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Re: Small heads in big engines

To: yak@doe.carleton.ca (Yatish Kumar )
Subject: Re: Small heads in big engines
From: sfisher@Pa.dec.com
Date: Tue, 01 Oct 91 14:25:36 PDT
>  Does anyone have any experience with this?? My Haynes manual does not seem 
>to identify a separate head for each engine.

You need to get more esoteric to find the casting numbers for each
engine.  If your head really came from a 1000cc engine (really either
997 or 998cc), I don't know what casting number it will have on it.
If it came from a Spridget with a 1098cc engine, the casting number
will be 12G295.

What you want for your 1275 is a head with the casting number 12G940.
This may or may not have smog-pump holes in it, which might have an
effect on the legality of the car in your municipality, so be sure
to get the head that matches your laws.  (That is, the casting number
12G940 was used on 1275 heads made before and after the smog pumps
were required.  There are minor advantages to the smog-pump 12G940
heads, primarily due to minor revisions to some critical casting
dimensions to handle the head involved in the external combustion 
that resulted from the injection of fresh air into the exhaust ports.)

If you really want to know why putting a small-bore head on a big-bore
engine is a bad idea in almost every possible way, get a copy of David
Vizard's book, "Tuning the A-Series Engine."

>  Does anyone have any info on performance CAM's for these  engines ?
>    ie. approx cost, and performance improvement.

You should REALLY get Vizard's book.  He tests a huge number of cams
and shows dynamometer output from different cams on otherwise identical
engines.  You can easily save ten or twenty times the cost of this
book in parts that you don't have to throw away when you find out they
don't work.

--Scott


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