[JLHarper]

What is the difference bewtween the YA/YC 455 code? I have seen them listed TOGETHER as one in a few books. Other times I have seen just the YA code listed for the 455 70 GTO automatic. I have never seen just the YC code seperate. Some think its the CA version motor. My car has RA induction system. Would a YC be correct for this resto project?
Thanks... Jeff

[JLHarper]

What is the difference bewtween the YA/YC 455 code? I have seen them listed TOGETHER as one in a few books. Other times I have seen just the YA code listed for the 455 70 GTO automatic. I have never seen just the YC code seperate. Some think its the CA version motor. My car has RA induction system. Would a YC be correct for this resto project?
Thanks... Jeff

[Dan Jensen]

Jeff,

I'm not 100% sure right now, but I'll tell you what I believe is the case here. As soon as I find out the answer, I will write another post.

Right now, I believe that " YA" is the only correct code for a '70 automatic 455 GTO. Now, I know to "never say never" in this hobby. I'm sure that there have been engine mix ups at the plants, as well as undocumented running changes that others may be able to share with us. Again, this is just my gut instinct in this matter.

I believe that the "YC" code 455 for 1970 was the optional 370-horse, big-valve, engine available on the big Pontiacs over the "YH" code 360-horse, small-valve 455. Up until '70, different codes were used for the different model lines (A,B,G,F), even though the engines were essentially the same. In 1971, the codes were simplified, where the same YC-code 455 was used in Birds, Goats, Prixs, and Cats.

Again, I'll write another post when I find out for sure about the codes.

[Dan Jensen]

Jeff,

Boy was I wrong on my first answer to your post. Please disregard it completely!

"YC" IS THE CORRECT CODE FOR YOUR '70 AUTOMATIC GTO! After digging out the '70 service manual, and Pete McCarthy's bible, both clearly show that YC is what you need. The GTOAA Legend has it listed incorrectly as YA, which is what I referred to in my first response. I made a note in that issue.

The 370-horse, big-valve 455 available in GPs and big cars is code "XF"!

Sorry about any confusion that I may have caused Jeff, and to the general readership.

Since even I can blunder when it comes to engine codes, I suggest to everyone to get an original service manual for your car. They have these codes clearly explained at the beginning of the engine section. Another good source is Pete McCarthy's "Pontiac Musclecar Performance 1955-1979". In it, he has all years listed.