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#63482 07/26/2006 10:58 PM | Joined: Mar 2005 Posts: 627 'Bolter | | 'Bolter Joined: Mar 2005 Posts: 627 | The 261 has a higher lift cam, valve guide heights above head surfaces are spec'd higher, and the spring tension is higher.
Is it truly fine and dandy to put the 235 head on a 261 block without changing these items?
Mike Barnes
1950 GMC 1-ton pickup
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#63483 07/27/2006 12:57 AM | Joined: Aug 2001 Posts: 1,299 'Bolter | | 'Bolter Joined: Aug 2001 Posts: 1,299 | I understood that you were supposed to use the 261 head gasket to locate and drill the steam holes in the head due to the siamesed cylinders of the 261. | | |
#63484 07/27/2006 4:27 AM | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy guys, if my hot rod memories are correct, that particular swap will result in an increase in compression ratio also, hope that helps. | | |
#63485 07/27/2006 4:33 AM | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy guys, if my hot rod memories are correct, that particular swap will result in an increase in compression ratio also, hope that helps. | | |
#63486 07/27/2006 9:21 AM | Joined: Aug 2004 Posts: 399 Shop Shark | | Shop Shark Joined: Aug 2004 Posts: 399 | yeah, got an 235 (848) head on the 261 - runns like a champ.
Verry poppular combination in the 50es.
Frank | | |
#63487 07/27/2006 3:54 PM | Joined: Mar 2005 Posts: 627 'Bolter | | 'Bolter Joined: Mar 2005 Posts: 627 | Yes, have the gasket and am drilling the extra holes but they are not really mandatory. However with a more aggressive lobe on the cam and more lift I can definate see that the guide height and spring tensions could be very important.
Am I the only guy who thought of this?
Mike Barnes
1950 GMC 1-ton pickup
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#63488 07/28/2006 12:57 AM | Joined: Aug 2001 Posts: 1,299 'Bolter | | 'Bolter Joined: Aug 2001 Posts: 1,299 | I have installed in my 235 an Isky full race cam and inner valve springs. Installed chrome moly tube pushrods also. They have been in it probably 30 years now and I did not have to do any real work for extra clearance. Somewher around, I have the cam spec card. | | |
#63489 07/28/2006 1:30 AM | Joined: May 2006 Posts: 8,351 'Bolter | | 'Bolter Joined: May 2006 Posts: 8,351 | I may be mistaken, but i seem to recall that the Canadian Pontiacs from the early '50s used a 261 with a 235 head as factory equipment.
That swap will increase the compression ratio, due partly to the smaller chamber, but also from the larger piston displacement. As far as the valvetrain goes, I don't think that the guide hight will make a difference, you'ld be using 235 valves. As long as the sprins were compatible with the cam, there shouldn't be a problem.
Bill Burmeister
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#63490 07/28/2006 2:26 PM | Joined: Mar 2005 Posts: 627 'Bolter | | 'Bolter Joined: Mar 2005 Posts: 627 |
Mike Barnes
1950 GMC 1-ton pickup
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#63491 07/28/2006 9:38 PM | Joined: Mar 2005 Posts: 1,513 'Bolter | | 'Bolter Joined: Mar 2005 Posts: 1,513 | Longbox,
You're only partly mistaken. "Early 50's" Canadian Pontiacs had a flathead six but starting in 1955 GM Canada used the 261 with the 848 head until 1962.
Curt B.
1952 1300 Canadian 1/2 ton restomod You Tube | | |
#63492 07/29/2006 3:08 AM | Joined: May 2006 Posts: 8,351 'Bolter | | 'Bolter Joined: May 2006 Posts: 8,351 | I knew it was some time in the '50s or '60s, thanks for clearing that up.
Bill Burmeister
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