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Hello. I have a 93 civic lx with a d15b7 engine that has been rebuilt by me about a year ago. The engine is running fine, but It seems it uses more gas than it should. I was thinking it might be due to a high altitude, at 5500 feet above sea level. The air is thinner and a lot hotter due to being in mexico, so less compression, and less power.

If I mill the head a little, (maybe 1-2 mm), it would give a higher compression ratio and even though the air is thinner it should still give a better power, giving better mpg.

I have a few questions.

How much can be milled off the head without having valve problems? I have seen a lot of different answers. I WILL clay it before so just to be sure, but I would like to know in order to calculate how much ratio will be.

How much mpg gain would be expected? enough for it to be worth the trouble?

Many people have suggested turbo for high altitudes, but all I have found is that in the end the turbo wont give much mpg gain, if any at all, and is way too expensive. A head mill will cost about 30usd here. And I can do the rest of the work.

Any suggestions?

Thanks in advance.
 

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Compression ratio improves Thermal efficiency, power per heat

You need to improve volumetric efficiency, power per space

Get a real small turbo.

Don't go high compression with the hot air.
 

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I know there are no problems when a y8 head which has bigger valves and a bigger cam. And a bit of a head skim. I believe there is quite a lot of room but have no actual numbers for you.

The y8 head mini me is its awesome for giving more pep. If you have junk yards around you can do it for quite cheap.

Although without tunning of any sorts you won't see as much of a gain and it wouldn't be as reliable.
 

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99 civic sedan ex
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If tuned right a turbo will give a huge gain in mpg and hp depending on how you drive. A guy on here used a turbo and got like 68mpg and had more than 200hp
 
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