What can be said about the 307 small block?

[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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[Robznob11]

Small bores - short stroke= low efficiency air pump, small bores = shrouded valves, blocks are known to have thin walls, that's why they did not stay around long, it was gm's attempt to stay in the economic/air friendly market and was a flop. Parts interchange with all others wich means it will cost the same to rebuild any small block. Witch now that it's 40+ years old probably needs done. So why not spend the same money on a more popular, more powerful, more reliable, easy to find 350. Just saying. If I had one that needed work I would put it in a land fill and find something worth investing in!

[Gregski]

Originally Posted by Robznob11

...So why not spend the same money on a more popular, more powerful, more reliable, easy to find 350...

I echo that.

[67 cst swb]

Originally Posted by Gregski

I echo that.

Ditto...
But keep the crank... hehehe

[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

Loaded lightly:

[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.

[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.

[special-K]

Yeah, the one I rebuilt didn't go to the machine shop. Didn't need to

[Robznob11]

Originally Posted by special-K

Yeah, the one I rebuilt didn't go to the machine shop. Didn't need to

You must have had a diamond in the rough. To answer your question from above. First off the 307 block had low nickel content which usually results in premature bore wear. Also as far as the thin walls it has to do with Gm's casting process. They had core shift. That's where the casting cores shifted and left cylinders thicker on one side than the other. You can't see it with the eye but you can with a sonic depth machine. On a stock bore probably not ever a problem but when you bore them the thin side becomes to thin and now we have a hot spot and detonation that adds to the already poor output. It's also weak and will not hold power . If you try to push it you would also have poor ring seal due to flex. Long story short there is no sence in putting money in one. In fact you can buy a fresh long block 350 for less than the parts and machine bill to rebuild one. But with that said I'm even beyond the 350 fix as well because I feel the lsx is an even more wise decision than one of those. But it takes a person willing to learn the ins and outs to make that step. As posted before unless your going for a numbers matching original combo there is absolutely no up side of a 307 as compared to other available options.

[rod1701]

Agree with the rest of the guys here. The good and the bad comments. I had a 307 in my 72 RS Camaro. Why it had an RS option with deluxe interior and a 307 I'll never know but it did. Engine was solid and reliable, never any problems but wanted more power so dropped in a 350 in its place.

If the engine is in descent shape, drive it and enjoy your truck. If it if smoking, leaking, and time for a rebuild consider a 350. All parts interchange since they are all SBC but 350s are prolific, higher displacement, will cost the same to rebuild. You will just have to invest in a solid rebuild able core but end up with better performance in the end. That is unless you prefer to keep things original, then you can save a few hundred on the core and rebuild the 307.

Someone above mentioned the bore and stroke of 307
3.875" same as a 283 (bore)
3.25" same as a 327 (stroke)
And by all accounts produced a fairly lack luster engine.

When you do the opposite with a 327 and 283
4.00" same as a 327 (bore)
3.00" same as a 283 (stroke)

You get the Chevy small block 302, arguably one of the baddest factory built SBCs ever.
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[Gregski]

Originally Posted by rod1701

Someone above mentioned the bore and stroke of 307
3.875" same as a 283 (bore)
3.25" same as a 327 (stroke)
And by all accounts produced a fairly lack luster engine.

When you do the opposite with a 327 and 283
4.00" same as a 327 (bore)
3.00" same as a 283 (stroke)

You get the Chevy small block 302, arguably one of the baddest factory built SBCs ever.

Interesting, so the 302 hit a sweet spot with just the right stroke / bore combo, since in the 307 the bore is too small and in the 327 the stroke is too long?

[special-K]

Originally Posted by Robznob11

You must have had a diamond in the rough. To answer your question from above. First off the 307 block had low nickel content which usually results in premature bore wear. Also as far as the thin walls it has to do with Gm's casting process. They had core shift....

I didn't know any of this and never heard anyone saying it. I guess ignorance is bliss. I was young, the motor needed top-end due to chain jumping (while boss borrowed it), and my idea was a small displacement engine that flowed well, hot spark, RV cam, for less throttle/more power for optimum gas mileage. It was a 3/4t 4wd with 37/14.50 tires and 4.57 rears that I ran 25-30 miles down the hiway, around town, and around muddy building lots. Dave, my boss had been building his own hot rodded Chevy motors for years and offered up his shop to me. He looked over my shoulder on it. It did go to the machine shop for cleaning and checking specs, but required no machining. I have since heard of similar cases over and over, which reinforced my thoughts. The machine shop I used was a leader in the nation for race motor building...Coleman Bros Speed Shop. Dave and Bill are rocket scientists. Dave can draw and write any diagram upside down so you can read it while he explains the concept. I ran my plan by him, he was impressed, and believed I had a good plan. He told me a stock iron intake would do the trick just fine, and confirmed the heads/headwork I had planned, as well as a carb recomendation. He never once suggested it was a bad idea to mess with a 307. There was no egging of the cylinders, no ridge, and journals mic'd out just fine and just took a little dressing. I guess I was lucky and never knew it. I figured a 307 was just a punched out 283 and those were known as great engines. A lot of the time I hear nay-sayin' on a smaller motor by the no replacement for displacement guys. I don't listen much because I've heard it over and over and know for a fact a smaller motor can spank a big butt. That's why we see people racing everything under the sun. I started out building hot VW engines, so you see where I'm coming from.
Any other thread on the 307 I have read ends up with people saying they aren't a power house but they last long. I'll heed these words with reservation and move forward with new knowledge to consider
http://www.google.com/url?sa=t&rct=j...,d.eXY&cad=rja

[Robznob11]

Well just to clear the air, 307 engines we not the only ones with these problems, my father in law and I but multiple sbc stroker motors. He has an old book written by Bill Jenkins (smokey) he and his team spent years researching Chevy castings. They detail the years and casting #'s to look for and those to avoid.

[special-K]

Yeah, I know the book. I never wanted even 300hp from that 307. I just wanted 350 power using less gas and I accomplished that. I went for more power when I swapped to an automatic and used a '70 350/250 stock hp truck engine. I put that 307 in the '70 C/10 and sold it. It ran really nice in the lighter truck with shorter tires and 3.08s. I'm all about vintage and for my '67 GMC project and I built a large journal steel crank high nickle '68 327. I may just build a 302 from another for the '68 project.

[motorcritter]

Overall, it's about gas flow efficiency- the bore/stroke relationship affects the ability of the air to get in and out of the engine. The 307 is maximised for what it is, an economy engine, i.e., pretty efficient but lacking optimized flow. Like any SBC, it will respond to the usual hop-up tricks, but there's still that limit on flow volume because of bore/stroke ratio. That doesn't mean 'pull it out and drop in a 350!', it just depends on what you want the engine to do. That said, those LSx and 383 conversions look a pretty damned good set of alternatives!
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[lv2tri2]

Originally Posted by Gregski

I must disagree, I think the air is the worst it has ever been,

now would it have been worse without these mandates sure, but its not better than in 1965 nor how it was in 1975 or 85 for that matter

That may be true in Sacramento. The air in San Diego, is without doubt, better than in was in the 70s.

[leftybass209]

Originally Posted by lv2tri2

That may be true in Sacramento. The air in San Diego, is without doubt, better than in was in the 70s.

Old thread, but yes the air is also better in the Sacramento area as well.

[palallin]

Originally Posted by 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.

My experience in a '68 exactly. This motor is no boat anchor. I should also echo others whose reports note it is reliable as can be. My second favorite engine after my big-journal 327.

[HO455]

Originally Posted by Gregski

I must disagree, I think the air is the worst it has ever been,

now would it have been worse without these mandates sure, but its not better than in 1965 nor how it was in 1975 or 85 for that matter

I have disagree. For simple proof all you have to do is watch old TV shows from the late 60's & 70's like the Rockford files and others that did outdoor filming in and around LA/LB. The smog is very visible. Being in my fifties I remember traveling from Reno to the Sacramento valley in the late sixties and seeing the smog below blocking the view of the whole valley as we drove over the Donner Pass in to California. Every time I have been back to LA/LB or the San Francisco region the last twenty years I have never experienced anything like that. There simply are no facts that back up that air pollution (at least in large Metropolitan American cities which is where the clean air movement started) is worse now than in the seventies.
OK done hijacking this thread. GM made the 307 to replace the 292 and fill that section of the engine power range with a motor that was cheaper to build and could be installed in cars.

[71cheyennesuperlongb]

When my origional 350 dropped a valve at 350,000 miles all I had was a 307 to replace it.At the time no parts stores had a 307 stock cam. Put in a stock 350 cam, thebest junk heads I had on it over a christmas weekend and back to work I went. It ran butter than my high milage 350. 120,000 miles later pulled the heads off, put on a reworked set of double hump heads.With a 700r trans it will melt the tires on takeoff,and twist the speedo back to zero. Not to bad for a boat anchor if you ask me.It was indeed a factory stroker motor from GM.

[68Stepbed]

All these responses and the actual reason for the 307 has yet to be mentioned. In 1967, SCCA put a 5.0L engine size limit on American sedans racing in the series. Ford, Chrysler and AMC designed engines to use to fit the limits. GM simply took the 283(3.00" stroke) crank and mixed it with the 327(4.00" bore) block to crate a 5.0L 302ci. The main journal sizes were even a match, so no extra machining was required. The small displacement limit was lifted in 1970. So for just over 3 years, GM produced approximately 10,000 302 engines for both "civilian" version Z/28's and the SCCA race prepped versions. That left a whole lot of 283(3.875" bore) blocks and 327(3.25" stroke) cranks laying around not getting used.

In just 2 short years only available in the Camaro SS models, the 350 had gained quite a reputation as a great performance engine as well as a great work horse engine with lots of low end torque, so it became the main engine in Chevrolet's arsenal for upper end models in all vehicle lines. That leaves room for a "base model" V8 option. Guess what they decided to do, you got it, put together the leftover 283's with 327 cranks and make the infamous 307. Since it was supposed to be primarily an economy engine, they put on wheezy heads that just didn't flow well and gave the 307 a reputation as a poor engine.

Truth be known, the 307 can be a decent street engine with the right top end package. A decent set of heads, a dual plane intake, and a proper sized carb will actually make the 307 wake up and surprise many people. Check out this article from Super Chevy.
http://www.superchevy.com/how-to/eng...e-performance/

Another little known fact, is that later 283 blocks can be safely bored .125" over.
3.875 + .125= 4.00. Boom!! You have a 327!!!

[Mike C]

28,103 67-69 Z/28's were built. I don't recall if the '67 motors were large journal or not, but all had steel cranks. All 283's were small journal motors and at the end of production they had gone to cast cranks.

The Z/28 parts, especially the '69 which had it's own forged steel crank and used the large journal 4 bolt main block, had nothing to do with regular production parts and using them up. These motors made great power because they had big valve heads, huge mechanical lifter camshaft with 7000+ rpm capability, an excellent high rise aluminum intake and a 780 cfm Holley.

All 307 were large journal which has nothing to do with 283's either. GM built the 307 specifically to do what it did. They put some in boats and I had a buddy start with a (believe it or not!) 307 steel crank to build a large journal 4 bolt main steel crank 327.

You've always heard that the square port big block heads couldn't work well on the street because the ports were too big for low speed torque. Turns out they never but a torque type cam in them because they were only available in SHP high rpm applications...

The 307 never made any power because it was in vehicles that were spec'd that way. You can build a 307 to make comparable power to most other mild small blocks as they respond to exactly the same cues.

[68Stepbed]

Originally Posted by Mike C

28,103 67-69 Z/28's were built. I don't recall if the '67 motors were large journal or not, but all had steel cranks. All 283's were small journal motors and at the end of production they had gone to cast cranks.

The Z/28 parts, especially the '69 which had it's own forged steel crank and used the large journal 4 bolt main block, had nothing to do with regular production parts and using them up. These motors made great power because they had big valve heads, huge mechanical lifter camshaft with 7000+ rpm capability, an excellent high rise aluminum intake and a 780 cfm Holley.

All 307 were large journal which has nothing to do with 283's either. GM built the 307 specifically to do what it did. They put some in boats and I had a buddy start with a (believe it or not!) 307 steel crank to build a large journal 4 bolt main steel crank 327.

You've always heard that the square port big block heads couldn't work well on the street because the ports were too big for low speed torque. Turns out they never but a torque type cam in them because they were only available in SHP high rpm applications...

The 307 never made any power because it was in vehicles that were spec'd that way. You can build a 307 to make comparable power to most other mild small blocks as they respond to exactly the same cues.

Learn something new every day. I stand corrected. According to this website, the early 302's may have been small journal, which would still make my statement partially correct regarding using off the shelf parts to meet the 5.0L requirements. The person that told me the info above retired from GM after spending his career at the Tonawanda engine plant. He said he used to buy the engine parts at cost to build his own engines. That must have been nice!

[leftybass209]

Originally Posted by 68Stepbed

Learn something new every day. I stand corrected. According to this website, the early 302's may have been small journal, which would still make my statement partially correct regarding using off the shelf parts to meet the 5.0L requirements. The person that told me the info above retired from GM after spending his career at the Tonawanda engine plant. He said he used to buy the engine parts at cost to build his own engines. That must have been nice!

Interesting theory your friend holds about the reason for the 305's existence. I would also suggest that there's much more that went into the decision to introduce the 305 other than parts just laying around that would have been specifically for racing applications. Every car manufacturer was looking far ahead of their current model cars, anticipating trends and chasing the most viable options to outsell competitors. They also had plenty of stock for dealers to take care of warranty issues, engine replacements etc. It's not like the supervisors over casting said, "Well we have 12 tons of raw metal, lets just spit out 283/327 blocks, cranks, and rods well beyond the proposed (xxxxx) number of vehicles that are going to be receiving these engines until someone yells, STOP!"

I love hearing from people who used to work at these plants. Their insight is extremely entertaining and often does contain truth that can contradict hearsay. It's also hard to believe that someone had retained an intimate and detailed knowledge database in their head of things that were as routine as working at a factory. I can't remember details of what I did this time last year at my job, so how am I going to remember 50 plus years later? I'm sure it's easier for some than others, but that's why records are so important.

No offense to you, if that sounded argumentative or belittling, that wasn't my intent.

[mike16]

its not a performance engine, and was never intended to be one. it ws built from parts already in the invantory so it was cheap. It was not a smog motor per se. it was the smallest v8 they had in that era, so it got good gas milage and because it burned the least amount of gas it produced less pollution. but it had all the same "smog' equipment that came on the bigger chevy engines. in fact when the pollution laws were ramped up it could not make the grade. it had a small bore compared to the 350 bore and some how that was detrimental when the laws were tightened up. It seems that produced more of the pollution the government wanted outlawed. and when tuned to eliminate those specific polutants, other issues came up. I dont know but it had to do with small bore long stroke vs big bore short stroke and the various polutants generated vs. what the government wanted eliminated. and of course there were the economic considerations and parts support.

the truck engines has a higher tin and high nickle content that the car motors did not. the tin content allowed the cast iron to flow better during the casting process. the higher nickle content hardened the cast iron to reduce cylinder bore wear

I would not make in a first choice for a performance build but remember that the 283 corvettes put out like 315 hp and the 327's put out like 365 hp with FI and it came up through the ranks with that heritage. It would not be my first choice but I have seen fools make them run like mad.