307 Specs?

[BluTrukker]

I am trying to formulate a plan for my 68. It has a 307 that was rebuilt by the PO, and it runs very good. I was hoping to get a few more horses without too much $$. I have a 670 CFM Carb and a very low mileage factory cam out of a 1968 Camaro SS with the 295 horse 350. Also I have a set of hedman headers. Would the cam fit? does anyone know the specs? Would it be worth my time to get an intake and install these items, or will the factory 307 heads be a huge choke point? Like I said, I don't have a clear plan for the truck yet, just looking to use what I have lying on the shelf.

[MrGoodpliers]

Not a whole lot of performance potential in a 307. Not to knock it though, I have one in a work truck that runs like a sewing machine... Just drive it.

[Brock]

a very simple power booster wouold be to take the mechanical fan off and replace with electric. I did this on my dirt track car and gained what felt like 15 hp...I had to take it off because it ran hot but I'm guessing your not going from 6000 rpm to 2000 rpm twice a lap I REALLY felt the difference when I went back to the mechanical fan

Another quicky power booster is switch to a high performance oil such as Royal Purple...its supposed to get ya 5-10 HP as well.

[airdale94]

You could look around for a set of 305 HO heads. I put a set on my 283. Some of them are 54cc, the rest are 58cc. The RS cam will fit but it's probably a top end cam. I would go with the heads and a bottom end cam. The torgue is what you're going to feel.

Sweet looking truck by the way.

[Brad]

Nice looking truck- I like that color combo and have never seen that before.

[BluTrukker]

The PO repainted it to the current sceme, but it is the original colors.

[BluTrukker]

I've heard a few times on this board of people putting 350 cranks into a 307. What would that gain? I have also heard that a 307 and a 327 crank are almost the same. True? If I have a 10/20 block isn't it strong enough to handle some more power? I would kind of like to keep the original block. Any ideas/options are appreciated.

[monte0185]

I personally like 307's a friend of mine had one in a vega that was just plain mind boggleing. Best thing to do is find you a set of vortec heads 10239906 casting# and get an intake and carb to go with the heads and a mid range cam. Comp cams 270 or 280. This will put it about 325-350HP depending on how new your bottom end is. Super Chevy had an article on this some time ago if you do some research you should be able to find it. Im doing this to mine right now.
.060 over pistons
Same heads
280 comp cam.
Chevy vortec intake 4bbl and holley carb.

Nothing special but will make decent power for a few hundred bucks.

[samwise68]

There was talk of putting a 350 crank into a 307 block, with 400 rods, along with an overbore to make a 333 cid. If I remember right, the thing made around low 300 for horse, along with a really flat torque curve that was around 350+.

Also, 307 and 327 cranks are the same. in theory, putting a 307 crank in a 350 would make you a fresh bored 327.

I personally like my 307. It's different. Gets pretty good mpg's, and has quite a bit of life left, despite getting tired.

If you have it, why not build it. You're only out the time and energy to put it together - plus, it's still a smallblock. Almost everything interchanges.

Just my 2 cents.

-Sam.

[monte0185]

A 307 is a 283 block with a 327 crank. Short stroke and can handle lots of rpm's. From the factory they werent very powerful but its a combination that can me made to be decent. oh and a 020 010 block is a high nickel block.

[67_C-30]

It is worth noting that the 307 isn't really a 283 block with a 327 crank. All 283's were small journal and all 307's are large journal engines. I only mention this in case someone tries to swap out parts. The 307 does share the same bore as the 283 (3.875"), and the crank is the same as the '68 and '69 327 large journal ONLY.

With all that being said, I built a 307 on a shoe-string budget for a friend years ago that ran really well. It was a '68 .030" over 307 with flattops, 58cc 305 H.O. heads that airdale mentioned and a L79 350HP 327 hyd camshaft. We put a set of cheapie FlowTech headers with 2 1/2" pipes and Flowmasters, and topped it off with a used 80's era Holley Contender dual plane intake and and a 600 Holley. It was in a '72 Nova with a TH350 a small 2000 Dacco converter and 3.73 gears. After we got it dialed in, it clicked off pretty consistent 8.90's - 9.00's in the 1/8 and pulled a best of a 13.91 in the quarter. That's defintely not world-eating numbers, but it was very respectable for a $1000 set-up.

[monte0185]

Originally Posted by 67_C-30

It is worth noting that the 307 isn't really a 283 block with a 327 crank. All 283's were small journal and all 307's are large journal engines. I only mention this in case someone tries to swap out parts. The 307 does share the same bore as the 283 (3.875"), and the crank is the same as the '68 and '69 327 large journal ONLY.

You are correct in the large journal small jounal specs. I was mearly refrencing the bore and stroke. Anyway. My friend has a 71 vega with a 307 and he runs consistant 11.90's in the 1/4. Now granted its been worked over greatly and is sporting a offenhauser tunnel ram and 2 450 holleys that took us forever to dial in but its been running those same times for nearly 10 years. All we have ever done is a tweek hear and there. I am only saying this cause i dont know of too many other built engines that have held together as long which to me goes to show its durability as well. Not that i wouldnt chunk my 307 out the window for a nicely built 406 in a heartbeat!

[67_C-30]

Originally Posted by monte0185

You are correct in the large journal small jounal specs. I was mearly refrencing the bore and stroke. Anyway. My friend has a 71 vega with a 307 and he runs consistant 11.90's in the 1/4. Now granted its been worked over greatly and is sporting a offenhauser tunnel ram and 2 450 holleys that took us forever to dial in but its been running those same times for nearly 10 years. All we have ever done is a tweek hear and there. I am only saying this cause i dont know of too many other built engines that have held together as long which to me goes to show its durability as well. Not that i wouldnt chunk my 307 out the window for a nicely built 406 in a heartbeat!

I was just clarifying. I only made the reference because I've seen several people over the years go out and buy engines that they couldn't use because of what they heard. It was nothing against you. A lot of people with little engine building experience don't know all the little nuisances and get themselves in trouble sometimes! I know a guy that went out and bought a 3970010 4" bore block and bought a 283 because he wanted to build a 302. He brought them to me to build, and told him they wouldn't interchange. He argued saying that he looked on Mortec and the 3970010 was used for 302/327/350's and he was told "all a 302 is a 327 block with 283 crank". He didn't know about the difference in journal sizes. Another example is "305 and 350 cranks are the same". It is true that they have the same stroke and will interchange. I'm sure you could swap them out and they'd even live in a daily driver, but they won't in high performance engines because of balancing. We put a 305 crank with 350 pistons and rods on the balancing machine one time to see, and it was way off for a high rpm engine.

[724x4a/cchevy]

Here's some info I stole off the hamb.
http://www.jalopyjournal.com/forum/s...&highlight=307
INSIDE THE 307 CHEVY....

It was produced by Chevrolet from 1968 until 1973, and was used in passenger cars and some trucks. They were all two bolt mains blocks and all came from the factory with two barrel carburetors. The 307 was slated from the start as a low performance, economical replacement for the 283, and was never considered a performance engine by Chevrolet.

Looking at the bore and stroke specifications, you will see that the 307 comes with a 3.875" bore and a 3.25" stroke. What it essentially was, is a 327 crank dropped into a 283 block. No mystery combo there...just an easy to produce base model V8 for Chevy cars using existing parts.

(So, you can think of your 307 as either a stroked 283, or as a small bore 327!)

To put into easily read chart form:

283 = 3.875" bore X 3.00" stroke
327 = 4.001" bore X 3.25" stroke
307 = 3.875" bore X 3.25" stroke

The journal sizes on a 307 are 2.45" for the mains, and 2.10" for the rods. Again, no hidden surprises here, just a common, cast 327 crank in disguise, folks!

All 307 blocks are two bolt mains, but there are several different casting numbers. One isn't really much better than any other, but I'll list them here for the purpose of aiding in identification, so you can be sure that you do indeed have a 307 on your hands.

3914636 (1968 passenger car)
3931174 (1968 truck block)
3956632 (1969)
3932371 (1969-1973)
3932373 (1969-1973)
3970024 (1969-1973)
3970020 (1970-1973)

The blocks are really nothing special. Externally, they look just like any other late 60s to mid 70s small block (400s excluded!), and they accept all such oil pans, accessories, and other bolt-on parts such as manifolds, water pumps, fuel pumps, etc.

Cylinder heads are a point of concern on 307s. Although they used common castings often shared with the tamer versions of their 327 and 350 cousins, they were saddled with small (1.72") intake valves due to their bore size. The many 307 head castings available are not your best performers, but we can work around that with proper machining and parts selection. More on that later. For now, let's just see what casting numbers were available on factory built 307 engines:

3911032 (1968, 70cc)
3917290 (1968, also used on some 327s)
3917293 (1968, 75cc)
3931633 (1968-1973)
3986388 (Used from 1968-1976 on 307 and 350 engines)
3927185 (1969-1976 307/327/350, 70cc)
3932454 (1969-1973)
3927188 (1970, 74cc)
3986339 (1971 307/350)
3998991 (1972-1973 307/350, 75cc)
3998993 (1972-1973 307/350, 75cc)

As can be determined from the list above, some low performance 327 and 350 engines were also equipped with these small valve heads, so they can be found easily for next to nothing or free, as any serious 327 or 350 build is going to involve discarding those castings in favor of better heads with 1.94 or 2.02 valves.

In addition, although I didn't list them here, any 283 head castings can be used on 307 blocks. This is good news for those wanting to keep a nostalgic look and flavor about their project, as it allows for the use of the old 283 "Power Pack" heads, and any number of choices from the 283 line-up. This expands your range of selection, and means that you can use 60s style heads with no accessory bolt holes for a cleaner, more traditional look if your 307 build is slated for use in a trad rod or custom. Just more fuel for thought.

Aside from their bore and stroke numbers, small valve heads, and specific casting numbers, the 307s are just another small block Chevy on the outside, so building one is still a fairly affordable deal. You just have to know what you're dealing with going in.

BUILDING THE 307...

307s got a real bad rap early on as poor peformers, and it stuck with them. The primary reason for this awfull reputation, however, comes from one single mistake on General Motors' part...they equipped the 307 with a wimpy, unhardened hydraulic camshaft. These cams wore out very quickly, leaving the engines way down on power and way up on fuel consumption. Many owners failed to diagnose this condition, and just sold their cars in disgust, or swapped in 327 or 350 replacement engines. The fact is, a simple cam swap would have put their wheezing 307 right back in the fight, had they taken the time to check it out!

So, obviously the first thing you should know about building a 307 is that you're GONNA have to buy a cam. Luckily, there are litterally THOUSANDS of factory and aftermarket grinds to choose from, so fear not, brave warrior!

The small valve heads, along with the bore/stroke relationship will play a critical role in camsfaht selection. It is easy to "over cam" a 307 and make it perform WORSE if you ignore these factors, so avoid the temptation to use the same lumpity cam your buddy is running in his built-to-the-gills 350! You want a hydraulic cam with sensible duration and relatively small valve lift. This leaves plenty of options open, and it should be said right now that building a 307 for anything other than mild street/strip duty with limited RPM (under 6200) expectations is a foolish affair given it's specific shortcomings. For this reason, we will be looking at cams in this relatively mild range.

[BluTrukker]

Thanks for all of that valuable info. This forum is a goldmine!

[68Stepbed]

I would say the cam you have would work well with the 307. If you had a decent set of heads, an aluminum intake, and the right carb, you could make that 307 a fine example of the little engine that could.

I do not recommend the 670 carb. Even with better heads, the engine just simply won't pull enough air through the carb to work right.I would recommend either a 500 Edelbrock or a Holley 500 2300 2bbl. Don't start thinking the 2bbl Holley will choke power becuase the engine came stock with a 2bbl. The Holley is still a performance carb. The stock Rochester 2bbl carbs were designed for economy. Anything bigger than 500 cfm on that small of an engine will be a crutch and will give you many problems.

Does anyone really know how the 307 came into existence?

In 1967, Chevrolet introduced the Camaro to compete with the Mustang in the "ponycar" market. The new Camaro also unveiled the new 350 ci small block only availble in Camaro SS models. Also in 1967, Chevrolet, Ford, And Chrysler started competing their ponycars in the SSCA Trans Am series racing. SSCA rules limited engine displacement to 5.0 liters. While Ford retooled and built a larger bored 289 block to make 302ci, Chevrolet simply took off the shelf and already in production parts to make their 302. They used the 4.00" bore 327 blocks and mated them with the 3.00" stroke cranks from the 283. SSCA rules also madated that the 5.0 liter engine also had to be sold in production cars, not just in their race prepped cars. Which led to the ever popular Z/28 Camaro with the new DZ302 engine.

Now with all the leftover 283 blocks and 3.25" 327 cranks, they decided to throw them together to make an "economy" small block to power the ever growing number of production cars and trucks coming off the assembly line. Has anyone ever noticed that 67 model cars and trucks had a basic 283 and were suddenly replaced in 1968 with this new mysterious 307? Also, 327's were few and far between after the 67 year. Chevrolet produced the 307 engines without having to retool to make newer engines. the only real change was the 283 blocks were cast with the larger main journals to accomodate the large journal 3.25" crank.

All R&D money went into improving the 350 and into big blocks.

[monte0185]

67 I didnt take it the wrong way I promise. I appologize if I come off like i did. I was just pointing out you were correct.

I have been building engines for many years and I learned from some people that have been doing it WAY longer than me and there are lots of tricks and combinations out there for small block chevys that goes back throught its lifetime of people modifying them and learning. I just usually tend to go for the underdog I guess cause i like to be different.

Well back on the Subject: Blu I would suggest you go to your local engine builder if you have one or if you dont Im sure lots of use here have a number in our wallets of one and talk to them about your options and what your budget will allow. I have found that money is usually what drives most of our builds at least it certainly does mine. But a good engine builder can usually give you lots of options and prices off the top of their head and give you any other information that may be of signifigace to your application.

Have Fun!! And GREAT looking Truck by the way.