Compression Ratio Numbers

A stock 1600 has 1585cc and a compression ratio of 7.3:1.

I kind of understand what the ratio mean, but what are the dis/advantages of having a ratio larger/lower than stock?

thanks Ant

Karls Vladimir Peña wrote in this friggin' newsgroup:

"Karls Vladimir Peña" wrote in news:c12vef$1bhtjb$ snipped-for-privacy@ID-209996.news.uni-berlin.de:

Thanks, but I am looking for the deck height and head cc's.

All other serious considerations aside, higher compression means greater efficiency, more power.

But reality is made of serious considerations. To accomodate higher compression you have to have the right fuel, correct valves, piston shape, head design, cam, exhaust, carburators, targeted application... everything. $$$$ and smarts can make it work. I have the $$$$ but I'm not smart or talented enough to make the engine so. :)

Go here:

Deck height should be between 3 and 1mm, one mm is pretty close. Bigger is not dangerous, just "wastes" power.

Stock head combustion chamber volume is roughly 50cc each.

You need accurate measurements and values, to arrive at a safe compression ratio.

The required compression ratio is differenbt for high performance cams. (usually they need a higher ratio, because increased valve overlap in them "wastes" actual compression pressure, and you need to make up for that loss by increasing the compression ratio.. )

Gene Berg believes in VERY low ratios, in favor of longevity and low temperatures. I don't share their opinion, they would recommend ratios much lower than 7:1 for stock or near stock engines, which to mee sounds stupid. Too LITTLE compression will only hurt the engine. Use stock ratio, for stock engines: around 7.3:1 for type 1 engines. Less than that will only rob power, and make the engine LESS economical. Thereby requiring more gas pedal to achieve same performance. Thus generating more heat, and consuming more fuel.

The higher the compression, the more power you get from any given amount of fuel burned. The burn process is more complete, and more efficient. Too much compression however will cause detonation/pinging. And engine meltdown will result. It needs to be RIGHT. Not too little, not too much.

Jan

Go to

Do not "guess" or accept numbers from anyone else, when trying to determine the best setup for your engine. One critical thing to do yourself is measuring the combustion chamber volume. It's all very easy, and the calculator doesn't leave any room for speculation or guesswork as long as you measure YOUR engine accurately.

Jan

I've built or helped build engines that run 14:1 compression ratios.... :) (kids, don't try this at home).

Jan

Jan Andersson wrote in news:c135eq$1d2u5c$ snipped-for-privacy@ID-72729.news.uni-berlin.de:

Thanks Jan, that is what I wanted to see, the numbers. I am just wanting to see what the numbers other folks are getting and that will tell me if I am in the ball park when I do mine. I don't want to have a head that measures 75cc and think I am stock.

And when measuring the head, I should have zero leakage around the valves, right?

Right. You can achieve this by smearing a thin coat of vaseline around the valve sealing area.

Jan

Jan Andersson wrote in news:c1eoq1$1gb0vl$ snipped-for-privacy@ID-72729.news.uni-berlin.de:

So the valves will leak some? In my mind I would expect them to seal and not leak. I guess they could weep and be within specs. Sorry my ignorance is showing. I tried all my life to cover it up and it still follows me around and shows up at all the right times. LOL

Sometimes yes.

That's how they should be. Ideally.

:D

Jan