Confirming SSI choice

[Iciclehead]

Hi guys, just getting ready to put in a full order with our host, one of the parts I am buying are the SSI heat exchangers.

The engine build has not yet been started, but I have most of the parts collected including a new engine case, new 74.4 mm crankshaft, Mahle 98 mm P/C's with the 10.3 compression, Carillo rods, rebuilt heads with dual plug, new valves, titanium retainers (thanks Steve!) and all the various geegaws and doodads that are required.

The engine will have an EMS on it (not yet settled which one) and likely 911S cams, coil on plug (if I can ever find a set up I like) and will use the PMO throttle bodies (already got those...they are beautiful!!).

Exhaust with SSI's are a little tight I know (as the engine will spec out at 3.4 litres), but I like them and I am not seeking maximum horsepower, just a good tractable engine that gives decent horsepower (I am hoping for maybe 260hp), good fuel economy and decent starting and driveability.

Question is, which SSI's to buy? The heads are from a 1979 Euro 911SC, have not been ported and I am presuming that the correct choice are the thin flange SSI's with the O2 bung in it. Note that these will be cut up to fit catastrophic perverters as per a thread on this forum.

Is that the best choice? Since I am replacing all the studs in the heads, would I be better off with the thick flanges?

Any advice would be appreciated....

Thx

Dennis

[KTL]

Even though you're replacing the studs, I wouldn't go with the thick flange. Reason being is because the thick flange SSI is sized to fit the smaller port SC heads or larger 3.2 Carrera (larger than "big port" SC) heads.

You would much rather have your headers port matched vs. having the thicker flanges. Port matching is more important for performance. Thin flanges are not a detriment. They're plenty rugged enough.

[911pcars]

You may already realize the recommended size for exhaust tubes for a 3.4 liter engine is 1 5/8" or larger depending on your end use. SSI's use 1.5" tubes which might cost you power you may or may not feel with your butt dyno. Other mods (e.g. chip, sport muffler, etc.) would provide cumulative results.

An alternative system uses 993 factory heat exchangers (1 5/8"). However, some fabrication is needed to fit them (re-clocking pass. side flanges), revisions for cabin heating and modifying the inlets (2) to your muffler.

The above costs might be a wash or less compared with new SSIs, but probably more if you want a bolt-in 993 kit.

More info here:
993 heat exchangers with 3.2 - Google Search

Sherwood