Curious about how well the 3.0 sc should rev.

[Tremelune]

Originally Posted by Bill Douglas

My 1979 Euro engine had some low down torque, and ran out of steam at high revs.

I thought the '79 Euro 3.0 had the big port heads that kept airflow strong up top...?

[Bill Douglas]

Yeah, big port heads, but lower compression ratio. A different sort of power to the '82 engine which is a 930/10. I much prefer the revy later engine.

[icarp]

It is not easy to understand what allows for a engine to rev rapidly
and above 5500 rpm. Sorry this is not meant to sound harsh

Most big port 3.0's run like a rocket , some 3.0's with the small ports do nicely as well.
kermit is one of them , even with 8.0 to 1 comp ratio. This running with either the stock 3.0 cam or the M1 the cam timing is an important part of the equation . This in addition to all the other ancillary parts .

Through the years there has been a lot of miss information thrown around
regarding this subject.

just some thoughts
Ian

[pampadori]

My 3.0 with stock SC cams and small ports running out to the red in 1st gear. While the heads and cams are stock, the ITBs, headers/exhaust, and flywheel/clutch are not. Sounds very similar to ian's video though. I think i also get an advantage from the 2.7 crankshaft which has a quick-revving nature to it.

https://youtube.com/shorts/ylSuvU8Vn10?feature=share

[fastricky]

The first post video is shows a very sweetly revving car, not just throttle response. Either just a luckily balanced motor with great break in/driving history or the motor was balanced. There are motors not as nicely balanced that don't rev like that which is what I'm hearing from the OP.

[Tremelune]

There's like four discussions happening here:

1) Throttle response - How quickly the engine will rev up in neutral

2) Torque/Power - How quickly the engine will rev up under load (how quickly the car accelerates)

3) Dyno curves - Where peak torque and power are on certain engines.

4) Behavior near redline - A presumed issue with the OP's engine above a certain RPM.

What are we trying to improve?

[Reiver]

I've had both the '83 SC in 930-16...US model, and the '83 SC Euro 930-10. Both revved freely and each has caught me with the rev limiter due to that.
The 930-10 is more of a performance motor with 9.5-1 comp and teh greater HP....now with SSI's and a freer flowing exhaust...much nicer. The US model never felt doggy either. Revved with ease to redline.

[fastricky]

Originally Posted by Reiver

I've had both the '83 SC in 930-16...US model, and the '83 SC Euro 930-10. Both revved freely and each has caught me with the rev limiter due to that.
The 930-10 is more of a performance motor with 9.5-1 comp and teh greater HP....now with SSI's and a freer flowing exhaust...much nicer. The US model never felt doggy either. Revved with ease to redline.

That isn't helping my SC craving right now. Or is helping? Depends on whose perspective you're asking in this household.

But my 73.5T sure don't rev like that. Boo!

[icarp]

Originally Posted by pampadori

My 3.0 with stock SC cams and small ports running out to the red in 1st gear. While the heads and cams are stock, the ITBs, headers/exhaust, and flywheel/clutch are not. Sounds very similar to ian's video though. I think i also get an advantage from the 2.7 crankshaft which has a quick-revving nature to it.

https://youtube.com/shorts/ylSuvU8Vn10?feature=share

Pampa, Wow your engine screams !! well done . I'll bet your cam timing has been retarded , that is what happens when I have used stock cams at a retarded setting, and a lighter rotating mass is a great direction to go in as well
I can't remember for sure which video I posted but I think mine was done at
1,500 ft of elevation in NM slight uphill

Your car rocks !!!!!
Ian

[ahh911]

Thanks Guys I appreciated the videos.
I'd like to show what my plain 81sc can do, will try but season is running out and have never posted a video.


Silly Question:
My cams were set to ~ 1.4mm, the range was 1.4mm to 1.7mm. This was done to keep piston to valve clearance of intake above 1.5mm. Is this slightly retarded timing? (It's been awhile)

I want to add, with timing set to 1.4mm, Intake piston to valve clearance ~ 1.5mm, Exhaust piston to valve clearance ~ 3mm. All cyl checked. Don't know what to make of this.

Phil

[Bill Douglas]

Originally Posted by icarp

I'll bet your cam timing has been retarded ,

Maybe I'm a bit retarded. The 1982 SC compared with the '79SC.

It's very free reving and not much low down power.

[icarp]

When I do my cam timing i use the degrees at .050" lift on the intake valve .
I often forget to then do the @mm for Z1 just for reference , for the other school crowd .
As you retard the cam the total hp is increased and it is moved up in the power band , advance it and you will increase the TQ and feel in the lower revs , with smaller total HP numbers , band width is about 400-500rpm from one extreme to the other .
So with the 911sc cams the numbers I like are between 3 degrees ATDC and
8 degrees ATDC @.050". As you retard the cam timing the likely hood of the
valves hitting the piston decreases . There is no rule that says one way is correct ,
it's just what you like .
Just some thoughts
Ian

For me 2800rpm should feel great , strong , fun, and more as revs climb , also there are good cams and lousy cams .

Yes the lower timing number @mm is a retarded number , higher number is advanced

[ant7]

Good post
As you say; where valve timing and ignition timing are concerned you have a certain amount of leway depending on where you want maximum power and torque, [all within safe limits of course] again as you say; there is a sweet spot amongst the varation in cam timing and ignition timing where you can get great results with these engines.

Originally Posted by icarp

When I do my cam timing i use the degrees at .050" lift on the intake valve .
I often forget to then do the @mm for Z1 just for reference , for the other school crowd .
As you retard the cam the total hp is increased and it is moved up in the power band , advance it and you will increase the TQ and feel in the lower revs , with smaller total HP numbers , band width is about 400-500rpm from one extreme to the other .
So with the 911sc cams the numbers I like are between 3 degrees ATDC and
8 degrees ATDC @.050". As you retard the cam timing the likely hood of the
valves hitting the piston decreases . There is no rule that says one way is correct ,
it's just what you like .
Just some thoughts
Ian

For me 2800rpm should feel great , strong , fun, and more as revs climb , also there are good cams and lousy cams .

Yes the lower timing number @mm is a retarded number , higher number is advanced

[David Inc.]

Originally Posted by icarp

When I do my cam timing i use the degrees at .050" lift on the intake valve .
I often forget to then do the @mm for Z1 just for reference , for the other school crowd .
As you retard the cam the total hp is increased and it is moved up in the power band , advance it and you will increase the TQ and feel in the lower revs , with smaller total HP numbers , band width is about 400-500rpm from one extreme to the other .
So with the 911sc cams the numbers I like are between 3 degrees ATDC and
8 degrees ATDC @.050". As you retard the cam timing the likely hood of the
valves hitting the piston decreases . There is no rule that says one way is correct ,
it's just what you like .
Just some thoughts
Ian

For me 2800rpm should feel great , strong , fun, and more as revs climb , also there are good cams and lousy cams .

Yes the lower timing number @mm is a retarded number , higher number is advanced

Well now I feel stupid. I didn't think through the mechanical action of retarding the cam and what that would do for powerband, I just took it as granted it was similar to ignition timing.

Herp derp I'm an idiot.

[pampadori]

Does this cam timing effect on where the powerband resides mostly have to do with the exhaust velocity/scavenging "pulling in" fresh air and fuel where there is overlap with the intake valves? Just trying to understand the "why" this does what it does.

And thanks for compliment Ian! I can't recall where i set the cam timing when i rebuilt it to be honest. It was a cold garage in the middle of winter 5 years ago and i just wanted the car to move on its own power again. I probably went by whatever was in Wayne's book no telling.

[David Inc.]

I think it has to do with the intake valve staying open into the beginning of the compression stroke. At low rpm this is obviously going to reduce compression, but at high rpm the momentum of the air is going to keep it moving into the cylinder even as the piston is coming back up.

[Bill Verburg]

Originally Posted by pampadori

Does this cam timing effect on where the powerband resides mostly have to do with the exhaust velocity/scavenging "pulling in" fresh air and fuel where there is overlap with the intake valves? Just trying to understand the "why" this does what it does.

And thanks for compliment Ian! I can't recall where i set the cam timing when i rebuilt it to be honest. It was a cold garage in the middle of winter 5 years ago and i just wanted the car to move on its own power again. I probably went by whatever was in Wayne's book no telling.

2 things
1) w/ a muffled system any 'scavenging' effect is minimized no matter what
2) scavenging does depend on valve overlap and w/ stock SC cams there is little to no overlap, yes retarding cam timing moves the power upp the rev range a little, most retarded was the '76/77 Carrera 3.0 spec here was .9 - 1.1mm, this was also used on the '81-83 RoW SC, most advanced was all the others @1.4 - 1.7mm, 3.2 split the difference @1.1 - 1.4mm

stock SC valve events


compare that to SCRS valve events


when you have a properly designed open exhaust w/ lumpy cams here's what you get, scavenging aka the 5th cycle

[MarkWard]

@ ahh911 I went through this exercise putting my stock low compression 3.0 ROW together. Unfortunately, I can't lay my hand on the valve to piston clearance I measured, but I can explain how I measured it.

Since your engine is assembled, I assume, and if you are asking about cam timing and valve to piston clearance, once you have set your cam timing. With the dial indicator still installed and zeroed, crankshaft at TDC for that cylinder in overlap, the valve adjuster nut loosened, carefully turn the valve adjuster in. Watch the dial indicator and you should feel the valve touch the piston. That measurement is your valve to piston clearance at TDC. generally .080" for intake valve and .100"for exhaust valve.

Certainly, with high compression pistons without proper valve pockets, valve to piston clearance could be less than a stock engine. You'll need to measure and see for your particular engine. As mentioned retarding the cam should gain you some clearance if you find you need it.

For my low compression 3.0, even at 1.7 mm where I set the cam, I had more than enough clearance for the intake valve and even more for the exhaust. I thought I had written down how many thousandths one full turn of the valve adjuster was but can't seem to locate it and would not want to tell you wrong.

To contribute to the thread, my 3.0 ROW with the larger intakes is very streetable with cams set to 1.7 mm. Above 3000 rpm it roars to life. Which based on this thread is backwards, Almost like a VTEC engine. The last way I would describe it is sluggish. Cams were reground to stock by WebCam and everything else stock. It's scary fun reving it out through the gears.

[hughc]

OK guys ,a little follow up on my original query.
I checked the timing and it was as it should be. 30* BTDC at 3500 rpm. I won't play with that.
I made a small adjustment (for the better) to the throttle rod and I gave the car three treatments of seafoam.
I got to thinking about the way I drive and maybe I was my own worst enemy. Thinking back, I realized that I had a tendency to somewhat lug the engine. Those engines have torque, for sure, but maybe I was often driving in a higher gear than I should have been.
So I became mindful of that and found that I started driving in a lower gear. I did that for a couple of weeks, especially while driving out to visit a friend that lives about 40 mi away on a farm. I pretty well did the whole distance in 3rd where I know I would have normally have been in 4th. For sure, it sounded kind of racy (and burned more fuel) but I think it was good for the engine.
At one point I took it up to 6500 in 2nd and I was happy with that.
So, a couple treatments of seafoam and a more aggressive driving style seems to have improved things somewhat.
I also got to thinking that since the engine pretty well runs out of puff at around 5500 there's really no need to take it up to redline. I'll leave that for the next owner.
Thanks again for your comments.
Hugh

[Walt Fricke]

An SC ought not to feel out of breath at 5500 rpm. Optimum upshift RPMs should be around 6,000-6,250 with stock gearing, though exhaust system variations will vary the torque curve some. A lot of supposition could be saved by a run on a chassis dyno. But if you are OK with how it runs, then no worries.