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The Pontiac OHC Six

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  • Re: The Pontiac OHC Six

    Re: The Pontiac OHC Six

    yeah, having a port for each cylinder is neat. Also the intake ports look like they are raised a bit, and the valves are angled as well, right?

    The 292 has a 1.75" taller deck than the 250 chevy engine
    They don't appear to be angled too much, but it'll be more apparent when I get the head off. Off the top of your head, did the 292 use a longer rod or taller piston? Per my rod/stroke ratio thread in the tech section, I'm wondering if GM lengthened the rod to get a better ratio. Bad ratios supposibly create rpm limitations (cylinder filling and/or piston speed issues?).
    Escaped on a technicality.

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    • Re: The Pontiac OHC Six

      Re: The Pontiac OHC Six

      I think Steve took the 6 cyl book when he moved....

      but quick googling shows the 250 is 5.7" and the 292 is 6.76" so it's an inch longer.

      My fabulous web page

      "If it don't go, chrome it!" --Stroker McGurk

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      • Re: The Pontiac OHC Six

        Re: The Pontiac OHC Six

        Ok, so I need to learn more about the impact of just increasing stroke over a half inch will have on stresses in the block. A turbo hopefully could cruch any cylinder filling issue if I go the 292 route. Interestingly if I did a .060 overbore (which I don't know the current bore yet) and the 292 crank it'd put me just over 300cid.

        I guess I should be looking at pistons with the diameter in the range of 3.875" to 3.935" ?
        Escaped on a technicality.

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        • Re: The Pontiac OHC Six

          Re: The Pontiac OHC Six

          3.875 is the chevy 283 and 307 bore size. Probably there are other engines that are close...maybe the 318 mopar? which is 3.91

          Most performance engines have a 4" or bigger bore

          Also it looks to me like the valve reliefs on the stock pistons are kind of severe, so it's not going to be easy to find other pistons that actually work

          My fabulous web page

          "If it don't go, chrome it!" --Stroker McGurk

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          • Re: The Pontiac OHC Six

            Re: The Pontiac OHC Six

            Think it'll be pretty easy to lay the head on its side and see how far the valve sticks below the block deck? Going for low compression too may help.
            Escaped on a technicality.

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            • Re: The Pontiac OHC Six

              Re: The Pontiac OHC Six

              KB has some AMC slugs with pretty short compression height and 3.875 bore, I think it is to make the 4.0L into a 4.6L

              Looked like a couple of different dish sizes, 10.8 or 21cc.

              I can't find much this morning, like the deck height or the crank pin diameter, but I think the AMC stuff may give you some flexibility. The numbers I'm using are for a 250 Chevy because I'm google-challenged this a.m.

              found this, couldn't resist posting here: http://www.youtube.com/watch?v=APCl012FXhs

              Edit 2 - my math may be fubar, working with no dimensions. Being a well known math f/u, I'd double check it. I couldn't find a deck dimension for the Pontiac, but if they use a 5.7 rod, a 3.53 stroke, and 1.654 compression height, I come up with a 9.119 deck height.

              If that is true, you would be pretty close with the AMC junk - the pins would probably need to be bushed or the rods honed. They are .931 (versus what I think is .927). The pistons appear to be pretty short, I don't know if they would hit the crank or not with the necessary short rods.

              9.119 deck height (probably a little more, but it's the number I can make)
              4.125 stroke 292 crank
              5.7 rod (a little wider than a SBC from what I read. How much wider? )
              ---------------
              1.3565 Compression height. The AMC slugs have a 1.353 CH.

              Then there is the valve relief question, but a 21cc dish has to be pretty deep in that small of a bore. The rod to stroke ratio is pretty raunchy at 1.38. I don't think you'll want to rev it, but it should make a pile of torque. Anyway, just thinking out loud.

              /edit three

              How much can you grind a 292 crank? I'm wondering about 1.88 pin (honda size) 6.0 inch SBC rods and an offset grind on the crank. Hopefully I'm way off on the deck height. If you offset grind it to get them zero decked with a 6" rod, you get the r/s ratio up to 1.45 (400 chevy), and maybe fillet enough to use SBC Rods? Would that even work?

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              • Re: The Pontiac OHC Six

                Re: The Pontiac OHC Six

                turbo > stroker

                With those tiny ports, I'd just stick to the stock bore/stroke and just let the turbo to the work.
                Life is short. Be a do'er and not a shoulda done'er.
                1983 Mustang GT 302/T5 http://www.bangshift.com/forum/forum...485-bbr-s-83gt
                1973 F-250 BBF Turbo Truck http://www.bangshift.com/forum/forum...uck-conversion
                1986 Ford Ranger EFI 545/C6 https://bangshift.com/forum/forum/ba...tooth-and-nail

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                • Re: The Pontiac OHC Six

                  Re: The Pontiac OHC Six



                  So Pete, Dan and Jim, how's the intake/exhaust looking compared to the Chevy?
                  The Chevy doesn't have individual intake ports. And the 1/6 exhaust ports are clearly different shape.



                  Intake manifold ports might line up?



                  Exhaust might fit but doesn't look like it would seal around the corner of the 1/6.
                  1967 Chevelle 300 2 Door Post. No factory options. 250 ci inline six with lump-ported head, big valves, Offy intake and 500cfm Edelbrock carb.

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                  • Re: The Pontiac OHC Six

                    Re: The Pontiac OHC Six

                    Better picture of the Chevy head. Bottom one is stock. Top one is mine ;D

                    1967 Chevelle 300 2 Door Post. No factory options. 250 ci inline six with lump-ported head, big valves, Offy intake and 500cfm Edelbrock carb.

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                    • Re: The Pontiac OHC Six

                      Re: The Pontiac OHC Six

                      Bolt patterns are completely different too.
                      Life is short. Be a do'er and not a shoulda done'er.
                      1983 Mustang GT 302/T5 http://www.bangshift.com/forum/forum...485-bbr-s-83gt
                      1973 F-250 BBF Turbo Truck http://www.bangshift.com/forum/forum...uck-conversion
                      1986 Ford Ranger EFI 545/C6 https://bangshift.com/forum/forum/ba...tooth-and-nail

                      Comment


                      • Re: The Pontiac OHC Six

                        Re: The Pontiac OHC Six

                        Back to back pictures. Thanks Guys. The notches in the 1 & 6 exhaust are interesting. Remember my manifolds and heads are the low-po single barrel stuff. I'll have to look at the sprint manifolds, though I intend on possibly making my own intake and exhaust. The Sprint head ports are supposibly the same, just the combustion chamber is smaller for more compression.





                        Escaped on a technicality.

                        Comment


                        • Re: The Pontiac OHC Six

                          Re: The Pontiac OHC Six

                          turbo > stroker

                          With those tiny ports, I'd just stick to the stock bore/stroke and just let the turbo to the work.
                          I agree, just tossing out some ideas.

                          For grins, I think I would still use the forged KB AMC pistons, 6" rods, and offset grind as necessary to get them zero'd. The pistons have to be lighter and would be happier at RPM. Better rod ratio as a RPM bonus.

                          How many CC's are there in the chamber on the Pontiac?

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                          • Re: The Pontiac OHC Six

                            Re: The Pontiac OHC Six

                            Bolt patterns are completely different too.
                            The manifolds are all basically "clamped" on using metal tabs on the studs in the head. There are very few holes in the manifolds themselves and the stud locations are not terribly different. Seems like it could be done. Although getting a good seal on the exhaust header(s) is a known problem with this setup and there could be similar issues on the intake side under boost...
                            1967 Chevelle 300 2 Door Post. No factory options. 250 ci inline six with lump-ported head, big valves, Offy intake and 500cfm Edelbrock carb.

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                            • Re: The Pontiac OHC Six

                              Re: The Pontiac OHC Six

                              Supercoupe T-Bird supercharger

                              :D
                              Thom

                              "The object is to keep your balls on the table and knock everybody else's off..."

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                              • Re: The Pontiac OHC Six

                                Re: The Pontiac OHC Six

                                Randal - did you take that welding class yet and buy a welder?

                                I have a set of headers from Dan - I offered them to Brian - who decided against them - I'll offer them to you now that you have this thing. Surely they would take some cutting up - but - they are for a 292 so the port location appears to be relatively close.

                                I'm going with langdons split iron manifolds for the 292 in the '54 so - I won't be using them.

                                If research does not yield an off the shelf piston / rod combination that would work with reasonable machine work, I'd leave the stroke alone - and handle it with boost! ;D

                                Are forged stock replacement pistons available?
                                There's always something new to learn.

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