Engine Update

Not enough deck

:)

That's too much deck, you're wasting energy. To lower the CR from 8.2 to below 8, you could get two birds with one stone by unshrouding the valves by making the combustion chamber around them bigger. Allowing better flow in and out. Combine that with a deck height of around .057 (.20spacer) and you get the best of both.

You can have ours. :)

Jan

Why not stick with 8.2 C.R. ? After all 7.5 allowed you to run 87 ocatne RON....

J.

If he stayed with 8.2, he would still need to modify the engine because there's not enough deck. It's not safe to run deck that tight.

Jan

....and you know those silly americans, all so afraid of cam degrees and compression :D

Jan

Allowing

Afraid, You bet! This is my first real engine build. I am just trying to build the engine to be reliable and economical. I don't need lots of HP and did not plan on going that route "This time". Now, with what I learn this time round and continue to learn here and other places, my next engine will not be so timid, but it will not be a whole hog either. As I have said before this is the second time to build this engine, the first time was pure stupidity on my part and I am very lucky it did not go up in smoke.

I am just not ready to make mods to the heads that you speak of as I do not fully understand what needs to be done and I do not have a manual yet that shows/talks about it. I need lots of pics and lots of How-To's before I would feel really comfortable doing it. I also don't have a set of heads to practice on other than a pair of 40 horse heads. And I just would not feel right cutting those up as someone out there may need them someday. 40hp heads are getting scarce and so are single port heads.

I know Jan is speaking good sound information and has the experience behind him. I on the other hand am just beginning to crawl in this VW engine arena. Some day I plan on just plunking down a big chunk of moola on a Sweet Jake Raby engine!! Turn Key, that is!! Now that is a real dream.

I think you would better off without the shims. My engine is pretty close to your measurements and because of the tight deck, you get a swirl effect in the combustion chambers. Efficiency goes way up and this is what Jake has been repeatedly telling everybody. I can tell you that it does work. I can't believe how efficient my 1600DP is now and it does not run hot.

My heads were 48 and 48.5cc so my CR was just a tad higher than your numbers and coincidentally, my tightest deck was .037". I went with it since my RPM is limited to 5500.

If your nervous about the .037, then get the case decked a few thou... but don't kill that engine with shims.

Raymond T. Lowe

-- E-mail=fullname,no initial-at-telus.net

OK, I'll bite. What about shims will kill the engine? Details Details

More prone to leak oil because there's one extra mating surface between cylinder and case. A realllly thick shim might throw a cylinder off center in the case bore, it's the last few mm of the "skirt" of the cylinder that centers it. Mind you, I'm talking about shims thicker than 3 quarters stacked together. Not a problem for you.

Jan

His CR is pretty good where it is. Shims will lower it into the realm of Berg, Briggs & Stratton, etc. Tighter deck = more quench = more violent swirl of the mixture = more efficiency. And the better the mixing, the less chance of uneven flame travel. Had a Berg inspired engine once. Ran good and cool but I'd hate to be the guy stuck behind me in traffic sucking in the half-burned exhaust.

Raymond T. Lowe

-- E-mail=fullname,no initial-at-telus.net

having the case decked will not increase the deck height .

Well, this thread has provided some good discussion, but I am going to stick with my original plan. I have ran this engine before, granted it is not running with the same P/C's now I bought new ones, and I ran it without spacers and had lots of problems with heat. Not going that direction this time. I will take the lesser side this time and put the spacers in and see how she runs. I don't want to go hunting blue ovals or bowties in it, just simple transportation with dependability.

Still waiting on the parts to come in. John C. must be on vacation, but I got time to wait. Used some of my spare time Sat morning to paint the jugs flat black.

Taped up the jug holes real nice, so as to not have any paint inside or on the external mating surfaces. Loaded up the paint gun with lacquer thinner and sprayed each jug really good till no more crude was left, nice and clean. Used the paint gun to spray air over the jugs to aid in drying as well. Broke out the Rust-O-Leum and sprayed each jug with it standing on one end and then on to the next one. Did a lite coat on each one. Went back an swaped ends with the jugs and sprayed again. I figured this would help insure a good coat top and bottom on each fin. Let them dry again for a few minutes and checked down between each fin to see if the paint had reach the barrel all the way around. Had a few touch ups to do for this, but mostly a nice coat of flat black all around.

One more "Too-Do" checked off my list.