One more 3.0 CIS question

dd74 · 05-12-2002, 10:57 PM

Hi all. Back to the engine section again:

I know the horsepower rating for a stock American 3.0L is 180. But does that rise in power if back-dated heat exchangers from a '74 are used in conjunction with, say, a Bursch dual inlet, single outlet muffler? And if so, how much might the final horsepower be? Anyone know? Secondly, what's the difference between a 180 horsepower American 3.0L and the 204 horsepower European version? Is it just the higher compression ratio (8.5:1 vs 9.8:1), or is there more to it than that? Can a 9.8:1 compression 3.0L run okay on California 91 octane super-unleaded pump gas?

Thanks for your input.

304065 · 05-13-2002, 06:08 AM

I'll be interested to hear from the experts on this one. I do know that much of the difference between the Euro CIS and the US version was the emissions equipment- which can be deleted for off-road use.

My PCA Club Racing run group at Lime Rock included SC's. At the end of the straights, more than a couple of the cars would shoot fire out of the tailpipes for about 6". That doesn't happen unless you are running an incredibly rich mixture in an NA car. So there are definitely tricks out there to get CIS to produce big power.

dd74 · 05-13-2002, 06:53 AM

Excuse me but what's an "NA car?"

Thanks

911jon · 05-13-2002, 07:03 AM

Early Euro cars (78 to 80) also used low compression pistons for 180bhp nominal rating. 1980 (might have been '79) cars were re-rated at 188bhp though no change was made to the motor. Porsche simply found the earlier statement of output to be overly pessimistic (typical of the company at that time).

The later high-comp engine was introduced for the 1981-83 model years rated at 204 bhp. These are nominal, average figures. Bear in mind that with a fine tolerance, hand-assembled engine, power output figures vary considerably from one unit to the next. Time also takes it's toll!

I cannot comment on US spec cars, don't know exactly what emissions equipment was fitted, but that was the story over here!

And no, I wouldn't try to run a 9.8:1 car on low octane fuel. Detonation would almost certainly result. How do you cope with 91 octane fuel! Our basic fuel is 95 octane, and I use the widely available 98.5 octane we have now. Sorry, shouldn't rub it in!

sammyg2 · 05-13-2002, 07:14 AM

NA means normally aspirated, IE non turbocharged or supercharged.

Yes, you can run an SC on 91 octane US spec gasoline. That number is an average of research octane and mechanical octane and is as good as you can get in most places around here unless you buy special fuel.
Some countries use one of the octane rating systems, but not both. That gives them a higher rating with the same gasoline.

makaio · 05-13-2002, 09:11 AM

Quote:

Originally posted by 911jon
Bear in mind that with a fine tolerance, hand-assembled engine, power output figures vary considerably from one unit to the next. Time also takes it's toll!

Jon, I thought the German government had a 3 % policy. Where all motors had to be within 3% of the claimed output. Either + or -.

I could be wrong, but I thought I read that before.

dd74 · 05-13-2002, 09:39 AM

Yeah, 98.5 is hard to come by. Out here in L.A., you can get it from select stations, but it's 5 bucks or more a gallon, I think. But isn't that about what you guys are paying in the UK?

dd74 · 05-13-2002, 09:42 AM

So in reference to Jon's statement about 98.5, what happens when you run a standard SC motor on octane like that, particularly with 8.5:1 compression? Any ideas? Anyone have any ideas?

Thx

Wayne 962 · Wayne 962's Garage

8.5 is low enough to be run on regular gas. 9.8:1 may be pushing it. The weird CA blends out here do suck big time. I can't get my 325is to stop pinging (and it has a knock sensor!)

-Wayne