I went for a ride in a 73 RS-spec

[porschenut]

I'd never been in an early 911 before. I always thought my 3.2 Carrera had a pretty responsive gas pedal.

Then a few days ago I was treated to a ride in a '73 S targa with a rebuilt RS-spec 2.7 engine. Wow! It was much more zippy than my 3.2. The first time he stepped on it, I got dizzy for a couple of seconds. That's only happened to me twice before: once in an instructor's race car on a track, and once while driving my 997 S.

The 2.7 RS engine is rated at 210 hp with only 8.5:1 compression. My 86 3.2 is rated about the same with 9.5:1 compression, but it certainly isn't as fast as that targa I rode in. I attribute this to the 3.2 being a heavier car, with a mild cam (the RS-spec has a 906 cam), with wimpy injection (Motronic vs. MFI), and loaded with emissions equipment.

Switching gears here for a second, the 2.4S engine of 1973 delivered 190 bhp. A year later, the 2.7S engine delivered 165 bhp. That's a drop of 25 bhp despite a displacement increase. That was the beginning of tough emissions regulations. Even the 911SC didn't exceed the rating of the 2.4S motor. It wasn't until the 3.2 Carrera of 1984 (207 bhp) that we saw horsepower ratings that exceeded that of the 2.4S. That's amazing to me.

No wonder the 73 S is such a sought-after car. With my RS clone project, somehow I have to find a way to rebuild the 3.2 motor with the zippiness of that S/RS car I rode in. That was MAGICAL.

[MotoSook]

Drop some mass off your Carrera and get the chipped tuned. That should help with the feel of your car.

As for your 3.2 rebuild, you can go to soem 98mm high compression pistons with 98mm Mahle or bore and plated cylinders...or better yet, get some Nickies from Charles at LN Engineering. If you don't have to meet emissions with the car, then you can go a little more wild with the cames, more than the 964 profiles. Are you changing induction or sticking with the Motronic?

My 76 with a 3.0 CIS engine is a pretty fun car to drive compared to the 89 Carrera I call the "Fat Bastard." There is a comfort factor in the Carrera that takes away from some of the viceral effect as compared to the lighter '76. Perhaps that's a bigger factor than simple power to weight ratio. Gearing makes a big impact of how the car feels too.

[GrantG]

Nothing responds as well as a well tuned MFI system...

[SpeedracerIndy]

Originally Posted by porschenut

...
Switching gears here for a second, the 2.4S engine of 1973 delivered 190 bhp. A year later, the 2.7S engine delivered 165 bhp. That's a drop of 25 bhp despite a displacement increase. That was the beginning of tough emissions regulations. Even the 911SC didn't exceed the rating of the 2.4S motor. It wasn't until the 3.2 Carrera of 1984 (207 bhp) that we saw horsepower ratings that exceeded that of the 2.4S. That's amazing to me.
...

Don't forget about the late 70's Carrera 3.0s and the 81-83 ROW SCs. They all had over 200 hp, we just weren't blessed with them here in the states.

[psalt]

Switching gears here for a second, the 2.4S engine of 1973 delivered 190 bhp. A year later, the 2.7S engine delivered 165 bhp. That's a drop of 25 bhp despite a displacement increase. That was the beginning of tough emissions regulations. Even the 911SC didn't exceed the rating of the 2.4S motor. It wasn't until the 3.2 Carrera of 1984 (207 bhp) that we saw horsepower ratings that exceeded that of the 2.4S. That's amazing to me.

Dave,

You have to be careful comparing hp ratings around this period, there was a change in the US hp spec (gross vs net) and all ratings dropped more than the engine changes would suggest. Take a look at the torque figures, they are more comparable and responsible for what you "feel" in a road car.

[porschenut]

Yes, you're right guys, I was referring to cars built only for the U.S. market. What amazes me is how badly the emissions and fuel efficiency requirements put a wet blanket on these sports cars.

[jluetjen]

Originally Posted by psalt

Dave,

You have to be careful comparing hp ratings around this period, there was a change in the US hp spec (gross vs net) and all ratings dropped more than the engine changes would suggest. Take a look at the torque figures, they are more comparable and responsible for what you "feel" in a road car.

Paul; Porsche has traditionally quoted in DIN PS, which as far as I know didn't change.

[psalt]

Yes, it did . The 165 hp rating for the 2.7 mentioned above was SAE net, the 190 hp was DIN, so the drop in hp was more like 15 not 25. Torque went up around 15 ft/lbs.

[Elombard]

I think the 2.2S motors are even more amazing then the 2.4. Almost the same HP even less displacement and a higher red line I think. Really need a light wt car to enjoy I would imagine. Even in a stock S of the day with some luxury items they were "difficult" off the line because they make such low torque at low RPMs....all heresay I have never driven the 2.2s just repeating what I have heard and some of what Anderson talks about in his book.

You cant get that zip from a 3.2 EFI motor and still meet emissions IMHO. As said above, if you keep the EFI, cams, euro Pistons, open up the exhaust, 7:31 R&P and lose several hundred pounds it will be pretty zippy.

I hear that the 3.2 Short stroke with carbs has a similar zip feel with even more grunt.

[Porsche-O-Phile]

Carbs and a set of hot cams will wake up any engine.

[dmcummins]

I had a 2.4S with 2.2s pistons in my 72. It also had carbs and a electormotive setup. It would definatly rev up and was fun to drive. But my 73 with the 3.2 euro motor in it is pretty zippy. Its really feels like a big step up. It just pulls hard from the start.

[Superman]

It sounds like you were a passenger. According to my understanding, if you had been the driver, your impressions would be much overwhelming.

[Jeff Higgins]

Originally Posted by GrantG

Nothing responds as well as a well tuned MFI system...

Absolutely. The throttle response makes it feel like there is a lot more power on tap than there really is. I would let SC or Carrera owners drive my car when it had the lowly 2.4 "T" motor in in, and none of them could believe it had only150 hp. It just feels much quicker than that. My new 3.0 on MFI is a whole different story, with darn near 100 more hp and the same throttle response... Yee-haw...

[dmcummins]

I do want to add that the 2.4s was a blast when the revs are up. I havn't driven a 2.7rs motor so I really can't compare.

[Doug&Julie]

Originally Posted by porschenut

Yes, you're right guys, I was referring to cars built only for the U.S. market. What amazes me is how badly the emissions and fuel efficiency requirements put a wet blanket on these sports cars.

You're not quite comparing apples to apples...the 2.4S was the top motor in '73 but the 2.7S was not the top motor in '74 - '77. We never got the top motor here in the states during those years. So instead, compare the 2.7S motor to the 2.4E motor of '73 and the 2.7 (non-S) to the 2.4T of '73. I think you'll find comparisons a little more favourable.

Congrats on the ride in the RS spec car! Must have been sweet.

[butzi73]

So, some more questions on the horsepower drop between the 73 2.4 and the 74 2.7.

I have a 2.7 from a '74S in my car. It does have cams and pistons, but besides whatever HP increase those modifications give me I have always wondered where the baseline drop in HP between the 2.4 and 2.7 came from. I've always been told or read that it was because of emissions controls, but I don't know specifically what those controls are on my engine. Paul mentions that taking into account the drop caused by the conversion from DIN to SAE there was still a real drop of about 15HP. For my engine, why? I don't have thermal reactors, just headers right out of the cylinders into a sport exhaust. Is there something else on my engine that I'm not thinking about that would be an emissions control that causes my engine to be 15 hp (baseline) less than a 2.4?

Thanks!

[Jeff Higgins]

Originally Posted by butzi73

So, some more questions on the horsepower drop between the 73 2.4 and the 74 2.7.

I have a 2.7 from a '74S in my car. It does have cams and pistons, but besides whatever HP increase those modifications give me I have always wondered where the baseline drop in HP between the 2.4 and 2.7 came from. I've always been told or read that it was because of emissions controls, but I don't know specifically what those controls are on my engine. Paul mentions that taking into account the drop caused by the conversion from DIN to SAE there was still a real drop of about 15HP. For my engine, why? I don't have thermal reactors, just headers right out of the cylinders into a sport exhaust. Is there something else on my engine that I'm not thinking about that would be an emissions control that causes my engine to be 15 hp (baseline) less than a 2.4?

Thanks!

The CIS system dictates cams and pistons. CIS will not tolerate any kind of reversion into the intake tract at any rpm, severly limiting - more like eliminating - any ability to use a cam profile that has any overlap between intake and exhaust valve opening. Even the "wildest" CIS compatible cams are "milder" than those that can be used with MFI or carbs.

Switching to PMO's, as you have, allows you to run a much hotter cam profile. If you did that, you should more than be able to make up for the difference between a CIS inducted 2.7 and an MFI inducted 2.4.

This period of "overlap" - where both valves are open at the same time - provides a degree of cylinder scavenging and filling that is impossible to achieve without it, at least in a normally aspirated motor. Unfortunately, it also causes a degree of reversion into the intake tract at certain rpm's, which will absolutely confuse the mass airflow censor in a CIS system.

[RWebb]

Originally Posted by GrantG

Nothing responds as well as a well tuned MFI system...

Grant, I often hear people say that. BUT... I've never heard anyone directly compare the throttle response of MFI to that of a performance tuned (aftermarket) EFI system.

... much less carbs

Have you done that?

Or are you comparing MFI to production DME systems?

[Grady Clay]

Originally Posted by butzi73

So, some more questions on the horsepower drop between the 73 2.4 and the 74 2.7.

... I have always wondered where the baseline drop in HP between the 2.4 and 2.7 came from.

It is called CIS.

Going along with that are no-overlap cams, thermal reactors, catylitic converters, etc.

There Is No Substitute for high compression, cam overlap, large direct intake and exhaust (and large displacement) to 'wake up' an air-cooled 911.
That said, the price is less fuel economy, emmissions non-compliance and some 'fussy' running on the street.

I like my 'toy' to be very lightweight, large displacement, high compression, wild camed, very responsive, high grip and very nimble. Porsche, our of necessity and regulation, hasn't sold a car like this to the public since the RS-61 Spyder in the early '60s. The good news is you can build one of these yourself to any level you please starting with a good 911.

Best,
Grady

[boba]

Originally Posted by RWebb

Grant, I often hear people say that. BUT... I've never heard anyone directly compare the throttle response of MFI to that of a performance tuned (aftermarket) EFI system.

... much less carbs

Have you done that?

Or are you comparing MFI to production DME systems?

I tend to agree there is more to it than MFI.

It is also cams, compression, and ITB vs common plenums induction. Power to weight also add to the feel.

All that said the early cars when correctly set up are a permanent grin induction device (PGI).