# Decoding Engine Codes



## 68greengoat (Sep 15, 2005)

Hey all,

I have a '68 GTO with a '73 Pontiac 455. Decoded the carb and found out it was a '73 Olds. Knowing I had a '73 engine I thought maybe it was an Olds too. After some quick decoding, thankfully it was Pontiac. Anyway, I'm getting off track. My question is, is there any way by looking at the engine code you can tell what car it originally came from? I know the last 6 digits are for matching the v.i.n. The beginning 23 of the engine code is "2" for Pontiac and "3" 1973. I was told a Tempest, but have no reason to believe that is true. Is there another code on the engine that designates what vehicle it was in? Any help is appreciated....


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## 05GTO (Oct 6, 2004)

If you can post the casting number from the rear of the block behind the #8 cylinder and the 2-digit letter code that is found on the front of the block just below the passenger head. Someone here will be able to identify that engine.


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## 68greengoat (Sep 15, 2005)

The casting number will have to wait until tomorrow. It is a YC block. Also, while crawling underneath the car I was thrilled to find that the rear motor mount bolts the go into the block, 1 on each side , are missing. Apparently, only the front ones are holding it in place. Suprised they haven't broke under torque of the engine. The holes are still lined up. Can a guy just replace the bolts in it's current position, or, am I going to have to raise the motor. Not sure how long the bolts will be. I know there is not much space to get at the mounting holes..... Thanks for the info 05GTO.


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## 68greengoat (Sep 15, 2005)

I have some numbers. To recap, I have a '73 Pontiac 455 that I'm trying to find what car the motor was originally installed.

Block casting # - 985428
2 digit letter code - YC

Hopefully this will help. Thanks...........


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## 05GTO (Oct 6, 2004)

68greengoat said:


> I have some numbers. To recap, I have a '73 Pontiac 455 that I'm trying to find what car the motor was originally installed.
> 
> Block casting # - 985428
> 2 digit letter code - YC
> ...


The casting number 485428 is for a 1973 455, the letter code YC shows it was a 4 bbl, 250 hp engine used with an automatic transmission. 

In 1973 Pontiac shows over 70 engine letter codes, they show 25 of those were used on the Lemans and GTO, the letter code YC is listed as one of the codes used on a GTO. 

Hope this helps,


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## 68greengoat (Sep 15, 2005)

Found this website from an earlier thread, GTO Engine Codes!
Block casting # is 485428 not 985428. Sometimes these numbers are hard to tell apart.


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## 68greengoat (Sep 15, 2005)

Cool. Just saw your reply 05GTO!! The letter code is very interesting... I knew the hp was somewhere in the 200+ range. I know that hp took a sharp drop as the 70's went on. It has been bored .030 making it a 462ci, has a mild cam(no specs at all on the cam, just has a lope at idle. Yes it's the cam and not a bad tuneup, ha ha!!), Ohio pistons(for whatever that's worth), Performer intake, Accel super coil and 8.8mm Accel wires. So it should be runin' a little better than 250hp. Would still like to get more umph out of it. Want to convert to a MSD electronic ingnition w/ignition box. Probably a 6A. Not sure that I need the limiter, wont be seeing any track. The rearend is out of a '71 with very lame 2.78 peg leg gears. Would like to put in a new rearend w/3.55 or 3.73 gears. Either a 12 bolt or 9 inch. I see Summit has a drop in 9 inch for a-bodies. I have seen tests done between the 12 bolt and 9 inch by HPP mag(along with a Dana 60 I believe) and it looked like the 12 bolt out performed the 9 inch. The tranny is a Saginaw. Want to upgrade that too. I know Muncie has a close ratio tranny that works well and would bolt right in. Know of any other good modern day tranny options that would bolt in without any mods that would work well with the forementioned set up?

Thanks for all your help....


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## 68greengoat (Sep 15, 2005)

Ok, my 12 yr old daughter just showed me how to add an avatar. As you can see the picture is fuzzy. I had to really downsize the picture I used. How can I clean it up? The original picture is very clear.....


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## Rukee (Feb 8, 2007)

If your not going to the track to race it then I would not worry about the close ratio tranny. I also would pass on a rear end swap and maybe go for a drop in limited slip diff with your choice of 3.55 gears. I would go with the 6A MSD unit for any performance car. You don`t want the rev limiter so much for the track as you do in case or if you spit out a drive shaft or smoke the clutch. That`s when the rev limiter pays off is when you break a u-joint or somethin stupid happens and it keeps your motor from blowing up too.


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## 68greengoat (Sep 15, 2005)

Not sure that I would be able to drop in a set of 3.55. I believe I have the smaller 10 bolt housing which would not accept that gear. I think I could only drop in a lower 3.xx gear without upgrading the housing or going to a 12 bolt. It really runs nice with the current setup, especially given the current gas prices. But you know how that goes, I'm still willing to sacrifice a few dollars at the pump in exchange for a little "throw back" performance. I also forgot to mention I want to change the heads too. I believe they are 4x. I was looking at Edelbrock performer rpm's. Also need headers. I know the 3.55 gear was common for GTO's in '68.

Thanks for your input......


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