Converting: Cali Carb Exhaust to 4-2 manifold

AKimball92

AKimball92

True Classic
Greeting all,

My next project consists of converting my original California emissions style exhaust to something using the 4-2 manifold. My car came with a 4-1 manifold, cat, and muffler. I have since replaced the cat and would actually like to keep it (tree hugger at heart). I purchased a 4-2 manifold, I believe one with the outlets going to the left of center. My car currently has the downpipe with the cup at the end found here that mounts directly to the 4-1 manifold:
https://www.midwest-bayless.com/Fia...downpipe-carb-na-fiat-x19-1975-80-oe-nos.aspx

Was there ever a OEM exhaust setup that has a 4-2 manifold with a catalytic converter?

I need to make a custom 304 SS 2-1 downpipe to fit but would like to make the lower joint match other off the shelf exhaust systems. I think I need a new but shorter single pipe downpipe to link the custom 2-1 pipe to the cat joint or does my 2-1 pipe need to stretch all the way to the cat? I think the latter option would be the better route but want to match the OEM design as much as possible for now.

Stretching the 2-1 all the way to the cat gives me more flexibility to tune the secondary lengths. Calculations coming up. If possible I would like to have the power match 3500-4000 rpm (performance street). I think I just answered my own question but would like everyone's feedback.

Once I get the system designed, pie cuts made, and welded together I plant to ceramic coat the manifold, 2-1 downpipe, and maybe the extension to keep everything looking fresh and cool.

T minus 58 days and counting to targeted completion!
 
kmead said:
No there was never a factory cat 4:2:1 system
Click to expand...
That's what I figured midway through my question. I think I might have to do the 2-1 directly to the cat. How do the straight to muffler systems work? Where is the flexibility in that system?

I attached some quick pictures of my current muffler cat system, taken while running late for work. I think I might purchase a new sprung 3 bolt joint and weld it back to the inlet pipe to the cat. I don't think I will be able to save that part. Then my 2-1 pipe will probably Y just above crossing thought the body opening (if the tuned secondary length is best near there).
IMG-3671.JPG IMG-3672.JPG
 
AKimball92 said:
Greeting all,

My next project consists of converting my original California emissions style exhaust to something using the 4-2 manifold. My car came with a 4-1 manifold, cat, and muffler. I have since replaced the cat and would actually like to keep it (tree hugger at heart). I purchased a 4-2 manifold, I believe one with the outlets going to the left of center. My car currently has the downpipe with the cup at the end found here that mounts directly to the 4-1 manifold:
https://www.midwest-bayless.com/Fia...downpipe-carb-na-fiat-x19-1975-80-oe-nos.aspx

Was there ever a OEM exhaust setup that has a 4-2 manifold with a catalytic converter?

I need to make a custom 304 SS 2-1 downpipe to fit but would like to make the lower joint match other off the shelf exhaust systems. I think I need a new but shorter single pipe downpipe to link the custom 2-1 pipe to the cat joint or does my 2-1 pipe need to stretch all the way to the cat? I think the latter option would be the better route but want to match the OEM design as much as possible for now.

Stretching the 2-1 all the way to the cat gives me more flexibility to tune the secondary lengths. Calculations coming up. If possible I would like to have the power match 3500-4000 rpm (performance street). I think I just answered my own question but would like everyone's feedback.

Once I get the system designed, pie cuts made, and welded together I plant to ceramic coat the manifold, 2-1 downpipe, and maybe the extension to keep everything looking fresh and cool.

T minus 58 days and counting to targeted completion!
Click to expand...

This is what I did:

https://xwebforums.com/forum/index.php?threads/cast-iron-4-2-exhaust-manifolds.32840/#post-278875

It has been a couple of years now and I'm very happy with the result!

Cheers,
Dom.
 
AK, I think when you do the calculations you will find the secondary tubes need to be rather long to achieve your power-band goals. That will pretty much preclude any use of the existing downpipe, so something will need to be designed to fit everything together. Likewise for other existing downpipe options like from the Yugo. It might be a real challenge to get enough secondary length and retain the cat. I'll be interested to see what you come up with. I need to build one for the same reason (replacing the single outlet CA manifold with a dual), but I don't intend to keep the cat...guess I don't trees as much you :).

To add some "flex" to the system (which you definitely should), consider something like this:
download.jpg


Also consider having the manifold done when you ceramic coat the rest of the system. It will significantly help with thermal management in the engine bay.
 
Okay. What i can tell you is that - no there never was a factory X1/9 exhaust system that used a cat and a 4-2 manifold.

For those markets that did not require a cat, Fiat always used a 4-2 manifold. And a fairly simple one piece muffler assembly. Like this:
x19 muffler.jpg

Note the downpipes were always part of the muffler. And that the downpipes bolted right to the manifold and came straight down and UNDER the rear chassis member - right about where the engine crossmember bolted on. Note also the muffler was not hung from the body at all - it bolted to the engine/tranny in 2 places (via the one bracket welded to the muffler that bolted to an extension of the lower engine mount, and via another bracket that connected it to the tranny ). And that the tailpipe always exited to the left via a cut-out in the valance. There were a few different manifolds and mufflers used throughout the years, but all were basically the same. This type system was used in most markets worldwide and even on the 1974 only USA model.

For those markets where a cat was required (mostly North America) Fiat always changed to a single outlet exhaust manifold. From there a single pipe made a series of really tight bends and exited the engine compartment on the right side through a new hole in the body above the chassis member. And then snaked around and back into a transverse cat. Then out the end of the cat and a 180 bend into a transverse muffler. Then a tailpipe exiting through a cut-out in the valance in the right side of the car. The muffler and cat were hung from the body, which thus required one or two flex joints in the system.

All of this means that - for those of of us in N. America with '75 on X1/9s wishing to use the better flowing less restrictive euro-type 4-2 manifold - there is no real easy bolt on solution......

Even after finding a euro-type dual outlet manifold - and watch out there are several different types - you really cant just use the matching euro muffler - because the tailpipe exits on the wrong side. Yeah - you could fill in your existing right side cut-out, and cut a new one on the left.....

Or perhaps find a euro performance muffler that has two or four exits under the middle of the car......yes they exist but shipping from europe can get pricey.......

Barring those options.....it is now custom time.....and full of PITA snags.....

First problem is finding a double outlet flange to start with. i know of no source for new ones. Perhaps salvage one from an old '74 muffler. Or have one made....Then have dual downpipes made to head off in the direction of a muffler. And then at some point a collector made to end in a single collector.

You could make the downpipes go down and under the chassis member. And then turn to the left and go into a collector and then into a stock-type USA muffler. Not easy... Or I suppose follow the USA routing of the downpipe snaking around and into a cat first....but that would be really difficult with all the tight bends required. I guess you could try to route the downpipes under the chassis member and swing around 270 degrees into a stock-type cat, but the downpipes would then have to hang really low to go under the cat first.....

Another option - easier - would be to start with a Yugo downpipe like this:
https://www.midwest-bayless.com/Fia...pipe-2-1-yugo-sohc-x19-w4-2-manifold-nos.aspx

That would bolt onto any X1/9 euro manifold and also form a collector. From there you would only need a single pipe joining that to a stock USA muffler. Much easier.....

Good luck. Hope this helps in some way. Let us know what you end up doing. Doug
 
Like everything else you will find a 'trade-off' decision to make. To get your desired "secondary" length you most likely cannot use the Yugo DP, its way too short. So do you sacrifice the power band in favor of simplifying the design, or do you create a complete custom DP with sufficient bends to allow it to snake around all the obstacles mentioned by Doug. But I'm sure after you've done the calculations and get the manifold in place it will become more clear.

Should you decide to create a custom DP, for the flange-plate to attach it to the dual-outlet manifold. I will be taking the drawing to a shop that cuts custom pieces like this for an estimate to make one. If it works out there might be the potential to get a couple extras made. However it might be awhile before I get over there.
 
I originally replaced the exhaust on my ‘85 FI car with an IAP/Vick’s header and this exhaust :

A1D6BE39-B506-45CD-B8B6-A5661A025C1A.jpeg


I switched to a Yugo manifold and down pipe extended to mate with the exhaust when the smog nazis cracked down:

314D4995-D00E-4954-866F-0394F6E836B5.jpeg


Maybe not ideal in runner length, but far better than the stock piece of crap.
 
Simplest way to make a dual pipe downpipe is to re-purpose a downpipe from another Fiat model. The downpipe from a 128 coupe is a good candidate. You definitely want to go under the chassis member near the engine support crossmember, and NOT try and snake your way thru the original USA spec exhaust hole in the bulkhead.

https://www.ebay.com.au/itm/332232303194

the downpipe from one of the later model FWD cars (like a Tipo) is larger front pipe sizes but doesn't fit the X19 chassis as neatly as the 128 coupe item.

The manifold (7691880) from the later model front drive cars (like a Tipo) is definitely larger thru sizes (ports) in the manifold, and flows best of all available cast iron dual outlet manifolds. It's not just the port size at the flange that matters (which is what everyone has measured in various threads) but the dimensions inside the manifold (a lot more difficult to measure) When you have a selection of dual pipe manifolds available in the one place (as I have on my bench) the differences are quite obvious.

a very simple front pipe made from a 128 coupe downpipe that mates to the standard large USA spec hanging muffler
bmck_exhaust.jpg
bmck_exhaust_2.jpg


SteveC
 
To help illustrate the difference in lengths between the Yugo downpipe (top) and the Fiat 128 downpipe (bottom):
7053.jpg
s-l1600.jpg
 
wow thank you guys for all the advice. It's a lot to consider in designing my exhaust. I was hoping to either snake the dual tertiary pipes through the stock US hole above the cross member to keep it higher off the ground but if it's not feasible it's not feasible. The last thing I want to do is to back up too far into a curb and ruin who knows what. I've personally made my own pie cuts and custom exhaust for our FSAE team and planned to go down that route. Honestly I considered doing a mock layup in PVC and seeing how it goes.

The standard Euro 4-2 straight to muffler, while flow numbers are certainly better, that looks like a lot of mass cantilevered off the engine. Did they tend to crack at all? I've seen various threads of people complaining about cracked exhaust but those might be mostly for headers so maybe I'm wrong.

I wish I would be able to remove the exhaust but my conscious would get the better of me.

I do have access to machine shop help at reasonable prices. I could fabricate the 2 port plate, shave one side for flushness and then either give them the manifold to match or drill and grind them myself.
 
The '74 X1/9 used a 4-2-1 system. The factory 4-2 manifold works very well coupled to a 2-1 pipe and routed between the control arm mounts. I used this manifold mated to a custom 2-1 exhaust for the first system I built for my '74 autocrosser. It worked quite well for a simple, cheap performance system.
 
Hey Andrew. Well your desire to retain a cat is certainly honorable, but that would be a very difficult task. Does that mean you will also be retaining the air pump and all the other emissions crap LOL ??

If it makes your conscience feel any better....in your year I think only the California spec X1/9s came with a cat. The other 49 states did not......

I reckon your car - if I recall being a Japanese spec ? - was from the factory probably made to California spec due to stringent Japanese emission standards at the time. which would seem to be the only logical reason Japan got a LHD X1/9.

Good luck making a flange from scratch.....and even better luck in finding someone who can bend pipes of the proper size to that tight of bends. Yeah - you will probably have to pie cut to get the bends that tight. I reckon the flow losses will outweigh any gains you might achieve by having slightly longer secondaries.....

Perhaps.....think again about just going out the bottom.....way easier.

And make it even easier by availing yourself of the advances and development that is the pinnacle of Slavic technology by starting with a Yugo downpipe. and hey - you would get to tell people that you you vastly improved the performance of your X1/9 by......using parts from a Yugo.....LOL :)
 
Steve Hoelscher said:
The '74 X1/9 used a 4-2-1 system. The factory 4-2 manifold works very well coupled to a 2-1 pipe and routed between the control arm mounts.
Click to expand...
Wasn't the US spec '74 the same design type as the Euro system, like in the picture RX1900 showed?
x19 muffler.jpg

So not a separate downpipe, but included one piece with the muffler?
 
That might be one source for the basic components to make a custom downpipe; cut the tubes off a used '74/Euro muffler. Looks like they will get you to the right spot underneath the chassis. From there you can bend around to the side and loop back toward the cat. Merging the two pipes near the cat will give the longer secondary length desired.
 
AKimball92 said:
The standard Euro 4-2 straight to muffler, while flow numbers are certainly better, that looks like a lot of mass cantilevered off the engine.
Click to expand...
I think that was the reason for the extension off the lower engine mount (see first pic below) on those early models, to help support the weight of the exhaust. The theory might be to make the entire exhaust a solid structure that 'moves' with the engine as a unit. But in my opinion that isn't ideal. Vibrations (both engine mechanical, and exhaust sound waves) are rather extreme in an exhaust system, so just supporting the weight may not be sufficient. Both in terms of transmitting noise into the chassis, and possible breaking. I seem to recall posts where that lower mount extension was cracking/breaking for some. Especially if you add the extra mass of a cat to it.

Pretty much all modern exhaust systems use some sort of flex-joint to allow movement between the manifold and the rest of the system. Closer to the manifold would be ideal, which in this case will mean two flex-joints (see the second pic below for an example...non-Fiat). But even having one flex-joint (like the one shown in a earlier post) at the merge point for the two secondary pipes will help to isolate the cat and muffler.

img_2963_1.JPG

251.117S.jpg
 
That’s how I made my custom exhaust for the ‘74. It’s still fully supported by the drivetrain but has a flex joint to keep things from cracking:

E7E0D44F-8DA6-4109-98AD-EB7EE1809756.jpeg

9A324C8A-3AF2-418C-8939-F5AE4A98A5C0.jpeg



Dr.Jeff said:
I think that was the reason for the extension off the lower engine mount (see first pic below) on those early models, to help support the weight of the exhaust. The theory might be to make the entire exhaust a solid structure that 'moves' with the engine as a unit. But in my opinion that isn't ideal. Vibrations (both engine mechanical, and exhaust sound waves) are rather extreme in an exhaust system, so just supporting the weight may not be sufficient. Both in terms of transmitting noise into the chassis, and possible breaking. I seem to recall posts where that lower mount extension was cracking/breaking for some. Especially if you add the extra mass of a cat to it.
Click to expand...
 
The late model cars went back to a rigid mount on the transmission mount just like the early cars. They don’t have that other mount arcing up over the side that Mark shows on his, but it effectively locks the exhaust to the engine.
 
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