Short-Stroke Shootout

In search of the small-bore sweet spot, we sample three early 911s with 2.2, 2.5, and 2.8 liters of displacement.

Short-Stroke Shootout 1
October 1, 2009

Don’t bring a knife to a gunfight.” When talking cars, that bit of wisdom translates roughly as “there’s no replacement for displacement.” Early 911 hot-rodders tend to agree, and they’ve been reaching for bigger guns for a long time now. The result is a rash of long-hood 911s with 3.6- and 3.8-liter flat sixes.

Porsche laid the groundwork for such swaps long ago. Stuttgart first added displacement to its air-cooled flat six for the 1970 model year, when the 1965–69 2.0-liter grew to 2.2 liters on a bore increase. In the quest to build ever faster 911s, however, Por­sche began to increase stroke, as well, creating 2.4-, 2.7-, 3.0-, 3.2-, 3.6-, and 3.8-liter engines between 1972 and 1998. One thing all of them have in common? Their “long-stroke” crankshafts.

The first long-stroke 911 crank was the 70.4-mm unit used by the 2.4 (1972), 2.7 (1973), and 3.0 (1974). Then came the 74.4-mm crank used in the 3.2 (1984), followed by the 76.4-mm unit found in the 3.6 (1989) and 3.8 (1993). With so many long-stroke options available, what would compel someone to build a short-stroke 911 engine based on the earliest, 66-mm crankshaft? Build­ing a short-stroke 911 is like thrusting through swinging saloon doors and into a shootout while packing a .22 instead of a Colt 45. That said, there’s something to be said for a .22. Like accuracy.

Maybe it’s just me, but the thought of a high-revving, short-stroke six in an early 911 is seductive. Many of the great 911 race cars won on 66-mm cranks, among them the 911R with its high-strung 220-hp 2.0 and the 911 S-Ts with their 2.3s and 2.5s. What short-stroke flat sixes give up in power, they make up for in the way they spin. They seem not just willing but desperate to rev. They’re a little sharper, a little more precise, and a little more responsive than the bigger sixes.

Then there’s the sound. A small-bore 911 coming on cam is an audible history of the 911R at Monza and the S-T at the Nür­burg­ring. Call it romanticism if you will, but let me assure you: I’ve never been accused of being a romantic (just ask my wife!). But I am a huge fan of tradition.

While considering a short-stroke flat six myself, a unique opportunity to evaluate three different combinations presented itself. Friends were planning a road trip to California and I would have at my disposal several short-stroke 911s. Car number one is my own, a 2.2-liter S with a short-ratio gearbox and a limited-slip diff. Car number two is Curt Egerer’s 1971 911T Targa with an old-school 2.5 and Weber carbs. Car number three is Randy Sten­son’s 1971 911T with a twin-plugged, 2.8-liter beast of an engine. I would spend time driving each on the freeways and back roads of the wild west before meeting early 911 hotshoe Randy Wells at The Streets of Willow.

Short-Stroke Shootout 2

Day 1 1970 911S 2.2

Let me get this out of the way up front: Impartiality is impossible. I love this car! I’ve owned this S for six years and have racked up nearly 15,000 miles on club trips alone. It rarely sits idle during the abbreviated driving season typical of the Midwest, which is nothing new for “Olivia,” as my wife and I call her.

The previous owner bought her in the mid-1970s and did a lot of track days and auto­cross­es over his 25-year tenure. So she’s well broken in, much like your first baseball glove or that pair of jeans you can’t bear to part with — or wash. Olivia’s got plenty of rock chips, a few minor oil leaks, and maybe even a stray French fry beneath her seats.

She was my first 911, so I didn’t know what to expect. I had read that the 2.2S lacked umph at lower revs, so Olivia’s eager, responsive nature was a pleasant surprise. Her powerband is exciting; I look for every opportunity to surpass 4500 rpm and feel the surge up to the redline at 7300. Freeway onramps are my pit out at Le Mans, every corner a rev-matched downshift homage to Tertre Rouge.

Over time, more experienced 911 drivers told me there was no way that Olivia was a stock 2.2S; she was too quick! Occasion­ally, I would drive other 2.2Ss and wonder why they didn’t have her punch. While talking with the previous owner, I insisted that something must have been changed in the engine, yet he assured me that the flat six had been rebuilt to factory specs.

“But of course you realize she has close-ratio gears?” he asked. So that’s what makes Olivia so much snappier, so much stronger off of low-speed corners. She sports a 904 mainshaft with close-ratio gears in second through fifth. Com­pared to the cost of getting more power from the already efficient S-spec 2.2, a close-ratio gearbox is a modest investment that makes a noticeable difference.

Of course, like most modifications, short gears are a compromise. Leaving Ohio with the goal of putting as much of the boring Midwest behind us as possible, the lower fifth and short 225/50R15 rear tires mean I’m cruising at roughly 300 rpm more than most of our crew. The 2.2S doesn’t seem to mind, though. In fact, it seems to find a happy place right around 4300 rpm, well above the speed limit. If my concentration lapses, it goes there, every time. Cop bait? You bet.

Short-Stroke Shootout 3

The short gears mask Olivia’s mere 2.2 liters up to about 100 mph, where aero resistance begins to overwhelm her. Late in the afternoon, on the wide-open expanses of western Missouri, I experiment with acceleration. To go from 60 to 100 mph in fourth takes about 13.5 seconds. Not bad — but not great, either. I decide it’ll be interesting to see how the larger engines in the other 911s stack up.

Pulling into our hotel in the little town of Stroud, Oklahoma, my satisfaction with the 2.2S and short gears is reinforced. But like any true gearhead, I can’t shake the feeling that a little more power would be nice. When I finally fall asleep, I’m looking forward to Curt’s 2.5…

Day 2 1971 911T 2.5

Day two starts off with a chuckle. Curt is one of these guys who grows restless during long Michigan winters and tweaks his car to break the monotony. This year, the “Gray Wolf” (as he calls it) evolved into a pseudo vintage rally car with steel wheels and auxiliary lights. Part of Curt’s rally motif is a pair of what our group calls “mud flaps” but what he insists are “official rally stone guards.” Taking the good-natured “mud-flap” comments in stride, Curt retired to bed unaware that we’d be applying “Mudflap Girl” decals to his stone guards in the wee hours.

Hundreds of Okla­homan miles pass before he discovers our chicanery. Now that Curt’s in on the joke, I boot him out and take the wheel of his hot-rodded T. Much like my car, this 911 was owned by a true enthusiast for nearly 25 years. A second similarity is that our engines were rebuilt “back in the day” by the head engine guy at Stoddard, Fred Truman.

While my 911S was rebuilt to factory specs, the Gray Wolf’s previous owner wanted more power. In 1979, there were few choices for larger pistons and cylinders. A common up­grade was to replace the 87-mm pistons and cylinders with 90-mm Mahles as used in the Carrera RS 2.7. With the 66-mm crank, this yielded a displacement of just over 2.5 liters.

The downside is that the resulting compression ratio is typically 7.5:1. Tru­man claimed 8.1:1, which is still mild. Curt has found an upside: He typically uses the cheapest gas he can find. 87 octane is the norm, which makes fill-ups a bit more palatable. Curt jokes that he’d buy 85 if they sold it at the pump.

Short-Stroke Shootout 4

Pulling onto the freeway, I quickly settle into a groove in the Gray Wolf. With­out question, there’s more torque on tap. Useful torque is available lower in the rpm range and less effort is required to gain similar speed. With Solex cams and an S distributor replacing the original T items, the 2.5 can be spun to 7300 rpm, although that might be a questionable policy considering that the original, non-counterweighted crankshaft still resides within the magnesium case.

Passing through Amarillo, Texas and switching from Interstate to more scenic four-lane state routes towards New Mexico, I struggle with how to describe the 2.5. It makes more power and feels stronger than the 2.2S, but the increases are subtle. It’s faster, but not a lot faster. Weight isn’t a factor; due to its lightweight seats and trim, this 2,300-pound T Targa is only 25 pounds heavier than my S coupe. If you swapped its custom 15×6.5-inch steel wheels for Fuchs and dropped the “rally bits,” they’d be dead even.

Repeating the same fourth-gear pull I did in the 2.2 S, the 2.5 is only about half a second faster from 60 to 100 mph. The 2.5 is actually slower for the first few seconds due to its stock gearing. But, as the century mark nears, 2.5 surpasses 2.2. The extra torque is most noticeable as the 2.5 easily overcomes aero drag.

All up, the 2.5 feels like a T (which it is) with more power across the board (which it has). The T was always touted as the more comfortable grand touring car, requiring less work and fewer shifts. The problem with 911Ts is that they cry out for more power. This 2.5 fixes that but retains the manners of a 2.2 T.

Curt, when asked to describe what he likes about the combo as well as what he would change, thinks for a moment. “If I ever blow this engine up,” he says, “I will rebuild it exactly as it is, except I will bump the compression to 9 or 9.5:1. That would make it just a bit more responsive. But honestly, I don’t need more power… it’s fast enough as is!”

115,000 miles have passed beneath the tires of the Gray Wolf since the 2.5 was built, so it will need to be freshened again at some point. Until then, Curt is satisfied. Unfortunately, satisfaction with the power I have is one of those life-lessons I’ve never been able to learn. I’m eager to drive the 2.8 to see what a little more displacement and a lot more compression feel like! Tomorrow, I’ll do just that.

Short-Stroke Shootout 5

Day 3 1971 911T 2.8

Our third day begins with breakfast at a small Mexican restaurant on the edge of Ruidoso, New Mexico. Curiously, it’s called the “All-American Diner.” As I chew on what may be the finest breakfast burrito ever constructed, I’m thinking about the 2.8-liter, twin-plug beast in the parking lot. I soon discover that it’s easier to separate a bear cub from its mother than it is to separate the keys from Ran­dy’s fist. It’s not that he’s afraid to let me drive, it’s just that this is the first real trip Randy has done with the 2.8 and he’s having too much fun in the car.

I’m now able to sympathize with all the mothers who have had to pry their child off of the mechanical pony outside of Kmart! The kicking, the screaming, the begging — by both parties. It’s quite embarrassing, actually. Taking a page from the parental handbook, I back off, knowing that my adversary will become more cooperative when he gets sleepy. It works. Somewhere in northern Arizona, I convince Randy he could use some rest.

This 16,000-kilometer 911T is unique, having been delivered new to its German owner with many S options. When the ’73 RS was unveiled, the buyer decided he would take his 911 back to the dealer to have as many ’73 RS 2.7 parts retrofitted as possible. The RS influence is evident inside: the smooth vinyl dash trim, door panels, and black headliner. The original Recaro fiberglass buckets have been replaced for this trip with later, more comfortable Recaro touring seats.

I’m not thinking about seats, though. I’m thinking about the 2.8. Starting on an aluminum Turbo case, Henry at Supertec Perfor­mance combined a 66-mm crank with high-compression 95-mm pistons and cylinders to come up with 2807 cc of high-winding flat-six fury.

Does the combination still exhibit the small-bore passion I’ve been preaching? Well, perhaps not quite like the 2.2 or 2.5, but it pairs short-stroke character with epic, crushing power! Picture Godzilla with a dozen roses for Mrs. Zilla in one fist while clutching and shaking a Tokyo metro bus in the other. And much like Godzilla, I’m crushing small towns beneath me while deepening my love — or is it lust? — for this engine combo.

Prior to this drive, the idea of twisting an engine conceived nearly 50 years ago to 8000+ rpm was disconcerting. I had already decided that any engine ever financed by my wallet would remain safely in the 7300-rpm range. What an epiphany then to mash the throttle in this 911 and watch the tach point to 8 before I can even contemplate what I’ve done.

Short-Stroke Shootout 6

In most cases, an engine will communicate what it’s willing to do and where its comfort zone is. In this case, I feel no weird vibes from the 2.8 as I repeatedly shift at eight grand. And the power…

Giggling like a prepubescent schoolgirl, I do 60–100 mph in just 8.5 seconds, a full five seconds quicker than in my 2.2. The 2.8’s punch is especially impressive because the five-speed 901 it’s hooked up to has standard 1971 gearing. The fabulous torque of the 2.8 pulls each ratio effortlessly. Thanks to some fiberglass and carbon-fiber panels, this 2,100-pound 911 is 175 pounds lighter than my car, but it’s also stifled by a factory 2.2-liter airbox and SSI heat exchangers that are two tips of the hat towards comfort. A pair of large-tube headers might bump horsepower up by 10 percent or so, but probably only in the upper reaches.

While more displacement means more horsepower, more compression makes for a more responsive engine. You don’t want to go overboard when it comes to compression, though. This 2.8 is running a compression ratio of 10.1:1 — the outer limit of safety if you want to log a lot of road miles without worrying about the quality of the “premium” fuel available in cosmopolitan towns such as Bovina, Texas and Pie Town, New Mexico.

I’d say Randy got this combo exactly right. It generates a torrent of usable power, yet is tractable at all speeds. If I didn’t know better, I’d believe a modern EFI system is responsible for the driveability. In reality, the twin-plug ignition system and the Supertec-modified mechanical fuel injection get the credit. We’ve experienced temperatures ranging from near freezing in the mountains to 100º+ F crossing the Mojave, with elevations ranging from sea level to nearly 10,000 feet. Not once have I noticed a cough or felt a flat spot. But, like any system devoid of computers to handle the air-fuel mixture, the high altitudes mean rich running. Even so, the 2.8 took it in stride.

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…

The Verdict

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.

Short-Stroke Shootout 7

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!

Also from Issue 177

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  • Interview: Paul Ritchie of PMNA
  • Market Update: 911 Turbo
  • Porsche Icon: 911 GT1-98
  • $0.79 911 Foggy Headlight Fix
  • Project 914 3.6: Details, and First Drive
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