engine rpm "sweet spot"

[911 tweaks]

I went for a ride in a 73 911S the other day and oh how they bring smiles to your face!! Those who have experienced this know exactly what I am talking about... or do you?

That is the point for discussion here. When that stock 2.4 S engine reachs 3800 to 4000 rpm and the rest of the way to redline, the motor totally transforms itself... total harmony or should I say a symphony amongst all of its moving parts... like this is where the engine most happy... it puls 4x harder than at lower rpms... the rear of the car squats down more as if to say it is time for real performance... all of those in the know understand what I am talking about.

So, enough drum beating here and I will get on with the question.

Question: How can that performance be duplicated (I know the porsche expression, "there is no substitute") in a SC car with a stk 3.0L engine AND move that rpm "sweet spot" down so it actually begins to happen at 3000 rpm?

If possible, maybe the discussion needs to begin with understanding the awesome harmony of specs in the "S" engine i.e. cam specs, head & valve specs, piston dome profile, crank spec, rod length etc. Maybe if these specs were ALL incrementally increased in "size/spec" to maintain the same proportions, what are the options to replicate this?

I understand some will want to know what is the budget... can we keep that out of the replies for now to get technical/spec information.

To assist the engine spec(s) suggested, transmission configuration welcome i.e. 7:31 or 8:31 ring/pinion, what gear #'s?

Application has no smog concerns, 90% street but the stk SC 3.0 is so lathargic compared to the "S" engine, you really can't even begin to compare them and that is what I am asked to do... make this guys SC "POP" from 3k to redline like a 911 S car. (and not go buy an "S" car)

Thank you! Bob

[jluetjen]

In general it's all down to the cams. Due to the overlap and the tuned MFI stacks, in the rev range that you are talking about the intake and exhaust tuning actually packs more then the cylinder's capacity of mixture in each cylinder. That being said, a 3.0 SC motor on Webers puts out as much torque/liter at it's peak torque engine speed of 4500 RPM as an early S does at it's peak torque RPM of 5200 RPM.

So I guess I'd say put some Webers on your engine. After that you're talking about pistons and cams.

[joetiii]

I think I recollect Steve Weiner's website article suggesting a 906 cam or GE80 in a 3.0+ liter engine will give a similar feel to the early S engine. So if you select a GE60 or GE40, you'll come on cam a little lower in the RPM range.

Camshaft selection

[jluetjen]

I also wrote a piece on this forum a while ago.

[911 tweaks]

thanks guys. WWWW OOOOO WWWWW what great info!!
I think I need to find someone who can tell me specific MADE & TESTED engine configurations as I am in no way capable of or wanting to design an engine here but great info to say the least.

Now to figure out how to solve my making a stk 3.0 perform like an "S" engine.
Sounds like carbs, pistons and cams... not in that order, but, where to begin?
Bob

[joetiii]

I just got home and decided to read up a little in Jim Schragers book on the early 911. In the book, he plots the torque curves of the various early 911s on top of each other. (sorry, no way to scan & post.) It is extremely interesting to note the differences in the shapes of the curves from the base '66 911 with its solex cam, to the 2.0S & 2.2S to the longer stroke 2.4S. If this isn't enough, he then adds the E & T engines into the equation to compare their performance and feel. Quite alot to digest.

To summarize, the 2.4S and its higher strung variant the 2.7 RS both make peak torque at lower RPM than the earlier 2.0 and 2.2 S engines. The larger displacement S engines both have steeper torque curves in the lower RPMs which I think gives you the "rush" you are feeling at 3500+.

How to duplicate that without pulling out the calculator and start using jluetjen's formulas on different cam profiles?

[Eagledriver]

The reason you don't feel that "pop" when you pass a certain RPM is that the engine has enough torque at the lower RPM that you don't notice an increase in torque at high RPM. Think of it this way. The SC is has just as much power between 4k and 6.5k as the 2.4S does, it also has way more power between 2k and 4k than the 2.4S does. You would need to "dumb down" the SC to make it more like the 2.4S.

You could do as others suggest and put in a cam that causes the peak power to be higher. The problem is you would need to raise the rev limit of your engine to make use of the power.

-Andy

[911 tweaks]

thanks andy, joe and others for your input here.

So, as andy says, "...put in a cam that causes peak power to be higher" I am not opposed to, however, would I be getting that "POP" feeling? If so, at what rpm? I am trying to have it happen starting at ~ 3k rpm...

Maybe this is not possible in as much as the 3.0L is what it is and can't be made to do such?

I would guess that adding a lo boost turbo would create this POP but I don't to go that route.

Maybe this is an engine builders secret and it won't be posted on a public forum like pelican?
(I am trying to bait someone in the know... ;-)

Anyway, as mentioned earlier, the cam profile is the heart and sole of the engine. The suggested readings from joe & john are major steps in the right direction to unlock this build formula.

Does anyone want to help me spec out this build here on pelican??? joe, john, andy anyone? This is WAY over my head but I have to believe it is do-able.

It just struck me guys... what about the "SC-RS" engine from 83' I believe the yr is? Does it possibly have the "POP" I am after? Maybe it is the 3.0 RSR of 74' vintage?

Does anyone know owners of these engines to ask if they have the addictive "POP" like the 2.4S has?
Bob