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Old 11-06-2009, 08:48 PM   #1
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Default Modded N/A engine/head: Use directly for a turbo setup?

I have come into the possession of a low mileage (50k) 1993 1.6L engine to replace the fairly broken (spun bearing? still don't know exactly what went bad but it made an awful racket when I decided to let it hibernate) 1990 block on my turbo car so that I can get it going again via the path of least resistance (versus rebuilding the broken 1.6 or rebuilding the spare 1.8L I've got kicking around).

The engine that I now have (bought sight unseen, I know, I know...) is configured as follows:
Stock bottom end
Head shaved (unknown how much / what compression)
Larger valves
Unknown custom cams
Adjustable cam gears

N/A, the engine made 118 RWHP. As you can see from the lack of details in the mod list, the previous owner was not very knowledgeable about what exactly was done to it by the machine shop...

So, the question is what to do about all the unknown stuff. Is there any way to easily identify what has been done to the engine? My brain is pretty dead from schoolwork but wouldn't a compression test tell me something about the potentially higher compression ratio? Cams, I suppose the valve cover can come off to try and figure out what the difference is vs. the stock cams.

The main question in my mind is do I install it as is with my existing turbo setup or should I put a stock head (conveniently enough, it came with one, along with a ton of other Miata "stuff") back on it? Based on the increased horsepower, which has to mean some better airflow, I'm not really able to think up what on that head would be counterproductive or work against the turbocharger setup.

My turbo car has a MegaSquirt, so adjusting timing to compensate for raised compression and cams should not be an issue.

I am looking for some initial feedback at this stage. I have a lot going on in the next couple of days of grad school, so it may be a while before I can poke at the engine to get information to feed back into the discussion. I won't be doing any actual mechanical work for a while...

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Old 11-06-2009, 08:56 PM   #2
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the slight bump in compression wouldn't bother me. you should benefit from the rest just as the N/A setup would.
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Old 11-07-2009, 04:15 AM   #3
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You could always cc the chambers and crunch the numbers. Once you know the compression ratio you can dial back timing accordingly and then work on tuning it.
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