1974 Exhaust - Any ideas?

I have had a Serra header and exhaust for a number of decades. It has a couple of issues. First, it is designed for 1975 and later cars so the exhaust is on the wrong sides (nobody making good performance exhausts for 74s back then). The other issue is that the header is tied to the engine and the rest of the exhaust is tied to the body using the 1975-> spring setup w/o any flex couplings. Remarkably, this has not caused problem but I still don't like it.

Serra X19 Exhaust System.jpg


Now that I've got a new engine in, I'd like to do a better job on the exhaust. I originally thought about doing a mirror image of the above by reworking the cat bypass pipe. However, after taking a few measurements, it appears that I could eliminate the bypass pipe except for a short section off the collector and go right into the muffler:

Serra X19 Modified Exhaust Configuration Mockup.jpg

My plan would be to use the 74 factory muffler mounts to tie the exhaust to the drivetrain instead of the body. The muffler would be a Walker or Thrush 17711 "Turbo" type (14" x 9.75 x 4.25, 2" I/O), same as the original which did not survive having rusted on pipes removed.

The only negative I can think of is that the muffler sits a bit lower but roughly the same height as the bottom of the collector. I suppose that removing most of the cat bypass might reduce back pressure a little.

Any comments or suggestions appreciated.


Thanks,

Don
 
You could look at a couple of things in a different way.

First find a muffler the right size with the in and the out on the same end. In this case you would keep the entry and the exit on the left side of the muffler.

Second once you have the right muffler you could add a flex coupling from the elbow to the muffler, this would move the muffler further to the right making the transition to the left side of the car that much easier.

The issue with what you have proposed, I think (and I may well be wrong), is that there isn’t enough room to flip the muffler and have enough room from where the bolted transition from the header is to the left side of the space for the muffler etc.

So do what you are proposing you would need to make a right turn from the header and then the U turn to the end of the muffler to then exit the left end. Basically a mirror image of what was delivered by Serra originally. I would think a good muffler shop could make just what you need to replace the existing set up you show.

A rough image of what you would likely need

154AD236-B5D4-4B3A-8D13-372A8CBF4A3B.jpeg
 
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This is what I was proposing as an alternative to what you had described.
View attachment 14441
Karl:

Thanks for the thoughtful alternatives. The first one has the advantage of getting the muffler higher. However, I really like your second proposal in that it gets the muffler up and I can use the existing cat bypass pipe. The only issue will be finding a muffler (haven't looked yet) with the ports on the same side. My original proposal actually appears to fit based on a mockup I did with the old muffler, but if I can find the right muffler for your second proposal, it almost looks too easy so I would prefer that route. If I mount the muffler using the 74 transaxle mounts, I probably could get by without the flex coupling.

Don
 
If I mount the muffler using the 74 transaxle mounts, I probably could get by without the flex coupling.
The flex coupling would likely still make things easier. One of the disadvantages of the completely rigid stock '74 system is that you have three separate points (bracket from top of bell housing, finger on lower transmission mount, downpipe to muffler) that have to align perfectly or forced into alignment.
 
The flex coupling would likely still make things easier. One of the disadvantages of the completely rigid stock '74 system is that you have three separate points (bracket from top of bell housing, finger on lower transmission mount, downpipe to muffler) that have to align perfectly or forced into alignment.
I would probably use the upper bracket only or some variation of it. The motor mount extension is likely not in a useful location as it sits pretty close to the collector and would be somewhat redundant as far as support goes. If I end up using the 75-> spring mounts which have already been added to the car, I'll definitely put in a flex coupling.
 
I like the idea of adding a flex coupling regardless of the direction chosen for the exhaust.

To keep things as simple as possible perhaps taking the existing solution and adding a flex coupling between the end of the muffler and the head pipe extension and then running a pipe back across to the left side from the right side of the muffler you have. This would be the least work and would keep the majority of the system as it is with the benefit of some flex and getting the pipe in the right place.

The flex coupling could also go in the lower run of the pipe from the header collector connection to the elbow up to the muffler, you would just need to remove 4” or so of that lower horizontal pipe. This would work for any of the approaches.
 
Following up on Karl's suggestion, I've searched a number of muffler manufacturer sites and have not found "same end" (that's what they are called) mufflers in anything below 2.5". I suppose I can use an adapter to mate to my 2" system. They seem to charge quite a bit more ($80 and up) for these than the garden variety ($30) as well.
 
Perhaps this help a bit. There was a discussion here a few months back about basically the same situation:
https://xwebforums.com/forum/index.php?threads/looking-for-2-25-crossflow-muffler.34116/#post-290456

You will find some alternatives in there.

Yes, most of the "same end" mufflers out there are 2.5". Mostly intended for a Camaro/Firebird V8. But...I think there was somewhat smaller diameter pipe version for the V6 version of those cars. Maybe only had 1 outlet. Not nearly as easy to find.

Hope this helps. doug
 
The SERRA exhaust looks a lot like my Header/turbo muffler setup I now have on both my Xs and in both cases they exit through the rear grill.

IMG_0376[2].JPG
 
The SERRA exhaust looks a lot like my Header/turbo muffler setup I now have on both my Xs and in both cases they exit through the rear grill.

View attachment 14489
That looks like a rather large exhaust pipe you've got there! If I had a rear grill (and a right side exit), I would use the exhaust as designed. The problem is a 74 has a left exit and I got tired of the funky look of the exhaust pipe squeezed under the right rear sheet metal.
 
Sorry, forgot about 74 differences. Go to Summit Racing and see if they have a turbo muffler with both entrance and exit pipe on the same end if there is such an animal. Or I guess a U pipe on the end of the exit and send the exhaust back to the left side.
 
Sorry, forgot about 74 differences. Go to Summit Racing and see if they have a turbo muffler with both entrance and exit pipe on the same end if there is such an animal. Or I guess a U pipe on the end of the exit and send the exhaust back to the left side.
I have found "same end" mufflers that would probably fit but nothing smaller than 2.5". Still searching for a 2", but I suppose I could use an adapter. I was trying to either keep it simple and avoid welding or doing something "nice" and use that to justify buying a MIG welder. I've still got my oxy-acetylene equipment from building my Cadillac exhaust in the early 70s but thought that instead of getting tanks, I should take a more 21st century approach.
 
and.....keep an open mind for other possibilities. Like the
saab 900 muffler 001.JPG
round Saab muffler in the pic below. You could go almost directly from your header into it - it has a side inlet. Out the end to your left tailpipe notch.
 
Grab your beverage of choice and go through here:
It will take a while, but I'm sure you will find some likely candidates. Like 6564 or 700086.

Good luck. Doug
Doug:

That is a very useful catalog. Thanks. I checked out 700086 but it only has a 1.75" outlet. I then checked 6564 which looks like it could work. The picture of it on some web sites does not match the configuration but that may be because they are using generic muffler photos. The Summit site cross referenced the part to a Walker Universal SoundFX Mufflers 17833 which looks like it could work. I just need to check some dimensions as it is 8" longer than what I had. The other nice thing about it is that it's only $35.


Don
 
Your header is pretty much identical to the PBS header.
I recommend you do NOT use it. The lengths of the primary tubes is plain wrong for a street engine. It is optimized for very high rpm peak power and creates problems at low rpms.
I had an exhaust system almost identical to yours with the PBS header and a Walker Dynomax Super Turbo muffler. It sounded good and fit well.
But I always had a serious bog between 2000 and 3000 rpm. I always thought it was due to the dual carbs.
But then I switched to the 1974 stock exhaust system and cast manifold and the problem was gone!
Mark Plaia then told me that he had a PBS 1600 motor back in the day and it had the same problem with this header.
I later went from the hot 1300 to a hot 1600 and it had the same problem with the header.

What I do recommend is that you get a Vicks header like the one shown in Carl's pic and go from there.
The "reverse flow" muffler (in and out on same side) is then the easiest solution for packaging.
We had one made (here in Germany), but you can probably find one.
 
If you do decide to stick with your header, then here is your solution. :)
This is the exhaust that I built with the PBS header.

Only mounting point is the trans bracket.

P1040415.JPG P1040416.JPG P1040417.JPG P1040418.JPG P1040419.JPG P1040420.JPG
 
Your header is pretty much identical to the PBS header.
I recommend you do NOT use it. The lengths of the primary tubes is plain wrong for a street engine. It is optimized for very high rpm peak power and creates problems at low rpms.
I had an exhaust system almost identical to yours with the PBS header and a Walker Dynomax Super Turbo muffler. It sounded good and fit well.
But I always had a serious bog between 2000 and 3000 rpm. I always thought it was due to the dual carbs.
But then I switched to the 1974 stock exhaust system and cast manifold and the problem was gone!
Mark Plaia then told me that he had a PBS 1600 motor back in the day and it had the same problem with this header.
I later went from the hot 1300 to a hot 1600 and it had the same problem with the header.

What I do recommend is that you get a Vicks header like the one shown in Carl's pic and go from there.
The "reverse flow" muffler (in and out on same side) is then the easiest solution for packaging.
We had one made (here in Germany), but you can probably find one.
I got about 40,000 street miles on it with no bogging or flat spots once I figured out the correct emulsion tubes for the DCNFs. I have also run it with the stock carb/manifold (to pass SMOG) and never noticed an issue. Back in the day, this was considered one of the better headers for an X. I knew several people that had them on their car back then.
 
If you do decide to stick with your header, then here is your solution. :)
This is the exhaust that I built with the PBS header.

Only mounting point is the trans bracket.

View attachment 14512 View attachment 14513 View attachment 14514 View attachment 14515 View attachment 14516 View attachment 14517
I like how the muffler clamp is bolted to the trans bracket. I see that the PBS header really hugs the block whereas the Serra header goes back a bit before dropping. I'm guessing the PBS tubes are shorter. Looks like the collectors on both end up in about the same place.
 
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