Curious about how well the 3.0 sc should rev.

[hughc]

I watched most of this video earlier today.

https://www.youtube.com/watch?v=6-o6xWOWFU4&t=908s

I couldn't help but notice how effortlessly that engine revved up to and beyond the red line, very close to 7000.

I often wondered if my engine was underperforming as it really seems to struggle after I get to app. 5500 rpm.

I've had it to redline but it was a struggle.

Is there something I should look at?

The cat has been replaced with a cheater pipe and the muffler has been replaced with a Borla 1 in 1 out.

Could the muffler have something to do with the engine's reluctance to rev freely?
Thanks,
hughc

[Hulley]

Not sure about the muffler but mine will run easily to redline, mine is stock with a M&K cat bypass pipe.

[Mark Salvetti]

I'm not sure what you mean by struggle, but it's possible that your throttle linkage needs adjustment. You just may not be getting full throttle. Lots of threads here about making adjustments, here is a good one:
Not getting full throttle?

Mark

[Gordo2]

Looks like he drops to 3rd gear at 90kph (55mph) @ 3,800 RPM // accelerates with shift to 4th @ 160 kph (99 mph) @ 6,600 RPM // and continues to mash the pedal in 4th until 190 kph (118 mph) @ 6,200 RPM.

Seems like normal acceleration for an SC / 3.0 operating in it's power band (~4k to 6.5k RPM) to me.

Drive it harder and enjoy...

[Bill Douglas]

My SC's engine has been balanced and rev's like a Honda. Imagine that. a Porsche engine as good as a Honda.

Not that I make habit of it but it rev's out to 9,000rpm I tend to not rev past 6,000rpm though.

[ant7]

The exhaust back box depending on the type fitted can be very restrictive especialy when you get past 5k RPM, Mine is the 3.2, but I was very surprised at how much faster it would rev and hit the rev limiter when I removed the standard back box and fitted the Bisimoto rear exhaust, not for everyone I know but for the time I had it fitted to the car it was great fun!
As others have said; make sure you are getting full throttle before you suspect anything else, it is also important to have a good rotar arm, distributor cap, and leads for high rev's as they can deteriorate with age.
Hope this helps.

[mikedsilva]

Originally Posted by Bill Douglas

My SC's engine has been balanced and rev's like a Honda. Imagine that. a Porsche engine as good as a Honda.

Not that I make habit of it but it rev's out to 9,000rpm I tend to not rev past 6,000rpm though.

9000!!!!

Is that really possible?
wow

[hughc]

Thanks guys,
I ever thought of the throttle linkage as I as thinking along the lines of anything but.
I'll have a closer look at that as soon as time allows.

The distributor was rebuilt 20K mi. ago and at that time the person that did the work (no names for now) advised that I set the timing at 16 to 20 BTDC. I've continued to set the timing as per Bentley but often wondered what would be the result of setting the timing at 16 to 20 BTDC.

For now I'll deal with the throttle linkage and take it from there.
thx again

[AlKidd]

My 3.0 pulls hard and steady from 3500 to my self imposed 6500 rev line. You do have to work the gears right to be in that zone. Not unusual for me to downshift 2 gears to pass someone.

[kenzinger]

I've always been terrified of the redline... Is what he doing in the video alright??

[icarp]

The 911 loves to rev to redline !!!!
The better it is tuned the faster it revs .
Ian

Here is a 20 sec video of Kermit reving .
https://www.youtube.com/watch?v=x6f0S2gz5ZQ

short vid 130 mph 4th gear

https://www.youtube.com/watch?v=F1_TpayD3D8

[Bill Douglas]

Originally Posted by mikedsilva

9000!!!!

Is that really possible?
wow

Yeah, you should go out to the garage and try it. Report back with details.

[pampadori]

Kenzinger - there is a page in the owners manual that mentions maximum safe sustained (cruising) rpms.
It is something like 6300rpm. Briefly seeing 6800 Or more isn't gonna make it sweat.

That being said, there are quite a few cars running around with broken valve springs so before you change your habits it might be worth pulling covers and confirming the springs are all intact.

[icarp]

More RPM fun with 911 sc

https://www.youtube.com/watch?v=BnQS571mNrE

Ian

[Schulisco]

Check the mixture with a Lambda tool over the whole rev band. Mine (930/16 with lambda control unit) was laggy too over 4000 rpm. It was way too lean. I figured it out without a Lambda tool while bridging the csv manually via switch on the dash when I revved it over 4000rpm. So I found out that it was too lean and checked and adjusted the sensor plate height and have the fuel distributor and the wur overhauled.
The recent discussion in another thread here by having the csv controlled by micro switch on the throttle is not necessary when the CIS works as designed.

Also check for vacuum leaks. They can also make the engine running lean. But such huge vacuum leaks influences the idle and cruise as well...how does the car starts?

Thomas

[hughc]

I don't understand. This is the third time I've tried replying to this thread so I hope this is the one that will stick.

Just to update on what's been happening I did check the throttle linkage and found some looseness and corrected that as best I could. The engine now revs up to red line somewhat quicker than before but not as quick as I'd like. But I can live with it if necessary.
I did a leak down test and it is what it is. #1 showed 23%. #2 at 8%, #3 at 12%, #4 at 7%, #5 at 11% and #6 at 18%. Not the best , I know, but with 200K mi I won't fret about it too much. I'll test it again before next season.

I did have an interesting conversation with Ian (icarp) and with his experience with these engines (see his videos above) I think his suggestions may be valid.
1. I should and will check the timing at 3500 rpm to see that it is at 30* BTDC. I'll adjust if necessary. That may be a valid point as I've only set the timing at idle.
2. Ian also mentioned, from his experience, the A/F ratio at WOT should be around 10 for maximum power, whereas my A/F instrument shows 12.5 at WOT. I'm not sure how to get it richer at WOT except maybe by some slight adjustment to the WUR which I am reluctant to mess with after my experience this past summer.
Maybe someone with more experience can chime in.
3. Lastly, not knowing how the previous owners may have driven this vehicle, the valves could possibly have some carbon build up so Ian is recommending that I do several treatments of Seafoam and start to drive it like I stole it. An Italian tune up so to speak.
So this is where I currently stand. Thanks to all of you that took the time to reply and offer comments/suggestions.
hughc

[Bill Douglas]

Originally Posted by hughc

IAn Italian tune up so to speak.

I don't know if it's placebo effect or not, but my SC always seems to run "better" after an Italian tune up.

[icarp]

Regarding the AFR, the WOT number is meant to be 12.8 for max power to the point of max TQ rpm, then it can roll off .3 to .5 points to a total of 13.4 up to the redline for our aircooled aluminum cased engines
I think there was a miss understanding on the phone, sorry for that .
I hope this helps . Make sure you pursue the ignition timing to the correct point 29* to 30* at 3300rpm ish . more timing past this point is not better unless the dyno says so.

SO THE 12.5 YOU HAVE AT WOT IS CORRECT !!!!!!!!

Ian

[hughc]

Originally Posted by icarp

Regarding the AFR, the WOT number is meant to be 12.8 for max power to the point of max TQ rpm, then it can roll off .3 to .5 points to a total of 13.4 up to the redline for our aircooled aluminum cased engines
I think there was a miss understanding on the phone, sorry for that .
I hope this helps . Make sure you pursue the ignition timing to the correct point 29* to 30* at 3300rpm ish . more timing past this point is not better unless the dyno says so.

SO THE 12.5 YOU HAVE AT WOT IS CORRECT !!!!!!!!

Ian

Alright. Thanks Ian. I'm glad there wont be any need to start messing with the WUR.
I'll verify the timing as soon as the opportunity presents itself.
hughc

[David Inc.]

Hugh, have a helper depress the throttle pedal from in the car while you watch at the engine. After they floor it see if you can still open the throttle any further from the linkage. As the bushings wear out the pedal won't get full rotation at the throttle body and you'll lose throttle actuation (even the bushings in the tunnel can mess with this).

The previous owner of my SC thought it was down on power but the PPI showed that it was just this plus a bent throttle linkage. He was only getting about 70% throttle.

Lots of other good advice here but I'd check this first. I know you said you checked the linkages for being tight but I'm not sure if you checked the full action from pedal to throttle. Ignore if you did.