Interesting find

[feller]

So I bought a parts truck and couple of years ago. It had a locked up engine, that i finally decided to tear into, I found out that it was not only the original motor (big surprise) but that it was a 307 according to the casting numbers, also the heads are from a 76, if im reading them right. The motor is a 71(again if I'm reading it right). Any chance this was built to address the 307 flaws?

Also I cracked open the rear differential, ring gear said 14 43 so that's 3.07, right? What a coincidence.

[71gmcC15]

What flaws are you talking about? I have a rebuilt original 307 in my 71 gmc. It works great. If you mean that the heads are not vare good then yes they probably wanted better heads. Being 71 was the first year for smog heads.

[jocko]

Technically speaking, there is really no way to definitively confirm an engine is original to a specific truck in this era. If you have an E rather than an S in the engine spot of your VIN and no 350 called out on the SPID, then yes it could be the original 307. It's a very good indicator, but there are no 'numbers matching' engines for trucks until they started adding partial VINs to the block pad sometime in the square era. Lots of trucks received factory warranty engines, even of what would appear correct casting dates. What is stamped on the engine pad on the front passenger side? (it's the machined area where the the head mounts to the block). This can narrow it down even further, if you haven't already checked there. Don't get me wrong - it probably IS the original motor - but unfortunately the best we can ever really say for these trucks is "all indications are that it could be the original engine" unless you know the history of the truck for certain.

What 307 flaws are you referring to? While not exactly a screamer at the track, I'm not aware of any flows associated with it. 76 heads aren't necessarily better than 71 heads, depends what the 76 heads came off of.

[71gmcC15]

I have found that the 307 is just as good as any small block in Stock forme. No it dont make power but still is a good motor. #stop 307 hate

[Warrens69GMC]

Did you measure to see if was not a 4" bore block? The head is off the one side.

[feller]

SPID casls for a 350/350.
Its a 2 bolt main motor.
And I was largely unfamiliar with 307s, i knew that a ton of Camaros got them, but no real personal dealings. My "307 flaws" comment came from a quick Google search that said if s bigger cam, "better " heads, and a a 4 barrel were installed the 307 would wake up a bit (one article dyno tested before and after and it made some decent numbers)

Flaw was probably the wrong word to use, "horse power shortcomings" would probably have been a better choice.

[71gmcC15]

If the spid says it has a 350 then it sould have a 350. Thats what I would think. Mabe the original motor got blown up and for a quick fix the slapped a 307 in it and thew on some different head to help it.and it happend to be the right year Theses pickups are old and it's hard to tell what has been done to them.

[Warrens69GMC]

Would you have been happier if it was a CSH code 350?

[feller]

Either way im not upset,(except for the 2 bolt block haha) I do feel like it would be cheaper, or better it it were a 350. Or make more sense to rebuild it.
The 307 is not nearly as common as the 350, or even the 305 in my area. So finding one was quite surprising, and uncommon.
This is why I was surprised.

[Warrens69GMC]

The 307 chevy was only produced from 1968-1973 so its less common than the 350 (produced 1967-2002 in different forms, and crates of today), and the 305 (produced from 1976-2000). The 307 does have its advantages and disadvantages. It has a bigger bore than the 305 to help power and reduce detonation, but a smaller stroke 3.25 vs 3.48

There are some builds around here of the 307, and the same things that wake up a 350, CAN be used on a 307, but sometimes NOT on a 305.

[Myself]

Find a good 350 block and throw that 307 crank in there with some flat top pistons and a gnarly cam..........large journal 327

[franken]

The 307 was, much like the 305 meant to make torque and get good mileage. Small bore, long stroke. Nothing wrong with them, just small engines and limited on power output.
It makes no sense to destroke a 350 to make a 327 for power output. There's a reason the 350 replaced the 327 just as there's a reason the 327 largely replaced the 283. More cubes.

[Myself]

[QUOTE=franken;8515487
It makes no sense to destroke a 350 to make a 327 for power outpu.[/QUOTE]

Sure it does......cause it will tach out over 7000 and sound wicked as hell with 180 degree headers!!