Does anyone happen to have the engine block deck height specification handy for a GMC six? (main bearing centerline to the top of the block) I'm thinking it's probably the same for all of them, but I'm mainly interested in the 270. I'm crunching numbers on connecting rod length, crankshaft stroke, and piston compression height for a possible crankshaft modification. My SWAG guess without tearing an engine down to a bare block is 11 3/8". Thanks! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Jerry - After searching through the few GMC Maintenance Manuals I have so far, I couldn't find the deck height spec listed in any of them. Some web surfing located this Inliners thread reply post that indicated an undecked 270 was measured at 11.3667". Mighty close to your 11 3/8" (11.375") SWAG.
Hope this may be of help.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
Thanks! I'm tinkering with an idea to do a 3/8" stroke increase, using the original GMC 7" connecting rods and a 94MM piston for a Japanese diesel engine. That comes out to approximately 310 cubic inches, and a 3/8" longer stroke than a 302. There's a LOT more 270s out there than those scarce and expensive 302 engines. The connecting rods will be sleeved down to use rod bearings for a Jeep CJ-3 4 cylinder engine, with the crankshaft offset-ground 3/16" for a 4 3/8" stroke. If a lighter weight reciprocating assembly is desired, 85 HP flathead Ford V8 rods are also 7" long, they can use the same bearings, and they weigh approximately half what the GMC rod does. I believe that with the right camshaft and valve springs onboard, that engine will turn somewhere around 5500 RPM and out-torque a 302. A Chevy 292 piston is also a pretty close fit, only requiring a little bit of block decking to get it close to the top. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
But if you started with a stock bore 302 you'd have 330 ci Jerry.
You know what Stroker McGurk said.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Yep- - - - -"There's no substitute for cubic inches!" There's a modern corollary to that one, which I coined while building round track and pull truck engines- - - - -"There's no substitute for cubic dollars!" It's always more fun to go racing on somebody else's money! Fortunately, I was usually able to find somebody willing to finance his own "Go fast- - - -Turn left" addiction, and needed an engine builder! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Yep- - - - -"There's no substitute for cubic inches!" There's a modern corollary to that one, which I coined while building round track and pull truck engines- - - - -"There's no substitute for cubic dollars!" [snip] Jerry
"There's no substitute for cubic dollars!"
Seen painted on the door of a Peterbilt towing a racecar trailer in the pits at Bonneville Speed Week a decade or so ago. Jerry, didn't you live in So. Cal before that? Maybe he copied you.
Bonneville is a real trip for gearheads like us. Made friends with the owner of a 34 Ford from Portland OR with a built 270 Jimmy. His way beautiful and much lighter daughter at the wheel. They limit it to 4800 RPM after they scattered one on the salt at 5500RPM. 170 something MPH two way average IIRC. The flies were terrible and lived in my camper for months till they froze.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
I built mostly round track dirt car engines in Atwater California about 70 miles north of Fresno, in the late 1970s. We ran at Merced (home track) also Antioch and Watsonville. The guy we spent most of our time chasing had a slogan on the back of his car- - - - -"When the green flag drops the "BS" stops!" He wasn't quite that PC about it, though!
Back when the NASCAR circuit had a west coast division, "Winston West" I was offered a position as crew chief on a W-W team that ran on tracks up and down the western USA. At the time, some pretty dicey family dynamics (a nasty divorce and child custody battle) kept me from being able to take the job. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
