[67drake]

Guys, from what I know GTO's that came with A/C could not be had with any lower rear end gear than 3.23's. Was this because it would be harder for the cooling system to keep up with an engine running higher RPM's while the A/C is on,or would the extra RPM of a lower gear cause damage to the A/C compressor,or ....?
Just wondering. I have an 8.5" GM rear I set up a few years ago and never got around to putting it in yet. But I hope to this coming spring. I put 3.42's in it,but am thinking I MIGHT want to set it up with even 3.73's or 3.90's.
Anyone know?

[Cammer-6]

there were some combos that got 3.55 and a/c but thats as steep as it goes.

[bigborehunter]

Basically with the older piston style compressors, it was very difficult to make them live at freeway speeds if your car was low geared. Plymouth tried for two years to keep a 340 four barrel and a/c compressor working but warranty claims were out of sight. The compressor failed. Late in the year they developed an a/c cut out switch and used these in the New York State Fury police cars for the first time. It was a success. Their higher gearing obviously helped too. I wouldn't want to try a banzai run with a 3.90 geared Pontiac carrying an old R6 compressor. Me thinks it would be a good grenade. Since Trans Ams had a/c and four speed 455s by 1975 they obviously worked out some system for WOT but remember the gearing wasn't low like in 1969 either.

[PB]

for '72's according to Eric Whites book...a 400 GTO w/ac got a 3.23 rear end...a 455 got the 3.31 IIRC, same with the 455HO's.

[68gtoMN]

Pat, the 455's did get the 3.31 gear because that was the closest gear ration to the 3.23 already available in the 12-blot Chevy HD rear end used in these cars. You certainly want the RPMs lower in an A/C application.

[Cammer-6]

66-7 Sprints could get a/c with the 6500 RPM redline
now that was a warranty challenge.
So they smartened up and said no a/c on RA or Sprints for 68.
Later they figured you couldnt sell cars,even race cars without a/c
so the RAs got it again but not with the wild ratios as in days past.

[74 SD455 Formula]

Drake,
My 72 455HO GTO has a 12 bolt posi with 331's and A/C. I drive the car on the freeway at 65 or 70 with no problem's.You've seen my car at Guss's,if you remember...For what it's worth I do have an Automatic.

[A.W.Dille]

Drake my 71 was geared the same as yours before I eliminated the A/C completely. Then I went to 3.55's when I was racing it. Going back to 3.55's when I get the new engine built. From what I understand though the higher gearing was to keep the engine from turning too many rpm's and burning up the compressors.

[67drake]

Thanks guys.
My next question then is does the higher RPM damage the A/C compressor if it is not turned on?
I never use my A/C anyway. I just turn it on for a few minutes a few times a year to circulate the freon and oil through the system. I'd hate to disconnect it,seeing as how it still works. I know if I pull the belt off,out of laziness I'll never put it back on,and the seals will dry up on the A/C system.
Jim,no kidding,I didn't know your car had A/C. Good to know it has lasted.

[rolling money pits]

Originally Posted by 67drake

Thanks guys.
My next question then is does the higher RPM damage the A/C compressor if it is not turned on?
I never use my A/C anyway. I just turn it on for a few minutes a few times a year to circulate the freon and oil through the system. I'd hate to disconnect it,seeing as how it still works. I know if I pull the belt off,out of laziness I'll never put it back on,and the seals will dry up on the A/C system.
Jim,no kidding,I didn't know your car had A/C. Good to know it has lasted.

my guess is no, i wouldnt, since the pulley simply freewheels when the A/C is off.

now, a pulley that's out of balance slightly? that's a different story......

the A/C pulley, much like the alternator one, is over driven, just not to as steep a ratio. IIRC, the A/C belt is quite long compared to the P/S and Alt ones, i would think a high RPM blast with the A/C off would be more in jeopardy of tossing the belt as opposed to any compressor damage?

[65WJ]

When you recieve your phs if you read the ama specs the ratios for ac equiped cars are listed.
For 69 the auto recieved the 3.23 and the manual 3.08

patrick

[OVERULD]

My 71 455 H.O. 4/Speed has AC and 12 bolt 3.31:1 out back. I drove it from Atlanta, GA to Dayton, OH and back in July 2009 for Co-Vention. Ran the AC all the way and we were cruising at 70 to 75 the whole time. Never heard a peep out of the compressor or the belt, and she still maintains a full charge of R12 today. I think I was getting low 40s out the center vent.

Windows were down in this pic but it was early morning and still cool on an overcast day, so I was listening to the engine monaing out its one-note song! (Which was pretty sweet music!)



BJ

[67drake]

Nice car overuled!
OK,another question then. Is there such a thing as a smaller diameter pulley for the A/C's crank pulley? It would have to look stock though.

[mechanic17]

You will not want those 3.73s or 3.90s unless for purpose-built racing. Been there. 3.42s will make you happy if the cam is suited.