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Re: [Spridgets] head question

To: spridgets@autox.team.net, derf <derf247@gmail.com>
Subject: Re: [Spridgets] head question
From: fastvee <fastvee@yahoo.com>
Date: Wed, 18 Aug 2010 11:29:48 -0700 (PDT)
I haven't had my hands on an 8 port Pierce head yet, but I have two of the
aluminum 5 port heads waiting in the wings that I have an opinion about.  The
aluminum heads should flow more, but depending on what engine they 
are
installed on it may be at the expense of port velocity. What is 
really needed
for our use is more flow with little or no loss of flow 
velocity, and these
ports are already pretty large. Despite what the 
retailers would have you
believe, there is no such 
thing as one head that will improve a 948 through
1380cc engine. My heads might get used one day, but I have done a good
inspection of the details and decided they won't suit my current engine build
plans. They are a good quality casting, and should be very good for the
mission they were designed for, which appears to be big bore engines and
oversize valves. I read somewhere that the ports were patterned from one of
Longman's race heads, and on my heads there are seat inserts installed so that
stock 1275 valves could be used. The result is that the port is much larger
than the insert ID. Boring the insert ID to match the port is what is needed
to eliminate the step, and flow obstruction, except that you won't have enough
material left to seat 1275 intake valves and have to go to oversize intakes.
It appears the step may not be totally eliminated with 1.40 intakes and I'll
need 1.42 intakes. The intake seat insert OD is large enough for three angle
 seating using the largest valves so the intake ports will clean up, but
probably will only work best with 1380 cc and up. At least in the exhaust port
the seat insert step is in the right direction for flow, but there is another
problem. To maintain a good ratio of exhaust to intake port flow if you use
the largest intakes you would need to use 1.22 exhaust valves, and the seat OD
is not large enough for the top cut, so larger seat inserts are needed for
1.22 exhausts.The valve centerlines being about .050" wider, the need to
install oversize valves, and the large chamber is why the head was designed
for the bigger engines IMO.  I would have designed an aluminum head with stock
size ports and additional material for porting to individual specs, capable of
starting off with stock size valves, and not having to mill the head to get
back to a standard CR. This would have allowed the widest range of use for the
head, and still have a core capable of
 modifications for racing or monster street engines. Also I could do several
valve jobs using stock valves on a street 1275 and then have the option of
putting O'size valves in the same seats or change the inserts and start again.
BTW calculations were done with the assumption of using Vizard seating details
in case you'd like to duplicate my math, and the only details I'm not certain
about are the chamber cc's since the measurement was done before selecting
final valve size and seating. I'd be OK with learning that my heads are an
anomaly. Anyone else "Build" their aluminum head from the bare casting?
John
Fogelsville, PA

--- On Wed, 8/18/10, derf <derf247@gmail.com> wrote:

From: derf <derf247@gmail.com>
Subject: Re: [Spridgets] head question
To: spridgets@autox.team.net
Date: Wednesday, August 18, 2010, 11:29 AM

Surely they must flow better than stock heads.

They need some other option besides dual Webers, though.
Anyone talk to APT about these?  If anyone is gonna flow test
them........................
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