200" flat top pistons

[Anonymous]

Hello. I recently purchased a '63 Comet with a 200" motor ('66 block). The fellow I purchased it from thought that the motor was a 170". After taking the head off to replace a blown head gasket I noticed that the pistons were flat tops. I thought that 200"s used dished pistons. What kind of difference am I going to see in compression values. I am also using a composite head gasket. Thanks, Curtis

 

[CoupeBoy]

Welcome to the forum,

You are in luck! since you have it all apart you could measure everything and get actual values and plug them into a compression calculator like

http://falconperformance.sundog.net/compcalculator.asp

And it will tell you what compression you started with and what it is now. You should also take this opportunity to verify that you have a 200 not a 170 (or 250).

-ron

 

[Hot 6t Falcon]

I think you've got a 170.

Since you've got the head off, it will be easy to check the bore and stroke.

a 170 has a 3.5" x 2.94" bore/stoke
a 200 has a 3.68" x 3.126"bore/stroke

You should be able to tell with a simple ruler. The 200 is a little over an 1/8th of an inch larger on both measurements.

For the compression, go to my web site in my signature and click on the "Compression Calculator" on the left side of the home screen. Put in the correct bore and stroke and "0" cc for the dished piston and then put in the gasket thickness you'll be using. .050 is a good guess.

Good Luck

 

[Anonymous]

Hi, and thanks for responding so quickly.The car is up and running and I am continuing to work on it as I drive it (I am working about 750 miles from my home and shop). The block is a '66 200". It has the five freeze plugs and the larger bore. The head is from the original motor - a 170". When I replaced the head gasket I noticed the flat top pistons. And so my question about the compression ratio with the flat tops versus the dished piston including the composite gasket. Any ideas? Thanks, Curtis

 

[Anonymous]

Ya' know I think this motor is a 200" but I could be a little confused. I am assuming that all 200" had the 5 freeze plugs and all 170" had the 3 freeze plugs. Did the later, '66 or so, 170" with the 7 main bearings have 5 freeze plugs as well or just 3? Thanks, Curtis. P.S. thanks for the link to your site. the compresion calculator is very handy!

 

[Anonymous]

I had a 1970 Maverick with a 170.
The car is gone but I still have the engine. The engine is blue and has five freeze plugs, not three. The Block casting is C8xx.