My 307 rebuild... yes a 307

[BMSJaX]

So I picked up a 307 outta a '69 c-10. It was stripped down when I got it and 90% of the parts came with it and all for $40! This block is not intended for any major HP so don't worry about cost vs a 350. The block just needs a hone and a clean up and fresh paint job. Heads will need to be rebuilt as the valve seals were leaking and the motor burnt oil bad. Here are some pics of the pistons that i've been cleaning up. They looked unusable at first but after letting them soak in degreaser for a while and a bead blast they look real good. The mold shop behind my work has a hot tank that they're gonna let me put them in to get the last of the glass bead/gunk out of them.

[Corts60]

Nice work! It's good to have something different!

[BMSJaX]

Having something other than a 350(which is already in the truck) doesn't bother me at all, but man some people get all upset when you rebuild something different! Something about cost effectiveness... 90% complete 307 for $40... or 350 bare block for $100(if your lucky)... hhmmm, I'm not great at math but.... hahahaha

[MacAttack]

Originally Posted by BMSJaX

but man some people get all upset when you rebuild something different!

I never let people get upset regarding my truck work - if they're willing to pay for their ideas regarding my vehicles.

Mac.

[BMSJaX]

hahahaha, i'm gonna have to remember that one! very nice!

[protrash64]

Had one in a 69 Chevelle and thought it was a great engine....driving from AZ to IL it would get nearly 20mpg with a Holley and headers. One of the original factory 'stroker' motors.

[sidthirteen]

Nice find BMSJaX!!! A little work and you got a nice motor to scoot around with. Yeah, I got few funny looks when I told people that I have a 305 in my truck. Sometimes you gotta work with what you got.....

[Captainfab]

Nothing wrong with a 307 at all. I have a couple that I'm saving for a someday project. I've been around a couple that were built and ran really well. One of them had 11:1 pistons 2.02 heads and a big cam......it was surprising! Keep us posted.....with pics of course.

[Chuck78]

Makes me wish I kept that 73 Camaro 307 that came in my 71 former SS396 Camaro... I am appreciating good gas mileage efforts for my truck, which is my good weather daily driver, replacing my 89 Suburban with 350TBI and overdrive to winter use (5200 lb truck that gets 22mpg highway w/ 2.73's!).

Now, I've got a 62 GMC 305D V6, which has a reputation of being a real gas hog, and no hot rod capabilities really, but an awesome workhorse truck motor that will pull down a house. After some tuning, HEI upgrade, and swapping the worn out Stromberg for a 500 cfm Holley 2bbl, I am getting much better gas mileage than expected. Granted, I have to keep it at 60mph on the freeway to keep the rpm's down, but I am getting about 18+ mpg. I'd expect it to remain the same when I put in a Tremec 5 speed with OD, as the peak torque of the 305 is at a pretty low rpm, but then again, 10mph more wind resistance of my updated good cruising speed might drop it down a fuzz.

Back to the 307, since the 305V6 parts are mailorder only, and a total rebuild kit is well over a grand, I wish I had a backup other than a 400 sbc in case my 305D V6 ever had a fatal breakdown. It'd be nice to have a 305 V8, 307, 327, or 350 to put in the GMC panel truck as a backup if the monster 305V6 ever took a crap. As it is now, I am building a good stock on spare parts for the truck, stuff that I can't get off the shelf anywhere, and I might even throw in a set of motor mounts for an sbc into the parts bin for road trips "just in case!"

There's merit in these times to building a moderate engine that behaves like a V8 when you put your foot into it, yet can be very streetable and almost economical when you need it to be.
I am SOLD completely on the 96-99? GM truck vortec heads for this same type of engine build, if not any streetable sbc build really. I think they will work fine on a 307 (3.875"x3.25"), but i know on the smaller bore 305 V8 (3.736"×3.48") that the vortec's valves are a bit on the wide side for the the tiny 305 bores.
I think a small V8 like this is a great thing for a well driven vehicle that serves more of a purpose other than hot rod/pedal to the metal. GM TBI (older OBD-1 computer), a simple aftermarket TBI, or a well tuned Quadrajet (or off the shelf Street Avenger) would go great on an engine like this with an RV cam or mild street cam for a good running street engine in a truck especially. A 5 speed or 700R4 and this type of build could make quite a practical yet still fun to drive engine in a 3000-4000 lb car or truck.
If you notice newer GM small blocks have a tendency to have smaller bores and longer strokes:
293 = 3.779" x 3.27" ('99-later, Gen.III, "LR4" 4.8 Liter Vortec, 6.278" rod)
325 = 3.779" x 3.622" ('99-later, Gen.III, "LM7", "LS4 front wheel drive V-8" 5.3 Liter Vortec, 6.098" rod)
345 = 3.893" x 3.622" ('97-later, Gen.III, "LS1", 6.098" rod)
350 = 3.900" x 3.66" ('89-'95, "LT5", in "ZR1" Corvette 32-valve DOHC, 5.74" rod)

(as opposed to the 302/327/350 @ 4.00" bore and the 4.125" 400 sbc)

as the engineers have learned that they can get more efficient combustion out of a smaller bore with a good cylinder head design, but then again, you have to find a middle ground between the long stroke/small bore (w/improved combustion efficiency) vs the downfalls of the long stroke's much greater piston speed and travel (more friction). I think the friction from a larger bore (more surface area on piston-to-wall contact - with shorter stroke - less distance/vertical friction) is going to be less than a small piston traveling a much greater distance, but I think finding a middle ground is a good thing.

Also, one other variant on the engine geometry tweaking, goes against the smaller bore principal, but the LS2 uses the theory that putting in a really long rod helps power and efficiency a lot (hence people ditching the 400's stock 5.565" rods for the 350's 5.7" rods or aftermarket 6" rods):
364 = 4.000" x 3.622" ('99-later, Gen.III, "LS2", "LQ4" 6.0 Liter Vortec, 6.098" rod)

[Chuck78]

Okay, now I am really wishing I had kept that 305, sold it for $75!!!!! Darnit!!!!! That was before I had the GMC panel truck!

Read this impressive article, stock 307 short block, cam/intake/Edelbrock aluminum vortec upgrade:
http://www.superchevy.com/technical/...nce/index.html

This goes to prove my theory of building an awesome daily driver engine out of these 3.875" x 3.25" 307 V8's! The Edelbrock E-Tec's are basically a slightly reworked aluminum aftermarket version of the stock GM iron vortec heads. I think GM Perf. Parts offers a special GMPP version of the vortec heads also, that flows a little better if you want a hotter cam. The stock vortecs with a mild cam are the best thing you could run hands down. the heart shaped combustion chamber in combination with the slightly smaller bore on the 307 will give you both performance and efficiency/economy.
I think on the 305, the 1.94 valves on the vortecs will be shrouded by the tiny bores, and I think I have heard of a special 305 vortec head, but I don't know anything about them without researching on the net. 305's have the longer 350's stroke, but a tiny bore.

As it is now, I have some spare 400 blocks and a 350 from an 85 Caprice that my dad bought, thinking I might want it as a backup engine to the GMC 305 V6. THe GMC V6 is such a cool and obscure engine, I like it a lot, but parts are $, and with it's MASSIVE internal component size (crank looks like it came out of a locomotive, it's so huge), it's not designed for hi-perf or high rpm's at all. They really wake up with ignition and carb mods, but still no hot rod and not that great of city mileage. The cool/unique factor is quite high, but my next options aside from the 351E GMC V6 would be a 200-some lb lighter sbc along the lines of a vortec 307/327/350 or maybe put to use one of my extra 400 blocks with a stock 400 rotating assembly, vortecs, and an RV cam. I know this 400 build would be overkill for the non-hotrod status of my truck, and would be much harder on gas, but it's what I have. If I had the 307, it'd be the hands down #1 top choice after milling over these thoughts in this thread!

[BMSJaX]

here are some pics I took Sat. after I had just started cleaning the block. Figured I'd get some before shots.

[BMSJaX]

Here are the stock heads. I'm gonna rebuild them but not sure if/how long I'll use them. Trying to budget so Vortec heads might not happen...

[Captainfab]

The Vortec heads would definitely help with the power, but I would be curious how the MPG would be between the Vortecs and the stock heads. The Vortecs should be as good if not better for MPG since they have a more efficient combustion chamber. Plus in theory an engine with more power requires less throttle opening to create enough power to move the vehicle.

Have you read this article on a 307 build? It's not what I'd call a budget build, but it may give you some ideas.
http://www.superchevy.com/technical/...nce/index.html

[Chuck78]

The vortec combustion chamber design (shared with the LS1 and fastburn also I believe) is hands down proven to be the most efficient combustion chamber that GM has ever made on a V8, so I'm sure the vortec will get far better milege than the old 307 heads. I think I recall someone stating that they flow better at a street rpm range than the fabled camel hump/double hump heads, which have 2.02 intake valves even compared to the 1.94 vortecs, and they also get much better gas mileage than those.

With gas prices creeping back up, I am really wishing that I had kept that old 307 for such an occasion!

One side note, at the time I had it, I was considering doing an oddball 307 with a longer stroke and 5.7 rods, and I actually found an AMC piston that had a very similar bore and was the correct pin location and piston height to use a longer stroke sbc crank. You couldn't have bored the 307 out .020 or 030, it would have been like .033 or something close (would have been .020 or something for the AMC engine). I browsed a manufacturer's entire catalog of pistons to find that. I think it was a 6 cylinder. It would have worked out to about a 332 or 334 cid I think?