3.2 SSI internal diameter of primaries?

[gliding_serpent]

GMR: I believe so for the SC. Both are 35mm. The 3.2 has a 38mm exhaust port (41 or something similar but it tapers to 38). My understanding is that the 3.2 SSIs have an extension that properly tapers things to 35mm.

[GMR911]

That would be interesting

[911pcars]

Originally Posted by gliding_serpent

Robert Diotte, the north america dansk rep just said 36mm.

Banging head on wall. I asked him to confirm.

So 35, 36, 37, 37.8. Again, i suspect 35 and the rest is misinformation.

I imagine the difference is that SSI used US-sized tubes and the Dansk tubes are manufactured with metric tubes. See the following chart: Yellow highlights 3 columns: OD - wall thickness - ID.



It seems 38mm tube (1.496" close enough to 1.5"). Manufacturing jigs wouldn't be affected and this tube is available in various wall thickness.

Using thinner wall material (1mm) results in a slightly larger ID (36mm or 1.417"), but 1mm is pretty thin. This is all conjecture on my part. Can this be confirmed?

Sherwood

[theclaw]

So they weren't that buried in the attic after all. Here are the OD measurements from part number 91-917SSI















This inside diameter was a little harder to get a precise measurement because it is tapered but my micrometer was just long enough to get in there. I got 35.3mm



Jeff

[911pcars]

Originally Posted by theclaw

So they weren't that buried in the attic after all. Here are the OD measurements from part number 91-917SSI

This inside diameter was a little harder to get a precise measurement because it is tapered but my micrometer was just long enough to get in there. I got 35.3mm

Jeff

Thanks. 35.3mm is 1.389", close enough to 1.375" as widely accepted for SSIs.

[theclaw]

Originally Posted by 911pcars

Thanks. 35.3mm is 1.389", close enough to 1.375" as widely accepted for SSIs.

I'd say close enough because some of my measurements may have been +/- 0.05mm.

[78SCRSMAN]

Originally Posted by Bill Verburg

expanding gas flow doesn't like step transitions, the best situation is matched ports that taper from one size(the port) to the tube size which for a 3.2(long or short stroke) will be 1 1/2 to 1 5/8" the smaller size being better below ~5500 the larger better above, for street and/or A/X the smaller size will probably work slightly better. but cam selection and where the sweet spot of the torque curve affect this too.

Thanks Bill!
I'm not a cam expert but I'm told the DC24's (with 108 lobe centers) I have are not great for high revs so I'm probably better off with 1.5" headers (35mm ID) it seems. That will save me the hassle of porting the exit transition to 38mm.

[gtc]

The old ones all have the same size pipes, it it just the flanges and exhaust port adapters that vary.

[RarlyL8]

John only used one size primary pipe for all SSIs. It was done the same way for 30+ years. The flanges and gasket protectors are where the difference lies to accommodate port sizes of the various engines.

[scarceller]

I run SSIs on my modified 3.2L and it pushes about 230HP at the wheels at 6000RPMs but after 6000RPMs HP drops off real quick, most likely because the SSIs can't flow after that.

And after 5800RPMs my torque takes a big nose dive!

But for a street 3.2L the SSIs work well.

[78SCRSMAN]

Originally Posted by scarceller

I run SSIs on my modified 3.2L and it pushes about 230HP at the wheels at 6000RPMs but after 6000RPMs HP drops off real quick, most likely because the SSIs can't flow after that.

And after 5800RPMs my torque takes a big nose dive!

But for a street 3.2L the SSIs work well.

I would think TQ and HP would level off if flow were a problem, not go down. You might wannna look at fueling, timing and maybe even cam timing.!?

230 HP at the wheels sounds nice tho! If I can reach that, I'll be a happy camper!

[gliding_serpent]

Originally Posted by scarceller

I run SSIs on my modified 3.2L and it pushes about 230HP at the wheels at 6000RPMs but after 6000RPMs HP drops off real quick, most likely because the SSIs can't flow after that.

And after 5800RPMs my torque takes a big nose dive!

But for a street 3.2L the SSIs work well.

230hp at the wheels is 264.5 at the fly is you factor 15% loss. Pretty sweet gains. I also agree that there is likely more to it than just primary size. One who knows more than I, suggested that the SSIs are fine and it is usually the sport mufflers that become the first limiting factor for flow/power at high end.

I have been studying Steve Wongs dyno charts on his website. The SSI setups have the real meat of their torque curves between 4.5k rpm and 6.25k rpm, with the peak around 5.25k. To me, that is ideal for a car that maintains a stock rev limiter. Larger headers with open exhausts have torque curves that peak closer to 6k or 6.25. Great if you increase the rev limiter, otherwise I would argue you are losing potential. I am obviously generalizing.

SSI setups with internal engine mods combined with a higher velocity muffler are getting into the 260's+ just like scarceller above. The SSI obviously does not have a defined "performance wall" but like anything, all components need to be tuned together for max benefit. The smaller primaries will always favor mid-range power however.

I mean, look at how small the 930 turbo exhaust ports are... 38mm for the 3.0 turbos, and 36mm for the 3.3's. At 260+ and 300hp with similar torque, neither had too much of an issue with power. The 3.2 is 38mm.

Many factors at play, primary diameter is only one.

[DG624]

I had some SSIs but sold them due to the smaller tubes to a 3.0L owner. I would like to see something that allows 3.2L cars to benefit from 1.5 or 1.75" primaries.

[panzerfaust]

Originally Posted by Bill Verburg

expanding gas flow doesn't like step transitions, the best situation is matched ports that taper from one size(the port) to the tube size which for a 3.2(long or short stroke) will be 1 1/2 to 1 5/8" the smaller size being better below ~5500 the larger better above, for street and/or A/X the smaller size will probably work slightly better. but cam selection and where the sweet spot of the torque curve affect this too.

hello bill

you dont want to match ports to flange diameter of exhaust manifold. ideally it should be 1.5-2mm larger than the port exit surface. you need to step for anti-reversion for proper flow.

1 5/8s SSI would be a good size on a 3.2 im thinking

[DG624]

I sent Eisemann an e-mail about primary tube size and this is the reply.


Dear Mr. Greene,

we offer the heat exchanger for the G Model in two versions:
1. heat exchanger with 38 mm outer piping diameter (1,49606”)

2. heat exchanger with 42 mm outer piping diameter (1,65354”)

Mit freundlichen Grüßen / With best regards

i.V. Sven Johann



Eisenmann Exhaust Systems GmbH
Saarstraße 45
71282 Hemmingen, Germany

Telefon:
+49 7150 9574-124

Telefax:
+49 7150 9574-120

E-Mail:
johann@eisenmann-technik.de


Internet:
Sportauspuff für Audi, BMW, Mercedes, Mini, Porsche und VW - Eisenmann Exhaust Systems GmbH


The larger 1.65354" outer pipe would be close to 1 5/8" if the tube wall thickness is similar to SSI. Seems like a viable option for larger engines.

[911pcars]

Originally Posted by gliding_serpent

230hp at the wheels is 264.5 at the fly is you factor 15% loss. Pretty sweet gains. I also agree that there is likely more to it than just primary size. One who knows more than I, suggested that the SSIs are fine and it is usually the sport mufflers that become the first limiting factor for flow/power at high end.

I have been studying Steve Wongs dyno charts on his website. The SSI setups have the real meat of their torque curves between 4.5k rpm and 6.25k rpm, with the peak around 5.25k. To me, that is ideal for a car that maintains a stock rev limiter. Larger headers with open exhausts have torque curves that peak closer to 6k or 6.25. Great if you increase the rev limiter, otherwise I would argue you are losing potential. I am obviously generalizing.

SSI setups with internal engine mods combined with a higher velocity muffler are getting into the 260's+ just like scarceller above. The SSI obviously does not have a defined "performance wall" but like anything, all components need to be tuned together for max benefit. The smaller primaries will always favor mid-range power however.

I mean, look at how small the 930 turbo exhaust ports are... 38mm for the 3.0 turbos, and 36mm for the 3.3's. At 260+ and 300hp with similar torque, neither had too much of an issue with power. The 3.2 is 38mm.

Many factors at play, primary diameter is only one.

Two: Boost pressure, not an insignficant factor that minimizes the need for big ports. Boosted and normally aspirated engines have different needs.

Sherwood