[Baron Von Zeppelin]

Some pictures to help.

Block ID and partial VIN


Head ID


Head date code
The date code on the block - near distributor hole - will also look like this example.

[79 Phoenix]

Thanks Baron! -- I did check out the crank on the Street section... The guys there very helpful with info. 100% sure I have a 71 crank and 99% sure it's a 350 crank. Now I will check out the block... which I know is a 350 block because of the bore. I also know the heads are 94's.
I know a lot of these things are basic but are a needed education for me.

[Baron Von Zeppelin]

The date codes decipher like this :

A201 = Jan 20 1971
B120 = Feb 12 1970
C302 = March 30 1972
D071 = April 07 1971

and so on , etc ...

[79 Phoenix]

Okay...Here are codes... There is a big "350" on the side of the block.

The last picture must be the serial# ? The Date appears to be Jan 15 (or16) 71.
Not sure what XR suffix means...

[Verdoro 68]

In 1971, XR meant 250hp 350ci with an automatic behind it.

[Baron Von Zeppelin]

Definitely 1971 block
#94 is a 1971 only - head ID number

The last picture is the partial VIN of the original car.
2= PMD
1= 1971 model year
Z= Fremont Cali plant
xxxxxx= last 6 digits of VIN

[79 Phoenix]

Originally Posted by Verdoro 68

In 1971, XR meant 250hp 350ci with an automatic behind it.

Any reason this engine couldn't be used with a manual transmission?

[79 Phoenix]

Now, in looking at the engine currently in my GT-37 (which I have assumed is the original), here is the block casting #...

Is this supposed to match the VIN or part of the VIN?

VIN on my car is 233371P160219

Any idea what WN indicates?

[79 Phoenix]

On further investigation of the engine that is currently in my car, I found the block serial # which includes the last 6 digits of my car's VIN. So, that indicates it is an original number matching engine, right? Also found the large 350 casting on drivers side.

Is there a way I can find out what WN means on the ID#?

[Verdoro 68]

There's no specific block for manual or automatic, so you could totally use that XR with a manual. I believe all cranks are machined to receive a pilot bearing, but I could be wrong.

Engine codes: https://pontiacpower.net/numbers/engine-codes/

WN looks like a 250hp 350 with a manual trans in '71. The numbers above the two letter engine code are just a production number. I don't believe they match anything else. The partial vin is stamped down on the lower front size of the block. That's supposed to match the vin plate on your dash.

[79 Phoenix]

Okay--Thanks so much for the charts and the info! yes, the partial VIN matches the 160219 on my dash VIN plate.

WN I guess is one of multiple suffix used on various A body 71 250 HP w/4spd designated blocks. ... I see it in the chart listed for a 71 250 HP 350 w/4 speed and mine's a 3 speed but maybe in 71 they didn't differentiate between 3sp and 4 spd with regard to the suffix.

Thank you guys for your time and patience helping me figure out what I've got in these 2 engines. I really appreciate it!

[Verdoro 68]

I don't believe the engine codes typically specified what type of manual transmission, just whether it was a manual or an auto.

[79 Phoenix]

Engine is now out and going to machine shop on Monday. First picture is block ID# that matches VIN. Transmission is not a Muncie but a Saginaw 3 speed. It has one groove... I am assuming it's original and what Pontiac put behind the 250 HP 350's.. .Does anyone know of a chart that shows how to ID this 3 speed?

[Mister Pontiac]

Be happy, because you have the Muncie M-13 there. Since it's original to the car (GT-37), it should have come equipped with the "Heavy Duty" Muncie M-13 behind the 350. The 3 speed only has one grove on the input shaft like your picture.

Another way to confirm is to count the bolts on the side cover. Across the top, it will have 2 bolts on the Muncie, but only one on the Saginaw.

To be 100% sure, post a picture of your transmission, including the side cover.

My factory 1972 GT came with the 350/3 speed, which is the same Muncie M-13 as yours.

Incidentally, the M-13 is my favorite transmission for street driving out of all of my cars! The gear spread is identical to a Turbo 400 automatic, but you get to do the shifting. And on the street, a Pontiac doesn't need 4 gears. 3 is perfectly suited to the job.

Enjoy!!

[79 Phoenix]

Thanks for the info! I cleaned it up a little more and here are some pictures. It does have 2 bolts at top of side cover...So I guess it is the M13? Also a yellow "RM" is stenciled on it in a couple spots. Not sure what that means.

[johnta1]

RM is the pick code for the 1971 M13 Muncie.


2.42 1st gear, 1.58 2nd gear

[Mister Pontiac]

I'm trying to remember what the RM stands for as well. John may well be right that it's a pick code, but it would have been the same in 72 then. My 72 GT has its original M-13, and it has the same "RM" yellow stamp (pics below).

And I'm not 100% sure either, but I always heard the ratio's were 2:48, 1:48, 1:00, same as a Turbo 400.

But to answer your question, yes indeed! You have the strongest 3 speed you could ask for there. And as a bonus, you still have the bracket for the back drive assembly attached.

That M-13 is plenty strong for a 350. Mine has 100,000+ behind the original 350, and another 20,000 behind a 455, all with zero issues. I expect none going forward either. I love the 'whine' you get from the gears in the M-13. Akin to the M-22 Rockcrusher gear whine, though not as pronounced. Heck, I luv the trans so much in my 72, I found another spare M-13 that I plan to put into my 71 GTO behind a (soon to be built) 455HO.

Congrats, and enjoy!

[79 Phoenix]

Here's picture of the Saginaw I once had in my 79 Phoenix... It was a 4 speed originally in a 77 Monza... But it also has 2 bolts in the top of side cover... By 77 I would imagine there were changes to the Saginaw design that might account for the 2 bolts rather than 1 bolt at the top of side cover like earlier versions?

[Mister Pontiac]

I would say so, yes.

The fact that you have the VIN match on your trans, and the date code falls in line with the car build date gives you extreme confidence that you have the original trans to your car, which would be the Muncie M-13.

Saginaws from that era had the single bolt on the top of the side cover, and they were weaker transmissions, all things being equal.

I don't know what happened to the designs as the later 70's rolled in.

[johnta1]

I fat fingered my response above and changed it to the correct RM code.
1972 also used RM as the code for the M13 Muncie.