is the difference?
It seems like the application is not entirely accurate as I was under the impression that the only difference by '73 was the air cleaner.
Even though my car has the Ram Air(air cleaner) option, am I to assume the exhaust I want is the one listed for non ram air?

Also, are the classic industries, classic exhaust, or any of the other lower priced options acceptable?
Gardner was recommended to me. But they were expensive even before things went completely bonkers.
FYI - It must be stock style exhaust. Every 2nd gen I hear that isn't OEM style exhaust just sounds wrong to me.

It will be a while before I need exhaust. But, no heat in the garage and a hatred of working barehanded in the cold means winter is pretty much just for research and parts acquisition here in Iowa.
I believe your exhuast manifolds have to make exhuast ports on your heads so what ever heads you go go with that. For example ram air 4 has round port so d port will not work. Makes sense? If you have d port then ram air 4 exhuadt manifolds will not work.

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Old 01-13-2022, 10:28 AM
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It’s about the exhaust manifolds. SD, RA3and 4 all have same exit points. So all could use the same downpipes

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Old 01-13-2022, 12:19 PM
"QUICK-SILVER" "QUICK-SILVER" is offline
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Quote:
Originally Posted by keith k View Post
I believe they are distinguishing between the exhaust manifolds and their outlet point.
1970 Ram Air III and IV, along with 71-74 round port cars, had a unique exhaust manifold outlet point, that required different headpipes.
Quote:
Originally Posted by Norwood View Post
It’s about the exhaust manifolds. SD, RA3and 4 all have same exit points. So all could use the same downpipes
Outlet point/exit point/ pipe mounting flange is quite a bit lower on RA exhaust manifolds than it is on log manifolds.

RA downpipes/headpipes wont reach the mounting flange on log manifolds.

Non RA downpipes would hang down like headers when bolted to RA manifolds.

Clay

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Old 01-13-2022, 05:28 PM
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On RA manifolds, "D" or " O" port I recommend the oil filter offset kit that was developed for '69 but fits perfect for second gen cars and gets the oil filter away from the manifold. It is almost touching it without the adapter.
Having used a bunch of exhaust systems, I will only run Gardner, but I have heard people speak well of Waldron exhaust. Don't ask about " Dronemaster" . Pypes required a few mods and tweaks, and sounded tinny to me. Every engine sounds different too.

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Old 01-13-2022, 05:31 PM
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In '73 Ram Air is basically just RPO WU3. fresh air inlet.
Only cars originally having RA manifolds were SD cars.
Even a 455 T/A had the logs ( non SD).

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Old 01-13-2022, 06:35 PM
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In addition to the great advice above, it's worth noting that the d-port cars with log-type exhaust manifolds (regardless of displacement--350 to 455) had 2-inch diameter head pipes. The over-axle pipes were 2.25", however.

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Old 01-13-2022, 06:48 PM
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I believe that as far as stock replacement exhaust kits are concerned the "Ram Air" versus "non-Ram Air" are all about the headpipes;
As mentioned earlier the exhaust manifolds for cars with RA exhaust manifolds require a tighter and lower connection point.

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  #10  
Old 01-13-2022, 09:52 PM
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Thanks for the help!

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Old 01-14-2022, 06:49 PM
SD455DJ SD455DJ is offline
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'73 & '74 Formula Firebirds with the 400 4-bbl & 455 4-bbl D-port engines could be ordered with Ram Air hood induction and both these engines had standard exhaust ('log') manifolds, so would use the "Except Ram Air" exhaust system (specifically the regular duty head pipes).

I included a couple pics of Ram Air equipped 455 D-port Formulas for examples.

Dennis
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Last edited by SD455DJ; 01-14-2022 at 07:03 PM.
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