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Weird cylinder head
Home away from home
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2008/9/15 6:21
From Kyoto Japan
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Has anyone seen a H74 head before. I was pulling one down earlier and noticed holes in the exhaust ports. These go vertically down facing the back of the valve. There is a cross drilling perpendicular to this running to each end of the cylinder head. What kind of emissions (?) stuff is this?

Posted on: 2/26 5:06
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Re: Weird cylinder head
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Trying to post pics but no cigar.

Posted on: 2/26 11:18
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Re: Weird cylinder head
No life (a.k.a. DattoMaster)
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Without pics it's a bit of a guess, was there a datto with a smog pump as some manufacturers used or an air admittance valve as others used to let some fresh air into the exhaust and burn up the rest of the fuel? Ford used a system that was just a one way valve, a number of others used small air pumps. Circa early 80s

Posted on: 2/26 21:03
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Re: Weird cylinder head
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Posted on: 2/27 3:08
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Re: Weird cylinder head
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From Stone Age somewhere in U.S.A.
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Nothing weird about it, it's standard A series head drilled for air injection. To the best of my knowledge they were used here in the U.S. and Japan and anywhere else that required emission controls. Like lamb said, for use with an air pump (smog pump). The reasoning was/ is that if one injects fresh air into the exhaust stream, it will cause all the unburned fuel to burn, reducing emissions. As far as performance, it's about the same as an H72 head, possibly slightly worse. If you are going to use it without an air pump, make sure that you plug the hole in the front of the head by the thermostat so as not to have an exhaust leak.

Posted on: 3/4 23:46
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Re: Weird cylinder head
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2001/5/3 7:04
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There are two kinds of H74 heads

yes those are H74 air-passage heads
* For air-induction. H74 was used on JAPAN B210 Van 1975-1976 with A12 engine

Induction was used in Japan. Also used in USA and was more common than smog pump (air-injection) which was only used in USA if i remember correctly. Both do the same thing but the pump steals some hp to compress the pump

H74 head came either with or without air passages. With air passages they were usually machined for an open chamber instead of having heart-shaped chambers

Performance same as H72 with same type of chamber. In other words, open-chamber H72 is similar to open-chamber H74. Heart-shaped chambers burn better than open but create more NOx. Open chambers have less NOx pollution but don't burn as efficiently so they added air induction to burn the leftover CO in the exhaust

Later on in 1977 Datsun started switching to high-swirl heads which have low NOx and low CO without need of air induction. By 1982 all A-series heads in USA, JAP or USA were this better type (either using off-set pistons or shaped ports to induce extra swirl)

Posted on: 3/10 6:03
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