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Guest Jeff in Colorado

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Guest Jeff in Colorado

Good morning all,

I'm looking at a Cutlass that has a rebuilt 455, and although the details are a bit sparse, I'm hoping someone can educate me a little. I know next to nothing about rebuilding beyond stock.

I am told the motor was bored out, didn't say how much, it had a performance cam and lifters installed during rebuild. No specs yet, maybe never as it was done several years ago and not much paperwork is available. It is a Y79 motor, according to the owner, compression ratio of 9.5:1. I thought that code would be easy to see, stamped on the top of the block but he said it is underneath and hard to see. Also it has the 10/12 bolt rear-end, but when the motor was being done, they put 3.42 gears in it. Sorry if I haven't got the terms quite right. He says he runs 93 octane but it will run on 92 or 91 also. I wasn't looking for a race car but this deal appears to be worth going for.

My questions: As the rebuild occurred at sea level and I am near Denver, elevation 5280 ft., is there going to be a huge problem keeping this car running here? Can the cam be changed back to something milder without major work included? Any other advice is sincerely appreciated.

Thanks.

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Good morning all,

I'm looking at a Cutlass that has a rebuilt 455, and although the details are a bit sparse, I'm hoping someone can educate me a little. I know next to nothing about rebuilding beyond stock.

I am told the motor was bored out, didn't say how much, it had a performance cam and lifters installed during rebuild. No specs yet, maybe never as it was done several years ago and not much paperwork is available. It is a Y79 motor, according to the owner, compression ratio of 9.5:1. I thought that code would be easy to see, stamped on the top of the block but he said it is underneath and hard to see. Also it has the 10/12 bolt rear-end, but when the motor was being done, they put 3.42 gears in it. Sorry if I haven't got the terms quite right. He says he runs 93 octane but it will run on 92 or 91 also. I wasn't looking for a race car but this deal appears to be worth going for.

My questions: As the rebuild occurred at sea level and I am near Denver, elevation 5280 ft., is there going to be a huge problem keeping this car running here? Can the cam be changed back to something milder without major work included? Any other advice is sincerely appreciated.

Thanks.

Well, without knowing more about the details of the build, it is difficult to tell you much. Option code Y79 was the Cutlass Supreme SX option code for model years 1970 and 71. This included a 455 engine, but "Y79" actually refers to the whole package, not the engine itself. Since the engine has been rebuilt to unknown specs, the original state is meaningless anyway.

What matters are the castings used (block, heads, intake) but even that is somewhat moot, as any Olds castings could have received different valve sizes, different cam profile, and different pistons to change the compression ratio. Again, without knowing what went into the motor, it is nearly impossible to tell what you have. The block casting number is located on the horizontal "shelf" above the water pump, just below the thermostat housing. The heads will have a large raised letter just below the no. 1 and no. 8 spark plugs. The year of the block will be found in the VIN derivative stamp that is on a small pad on the block below the no. 1 plug (and usually covered by the PS pump bracket). Suitability for high altitude operation will really be a function of carb jetting and ignition advance profile, which can be adjusted without going into the motor itself.

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Guest Jeff in Colorado

Thanks for the help, that's already much more than I knew for certain.

You are right of course, about the intake etc. being key to understanding more than the original motor specs.

I agree there's not much at all to go by on the details of the build, but even what you have stated is very useful to me. I did some googling, just not that skilled at it sometimes. I did read up on the designations on Cutlass in general and the VIN codes, and if I am to believe the seller, and I am leaning that way, in conjunction with the VIN, the motor is original, albeit rebuilt. I do need to find a way to pin down exactly how much it was bored out and what parts were used. It's been a few years since the rebuild, and only a couple thousand miles on the car after that so it seems any major issues as to the power plant would have surfaced by now or at least be showing symptoms. Just trying to avoid a real disaster, and learn at the same time.

Seems I do remember now that you mention it, the high altitude adjustments should be pretty simple. The car has HEI, should have mentioned that, so along with the four barrel, I or a reasonable back yard mech should be able to adjust it, it hasn't been that long since I routinely did such things.

Thanks again for the help with the casting number locations and such. Appreciate it.

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