SSIs - Thick or Thin? That is the conundrum.

[thefaculty]

Hi everyone,

Lots here on the advantages of thick flanged SSIs over thin. and here is my conundrum for the '79 SC.

I want to replace my factory heat exchangers for SSIs and a new exhaust. When it comes to the SSIs I was going to have my mechanic do it because I was worried about snapping a stud. Right now I have the CIS out as I chase oil leaks (engine in - yup!) and yesterday deleted the EGR. While undoing the tap where the EGR meets the exhaust minefield this came out really easily so I decided to take a tentative go at the exhaust studs as well. Just to see if they would move a little or not.

I tried one, it came undone nice and easy so I moved to the others. I am very lucky as all twelve unscrewed in full and only 1 brought the stud out with it.

So, right now my studs are intact and I know I can take the original heat exchangers off myself and replace with think flanged SSI. However, my engine has 125k miles on it, it runs well but someday will need a rebuild and when that happens I would most likely bore up to a 3.2. For this I would need the thick flanged SSIs.

Question therefore is... do I go further now and try pulling the original head studs and replacing with the longer studs that accept the thicker flanged SSIs or do I count myself lucky and just go thin flanged with the original studs?

I am very new to all this so the prospect of snapping a stud is very daunting.

What would you do?

Grateful for any and all advice!!

[r lane]

Not sure what you mean by boring up to 3.2. 3.0 and 3.2 are the same bore, 95mm. Unless you plan to change heads, no reason to go to a thick flanged header. I guess thicker is better than thin if there was no down side to the change, but I haven't run into a problem with the thin flanges warping. If you do elect to restud, oxy acetelene torch, and be gentle. You may get lucky, you may have to drill a few. 2 fluted carbide bits. Bob

[thefaculty]

Originally Posted by r lane

Not sure what you mean by boring up to 3.2. 3.0 and 3.2 are the same bore, 95mm. Unless you plan to change heads, no reason to go to a thick flanged header. I guess thicker is better than thin if there was no down side to the change, but I haven't run into a problem with the thin flanges warping. If you do elect to restud, oxy acetelene torch, and be gentle. You may get lucky, you may have to drill a few. 2 fluted carbide bits. Bob

Thanks Bob - just copying what my mechanic and I discussed and due to my inexperience may well have used the wrong term there. Thanks, always learning!! Based on what you've said here I do not think my expertise extends to safely managing an oxy acetelene torch, and that aside, I am doing this in the entrance of my studio where I also live so my thoughts are to perhaps go with thin, save myself the trouble, and when we do upgrade to a 3.2 switch the SSIs then. I believe the thin-flanged should still carry a good resell value a couple of years from now.

[shadowjack1]

I would not temp fate. Go with the thin flanges.

[Jeff Higgins]

The flange thickness is not the only difference between these heat exchangers. The later thick flange design also features a portion of the primary pipe that extends up into the exhaust port. The exhaust port on the later heads that are designed to accept these have an enlarged portion of the port that these primary pipe extensions slip into. They will not even fit into the exhaust ports of the earlier thin flange compatible heads. Here is the difference:

[thefaculty]

Wel there my answer right there then! I’m confused as to why my mechanic would even suggest this then. He’s incredible and really know his stuff! Thanks Jeff!!!

[Jeff Higgins]

Maybe he thinks he can just cut the extensions off. I wouldn't recommend it, though.

This was actually Porsche's first attempt at lining the exhaust ports and providing a heat sink (that thick flange) in an effort to get some of the heat out of the heads. This eventually developed into the ceramic port liners in later motors, I believe starting with the 3.6's.

[Bill Douglas]

There seems to be quite a lot of oil around. i'd check the headstuds and state of the engine before spending money on SSIs.

[tirwin]

I'm just guessing here, but maybe your mechanic was talking about the diameter of the exhaust? As a general rule, when increasing from a 3.0 to 3.2 it is recommended to go with larger diameter. If memory serves, it's 1.5" vs 1.625". Maybe he was saying your exhaust setup might be constricted if you increase the displacement down the road?

Just thinking out loud.

[thefaculty]

Originally Posted by Bill Douglas

There seems to be quite a lot of oil around. i'd check the headstuds and state of the engine before spending money on SSIs.

Thanks Bill. I have just pulled the alternator, fan and shroud off and am cleaning up a huge oil spill. The breather hose was so brittle it was cracked in two and who knows how long for. The dirt here is old, old, old! I have no idea how to check the headstuds but can confirm that when it did leak the areas indicated the sump plug and triangle of death.

If you could help me by telling me what to keep my eyes out for I most certainly will. What I can't afford to get into right now is a rebuild.

[thefaculty]

Originally Posted by tirwin

I'm just guessing here, but maybe your mechanic was talking about the diameter of the exhaust? As a general rule, when increasing from a 3.0 to 3.2 it is recommended to go with larger diameter. If memory serves, it's 1.5" vs 1.625". Maybe he was saying your exhaust setup might be constricted if you increase the displacement down the road?

Just thinking out loud.

Nope - he sent me a list of parts tp order and told me specifically to get the thick flanged SSIs so that we wouldn't have to buy again when we do a rebuild. Weird. He doesn;t love to be questioned but I'll ask him when I next see him.

[911pcars]

Originally Posted by tirwin

I'm just guessing here, but maybe your mechanic was talking about the diameter of the exhaust? As a general rule, when increasing from a 3.0 to 3.2 it is recommended to go with larger diameter. If memory serves, it's 1.5" vs 1.625". Maybe he was saying your exhaust setup might be constricted if you increase the displacement down the road?

Just thinking out loud.

As a reminder, the tube diameter for current SSIs are 1.5”, no matter whether thick or thin flange. 993 heat exhangers are 1.625” and, other than aftermarket headers, a viable options for the 3.2 engine. They’re also lighter than SSIs.

Sherwood

[gtc]

Just get the correct SSIs for your motor (thin flange). Their resale value is good, so you can always sell them later if for some reason you need the thick flange or larger ports (for 3.2 Carrera heads).

[Jeff Higgins]

Originally Posted by 911pcars

As a reminder, the tube diameter for current SSIs are 1.5”, no matter whether thick or thin flange. 993 heat exhangers are 1.625” and, other than aftermarket headers, a viable options for the 3.2 engine. They’re also lighter than SSIs.

Sherwood

Aren't the flanges on the right bank of 993 heat exchangers clocked 90 degrees from those on every previous engine?

Everything else:



993:

[Bill Douglas]

Originally Posted by thefaculty

and am cleaning up a huge oil spill

Ha, that's good news it's a spill and not coming out one or two places.

To check the headstuds you need to take the valve covers off and very gently (no torque applied) check the headstuds for tightness. If they are broken, as you can imagine, they turn with lmost no resistance.

[Flojo]

you nee the thin flange version for your 3.0

congrats on no stud ripping.

[tirwin]

Originally Posted by 911pcars

As a reminder, the tube diameter for current SSIs are 1.5”, no matter whether thick or thin flange. 993 heat exhangers are 1.625” and, other than aftermarket headers, a viable options for the 3.2 engine. They’re also lighter than SSIs.

Sherwood

I know. The thick/thin flange didn’t make sense to me as to why that would be the priority. I would be more concerned about having to swap the SSIs for something bigger down the road if he went from 3.0 to 3.2. At that point the flange doesn’t matter.