260 Buildup Part 1 : Tigers List Archive : The Sunbeam Experience

260 Buildup Part 1 #1
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Mail From: "Ronak, TP \(Timothy\)" <(email redacted)>

Bugz,

I needed to shorten this one so here goes ...

Bugz,

I too have my 260 on the floor and plan on someday perhaps 'tricking it
out' but at this point I do not have it apart. While I have not built my
260 I did do some research as well and understand that the valve
diameter differential in size is only likely to affect the Intake Valve
as the centerline of the valves is standard for ALL small block Fords as
I understand. This is unless you use a TFS twisted wedge head or some
other exotic head. The net clearance increase requirement with a Hi Po
head is about 1 tenth of an inch overall for a 1.78 inch from a 1.67
inch valve. This means that at the bore edge you only have an increase
of 1 - 20th (1 tenth divided by 2) of an inch in the face diameter of
the Hi Po valve where it would potentially contact or interfere with the
bore edge. To me this seems like a doable swap so I am unsure why the
cautions of not doing it unless the cooling passages are a problem. Worn
Valve guides may be a factor but unlikely.

If you went to a 1.94 inch intake valve the diameter increase is 1.94 -

1.67 = .27 inches divided by 2 still gives roughly only .149 inches in
increased diameter at the Bore edge. This is NOT a huge amount. 2.02
valves may become an issue on the intake size as this valve gives and
increase at the bore interference of 2.02 - 1.67 = .35 inches or after
dividing by 2 gives .17 in interference and this may me a constraint
although by my math it still looks like it will work as I measured the
GT40P head.

The real solution could be to bolt a late model head ... like a GT40-P
with some domed pistons to keep compression at 10.0 - 10.5:1
compression. I have a set on the floor of my garage and the intake
measures 1.840" on the face and the exhaust measures 1.450" on it's face
with the distance from outside edge to outside edge at roughly 3.460".

The intake appears closest to the edge of the bore at .340" and the
exhaust at .400". This is with the 4.000" bore of a 302 block. The stock
bore on a 260 is 3.800 at standard bore and we have still .150" of
clearance to the GT40P valve edge to the approximated 260 bore edge
using my calipers and scoping it out. So assuming Gaskets for the larger
bore head can be used to ensure the fire ring is compressed by the head
(260 Gaskets may have too small a fire ring), and that the 260 cooling
passages are compatible to the late model heads cooling passages, dowels
are the same, ... etc... they should work out. The real issue is whether
they will perform and flow well given the valve proximity to the edge of
the bore. It may 'shroud' the valve and may need a Big Block Chevy trick
(and Large Valve Small block Chevy trick) where you flow notch the block
to improve airflow out of the intake and into the exhaust. This will
increase the final combustion chamber volume and with a small cubic inch
engine this will be hard to gain back with head milling. If you use the

289 head with the 54cc head and put slightly larger valves I am sure it
can be made to work unless I am overlooking something. My guess is that
if Doane Spencer ran a 260 then he probably did all of this. One other
point is that increasing Cubic Inches tend to lessen the lumpiness of a
specific cam and that means that a building a small inch motor it would
be wise to run one of the milder hydraulic rollers. Perhaps even a Stock
ford or an E303 rather than an all out unit.

An aftermarket set with 1.94 intakes could also be a choice.

Best Regards,

Tim Ronak
Services Consultant

Akzo Nobel Coatings
23961 Via El Rocio
Mission Viejo, CA 92691

Bus: 949-305-5393
Fax: 425-955-6268
Cell: 949-289-3357
email: (email redacted)
Personal email: (email redacted)

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