# Mystery engine in '66 GTO convertible



## Exit32 (Mar 25, 2009)

I own a '66 GTO with a copy of the original factory manifest from PHS showing it to be a tri-power car. My GTO was built during the first week of November, 1965, so it's an early '66.

The engine's casting date is J85, which I believe means that the block was cast in September, 1965 -- just about right for a vehicle that was assembled in early November, 1965. The engine appears to be original, except someone removed the tri-power setup and replaced it with a QuadraJet at some point.

The mystery is that the code stamped on the front of my engine is YF rather than WS as I think it should be for a '66 tri-power GTO. Some knowledgable GTO people believe that maybe Pontiac ran out of WS engines at the factory and substituted a YF engine to keep the line running. Others guess that the dealership swapped out the original engine and installed a Bonneville engine in its place.

I've owned this GTO for more than 15 years now and haven't thought much about my YF engine until today, when I came across a post in another forum where the owner of another '66 tri-power GTO also says he has a YF engine. The post to which I refer is located here:

Phorum :: Pontiac GTO Forum :: 1966 GTO TRI POWER

This makes me believe than more than one '66 tri-power GTO was factory-equipped with a YF engine. Do you guys have any additional insight as to why my GTO has a correct-date YF engine under the hood? Are there more of these mystery GTOs out there?


----------



## geeteeohguy (Feb 2, 2008)

My research indicates you have a 325 hp, 4bbl, automatic trans engine (389) with 10.5 compression from a big car. If it has 092 cyl heads, they are the right ones for the YF 325hp engine. In all liklihood, it was changed out in the past.


----------



## Rukee (Feb 8, 2007)

If the tri-power motor blew up under warranty (and alot of them did!) it would have been replaced with a 4bbl block from the dealer. They would use the 4bbl block and swap out the tri-power intake and cam.


----------



## Exit32 (Mar 25, 2009)

I really appreciate the theories from geeteeohguy and Rukee about why my GTO has a YF engine. Yes, it does have 092 cylinder heads, and the dates on the heads indicate that they're the original heads that came with the YF engine. If this is a replacement engine, it's very coincidental that all the engine and head date codes are consistent with the build date of the car itself. Could happen, I guess.

BTW, my GTO convertible is equipped with an automatic transmission and was highly optioned with factory air, power windows, power steering, power brakes, power antenna, etc., etc. It appears that someone checked-off almost every option available when the car was ordered. Given the way the car is equipped, I doubt it was abused by the original owner, but lots of stuff could have happened to it before I bought it in 1992.


----------



## topfuel67 (Dec 23, 2008)

If you could get in contact with each of the previous owners and document that each one of them confirmed they didn't change the motor you might have a case. I would then contact a major Pontiac magazine and see if they could even dig a little deeper and contact some of the line workers and confirm that happened. I've read articles over the years about things like that happening. Plus you could get your car in a magazine!


----------



## Too Many Projects (Nov 15, 2008)

If you have the PHS docs the engine unit number on the billing history should match the number stamped on the block right by the YF. If that doesn't match, I doubt it was installed at the factory. Still could've been changed by a dealer but then that isn't the born with number matching engine either.


----------



## Exit32 (Mar 25, 2009)

Thanks for your replies, topfuel67 and Too_Many_Projects. I have contacted previous owners -- with the exception of the original owner -- and they have no recollection of an engine replacement.

Per Mitch's suggestion, I looked at the PHS billing history again, but I can't find the engine unit number. Maybe I'm looking in the wrong place, so I'm including a copy of my billing history with this post. Perhaps someone here look at this document and determine the engine number that originally came with the car. Then, I can compare that with the engine number stamped on the block. Here's my GTO's billing history document:


----------



## Too Many Projects (Nov 15, 2008)

Exit32 said:


> Thanks for your replies, topfuel67 and Too_Many_Projects. I have contacted previous owners -- with the exception of the original owner -- and they have no recollection of an engine replacement.
> 
> Per Mitch's suggestion, I looked at the PHS billing history again, but I can't find the engine unit number. Maybe I'm looking in the wrong place, so I'm including a copy of my billing history with this post. Perhaps someone here look at this document and determine the engine number that originally came with the car. Then, I can compare that with the engine number stamped on the block. Here's my GTO's billing history document:


Now that IS interesting. The blank space between the ignition code and color code should say engine unit no with a 6 digit code above it in line with the rest of the numbers. Maybe this was a special order unit, like a COPO.
And boxes 75-76 call out a YR code, so the YS could still be a replacement but the absence of a unit number or even the designated space, is a mystery unto itself.


----------



## geeteeohguy (Feb 2, 2008)

I think I have your answer, thanks to your posting your build sheet. TMP is right: lines 75-76 are the engine code your car came with. I looked it up on ultimate pontiac .org on their engine code chart (the best I've found so far) and YOUR car came with a YR code engine: a 360HP, 3x2bbl with 2speed automatic. So, you have a documented tripower ragtop! With the wrong block. My bet is that the dealer did NOT replace it, because just the long block would have been replaced. They would have used the original cylinder heads, and switched them over. Your current engine has the correct for a YF block heads, etc. I suspect somebody like myself, with a lot of hair, a little beer, and zero wisdom, blew up the original motor in the late '60's or early '70's and put your current motor in place. Not a big deal, because your car is a documented 3x2 convertible, and it's a great year with great options. Now, where did I leave that old YR block I was using as an anvil.....


----------



## Exit32 (Mar 25, 2009)

Again, thanks for the great replies here. Don't know why, but I always thought the correct engine for my car was the WS engine instead of the YR code listed on the PHS billing history sheet. Was the WS for 4-speed cars and the YR for automatics?

Anyway, I'm going to take another look at the letters stamped on my block. In poor lighting, YR and YF could look very similar to one another. I'm also going to get the date code from the QuadraJet intake manifold. I'm wondering if my block, heads, and manifold casting dates are close enough to indicate that they've been together from the beginning.

I've always been puzzled with the way my GTO was originally ordered. Betcha there weren't many automatic tri-power convertibles with factory air back in the mid sixties.


----------



## geeteeohguy (Feb 2, 2008)

No doubt, you have a well optioned and fairly rare car. The W code blocks went in stickshift cars, the Y code blocks went into automatic cars. Your original YR engine would have had 093 (10.75 compression) heads. The YF block came with 092 (10.5 compression) heads. Your 092's are not GTO heads. As for the Quadrajet, that is the wrong manifold/carb for a '66. Your car was born with a tripower, according to your build sheet. That's what makes it special. The correct 4bbl setup for all '66's was a Carter AFB on a like manifold. An AFB won't work on the Q-jet manifold without spacer plates, cobbling, etc. Time to find a '66 tripower set-up!


----------



## Exit32 (Mar 25, 2009)

Just got the date code from my GTO's intake manifold: L049. I think that translates to November 4, 1969. You're right -- it's time to start looking for a '66 tri-power manifold and carbs.

BTW, I found another reference to an early '66 tri-power GTO convertible equipped with the YF engine:

1966 GTO Parking Lot - Ultimate Pontiac GTO Picture Site

They claim this was the first GTO produced for the 1966 model year. I realize, of course, that someone could have installed the YF engine after this car left the factory. It's very likely that's what happened to my GTO, too.


----------



## VettenGoat (Jun 19, 2007)

WS is a tri-power 360hp motor with a manual transmission. Geeteeo is correct, yours (a tri-power with and automatic) would have been a YR. Back in the day, it was not uncommon for owners to swap out their tri-powers for a four barrel as the trip's had a bad reputation for flaming out. Unless the original motor ate a valve and destroyed the piston, I agree that it is unlikely a dealership would have swapped out the whole motor. 
Mike


----------



## Exit32 (Mar 25, 2009)

I really appreciate all your input, guys. I learned a lot. And thanks to geeteeohguy's suggestion, I have located an OEM tripower set up with a J85 casting date that matches the dates on my block and heads. It's expensive, but I think I might pull the trigger on this.

In the back of my mind, I still have lingering doubt that my GTO's engine was ever replaced, but I agree 100% that the YF engine is not what should be in there. I keep coming back to my engine's date codes being in-synch with the car's build date, and the fact that this is an early '66 automatic, factory-air, tripower car. Plus, I found evidence of two other early '66 tripower GTOs equipped with YF engines like mine is. I don't think Pontiac's YF engine was very popular in Catalinas and Bonnevilles back in the day, so I have to wonder why three early '66 tripower GTOs are equipped with YF engines.

I plan to continue my research on this. In the meantime, has anyone here done business with Mike at Pontiac Tripower and is this a good source for a tripower set up?


----------



## geeteeohguy (Feb 2, 2008)

Exit32, you're getting into what I personally love about the hobby: the detective work. Trying to decode history. A lot of fun,and challenging. All I personally have to verify your car is the build sheet and my own reference sources. I wasn't at the factory when your car was asembled. What really DID go on that day?? If I were you, I'd get the tripower (if the guy is reputable) or you could hunt one down "on the cheap" over time. I would also keep plugging away at your engine ID. One thing, your engine has 10.5 compression, which is a tiny bit more compatable with today's low octance fuel than the stock, 421-headed 10.75 compression GTO engine. BTW, virtually ALL '65 and '66 tripower automatic cars I've seen in the past 30 years were originally 4 bbl cars. Tripower was MUCH more common with the four-speed. Your highly optioned RAGTOP is a real prize!


----------



## Tri-Power (Jan 10, 2008)

I always thought it was wierd my car had AC, automatic, PS etc, but a tri-power backing it up. Glad to see there is atleast another '66 running around with a ton of options. On a side note, since this thread has essentially turned this direction; Does anybody know of a way to figure out if a car is 1 of 1, or how many exactly like it were ordered? I sure know mine could be 1 of 1. But haven't found an exact way to figure it out. I believe it would be fairily easy to write a quick, rough program (assuming PHS would grant you the info, the hardest part would be inputting all the data) that could output a simple integer that tells you how many exact matches to the options you selected were made in a certain year.


----------



## Exit32 (Mar 25, 2009)

Tri-Power said:


> I always thought it was wierd my car had AC, automatic, PS etc, but a tri-power backing it up. Glad to see there is atleast another '66 running around with a ton of options. On a side note, since this thread has essentially turned this direction; Does anybody know of a way to figure out if a car is 1 of 1, or how many exactly like it were ordered? I sure know mine could be 1 of 1. But haven't found an exact way to figure it out. I believe it would be fairily easy to write a quick, rough program (assuming PHS would grant you the info, the hardest part would be inputting all the data) that could output a simple integer that tells you how many exact matches to the options you selected were made in a certain year.


My wife bought a new 2002 Thunderbird back in 2001, and there are a few T-Bird enthusiasts that are able to tell how many "identical" cars were produced (i.e., same year, color, trim, and options). As I recall, there are 34 cars like my wife's.

BTW, Tri-Power, may I ask you for the build date of your '66 GTO equipped with tripower, automatic, and A/C? And the casting date code on your engine? Just curious.

I think it's easier to determine this with newer cars because options are often sold in packages today, rather than individually as they did in the '60s and '70s. For example, there were about 300 unique ways to build a 2002 T-Bird, but probably thousands of ways to build a mid-sixties GTO.

I've never found a way to determine how many GTOs like mine were produced in 1966, but it sure would be interesting to find out.


----------



## Tri-Power (Jan 10, 2008)

I can get you that info sometime soon, but i go to purdue, and for saftey my GTO and all of it's paper work resides at my parents house. I'll let you know when I make a trip back home. I do know the build date is very early. I believe it is late september (1965), but I will give you the specifics another time.


----------

