[Ramairnacho]

I spoke with a man building a 1970 automatic trans am may built car. It's a basket case and missing engine but previous owner bought it in 1980 and told him it had #13 heads with a yz engine. He spoke with another expert in Altanta area and he said he had a ram air 3 auto with ac with #13 from factory. I have heard that with ac you would expect to have #13 before. I went throught this simular situation and was under impression that #12 is correct but not 100% sure. Another idea I have is that the factory ran out of #12 's and used #13 heads but no proof just an idea. The chamber is slightly bigger in #13 heads I believe bringing compression ration down slightly and was wondering if horse power was lost by this. In modern times with different fuel and adding dishing pistons not to ping with #12 are the #13 a good choice running 91 oactaine and stock style pistons or will it too ping and will need dish pistons.?

[Kenth]

NO #13 heads on 1970 YZ from factory, ever.

If you have to lower static compression for use of lower grade fuel i would use dished pistons for correctness.

JMHO

[Formulabruce]

Took apart a factory original 70 GTO RA3 auto/ AC. It had original heads, #13, rotted out sitting on cape cod. Low miles car.
Yes lower CR CAN HELP with vacuum, and driveability with AC.
Have seen a few auto RA birds with 13 heads as well, 1 was a original calif car. Other made in CA and sent to Texas.

[Ramairnacho]

Originally Posted by Formulabruce

Took apart a factory original 70 GTO RA3 auto/ AC. It had original heads, #13, rotted out sitting on cape cod. Low miles car.
Yes lower CR CAN HELP with vacuum, and driveability with AC.
Have seen a few auto RA birds with 13 heads as well, 1 was a original calif car. Other made in CA and sent to Texas.

Then where ra3 auto ac cars suppise to have #12 and parts ran scarce? Factory error or its suppose to be #13? This is a big mystery and makes me wonder. I have #13 and bought date code #12 !s and my new friend building his ta thinks his car came with #13's. Since it too has ac.

[FrankieT/A]

Originally Posted by Ramairnacho

I spoke with a man building a 1970 automatic trans am may built car. It's a basket case and missing engine but previous owner bought it in 1980 and told him it had #13 heads with a yz engine. He spoke with another expert in Altanta area and he said he had a ram air 3 auto with ac with #13 from factory. I have heard that with ac you would expect to have #13 before. I went throught this simular situation and was under impression that #12 is correct but not 100% sure. Another idea I have is that the factory ran out of #12 's and used #13 heads but no proof just an idea. The chamber is slightly bigger in #13 heads I believe bringing compression ration down slightly and was wondering if horse power was lost by this. In modern times with different fuel and adding dishing pistons not to ping with #12 are the #13 a good choice running 91 oactaine and stock style pistons or will it too ping and will need dish pistons.?

Is this car Lucerne Blue originally?

[Kenth]

All Pontiac V8´s were assembled at Pontiac plant #9 and the V.I.N was stamped at the vehicle assembly plant anywhere in the country, so how would the #13 heads got to an engine built with #12 heads? Plant #9 did not know the YZ engine would end up in an AC car, Firebird or GTO, they just knew an YZ engine is an YZ engine and YZ engines uses #12 heads. AFAIK

['ol Pinion head]

Been down this road before...

https://forums.maxperformanceinc.com...d.php?t=688198

['ol Pinion head]

It's unfortunate, but there have always been the corner cutters, anything to save a buck on a poorly thrown together build.

Another earlier example:

https://forums.maxperformanceinc.com...d.php?t=739073

[Formulabruce]

And so we have many Pontiacs with Factory #12 heads, that are NOT Ram Air engines as well, made in Pontiac plant 9. " GASP!!). Just saying, making more of this than it is. Now $2,000 plus to get a set of large valve heads completely done ( right).

[Ramairnacho]

This topic is very controversial from all group experts. Now I believe both are correct from what I have learned. Did these heads have drippers on yz and ws engines being #12 or #13. My yz is a factory 4 bolt main.

[Kenth]

Again, #12 heads is used on 1970 WT, WS and YZ engines.
#13 heads is used on 1970 WX, XH and YS engines.
Pay attention on the engine codes, finding #13 heads under the hood of a 1970 RamAir III car may indicate a Grand Prix engine replacing the blown up original engine.

All 1967-70 4 B.C. engines, exc. RAIV, XV 400 and YH 455, uses the #9780969 baffle on the heads under the valve cover.

[Formulabruce]

WT is NOT a Ram air engine.. , and yeah, it has #12 heads. Oh, and could get AC Too!

[Ramairnacho]

Originally Posted by Kenth

Again, #12 heads is used on 1970 WT, WS and YZ engines.
#13 heads is used on 1970 WX, XH and YS engines.
Pay attention on the engine codes, finding #13 heads under the hood of a 1970 RamAir III car may indicate a Grand Prix engine replacing the blown up original engine.

All 1967-70 4 B.C. engines, exc. RAIV, XV 400 and YH 455, uses the #9780969 baffle on the heads under the valve cover.

Did ram air engine have the baffle rocker drippers with #12 heads then?

[Kenth]

Originally Posted by Formulabruce

WT is NOT a Ram air engine.. , and yeah, it has #12 heads. Oh, and could get AC Too!

Anyone said it was?
And you could get AC on a 1970 RAIII car too.

FWIW

[Kenth]

Originally Posted by Ramairnacho

Did ram air engine have the baffle rocker drippers with #12 heads then?

4 B. C. means 4 Barrel Carb and engines with #12 heads got Quadrajets, so yes Ram Air III engines got got the baffle rocker drippers too.

[thepontiacman]

The 70 YZ 's that i have had or seen over the years had 12's.

Had a guy who had a XH transplanted in a 70 TA and told me that brother of original owner said the 13's were original on that car. I went to his garage and date codes matched the XH block in car. Intake, exhaust, carb and brackets/pulleys were original and dated to car.
XH block and 13's were Jan 70 dated. Car was a early June build. correct parts were may dated.

[Ramairnacho]

Originally Posted by thepontiacman

The 70 YZ 's that i have had or seen over the years had 12's.

Had a guy who had a XH transplanted in a 70 TA and told me that brother of original owner said the 13's were original on that car. I went to his garage and date codes matched the XH block in car. Intake, exhaust, carb and brackets/pulleys were original and dated to car.
XH block and 13's were Jan 70 dated. Car was a early June build. correct parts were may dated.

Hmm did factory run out of yz code blocks at end of year? If so that explains why #13 where seen on automatic ta.

[Transamric]

[Held for Ransom]

1st picture: original 1970 YZ block w/AC - 12s with baffles.
2nd picture: rebuilt 1969 WT block - 13s with baffles.
3rd picture: 1969 dated 12.
4th picture: touched 12 for early 1970 YZ block.

[Kenth]

Shields on valve springs were not used on 1970 Ram Air or 400 M/T #12 heads from factory.
In fact NO Ram Air heads got the shields due to stronger valve springs used on these heads.