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Mod | | | Forums66 Topics128,071 Posts1,055,901 Members48,429 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
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| | | | Joined: Jan 2009 Posts: 38 New Guy | | New Guy Joined: Jan 2009 Posts: 38 | I just got an old 51 GMC. What is a safe cruising RPM for the ole GMC six? My AMC 258 and the Ford 300 could safely run 3000 rpms all day long. Someone told me that those old GMC motors don't like seeing anything higher than 3000 rpm. | | | | | Joined: Dec 2004 Posts: 1,897 Shop Shark | | Shop Shark Joined: Dec 2004 Posts: 1,897 | 3000 is a good benchmark. A fresh motor in good repair wouldn't have problems spinning 3600, but a truck that has been sitting will likely have sticky valves at higher rpms. The 228 6 ctlinder is a good motor. The 270 and 302 6 cylinders are even better. | | | | | Joined: Dec 2003 Posts: 2,733 Shop Shark | | Shop Shark Joined: Dec 2003 Posts: 2,733 | I've seen a lot of old Chevy sixes run at 4K +. I've said it before and I continue to say it. - most of you guys are afraid of this engine. They didn't exist for so many years without taking the abuse of a whole lot of us threw at them. I know of Jimmys set up for racing that run over 6K.
Go ahead..stick your foot in them. | | | | | Joined: Jan 2009 Posts: 38 New Guy | | New Guy Joined: Jan 2009 Posts: 38 | I think I'll stick with 3000 rpm for a cruisin' RPM. From what little I have been able to gather, it sounds like the GMC six is a better motor than it's Chevy counterpart. The thing that worries me is the whole gettin' parts. It doesn't seem like there is a lot out there for those old Jimmy in-lines. | | | | | Joined: May 2001 Posts: 7,438 Extreme Gabster | | Extreme Gabster Joined: May 2001 Posts: 7,438 | The parts are out there. They aren't in stock in a lot of places that have 235 parts in stock but they can be ordered. For more specific info on your truck and engine, check out oldgmctrucks.com | | |
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