biger valves in 170 head
- Thread starter artmac
- Start date
IIRC the 170 can go up to 1.75 max, sam as any cast head, because you start getting into compression chamber issues, like reshaping.
the intake and exhaust are already so close to the walls that on my 250 head they had to shave some off just so the valve can open properly.
talk to mike @ CI cause he knows what you can and can't do to a 170 head.
the intake and exhaust are already so close to the walls that on my 250 head they had to shave some off just so the valve can open properly.
talk to mike @ CI cause he knows what you can and can't do to a 170 head.
Howdy Artmac:
Couple of questions, first; What casting # 170 head are your using?
And a couple of FYIs- The 1st iteration of the 170 in 1961 had 1.52" Intakes and 1.26" exhaust. In '65 170s got an increase in intake valve size to 1.64" and exhaust valve size to 1.38". That remained unchanged til the end of the 170 in 1973. The 170 heads changed slightly in that time. The main differences were in the shape of the combustion chambers and added material to strengthen bolt hole ears. The earliest 170 of this era had what is called a kidney shaped chamber that were usually a few CCs smaller than later 170 heads. From '65 to '72 it is not uncommon to find 200 castings on 170s and visa versa. From C9xx on there appears to be no differences between 170 and 200 heads. Even the flat-topped log 250 C9xx- M castings have been found on 170s as well as 200s.
Q- "Is it posiable to use the 250 valves in a 170 head without hitting water?"-
A- Yes. the largest 250 valves, beginning with the D7xx castings were 1.75" intakes and 1.38" exhaust. The problem is that the 170 have a bore of 3.5". While the 200/250s have a bore of 3.68". Increasing the valve size, either intake or exhaust comes that much closer to the bore. The bore is the limiting factor. The valves, Stock or later, are shrouded to the point that increasing the valves diameter will have little positive effect. But yes,It can be safely done. Going from a 1.68" to a 1.75" head will only increase the radius by .035", so no fear of "hitting water".
Can it be done? Yes. Is it worth doing? questionable.
Now if you have an early, '61 - '63 170 head, the simple thing to do is to find a '65 and later 170 or 200 head for a nice increase in both intake and exhaust valve size.
If you want to increase flow on a 170 head, you'd be money ahead by focusing on a performance (at least three angle valve seats) valve job and back-cutting the intake valves.
Hope that gets you the answer you wanted.
Adios, David
Couple of questions, first; What casting # 170 head are your using?
And a couple of FYIs- The 1st iteration of the 170 in 1961 had 1.52" Intakes and 1.26" exhaust. In '65 170s got an increase in intake valve size to 1.64" and exhaust valve size to 1.38". That remained unchanged til the end of the 170 in 1973. The 170 heads changed slightly in that time. The main differences were in the shape of the combustion chambers and added material to strengthen bolt hole ears. The earliest 170 of this era had what is called a kidney shaped chamber that were usually a few CCs smaller than later 170 heads. From '65 to '72 it is not uncommon to find 200 castings on 170s and visa versa. From C9xx on there appears to be no differences between 170 and 200 heads. Even the flat-topped log 250 C9xx- M castings have been found on 170s as well as 200s.
Q- "Is it posiable to use the 250 valves in a 170 head without hitting water?"-
A- Yes. the largest 250 valves, beginning with the D7xx castings were 1.75" intakes and 1.38" exhaust. The problem is that the 170 have a bore of 3.5". While the 200/250s have a bore of 3.68". Increasing the valve size, either intake or exhaust comes that much closer to the bore. The bore is the limiting factor. The valves, Stock or later, are shrouded to the point that increasing the valves diameter will have little positive effect. But yes,It can be safely done. Going from a 1.68" to a 1.75" head will only increase the radius by .035", so no fear of "hitting water".
Can it be done? Yes. Is it worth doing? questionable.
Now if you have an early, '61 - '63 170 head, the simple thing to do is to find a '65 and later 170 or 200 head for a nice increase in both intake and exhaust valve size.
If you want to increase flow on a 170 head, you'd be money ahead by focusing on a performance (at least three angle valve seats) valve job and back-cutting the intake valves.
Hope that gets you the answer you wanted.
Adios, David
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