Small Block & Big Block Chevy Specific - mystery of the 307

hey im only 19 and i have not been around the chevy sbc corner if you get what im saying... i have some questions some of you guys who know the ins and outs of the chevy small block could tackle.

is the 307 the same as teh 327?

why does the 71 307 produce 70 more horse then the later versions that remain carbureated?

what is the compression of the 307 for the first run of the engine?

are the 305 307 327 357 396 and 400 sbc engines all share the smae block casting?

any info will be greatly appreciated thanks.

The 307 has the same bore as a 283 and the stroke of a 327. Chevy didn't make a 357 of a 396 small block. The 400 has larger main journals. After 1970 auto makers changed the way the rated engines. The swithed from gross to net. Also after 1970 automakers had to comply with stricter emissions standards.

Plus the emissions standard usually meant lower compression ratings. 1969-70 were the high water mark years for horsepower.

Derek

my 85 toronado has a 307 :pimp:

thank you guys for the info, i have some questions, i dont want to mention the blue oval but the ford 302 is well the 302.... in that there are 302 parts... in the chevy world can parts be switched over do 327 cams fit 307 blocks? and heads and intakes. or is it pretty much just a backlist motor that never really got any attention?

you can interchange small block parts, like putting 305 heads on a 350. 307 IMHO aren't worth modifying, and with 305/350 engine easily attainable I'd set your sights there as a starting point.

Derek

well i got the truck in and she started right up, its pretty health 307, the prior owner has done some whack shit, its running a 4barrel i think its a webber but its still running the 2 brl factory cam, it idles smooth, i dont think im going to be building this motor up i will prob settle with a mild 350 crate motor as for now though the 307 has plenty of omph to get the s10 running.

The 307, 327, and 350 are all the same. The difference is bore and stroke. Forget the 350 crate, punch the bore of the 307 to 327, and get a set of high flowing heads (double hump heads are cheap), and get a good cam, intake, and carb. It'll be cheaper than a good crate and I guarantee if you build it right, the 327 will kill most of the 350s you'll encounter and run with the rest. I have a built 327 in my '69 Camaro backed by an m21 and 3.73s out back and I have no problem against ls1s, lt1s, and 350s. Not saying it can't be beat, but it's a lot cheaper and the 327 really likes to rev.

The 307, 327, and 350 are all the same. The difference is bore and stroke. Forget the 350 crate, punch the bore of the 307 to 327, and get a set of high flowing heads (double hump heads are cheap), and get a good cam, intake, and carb. It'll be cheaper than a good crate and I guarantee if you build it right, the 327 will kill most of the 350s you'll encounter and run with the rest. I have a built 327 in my '69 Camaro backed by an m21 and 3.73s out back and I have no problem against ls1s, lt1s, and 350s. Not saying it can't be beat, but it's a lot cheaper and the 327 really likes to rev.
I hate to say it but you are "close but no cigar" buddy. Although you are correct with regard to the 327 and "double or camel hump" heads being cheap good horespower (I used this combo for years), you missed the mark as to what fits what. 62-67 327's are small journal engines. 68 & 69 327's are large journal similar to a 350. As a matter of fact, latter 327's (i.e., large journal engines) can be made into a 350 using a 3.48 stroke crank and 350 pistons. Conversly, you can make a killer 327 4-bolt main engine by using a 350 4-bolt block with a large journal 327 crank and pistons. 327 & 350 large journal rods are identical. Pistons differ in that they have different compression height (pin location). The 307 is the red-headed bastard step-child of the Chevy engine family. Possessing a 327's large journal stroke of 3.25" and the 283's bore of 3.875" it had neither engines potential. Unlike earlier 283's from the 50's and early 60's (which could be overbored .125" to a 4.000" bore), the 307's made from 1969-up cannot be overbored beyond .060". You can put a 327 forged steel crank inplace of the 307's cast iron unit but why bother. If you use a head with larger than a 1.72" intake you will have a problem with valve shrouding. I'd suggest you use the 307 you have and look for a better candidate to mod by finding a good 350 as they are easier to find these days. FWIW: the 400 was different from all other small blocks in that the cylinder case possessed siamesed bores of 4.125" diameter (still on 4.400" centers), a 3.75" stroke crank and a much shorter rod. Built correctly it can make a lot of power (.030" over creates a 406cid engine) but factory parts are getting harder to find as the stopped making this engine quite some time ago, although the aftermarket has stepped up with parts.

I wouldn't waste your time with a 307. The heads did not
have hardened seats. I got one in my '68 El Camino and the
valves were sunk in anywhere from 0 to 1/8". I put 305 heads
on it and it's run for 10 years, but it's still a weak little pig.
350 for sure, unless you want to go stroker.

I was referring the the large journal 327s, but I didn't realize you couldn't punch a 307 out that far. thanks

I just did my senior research on Chevy muscle cars and I've found that the 307 is a 283 block with a 327 crank in it? I think thats what I read. Anyways I'd get a 350 and spray it. my 2 cents

WOW, thanks guys for all the info, the truck is running good but it def does not resemble anything close to the power a small block chevy is known for, as for building it up i wrote some emails out to edlebrock and well you guys are correct, i could slap heads on it but i cant get any serious lift out of the cam, clearnce problems after .450 lift. there for i will let her be, then a 4 bolt 350 and some spray, im looking for a dependable turnkey street dogger, that wont see teh strip but once a season. thanks for the info again

look for an 87+ 350 block from either a camaro or firebird, or any sort of GM truck. make sure its a 350 block and not a 305. i say this because its a 2 bolt main with a factory roller cam. the 2 bolt mains can be splayed and they end up stronger than a 4 bolt setup, and the roller cam opens your cam options up but more importantly should make them cheaper as you dont have to retrofit anything. run a GOOD set of heads (no factory heads period as none are worth the money) with a decent sized cam with a good intake and carb combo and it will run good. make sure you match the heads/cam/intake/carb combo well. that will make for the best performer.

myself, im going with a 224/230 .560/.598 112LSA cam from combination motorsports with a set of patriot SBC heads CNC ported and a holley stealth ram with 52mm throttle body and maybe some 30lbs injectors. it will also have new comp lifters, hardened pushrods and 1.6 comp roller rockers. from what ive seen in the LT1 world ill need to shift around 6200 but im hopin to make almost 400hp to the wheels with a stock L98 bottom end and a t56 6 speed combo in my 91 trans am. ill be happy with 380+.

I hate to say it but you are "close but no cigar" buddy. Possessing a 327's large journal stroke of 3.25" and the 283's bore of 3.875" it had neither engines potential. Unlike earlier 283's from the 50's and early 60's (which could be overbored .125" to a 4.000" bore), the 307's made from 1969-up cannot be overbored beyond .060". You can put a 327 forged steel crank inplace of the 307's cast iron unit but why bother. If you use a head with larger than a 1.72" intake you will have a problem with valve shrouding. .


Uhhhh..... Don't know where you got your information from, but the 327 that I built from a '71 307 begs to differ with you. not only was this block bored out .125 over but I can still go another full .060 over if I want. these blocks typically had just as much metal as their 350 counterparts, just their bore was not as big. This is not the first one of these I've built either, I love guys like you that think the 307 is junk, go ahead give it to me I'll just make another 327 that will blow your doors off. hmm another 400hp, that's just too easy with these. The small block heads will fit these, what's this about valve shrouding :bs: . The only thing you have to remember with the conversion to a 327 with the 307 is that you have to order the correct 327 piston's in the stock size, not overbored....Duhhhh. Now 305's you can stroke them to a 334 but why go through all that trouble unless you get the heads that can help them breathe. All types of engines can be built, just don't take the word of someone on a message board just because they think they know what their doing. Talk to a reputable machine shop and see what they say about what you want to do. Sometimes you have to find one that's been around awhile that will remember these tricks to save money.

I wouldn't waste your time with a 307. The heads did not
have hardened seats. I got one in my '68 El Camino and the
valves were sunk in anywhere from 0 to 1/8". I put 305 heads
on it and it's run for 10 years, but it's still a weak little pig.
350 for sure, unless you want to go stroker.


Then have your local machine shop put in hardened seats, it's not that expensive. 305 heads are 54cc's no wonder it's a weak little pig, you'd be weak too if you couldn't breathe.

look for an 87+ 350 block from either a camaro or firebird, or any sort of GM truck. make sure its a 350 block and not a 305. i say this because its a 2 bolt main with a factory roller cam. the 2 bolt mains can be splayed and they end up stronger than a 4 bolt setup, and the roller cam opens your cam options up but more importantly should make them cheaper as you dont have to retrofit anything. run a GOOD set of heads (no factory heads period as none are worth the money) with a decent sized cam with a good intake and carb combo and it will run good. make sure you match the heads/cam/intake/carb combo well. that will make for the best performer.

myself, im going with a 224/230 .560/.598 112LSA cam from combination motorsports with a set of patriot SBC heads CNC ported and a holley stealth ram with 52mm throttle body and maybe some 30lbs injectors. it will also have new comp lifters, hardened pushrods and 1.6 comp roller rockers. from what ive seen in the LT1 world ill need to shift around 6200 but im hopin to make almost 400hp to the wheels with a stock L98 bottom end and a t56 6 speed combo in my 91 trans am. ill be happy with 380+.



This is the best advice I've seen in this topic. :thumb:

WOW, thanks guys for all the info, the truck is running good but it def does not resemble anything close to the power a small block chevy is known for, as for building it up i wrote some emails out to edlebrock and well you guys are correct, i could slap heads on it but i cant get any serious lift out of the cam, clearnce problems after .450 lift. there for i will let her be, then a 4 bolt 350 and some spray, im looking for a dependable turnkey street dogger, that wont see teh strip but once a season. thanks for the info again

Talk to a machine shop that knows what they are doing, I wouldn't trust edelbrock to give advice on a motor you want to build yourself, remember they build motors so they can sell them they are not interested in your build up cause they won't make as much money off of it. you can do a lot more with your engine than you are being led to believe. Talk to your local machine shop shop that builds performance motors they can help you more than you think. That's if you are interested in saving some money. The other way would be to follow the advice of the guy who said to find a later model 350 with the roller cam setup and 1 piece rear seal.

The small block heads will fit these, what's this about valve shrouding :bs: .
By valve shrouding he means the valves would be too close to the side of the cylinder walls, not that they wont fit. The closer they are to the side of the cylinder the worse they flow because you are blocking off a large portion of the valve from flowing any air. The same head will usually flow better on a 4.125 bore than a 4.00 bore just for that reason.
Before you call BS and start posting things like Duhhhhh maybe you should realize what somebody is saying first.

well of course any head will flow better on a larger bore, but what he said is that you can't go over a 1.72 inch valve, which is BS when you step it up to a 4in bore which is what a 327 is.

The 307, 327, and 350 are all the same. The difference is bore and stroke. Forget the 350 crate, punch the bore of the 307 to 327, and get a set of high flowing heads (double hump heads are cheap), and get a good cam, intake, and carb. It'll be cheaper than a good crate and I guarantee if you build it right, the 327 will kill most of the 350s you'll encounter and run with the rest. I have a built 327 in my '69 Camaro backed by an m21 and 3.73s out back and I have no problem against ls1s, lt1s, and 350s. Not saying it can't be beat, but it's a lot cheaper and the 327 really likes to rev.
must be a slow sleepy neighborhood :judge:
imo seeing as how i rebuild sbc and ls1 all day for a living
i recommend u look into a vortec engine from the mid 90's
came with roller cams and the vortec heads
most any machine shop worth using can machine the heads to use
screw in rocker studs
look for 350 4in bore engines and not the 305 engines
this engine can make some good power if u select the right combo
with of course a DP 4150 650cfm and dual plane intake

must be a slow sleepy neighborhood :judge:
imo seeing as how i rebuild sbc and ls1 all day for a living
i recommend u look into a vortec engine from the mid 90's
came with roller cams and the vortec heads
most any machine shop worth using can machine the heads to use
screw in rocker studs
look for 350 4in bore engines and not the 305 engines
this engine can make some good power if u select the right combo
with of course a DP 4150 650cfm and dual plane intake

Nope, not slow and I never said my car was the quickest around. I'm just saying that for the money it would be a good investment. Besides, if you you build sbc all day, then you should know what the 327 is capable of.

well of course any head will flow better on a larger bore, but what he said is that you can't go over a 1.72 inch valve, which is BS when you step it up to a 4in bore which is what a 327 is.
You obviously did not read what I wrote. I stated that (and I quote), "If you use a head with larger than a 1.72" intake you will have a problem with valve shrouding." Of course a 1.94 or 2.02 (or even a 2.08 for all I care) will fit but the proximity of the edge of the valve to the cylinder wall (on a 307's 3.875" bore) will tend to reduce the flow of the open valve.

A couple of questions regarding the Chevy (not the later Olds) 307:
1) Why were there no high performance versions made?
2) Why was production discontinued after 1973?

Nope, not slow and I never said my car was the quickest around. I'm just saying that for the money it would be a good investment. Besides, if you you build sbc all day, then you should know what the 327 is capable of.
:werd: the 327 wouldnt be used in drag racing today if it werent a good powerplant. theres a shitload of things you can do. hell i have a bunch of 383 parts if you were interested. you have a good starting point, go from there. the vortec heads are decent heads, but theres better out there.