Can a 3.0 safely rev to 7,000 RPM on a consistent basis?

[Superman]

I think a stock SC engine will rev comfortably beyond 7000 rpm. I think the ages of my valve springs (230k miles) and 20/21 cams should make me a bit conservative about testing this out. My rev limiter kicks in at an indicated 7000 rpm, on the nose, but I think my tach is a tad optimistic.

My owners manual says Max Permissible Cruising RPM is 6300. It says Maximum Engine RPM is 6500 +/- 200. Max hp at 5500. Max torque at 4200. Again, according to the owner's manual.

But here's the rest of the story: With the 20/21 cams, the engien makes power until you back off. It is strong right to the indicated 7000 rpm. But the power band is so broad, there is no need to shift this high. Shifting at early-to-mid sixes places you in the sweet spot for the next gear anyway. So, the question becomes moot for stock motors that don't make power at 6500 rpm, and moot for those with 20/21 cams because these rpms are unnecessary. The question is better for engines that have been modded to make maximum power in a short band at high rpms. But if you're doing that, you have dumped the CIS system and built your engine specifically for that kind of performance, in which case you should have installed stiffer springs.

You're certainly not going to hurt this engine's bottom end at 7000 rpm.

[rdane]

I am looking at 2 SC's dyno runs with 20/21 cams. They make peak HP and torgue before 6000rpm and after that are on a down hill long before either hit the rev limiter. Both a '79 and an '83 SC are out of breath with CIS and 20/21 cams at 6000rpm. No problem pulling 7K mind you but why would you want to is the obvious question.

Peak HP on my car is 182HP at 6100 rpm with 20/21s. At 6900K rpm it is down to 166HP. Torgue starts dropping at 5500rpm

Superman's '83 dyno shows peak power at 5800rpm and 173hp and then declines pretty quickly as 6500rpm shows only 160hp. Torgue starts dropping at 5000.

So while the cars feel very quick to 7K with CIS and 20/21 cams, the reality is the power is declining after 6000rpm. To stay in the power band of 4500 to 6000rpm during a shift all you need to do is shift a bit above 6K. Say around 6200rpm, which amazingly enough is the factory red line

From the look of your Reseda dyno numbers lo0ks like your SC engine was actually just under 160peak HP and not the tweak in the end of 164. Another stock '81 with SSIs was at 159hp here. Those dyno numbers also show 6000 as a dropoff point.

The only dyno numbers that I have seen a 3.0 engine..and not an SC mind you, pull HP past 6K is Noah's. That early 3.0 with 964 cams actually is still pulling @ 6500rpm where his dyno ends at 203 peak HP. His torque #s are inline with the rest of us...only his HPs are skewed out of norm. Different dyno and days on some of it I suspect. But no question it is the only street 3.0 engine I have seen making HP past 6000rpm.

[dd74]

Originally posted by Superman
But here's the rest of the story: With the 20/21 cams, the engien makes power until you back off. It is strong right to the indicated 7000 rpm. But the power band is so broad, there is no need to shift this high. Shifting at early-to-mid sixes places you in the sweet spot for the next gear anyway. So, the question becomes moot for stock motors that don't make power at 6500 rpm, and moot for those with 20/21 cams because these rpms are unnecessary. The question is better for engines that have been modded to make maximum power in a short band at high rpms. But if you're doing that, you have dumped the CIS system and built your engine specifically for that kind of performance, in which case you should have installed stiffer springs.

You're certainly not going to hurt this engine's bottom end at 7000 rpm.

Jim: this says a lot, and thanks. Question about the power band, though: does this theory of shifting in the early-to-mid-sixes to stay within the sweet spot apply to both small and large port 3.0 engines that have 20/21 cams and SSIs? Or is more likely the small port 3.0 will find or stay within the sweet spot more easily than the large port 3.0?

Thanks.

[rdane]

Originally posted by Superman
With the 20/21 cams, the engine makes power until you back off. It is strong right to the indicated 7000 rpm.

My point in case you missed it ,was neither Superman's engine (done at 5800rpm) or mine (done at 6100rpm) with 20/21 cams is "strong" at 7000rpm. But both have an exceptionally flat torque curve. Maximizing shift points is dependant on the gearing of your transmission.

Noah's engine however does pull and is "strong" right to the point he shut it down at 6500. Down side is his 964 cams are very peaky on the torque dyno graph in comparison to the 20/21 dyno.

[aigel]

Bernd:

That's an excellent thread. You should translate it for the folks not capable of reading German. Hehe ... It is very interesting how the same issues come up on either side of the big pond. I am jealous that we can't go for 160mph bursts on public roads. Even on the track here, before you hit top speed, the next turn is coming!

I registered and will at least lurk on the German board. Looks like there is some excellent information to gather for a 911 rookie like myself.

Cheers, George

[Superman]

My butt-dyno results suggest that my engine is still making power at 6000 and 6500 rpm but Dane makes a good point, and one that is backed up with data. We are probably saying the same thing. Shifting actually depends upon which gears you're between. At 6000 rpm in first, my car is going about 37 mph, which is about 3300 rpm in second. So, not a bad idea to stay in first a little longer so that when I shift, I'm closer to my sweet spot at 4000. For other gear transitions, shifting at 6000 or even a little before would be ideal. Noah's engine is set up a little differently. Okay, a lot differently.

Dave, early 3-liters are going to be a little stronger at the top end, while later SCs will have torquier bottom ends, but the difference is not that great. With both early and late SCs, what we're finding is that the 20/21 cams must make them much more driveable. If you'll forgive me, a lot more "V-8"-ish. In fact, the dyno guy said if he did not know my car was a Porsche, he'd swear it was a V-8. Stock SC cams are fairly different, stacking the power in a short band with a steep curve at both ends.