I'm still hashing over compression ratios. I've been reading online that these motors don't or won't run compressions as high as 9:1 without taking extra steps. Like aluminum cylinders or electronic fuel injection. Mainly just because of the heat involved.

Has anyone "got away" with running higher compressions like this on stock cylinders?

*** IF anyone has any feedback on what fuel grade they are running at their higher compression and if they are getting any knocks ect... I would also greatly appreciate that information too.

Thanks everyone!

James

I have like 19 to 1 buts its in a TDI

I am running about 11 to 1 in mine. Very responsive. Zoom Zoom

Mine is 8.8 to 1 and I run premium (93 around here) without issue...

9:1 on a 2056 with no special cyl. or heads ...

91 octane, runs great, gauge says it's running too cold, as a matter of fact ...
Andy

euro pistons get me what? 9 ish to 1? i run 89....runs cool too.

Euro's are 8to1 Aaron.....

I am running 8.2to1 and can run 87,89 or 91 gas without any problems.

Geoff

AAAAHHHH the urban legend is back. Compression does not equate heat. The problem with running very low compression ratio is that it is very inefficient. All of the fuel air mixture does not burn inside the cylinder where it makes the most power. Some of that unburned mixture escapes from the cylinder and continues to burn on its way out the exhaust. This is what raises the head temps. If you run higher compression ratios then more of the mixture is burned inside the cylinder. Power is made through heat. The more heat you can keep inside the combustion chamber the more efficient the engine will be.

Higher compression = better fuel mileage, better throttle response, more power
Low Compression = Poor gas mileage, poor engine efficiency

With a higher compression ratio and proper camshaft design you can run much higher compression. Your car will be much more fun to drive.

This is one take on the situation.
http://www.theoldone.com/articles/The%5FSo...%5FHead%5F1999/

I ran 8.9:1 on 89 octane without any problems. My engine ran better on 89 than 93. I am building a 2056 right now that has 9.5:1, should have no problems running on 89.

Also a friend of mine in the petro-chemicals industry desribed such:

Running a higher-octane gasoline blend allows you to advance your timing more, as it has a lower flash (ignition) temperature and burns slightly slower.

Higher octane does indeed burn slower. More timing= more negative work. Run the lowest octane gas you can without the car pinging.

In my testing and experience I have seen that inadequate CR for the combination makes MORE heat than too much CR! I have seen engines with compression so high that they would barely start not run any hotter than a low compression pig!

The LEAST compression I run is 8.8:1 with any of my combos except for bus engines and they set up between 8.0-8.3:1!

The key is the right camshaft and the rest of the combination to make the engine easier to tune and more seponsive to change..

Low CR is the WORST thing that can be done to these engines. It kiolls efficiency to the point that EGT skyrockets and thats very hard on the exhaust valves and seats.

but isn't that what VW/Porsche wanted to do in the first place to meet emissons, Jake? High EGT temps/High combustion temps to clean up the emissions?

Geoff

While melting the heads and dropping seats....

The factory could have done a much better job with these engines than they did..

Emissions follow efficiency...

CO gets better, but NOx goes up, way up, with flame front temp

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CO gets better, but NOx goes up, way up, with flame front temp

Yes, but only HC and CO were being measured when the engine was being designed. NOx measurement didn't come into play until after 1980. The first catalytic convertors (so-called oxidizing or two-way convertors) only handled HC and CO emissions, too. The cats on the '75 and '76 914s, for example, were oxidizers. The later three-way or oxidizing/reduction catalysts handled HC, CO, and NOx.

The ironic thing is you can take an engine that, bare, spews out HC numbers of 300ppm, and similarly terrible CO and NOx numbers, just add a $75 three-way cat to the exhaust pipe, and your emission numbers will fall to 10% or less of the pre-cat numbers. However, if you really do nothing else, the cat will die in 10-20K miles and the emission numbers will climb back up again. The O2 sensor and the related electronics and mixture control are there primarily to control O2 levels to the point where the cat will continue to live for 50K miles or so.

I have had 10:1 2270s pass emission tests in CA and many other states without me even trying to make it happen!

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I have had 10:1 2270s pass emission tests in CA and many other states without me even trying to make it happen!

Only because they don't measure NOx for pre-'80 cars in CA. Well, they measure it, but there's no limit. Higher compression will help HC and CO, since, as you say, those numbers improve with better efficiency, and higher CR improves efficiency. In other states, they use the Federal limits where they test emissions at all, and the Federal limit for cars pre-'75 cars are quite high, and actually pretty hard to not meet in a car that's running properly. Some early 911S cars with MFI had some difficulty in CA until they became exempt, because the factory tuned the cars so close to the CA limits in effect at the time. When dyno tests came in, they'd reguarly fail even when running perfectly in stock trim. Too much cam overlap, I believe. These weren't "torque" engines.