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GMC Big Strait 6; 426,477,503,707?

Discussion in 'The Hokey Ass Message Board' started by BlackCherryImpala, Aug 2, 2008.

  1. off to see if the big int 6 is still available.
    BTW nice math. Good work and excelant explanation. Impresssive to say the least
  2. BlackCherryImpala
    Joined: Aug 3, 2006
    Posts: 131

    from Girard, KS

    I'm working on the purchase of a 33 International 1 1/2 ton. Wouldn't that be really cool with one of the big IH sixes. I salivate at the thought.
  3. no bux rod
    Joined: Mar 26, 2007
    Posts: 123

    no bux rod

    Let's see some photos, I'm drooling....a really big 6 in a T-bucket with the needed reinforcements sounds cool.

    N B r
  4. Piper106
    Joined: Jul 29, 2006
    Posts: 118


    Some of the monsters were built as late as the 1970s.
    Looked at the 1972 Statistical Issue of Automotive Industries and it lists for gasoline engines;

    501 cubic inch 6 cylinder 4-1/2 bore x 5-1/4 stroke 215 HP @ 3000 rpm
    451 foot lbs torque @ 1600 rpm

    Brennan (mostly tractors I think)
    620 Cubic inch 6 cylinder 4-1/2 bore x 6-1/2 stroke 250 HP @ 2000 rpm
    500 foot lbs torque @ 1200 rpm

    605 cubic inch 6 cylinder 4-5/8 bore x 6" stroke 177 HP @ 2000 rpm
    515 foot lbs torque @ 1000 rpm

    800 cubic inch 6 cylinder 5-5/16 bore x 6" stroke 250 HP @ 2000 rpm
    718 foot lbs torque @ 1100 rpm
    800 cubic inches is not small; 30" wide 43 -3/4" high, 76-1/2" long

    Geared for about 2100 rpm at 70 mph, and multi-disc clutch (I'm thinking maybe from a top fuel car) and one gear would be OK (well maybe a little rough pulling into a parking space at the local A&W for a chili dog).

    Last edited: Aug 5, 2008
  5. I went into work today and added a pic of the V12 to my computer to use as my desktop background (not supposed to surf the net on company computers). Anywho, the engineer who sits across from me looked at it and started chuckelling, he worked for a guy who used to run a Kenworth between K-Zoo and Nebraska that had one of them 12's in it... and he said to show it to another engineer who works with us, he's got some good info on them. (I work at Detroit Diesel, these are 30 year + guys).

    Any first hand experience on how big the Group I (big big 6's) are compared to the Group II sixes (the 228, etc).? I'd be curious to see if the weight is worth the percieved displacement advantage (power to weight ratio, etc.)

  6. Zig Zag Wanderer
    Joined: Jul 6, 2007
    Posts: 564

    Zig Zag Wanderer

    i don't have dimensions but here is an example of the "big big" GMC six

  7. Or not. :)

    Thsnks though!

  8. fiftyv8
    Joined: Mar 11, 2007
    Posts: 5,119

    from CO & WA

    Man I just pic's and torque figures and lots of them.
    Come on lay a few down please!!!
  9. Silent_Orchestra
    Joined: Jun 17, 2007
    Posts: 1,313

    from Omaha, NE

    The big sixes are sweet...but more practiacal is the 702 GM's a couple of examples that have been done...A video of a speedster of sorts with one...sounds sweet...but I like the old hit miss engines poppin' off in the background noise better...

    and the Blastolene B-702...

    and some pics of the B-702...I think it was in Street Rodder mag too...not sure I'll have to look

    Attached Files:

    Last edited: Aug 7, 2008
  10. BlackCherryImpala
    Joined: Aug 3, 2006
    Posts: 131

    from Girard, KS

    I have finally found some more info on the big GMC straight 6 engines. I still have not found any pictures.

    707 is actually 706.9 cid
    Bore 5.00 x 6.00 Stroke
    Torque 630 @ 1200 RPM
    HP 225 @ 2200
    Truck Series 900 -970 gas

    503 is 502.7 cid
    Bore 4.56 x 5.12 Stroke
    Torque 422 @ 1200 RPM & 455 @ 1000-1600 RPM
    HP 200 @ 3000 & 255 @ 3200
    Introduced in 1949, discontinued in 1959
    Series 740, 750, 850 & 890 gas
    (Higher torque and HP figures are from the 1955 and later engine)

    477 is 477.1 cid
    Bore 4.50 x 5.00 Stroke
    Torque 382 @ 1000 RPM
    HP 153 1/2 @ 3000
    Introduced in 1941
    Series 750, 850 & 890 gas

    426 is 425.6 cid
    Bore 4.25 x 5.00 Stroke
    Torque 342 @ 1200 to 1400 RPM
    HP 177 @ 3200
    Introduced in 1939
    Series 640, 640H, 720, 800 & 870 gas

    360 cid
    Bore 4.12 x 4.50 Stroke
    Torque 297 @ 1000 to 2000 RPM
    HP 155 @ 3200
    Introduced in 1939
    Series 620, 700 & 770 gas

    I must have the 707. If you check, the Torque figures are the same on the GMC Twin Six or V-12 as on the 707 straight 6, 630. I think i will need to find a very old metro bus. What did that GM travelling future bus have in it that sold at Barrett-Jackson a few years back?
  11. NOT true! Mopar built an INLINE 413 inch straight Six, that was in Imperials and medium-duty trucks in the late '30s. It was the largest six that Chrysler ever built for road use. This is a great bar bet, BTW, or a rod show trivia question!


    Larger trucks used another family of in-line flathead six cylinder engines. There was a 331 cubic inch and a mammoth 413 cubic inch lugger was available in the T series and up. There may have been another engine in the 370 CID range, but I am not sure about that. The 331 was highly regarded in trucking circles as a durable, hard working engine. The 413 was equipped with two single barrel carburetors and had a very large appetite for gasoline. It was noted for twisting the drive sprocket off the end of the camshaft.
    Last edited: Aug 12, 2008
  12. Silent_Orchestra
    Joined: Jun 17, 2007
    Posts: 1,313

    from Omaha, NE

    The Futurliner used the GMC 302 Six, here's a link to the Futurliner site...
  13. Good day,
    I am new here. Recently purchased a 1948 GMC ACR723. Overall it is really good shape and I am going to use it for some sort of project. I do not have all the details worked out yet but I do plan on maintaining the dual tires. I will probably run 22.5 low profile tires and lower the truck.

    I am toying with engine choices. Currently it does have a 503 inline 6 that does run but I was considering a big block due to the mass of the tires and wheels. Other than that, there will not be much weight involved.

    I stumbled onto this thread and site researching the motor. The guy I bought it from believes he replaced a 426 I6 with the 503, but there is a slight chance it was the other way around.

    Is there a simple way to differentiate the 426 from the 503
  14. BlackCherryImpala
    Joined: Aug 3, 2006
    Posts: 131

    from Girard, KS

    I know on the smaller GMC straight sixes there is a stamping next to the distributor with the cubic inches. I don't know about the big boys as I haven't had the opportunity to see on that close.
  15. Fiorano
    Joined: Nov 22, 2007
    Posts: 212


    where do you find these things? tractors or old trucks?
    mmmm kinda makes me think of the old aero engined cars....
  16. 44todd
    Joined: Feb 12, 2011
    Posts: 2

    from MN

    Hey all.. I was doing some research on the GMC 477 motor and wound up here.
    I bought the inventory of a local shop that opened in the 30s.
    Included was an NOS box of Sealed Power brand piston rings marked GMC 39-48 477 motor standard bore. I'd like $75 anyone interested? Todd 218-208-2080
  17. PackardV8
    Joined: Jun 7, 2007
    Posts: 889


    I saw one of those 707" GMC monsters recently. It was at least 4' tall from pan to rocker cover and nearly that long.

    jack vines
  18. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547


    they are the size of a old 14L ( 855 cid) standard diesel 6 cyl made for torque not speed .
  19. Truckeez
    Joined: Jan 17, 2007
    Posts: 192


    tooooooooooo Baad this thread could not have stay'd purely big azz gmc 6 --> STRAIGHT 6
    (all that other- international , etc , v6, twin 6, v12, stuff belongs somewhere else..........).

    about the odd big kind of G M C that we cannot even find a picture of searching the net.
    the manifolds are on the passenger side.
    the 308 , 356, 400, 426 are all the same series

    the 503 or whatever up to 707 are a different bigger series.
  20. Hammerdick
    Joined: Apr 29, 2018
    Posts: 1


    For what it' worth to those who want a RD 450 IH (not red 450) look for the split exhaust manifolds, sounds unreal when engine is tuned right, really cackles and get a RD 501 intake. It's got a 4 barrel Holly, stock 450 is a 2 barrel. My dad took a 501, balanced and blueprinted, no governor in a single axle rotisserie restored 1946 KB 10, single axle box body, and no truck on the road today would run with it. We still have it. We ran 15 or so 450's in concrete trucks and certain engines, not sure why would run like banshees. 501 was usually lazy but stout, 549 was strong. Loosen valve settings and make sure carb jets are right
  21. jetnow1
    Joined: Jan 30, 2008
    Posts: 1,593

    from CT
    1. A-D Truckers

    You might be able to go straight with no trans but reversing out of the a and w stand would be a bitch.
    doyoulikesleds likes this.
  22. Roger Marshall
    Joined: May 15, 2018
    Posts: 1

    Roger Marshall

    The 413 was a misfit 440block. They were also used in the Chrysler Imperial and other fancy Chrysler cars. My Dad put a 413 and automatic transmission into a early 50's Ford bus for a church. However they sold it while I was away in the Army. Never got a chance to drive it. I'm looking at a 52 GMC 620 TRUCK WITH THE 426 INLINE. 5 SPEED TRANS. BEAUTIFUL TRUCK.
    6narow likes this.
  23. 6narow
    Joined: Jun 1, 2008
    Posts: 517


    You forgot about the GA series Ford engines from WWII. V8 version of a R-R V-1650, it displaced 1100 cubes and made 500 HP.
    ...getting back to the question at hand, those engines the OP mentioned are very large. I'd think you'd have to build a custom frame to fit one, or build a hotrod from a straight truck or a tractor-trailer rig.
    I've seen some youtube videos of a rat rod featuring a 534 cu. in. Ford Super Duty V8.
    The sound alone was very cool!
    Got me to thinking about building a similar rod from a 30's Chev and powering it with a GMC 637 V8.
    That'd be a hell of a drag race!
  24. 6narow
    Joined: Jun 1, 2008
    Posts: 517


    Was gonna give you some specs on that 707 but my Motor's Manual only covers 1936 to 1946. 477 is the biggest GMC engine they list for that time.
  25. Relic Stew
    Joined: Apr 17, 2005
    Posts: 1,127

    Relic Stew
    from Wisconsin

    Necrothread, but a GMC V12 '32 was built in Australia and used in the Fury Road movie. I read that they blew the engine up by over-revving it, and had to scramble for a replacement.

    Prior to it's movie appearance;
  26. KenC
    Joined: Sep 14, 2006
    Posts: 472


    There was more than one 413. I had the RB version in a 58 Dodge Royal. Easy swap from the 326 poly. This is about the other 413:
  27. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,971


    When I was in the Air force O11A fire trucks ran a 803 cu in continental 6 cyl gas burner.
  28. 6narow
    Joined: Jun 1, 2008
    Posts: 517


  29. wireflight
    Joined: Oct 13, 2020
    Posts: 1


    Just plumb a second "starter" motor to turn backwards. If you're doing this with an air starter, you probably want a 5+ gallon surge tank and a rotary screw compressor, plus a flow regulation valve would be nice to "finely adjust" your speed. In-out drive for the compressor: an electric clutch won't handle the strain. Planning is everything — at least until you reach the point of execution.

    If you're doing this with electrics, mmmmm, might wanna rig-up a drive section from an EV and call it a hybrid, because you can't always park on a favorable grade — and if using a "traditional starter," an unfavorable grade at the proposed combo's weight would likely lead to either some combination of (a) "premature maintenance issues" and "incredibly-slow reversing" or (b) lamentable calls to your insurer.
  30. Wrench97
    Joined: Jan 29, 2020
    Posts: 142


    Very old thread I know but if you have never seen one of the "big sixes" they are a interesting engine.
    503 ci.jpg

    Good series on rebuilding a 503 out of a fire truck here>

    The 707's seem to have mostly been used in GM's Yellow Coach bus division for busses, I suspect the advent of the 6 71 Detroit diesel and GM's purchase of Cleveland Diesel in 1938 made the big gas engines less attractive to GM. It's very hard to even find pictures of the 707 let alone a surviving engine.

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