# YC stamped engine in 1970 GTO?



## CoolBlueSapphire (Mar 18, 2015)

I was looking at a 1970 GTO with automatic tranny, ram air induction & A/C, with a YC stamped 455 in it. The previous owner told current owner that this was the original engine. I could not make out the stamp on the heads due to rust, but I am nearly positive it was not "64" - unless it was altered in some way.

From all of my research, this is highly unlikely the original engine. Am I correct? 

Thanks for your input!


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## mallsup (Feb 24, 2015)

I own a 1970. If my research is correct, the 455 ID code is YA. Also, the 455 was not a RamAir that year. Both RamAir engines were 400 CID. I am not an expert, so please get additional input, as I could be wrong.


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## rickm (Feb 8, 2012)

you have to read the block # n date code on a Pontiac engine to identify it. the 2 letters in the front were used for numerous engines in different years.


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## CoolBlueSapphire (Mar 18, 2015)

mallsup said:


> I own a 1970. If my research is correct, the 455 ID code is YA. Also, the 455 was not a RamAir that year. Both RamAir engines were 400 CID. I am not an expert, so please get additional input, as I could be wrong.


My understanding is that all 1970 GTO's that had 455's were "YA". But I also recall I had read an article citing that at the end of the 1970 model year a 455 HO engine was available. This would lead me to believe something other than "YA" was possible? Then again, you can't believe everything you read.

I also read that in 1970, the 455 could be ordered with a Ram Air option, but it only included the air cleaner & hood option - none of the other features like exhaust manifold, cam ....


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## CoolBlueSapphire (Mar 18, 2015)

rickm said:


> you have to read the block # n date code on a Pontiac engine to identify it. the 2 letters in the front were used for numerous engines in different years.


I couldn't easily see those codes, but the YC on the front of the block and the lack of "64" on the head hinted to me there was no point in digging any deeper. My main concern was if it could possible be the correct engine for a 1970 GTO before I started digging in to see if the others numbers matched.


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## rickm (Feb 8, 2012)

to see the block # n date code easily, stand on the drivers side where the fender meets the door. you can shine a flashlight behind the open hood n see the dist. area of the block easy to get the info.


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## PontiacJim (Dec 29, 2012)

1970 GTO 455/360HP HO engine, order code L-75- block code for the automatic is YC & YA. Manual trans was code WA. The YC code was found in only 1 book (which is basically a Pontiac "bible") that I have while the YC code is listed as a 1971 455 engine. The 455 is called an HO engine in the GTO where 71 and later had both a "standard" lower HP version or the higher HP "HO" engine with the aluminum intake.

Heads are#64. Full casting number is 9799364.

I have several references to the 455 "ram air", so it may have been a package option.
455 CI Q-jet # for manual trans is 7040267 -non ram air
7040279 -with ram air
automatic trans is 7040268 -non ram air
7040278 -with ram air

Number of GTO's equipped with the 455HO YA/YC engine is listed as 2227 (241 Convertibles).

More investigation is definitely needed and I would get the PHS documents to verify the L-75 455CI option, along with the rest of the info for the car.:thumbsup:


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## CoolBlueSapphire (Mar 18, 2015)

PontiacJim said:


> 1970 GTO 455/360HP HO engine, order code L-75- block code for the automatic is YC & YA. Manual trans was code WA. The YC code was found in only 1 book (which is basically a Pontiac "bible") that I have while the YC code is listed as a 1971 455 engine. The 455 is called an HO engine in the GTO where 71 and later had both a "standard" lower HP version or the higher HP "HO" engine with the aluminum intake.
> 
> Heads are#64. Full casting number is 9799364.
> 
> ...


Thanks! Yeah, it is a shame there is so much conflicting info out there, and in this case - concerning YC. I had also found it to be a 1971 455, but then again found another source that had indicated it to be found in a manual Judge for 1970. Still seems that we agree that it should be a 64 head, which still is a red flag as to originality.


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## BearGFR (Aug 25, 2008)

Like has already been said, the only way to know for sure is to start with the date code by the distributor. YC could be any of:

1965 389 290 HP YC A 10.5 066 76 / 9778776 1-2 7025060/61 A/C Block Casting # 9778789 Should have full head production number under valve cover - 9778776 
1966 389 290 HP YC A 10.5 066 092 1-2 7026060/61 A/C Block Casting # 9778789 
1967 400 265 HP YC A 10.5 254 143 1-2 7027060 Block Casting # 9786133 
1968 400 290 HP YC A 10.5 254 (2)15 1-2 7028060/70 Block Casting # 9790071 
1969 400 290 HP YC A 10.5 254 46 1-2 7029060/70 30 degree intake Block Casting # 9790071 
1970 455 360 HP YC A 10.25 067 64 1-4 7040268/RA 7040278 GTO /1970 - only year hi comp 455 Block Casting # 9799140 
1971 455 325 HP YC A 8.2 067 66 1-4 7041262 Block Casting # 485428 
1972 455 250 HP YC A 8.2 067 7E5 1-4 7042262/72 Early head no center exhaust divider Block Casting # 485428 
1972 455 250 HP YC A 8.2 067 7M5 1-4 7042262/72 Block Casting # 485428 
1973 455 215/250 HP YC A 8.0 067 4X 1-4 7043262 Block Casting # 485428 
1974 350 155/170 HP YC A 7.6 555 46 1-2 7043062 Block Casting # 488986 
1976 400 170 HP (Early) YC A 7.6 255 6X 1-2 17056160/64 A/C Block Casting # 500557 

Until you know the model year, there's no way to nail it down. 

Bear


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## randy brevick (Sep 22, 2017)

BearGFR said:


> Like has already been said, the only way to know for sure is to start with the date code by the distributor. YC could be any of:
> 
> 1965 389 290 HP YC A 10.5 066 76 / 9778776 1-2 7025060/61 A/C Block Casting # 9778789 Should have full head production number under valve cover - 9778776
> 1966 389 290 HP YC A 10.5 066 092 1-2 7026060/61 A/C Block Casting # 9778789
> ...


1970 gto 455 ho yc engine with # 64 heads match vin # to the block lower left front side of engine. than you know if the engine came with your car.


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## Pinion head (Jan 3, 2015)

Late 70 model GTO's with the 455 & Turbo 400 drivetrain received the '70 model YC coded 455 engine. Have an YC short block out of a late production 455 '70 GTO.

Quickly checking engine numbers on the face of blocks...

-When looking at the assembly number above the two letter engine ID code, does that number start with a *(*. If it does, the YC coded block is out of a '71-73 455 car, a very common 455 engine for those years, ESP in Grandvilles, Bonnevilles. 
-The Fremont assembly plant typically, stamped the partial VIN up high on the passenger side face of the block. often the gang stamp holder was held at an angle on Fremont installed blocks. All other assembly plants, the confidential VIN was stamped in the common spot, on the face of the passenger side of the block, further down, stamped vertically next to the outboard side of the timing cover. 

When the Ram Air option was ordered on a '70 455 GTO, it only consisted of the air induction pieces; ie, the RA upper pan, flapper asm & cable, & '70 model RA carb tub. Dport log manifolds were also used on all '70 455 GTO's, RA equipped, or not. The '70 Dport RA exhaust manifolds were used on the '70 RA III engines.

From quickly reading the above posts & charts, there are numeous errors. 
The most glaring error that effects this thread, is there were no 7040278 or 7040279 Production 455 RA application Q-jet's. Instead, the normal 70 RA 400 Qjets were used when RA was optioned on a '70 455 GTO: 
-7040270 (auto) 
-7040273 (manual trans), 
-7040570 (CA emissions auto)
-7040573 (CA emissions manual trans)


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## mark in ohio (Dec 10, 2020)

CoolBlueSapphire said:


> I was looking at a 1970 GTO with automatic tranny, ram air induction & A/C, with a YC stamped 455 in it. The previous owner told current owner that this was the original engine. I could not make out the stamp on the heads due to rust, but I am nearly positive it was not "64" - unless it was altered in some way.
> 
> From all of my research, this is highly unlikely the original engine. Am I correct?
> 
> Thanks for your input!





CoolBlueSapphire said:


> I was looking at a 1970 GTO with automatic tranny, ram air induction & A/C, with a YC stamped 455 in it. The previous owner told current owner that this was the original engine. I could not make out the stamp on the heads due to rust, but I am nearly positive it was not "64" - unless it was altered in some way.
> 
> From all of my research, this is highly unlikely the original engine. Am I correct?
> 
> Thanks for your input!


I bought a 1970 GTO from the west coast with a 455 YC code motor and #64 heads, Not a Judge but a low optioned, 8 in all and has the standard dog dish hubcaps. I bought if from the original owner and the VIN stamping on the block matches the VIN of the car, Therefore this is a numbers matching GTO with the YC motor. They do exist.


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