Am I choking my 3.2?

[Thrasher]

Apparently when my PO had his shop swap out a perfectly good set of B&B headers and muffler for a stock exhaust to meet emissions for the sale, he wasn't being very particular. I checked the part numbers last night and I found out that my 3.2 '84 Carrera has a 3.0 '83 SC exhaust system.

I know the pipes for the SC exhaust were considered even a bit small for the 3.0, so I'm thinking they're really too small for my 3.2

I actually have the B&B exhaust in my basement, but was thinking I'd sell it because of emissions, to use the proceeds to buy a Steve W. chip, various other upgrades and cover the entry into a few DE's.

I recently bought a stainless euro premuffler to replace the cat in the OE system, and had planned to add a second outlet in the stock Bischoff muffler for better sound/flow. I could easily put the cat back on every two years in time for my emission test, but swapping out the headers/muffler/oil line every two years is sounding like a real bummer - unless it's really worth it.

The car is primarily used for fun, not commuting. I plan on doing 1-2 DE's per year, but no racing.

What would you do?

[RickM]

IMO, a properly sized exhaust will give one of the biggest HP bangs for your buck. If the header/exchanger IDs are smaller than the 3.2 then I'd swap out to at least 3.2 diameters. Add to that the premuff and second outlet sound and you're set.

Someone here for sure will have the sizes.

[jmohn]

I don't think there were any serious differences between the SC 3.0 and the Carrera 3.2 exhaust systems. The after-market headers (SSI, etc.) are the same for both engines (the real HP upgrade being the header design not pipe size).

Jerry M
'78 SC

[Thrasher]

I thought I read somewhere that the stock header pipes in the Carrera heat exchangers were a larger ID than the SC.

I think you're right about the SSI's being the same pipes for SC and Carrera, with the only difference in the Carrera model being flange thickness.

Can anyone verify the ID of a Carrera header pipe vs. the SC?

Also, the muffler has a different part number - anybody know how these would differ (from '83 SC to '84 Carrera)?

[Thrasher]

I removed the SC headers today and measured. The ID of the header pipe is 35 mm. The exhaust port opening is 40 mm - identical to the ID of the B&B header pipes.

I still don't know the ID of the Carrera header pipe - can anyone help?

[911mot]

84 Euro Carrera Header:

[Thrasher]

Interesting. I used a digital caliper to measure the SC header. The SC measured that way looks to be about 2-3 mm smaller in diameter.

That comes out to about 172 mm, or about 16% more area (1134 sq mm vs 962 sq mm). Hmm...

I keep thinking the Porsche engineers enlarged those pipes to accomodate the 3.2's greater exhaust volume than the 3.0

Would a dyno see that difference?

[Bill Verburg]

The Carrera pipes are not only bigger but double walled, keeps the heat in the pipe and raises the speed of the gases through them.

[Thrasher]

Bill,

This all became moot when I re-acquired the B&B headers and muffler that the PO had a shop remove prior to the sale to me. I realize that the concensus is that the B&B pipes are actually a bit oversized for the standard camshaft 3.2, but the sound is great and it's an all-stainless system. I'm keeping the SC exhaust for bi-annual emissions testing.

I'm really pleased with the look and sound of the B&B, although it's possible I've lost some lower end torque. My question is this: can a chip regain me some of that torque? I'm running a stock '84 chip, which I understand is very conservatively mapped for 87 octane. We have 93 octane here, so I'm thinking a Steve Wong chip would be a good thing even if I don't pick up gains with the exhaust.

Craig

[Tyson Schmidt]

The 3.2 Carrera has 38mm exhaust ports. The SC are 35mm.

SSI's are 35mm, which is why they make a bigger difference on a 3.0 than a 3.2. They are too small for a 3.2.

You should put Carrera exhaust back on that 3.2.

[DG624]

I read that for the 3.2 you need 1 5/8" to 13/4 (track). Does SSI make a 1 5/8" system and if not then who does? Why change to a system that does not fit?

[Bill Verburg]

Does SSI make a 1 5/8" system

No, All SSIs have primary ID of 1 3/8"(1 1/2" OD)

B&B are available w/ either 1 1/2" ID(1 5/8" OD) or 1 5/8" ID(1 3/4" OD)

There are other sources for headers only such as George Narbel, 901 Shop and Bursch

[DG624]

Bill,

Looking at the exhaust systems GHL, B&B, SSI...some seem to be unequal exhaust length. SSI is covered so it is hard to tell. GHL seems too short and B&B seems to be more equal length. I have tried to contact the SSI company but can't find it. DOes the Narbel shop or others have heater boxes. If I am going to the trouble of replacing I would like to get some power and weight improvement.

[Bill Verburg]

Of those mentioned SSI is closest to being equal length.

That said the most recent research says that equal lengths aren't the most important criteria, collectors and transitions from the collector seem to have much more impact on ultimate performance.

In addition the 5^th cycle of a 4 stroke engine ie the exhaust scavanging time, is almost non existant w/ smog cams.

[RideShoot&Drink]

Thrasher, I have a complete exhaust system from 85 Carrera: heat exchangers, cat, muffler, cross pipe. All is in pretty good shape. Email me if interested.

[Thrasher]

Originally posted by Tyson Schmidt
The 3.2 Carrera has 38mm exhaust ports. The SC are 35mm.

SSI's are 35mm, which is why they make a bigger difference on a 3.0 than a 3.2. They are too small for a 3.2.

You should put Carrera exhaust back on that 3.2.

Tyson,

are you saying I should remove the B&B headers and single-out muffler to go back to a single outlet Carrera exhaust?

I'm thinking you're under the impression my car is still running the SC pipes, which I'm not. I'm only holding onto that setup for emissions.

Craig