Power of 307?

[syncrov69]

I like to know if a 307 have a respectable power in a 1968 if you compare to a 250? Is it easy to modify to give it more power! What is your trick to upgrade the power of this engine! Many parts is available? Do you have suggestions and prices? Both engine have a 3 on the tree. Is it interestimng to put Hurst Indy floor shifter conversion? Thank's

[ChevLoRay]

The 250, as I remember, was rated at 155 horsepower. The 307, was rated (again, I think) at 195 horsepower.

I get the impression your truck has a six and you have an eight that you want to use. Is that right? Unless the 307 is ready-to-run when you drop it in, and you are wanting more power (Tim Toolman Taylor grunt inserted here), you will want to consider other options. Basically, it doesn't cost any more to build a 350 than it does to build a 307. But whatever you can put on a 350 to dress it up, can also be put on a 307.

[syncrov69]

I'd like to buy a truck with 307 but I don't know what is the capability on the raod of this truck?

[Long Roof]

I have a 307 in my Jimmy. I like it. I think I read that it has 255 hp in a stock truck. It's basicly a cross between a 283 and a 327. It has the 283 bore and the 327 large journal crank. It has decent torque for such a small engine. It's a small block so you can toss in about any combo of parts. I guess I would say its about like a 305 of the 80's.

[streetstar]

I have a 307 that was original in my '69. Mine had quite a bit more power than my 305 equipped 84 Sierra. I just did some basic things to it. It was my first truck, so i did the standard 4 bbl/intake swap - changed the exhaust to duals and kept it tuned right.

I have stated on here before that i think the 307 gets a little bit of a bad rep --- it performs better than its numbers indicate it should. Better than most 283's and quite a few stock 327's.

I am planning on "freshening up" my 307 with some vortec heads, dual quad Holley 450's , some new gaskets, and some rams horn type manifolds and finned valve covers -- i think the old internally balanced engines look cool for a nostalgia piece --- but my short block is still good - i don't think i would ever go too far out of my way to build one of these with the wide availability of 350's out there

[67_C-30]

I agree with these guys, the 307 is a very underrated engine. They have adequate power and with a good tune, they are very good on fuel. We put a set of 461 62cc double humps, a L79 camshaft, and 600DP Holley on an Edelbrock intake with 1 5/8 headers on one of my buddie's '69 Nova it ran in the mid 13's at 98 in the 1/4. It surprised all of us that it was that fast for a small engine. They are much stronger than the late '70's and 80's 305's and real close to smogged out late 70's 350's.

[samwise68]

i have absolutely no gripes from my little 307 - and this is coming from a 6 guy!

granted, it's the first smallblock i've owned and/or driven (limitedly), but i'm impressed by the little mouse's guts. it'll lay down a decent scratch in first no problem, along with a hard shift into 2nd, she'll scream and lay down some more. and this is just with 3.07 gears.

personally, i like the odd ball motors, so to speak. straight sixes, the not so popular small blocks, etc. so, thats my vote. the 307 has yet to disappoint me as a teenager with high octane running through my veins, or...maybe some 87 unleaded? hah.

-Sam.

[bucky_21_7]

I'm happy what i'm hearing guess i'm in the mists of building a 307 that came out of a 68. I'm puting a small cam, edelbrok performer intake 600 edlebroke carb, headers and gear drive on it and i hope it makes good power.

[RicksTrucks]

I still have the 307 that originally came with my 69 SWB. Cracked a head a couple years ago and replaced it with a crate 350. Have new heads now and want to put it back together and may put it back in the 69 to keep everything original. Even bought a rebuilt 2 barrel carb like the original one that went bad after moving it to the new 350. Was talking to some guys and they said to put an RV cam in it and that woudl help the performance and gas mileage.

[KFreddy]

Searching around I found this interesting write up at

http://www.jalopyjournal.com/forum/

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 performers, and it stuck with them. The primary reason for this awful 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 literally THOUSANDS of factory and after market 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 camshaft 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.

All that being said my .02cents would be to call the Crane, and Comp Cams tech lines and ask for their suggestions insofar as a cam choice.

Good luck too you,

-Fred

[BCOWANWHEELS]

streetstar thats too much carburation for a 307. it will be a gas hog and run real rich. 1 600 cfm vac. secondary holley or better a q-jet will be optimum for that engine.

[streetstar]

Originally Posted by BCOWANWHEELS

streetstar thats too much carburation for a 307. it will be a gas hog and run real rich. 1 600 cfm vac. secondary holley or better a q-jet will be optimum for that engine.

You have to tune it to run on the primaries at partial opening only at low rpm for best performance. It takes a ton of work to set it up compared to a single 600, but its fun when done properly. Plenty of 283's ran with 3x2 setups way back when, which is even more carbureation-- lots of 327's with dual quads too
This engine will most likely not be going into a truck, but a street rod for one of my dad's projects

[special-K]

I`ve taken greif over my support of the 307 over the years while I`ve seen lame 305s dropped in left and right.All these earlier V8s are good motors.I see good support of this baby-8 now and all is good.A stock 307 is under 200hp,I believe.Play with it a bit and it will run with 350s and be a bit less thirsty.
This motor came out when the 359s were still 4-bolt main.I think this is where the lack of love stemmed from years ago.That,and it was never the heart of a performance vehicle.But to compare to what came to follow,it`s just another member of the good ol`early blood simple V8 family with plenty of iron built into it.Some even argue that what you gain from the 4-bolt is 1/2 lost in weakening the block from drilling the two extra holes.There are certainly plenty of built 2-bolt 350s out there.

[67_C-30]

I agree. I've never seen a 500HP or below SBC fail because of 2 bolt mains. I've seen some radical dirt track engines that run at sustained high RPM use experience some main cap walk, but if you build a street engine and your tolerances are correct, you will have no trouble at all with a 2 bolt main engine. I had a 2 bolt main 350 in my race car that ran high 11.90's in the quarter and I have over 300 timeslips from when I had that combination, and the engine never failed. In fact, I sold it to a friend and he still has it is a '71 Chevelle.

[gkolmatycki]

If you just want a cruiser with a little bit of a peppy attitude, the 307 will do just that. But if you want a racer, you'll have to spend some $ and work hard to get there with a 307.

Coming from experience....I origianally had a 250 inline six with a 1 BBL carb in my '69 with a 3 on the tree manual tranny. It got decent gas mileage (14-16 mpg) and had decent power. Then I got a 283 2 BBL for $100 when the old inline six went. It is a stock engine with a rebuild back in the late 90's, but I did a 4 BBL quadrajet and intake swap on it. I also installed a true dual magnaflow exhaust system and a rebuilt TH-350.

Honestly, the SBC 283 with a 4BBL carb, performance exhaust, and a TH-350 tranny has a lot of power. It's puts out roughly about 220 HP/300 lbft (by the old standards). Personally, I know it does 0-60 MPH in under 10 seconds. I'm guessing it could probably do the 1/4 mile in about 16-17 seconds, but haven't tested it yet. Mind you, I have really steep rear gears (4.56). Gas mileage is about 12-14 mpg too.

But you can never have enough power (Grunts like Tim Allen)....Soon when I save up some $ though I wanna build a 350 with at least 320 HP and 350 lb/ft of torque.