1974 Exhaust - Any ideas?

Ulix, what is the problem with the SERRA header, it looks just like the one on my Bertone, having a collector just under the frame rail. I noticed no bogging with the DATRA but when I ran the dual DCOES it would run way too rich just off idle that I could not tune out....are you saying the header was causing that? The header I'm using did come with the motor that was used in a race car.
 
On my car (and on Mark's) it caused a reversion effect. At a certain rpm (between 2000 and 3000 in my case), the pulse waves of the cylinders interacted such that a pressure wave went back up the runner and pumped exhaust gas back into the combustion chamber.
This causes a drop in power, because there is littel fuel to be burned.
The O2 gauge shows rich, because it measures residual oxygen. There is not much oxygen in exhaust gas, so it shows rich even though it isn't.

So for that reason, you could have seen the effect of reversion.
It happens to varying degree and at varying rpm from engine to engine depending on a number of factors.
 
So is there a jetting solution that overcomes this, I'm not really interested in trying a different header. I gather the problem is the runners are too short? Sorry for vectoring this thread but trying to fix off idle jetting on the DCOEs drove me to the point that I had to remove them (driveability and fouled plugs) and I'm currently running a single carb which according to the air/fuel gauge is jetting just fine even off idle.
 
I ended up putting together an exhaust system similar to the one I proposed at the beginning of the thread. It uses a Thrush Turbo 17711 muffler and sections of the original Serra cat bypass pipe and sections of the Serra tail pipe.

Serra Header with Driver's Side Exhaust Exit.jpg


The exhaust is supported by the header on the right and a reinforced rubber strap with a metal fitting that fits under the muffler clamp holding the tailpipe on the left. The strap is flexible enough to allow for any expansion while providing vertical support for the muffler and tailpipe.

Compared to the original Serra design (for 75->), this approach removes about 40" of pipe, 247.5 degrees of bends, and about 4 pounds of weight. It sounds pretty much the same as the original design as the Serra supplied muffler is nearly identical to the Thrush 17711.
 
A lot of us are finding that generic "turbo" mufflers do the job, light, smallish and cheap. They rather replicate the stock muffler sound but with some attitude. If you like the sound that glass packed mufflers make you may not like the sound a turbo muffler makes but straight through glass mufflers need to be rather large to tone down an X or need two of them in series.
 
What Carl said. Two glass packs in series:

30557C84-DD00-4E21-B620-3A01266DE53D.jpeg


carl said:
A lot of us are finding that generic "turbo" mufflers do the job, light, smallish and cheap. They rather replicate the stock muffler sound but with some attitude. If you like the sound that glass packed mufflers make you may not like the sound a turbo muffler makes but straight through glass mufflers need to be rather large to tone down an X or need two of them in series.
Click to expand...
 
My buddy Erwin has a glass pack and cat on his Bertone and it's probably the baddest and best sounding X ever but I bet he has to wear ear plugs to drive it.
 
carl said:
A lot of us are finding that generic "turbo" mufflers do the job, light, smallish and cheap. They rather replicate the stock muffler sound but with some attitude. If you like the sound that glass packed mufflers make you may not like the sound a turbo muffler makes but straight through glass mufflers need to be rather large to tone down an X or need two of them in series.
Click to expand...
I'm fine with the sound of the turbo muffler. The car has had one on it since 1981. They have them on sale at Pep Boys for 25% off, and the local store had one in stock - $24 including tax. Been thru the glass pack thing with big American V8s in the 60s. I think they are a bit much for my ears at this point. I'm not sure the Turbo muffler is any louder than the dual DCNFs behind my head.
 
My dual IDFed spiders taught me it didn't matter what mufflers I used, the intake howl always trumped (sorry to use that term) the exhaust note.
 
I removed the exhaust system and coated it with Rustoleum 2,000F paint. After the final heat treatment stage at 600F it takes on the appearance of powder coating. The system is much less visually intrusive without the shiney muffler:

1974 X19 Exhaust with Serra Header.jpg
 
A selfless plug for my FS items, but I'm currently selling a Euro 4 -2 exhaust manifold and down pipe. While similar to the stock '74 system, the ports are larger and will flow as much as your header. It also benefits by being an OEM item, designed for our cars. The full length dual down pipe makes for easy custom exhaust fabrication. I also have a used but excellent condition trans mount with cat bracket, if you require it.
 
carl said:
My buddy Erwin has a glass pack and cat on his Bertone and it's probably the baddest and best sounding X ever but I bet he has to wear ear plugs to drive it.
Click to expand...
Ha, I just now saw this post. I don’t wear earplugs, but I was the only car that could be “heard” on the Summit Point video footage
 
I found this Italian Performance Sport exhaust on the web in Italy.

Italian HP Exhaust.jpg


Only problem was all the mounting brackets and where the down pipes mount had to be relocated to line up with my '74's stock positions. Which was extremely difficult to get exactly right, took many many tries but fits like a glove now.

Exhaust sound is yet to be heard but it is like half the weight of the stock USA anchor!
 

Try a few different mufflers. I liked how a flowmaster sounded. Always use a flex joint unless you want it to crack.
 
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