Factory Torq and Horsepower GMC Six 248-270-302?

Posted by: DeuceCoupe

Factory Torq and Horsepower GMC Six 248-270-302? - 04/07/09 10:53 AM

I've been following the Nicson and other posts and trying to learn about the GMC Six and add it to my computer and dyno database.
I have a lot of car manuals but very little truck info.

Would anyone be able to post factory torq and power ratings (gross or net or both!) for the GMC sixes
228-236-248-256-270-302?

Any or all would help, searched all over the web and couldnt find this info.
Thanks very much
DeuceCoupe
Posted by: Ron Golden

Re: Factory Torq and Horsepower GMC Six 248-270-302? - 04/07/09 11:31 AM

I found some info at Old GMC Trucks.com. You'll have to do a lot of looking thru their pages and tech info. I'll do some more looking to see what I can find. We have quite a few old tech books, motor manuals at the shop.

228 cid
HP: 100 @ 3400 rpm
TQ: 182 @ 1200-2000 rpm

248 cid
HP: 114 @ 3600 rpm (125 HP also listed for later models)
TQ: 202 @ 3400

Ron
Posted by: chevman32

Re: Factory Torq and Horsepower GMC Six 248-270-302? - 04/07/09 03:55 PM

My 1954 GMC pickup has a plaque that states the horsepower of sthe 248 at 118. Torque is not mentioned.
Posted by: JasonS

Re: Factory Torq and Horsepower GMC Six 248-270-302? - 04/07/09 05:52 PM

302 1952-54: 145@3600 ; 262@1200 7.2:1CR

302 1955: 155@3600 ; 268@1400 7.5:1CR

302D 1955: 155@3600 ; 268@1400 7.5:1CR

302 1956-59: 160@3800 ; 268@1600 7.5:1CR
Posted by: DeuceCoupe

Re: Factory Torq and Horsepower GMC Six 248-270-302? - 04/07/09 08:53 PM

All,
This is helping a lot!
I am searching the web for old carb sizes, next need to hunt for compression, valve sizes (big head vs little head), and cam specs (as if).

Please continue to post any other easy tidbits of info you find, it all comes together like a jigsaw puzzle eventually.
Posted by: don 1450

Re: Factory Torq and Horsepower GMC Six 248-270-302? - 04/08/09 05:53 AM

From the GMC Maintenance Manual 1955-1959:

270A 130 hp @ 3400 rpm

270B 140 hp @ 3400 rpm

302 160 hp @ 3400 rpm

God's Peace to you.

d
Inliner #1450