Curious about how well the 3.0 sc should rev.

[ahh911]

Ian's car revving adventure shows some faith in it's internals.

With the stock sc cams, it doesn't pull as hard past 6000, thankfully, I wouldn't have the guts to let it sit there at 7krpm. But it does pull very nicely to 6000rpm.
I love the 81 cis, around the 10th year of cis development for the 911, so it'd better be the best.

[hughc]

Originally Posted by 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.

Yes, that was the first thing I checked and I did find a bit of play, which I was able to take up by 2 turns of the connector at the throttle body.
As I mentioned earlier, that made a difference and allowed me to reach red line, only Not as vigorously as I would like.
I'll check the timing as per Ian's recommendation and see what that gives.
If I had the resources I would like to swap out the cams for the ones Ian is using.
But we all know swapping out the cams on a 200K mi engine could get very expensive and at this stage of the game I don't think I'm ready for that expenditure
Thanks

[Dave Kost]

The throttle rod coupler can wear out and cause the throttle plate not fully opening.
https://www.pelicanparts.com/More_Info/91142308102.htm?pn=911-423-081-02-M260

[Tremelune]

If your car starts sputtering above a certain RPM, it's not throttle related. When does it sputter? Wide open throttle? Partial? Is it struggling to make enough power to move the car faster? All gears?

My money is on timing and fuel delivery.

[icarp]

Originally Posted by Tremelune

If your car starts sputtering above a certain RPM, it's not throttle related. When does it sputter? Wide open throttle? Partial? Is it struggling to make enough power to move the car faster? All gears?

My money is on timing and fuel delivery.

I think Hugh is reffering to a lazy feeling of the engine, not wanting to charge to redline .

Not based on a missing of spark or fuel. If the advance is incorrect then that might do it .
Ian

[ant7]

If you have the time, Try removing the rear silencer just as an experiment, and see how much quicker the car gets to the red line,[yes it will be quite loud] if it has the original back box still in place it is surprising how restrictive it can be at high RPM.
Just a thought from my own experience.

[hughc]

Originally Posted by ant7

If you have the time, Try removing the rear silencer just as an experiment, and see how much quicker the car gets to the red line,[yes it will be quite loud] if it has the original back box still in place it is surprising how restrictive it can be at high RPM.
Just a thought from my own experience.

Thank you for that suggestion and I may consider it down the road as I also still have the original silencer in my garage that I could also try. But first and foremost I will verify the timing as per Ian and get that behind me.
hughc

[ahh911]

Ian's first gear, speedo is in km/hr.
Thought it was 2nd in mph with different gearing.

For first gear, it seems about right, looks similar to mine without being too picky. Someone stripped out cat, otherwise stock but I rebuilt top end. I think it pulls faster on mine till around 5800, then it would die off and Ian would blow by me.
Phil

[Bill Verburg]

There's a difference between revability in gear and in neutral

in neutral it depends on the rotating mass, cams, cr and exhaust, assuming all is nominal
in gear it depends on gear ratio, which includes cwp and tire OD, rpm, and mass of the vehicle as well as the base items in the neutral rev scenario

all cis 911s peak out hp at ~5500 hp and have heavy stock rubber clutch disks and tall gearing for fuel economy, none wil rev like an earlier engine w/ l/w clutch, fly wheel crank , cam timing and freer exhaust

[Bill Douglas]

Originally Posted by Bill Verburg

all cis 911s peak out hp at ~5500 hp and have heavy stock rubber clutch disks

Are you sure re the stock rubber clutch disks? Maybe when new but I don't think there are any driving around with those these days.

I've read/heard somewhere that you shouldn't rev the car too much in neutral. It should be under load when you are giving it some revs.

[ahh911]

I too have heard not to rev unless under load, but, when I switch to the next higher gear, lot's of times I'll push the clutch without releasing the gas pedal quickly enough and am pretty sure revs blip to 6krpm and above, freewheeling for a second, so, don't know what to say other than it happens from time to time, though not intentional. Come to think of it, every time you shift the engine is freewheeling? Shift properly at 6000rpm and the engine is freewheeling till the next gear and clutch pedal is back up.

In first gear, I don't have an lsd, if I punch the gas while rolling at 2000rpm the tire breaks traction by around 3000rpm. Second year on pilot sport all seasons, the decent ones, but they're getting worn. My point is, there is a lot of grit down there and it will fly to 6000rpm very quickly but you need some skill to keep the wheels from spinning. This is a rolling start, so no clutch drops whatsoever, I never thought the car would be this fast, maybe one day an lsd.

[icarp]

M1 cams will provide GRUNT, but you need to give the engine the fuel it needs to make the power . I can get 0-60 in 5 secs flat if all the stars align .
1/4 mile in 14.0 at 101 mph and no burn out . all that at 8.0-1 comp ratio, my car is a street car, pulls great @ less than 3,000, it has to, to to get the low time numbers
I beat the 2018 honda civic type R all 4 races as well as the WRRX STI subie .
The feel of this cam is power and smooth with a charge at 4,000 to 7000
all this on a stock internals 3.0 , Stock spring plate clutch and steel pressure plate , SSI, dansk 70 mm sport muffler , 205/60/15 front , 225/60/15 rear tires ,
45 mph 1st, 73 2nd ,103 3rd , 131 4th , 146 5th
28 mpg @80 mph, Porterfeild R4S brake pads ,

228 hp at the crank ,in this config , on mustang eddy brake dyno,

Just about the most fun ever !
Ian

[Bill Verburg]

Originally Posted by Bill Douglas

Are you sure re the stock rubber clutch disks? Maybe when new but I don't think there are any driving around with those these days.

I've read/heard somewhere that you shouldn't rev the car too much in neutral. It should be under load when you are giving it some revs.

I did say 'stock'

but even so relatively small changes in the engine rotating mass make noticeable differences in the slope of the rev acceleration curve.

I recently experienced this in one of my 993 engines, It's a 3.6 993 in my '76 C3 w/ RS cams and custom Wong chip, Fabspeed headers etc, went from steel to an Aluminum Sport Clutch, The difference in mass was only a few pounds but the engine response both loaded and unloaded is phenomenal, there was a corresponding reduction in lug ability of the motor

additionally, this motor revs considerably quicker than the 3,8RS in my 993 w/ much heavier g50 competition clutch set up

As to revving in neutral, you do realize that from day one that these cars were timed at 6k rpm in neutral

[ahh911]

Originally Posted by Bill Verburg

all cis 911s peak out hp at ~5500 hp and have heavy stock rubber clutch disks and tall gearing for fuel economy, none wil rev like an earlier engine w/ l/w clutch, fly wheel crank , cam timing and freer exhaust

I've read this many times, I don't have a dyno, let's get that out of the way.
Maybe a touch more compression, cams were SC reworked, timing was set at the point where max valve to piston clearance at edge of timing spec. No cat, regular exhaust. 81sc usa.

I don't know why it's contrary, but at 5800-6000 rpm the car gets a final deep breath, then backs down. It seems to pull harder than anywhere else at that final stretch, in 2nd it most noticable. Why is that 500 rpm more than others? Am I full of it? But there have been many times where this last blast arrives and I'm thinking wow, where did that come from? Some sort of deception, power back down, vacuum advance kicks back in and off it goes again? Don't think so, is there something with my timing and no cat pulling in more air showing a hint of what's possible? Don't know. I didn't mention this earlier figuring no one would believe me. I just did it again several times today.

Phil

[Bill Douglas]

My '82 Euro that's had the internals balanced, SSI's, doesn't back off at any revs. I've red lined it in top gear and it was keen to go faster. I wasn't.

[ahh911]

Originally Posted by Bill Douglas

My '82 Euro that's had the internals balanced, SSI's, doesn't back off at any revs. I've red lined it in top gear and it was keen to go faster. I wasn't.

All we have in common is free-er exhaust.

Between 5700/5800 and 6000 it's a weird sensation, as if all of a sudden air is available freely and flows with ease through the engine, it just feels effortless at that point and it just whips the car along. (Breathy, is that a word?) Also, with free rev talk being the subject of this post, I hung around 6400 rpm the other day, there was a slight high frequency buzzing sound, very faint, that didn't appeal to me.

[Bill Douglas]

Originally Posted by ahh911

All we have in common is free-er exhaust.

Yeah, it's definitely the exhaust. All SC's should have them.

[911SauCy]

Originally Posted by Bill Verburg

all cis 911s peak out hp at ~5500 hp and have heavy stock rubber clutch disks and tall gearing for fuel economy, none wil rev like an earlier engine w/ l/w clutch, fly wheel crank , cam timing and freer exhaust

I have dyno sheets that prove otherwise.

After I replaced my rubber clutch that is... The rubber was good, but certainly not great

[Bill Verburg]

Originally Posted by 911SauCy

I have dyno sheets that prove otherwise.

After I replaced my rubber clutch that is... The rubber was good, but certainly not great

do tell
torque peak/hp peak
1976 911 S 4000/5800
1976 Carrera 3.0 4200/6000
1978 US/ROW SC 4200/5500
1980 SC/RoW USA 4200/5500
1981-83 SC US 4200/5500
1981-83 SCRoW 4300/5500

[Bill Douglas]

My 1979 Euro engine had some low down torque, and ran out of steam at high revs. Well, not really ran out of steam but there eas no point in going over 5,000rpm because it didn't have any power gain.

But my 1982 Euro is a completely different beast. No low down power but the more you rev it the more power it gets. Red lining it in top gear it was feeling lively and wanted to go faster.

No rubbber centered clutches. I think they were swapped out many decades ago.