If your old head is still good and you want to retain the turbo setup then I'd
recommend using the old head & cams. Turbos and high compression are a bad
combination (at least without direct injection) and swapping worn cams/lifters
often leads to accelerated cam wear.
----- Original Message -----
From: Ashraf Farrag
To: Miata Power List
Sent: Sunday, November 01, 2009 9:27 PM
Subject: Modded N/A engine: 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 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...
TIA,
--Ashraf
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