Not sure about a Lemans, but I had a 71 Olds 442 and spent some time playing with it. To be clearer, I spent $23,000 restoring it after spending about five years trying out different cams, rearend gears, and going from a Muncie four speed to a T400 tranny. (I never did remove the clutch pedal because I figured I might go back someday)
Anyway, if you wanna leave it stock great. If not get a new intake and put a 4 barrel on it. If you are looking for good driveability get something in the high 300 as far as the rear gear ratio. I had a 410 in my Olds for a few weeks and decided it was fun as hell from stop light to stop light, but for a highway drive it SUCKED. I ended up with a 370 ratio and a Moroso Brute Strength Posi carrier, in my GM 10 Bolt. (The guy before me blew his rear end and decided to sell it instead of rebuilding it, what a JACKASS. I never found a reasonably priced 12 bolt over the 16 years I owned the car)
Anyway, I don't know if that helps, but I got my parts from Summit Racing and NEVER had a problem dealing with them. I rebuilt the engine three times with parts from them and would order from them again.
If yo ureally feel crazy and don't want a crate motor, go by some old beater and steal the engine and trans from it. For example mine was a 71 with a 350 and a 4 speed in it. I bought a rusted out 1968 Olds 98 that had sat in a farm field for years. I only wanted the engine and trans for rebuild. The 68 98 came with a Olds 455 that put out 365HP and 510TQ and had the Olds "C" heads I was looking for. That was also where I got the T400 tranny. I junked the car after canibalizing it. I had the block machined and the heads done and put a mild build on the engine with a nice streetable Comp Cam. Loved the car once all was done, so I did a frame off restoration (the $23,000) and loved it more.
Took it to the track once and ran 12.7's with street tires spinning through second gear and the exhaust still bolted on it. I only sold it because I needed the down payment for my new house I bought a year ago.
The selling of that car brought me to the purchase of this one. Go figure, I missed the power under my foot.
I really don't know, and no one will be able to give a straight answer because it could be anything: 2.56, 2.78, 2.93, 3.08, 3.23, 3.36, 3.55, 3.90, 4.11*, 4.33.
I am fairly certain that 4.11 and 4.33 were a dealer intall option.
What you can do is check the top of the axle on the passenger side, or maybe a tag bolted to your diffi. Although that doesn't work most of the time, on my 69GTO it is rubbed off. But there is another way. Jack up the back of the car, and use jack stands for safety. I found my ratio by spinning the rear wheels in neutral, but I have heard that it can be in gear and by spinning the driveshaft. Put a chalk mark on your driveshaft and the U joint lining up. And another mark on your rear tire straight up.
First find out if you have a posi rear or straight axle by rotating one tire, if both tires turn in the same direction: posi, different straight. For straight axle rotate the rear wheel until you get one full turn of the driveshaft. Guage how many turns the tire has done. Multiply by two. Thats your gear.
Most of the late 60's 2bbl 350 Lemans came with a 10-bolt 2.73 non-posi gear but almost anything was available so you have to check as Arch describes above. The 2.73 is a good highway gear but limits take-off power. For spirited but still highway-worthy driving I like a 3.23 gear for a stick or 3.55 gear for auto. Anything higher than this is best kept off the highway except for short drives.
The rear ends used on the Pontiacs (BOP) were different than used on Chevys and the parts do not interchange. But gears should still be easy to find if you want to make a change. Limited slip rear-ends were not uncommon but the original clutch packs are usually worn out and when I tried to have one rebuilt 10 years ago I found replacement parts were impossible to find. But maybe this has changed.
Putting a 4bbl manifold and carb on a stock 350 will give an immediate power boost, as will installing dual exhaust. Just about all of the engine parts including the heads will interchange with the 400 so you can go nuts and still keep the 350 block.
My '69 conv came with the 4bbl 350, turbo 400 and a 3.55 gear but this was very unusual. The 350 will not make quite as much power as a 400 but they are very durable, run cooler and put less strain on the starter motor which are definite benefits. I actually dirt-track raced LeMans bodies with Pontiac 350's years back and was quite successful. I would never consider trying this with a Pontiac 400 engine.
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