What can be said about the 307 small block?

[Gregski]

I usually post in the Third Gen (73-87) section as I have a '74 GMC (which I love dearly) so don't tell it I'm looking at the Second Gen (67-72) trucks, LOL

Anyway I thought they came with 283, 327 or 350 small blocks, but then I see on the Wiki there was a 307. So I got to ask what can you tell me about this engine? It appears to have had a short life span 68-73. Honestly I have never heard of the 307, but than again I aint no expert by any means

[hamjet]

307s were popular in smaller body cars like the camaros, novas, some full size cars and pickum ups. They only came with 2 bbl carbs as far as I know, around 200 HP. it got you around town pretty well. I remember in my young years, (18-27) they were known to spin bearings, but that could be from everyone I knew beat the snot out of them. I have one in my 69 c-10 and it runs well. In my humble opinion I felt they were a fine engine that got the job done...

[hugger6933]

They were economical compared to the 350 of the time. A good bit less power but they were a small block and respond well to a slight bit of modification like a [little bit] bigger cam and headers and intake manifold with 4 bbl. Lot of guys that mod them say that it increases the gas mpg of the motor, but those same mods could increase a 350 in the mpg category as well. Jim

[MARKDTN]

Smaller bore than a 350, same stroke as a 327. Decent engine. Similar strategy as a 305 in the later vehicles. It's a small-block so same reliability as a 350 really. I wouldn't NOT buy a truck because of a 307 but I wouldn't go looking for one either.

[Gregski]

Originally Posted by MARKDTN

... I wouldn't NOT buy a truck because of a 307 but I wouldn't go looking for one either.

Beautifully summed up!!! thank you, I get what you mean

[ksshane]

I had one in my first c10, a 1970 and it ran just fine even with the 2bbl carb on it.

[GRX]

The 307 is a great engine. However, being an under-square design (bore smaller than stroke) they do not lend themselves well to performance applications. Which is why you do not see many hot 307 builds.

[turp mcspray]

Chevy stroked the 283 in search of more torque.

[TobyArnot]

Smog Motor

[1972RedNeck]

Originally Posted by TobyArnot

Smog Motor

1968 = probably not

[GRADYS Performance]

Actually 1968 was the beginning for smog motors. In a small block that is the year they went to PCV valves and did away with road draft crankcase ventilation.

[Gregski]

Originally Posted by 1972RedNeck

1968 = probably not

that's what I thought, always associated the mid 70's with the birth of the Catalytic converter and the Dark Ages of SMOG

[imjeff]

Had one in my 69 Chevelle. My wife daily drove it a few years and I daily drove it a few more. Sold the car last year and the new owner loves it. Stock motor that will still twist the tires, sounds good and got good mileage. Definitely NOT a "smog" motor.

[special-K]

Originally Posted by Gregski

that's what I thought, always associated the mid 70's with the birth of the Catalytic converter and the Dark Ages of SMOG

The dark ages of smog began to end in '65 for California and by 1975 the Fed mandated catalytic convertors on cars and 1/2t trucks. We hate to be regulated, but no one thought of air pollution when they started making cars. Our air is much better now, thanks to emissions control. Grady is correct with his statements. I always figured all V8 displacements increased due to added emissions/drop in compression to compensate.

[davepl]

Originally Posted by TobyArnot

Smog Motor

Que? That's just silly. No one cared about smog in trucks in 1968. The compression is terrible, I'll grant you that.

I've got the old GM dyno graph in my hand - using SAE NET they made 130hp.

The smallest car Chevrolet makes today - the Sonic - has a 1.4L engine that makes 138hp... 8 more than the 307!

My Dad had one in his '68, and I had one in my '69. They're so low compression and so low-revving that as long as you don't burn an exhaust valve (stuck heat riser usually does it) they're seemingly indestructible. Chip above indicates there may have been reliability issues when new, though my admittedly small sample size didn't experience that.

So, they'll always get you there. Just not in a hurry. I wouldn't rebuild one unless it was a special truck of some kind that warranted the original motor. If you wanted to ball-hone it and stick new rings and bearings in it, that's once thing, but before I took one to the machine shop I'd just find a 350.

[FrankenCub]

I have a 307 in my truck now, it's been a real good engine. As others have pointed out it's lacking of power but I can't complain. It does what I ask of it and I do a lot of fire wood hauling. For now, it will be replaced an a couple weeks. I also had one in a '69 Chevelle that I beat the livin crap out of, the car long deceased before the engine.

[65standard]

The 307 isn't popular because it was never offered in a high performance version from the factory.


But that doesn't make it a bad motor. Just look at it as a 283 stroker and envision it with the same potential performance upgrades as any motor.

[special-K]

The 307 is a great motor. I never heard of them known for spinning bearings. Why would that be? In fact, they have a reputaion for out lasting 350s. I have had great life from them. I threw a timing chain (actually, my boss borrowed the truck and did me the favor) before I replaced it. Bent valves helped me to decide to rebuild, since it ad 130k on it. There was no detectable ridge in the cylinders and the crank required no machining. This was in a K/20 4spd mountain farm truck with 4.57 rears that earned it's keep all it's life.
Guys who are all about cubic inches have no use for them...give them to me. It's a durable AND economical engine. When I rebuilt the one I mentioned, I put an RV cam in it, 64cc 1.94 exh heads, OEM cast iron 4bbl intake, HEI, and Holley 450 CFM carb. It pulled better than a 350 and got 13+ mpg with the 4.57s, 37/14.50-16.5s, utility bed w/pipe rack, tools, and materials. That truck turned a lot of heads when they saw it winding tight slinging four rooster tails of mud. Like I said, great motors

[gvw5400]

For what it's worth , the 307 is an over-square engine design. The bore is 3.875" (283 bore) and the stroke is 3.250" (327 stroke). It is a good engine that can be built up like any small block. In fact the 307's bore is larger then the bore of a 305.
307= 3.875"
305= 3.736"
All the Best , Dirk

[Robznob11]

Boat anchor... But every back yard has a good 350 to replace it with

[motorcritter]

The only reason the 307 is coming out of the '70 C10 is that it's tired and smokes, plus, I'm done with carburettors. I haven't decided what will go in there, I've got a TBI setup, another TPI engine, an LT1 w/ 4L60E, and a couple of Benz diesels (OM 616 & OM 617). If I could get a driveline out of a Benz Sprinter van for less than the giant money they command, I'd do one in a heartbeat. No problems with a 307, or a 305, for that matter. An LSx is a whole 'nuther thing, altogether. I just want more power, no carbs, and 'newer stuff'. Everybody's got their own preferences, and that's what makes this group of folks great!
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[67 cst swb]

Every 307 I have ever had, I took apart, kept the crank put it in a 350 block and built a large journal 327. Ok, so maybe twice I have done this.

[chip46wis]

Im old enough to remember these 307s new----many had bad clearances/rings/cams.A rebuild with -good- parts and they were a pretty good motor.

[motorcritter]

My uncle always preferred a 327, because they would wind up tight and quick. Good heads and a good cam, they would really step out there. He had one in his '62 Impala convertible- that car probably convinced me to be a ' Chevy guy'. That and his '35 5 window Ford, with an even meaner 327 in it. 'Ain't nothin' like it, anywhere else!'
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[special-K]

I'm confused. How can a small block with smaller bores have thinner walls than one with larger bore?

I had a boat anchor, that with very little money I rebuilt to 250hp*, in a 3/4t 4wd with utility bed and ladder rack that was always full of tools in the bins, materials, generator, metal brake, step ladders, and ladders, walkboards, and pump jack poles on the rack. I also plowed snow with it, and went to the beach or into the mountains for fun family weekends. I never took it to the drag strip, but it did put food on my familiy's table, a roof over their heads, health insurance, heat in winter...you get my point. I started my business 37 years ago with my truck and I attribute part of my success to that truck. While other guys were making payments on their new early-80s gas guzzlers, I was reinvesting my money back into the business and enjoyed a better cash flow sooner.

* I rebuilt it at 120k+ because the timing chain jumped. No burnt valves, guides and seals still good, no detectable ridge in the cylinders, and no machining required on the crank. I just took the chance to rebuild it because I commuted with it 1/2hr to 1hr+ each way and wanted to see what I could do with it. after running my thoughts past Dave Coleman of Coleman Bros, Speed shop (a leading eastern machine speed shop) he confirmed my needs would be met with my plan. I've never seen a 350 look as good inside with those miles. In fact, top end or cam always needed it by 75-80k

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