305 vs. 307 street build opinions

[tracterman2]

Okay I have a stock 307, I haven't even driven it yet...it does run, I ran it this past weekend for the first time in 15 years, it was a glorious event. Anyways I really enjoyed reading the thread on the 305 build....well not really a build just opinions on giving the engine a kick in the pants. My question is what is the difference in the 307 and 305?? Why did they do away with the 307, are there differences to the point that the other mouse motor parts won't interchange?? I don't know much about the 307 and am just wondering are the things said about the 305 safe for for the 307 also?? I have heard that the cam is the major flaw in the 307...the engine isn't allowed to breath...why do so many not like the 307?? I've read alot on here and it seems to have a bad rap...is it not a small block chevy also?? I would also like to know opinions of people that still have the 307 and what they think about them. I would like to give mine a kick in the pants one day soon, I have to two barrel and ram horns...it is BONE stock, well I did add HEI the other day. I was wondering on dual plane intake, four barrel (around 500-600cfm), mild cam...well rv cam anyways, headers, dual exhaust...what about the head??..what about old 305 camaro heads?? would they work? I don't want a screamer...just something that will push my little truck around and suprise people from time to time. What do you guys think?? I love hearing peoples opinions and their experiences on here. I think thats one of the best parts of a site like this. Thanks again. By the way my 307 has 44,000 original miles on it and purrs like a little kitten...I couldn't believe it after 15 years.

[special-K]

I`d take a 307 over a 305.

[Bowtie001]

I have never done it, but I have heard a few things about both of those.
A either can be stroked, I think the 305 gives 335 and the 307 gives 328. The 307 has a bigger bore and a shorter stroke than the 305 does. I have also heard that in some instances a 307 can be bored to 327, which would be interesting, but I would sonic test the block first.

If you're not increasing size, I'd stay with the 307 because it's 'period correct' and a bit more different. I'd throw a set of vortecs on there (cheap) and an itty bitty cam (and that way you can use stock vortecs without worrying about the cam lift) and make a nice round 300 hp with a edelbrock air gap and 500-600 cfm vacuum secondary.

The 305 is a variant of the 350 engine family and the 307 is a variant of the 327 engine family... there were not that many differences that I know of.
Just my opinion though, there will be many more.

This may help
http://en.wikipedia.org/wiki/Chevrol...l-Block_engine

-Brian

[tracterman2]

I think I messed up on the title...I'm not going to get a 305...I'm sticking with the 307...I was just wondering about differences in the two...why Chevy moved away from the 307 to the 305...I guess it was the 307 and 327 being moved to a 305 and 350. I do want to keep my 307...figuring out ways to do things with engines that most just throw away is very intriging to me

[68speedalert]

The 307 was a 283 block (the bore size) with a 327 crank (stroke size).

It was never built up for power like the 283 & 327. It was never highly thought of in the day. They always seemed to burn a lot of oil.

I always wondered why that was, since they were 283 blocks (one of bow-tie fans' favorite).

A good friend of mine is a small-block guru. He said it was because the later 307's were newer castings and that Chevy didn't let them harden enough. Therefore they wore out rather quickly. I have no way of knowing the truth, yet have no reason to doubt him.

The tremendous 302 was a 327 block (bore) with a 283 crank (stroke). It was an extremely fast high revving engine.

The 305 didn't come out until about 1976. My guess was to have something other than the straight six for the cars.

[RACINJASON22]

I'm with special-K. The 307 is definatly still a SBC and IMO better than the 305. There has been a lot more 305 discussion because they are more readily avilible these days over the 307. The main reason for my opinion is that with them both being compareable in cubic inches is that the shorter stroke of the 307 is more suited to the lesser inches. REV, pickup (seat of the pants) will seem way better to you over the 305. Good luck with your build and I think you will be happy as long as your realistic in your goals, RJ22

[DavidS]

Classic Trucks Magazine had an article on a 307 build a couple of years ago. Check their web site to see if they posted it there.

[Longhorn Man]

normal 305 heads are a great upgrade, and much cheaper than vortecs... if you can't get 305 heads given to you, then you aren't trying hard enough. (you may have to take a whole engine, but then you have scrap crush weight afterwards)

[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 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.

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

[tracterman2]

why are they better?? do the 305 heads have a smaller combustion chamber, increasing compression?? or do they have larger valves in them?? I have heard the 307's do not breath very well...I was told it was the cams though..they say they do not have very much lift at all. I'm sure I could find some heads fairly easily...I know where there are some 327 heads at...would that work??

[bedsled71]

i have a 68 307 in my trucks. runs great but its not stock..mild cam with 85-305 heads on it which raised the compresson, edelbrock manifold and 4 barral carb, 600 cfm.. and bored over 60 . i raced a friend with a 350 and beat him no problem .. sucks thought because my power only goes to one wheel

[Zoomad75]

My 69 Nova came from the factory with a 307. It was an absolute dog due to a couple of burnt valves. I did a quicky valve job in High School Auto shop and started bracket racing. A 307 2bbl with 2.73 gears at Denver's altitude is no ball of fire, but amazingly consistant. I was able to shave 3 seconds off (no kidding) by swapping out the wheezy 2bbl for a well tuned q-jet. Due to the high gearing it just didn't have the pull out of the hole, but would cruise at 80 turning barely 2000 rpm.

The poor tired 307 was a good economy engine but even in a light Nova, no power house. I couldn't imagine a 307 in a truck without some bolt ons for help.

Might want to keep in mind that there were two types of 307's. The early 67/68 had small journal cranks while the 69 and up had the large journal cranks (same size as the 350). 302's and 327's made the change to the large journal cranks at the same time.

I can totally understand rebuilding a 307 for restoration purposes, keeping a truck numbers matching and all that. Rebuilding a 307 for performance is a waste of time when 350's are pleantiful and still cheap. The cost to do the same mods to a 350 is the same and you would yield more power. Better bang for the buck.

I'm not against anybody building one to be different with the performance mods listed above, its your choice. Just don't expect the same output as 327 or 350 with the same mods.

One other note that one touched earlier...The 307 blocks are said to be low in nickel content. Meaning accelerated bore wear on high mileage engines. Sometimes you may not have enough meat in the block to bore for oversized pistions. Might need sonic checking.

By the way, anybody that wants my old 307 can have it. It's in Denver if anybody wants it.

[68speedalert]

Originally Posted by Zoomad75

........
One other note that one touched earlier...The 307 blocks are said to be low in nickel content. Meaning accelerated bore wear on high mileage engines. Sometimes you may not have enough meat in the block to bore for oversized pistions. Might need sonic checking.

That's what he told me.....thanks for the refresher.

[oldgold70c10]

I am currently running a tired old 305 in my truck right now, and, given the 67-68 flavor I am planning on doing my truck in, have thought about the 307, especially since I know where two untouched 68 307 are that could be had fairly cheap, but the "soft block" comments have had me concerned.

The 305 gets a bad rap because it was usually an economy "smog motor", but the longer stroke should give it more low end torque, plus it uses a 350 crank, and I haven't heard anything about soft block castings.

I know that 350's are almost overused to the point of seeming like a generic V8, so it is tempting to build something else just to be different, even if it is a smaller engine, after all, lots of people build 283's, and they are smaller than the 305 and 307.

I personnaly am thinking of stroking a 350 out to a 383 just to be different, but still want to consider other engines.

[Longhorn Man]

Yeah... no one has a 383.

[oldgold70c10]

Originally Posted by Longhorn Man

Yeah... no one has a 383.

Yeah, I know, they are almost as rare as those 302's

[crazy longhorn]

Originally Posted by Longhorn Man

Yeah... no one has a 383.

And they dont run worth a chit.....RIIIIIGHT! IMO, that little 307 has far more potential than the 305. Any time you open up the bores, the valves "breath" better........same deal on the 383 vs 406.....1/8" bore makes a big diff on how the little engine runs upstairs Back in the early 60's , the good old boys wer strokin 283's with sj 327 cranks. This was BEFORE GM built the 307, & let me tell you , the diff tween a factory 307 vs the HOTROD 307 were different as day & nite! If you add a set of Vortec heads & a mild cam to that 307......Ill bet you cant get your buds to believe that its NOT a 327! L

[tracterman2]

I have a a stroked 283!!! Its the biggest little stroker around!! yeah right

[wibilly]

personaly i would grab those small journal rods to stroke a 400 sb if you wanna be a little different and nobody has to know just how different you are

[special-K]

I built a 307 from a`71 K/20:
*1.94 valve heads
*stock 4bbl manifold
*450cfm holley Economaster
*HEI-weight & spring kit
*stock bore
*Crane Blazer cam...RV-type
*Cloyes dbl row timing chain
*Melling hi-volume oil pump
*headers
Ran like a strong 350 and got 15 mpg with a 4spd,4.57s,and 14.50/37 mud tires.

[RACINJASON22]

Still with special-k and now crazy longhorn the 307 to me has much more favor in my garage.

[pissonNOS]

right now im running a 307 and ive put the HEI msd headers intake 4 barrel almost all the add on goodies that you can and we bored it out as well and I must say its a strong running engine and like stated above sure surprises some people when u tell them its only a 307

[special-K]

I had all the torque I needed to move it along and stay out of the secondaries.Ain`t that what you want from a motor?Then,have the power when you want/need it?I ran my plans past Jim Coleman from Coleman Brothers Speed&Machine and he agreed that I`d get the best of both worlds out of my build.He talked me out of anything but a stock manifold.This guy`s a genious.He can explain complicated dynamics while drawing you diagrams upside down and backwards so you can follow along with him.
BTW,I rebuilt the motor at 120,000 miles due to a jumped timing chain while my boss borrowed the truck.I knew it was slappin`the cover and had the parts under the seat and was babying it along.Anyway,he can walking back after throwing it and macking-out the pushrods and valve stems.Once inside,there was no noticeable ridge in the cylinders and nothing appeared to require machining.No burnt valves,either.It got the royal treatment,including a trip(to the building next to Coleman Bros.)to Ladd`s porting service(and polished),and the rotating assembly went next to them to House of Balance.In the early`80s guys thought I was nuts wasting my time on a 2-bolt 307.Many were impressed with the results.
These days,many experienced engine builders will argue the benefits of a 4-bolt are countered by the loss of strength from the extra holes.At least,to the point that it`s an insignificant difference.

[RACINJASON22]

I know it's starting to sound like I'm sucking up to special-K or some thing but I don't even know him. I am a firm beleiver in a mild port matched stock GM four barrel intake (not for all engines) And also the qualitiy of some of the production 4-bolt blocks, 2-bolt machined for splayed caps the strongest other than after market IMO. Thats a little off subject I guess. Just adding to his post.

[qksilver]

Coleman brothers brings back many memories. I grew up in Bethesda, so you had Jimmy Ray and Coleman bro's plus Steve down at Douglas speed and sport, the old Maryland Hi performance and Rizzoli (RCD) then ATI in Silver spring.