'67-'72 GM A-Bodies

I've noticed that '72's seem to be somewhat cheaper, would these be low-compression unleaded fuel cars? Is that why there's a discount?

ShadowSix wrote: In reply to Gasoline: Nice cars, I'd like to some photos of the GS455 Stage 1 clone when you're done! Any advice on where I can get a primer on these things? Good books, a decent forum, etc?

V8Buick.com Bunch of nice and very helpful guys.

Compression dropped in 71 or so for unleaded, power went from gross to net (headers and no accessories to full factory exhaust and all the accessories) in 72, emissions crippled the engines further and further every year till 78 or so when you had 120hp Corvettes and such.

This chart is for the 500" Cadillacs, but you get the idea. http://en.wikipedia.org/wiki/Cadillac_V8_engine#World.27s_largest

'72s were not unleaded-fuel, but they were getting emissions-choked and were down on power a bit compared to the cars just a few years older. They also started getting into the safety-bumper era.

I'm partial to Pontiacs. Here's mine:

It's been in the garage for the last 20 years or so; it was my daily before that. Hasn't been driven in about 6 years, unfortunately. It's patiently waiting for me to retire and spruce it up. I should sell it but it's hard to sell a car that you've known for 45 years and owned for 30.

In reply to Duke:

I'd always read GM dropped compression in 72 to prepare for unleaded fuel.

Yes, they did, but they were not running cats and they didn't require unleaded until 1975, I think.

It looks from that chart you posted that Caddy dropped compression twice, once from 10.5 to 10.0 for 1970, then again from 10.0 to 8.5 for 1971. That said, if you read the paragraph above the chart, a lot of the power "loss" was in the conversion from gross to SAE net. The Caddy 500 went from 365 gross hp to 235 net hp. So all but about 80hp of the power loss was just on paper? Is that right? I know bumping compression back up requires a tear down, what about the other stuff? Can I get that hp back relatively easily?

Subsequent loses can be attributed to weaker camshaft profiles, catalytic converters, and cylinder head design.

Kenny_McCormic wrote: In reply to Duke: I'd always read GM dropped compression in 72 to prepare for unleaded fuel.

They dropped compression for emissions reasons. IIRC that's about the timeframe when NOx emissions were being targeted. Then '73 gave us EGR valves to knock NOx even more, and the final bullet was catalysts in '75. And then a decade or so to figure out how to make an engine run well and still keep the cat happy.

ShadowSix wrote: The Caddy 500 went from 365 gross hp to 235 net hp. So all but about 80hp of the power loss was just on paper? Is that right?

It's very hard to say since the switch from gross to net happened in a time when engines were changing drastically every year, but chew on this.

"Gross" horsepower was often done with no accessories attached to the engine, without the as-installed exhaust system, no air filter, and ignition timing tweaked at every measuring point. And then it was multiplied by some magical fantasy-land factor which could be above or below 1.0 depending on how they wanted to market the engine and what the other guys were selling. (Ever notice that even though the engines kept getting bigger, with bigger and better heads and carbs and camshafts, peak HP of the best engines managed to ALWAYS be 425hp throughout the 60s? Excepting engines like the L88 which was only rated at 435 but was reckoned to be closer to 535? Or that the Boss 302 and the Z/28 made "290"hp?)

those HP rating shenanigans are the reason they were forced by the insurance industry to go to a standardized SAE method of rating them.. but they still do some shady stuff when rating them, as evidenced by cars like the LS1 powered Vettes and F bodies that were putting the SAE rated flywheel horsepower and torque down to the wheels..

I still get a kick about the, what was it, '74 455 Super Duty?

"It makes this much power, and we have put a tab on the carburetor to limit throttle opening to guarantee it. Don't remove the tab or the engine will make more power!"

20 years later, Nissan had a "276"hp turbo car with restrictors (or somesuch) in certain vacuum lines... clearly marked as to location, and removal of those bits would result in far greater boost that the engine computer just so happened to have been mapped to work with.

Kenny_McCormic wrote: Subsequent loses can be attributed to weaker camshaft profiles, catalytic converters, and cylinder head design.

Correct. There was a huge drop in compression, cam duration, head flow, and other factors because of the emissions laws. That, combined with the change from gross hp to net hp and everyone blames the emissions equipment.

When it comes to performance muscle cars, you are faced with some interesting challenges as far as power is concerned. You can get an older car/engine, but that 365 gross hp that everyone thinks is so hot is actually 275 net hp that requires premium fuel and possibly a lead substitute to keep the valve seats happy. Old-school muscle is just that: old school. Its really not that awesome. These days you can make 500 hp on 87 octane.

In reply to curtis73:

Makes sense, I'm kind of thinking that if I got one of these things I'd get something fairly pedestrian like a small block skylark and modify for drivability and appearance. I want one to cruise in, not to race.

BTW, thanks for the v8Buick link, gasoline!

My first car was a 1971 Pontiac LeMans, my first two race cars were a 1968 Cutlass and a 1971 Gran Prix, but I won lots of (circle track) races all across SoCal in 1968 Chevelles.

To me the 68 Chevelle, with the narrow slot taillights and wrap around grill trim is by far the sexiest of the lot... but I may be biased.

But if you ever plan on turning, do yourself a huge favor and ditch any big block plans and build yourself a small block, preferably with aluminum heads and intake. Balance is key in all forms of motorsports, and with the right front to rear balance, these cars can corner surprisingly well.

In reply to Flyin Mikey J:

Yeah, I can't say the Chevelle isn't a classic. It's a great car that deserves the popularity and place in history it has achieved. BUT, I feel like I've seen hundred or thousands at car shows and drag strips. In comparison, the Buick GS and Olds 4-4-2 just aren't as common, I'm a sucker for the oddball I guess.

And thanks for the tip re: big blocks and turning. I don't ever plan to race one of these cars, but I would like to end up with something that handles respectably (if for no other reason than just for general safety).

You can get aluminum cylinder heads for most any GM engine these days for relatively modest money; combined with an aluminum intake and radiator, moving the battery to the trunk, and other lightening techniques, you can really improve the balance of those cars. There are any number of companies selling improved suspension components as well.