SSI Exhaust – Heater System Workaround

[dkirk]

I recently had an SSI exhaust system installed on my 1988 911. As I don’t have access to a rack, I had the work done by Zero to 60 Garage, a premier Porsche shop in Sherwood WI. The challenge was how to plumb the air ducting into the heater boxes as the heater box inlets on the SSI system are oriented differently from the stock exhaust system.



Several methods have been done in the past, including removing the engine mounted electric blower and back dating the engine cooling ducts so air is supplied via the engine cooling fan to each heater box. I thought this was a huge step backward as the electric fan is an improvement over the old school system. For me, keeping the engine compartment totally stock appearing was very important and the thought of a duct running over the cooling fan to feed the passenger side heater box was not acceptable.

Prior to system installation, I noticed that the rear bumper cavity is rather large and unobstructed and seemed like an ideal location to run the duct across to the passenger side heater box. I mentioned my thoughts to Dave Treichel, owner of Zero to 60 Garage and they agreed to give it a go. The end result is that it worked out beautifully – all goals were met and the heating system works as well as it did in stock configuration. The most difficult item to fabricate is the “T” duct, which splits the airflow from the electric blower. This has to fit under the engine pan to keep the stock engine bay appearance. Zach, one of the associates in the shop, fabricated this nice piece made up from the stock stainless-steel cross-over duct. The angles and curves here are somewhat complex so I can’t give dimensions:





Installed, the ducting plumbing is arranged as shown:




The end result is that everything fits and works perfectly. The inward facing lip on the rear valence was drilled in 5 locations (.062” dia drill) such that safety wire is used to hold the duct in place. The installation is neat and unobtrusive.

Being that I’m an over-the-top perfectionist plus an aviation enthusiast, I thought I would compliment this ductwork by replacing it with aircraft-grade 2.5” ID silicone tubing that is wire-reinforced and is rated for-80 to +450 deg F. For the safety wire wrap points and to provide protection of the duct material, I chose silicone sheet baffle seal, .093” thick X 1.5” wide, held in place with .032” dia stainless safety wire.
All of these components are available from Wicks Aircraft. It takes 8 feet of ducting and 4 feet of baffle seal to do this job. At $16.40/ft, the ducting isn’t cheap but my Porsche’s worth it.

With the duct installed in the rear bumper cavity, this is what it looks like from the passenger side heater box attach point:



The driver side attach point looks as follows:



A view through the bumper cavity showing the duct in place appears below:



Testing the heating system once underway indicates that it works very nicely with no noticeable changes in either airflow or air temperature when compared to the stock system. My engine bay still appears totally stock and uncluttered:



I’m of the opinion that this would be a valuable kit to market to those ’84 to ’89 911 owners converting to an SSI exhaust system, who would want the features previously described. The “Y” pipe could be a plastic component as only ambient temperature air flows through it.

Most importantly, the SSI system is a valuable upgrade in several respects. The engine torque curve seems noticeably increased everywhere, even low down in the rev range. The system is complimented by a Dansk “Sport” muffler, 2-in, 1-out. The equal length of all header branch lengths lends an old-school quality to the exhaust note – very 911 S sounding. And the all-stainless construction will never rust. Now I need to invest in a mirror for my garage floor so I can admire these nice parts without crawling under.

[Jack Stands]

Those SSI heat exchangers are truly works of art, though may be an issue as they remove the catalytic converter (if you make emission inspections in your area). You did a nice job of keeping the engine bay looking stock.

[Discseven]

Dave...
.

[pmax]

Originally Posted by dkirk

Off topic question, what's that at the top left corner where the CC unit originally was ?

[dkirk]

pmax - That is the cruise control unit as fitted to the '87 through '89 models.

[pmax]

Originally Posted by dkirk

pmax - That is the cruise control unit as fitted to the '87 through '89 models.

Ah, got it. It does reduce clutter with fewer vacuum hoses in that area of the engine compartment. My 87 still has the "old school" variant so 88- then ?