Seems like the Chevy 302 is looked at as one of the better engines chevy ever built. Why is the 307 not in that same league. What are the reasons this is so. Stroke-bore differences? Was just something i was thinking about lately.

The 302, actually 301.594, (4" bore x 3" stroke) was built as a performance engine from the start for the early Z28 Camaro with high compression, hot cam, good heads, etc...GMs response to hot rodders that had been building the same thing (but coined a 301) for years. Take a std 283 and bore it 0.125 over to 4" and with the 3" stroke you have a lot of rev potential in a small package.

The 307 was introduced in 1968 when emission standards were kicking in and was meant to be a 'clean' engine to replace the 283, not a high performance one. The 307 retained the same bore as the 283 (3.875") but used the 327's stroke of 3.250" and didn't have performance parts.

I thought the 302 was a 327 block with a 283 crank????? Can you even bore a 283 that much??

I've not heard anything bad about the Chevy 307 other than it wasn't big on power, just an economy engine.

I don't look at the 302 as one of the better engines Chevy ever built. Yeah it came with alot of performance goodies on it, but IMO it's very impractical unless you plan on racing it or running a high winding engine on the streets. <----can get old quick

Other than being very close in displacement - there is nothing else close about the 302 vs. the 307.

Let's see:
Holley 4 bbl vs. Rochester 2 Jet
Aluminum high rise intake vs. cast iron low rise intake
Big valve heads vs. small vale heads
Solid lifter vs. hydraulic lifter
etc. etc. etc.

A couple of years ago in one of the small block engine masters challenges an engine based off a 307 block nearly took home all the marbles. John Beck from Pro Machine wanted to screw with everybody's perceptions of the lowly 307 and his entry came in a strong third place finish.

Thomas

I thought they built the 302 for the z-28 because of a rule in the trans am racing series back in the late 60's

we used 307's in our race car
they were bored 60 over to a 318
that way we could still use a 4 barrel
if we ran a 350 we were only allowed to run a 2 barrel
and no one ever ran 350's back then because the 307's would smoke em with ease due to the rules
plus they turned on so much quicker - due to the shorter stroke
those 307's were some good motors when they were built right

I thought the 302 was a 327 block with a 283 crank????? Can you even bore a 283 that much??


When GM built the 302 it was indeed a '327' block with the shorter stroke (ala 283) crank and intended to race Trans Am. But, hot rodders had been building 301s for years by boring the (57-64) 283 to 4 inches with little problems. Since GM already had a 4-inch bore block, it was a simple matter to drop the 3" stroke crank in and keep cylinder wall integrity.

I'd like to see the possibilities of a 307. That would be cool.

Everything and everyone above is 100% on the money!
It is a fact that the 302 was built in the very, very beginning as a pure performance engine. True, transam requirements were what stimulated the 302. True, the 307 was not intended as a performance engine, but rather an economy engine with a little more low end torque than the 283 (due to the added stroke). I guess you could kind of look at the 302 and the 307 as engines that got their cranks swapped. The 302 (4in bore, same as 327) got the 283 crank and the 307 (3.875 bore, same as 283) got the 327 crank.
The 302 got ALLLLLLLLLLLLLLLLL the hipo parts from the past and the 307 got ALLLLLLLLLLLLLLLLLL the economy parts from the past.
Yes, the 302 was strictly designed to do its best at high rpm levels, but, properly blueprinted and tuned, by a guru such as Bill Jenkins, a 302 could dyno at nearly 500hp (ya, ya, I know, that was at 8 bazillion rpm), but still, 500hp is 500hp. And also, keep in mind, this engine was built when EXPENSIVE premium gas (it was called ethyl back then) was less than .30cents/gal!!!

Now, let me throw in something about a 307. Anyone remember the 365hp, 375hp or even the 350hp (L79) 327 engines?? The ONLY difference between a 307 and a 327 is 1/8in bore. How about we remove the heads from a stock 307, increase the bore by .030-.060, swap the the flat top 307 pistons for 8 domed pistons, replace the stock 307 hyd cam for a really hot (.480 to .500in lift) cam and then stick on some mildly ported 2.02 heads (maybe from World) and stick on a very efficient intake and at least a 700cfm carb and something that makes pretty good spark, and guess what you might end up with. Will all of this cost more than a 350 crate engine? Probably. But, a 307 CAN be built into a very nice performer.

I think the CanAm rules stipulated no more that a 5 litre engine, hence the 302.

Ok, Who's ready to buy my 63k mile 307 motor sitting on my shop floor?????

Anybody??? :D

I'll bid $15.00 if you'll deliver it to Kansas City :)

But seriously, I just bought a nice 1970 Malibu "take out" that was replaced with a 502 complete for $200.00

I just sold my 307 longblock for $100, guy wanted it to put in an old pickup.

Nothing wrong with a 307. It has a bunch more torque than a 283 and you modify it just like you would a 283. No giant heads or cam.

We used to run a highly modified 302 in a drag car several years ago. Used to leave the line at over 9,000 rpm. Saw it reved to 10,000 a few times. To this day I have yet to hear another motor that sounds like that one did.

Another problem with the 307 (from GM's point of view at least) is that all other things being equal, it is a "dirty" (emissions wise) engine. In the small block family, the more over square (where the bore is larger than the stroke) the engine the more clean it can be. The less over square, or the more it approaches square (bore and stroke are equal) the dirtier it tends to be.

Part of the problem is that the smaller bore small blocks can't take advantage of the big valve heads, thus overall flow is limited, thus potential is limited. A 307 can benefit from any of the tried and true hot rodding techniques that show such great results on almost any small block, they just have somewhat less potential on a 307 due to it's disadventageous bore/stroke combination.

Everything and everyone above is 100% on the money!
It is a fact that the 302 was built in the very, very beginning as a pure performance engine. True, transam requirements were what stimulated the 302. True, the 307 was not intended as a performance engine, but rather an economy engine with a little more low end torque than the 283 (due to the added stroke). I guess you could kind of look at the 302 and the 307 as engines that got their cranks swapped. The 302 (4in bore, same as 327) got the 283 crank and the 307 (3.875 bore, same as 283) got the 327 crank.
The 302 got ALLLLLLLLLLLLLLLLL the hipo parts from the past and the 307 got ALLLLLLLLLLLLLLLLLL the economy parts from the past.
Yes, the 302 was strictly designed to do its best at high rpm levels, but, properly blueprinted and tuned, by a guru such as Bill Jenkins, a 302 could dyno at nearly 500hp (ya, ya, I know, that was at 8 bazillion rpm), but still, 500hp is 500hp. And also, keep in mind, this engine was built when EXPENSIVE premium gas (it was called ethyl back then) was less than .30cents/gal!!!

Now, let me throw in something about a 307. Anyone remember the 365hp, 375hp or even the 350hp (L79) 327 engines?? The ONLY difference between a 307 and a 327 is 1/8in bore. How about we remove the heads from a stock 307, increase the bore by .030-.060, swap the the flat top 307 pistons for 8 domed pistons, replace the stock 307 hyd cam for a really hot (.480 to .500in lift) cam and then stick on some mildly ported 2.02 heads (maybe from World) and stick on a very efficient intake and at least a 700cfm carb and something that makes pretty good spark, and guess what you might end up with. Will all of this cost more than a 350 crate engine? Probably. But, a 307 CAN be built into a very nice performer.

I'm thinking that a stock 307 short block could be mated to a set of stock Vortec heads, milled down to give about 9.8 static compression, with a Performer RPM intake, headers, a Q-Jet, and something like a Comp XE262 cam. With the right converter, gears, and tuning I bet you could drop it into a Chevelle and go 13's in the quarter mile. You'd go 13's easily in something lighter, like a Nova. Assuming the short block was free and needed no machining, you wouldn't have much over $1,000 in the motor.

There's a guy over at Steve's Nova Site doing 13's with a 307. Not sure what heads is using but I don't think their vortec or aftermarket. He has a 3rd gen, I think it's a '74.

edit: it's 14.02 and in a '78 (I was close)

I built a 307 that makes roughly a horse per cube with around $1000. Its standard bore with world products torquer 305 heads, about 9.5:1 compression and a 214/224 degree cam. I built the motor for the hell of it and I was very pleased with the performance.

i've got my Npva's original 307 yet- well, actually, it's in an 81 3/4 ton Chevy 4X4 truck right now- and have been pondering what to do with it once my cousin gets motivated to build a 350 for that truck..

Ok, Who's ready to buy my 63k mile 307 motor sitting on my shop floor?????

Anybody??? :D


LOL ... I was thinking the same thing, as I just pulled the numbers matching 307 (61k miles) out my '68 Chevelle and now it's sitting on the back of my trailer under a tarp.

Not sure what to do with it ... Take it to the dumps ... Let me 16yr. son pull it apart to see how a motor works ... Any suggestions?

Now how about the 305? even worth building anything out of one? I only ask because I have one on the stand that needs machining and I'd like to do something with it..possibly temporarily use it as a replacement in the Malibu until I rebuild the original 350. I know the bore is a wopping 3.735 with a 350 crank. I suppose what I'm asking is if it's capable/worthy of destroking, or some combo to produce a decent cruiser?

Hmmmm, the ideas are flowing now. My 69 has the original 307 in it, nothing wrong with it. I put a set of 350 heads on it, it really could use a 4 BBL intake and a better cam. The possibilities are endless :).