Possible to extract more power from euro 3.0 carrera than 3.0 SC?
 

I know that a popular upgrade on the 180 hp 3.0 SC is to increase the compression. By increasing the compression from 8.5:1 to around 9.5:1 it's possible to get about 20 more hp. The SC's that originally have 9.8:1 in compression have 204 hp stock.

My engine, a 3.0 carrera (930-02) has a 8.5:1 compression ratio. But it has 200 hp in it's stock form. Is it then wrong to assume that by increasing the compression to 9.5:1 - 9.8:1 the power would increase to around 220 hp?

If this is true, then this engine is 20 hp ahead of the SC engines, before taking bolt on upgrades into the equation.

So, if a 8.5:1 180 hp SC engine can produce 230 hp with raised compression, better exhaust (headers or SSI's) and 964 camshafts, then most likely the 3.0 carrera can produce 250 hp with the same improvements? And if not, what is the hindrance?

I should also add that the bore and stroke is the same between the different engines. As are the size of the valves and the exhaust ports. But the intake ports are bigger on the 3.0 carrera (39) than the SC's (35). The ignition timing is also a bit different.

The camshafts on the 3.0 carrera are identical to some of the SC engines, including the 204 hp versions.

All these numbers are taken from the book "how to rebuild and modify porsche 911 engines" by Wayne Dempsey.

I am suspect that bumping compression from 8.5 to 9.5 will inot ncrease effency 10% (20hp). Years ago I think I read it is about 4% or possably up to 8HP.

I suspect that Porsche managed its HP numbers at times.

I do not think the early 3.0 Euro car had an Air Injection Pump that took a few HP to drive. Nor do I think it had a cat which took up 4-5hp.

The early 3.0 Carrera also had a bit different valve timming that moved the TQ up the RPM range giving it a few more peak HP.

What is good about the earlyer cars 3.0 through 79 is they had larger intake ports. Only the 80-83 SC's had the smaller intake ports you note.

However, if you put in later Euro pistons, headers, and a sport muffler, you should get over 200fwhp.

The efficiency of the ideal Otto cycle vs. compression ratio in thermodynamics is calculated as follows. The quantity <!-- MATH $V_1/V_2 =r$ --> V1/V2 = r is the compression ratio:



The ideal Otto cycle efficiency is shown as a function of the compression ratio. As the compression ratio, r , increases, <!-- MATH $\eta_\textrm{Otto}$ --> http://web.mit.edu/16.unified/www/SP...tes/img387.png increases, but so does the temperature T of the mixture at peak compression . If T is too high, the mixture will ignite without a spark (at the wrong location in the cycle aka predetonation).

Simplified:

engine efficiency = 1 - ( 1 / (r ^ (K - 1))) where K = 1.4 for normal air

or:

1 - (1 / ( r ^ 0.4))

therefore efficiencies for:

8.5:1 CR = 0.57515
9.5:1 CR = 0.59364
9.8:1 CR = 0.59866
10.5:1 CR = 0.60959

for a 200 hp motor, the efficiency increase from 9.5 to 9.8 is .005 or appx. a 1 HP gain

There you go.

My reference was from memory and a book I looked at from someone called Smoky Joe or something that built V8 race motors.

I think you meant rwhp, not fwhp when you gave your estimate. ;)

I am probably wrong (or rather the references I have are), but I know I have read several places that a one point increase in compression ratio roughly equates a 10% power increase.

It does make sense that by not having a catalytic converter or air injection pump more power is available. But, did the R.o.W. SC's have these things? 1980-1983 USA and Japan SC's made 180 hp with a 9.3:1 CR, while the R.o.W. SC's of the same year span made 204 hp with a 9.8:1 CR (except in 1980 when the R.oW. SC's had a 8.6 CR and made 188 hp). I thought the emission restrictions were stricter in the US and Japan at that time, and that the addition of catalytic converters and air injection pumps, along with a 0.5 lower CR, thus explaines the 24 hp difference between the models.

If this is not the explanation, then what is? And if it is the explanation, then the fact that a 1981-1983 R.o.W. SC 3.0 makes 204 hp at 9.8:1 while the Euro-Carrera 3.0 makes 200 hp at 8.5:1, both without cats or air injection pumps, should make it probable that the Carrera could make more than 204 hp at 9.8:1.

The early 1978-1979 SC's only had 8.5:1 and made 180 hp. I assume they didn't have air injection pumps, and perhaps not cats? And that to meet stricter emissions regulations, in 1980 the USA and Japan SC's had air injection pumps and cats fitted, and at the same time had the CR increased to 9.3:1 to compensate for the incurred power loss and thus staying at a 180 hp output.

Btw, I already have headers and a very good custom made sports muffler, so I am very curious as to where that puts me so far. In the future I plan to upgrade to a distributorless computronix DIS6 ignition, and to increase the CR as far as I can go without causing detonation on street gas. My goal would be to achieve 250 bhp.

Dont forget the C3 has the 2.7 lighter crank which makes it a really nice rev happy engine

You'll need to go SSI and drop the CIS to get 250 IMO. Twin spark will help but I would dump the CIS pistons also. A compression hike will get you more than 1hp but nowhere near 20. Cams are also a good idea.

250 fwhp from an SC or a C3 is not a cheap exercise. Better to drop a shorter final drive in with SSIs and a balanced bottom end, optimise everything, match the ports, fit some sort of decent mappable intake and enjoy it at that.

No, I think he was right. Flywheel HP. Not frontwheel hp. Otherwise I have to forget what I've learned through painful and expensive experience.

For 250hp(flywheel or factory rating) get 98mm P&C's for a 3.2 short stroke with S or GE40 cams, 1 5/8 headers, sport muffler, carbs. Better yet, convert it to MFI.

This will be a very fun motor. Basically a big 2.7RS motor. (2.7=210, 3.2=250).

Or was it Smokey the bear? JK, thanks for the grin. :p

I assume you mean Henry 'Smokey' Yunick, one of the most legendary race car mechanics/builders of all time.

I would keep it under 3 litres and forget targeting a HP number. Just optimise: build a sweet, balanced bottom end, help it breathe better and stick a shorter final drive in it or regear to get close 1 to 4 and a leggy 5th. Then drive it forever :cool:

I get the two mixed up so I am not sure. It may have been 20 years ago so I do not count on my memory to be spot on.

SW, I wonder, dose the formula reference the effective compression ratio in some way? That is, a SC with 8.5/1 measured compression is closer to 7.5/1 effective compression.

I wish I had your math skills.

I know that with each compression bump we see less and less gain.

Not quite right. You have the difference of increase, not percentage increase. .... (0.59866/0.59364) =1.00846 ...x200 = 201.69

So .8% (.008) more efficiency. (for 9.5->9.8) and, 1.7_HP of theoretical increase. (clearly worth a few grand)

right on ... I was just checking to see if anyone was awake :D

Euro Pre-Muffler
 

Seems to be alot of questions surrounding the various OEM European Pre-Mufflers. Can anyone clear up the difference between

• P/N 911 183 111 00
• P/N 930 183 111 00

I believe the P/N starting with 911 was originally designed for the 3.0L SC motors 1978-1983 but fits 84-89 Carrera 3.2L also. Whereas the P/N starting with 930 was originally designed for 84-89 Carrera's and Turbos.

Are there any significant differences or concerns interchanging these parts on SC's and Carrera's. Note the OEM Cat P/N 930 113 230 25 is the same for all 1980-1989 911's

Thanks, Doug