2-1 Downpipes Distinguished

[opus10583]

There are three offered by the usual sources, yet Bradley Artigue lists the same part number for '67-'74; so what are the differences?

Thanks,
Mark

[Sunracer]

Here's what I recall over the years from cars I've had apart:

4 studs from Mani to HP till the advent of the FI cars in 1980, these also have a bung for the O2 sensor

after 75 once catalytic converters were added, the routing changed, and the down pipe routed away from the transmission to the outboard edge of the car where the converters were hung. Prior, they ran inboard as the exhaust was hung along the driveline.

1438 stuff has smaller ports than the later 1608, 1592 and later engines.

Two liter stuff is the biggest.

This is all from memory so corrections from other posters might be in order : )

PB : )

[opus10583]

I saw a post in another forum which indicated the 1438/1608 manifold had the largest runner and outlet sections.

"larger ports thru the middle and larger outlet holes (37.5mm as opposed to 32.5mm)"

...So I would expect the earlier downpipe to match. Wondering if anyone knows the specs of what's offered out there.

[Sunracer]

the 1438 stuff I have seen is tiny

[bradartigue]

The reference provided by FIAT was for the replacement part numbers, not necessarily the new parts. So they had a single part # for replacement and it never matched the original part. Kind of goofy. I have different manifolds for each engine type (1438, 1592, 1608, 1756, 2000) and within types (2 types for the Spider 2000, for example).

[opus10583]

The reference provided by FIAT was for the replacement part numbers, not necessarily the new parts. So they had a single part # for replacement and it never matched the original part. Kind of goofy. I have different manifolds for each engine type (1438, 1592, 1608, 1756, 2000) and within types (2 types for the Spider 2000, for example).

Now we're getting somewhere!

Hi,

Based on what you know; what should I be looking for in order to replace the 4-1 of my '78 1800 with the most mellifluous 4-2 manifold / 2-1 downpipe combo?

I'm not looking to "hot rod" a 33-yr old FIAT, I want it to sound like the soundtrack of my second favorite dream.

Thanks,
Mark

[bradartigue]

Any of the 4-2 types from the 1800 series will do. They are quite common. I'd get the FIAT setup and not a header, unless you just want a noisy, hot(ter) enginer compartment.

Likewise any of the 4-2 types from the 79/80 CS2 that had 4-2 (not common but there is one in my shop right now, so not really rare either) but you may have to do some fabrication work so it does not hang too low. Same with the later 4-2 installed on the fuel injected cars.

The earlier stuff from the 1592 is too short, you'd have to add a spacer between the manifold and downpipe; and the 1608 and 1432 were too small and from a different engine series, you'd do a lot of work for no gain, probably a loss since the pipes run differently and are smaller.

[opus10583]

Thanks, Brad; but now I'm even more confused:

I thought the only 1800 with 4-2-1 was 1974?

[Sunracer]

Opus, what is the year of your car, and did it originally come with a catallytic converter, this will make it easier to answer your question. PB

[opus10583]

1978 49-state 1800. no cat, 4-1 exhaust manifold. But my question, such as it is, has nothing to do with the car's current or OEM setup.

I want to fit a stock FIAT 4-2 manifold and 2-1 downpipe system, and there is a tremendous amount of conflicting, contradictory and often plainly wrong information on the Web. Even here.

I've seen everything from 'the 1400 manifold is the best and bolts up just fine to an 1800' to 'nothing but 1974' for the manifold and then 'one-size fits all' to 'the early stuff is soda straws' on the downpipe...

I am very confused, and need to get something into place soon.

[Sunracer]

1978 49-state 1800. no cat, 4-1 exhaust manifold. But my question, such as it is, has nothing to do with the car's current or OEM setup.

I want to fit a stock FIAT 4-2 manifold and 2-1 downpipe system, and there is a tremendous amount of conflicting, contradictory and often plainly wrong information on the Web. Even here.

I've seen everything from 'the 1400 manifold is the best and bolts up just fine to an 1800' to 'nothing but 1974' for the manifold and then 'one-size fits all' to 'the early stuff is soda straws' on the downpipe...

I am very confused, and need to get something into place soon.

if you are going to fit an entirely new system, a 2 liter FI will be the best choice. 6 bolt flange to prevent the leaks you can get with the earlier 4 bolt flange between the manifold and down pipe. The exhaust manifold will bolt right on. As Brad says it might hang a little low-about an inch max. An exhaust shop could remedy this easily. It will allow you to fit an oxygen sensor for tuning if you wish, or the hole is easily capped.

If you are not going to do a new system then the question becomes-does your existing system run under the passenger floor about half way btw the trans tunnel or does it turn to the center of the car and run along side the transmission. I am in Ca and have seen few federal cars. PB