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?

[930cabman]

I am very new to this and just getting my basically stock fresh 2.7 rolling down the road. So far I like it as it doesn't seem to add much weight and the power curve seems not too aggressive. Interested to hear other /6 boys reactions
(IMG:style_emoticons/default/popcorn[1].gif)

[Freezin 914]

What a nice write up, I enjoyed reading through it very much.

Unfortunately, I have never had the pleasure of driving or getting a ride in a 6.

All I can say is having owned a 2.7, and a 3.0 powered 911, I can see the allure of having a 6 powered car. My 2.0 is very fun to drive but lacks any kind of grunt in my opinion.
I think about having the power I have from my 911 in my 914 and I think it would be glorious.
But budget is a concern for me, I think the best I will be able to do would be a 2056 with either stock Djet, or maybe an aftermarket FI system.

Thank you for the post, I personally appreciate the insight,

[914Sixer]

Good information because the average 914 guy is not going to have the ability to make such and assessment.

[mlindner]

Davehg, thats great information and assessment. I have a 2.2 E with S pistons (9.5 to 1) Mod-Solex cams and 40 PMO's. Wish it was a twin plug but makes plenty of power above 5K to 7. Seems to fit the car very well at speed and city driving very similar to a four. Best, Mark

[sixaddict]

Fun read….. and did not have to spend big bucks on all those builds.
I had a unique experience to compare a few years ago.
Normally ran this guy with a 3 liter with 46s and some other “stuff” but reasonably $$.
Had an issue so switched engines to a carbureted 2.7 so as not to miss a DE weekend.
With the bigger engine I could run down stockish 3.2 911s…..even on the longer straights whereas the 2.7 didn’t give it the long legs needed for speed. Had a 3.6 but decided the $$ for installation wasn’t in the cards…….i could also hurt my 901 with regularity without all that torque.

[JmuRiz]

This is relevant to my interests, I took a 2.7 CIS and am having it built to a 2.8 (stock stroke with slightly bigger Nickies and Mahle pistons...not a REAL one) with a DC40 cam and carb. Should be a hoot and I could do the trans mount up as stock as possible.

One of these years I'll finish it and see how it all works. I'll compare to my brother's PMB 2.3i setup that was just completed (IMG:style_emoticons/default/biggrin.gif)

My friend/mechanic Eric Wills works on 2.7RS and 2.8RSR engines and loves a stock 2.7 RS MFI in a long-hood or mid-year 911. Helps that he's an MFI tuning wiz!!! it's not the easiest but when it's tuned right it works way better than a 2.7 should. Just something about the bore/stroke that works.

[infraredcalvin]

Thanks for that assessment, I’m struggling in building my next motor, I’ve got a 3.0 core and a 2.7 core waiting for my attention. I have a 3.4 twin plug 6 in my current track/street car, but it just feels heavy and a bit lazy. I always thought an 2.7rs spec motor was the right fit for a flared 6.

My last track car was narrow body, 1800lbs with a built 2.2 -4, putting out about 160hp to the wheels. IMO that was the perfect engine spec for a narrow body. It pulled nicely through all the gears., and it made you respect momentum on the track. It’s been newly rebuilt to a 2.3 and i have yet to fire it…

[Shivers]

That was great, Thanks

[gereed75]

Really interesting to hear these insights. I am running a 2.4 S spec carbed motor with Mod Solex cams in a narrow body original six. I have never had the experience of a truly big six.

Two things jump out at me reading this thread.

One is the mention of character. As the motors get bigger and tires get fatter (ie flares), I think you might begin to loose some of that sporty light weight fast rev feeling. At some point the motor has to start to dominate the character of the car. Not saying that is bad, just different.

The second is the feel of that engine behind your head. The sound, the mechanical noise all is pretty sublime. Best way to enjoy an air cooled flat six short of a 910. The 911 experience is fine, but more isolated and GT vice pure sport

My vote for dream shot motor is a short stroke 2.4 MFI. Some here have done it. Must be incredible!

[mb911]

My 2.4s with solex is awesome for how I use it. I had a 2.7 in the last six I had and that was nice as well. I drove a few friends 3.2s and they were for some reason bulky feeling. The 2.7 was always a perfect match in my opinion for the 914. Never drove a 3.6 in one but did in the 964 I had. Good torque. I favor the small displacement sixes myself for there willingness to rev

[SirAndy]

I find my 3.6L very streetable and well behaved around town.

It's been in front of the same bone stock 901 for 18 years now.
(IMG:style_emoticons/default/driving.gif)

[mb911]

I find my 3.6L very streetable and well behaved around town.

It's been in front of the same bone stock 901 for 18 years now.
(IMG:style_emoticons/default/driving.gif)

I think that’s a testament to your driving ability and understanding of the combo for sure

[davehg]

My vote for dream shot motor is a short stroke 2.4 MFI. Some here have done it. Must be incredible!

My friend has a twin plug 2.4 short stroke with PMOs in his 72 911. It's magnificent. An MFI would be just as much much if perhaps more.

On the 3.6 - I drove my friend's 3.6 many times including many runs up and down Hwy 74 and around Idlywild. It was a beast, and it was so much fun to stay with the modern cars too. But I was always conscious of the power and need to measure my right foot, and even with wide wheels, it definitely encouraged hooliganism. The rear often broke loose if I wasn't careful.

[Steve]

(IMG:style_emoticons/default/agree.gif) With all the opinions. My first six conversion was back in 1986 with a stock 1974 2.7 motor with new PMO webers and 1 5/8” MSDS headers. Back dated the flywheel to a 2.0 flywheel and it bolted right up to the stock 914-4 trans. It was fast for its time and I could keep up with 3.0 and 928’s at that time. The gearing felt right and 140 lb rear springs felt perfect.. 15 years later Camrys were quicker and most other cars. Instead of overhauling the 2.7, I bought a stock euro 3.2 motor. Now the car felt all wrong. 1st gear was worthless and second gear was too tall to use as first without slipping the clutch. I then upgraded to a 915 trans to match the motor and now since the drive Train is heavier, had to upgrade the rear shocks to 200 lb springs, flared fenders, etc. Now the car was perfect but most modern cars could still kick my ass 0-100 so I recently sold the 3.2 and bought a 3.6. I mainly use my car for local drives and cars & coffee. Haven’t done an autocross in years, but note that 914-4 cars were quicker in an autocross than my 2.7. Even with a 2.7, it’s hard not to do throttle induced over steer and lengthen your time around the course. Only at streets of willow were i able to take advantage of the wider corners and longer straight aways. This was my experience. The 2.7 or 2.8 variant is the best bang for your buck. Otherwise a subi EZ30D makes more sense unless you have some disposable income for a big six.

[Dr Evil]

Spot on. I like the 2.7 for our cars in all of its iterations. Respect for the transmission set up is key and bigger really does benefit from a different transmission/gearing, at the lest. Current build is getting carbed 2.7, old car has a 2.7 CIS with SC cams and was a nice flat torque curve on it.

[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.

[targa72e]

Great comparison. Many do not have the advantage of comparing different configurations and have the go by internet and butt dyno comparisons which are not always informative as they are singular experiences.
I have had 4 different engines in my car over the last 6 years. I have used it as a test mule. I detailed the dyno results and impressions on Pelican.

https://forums.pelicanparts.com/porsche-911...-2-4l-2-5l.html

These were all comparisons with the same car, same exhaust and same transmission same dyno. I have a 5th engine that will go in the car soon, 3.0 with 9.3 to 1 pistons, big port heads, 964 cams with CIS (very interested to see how it compares).

If you look at my link posted above you will note that the current 2.5 makes more power and torque than my highly blueprinted stock class 3.0 SC PCA race motor with CIS above 2.5K.

That said I am just starting a GT build and my current engine plan is 2.8. 10.5 to 1, twin plug with DC 60 cams and EFI. Its all about the character vs absolute power.
The most fun to drive engine I have had in the car so far was the 2.7 RS+ with Mod S cams. Based on that experience a little more compression combined with a little more cam should be the magic sweet spot in personality.
My car also has a short ratio gear box with stock 1st and 2nd gears with KA 3rd, S 4th and stock ZD 5th. The shorter gearing makes the legal speed acceleration that much more fun, with a tall gear for highway cruising. I plant to use similar gearing on my GT build.

john

[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"

[peteinjp]

I certainly haven't had the opportunity to use various engine setups as this is my first 914-6. Glad know I got the right Combo! My car has 2.7 MFI with S webcam grinds and S spec heads- single plug narrow body and with sticky 195/55 tires (A052) and short gears (A, E, KA, Q, and Y) it's a great combo for street use. Character and balance are the words for sure.


For me it's hard to image a better classic driving experience than the light, nimble 914 chassis, manual steering and brakes along with the responsive free revving power/sound of the 2,7 MFI 6 just inches behind me. I guess if I were to wish for more I would like a bit higher redline as I do find myself bumping the fuel limit governor from time to time. Also the 2.7 is perfect with just my self and a kiddo or my wife but when I have a heavier passenger acceleration does feel a bit dulled. Amazing how just that much a of a weight difference affects the character of the car.

But aside from showing off for friends for the most part it's just me- rowing the 901 and working the pedals- heading out before sunrise for few early morning hours in the mountains. There are the cars on the momentum side of the spectrum and cars that you can make speed with the throttle. Cars the you have to slide and cars that you can't slide without taking chances - and there are cars that fit right in the middle- and that's what my narrow 2.7 is for me.

Pete