I am wanting to do a compression change on my Slant 6. I have the super six setup and 2.5" single exhaust with a turbo muffler for modications so far. My compression tests came out at around 150 on all cylinders. And I believe it was rebuilt just before I bought it - about 4,000 miles ago. That is what the guy told me. And with the compression looking so good, I have to believe it. I don't burn any oil. I was searching for this on this site, and haven't really seen any good answer. It looked like shaving off .100 looked good for some. Would that be good for my slant six?

What year is the engine?
What type of head gasket is on there now?
Was anything milled off the head or block deck during the first rebuild?
What type of fuel do you plan to run?
DD

What size is the motor? 170, 198, 225? Makes a difference on what ratio change per amount of milling.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I have a 63 Dart 270. When we bought the car a couple years ago, the guy told me it had just been rebuilt. But that was it. At the time, that was the first time I had seen a slant 6, the car was for my daughter, and so I wasn't prepared to ask him the questions you asked.

Thus, I have no idea if the head had been milled before. As for fuel, it currently runs on 87 octane with no problems. I think I can get up to 92 octane from the local stations here in Sacramento, CA.

I do know it is a 225 Slant 6. And as far as I know, this was purely a stock engine. As we bought the car with the original one barrel, and the original muffler system (small pipe). There was nothing here to say he started work on fixing it up any. And it has all the chrome, and needed interior work. The body work is minimal. And we got it for $900. That told me he really didn't put a lot into the engine. It was a grandpa, toot around town, hobby car. With stock wheels and hubcaps even.

I don't know what head gasket is on there, but we will probably find out, once we remove the head.

The only way to accurately answer your question is to remove the head and measure the comustion chamber volume and the space between the top of the piston and the deck surface. With that information your compression ratio can be computed and a sane recommendation made for how much, if any to plane the head. Anything else is gesswork at best since slant six heads and blocks tend to vary widely even within the same model year.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Go see the article I have linked below.

It looks complicated, but is actually straightforward and very accurate:

http://www.imperialclub.com/Repair/Engi ... ession.htm

-Mac

Thanks again for all the info. I sent that info to my buddy who is taking off the head. He lives an hour away from me. Does anyone want to say what brand or type of head gasket I should be looking at purchasing? Is that something I will find out once we do the math?

It's something you should decide first since the compressed thickness of the gasket is a factor in your calculations.

_________________
David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Yeah, I am going to have the head taken to a machinist who does racing engines for people. I understand from another person, that this guy will do all that math, and tell me what gasket to get and all. Wish I would have known that before bothering all of you. But then again, I have learned a lot from you. Thanks thanks, and more thanks.