Frankly, there’s just no hair in this cake. Only thing is, it’s one painfully expensive cake! 95-mm cylinders like expensive aluminum 911 Turbo crankcase halves, while the twin-plug heads and distributor, custom Mahle pistons and cylinders, custom-bored throttle bodies, and specially calibrated MFI pump help make this a $25,000+ 911 engine…
Without a doubt, the 2.8 is the most fun to drive. That said, people who can and will cut a check for an engine that costs more than the car it’s going into are few and far between. So let’s look at the other choices on the menu.
Certainly, the 2.2S is a gem among production 911 engines — and a close-ratio gearbox makes it that much better. But the cost to build a 2.2S is similar to (or more than) the cost to build a comparable 2.5. In this case, then, I believe that bigger is indeed better.
Much as I love the 2.8, three days in these three cars have told me that the smart pick is somewhere in the middle. Curt’s 2.5 with the compression, twin-plug heads, and MFI of Randy’s car plus a close-ratio gearbox would add up to a package that would be exciting to drive and one that could be accomplished on a reasonable budget.
So what about compression? First, carefully consider the kind of fuel you’ll be running. If you want to play it safe, 9.5:1 will get you 200 hp depending on camshafts, head work, and redline. Bumping the compression to 10.5:1 or so might add another 10–15 percent peak horsepower, but you’re pushing the limits of pump gas. If you get aggressive with cams, port sizes, and compression, 100 horsepower per liter is plausible — but you may end up with more of a racing engine than one suited to the street.
There are other things to consider, like ignition and induction. A twin-plug setup will improve driveability and is a good idea if you’re leaning towards a hotter build. As for fuel injection? Without a doubt, carbs tend to be cheaper. Plus, MFI will require modifications to work with a larger-than-stock, high-compression, high-winding engine — mods that can add thousands of dollars to the initial purchase price of a complete MFI system. When all is said and done, however, a calibrated MFI system will typically make more power than carbs, and MFI is sexy! So, for my dream engine, I will save for a few more months and splurge on MFI.
One last piece of advice: Consider a good set of connecting rods if you’re going to twist the engine past 7300 rpm. Factory rods carefully inspected and fitted with high-tensile hardware can operate north of 8000 rpm on a limited basis, but they will fail if repeatedly exposed to high rpm. It may take a while, but it’s only a matter of time. And, once you’ve made the five-figure investment to build a 911 engine, a set of Carrillo or LN Engineering rods are cheap insurance against catastrophic rod failure at 8000+ rpm.
So will you take the easy road and go with a long-stroke 3.0, 3.2, or 3.6? Or will you take the road less traveled lately and build a short-stroke? If 8000 rpm sounds good to you, just remember that Billy the Kid and Wild Bill Hickok were famous because they held the fastest — not the biggest — guns in the West!