I have a D code 4V 289 with a 9.0:1 compression, how is this different from the A codes compression of 10.0:1. Does the A code have different heads, I am confused? Can I get a simple definition of engine compression.

 

The compression ratio for your car was determined by the pistons. The 64 'D'code 4 barrel carb engine uses the pistons that were used in the 65 thru 68 'C' code 2 barrel carb engines. The 'A' code 289 had a different set giving them a 10.0:1 ratio.
Jim

 

Static compression ratio
CR = A/B
B= volume of combustion chamber when pistion is at top dead center
A= volume of cylinder at bottom dead center + B
Bis a bit tricky depending on the combustion chamber shape, thickness of the head gasket, and dish or dome of pistion.

http://en.wikipedia.org/wiki/Compression_ratio
http://e30m3performance.com/myths/mo...comp_ratio.htm

 

OK, I am still a little bit confused, are the pistons in the block or the head? If I buy new heads, they don't come with pistons do they.

 

The pistons are in the block and the valves are in the head. Go to this page and scroll down to the engine model
http://en.wikipedia.org/wiki/Internal_combustion_engine

 

http://www.howstuffworks.com/engine1.htm


Norm

 

Cool, thanks for the links, so to improve the compression, I just need to get different pistons. I checked on Summit and they are only like $25.00 a piece, and I should do this when I put on new heads, cam, intake, carb etc.

Or should I just store my D code and get a larger crate motor, for a little bit more $.

 

Time to do some reading, as there's a wee bit more to it than buying parts and bolting them up.

Heads will also affect CR, as will block machining on a rebuild. I assume that you do want to be able to use readily available gasoline. The wrong combination of pistons/heads/cam/rockers will result in piston/valve contact. Old heads aren't very tolerant of unleaded fuel. Lots more.

Actually, you probably would be better off getting a crate motor, as all of the 'bugs' should have already been worked out. I'd stick with a 302/5.0 with a minimum overbore for now. I'm not that crazy about stroker motors in general, less so in an engine with such a short deck height and short rods as these.

Norm

 

Your heads will fit and work well with higher compressionpistons as used in 65 and 66 289 engines with a 4 barrel carburetor. Boring your engine oversize will affect the compression ratio ina veryslight mannor. Getting a valve job if the heads come off is a good idea. Don't let other people spend your money.
Jim

 

Agreed. And a 40 year old block might need a light deck cut too.

Anyway, a red flag goes up when an obviousnewcomer to engine building goes straight from asking where the pistons go to talking about new heads and a cam.

solid - don't take the above as insult in any way. We all started out at that same level of automotive knowledge.


Norm