I picked up this complete 1968 307 SBC engine on the cheap, and was wondering if it can be safely bored out to 4 inches? Since it already has the large-journal crank and everything but the bore is the same as a large-journal 327, can it just be bored out to make a 327? Or, are the cylinder walls too thin? I've heard of this being done, but don't know if it is a proven option.
[ QUOTE ] Can you Machine a 307 SBC into a 327? [/ QUOTE ] i dout it but i did ask about some 307 ideas in this post....joe http://www.clubhotrod.com/forums/showthread.php?s=&threadid=2403&highlight=%2A307%2A
Probably not, but you could swap the crank into an cheap and easy to find 350 block,to get a 4" bore.
I know a fellow who bored his 307 the 1/8 of a inch to make the 307 into a 327. It ran around 100 miles or so and got water in the 3&5 cylinders area. He was REAL hard on his stuff .........
Hey, .60 over is as far as you can bore the 307 block. It works out to under 317cid...like 316.2 or something close to that. I think that the 307 gets a bad rap because of it's heads, perhaps if you bore it over, put in a cam and change your heads and intake you could have a neat sbc. It is just an idea. Then again that is what I have just done with a 307 to put in my truck...so we will see what happens. Anyhow good luck. Otto
Years ago, some (now defunct) local speed/machine shop tried to convince me to let them bore a 307 block out to four inches to replace the damaged standard bore 350 block I brought them. The idea just didn't sit well with me, so I asked the opinions of a few well respected small block Chevy gurus in town, and they all agreed that the 307 block is too weak to handle that kind of overbore. (Most would not bore them more than .040"). Just build the 307...replace the stock, unhardened cam with a quality aftermarket grind, drop a set of 77-85 305 heads on the motor, toss on your favorite bolt-ons, and go! A small block Chevy is a small block Chevy...they ALL rank as Mankind's Greatest Acheivement, and will easily propel your heap to nine second ETs while running flawlessly for 400,000 miles...you can get parts anywhere...not that you'll NEED to with them being so ultra reliable...but you COULD if you wanted to! Don't believe me? Just ask EVERYONE! (Eight billion street rodders CAN'T be wrong...right?! Join The Movement!!)
Along with the 267SBC the 307 is kinda a dud.They where made to put in chevy wagons & trucks for pulling power. I would either leave it stock or get something else. As all SBC they are relieable & you can get a shitload of dress up parts cheap!! JimV
I appreciate the sbc engines attributes but seen darn few of them ever make it halfway to 400,000. I saw a helluva lot more of them in my shops over the years with the cam gone at around 100,000 and even as low as 40,000. Timing chain so stretched out it wears holes in the cover at not much over 100,000. Valve covers you can't keep sealed, on and on. I agree with just building it, put on some of the good 305 small chamber heads and thrash it till it needs building again. And if you want a 4 inch block, save your money and get a 2 bolt, once it's bolted together nobody knows the difference and it isn't going to fly apart anyway. Leave the 4 bolt blocks for the guys buiulding serious power.
Gotta go with the ones who say build it... the 307 in the Chevelle was phenomenal. It would have really rocked with the 305 heads I bet... I'll have to build it up someday and find out! Jay
'Appreciate the input. So, looks like boring the block to 4 inches is pretty iffy (not advisable). I have a set of 305 heads that I could put on it, and go the rebuild route. 'Guess those 305 heads are all the same...
The 305 heads have small chambers and valve sizes that will clear the smaller bores. They're plentiful, cheap and a GREAT bolt-on upgrade for 307 engines. The main thing that killed the 307's reputation was the fact that GM installed non-hardened camshafts in them. After a few thousand miles, most had wiped out cam lobes and ran like crap! A simple swap to a better cam is an easy fix! (Don's Hot Rod Shop sells 327/300 horse spec hydraulic cam and lifter sets from Crane for like $85. That would be a KILLER grind for a street driven 307.) Intake manifolds, headers, distributors, valvetrain parts, dress-up items, etc all interchange with other small block Chevys. Take your pick from factory or aftermarket goodies and have at it!
Man, even most die-hard small block guys hate 307's. Hack's cam recommendation is a good one. It's my opinion that good cam selection is the key to a good running SBC. Throw some decent small chamber 305 heads on it to bump compression up to around 9:1 or so, and you'll be pretty happy with it. You're basically ending up with a 1/4" stroker 283 if you wanna look at it that way. That's what I'd tell people it was too if I were you, just to fuck with them. I personally wouldn't build a 307 unless it was all I had, and upgrading to a 327, 350, or 400 block wasn't an option. However, if you want to get your car going on the cheap, throw it together with the 307, and snatch up a 350 block to either build the 327 (with the 307's crank) or a 350 to bolt in later on. Find a good used (assembled) set of (mid-80's) HO 305 heads, a good new hydraulic cam/ lifter set, and finally a used Edelbrock Performer intake and 600 cfm carb which will work well with the combo. Gaskets and a good timing chain for the SBC are cheap, so that won't add much more to your build cost. If you do some serious swap meet scrounging you'll probably only have about $300 (give or take) invested in parts, and will have a pretty good running and reliable SBC. As far as boring the block goes, I agree that .060 over would be the maximium, but I don't know if I'd even go that far. Here is an excerpt taken directly from an article written by Smokey Yunick circa 1973. He's talking about a 350 block, but the same principals apply to other SBCs. "Now we're ready to open up those cylinder bores. You'll recall that at the beginning of this article I said we'd be building an engine with a 4.030-in. bore, but that we'd start with a 4.000-in. bore block. Some of you might wonder why I recommend a .030-in. overbore instead of a .060-in. increase. The reason for this is that I've sectioned a lot of blocks, and nominal wall thickness seems to be consistently in the neighborhood of .140-in. Now one of the secrets of the Chevy block is that it's light. The Chevy engineers put the metal where it belongs, but they didn't overdo it. I'm sure there's more to the story than just good engineering - it's also cheaper if a block weighs only 163 lbs. instead of 173 lbs. So if you bore .060-in. oversize, which is a .030-in. cut all the way around, you're down to .110-in., assuming the cylinder core was right on. But you have to believe that the cores don't usually go in exactly straight, that they do shift a little bit during any mass-production casting process. Suppose the core shifted .030-in. Now you're down to .080-in. wall thickness, and that just won't do the job. With a .030-in. overbore that same cylinder would have a .095-in. wall thickness and that's OK. Unfortunately, Chevy blocks aren't made of a very hard cast iron. It's fairly soft. A MoPar block, for example, has a much harder or tougher cast iron. Using a soft cast iron isn't necessarily a bad idea, though. In fact, for normal street use, which is what these engines were designed for, a soft cast iron lets the rings and everything get acquainted faster to seal better, and that's good. From the racer's standpoint, a harder cast iron would be more desirable, so when a guy overbores .060-in., he's already made a mistake. Now, a lot of races have been won on .060-in. over engines and a lot more will probably be won in the future. However, it's my guess that those same guys would have gone faster with .030-in over engines." I think that kind of explains why serious overbores are generally not a good idea for most street oriented small blocks. I'm definitely no expert, but I'd say that Smokey Yunick was....hope that info helps.
All the above statements are good advice. now for my two cents on the matter. Your question is, can you machine a 307 block to four inches to build a 327? (you could also build any number of four inch bore motors, 350, 302, 383, etc, just takes the right crank) The simple answer is yes..............HOWEVER!!! Not all blocks can take the overbore. Your 1968 block will not take the overbore. When the four bolt main 350 block became the hot set-up in the small block chevy world, (1970 ish) Chevy changed their casting cores. They used several different cores up until 1970 to make the 283, 327, and the 350 (starting in 1968). After 1970 they simplified the casting for the small block down to two sets of cores, one set for the 400 small block and one set for the 307, and the 350. These were the only small block available after 1970. The 307's were cast using the same cores as the 350, they just had a smaller hole punched into them. This makes for a thick cylinder wall. Any good machine shop should have a sonic tester in house. Any block that you want to bore over a lot, should be sonic tested first! I have personally built nine 307 blocks into 350's simply by over boring the blocks the extra eighth inch. you have to use a later block to do this however, and these were stock and mild street engines at best. My personal 1971 Nova had one of these blocks with a cast crank, stock rods, cast pistons, a 1970 LT-1 solid lifter cam, stock 1969 Q Jet iron intake, Q Jet , 441 heads with 1.94 1.50 valves. A 2600 stall converter and 10 bolt with 3.36 and later 3.73 gears, and ran 14.0 et's all day long!! Our track is at 6000 ft altitude (air density is closer to 8000 in summer months) so a fourteen second street car here is actually kinda fast! LOL. Point im making is that it can be done, but is it really a good idea? Probably not these days, Those motors were all built on really tight budgets and were the exception to the rules and good practices. Either run the 307 with some good bolt-ons or find a 350, use a modern type camshaft grind though, they are so much better than the ancient ones from days gone by really. Hope this gives you some insight and helps to answer some questions. Good luck!!!
Any SBC with more than 327 CID creates a lot of side load in a hi-horse engine. Yunick never used huge SBCs, he kept them small. They produced power because the design was straight up and basic. Thats what makes power and wins races.
The 307 works great with 305 heads (416 casting or 305 vortec heads) and a edelbrock cam/lifter kit. If you can get the 350 block, make the 327 and use the 350's Vortec heads (best) or use the 416 casting 305 heads (might want a lil port work
Why spend the $$$ on boring out a 307 block when you could go with a .030" over 350 block and the 307 crank??? That would turn it into a 331 ci motor. Da Grumpster wrote a book on 331 ci motors.. He also won alot of races with them..
I've you've got it and insist on using it go for it,my dad had one in his 67 nova .030 pver flat tops and good heads and cam,victor jr.and 750 holley with 3.73 gears full street show car it ran 13.30s all day...he only used it because it came with a car and was fresh so he added top end parts and it worked great till he got a 400 to put in Cb
----------------- Right on. The reason the the 307 got a bad rap as a 'performance engine' is that it was only ever offered in passenger car form as a very mildly cammed, 2-bbl, low compression 'entry level' V8 (it replaced the 195 hp 2-bbl 283 as Chevy's base V8 engine starting in the 1968 model year) Remember too that at exact time the 307 was introduced as the base V8, Chevy also came out with the 350, which due to it's bigger 4-inch bore (which allowed for 2.02 or bigger intake valves) and it's greater overall displacement, became their 'engine of choice' for developing into a performance engine. However, the 307 is still a SBC (actually consider for what it really is - a 'stroker 283' - and it you can see it in a whole new light!) and any of the hop-up tricks that Chevy used on the 283 and other factory 'hi-po' offerings ie - a better intake, more carburetion, more cam, more compression and bigger valves will work just as well on a 307 too. Intake valve size is effectively limited by the bore size, (as it is on the 283 as well) to 1.94's but that's not really a problem on a street engine. Proof of the 307's untapped 'performance' potential is that both OMC and Mercruiser used the basic 307 shortblock for a number of years as the basis for their factory-rated 225, 235 and 245 hp 4-bbl marine conversions. If I was building an engine, I wouldn't go looking for a 307 to start with but if I had one and didn't need an engine with a lot of displacement or wanted a replacement for a 283, I wouldn't hesitate to hop one up a bit and use it either. Mart3406 =========================
when i was running a dirt car. we were allowed up tyo 355 ci. we were running a 327. 307 carnk in a 350 block. won some was always in the top 5. now if you insist on a 317. you need a 62-66 283 block one that the part number ends in 870. they are 327 blocks that are not bored to 4" they are also clearenced for the 327 crank. use the small 327 crank and bore to .060 over.
I agree with Mart...use it as a stroked 283....if it is just a motor you have ....they can still get you down the road with a smile....
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