Young Man

What is the differents of G and Ga hesads

Oldsmaniac

I believe G heads are 71 455 heads while Ga are 72 455 heads. No real difference just the casting number unless they are Toro heads or 442 heads with bigger intake valves.

alek72us

G heads have big valves and Ga heads are small valves. at least thats what i have been told.

citcapp

According to the tech section the G with small A is a hardened seat head. It also states that G-K heads have hardened seats. A little confusion hear. Also states some E & F heads may have hardened seats. Description not real clear. Perhaps someone else can add more. Also states rumor is early C heads have the best flow. Any hard test bench evidence to prove this. Also what year C heads are they talking about

2blu442

I agree with Oldsmaniac, both can be either large or small valve heads depending on what the application was. The wiki site has more details on the differences between heads. There's a link under the reference section on this site. If you have time it's a great place to read up on details of these motors.

Pat, I've not seen E heads with hardened seats. I don't know about F's but since they're the same vintage as E I would doubt they have hardened seats either. I've heard C's are the best big block and #5's are the best small block for doing head work to them. But suspect this is just a old wives tale (can I say that without getting the PC police on me?) that's been floating around for a while. It appears to me that all but the J's have similar castings and should be able to be worked for better flows. I've heard the J's can also make good power, but it takes a lot more work to make it happen than with earlier heads. I had a set of 260 heads once... they had TINY ports. John

don71

I don't know exactly either.

I don't think its the spring seat depth either. Olds did have differents depths on the intake/exhaust on some heads.

The AIR bosses are not drilled, so that ain't it.

We do talk about C heads being the best.

Heres one you don't see often. Supposedly 1969 88's

Warhead

Ditto for the most part. I too, have never pawed an E with hard seats, had to have mine done.

Not an old wives tale, the early heads had a lower port floor, but less bowl, but only moved about 5-10 cfm more, max. Lowering the floor more, picked up another 10-20 cfm for us, depending on how brave we got. You can not lower a J head like an early C or 5 casting.

Measure from the deck to the intake port floor (with no valve in it), and you will definitely see what I am talking about. Measure the inside dia of bowl, at the end of guide also.

Since they flowed so close to each other, the big performance advantage is the ability to run taller valvesprings in the later heads, due to deep spring seats. There is a much better valve spring selection for the later head's installed height, (once you remove the rotators) when you run large camshafts. Note...some G heads have 2 different spring seat depths.

Have your shop check for the spring seat depths.
Jim

2blu442

Thank you for clarifying Jim. I'd heard that often, but never had anyone say exactly what was different in the castings. John

citcapp

Thanks for the clarifications

Rickman48

If I recall correctly, the heads w/2 different spring pocket depths were for the 'rotators' on the exhaust valves, which were 2-3 times thicker than a regular retainer.
Don't know why they just didn't use a shorter spring - -???
I do know there was enough 'meat' left to equalize them - using the cutter for P.C. seals.

Run to Rund

I have accumulated one set of E and several sets of GA heads. The E has deep spring pockets but no hard seats. I have GA with 2"I, 1.68E without seats, and GA with 2.06"I, 1.63E and hardened E seats. I thought at one time I'd use the hardened seats for street driving with unleaded gas, and the taller installed spring height for a better selection of good springs, but none of that has happened yet. I can tell you that getting just the spring tensions you want with earlier heads is a real pain. I like to use chrome moly spring locators so they don't dance around on the early heads that don't have much of a spring pocket. That takes up .06" of the already meager installed height. I run stock rockers and if you use +.050" locks and Isky 507STA retainers for more installed height and minimal impact on retainer to guide clearance, the retainers hit the rockers. It would have been easier to grind the GA to a C and use the late heads.

Young Man

Now I know a little more. I have found a-71 455 whit G-heads and I´m think I gonna bay it. I have one -74 whit J-heads but that type of engine have to little hp

Warhead

#1 yes
#2 They used the same valvespring, I/E. Production costs, maybe.
#3 Be carfull there.
Not all P.C. seal cutters have a seat cutter, If I were to cut seats, I would do much less of a cut, and only on a mill. Spring seats in the heads are generally no more than .220" thick. Cut a couple of junk heads in half, to see.

Jim

Warhead

Nothing wrong with J heads,
I would let condition, and price steer me, here.
Jim

Young Man

Yes you are rigth, I`m on a low budget but that engine I found is a turnkey and I got it for 1000 dollar. Rebuilt that with J-heads will cost me same money. Parts are expensive here in Sweden

joe_padavano

All Olds heads from the 1971 model year on have hardened seats. That's G, GA, H, J, K, and KA for big blocks. This was done to comply with the federal requirement to operate on low-lead (and later, no-lead) gas. This is also why compression ratios dropped in 1971. This rumor is almost as hard to kill as the headers and Supremes rumor. The little A has nothing to do with hardened seats, since there are also CA and DA heads that do not have hardened seats.

The G and GA heads have the same casting number. The diameter of the valves and the depth of the spring pockets are set by machining AFTER the head is cast. Either head can be machined for the valves or the pockets. Same thing goes for the A.I.R. tube holes.

The A has been used by Olds for a long time to indicate a minor change in the casting design. A major change causes the casting letter or number to be changed, but a minor change just gets the rev letter (just like on engineering drawings). That's why you have F and FA 455 blocks with the same casting number.

citcapp

Thanks Joe,

Won't need to ask that question again. But you might have to answer it a few more times. Now tell me about 442 stripe placement again.................................