Big six engine choice impressions, My favorite was surprising Options

[davehg]

Over the past eight years, I've had the chance to spend quality time in a number of big six conversions, including a 2.7, a 3.0, a 3.2, and a 3.6. I currently own two 914's with a 2.7 twin plug and a 3.2 chipped motor, and recently had an RS2.7 MFI engine completed for my 74 911s that formerly housed its original 2.7 CIS engine (now crated).

I've formed strong opinions. I'm a big believer that for a street car, the engine should fit the character of the 914 while still providing that something special that a bigger displacement engine gives. So here goes:

Let's start at the top of the displacement heap - the 3.6. It's a beast of a motor, and it renders the 901 a challenge to use (and greatly adds to the expense if fitting a 915 or something else). You effectively need to start in 2nd to quickly accelerate if using the 901, and even with a limited slip, it can overwhelm the balance of 914. On a track, this motor would be so much fun in the straights, but around town it does tend to dominate the 914 even when fitted with wide grippy tires, so you have to drive with more care when getting on it in the twisties. It also tends to make you lazier in keeping up momentum because you have the motor's torque and HP to fall back on. If you want to build the most bad ass streetable 914 GT monster and have plenty of disposable income, the 3.6 is where you start.

The 3.2 fares a bit better on overall driveability. While first gear is mostly unusable unless you want to gamble, it has terrific torque in 2-4th and would be my first choice for an autocross focused car because the torque and power down low are so usable. Plus, a stock 3.2 needs precious little tweaking (maybe a chip) to achieve decent HP numbers (e.g. 220). Sure you can hop it up to a wild twin plug PMO build, or if you feel especially financially irresponsible, do one of the new ITB/crankfire builds like I saw at the Air & Water EMPI booth, can get even more power. But like a 3.6, a 3.2 build will start adding up fast, and you're having to deal with bigger brakes, better cooling, and potentially chassis stiffening and suspension upgrades. Still, I get why this is a popular engine and I love mine as it lets me do things I couldn't do in my 2.7 (whether I should do them is another question).

(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-21443-1719381164.1.jpg)

The 3.0 is interesting - to me it's the "Jan Brady" of engines - less power and less tweakable than a 3.2 but less expensive and considered more stout than the stock 2.7. IMHO it's quick but it lacks the full torquey grunt of the 3.2, doesn't quite have the excitement at the top of redline, and takes lots of additional $$$ to build into something that would just equal a chipped 3.2. Admittedly I've not spent as much time in a 3.0 but I get why they are popular alternatives to bigger flat sixes, and it's a very responsible choice if you're not doing a gonzo build.

Which brings me to the lowly (and wrongly but much maligned IMHO) 2.7. A stock 2.7 puts out 170hp max, and while it's fun and quick, it's not fast. In stock CIS form it has a limited torque range, and it makes more noise without delivering much pull above 5k. It was pleasant enough in my 911s but the best I could say was that it delivered a pleasant touring feel and great MPGs. After less than year, I quickly determined I needed more grunt.

Which brings me to the twin plug 2.7: with a solex grind cam and Webers (or PMOs) this is such a lovely engine. It absolutely fits the character of an early 914 - it has personality, grunt, it revs past 7k and howls like a banshee all the way there. Below 5k it delivers nice torque even from down low. Driving on twisty roads, it is perfectly happy between 3-5k where it pulls hard out of corners. Yes, it may need additional machine shop work at the outset, but even factoring in those costs, it's still a relative bargain compared to its bigger brothers - and you have lots of choices on cams and pistons to achieve either a nice low to mid torquey motor with a solex cam or a screamer with high compression pistons and S style cams. And with a front oil cooler, shuffle pin and other mods, you won't suffer the ills that the smog choked 75-77 motors suffered. You'll just cry once at the machine shop.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-21443-1719381165.2.jpg)

Here's why I think a built 2.7 best fits the authenticity of the 914 - Personality! You have to work it to keep up with the bigger sixes but it lets you carry momentum through the turns better, and it sings to you all the way to redline. The main culprit I'm finding is fuel efficiency, as I'm getting maybe 15-16mg whomping it where the 3.2 turns closer to 20 mpg (and the stock CIS can deliver as much as mid 20s). And then there's the extra cost of twin plug setups, which while cheaper than an MFI setup, still add up.

I'm still early days enjoying the RS2.7 MFI build in my 1974 911, but I think even with limited seat time, it's quickly become my ultimate favorite 2.7 for a street car. The payoff of the MFI is immediate acceleration, nearly flat torque through the entire RPM range, with linear power delivery that starts strong and just continues to build. The gorgeous soundtrack and Swiss watch feel of the motor are the stuff of air cooled dreams and I finally understand the love for the 1973 RS2.7 Carrera. Plus you can easily see 230-240hp if you invest even more for a higher compression build (I had seat time in a high compression 3.0 MFI build that bowled me over).

Problem is it's very cost prohibitive to build and MFI engine starting from scratch. Nothing is cheap with an MFI, and it takes special know how to tune and tweak unlike the relative ease of a PMO. Aside from expense, the MFI does punish you with 12mpg average when pushing hard. But if I had only one engine I was able to put in my 914 without worry of cost, the RS2.7 MFI might be it.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-21443-1719381165.3.jpg)

Which brings me to a special 3.0 RSR build that I had the pleasure of getting a brief ride in. With MFI and high compression pistons, it was close to 330hp and had an 8k redline. It was the most glorious sound and feel I've ever experienced in a 914 (and that included a 2.5 short stroke carb'd motor below from the same engine builder that had me salivating the first time I rode along). Both of those cars were track focused cars with license plates, and I wouldn't consider them streetable or livable for day to day. But they were sure amazing and they live in my 914 dreams with their sound and character.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-21443-1719381165.4.jpg)

So there - I said it - I think the 2.7 of the bigger six motors, best fits the 914's character on the street, and price wise may be the best bang for the buck (assuming you've got a good block to start with). I'm ignoring the 2.3 and 2.4 which aren't big sixes though I know they can make some healthy numbers, and I've yet to experience a 2.8 or 2.9 build.

Big thanks to Bernd Buschen who made all these engine experiences (save for the 3.6) possible.

What's been your experience/opinion on the big sixes?

[campbellcj]

Great write-up and I've had a lot of fun with my fairly extreme carbed 2.7 but alas it's got a leak that will require a teardown someday to fix. Runs so well that I am putting that off as long as I can.

Previously this car had a 2.2 E/S carbed 'frankenstein' engine that ran great and sounded nice but left me hungry for (much) more power.

Ultimately I'd love to go to a 2.5 short-stroke or 2.8 'RSR' with MFI but probably will stick with Webers on this car from a cost and maintainability standpoint.

[930cabman]

Great write-up and I've had a lot of fun with my fairly extreme carbed 2.7 but alas it's got a leak that will require a teardown someday to fix. Runs so well that I am putting that off as long as I can.

Previously this car had a 2.2 E/S carbed 'frankenstein' engine that ran great and sounded nice but left me hungry for (much) more power.

Ultimately I'd love to go to a 2.5 short-stroke or 2.8 'RSR' with MFI but probably will stick with Webers on this car from a cost and maintainability standpoint.

Can you describe "fairly extreme carbed 2.7"

[campbellcj]

Great write-up and I've had a lot of fun with my fairly extreme carbed 2.7 but alas it's got a leak that will require a teardown someday to fix. Runs so well that I am putting that off as long as I can.

Can you describe "fairly extreme carbed 2.7"

Last time the engine was apart I had some new 2.8 P&Cs and I wanted to go higher compression with Mahle Race pistons but there were supply-chain/lead-time SNAFUs and my bank account was running dry so stuck with the existing cylinders and JEs which were reusable.

Pasted in from my notes file -

 2.7 (90mm bore x 70.4mm stroke) rebuilt and race-prepped by Galen Bieker (December 2013) on early 7R magnesium case (#6342207); line-bored; timeserted; oil mods; new 930 oil pump; STD/STD crank; 90mm Mahle Nikasil cylinders; 10.5:1 C/R JE Pistons
 Doherty Racing Cams (DRC) DC42 "mod S" cams; ports 38mm intake/34mm exhaust; flowed and polished; decked for increased compression; new valves and guides; polished and rebushed factory rods; new OE rockers; ARP fasteners; AASCO racing valve springs and titanium retainers
 Dual Weber 40IDT3C carbs rebuilt and rebored to 46mm by Bieker Engineering; PMO tall manifolds; K&N filters with flat metal tops (watershields in spares); PMO billet fuel bars; solid metal lines thru tunnel and braided AN-6 lines elsewhere
 JB Racing magnetically-triggered twin-plug distributor; Dual MSD-6AL CD’s and matching coils; MSD plug wires
 Carrera pressure-fed chain tensioners
 Turbo lower valve covers and sheet metal modified for twin-plug
 Series 900 911R/RSR style raw fiberglass shroud and air blockoff
 Short-geared 901 5-speed gearbox (A,GA,Ka,Q,V) extensively overhauled summer 2022 by TLG Auto including NOS R&P; 904 mainshaft and GA 2nd gear; new CMS billet intermediate plate; refreshed Guard TB differential
 Fresh sport clutch disc, pressure-plate and lightweight flywheel summer 2022
 237bhp/199ft-lbs at rear wheels (POC official dyno 2017)

Peak power is around 7500rpm w/ these cams