Darryl's 3.0 CIS to 3.2 "Short Stroke" Engine Project

Last Updated on January 31, 2025

Most Current Photo of the Engine Being Converted

PROJECT SYNOPSIS

November 2024 - The Decision to Re-Engine my 1974 Porsche 911 - A funny thing happens about the time one turns 65 years old. I'm starting to see my life trajectory realizing that you don't see many 80-year-olds driving, let alone working on their antique Porsches. I just wrapped-up the complete mechanical rebuild of my 1974 Porsche 914-4 I've owned for over 30 years. This work focused on increasing it from a 1.8 to a 2.0 liter, replacing the problematic stock L-Jetronic fuel injection with Weber 40 IDF carburetors and using a camshaft profile that takes full advantage of them. The result is it has completely changed my view of stock vs. performance engines. I've got to say my 914 is so much more fun to drive with significantly more power and certainly much easier to keep running without that antique fuel injection system. This epiphany as my life enters its "4th Quarter" has made me look at my 1974 Porsche 911 from a completely new perspective. Like finding the perfect sad little mutt at the shelter, I ran across my 911 out walking my dog, sitting in my neighborhood European car repair shop for months waiting for of all things, a window regulator rebuild and an owner loving his temporary free garage space.

A diamond in the rough sitting outside the repair shop in Kenmore back in 2004.

The 1980 3.0 engine as found in 2004 and a gold "Dr. John Walker" sticker (a clue!).

I've owned this "mutt" 1974 911 for over 20 years now, purchased in running condition for $9,500 in 2004. I know the CIS fuel injection system on the 1980 3.0 engine that came in it can't run trouble-free forever. My little voice is telling me the plastic (polyamide) fuel lines and rubber components like hoses and seals really should be replaced before they become so brittle they fail under the high pressure (32 psi) of the fuel running through them and potentially cause a fire of Tesla proportions. It's also becoming clear that replacement parts for the Bosch CIS system are becoming more and more expensive and problematic to repair or replace as time marches on. This part sourcing issue is even more acute due to the fact the CIS system in my car is a one-year-only configuration.

Weber IDA carubretors on the factory "twin spark plug" 911R.

I've decided that I want to repeat what I did to my 914 and set the car up to be "sustainable" as in less complicated and have fewer potential points of failure. I've come to the decision to "backdate" it to use Weber 40 IDA-3C carburetors as was found on the 911 engines in the final years before fuel injection and on legendary race cars like the 911R.

The 1981 CIS fuel injecton equipped 3.0 donor engine.

The broken Dilavar head stud discovered on the donor engine.

The inside of the case of the donor engine with sump plate removed looks very clean.

The other opportunity that presents itself is I have a "spare" 1981 3.0 engine I picked up off Craigslist in 2011. With only 157K miles on it, relatively low-mileage for a legendary "bullet-proof" 911SC aluminum case engine, it's the perfect starting point. Upon partial tear-down and close inspection, other than a broken Dilavar head stud, the intake valves are spotless, the exhaust valves are all a uniform brown color with no deposits and the inside of the case is shiny aluminum without any sludge in the sump so it appears to be a healthy and well cared for bottom end to build upon. Since the broken head stud requires removing the heads, pistons and cylinders to replace all 12 of the lower Dilavar head studs with steel, why not leverage that unavoidable labor cost to build something more interesting than a stock 3.0?

The "Bible" 2nd edition and latest new and expanded 3rd edition.

After studying Bruce Anderson's "Porsche 911 Performance Handbook" and a little research on the various 911 internet bulletin boards, I've learned that 911SC engines destined for the USA were significantly "de-tuned" to 180 horsepower to comply with federal emissions standards, a big difference from the ones built for the ROW (Rest Of the World) with 204 horsepower. One major difference was the ROW heads on the early '77 to '79 engines had "big ports" that significantly increased the volume of air/fuel mixture reaching the combustion chamber. Like all "ported" heads, the increased intake volume then provides the opportunity to reap quite noticeable performance benefits with increasing the displacement. Serendipitously, it happens the OEM manufacturer Mahle Motorsports recently re-released the "Max Moritz conversion" a 3.0 to 3.2 liter "slide-in" big bore kit that requires no special machining of the stock heads or case to increase the compression ratio from 9.3 to 10.2 and create what's called a "short stroke" 3.2 engine.

The stock USA 1981 911SC 3.0 horsepower and torque curves as per the sales brochure (missing legend, curves start at 3000 RPM).

The "short stroke" 3.2 horsepower and torque curves as per Bruce Anderson's book.

The Mahle Motorsports "Max Moritz conversion" 3.0 to 3.2 P&C set as shown on their website.

So who is this "Max Moritz" who had enough "stroke" with Mahle that they used his design to make a piston and cylinder set? In 1970 a new team hit the German racing scene. Max Moritz owned a Porsche dealership about a half-hour drive from Stuttgart in Reutlingen and sponsored a Porsche 914/6 which right from the start was one of the quickest in the 2-litre GT category in Europe. But this was only the beginning, which was followed by successful entries of various Carrera RS 2.8 models and the well-known RSR in the 1974 Deutsche Rennsport Meisterschaft. In the following years until 1978 the legendary Jagermeister colors were on Max Moritz top cars and drivers like Reinhardt Stenzel, Helmut Kelleners or Manfred Schurti, with guest starts of motorsports heroes like Jacky Ickx, Harald Ertl, Jurgen Barth, Derek Bell and Ecki Schimpf fought with Porsche 934s or 935s for the crown. Now one of Max's 3.2 "short stroke" engines will be going into my 1974 Porshe 911, the perfect "period correct" tribute.

The Max Moritz Racing's Jagermeister 935 being campaigned in 1978.

Since we're already starting with a significantly "oversquare" engine where the bore exceeds the stroke, precisely how does a "short stroke" 3.2 compare to the stock '84 to '89 Carrera 3.2? The stock 3.2 has a 95 mm bore/piston size with a 74.4 mm crankshaft stroke producing a 1.28:1 oversquare ratio. When you take a 3.0 crankshaft with a 70.4 mm stroke and add a 98 mm big bore P&C set, it gives you 3.2 liters with an even higher, 1.39:1 oversquare ratio, shorter stroke = faster rev capacity compared to the stock Carrera. Just for comparison, modern 18,000 RPM red-line Formula One engines generally have a 2.5:1 oversquare ratio.

Test-fitting RS-style SSI headers / heat exchangers, red caps show where M6 studs needed to be installed into the engine case.

Add a slightly "hotter" cam such as a 996 profile with a backdated RS-style SSI exhaust and significant horsepower and torque gains in the mid 200s for both are easily realized while retaining easy starting and smooth idling. Assuming the bottom end of my 3.0 "donor" engine is sound and doesn't require machining, the cost of a machine shop refurbishing a set of "big port" ROW heads is the same as USA heads and the old USA heads can be sold as a matched-set of rebuildable cores. I also have the complete 1981 CIS system to sell in pieces or as a complete unit. The only incremental cost to all this performance gain is the cost of the Mahle P&C set which is $4,400 and a performance camshaft kit is about $1,200. I've chosen to use the lighter, stronger $2,200 Carrillo "H-beam" rods as an insurance policy in the event the engine is accidently over-revved if I should miss a shift and just to lower the rotating mass to make it spin-up even quicker.

The 6 ROW "big port" head cores, the 6th (w/o valves) came all the way from Japan.

The magic 1977 to 79 ROW "big port" head's part number cast into each head

Now I'm committed to this plan and have assembled a clean set of ROW "big port" head cores which I have already sent off to get in the queue at Walt Watson's Competition Engineering for refurbishment. I've also purchased the Mahle Motorsports "Max Moritz" 3.0 to 3.2 P&C set and the Carrillo rods and will purchase a performance camshaft kit in the immediate future just to have them in hand. I've already gone ahead and purchased and performed all the external engine backdates and restoration on the engine. Now all the new parts are on display in my showroom instead of in boxes on a shelf while the months pass waiting for Walt to work his magic on the heads. I'm already in at a little over $21,000 invested (with tax and shipping) in the Mahle Motorsports P&C set, Carrillo rod set, ROW "big port" head cores, Weber carburetors, SSI exhaust and all the miscellaneous parts to backdate the engine so buying them now is a hedge against the certain cost increases and possible supply chain issues that would come with waiting.

The externally restored and converted donor engine on display.

The irony is the happy 180 horsepower CIS-equipped 3.0 engine in my 1974 911 continues to run flawlessly so removing it does come with a heavy heart. I'm sure it is of value to somebody needing a match for their '80 911SC so I could recoup some of my investment in the new engine but I hate to part with it. Until then I'll keep it alive and enjoy driving my 911 knowing that in the not so distant future, a much more exciting chapter waits to be written in my ownership story of my little "mutt" 911.

The original 3.0 engine as it sits in the car today.

My 1974 911 as it looks today after over 20 years of iterative refinement.

PROJECT PHOTO JOURNAL ENTRIES START HERE (IN CHRONOLOGICAL ORDER)

Up at 4 AM to catch the morning ferry to Orcas Island answering a CraigsList ad in October of 2011.

Unloading the 3.0 engine and 915 transaxle purchased for $6K in 2011, a sliding bed and topper on my F-250 is a handy set-up.

The 3.0 engine separated from the transaxle and placed on the engine stand in July of 2022.

Checking the intake valves after removing the CIS system from the engine, Phase 1 began on November 19, 2024.

Test fitting the new PMO 40 mm intake manifolds in the darkness of the November bomb cyclone power outage.

The broken Dilavar head stud discovered on cylinder #4.

The missing lower right head stud on cylinder #4 but look how clean inside the heads!

The "CIS Delete" engine wiring harness from Restoration Design.

Vapor honing started with all the nooks and crannies of the fan housing.

Test fitting the new heat backdating ducts & Weber 40 IDA-3C carburetors on the PMO manifolds while basking in parabolic heat.

Degreasing the right (passenger) side of the top of the engine with small brushes and aerosol carburetor cleaner.

Before & after with the right top side done, left side awaiting degreasing.

Finishing the left top and front degreasing using compressed air to blow out the big chunks scraped loose with a wooden pick.

The top and front of the engine all degreased except areas behind the main pulley and distributor.

Soaking the exhaust stud nuts with Maltby penetrating fluid, reapplying for several days.

Scrubbing the orange fiberglass cooling shroud with purple degreasing cleaner.

Vapor honing the orange fiberglass to remove grease from deep scratches.

Giving the orange fiberglass a light coat of gloss high temperature clear engine paint.

Using the oxy/acetylene torch to heat exhaust stud nuts red hot, lots of stooping over on the inside ones.

Using the oxy/acetylene torch on the outside ones was much more leasurely sitting down.

Several iterations of red-hot, quenching with penetrating fluid and careful wrenching.

The old "thick flange" exhaust liberated from the engine.

The reward for patience, all 12 nuts removed without breaking a single stud.

Degreasing and scrubbing the engine tins with purple cleaner.

Hosing off the engine tins with water after degreasing with the purple cleaner.

The greasy, naked underside of the engine ready for degreasing, note later type oil sump feed tube.

The naked underside of the engine after degreasing with carburetor cleaner is done.

The old oil pressure relief valve cap had seen some abuse.

The oil relief valve cap wouldn't budge so first a little MAPP gas torch heating of the aluminum case.

A couple whacks with a custom-sized drag link socket and impact driver.

Using the custom-sized drag link socket on a long breaker bar "popped" the cap loose.

The improved later-style oil pressure relief valve cap uses a 15 mm hex head instead of the slot.

The stripped underside of the engine all degreased, wire wheel brushed and ready to paint the cylinder fin cooling ducts.

New head to case telescoping oil return tubes anchored to the head using a hose clamp and C-clamp.

Using a plastic pry bar and dead-blow hammer to tap the telescoping oil return tube into the case.

Carefully positioning the circlip into the groove in the tube once the tube is fully inserted into the case.

All four oil return tubes, all new gold cadmium plated hardware and restored oil sump plate intalled.

A larger 131 mm diameter off a 2.7 engine, single belt crank pulley purchased off eBay. Bigger pulley + faster fan rotation = cooler engine.

Many hours spent at the vapor honing cabinet basking in parabolic heat.

All the engine tins and mounting brackets vapor honed and painted with semi-gloss, high temperature engine enamel.

Disassembly and cleaning of the distributor, the vacuum canister removed and will be centrifugal advance only after recurving.

The cleaned distributor with the polished stainless steel vacuum canister delete panel I fabricated.

One of two locations of M6 stud placement for the anchoring tabs on SSI heat exchanger on tang cast into the bottom of the engine.

Drilling one of the two 7/64" holes for M6 studs for the SSI heat exchanger anchoring points.

Tapping the hole with an M6 "bottoming" tap for one of the two SSI heat exchanger anchoring points.

The two M6 studs installed in the tangs cast into the bottom of the engine case ready for SSI heat exchanger installation.

A brand-new Porsche Classic oil cooler installed.

The new backdated oil sump feeder tube required for the new RS-style SSI exhaust system.

The new backdated oil sump feeder tube routing around the underside of the bell housing.

The freshly installed M6 case studs securing the new SSI heat exchangers.

The new SSI RS-style exhaust headers / heat exchangers installed, ready for the muffler.

The head studs from the thick flange header flanges required a 12 mm spacer, thin flange studs required on the new heads.

5 of the 6 ROW "big port" head cores, the 6th currently on its way from Japan.

The magic 1977 to 79 ROW "big port" head's part number cast into each head

PMO fuel pressure regulator and intake port phenolic insulating spacer set to keep fuel from boiling in the carburetor bowls from Partsklassic.

The phenolic insulating spacers installed on the intakes.

The additional intake stud length requirement noted with phenolic insulating spacers.

The new Restoration Design CIS delete engine wiring harness, new spark plug wires and new Weber 40 IDA-3C carburators installed.

Backdating the crankcase ventilation cap to first edition "0R" from fourth edition "3R" with abandoned CIS thermo-time switch.

The spark plug wires cinched-down using existing holes plugged with original-style wire holders and new PMO throttle linkage installed.

The original-style rubber 3-wire holders really tame the spark plug wires and 14-pin engine wiring harness is plug-and-play.

The larger 131 mm crank pulley required a longer fan belt, 9.5 mm x 725 mm.

The new MSD coil with the label removed and new coil bracket installed.

The 6th ROW "big port" head arrived from Japan on MLK Day.

Now I have the complete set so I can ship them to the machine shop.

Checking with my dial depth gauge using the far right head as the baseline.

The new head from Japan has 0.001" more material left after flycutting than the baseline head.

I was able to find six perfectly sized used boxes at a local used box vendor.

The head fit perfectly with 3/4" thick honeycomb cardboard lining and rolled bubble wrap to hold it in place.

I found a box in my loft for cutting down and creating the exact custom sized box, first row of heads placed inside.

The second row of heads placed inside and ready for closing.

The custom box sealed and wrapped with strapping tape, total weight 51.6 pounds and insured for $2,800 when shipped.