Why do you think Chevy went with the small bore (265 c.i.) 305, when the blue oval manged to pass emissions & get decent gas mileage with heir 4"x3" 302 in all kinds of vehicles for years?

If Ford did so well with their 302, what was the Chevy engineering dept thinking when they went with the hard-breathing, detonation prone 3.75" bore 305?

 

GM was probably thinking how much cheaper it would be to use the same block casting only with a smaller bore to meet the emissions laws/standards of that time...rather than refit and retool the whole shebang. It's all about the $$$$$$.

 

Aren't smaller bore less prone to detonation?

 

Yes they are! The 305 is actually less detonation prone than a 350. 350s of the same year ran roughly 1/2 to 1 full point of compression less than a 305. A 78 350 was advertised at 8.2:1 and runs less than that in actuality. The 305s also had a smaller camshaft, further increasing the dynamic compression ratio.

 

Greenyone,

Yes, I kind of figured it was ultimately all about saving some Chevrolet corporate bucks.

I bet there would have been be a lot less "Forget the 305, just swap in a 350" here if Chevy had simply made a small cube combo using the 4" bore x3" stroke 302 instead of Mr. small bore 305.

Then again, the 302 equipped Mustangs then were still a lot lighter than 3rd gen Camaros.

Water over the dam, just thinking.

 

GM was able to re-use exhaust parts, intake manifolds, cams, head castings and flywheels between the 305 and 350.

A non-HO 302 Windsor and 351 Windsor have difference balance, firing order, deck height and other stuff I forgot. These prevent the parts sharing to the extent I mentioned above.

Financial advantage: GM.

 

Don't forget Chevy done the 302 1st in 1967, before ford did it in 1968.

My take on your question though is torque, fuel mileage and price.

The short stroke 302 did not make as much low RPM torque. By limiting the bore and keeping the long stroke they had a small cube, emission legal, good fuel mileage engine that had good torque and that torque helps to sell cars.

The chevy 305 is not a BAD engine, it is just a bad choice for performance use, higher RPM use. I mean really go drive a '84 Z28 5 speed car and from 1st to third gear you really forget it's a 3400 lbs car with only 150 HP.

Us gear heads can't leave well enough alone and we want more power, more RPM.. At that point the small bore of the 305 becomes a factor as the engine can't breath well at RPM even with major mods... It's the engine with asthma

 

The Frod heads were better BY FAR than the GM ones.

Look at the head bolts. Frod uses only 4 bolts around each cyl; the SBC uses 5.

A design decision made back in the 50s, when gaskets and all that goes around them, was FAR less reliable than today. Back then, the SBFs were TOTAL CRAP; go drive a 272 or 292 car vs a 283 car (stock vs stock of course, including 1957 gasoline and motor oil) for 100k miles (pretty much the lifetime of a car back then), you'll see. (speaking strictly as someone who worked on a 57 Frod with head gasket problems in 61 while my mom P&Med at my dad while he was trying to do his best)

Fast-forward to 1986... sure, the compromises the Frod engineers made back then, turned out to be advantages once the surrounding technologies changed, and the less restrictive port routing turned to their advantage. Plus of course, the fact that their cars in the late 80s, were about as substantial as the foil you wrap your corn cob in when you grill it.

Oh, ..... did I forget to mention, ... you think OUR cars from the mid 80s are "rare" today... well just TRY to find an equivalent Frod product (Mustang, Capri) from the same time frame, that's still capable of actually DRIVING under its own power. Even some lame-a$$ 6-cyl one. The CAR, regardless of the "motor", was a total piece of monkey excrement. Pushing around 400 lbs less will make even the PIDDLIEST motor seem DIVINE by comparison, if you forget to take that into account.

 

Most of the "critical" parts between the 302 and 351 are interchangeable. The intakes are different between the two because of the deck differences like you mentionted, but the cylinder heads are usable by both 302's and 351's equally.

I'll personally take my notch any day of the week over a typical thirdgen. The real question is: why did Ford even bother with the 302 when the 351 fits directly in the same place with very little adjustments needed..

 

CAFE

You'd think they would have offered the option in some limited form though.

 

They did! It was called a Cobra-R or a Lightning.

 

Cobra R's are at the end of the foxbody era, and that's REAL limited production (still counts though, I guess).. haha. The Lightning is cool for a truck, but the 351 model is meh. They could've built a nice bruiser out of the typical notchback or hatchback models with a 351W installed.

 

As was said, above, the GM 305 was for COST SAVINGS. But it was also for EMISSIONS and fuel economy. Cost has been covered. But not mentioned to this point is the fact that smaller bore motors also burn cleaner and more efficiently than larger ones. That was very important in the era before cylinder heads were built with little regard to the swirl and tumble of the incoming mixture.

If you look at later LS motors they STILL TO THIS DAY don't use a bore/stroke ratio like a plain-jane Gen1 350. Yes, some of the more exotic ones might, but not your typical work-a-day 5.3 or 6.0L engines that GM pumps out by the kazillions. They STILL TODAY try to keep the bore on the smallish side and make the displacement with a longer stroke.

Ask some of the guys who have built performance-oriented 305s using Trick Flow 305 cylinder heads (the ONLY readily available 305-dedicated cylinder head on the market at a regular-guy price) how well their combo works. Most will tell you it kicks some serious *** for its displacement. If you put a head on top that can actually fill those small bore cylinders, it can make power like the designers of those wheezing, low compression 305s never dreamed of back in the 70s and 80s.

 

the only advantage of a bigger bore is the ability to use bigger valves, which allows more airflow. from a combustion standpoint, it's actually more beneficial to have a smaller bore. the cookie cutter gen3 and gen4 engines (and even the new direct injected gen 5) that GM produces by the millions every year all have small bores with long strokes, and they make it work because they designed some awesome ports that move a lot of air really fast at low lifts and stood the valves up straighter to help those ports get air in and out of the chamber. yes, it's true that GM does make some really awesome big bore (4" and even 4.125") engines, but those aren't the cookie cutter engines that make up the vast majority of the fleet..

 

Damon & Novaderrik,

Pretty astute & interesting engineering observations. Certainly all makes sense, & explains a lot.

 

it's the kind of stuff you absorb when you subscribe to half a dozen car magazines for a couple of decades..