Modded N/A engine: Use directly for a turbo setup?

Ashraf Farrag ashraf_farrag at
Sun Nov 1 21:27:22 PST 2009

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 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.

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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