Ok, so I found a used motor which I'm told is a good running 455. Here's the engine number stamped on the front left tab in front of the exhaust manifold. I need someone to decipher for me. 34M725139. Also if you could provide a link to a site so I can do this for myself in the future would be great. Thanks for any help.

 

That's what they call the VIN derivative. It's a shortened version of the vehicle identification number on the dash. Here's what it means:

3 = GM division = Oldsmobile
4 = model year = 1974
M = assembly plant = Lansing MI
725139 = assembly plant sequential number

There is a technical data base at this site that you can access and look up all kinds of info. There is another technical data base at www.442.com that can also be beneficial.

Randy C.

 

Thanks for your reply. I'm actually trying to figure out if this is a 455 motor & not a 350. Is there a way to tell the difference between the two? Thanks

 

The front of engine above the water pump should read 396021 on most 455 blocks from 68-76

 

Simple.

The 455 is wider than the 350.

Almost all parts from one can be bolted on to the other (whether they'll work well is a different question), EXCEPT for the intake manifold, so just look at the intake manifold, and you'll know right away.

Here are two pictures:





- Eric

 

Edited: Nevermind, I checked the link above, and answered my questions.

 

Just to throw a little more information out here it looks like the 350 is about 13ish inches across the intake and the 455 about 15ish inches. John

P4210524.jpg

P4210523.jpg

 

Ok, so the motor I have has an Edelbrock Performer 455 Oldsmobile Intake on it & that intake won't fit on a 350 so I can be sure it's a 455 motor.? Thanks for clarification.

 

They also made small block performer mainfolds, but if yours says 455 then yes it must be a big block. It still could be a 400, 425 or 455 The way to know for sure is check the number with the large letter behind it between the water pump and intake manifold. I can come up with a picture of the location if that would help. John

 

Hi John
Yes, let me know what the letter should be behind the water pump. A picture of what I'm looking for would be very helpful. Thanks for the help.

 

Here's a link to a thread with several pictures. I just realized there's no 455 in this old thread, but there is an example of a 425 with a letter D after the number and a 350 with a large 2 after the long number. That's where you need to look and if it is a 455 there will be a large F at the end of the numbers. Depending on what year there may also be a small capital A to the lower right corner of the letter F. Let us know if you need anything else. John

https://classicoldsmobile.com/forums...s-engines.html

 

A light scraping with a screwdriver usually reveals the casting number of the block. If it's convenient, you might stuff the business end of the car wash wand down there and blast it clean. You really only need the large main ID letter or number (or combo for 1977+ motors], but the final 3 digits of the 6-digit casting number can't hurt. MOST with few exceptions have the large main ID right next to the oil pressure sender, on the engine's LH side. Far and away the most common are the 68-76 "2" 350 block, and the F or Fa 455 blocks. After the weight reductions for 1977, You will find 2B 260, 3B 350, 4B or 4A sometimes 403, and various 307's that often don't have this (######-Main ID) format; typically they will say "5.0L" or similar in that area among the other chracters.

common 350 #2 ID:



Actually, note the "SP" mark cast in there- this is a siamesed bore 350 which MIGHT be the root of the "Solid Main Web 403" rumors.

A hella-rare 403 casting ID:
3364_403-Block_CN1554990-X4A-1.jpg

Another not so common 403 casting, allegedly a SMW unit:

6077_SMW-403_BLOCKS_CN2-22528096.jpg

A less-uncommon "4A" 403 casting- like in my 85 442 at this time

5262_75-Cs_ENGINE_403-4A_CN0-554990.jpg

5243_Gas-Prices-HIGH.jpg

5293_OLDSMOBILE-HQ_A4a-Steamy.jpg