Flat-six sweet spots

[Deeks]

Having absorbed so much information about all 911s from this BBS in the last year or so, and being in a Porschless position where I can day dream about which year/car I will buy once I've graduated - I was surprised to hear in a recent post about how the 3.2 motor produces a lot more top end power, compared to the 3.0 SC, which produces more grunt at lower revs.

I always thought that the 2.7 MFI was the last of the "free revving" engines and that post '74 (oil crisis) engines were generally more "torquey" producing their peak power at lower rpms. Why this change in the 3.2 then ?

Where is the sweet spot in your engine ?
I'm particularly curious about the 1976/7 Carrera 3.0. Is this a revvy 3.0 litre or is it similar to the "grunty" 3.0 from the SC ? I know they have different injection systems.

[Bill Verburg]

As the owner of a C3(and previously a 2.4S) for the past quarter century my comments may be pertinant. The C3 was a nice revvy(6800 &#177 200 rev limiter) motor especially when SSI exhaust is used(the valves are the same size used through 964 engines and the largest ports until the 3.2) . The early SC got the "grunt" rep because their cam timing was advanced the most(6&deg more than a C3 but other wise the same cam used until the end of the Carrera 3.2 run in '89). The 81-83 SC got back the revvy feel w/ higher compression and the same cam timing(but with smaller ports) as the C3.

the 3.2 was a compromise in cam timing splitting the difference beteen the early SC and the C3. That combined w/ DME and high cr(particularly in the euro engines) brought back the revvy feel.

The feel is determined by the shape of the toque curve not the absolute magnitude of it.

964s are torquers 993 revvier and 993RS even more revvier.

There was an interesting interview in Pano a few years ago w/ a factory engineer about the shapes of the torque curves, he described them as a pouncing panther or buffalo shape, the panther being revvier and more sporty feeling.

[Deeks]

Interesting...

My uncle who owned a C3 prior to his '89 3.2 says that the C3 always FELT quicker and more responsive than the 3.2 although he knows that in real terms this isn't true.

So does a C3 engine have a more revvy nature than the 204bhp "Euro" SC motor or do you think they would feel virtually identical ?

cheers

[masraum]

I love the feel of the 3.2L cars (I suppose that's why I bought one. To me the shape of the SC torque curve felt more like a high performance V-8 with the most power in the middle and sloping down each direction from there, while the 3.2 feels more like the price of stocks before they went to crap, just climbing in a virtually straight line to redline except for the kick in the pants in the 4000-4500 range.

I don't have any driving experience, but from what I've read (as much as I can get my hands on) I think the rep of the later larger displacement cars comes when comparing them to the old 2, 2.2, and 2.4 L S motors which I believe had even steeper torque curves.

[VincentVega]

I currently have an SC and a Carrera, dont ask. I was driving them back to back last weekend to figure out which one I will sell. After about 2 hours of driving the same roads the SC, w/ SSI's has much more power down low, much more. The Carrera feels slow almost, maybe partly because it's quieter, stock exhaust though. However, as the others have said the Carrera pulls at speed better, say 70-100. The SC has legs, but the Carrera seems to really move after 70 mph or so.

I cant complain about either car really, too bad I dont have the space for them both.

[Eric Mckenna]

i LIKE THE FEEL OF THE EARLY 70S 2.2 LTRS.. IS THERE A WAY TO HAVE THE REV AND GAIN SOME LOWER END GRUNT? MAYBE ?

ERIC

[Bill Verburg]

Don't forget that the weight of the earlier cars is always less than the weight of the newer ones. That makes a big difference in the response of the engine and chassis and brakes.

[speeder]

Good question, Eric. I like the 2.2S motor also, maybe my favorite early car is the '70-'71 911S, the lack of bottom-end grunt on one of those would not bother me. They have virtually the same torque as a "T" down low, (sufficient for city driving), and scream when you stand on them. Plus the cars are light, and we like that.

As for the Carrera vs. SC arguements, this has always baffled me around here. I worked at the dealer when these cars were new, so at least in stock form I can tell you that the 3.2 motor should have a LOT more torque. This will be most noticable when, say, you shift 1-2 at low to moderate RPMs and then stand on it. If you do this in an SC and Carrera side by side, the Carrera will walk all over the SC. 10 times out of 10. Now, 14-19 years later, (depending on year of 3.2), if it does not perform there is something wrong. Both models, (SC and 3.2), have bugaboos which will severely reduce performance while still allowing the car to seem like it is "running good". Ask me how I know.

Lastly, ALL changes to the performance characteristics of the (stock) 911 have been in the direction of drivability, ie. torque, and the differences in early to late SC cam timing produced the opposite result as described above. Advancing cam timing, (80-83), moves the torque curve downward= more low-end "grunt".

[Bill Verburg]

The early SC got the "grunt" rep because their cam timing was advanced the most(6° more than a C3 but other wise the same cam used until the end of the Carrera 3.2 run in '89). The 81-83 SC got back the revvy feel w/ higher compression and the same cam timing(but with smaller ports) as the C3

And where exactly does it say retarding moves the torque down?

[speeder]

The early SC, ('78-79), w/ the 930/04 motor had the most retarded cam timing, in 1980 they advanced the timing 6deg. for the purpose of low-end torque, or "grunt" as you put it.

You basically got the timing changes backwards when you said that "the early SC got the 'grunt' rep because their cam timing was advanced thr most", it was the later SC, 930/16 motor that had its timing advanced 6deg.

[jhugh]

My 3.2 (recently rebuilt with C2 cams, computer & exhaust mods), for all the mayhem that breaks loose around 4K, has plenty of lowend torque.. certainly enough to maintain streetlight esteem amongst the Mustangs and Camaros.

That said, the "sweet spot" is definitely from 4K to 7K. It just screams up there. What an addictive feeling!

I've never driven an SC. I have driven a '73 911E with PMO carbs, S cams and extra displacement (2.7 or 2.8?) p's & c's. That car also screams and really pulls up in the high rev ranges. But not as hard as my 3.2. And the lowend doesn't even compare. It's very boggy off the line.

[RickC]

Thought my 87 3.2 ran great - just like they said. OK down low, wild over 4,000. Then adjusted the valves and a good deal of maintenance, and my wrench adjusted the CO (was way too lean) and the tired air meter flap.

A whole world of difference down low after that. Way more torque, with a still strong top end (though not as abrupt/wild a change of temperament at 4,000).

[widebody911]

With my 3.6L, it really starts to come alive ~3500, and then at ~5100, there's a noticable 'kick' as the secondary plenum kicks in. With the light flywheel, it revs pretty quickly.

[Bill Verburg]

I think I see where the confusion comes from, In the spec books there are 2 different cam timing specs for '78-79, ROW @ 7&degBTDC and US @ 1&deg BTDC, according to the spec books the timing was reversed (ROW vs US for 82-83)

• 76-77 Carrera 3 IO 1&deg BTDC
• 78-79 930/03 ROW IO 7&deg BTDC
• 78-79 930/04 US 49state IO 1&deg BTDC
• 82-83 930/10ROW SC IO 1&deg BTDC
• 82-83 930/16 US IO 7&deg BTDC
• 84-87 930/20 ROW and 930/21 US IO 4&deg BTDC

All#s are from the spec books for the year/model(there are many other niche market specs)

The US 930/04 cam spec is the same as the C3 but the engine was so hampered otherwise the power/torque characteristics (172hp/189ftlb) were way down from the 200hp/118lb/ft of the C3. For comparison the ROW 930/03 was rated@ 180hp/195lb/ft

Due to multiple other changes to the engines for different markets and for different years the only meaningful comparison of otherwise almost identical engines with regard to cam tming changes is the '76-77 C# 930/02 200/188 w/ retarded cams and '78-79 ROW 930/03 180/195 w/ 6&deg advanced cams.

My post correctly stated the facts

The 964 and 993 in an early chassis confuse the issue because they have so much hp/torque relative to what was there previously and they pull so effortlessly anywhere in the rev range that you forget what a cammy engine feels like, In my own case swapping a stock 964 for a stock 993RS highlighted the difference.

I am sure that the same could be said for thiose that have recammed their 3.6 t/ps(Rich?)

[arrivederci]

All this talk of early cars having peaky torque curves. How about this? http://members.rennlist.com/jpinkert/pepe%20dyno%20run.jpg

Yea, I know its T, not an S. But the small motors can feel torquey too!

My experience with SCs and Carreras is similar to others expressed here. The Carrera's feel fastest on the top end. But they -may- be just as ballsy down low, its just the rush on the top end makes it feel slow.

[Bill Verburg]

Pouncing pussy cat?

I found my 2.4S to be almost unuseable as a daily driver due to the peakiness off the torque curve. Your T looks more similar to a 964(other than the magnitude of the #s)

[rdane]

Add SSIs and the 20/21 cam and the early SC climbs hard right to 7K in every gear. It no longer "dies" @ 6K. Far from it actually. For around town the car literally starts pulling at 1K.

Big difference from a stock SC of the same year.

Do the same to a 3.2 and you'd just have "more" of the same I suspect.

[zymurgist]

Originally posted by Eric Mckenna
i LIKE THE FEEL OF THE EARLY 70S 2.2 LTRS.. IS THERE A WAY TO HAVE THE REV AND GAIN SOME LOWER END GRUNT? MAYBE ?

ERIC

Yes. The guy who built my engine did it.

It's a 2.4 with MFI and 2.2 S heads and S cams. He had the MFI pump built to his specs. Don't know how to duplicate it, but it's got just enough torque to pull away from a stop sign in second if I really have to. And at 5000 rpm it's just mechanical music, adrenaline surge...

[Randy Webb]

The 3.2 heads flow a LOT better than the 3L.

Note that the original post really referredtwo very different issues:
1. how much power a motor can make at high revs,
2. how freely the motor will increase its revs (when you 'gun' it).

There is no necessary relation between these two concepts, tho they are often fairly well correlated, as lighter valve train, rotating, and reciprocating components provide both high absolute revs and faster spin up.

[rs911t]

Sweet spot? Oh, 3500 to 7300!