how can i increase the compression ratio of my 200 I6?

[random hero]

i am debating on either changing the pistons, or milling the head. i'm leaning more towards the pistons though, due to the fact that i think it would be cheaper. so my question to you...forsix forum members is... if you have done either of these, please tell me which one you did, your results, and your compression ratio...if you know it. keep in mind that i have a 200 I6

 

[Mustang Boy]

i think milling the head would be cheaper than buying new pistons and having them installed

 

[Junk-Falcon]

i am running

 

[matt1967]

well, here's what you can do. have Egge Machine make you a set of flat top replacement 200 I6 pistions ( in stock or whatever oversize you want ) but, have him ( Bob ) move the connecting rod pin placement .010 down the pistion skirt, this will make the pistion .010 closer to the deck, so you should have .015 deck height rather than .025, then, have the block decked .005 just to true it up, and to make things even. given those values, if you mill your head .025 to make up the diffrence of the thicker head gasket ( figured .050 ), you'll have 9.6:1 with a flat top pistion, you could go dome, and get more if you wanted.

 

[random hero]

thats exactly what i was looking for, thanx you very much for your input

 

[80Stang]

Figured out a list of ways to increase CR:

1. easiest (bolt on with no machining or whatsoever): Ford 4-cyl. 2.3L HSC flat-top pistons
2. mill the block to zero deck height (typically needs around .030 cut, but MUST be measured). This will also have more positive effects than just raised CR
3. mill the head to reduce chamber volume
4. thinner head gasket (easy but limited increase, and where to find much thinner than what are generally available? Unless custom.
5. increase bore (not much effect but it will increase CR; avoid this)
6. increase stroke (not so easy way to do it in a 200, and for CR increase alone it is absolutely not practical, but it will increase)
7. Piston placement upper in the block // Matt's custom pistons / piston pin mods. Price?

Someone could add more if you can come up with.

 

[lyonsy]

put turbo/supercharger on.
otherwise shave that head

 

[matt1967]

Figured out a list of ways to increase CR:

7. Piston placement upper in the block // Matt's custom pistons / piston pin mods. Price?

Egge will do them for around $225 per set, including pins. but you get whatever you want, he'll do it. he wouldn't make me turbocharger pistions because he can't do forged. ( I got mikes cast flat tops NE way, cause of the head I decided to use ) but he can do anything in a cast pistion.

 

[Anonymous]

How high do you want to go?

Mine has the 2.3 litre pistons, 0 decked and the head is milled .080.

Compression ratio is right around 10.5:1

Later,

Doug

 

[mugsy]

I had my block decked 0.030 to "zero" out the piston top with the deck. Then had the head milled 0.040 to get to 52 cc (I think that wass the volume). With a dished piston and assumed the composite gasket was 0.043 thick resulted in a 9.3:1 compression. Use the compression calculator to verify your dimensions. The engine has adjustable rocker arms, so the trim was no big deal.

I was lucky in that the machine shop I was working with was pretty excited to help me get the dimensions I wanted. I was able to go there on a Saturday and measure the combustion chambers while the head was in the mill. The guy basically would take 0.010 off, I would cc the heads and he would cut again. They thought it was cool that some one was trying something more than just a "standard" rebuild on an small six.

 

[Hot 6t Falcon]

Random,

Howdy.

Some things to think about;

1. The stock 200 piston has a 7cc dish ( a "california" piston has a 14cc dish).

2. You can replace the pistons with 2.3 tempo "hi-Swirl" pistons which are the same dimensionally excpet there are a "flat-top."

3. Milling is the cheapest, easiest way UNLESS you need a rebuild (bearings and oversized pistons) If you ALREADY are buying new pistons, for say a .030 cleanup overbore, then by all means get the 2.3 pistons.

4. When you pull an engine apart, you'll need a new head gasket; and that gasket WILL BE THICKER THAN THE ORIGINAL GASKET. Original Ford gasket were steel shims and were .024 thick compressed. Modern gaskets are are Victor (.044 compressed) Felpro (.050 compressed) and Corteco (.050 compressed). So you need to mill the head roughly .030" to MAINTAIN original compression.

5. Milling the block (called "decking") can, or should, be done while you have the block apart for pistons and bearings. You can do it for TWO REASONS. The first .005" or .010" is to get a FLAT surface for the headgasket. After that, it is to raise compression. The compression goes up faster with Decking the block than by milling the head. The head's combustion chamber is a "D" shape and the piston bore is a full circle. So .020" on the head is not as many cc's as .020 on the block.

FINALLY,
Goto to web site in my signature and on the left sidebar goto the "Compression Calculator" It is preset to a Stock 200. Try setting the pistons to "zero" cc. Make the head gasket thicker. Reduce the combustion chamber cc to a smaller number. A .010" cut is approx 2.4 cc.
Try reducing the "deck' clearance.

Good Luck