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I think Richard ment to post this here.........


techinspector1 ..........

"more reading on compression ratio...
http://www.clubhotrod.com/forums/sh...on+ratio+101%2A
http://www.clubhotrod.com/forums/sh...on+ratio+101%2A
The same combination , flat-tops, 4 cc's, 9 cc's but with 64 cc heads will yield 10.44:1 c.r. and if you do that, you'll probably need more cam to bleed off some of the compression. When you do that, you move the power up in the rpm range away from streetability. Take some advise from a geezer and build it 9:1".


I agree with Richard on his recommendations on a 9:1 compression motor.

Now not to throw stones at anybody, but when you have had a few years in the automotive field your going to find that what people tell you about their engines is sometimes a little misinformed. Compression ratio is a good example. People will buy as set of pistons with an advertised ratio of 10:1 or whatever, but have not read the fine print that compression is with a head of so many cc's and such and such a thickness of head gasket. They also assume that the combustion chamber on mass produced heads are actually what the manufacture claims (if your in the engine rebuilding portion of your course now, you are likely doing head cc'ing and balancing volumes and are finding that all is not as it's claimed to be.

Another important part of building your engine will be camshaft selection as Techinspector says. By now you should have gone through the difference between static compression ratios which is mathematically determined and effective compression ratios which involves factors such as cam timing, volumetric efficiency, air density etc. These are the factors that the engine will really have to live with in real life vs. what sounds good on paper. A good example of this was a 57 Dodge I had a few years ago, it was running a 10:1 compression 440 and did really good where I live (4500 feet) but when I went out of town, (lower altitudes) even with the best gas I could find I needed to back off the timing and performance went down the tubes.

Now most of the geezers here (according to streets I'm one of them ) have found out for ourselves some things that seem to hold true we did that by experimenting. Some of the things I have found are:

1. Running lower compression ( 9:1 for me) and decent timing makes more HP than higher compression and retarded timing.

2. You can run SLIGHTLY higher compression with aluminum heads (my experience is about 1/2 a point).

3. If it's a street driven motor, especially one that's going to be driven is cool weather a heat crossover is a GOOD thing. Personally I kick myself every morning for going with the Performer RPM heads (no heat crossover) instead of the Performer heads on my Mustang.

4. Carbureted engines are a lot more sensitive to altitude and air temp changes than EFI engines and can be a real bear if your running on the ragged edge of compression.

5. There is such a thing as too much, be it compression, cam, valve size etc (especially if your looking for low-mid range power).

At this point in your life I encourage you to experiment and find out for yourself!!!!! It's the way your going to learn and will make you a better Tech (it's called paying your dues). Good luck with your project and keep us posted on how it's going.