Q: OHC Conversion to V-8
OK gang I really need some help here. I’ve been looking for a 1968 convertible 400 car for about a year now, however I’ve not been satisfied with the condition/options of the cars for the $. Consequently I’ve entertained the idea of just building my own. I am somewhat of a purist so I don’t want to screw up a nice/clean original example. So I found a reasonably clean six cylinder convertible, non matching #’s OHC six. It does have a four barrel, but its not a SPRINT option, 3 speed manual on the floor. No PS, PB, manual top. I’m planning on building the car and keeping it forever, so I will not try to pass it off on anyone else. Here’s what I want to do/ am consiereing. 400 or 455, streetable that will run mid to low 13’s. Engine cam intake carb ect I’m fine with questions I have are: Will the existing 3speed work with either engine?(I am not a total idiot but just figured I’d ask) if not which manual trans, should I use? Where to find and how much? I haven’t ruled out going to a 4speed auto( like the one in HPP 1967 Goat) opinions on this welcome if anyone has tired it. IT has manual drum brakes(recently rebuilt/lines cylinder ect works great) are they sufficient or will I need to upgrade to account for extra weight of V8 trannie ect. Suspension: new front/rear springs? I know some guys like 6 cylinder springs for weight transfer. Suggestions? Or other issues I have not considered any and all advice is greatly appreciated.
A: You asked earlier about converting to a V-8 and stick. There are differences in the clutch setup between the OHC-6 and a V-8. The z-bar is longer on the OHC-6 since the block is narrower. Also a OHC-6 runs much better with the correct 4-speed, which will not last long with a V-8. They originally came with a Saginaw with a 3.11:1 first gear ratio. Most Muncies used a 2.55:1 first ratio. Going to a steeper rear will work well with both engines. The OHC-6 will rev higher, but it stops making real power around 4500 RPM.
A: I can tell you the transmission behind a six is a Saginaw 3-speed, very light-duty, not likely to hold up behind ANY V8! Also, the OHC6 has a different bell housing and probably different Z-bar than the V8 applications, so to do a 4-speed, you will need a Muncie to be period correct, or a Borg-Warner T-10 (I think the T-10 may be a little stronger), and most of the rest of a 4-speed change-over. The 700R4 Automatic is a good transmission, but only comes in a Chevy bellhousing pattern. The 200-4R is run behind VERY hot V6 Buicks in drag racing, but you’ll have to do some research to see how they do that, it does come with a dual-pattern bell housing. The 200-4R also fits better, Gary installed one in his 1967 Tempest Sprint with no chassis mods, just moved the crossmember back to an existing set of holes in the frame. There are no additional holes in the ‘bird, but it is still likely to be easier to make a 200-4R fit than a 700R4. The driveshaft even stayed the same in the Tempest!
Also, although drum brakes are, shall we say, adequate, there may come a time when you need MORE than adequate! You will NEVER regret changing to disc brakes! Especially after going through a puddle and having NOTHING! You’d have to be a bit of a daredevil to have drum brakes in a car capable of turning low 13’s!
By the way, I would probably be interested in aquiring the bell housing and Z-bar from your OHC6 after you remove them, as well as the flywheel, and any other six-specific related clutch parts.
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Content last modified: January 16, 2014 at 2:59 pm