rocket69

Hey guys,

Most of the decoding info I've used comes from 442.com. For decoding heads, it's described as G heads being from '71 and Ga heads being from '72.

So, I understand the difference between the two, but the site was vague as to how Ga would actually appear on the head. Is it literally an upper-case 'G' followed by a lower-case 'a', or is it the 'G' in the usual place and size, and an upper-case 'A' half the size, about an inch and a half to the right of the 'G'?

There's a pretty significant HP and torque difference between the two, so of course I'm curious...

2blu442

It's the normal sized G with a capitol A less than half the size to the right down low. I believe the heads alone are the same between the two as far as performance, but that the compression may have dropped. Also that may be the year that they began measuring the horsepower from the rear wheels rather than the rear of the crankshaft which made a big difference in numbers, but actual on the street the change isn't that dramatic.

88 coupe

My source says the chambers are the same size. Compression difference would be in the pistons.

Never happened. They have always, and still do, used engine dynos.

The Feds set standards for dyno testing by the manufacturers. Under the new regulations, all accessories/belts had to be on the engine during the pulls. Prior to that time, accessories were not necessarily used.

Not much of the difference was due to the new testing procedures.

Most of it, was an accurate measurement of the the actual power loss caused by the higher gears, lower compression, leaner mixtures, and earlier ignition, needed to meet EPA regulations.

It was, when it happened.

A "conspiracy theorist" could conclude that the Government mandated those regulations, in order to lessen the impact of the lower HP numbers.

Norm

vette442

The 1971 and 1972 engines across the GM line did not change much other than on paper. The biggest change was from 1970 to 1971 when compression dropped. You will not notice a difference between using stock '71 G heads and stock '72 GA heads. The 250 (U)/270 (V) net hp 455s in 1972 are roughly equivalent to the 340 gross horsepower 455 of 1971, just like the 200 net hp 350/4v/N10 of 1972 is essentially the same engine as the 1971 265 hp 350/4v.
Terry

Kaline

To build on this 1971/1972 cylinder head discussion, what were the differences between the 1970 10.5:1 compression 455 and the 1971/1972 8.5:1 compression engines? Larger cylinder head chambers? Dished pistons? A combination of the two?

Fun71

Dished pistons. Head combustion chambers were the same volume.

Kaline

@Fun71 thank you very much!

I also found this very useful info on Oldsmobile cylinder heads: https://oldsjunction.classicoldsmobi...sfaq/ofhed.htm