You have taken this system about as far as it can go.
There are deminishing returns on mods after backdating the exhaust. I doubt if you are seeing 230hp - only my opinion.

To go further you need to lose the CIS and the CIS pistons and add FI or carbs. I would think max STREETABLE hp for a 3.0L SC engine to be ~250. Any more (usefull) power would come from boosting.

I think you'll find that while it's possible to get 1.5HP/cu in. it's going to require shifting the powerband higher in the rpm range and will hurt lowend torque. I once built a 500HP 302 Ford engine for dragstrip usage and while it was wicked fast it was also undrivable under 3000rpms. From what I have seen of 911 engines they are a much better starting point for high rpm HP with nice large unresticted ports, excellent balance, and light easily revved compontents. My 2.0E engine loved being driven above 3000 and throttle response through the non-original Zenith carbs was very sharp once I tuned them. Currently I'm halfway through installing a 3.0SC into my car with early exhaust and modified Zeniths and I'm expecting around 200-210 HP. While I'm sure you'll get to 275-300, you'll need to consider other things like gearing for example that allows you to stay in that higher powerband. Bigger cams will require higher static compression to maintain the same dynamic compression of a lessor cammed motor due to compression losses at overlap, once you're into the operating range (read powerband) of the cam those losses go away due to the momentum of the airstream. Proper exhaust scavenging will also be critical. What I'm really trying to say hear is that a high rpm/high HP NA motor is a package deal, everything needs to work together to pull it off sucessfully. Good luck on your project.

I agree with Rarly8 bout boosting
 

What about supercharging? Could he still do it at this point with those cams?

ok so I went and looked by the driver side door and the weight on my 1975 says 3086lbs and I looked for the 911 technical specs for that year and found this info: 1975 911 S (US), 911 Carrera S (US) 1100 kg which would be 2425lbs. Which one of these numbers is right? A 1975 can't be 3000lbs!?!?

--Michael

I believe the sticker on the door is GVW (Gross Vehicle Weight) this is the weight of the car plus full payload and passenger capacity not the weight of the car. Somewhere I have the actual figure but I seem to remember the '73 weighing around 2300-2600lbs.

john_cramers post with the facory specs should tell you what you can expect with a properly built 3.0

you can see 300 HP...... and a bit more if you stretch the envelope

realistically using cis or carbs you could get into the 230~250's

to get at the fringe of engine output you'd have to go 10.5:1 or better compression, use MFI or EFI and live on race gas,

free flowing exhaust would be mandatory

So you're saying, Warren, that the most to be expected from the mods are 14 to 16 hp at peak, 20 to 25 mid-range. So that's, what, 220 to 225 total, right? That can't be too bad for a 2300-2400 pound car, right?

I'm going to agree finally. With Warren (always a safe bet). I think my engine may be over 200 hp (stock was 180), but again, the real benefit is in low end torque and high end power as well. The stock engine used to make power only between 4000 and 5500 rpm. Now the power does not trail off at all...makes great power at 6500 rpm, actually. And is very fun to drive at 2500 or 3500 rpm. I'd believe a 25 hp improvement at 3300 rpm. But overall, peak horsepower, these mods probably make 200 horses or so.

Yes, a 230 hp engine in a 2300 lb car would be quite fun to drive. A good driver in a car like that is going to be pretty quick. Depending on tires, of course.

I will say this, the car is squirrlier now. I mean, I used to have to be careful with the throttle in 1st gear, expecially on wet. Now, I have to be quite careful in 1st always, and the tail can even kick out in second. I mean without dropping the clutch, just throttle.

Be happy with your car's power, at least for a while. Learn to drive it. You have a very quick car.

Anyone who says you CAN NOT get 400 hp out of a naturally aspirated 3.0 litre engine has not been around racing much. 3.0 litre engines have been producing over 600 hp for years. You can't do it by changing your air filter or exhaust or by replacing the coil. Also, if you want to get that kind of horsepower by just bolting something on the outside of the engine, turbo or superchargers are the only way to go. But when someone says it is impossible to get 400 hp out of a 3.0 litre, I beg to differ. It won't be something you want to drive on the street, but I think I mentioned that. It won't be built by a do-it- yourself shade tree mechanic in his backyard on Saturday afternoon either. But it can and has been done. You can't get more than about 250 hp out of a 3.0 below 7000 rpm either. It will take racing fuel but racing fuel alone won't do anything for you. The entire engine has to be modified beyond the comprehension of the average do-it yourself mechanic. By the way, there are motorcyles with stock engines less than 1 Litre producing over 140 hp. So engines are not limited to 100 hp per litre. Just take a look at the specs on some of the formula racing engines over the years.

The point being made hear is that there are limits to streetable horsepower in naturally aspirated and forced induction. I don't feel that requiring race gas can be considered streetable, I also don't feel that a car that shakes and coughs below 3000 rpm is streetable either. As for forced induction a car with a huge turbo and a lot of lag isn't all that streetable either. I made mention of a 500hp 302 that I had built which equates to 100hp/liter but it wasn't streetable by any means. I do feel that the 911 engine is capable of 90-100hp/liter in streetable trim due to the fact that it started life as a high performance engine and it's head configuration reflects this but hp levels that high will most likely be on the edge of streetablity. There is only one way to build huge HP figures from a NA engine (without increasing displacement) and that's with rpms. Everything needs to be maximize toward high rpm airflow the heads, valves, cams, intake system, and exhaust all neet to be capable of flowing a lot more air, the problem with this is airflow at lower rpm will be so slow that torque will suffer greatly and therefore driveability will suffer. Another requirement of high rpm HP is an "oversquare" engine (big bore, short stroke) this also hurts lowend torque. As HP and rpms are increased engine strain and wear increase exponentially, which is why race engines have such a short life span.

I think john_cramers factory power outputs (or thereabouts) are a pretty good idea of the maximum for a 2 valve per cylinder Porsche engine.

More is possible - there is a 370ish hp 3.4 here in New Zealand but this required:

- 10.5 c/r
- RSR cams
- 50mm TWM induction
- MoTeC M8
- big enough headers

This is thousands of dollars in parts alone, and probably represents what Porsche themselves would have done to the engine with modern technology.

My own (finished!) engine is a 3.0 with 98mm p&c for 3.2 (a 6.5% increase). It is twin plug, has 10.3:1 c/r and S cams with 40mm throttle bodies and ported heads etc. With SSIs and a regular muffler, I will be very very pleased with 270hp, or 85hp/litre. And yes, it is streetable (EFI, very light car). I will supply a dyno run next week after it is tuned properly.

Look at Porsche's own power claims - anything over 80hp/litre required S cams, eg:

- 204hp SC (higher compression - 9.3:1) 68hp/litre
- 231 (Euro) Carrera with 10.3 c/r (I think) - about 72 hp/litre

I just can't believe that you can depart too far from the result of S cams in the 3.0RS - 230hp with 9.3 c/r. Sorry. I am hoping for just 25 hp above that (ie 230hp + 6.5% to give 245hp, then gap to 270 is 25hp) from twin-plug and 1 point higher c/r , larger ports and throttle bodies and modern fuel management.

Also - the usual quoted weight for a '75 is 1075 kg without air con (2365lb).

Two other data points:

310hp from a short stroke 3.2 (thus 3164cc):
http://www.williams.co.nz/stallion.htm

Kurt Starnes 3.2 short stroke with RSR cams approx 300hp:
http://www.williams.co.nz/stallion.htm

Remember these are 3.2s - the equivalent 3.0 is 93.5% or only 280hp. I would assume these engines are on the edge of streetable.

Cameron - when you say without a.c.
 

...are you talking about a.c. in total, including the interior vents and the blower in the trunk's smuggler's box up front, or are you only counting the compressor on the engine and the condensor?

Thanks.

Cameron - just saw your other post --
 

the 3.0 is 93.5% of a 3.2 at what point? When it is short stroked to a 3.2 or stock? I'm not certain.

Thanks.

Cam, your engine sounds awesome.

I've been contemplating a 3+ltr MFI conversion for my car as a long term project - which should get the thing up and going.

Looking forward to hearing your seat of the pants impressions when you've got the car sorted.

Good luck.

Cam I'm dying to see this new engine in action. Nice setup :)

What I understand is that in 74/75 air con wasn't standard and the weight quoted reflects this. I think most of the weight increase to the SC was the air con (up from 1075 to 1160kg, although flares and wheels/tyres must have made a difference). I assume it is the whole system - lines and all.

Take this with a grain of salt - it is partly a guess, partly a vauge recollection of something I have read. The numbers are based on the info in the Cotton book "Original Porsche 911".

I checked the displacement numbers when I got home last night - I wasn't quite right on the displacements - note 3164 is Carrera displacement, 3186 is short stroke SC displacement:

3.0 SC with 95mm pistons and 70.4mm crank = 2994cc
3.2 SC with 98mm pistons = 3186cc (ie 6.5% bigger due to increase in piston size)
3.2 Carrera with 95mm pistons and 74.4mm crank = 3164cc (due to longer stroke)

Putting 98mm cylinders on a 74.4mm Carrera crank gives 3.4 litres.

Basically, the bore increases with the 98mm pistons and cylinders by 3mm. 3mm / 95mm = 3.16%. 3.16% squared (remember Pi*r^2 for area) gives 6.4% increase in area of piston top. Oooops, it is 6.4% not 6.5% ;). You get same result with 3186/2994 - 1.

Thinking again, to clarify, you could consider a standard 3.2 Carrera as a "long-stroke" 3.2 (74.4mm stroke) and a 3.0SC with 98mm pistons and cylinders as a "short stroke" 3.2 (70.4mm stroke).

My engine? Well, it runs but is running rich and needs tuning before driving any distance as too much fuel will impede the rings seating properly. It will get off the truck and straight on to the dyno in the next day or two.

First impressions (about 2km of driving) are that it is amazingly torquey and very fast.... below 4k revs or so. I can only begin to imagine what happens over 5k when the S cams start to do their thing.

I should have the car run in by the end of the month and can report then on full throttle and 7k rpm. I will hopefully have it safely back home by next week and can start driving!

Bill - I will try and make my merry way down to Wellington at some stage (roooooad trip) and will let you know :)

Although I am normally a very busy man, I will be sure to put by a couple of days spare to take over the running in chore Cam.
Usually wouldn't offer, but us Pelicanites should stick together, even in the hard, laborious times.

I feel my services would be of most use near the final, higher rpm break-in period, as that is my self appointed area of expertise.

Bill: you will have to wait :)