Why weren't chevy 307's and 305's used as performance engines? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-08-2011, 11:20 AM
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Why weren't chevy 307's and 305's used as performance engines?

When I grew up in the 80's, there were still LOTS and LOTS of 68-72 Chevelles and '68-'74 Novas around. I used to joke that you could walk over a busy highway overpass, be blindfolded, and drop a tennis ball over the overpass, and chances are you'd hit a Chevelle or a Nova! Even in the mid to late 80's....

Anyway, many of these cars came stock with 307's, and still had the 307 badges. In fact, my step-father owned a Chevelle with a 307, and I also had 2 other friends who owned Chevelles that came with 307's originally. Not to mention the people I knew who owned 307 equipped Novas.

However, when It came time to try and increase the performance of these cars, it seemed the first thing everyone did was to get rid of the 307, and replace it with anything from a 283-302-327-350, etc.

I asked why this was, and I was told by more than 1 person that the 307 was a completely different engine than the 283-327-350-400 gen 1 small block, and that it just wasnt any good for performance.

Later I learned that the 307 was in fact a member of that same gen 1 family, so why didnt people seem to like the 307?

Then we have the 305.......
I was also told by many of the same not-so-knowledgeable people that the 305 was also a different engine than the 350, etc., and wasnt much good for performance, even though it was used by GM as a standard equipment performance engine in the 80's-early 90's in several cars. However, many people still seemed to want to remove it and replace it with a 350.

Now, I can understand why someone would replace a smaller engine for a larger displacement engine, but that didnt seem to be the primary reason that people were replacing these 2 engines.... In fact, I met 2 different people who built 283's, and swore by them! Obviously a 283 is smaller than a 305 or 307, so why not use the 305 or 307 if its made from the same engine family?

There is also the 400 Chevy, and I know another guy who owned a '73 Nova who replaced its original engine with a modified 400, but it didnt last too long... The 400 supposedly has such a big bore that it effects coolant passages and wall thickness, which is bad for high horsepower purposes.

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Old 05-08-2011, 11:28 AM
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Old 05-08-2011, 11:47 AM
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305s 307s

Hello,These are my thoughts on this, We used to say," There is no replacement for displacement" 307 had a decent stroke, same as a 327, and 305 was the same as 350, but both had small bores, so it was allot easier and cheaper to find a 350 to replace it,350s were everywhere in the junk yards, and if you were lucky it was a 4 bolt main,put in a nice cam,intake and holley and have some fun..... Just my thoughts
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Old 05-08-2011, 12:33 PM
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Because in every line up you have to have your economy engines as well.
The 307 was created by taking two small blocks and combining them.
The 307 has the bore of a 283 @ 3.875 and the stroke of a 327 @ 3.250.
It came with a single exhaust, 2 barrel only carb, small valve big chamber wheezer heads, dirt low 8.5:1 compression ratio, low ignition timing and last but not least, a set of snail high rear gears around a 2.73 ratio. The only good thing the engine got was bad, which was a 300 horsepower 327 cam. However when used with low performance parts it didn`t help matters any. The next bad thing to happen which gave 307`s a really lousy rep was the cams went flat prematurely usually taking out the rest of the engine with it.
As for the 305, it has come in some "performance" applications, but they weren`t anything to brag on. The 305 was made using the 350`s stroke, but a small bore. The bore is 3.736 inches and the stroke is 3.480 inches. This
engine came along in 1976. It was deemed a good idea at the time because chevy needed a engine that was small displacement, made enough power and met emission standards for the time and the 305 did that. Chevy also got adventurous during the later years when they tried a 262 cube small block that was a failure, then later a 267 cubic incher that was also a failure. Both were discontinued after 2 years of use.
Chevy discontinued the 307 in 1973. The 307 can be built into a excellant performance platform with the right pieces. take a 305 and a 307, put a equal amount of cash into them both, then install them in identical cars with identical gears, the 307 will blow the 305`s doors off. The small bore of the 305 hurts breathing potential. The 305 was dropped from production in 2000.
The next question, why don`t many hot rodders build 307`s and 305`s?
Why put the money into small cubic inches when you can build a 350 not only cheaper but will make more power? If I were building a daily driver street engine where fuel economy was important I would use a 305 with a factory roller cam. Add the right pieces to it with the right rear gears and it`ll deliver excellant fuel economy and good power in a V8 package. I`ll likely never build a 307, they`re hard to find now days and they didn`t come with a roller cam block and all I use is rollers. Mostly I rob the crank out of`em, have it balanced, get a 1 piece to 2 piece seal adapter and slap the crank in a Vortec 350 block.
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Old 05-08-2011, 08:13 PM
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My 70 model Nova came with a 307 2bbl three speed standard. It had 17,000 miles on it when I got it. I installed a Tarantula intake Holley 1850 carb, Crower hydraulic camshaft and rev kit, Cyclone headers, Mallory dual point and a Muncie four speed. Car would run 13.50 quarter miles times all day long. Drove it back and forth every two weeks from Beaumont Texas to Abilene Texas for over a year with weekly trips to the Abilene drag strip. I wish I still had it.

Vince
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Old 11-10-2012, 06:47 PM
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My theory is that it is so much easier to get performance out of the 350, why bother with the 305/7.

Some performance cars, however, did come from the factory with 305's; Monte carlo SS, Z-28's transams etc. All of these could run mid to low 15's which, comparatively speaking to 350 equipped cars and others, is/was pretty good.
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Old 11-10-2012, 07:55 PM
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i think they were a boo boo. 305-307.not great mpg or power. the 327 move to 350 was cool but those inbetweens seem lost. i like em, you can build em. but they are kinda like a red headed step child of an engine.course they can haul *** , their chevys !!!when you do see one haulin *** its cool. them hot rods dont have to be super fast to be cool. they are street cars.course we all love power. i like a car that turns out for its intended purpose.power or mpg built.i dont like em so dang radical that you have to take off at 3-4 grand either. not to drive. ive done it. it sux.big boo boo
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Old 11-10-2012, 08:30 PM
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I've owned both. A 305 in a '77 Nova and a 307 in a '72 Nova. Both were good daily drivers, neither would break the rear tire (yes I said "tire") loose without dumping water under them.

I installed headers on both with header mufflers. They sounded good and overall I was happy with them. But performance isn't a word I would use to describe either of them.
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Old 11-10-2012, 09:06 PM
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I had a 307 in my 69 Chevelle and amount of money I spent of building a performance 307 was a lot. The result I end up was replacing it with a 350.
Had I started with a 350 it would be cheaper in the long run. To do the work on a 307 it would cost the same of doing the same work on a 350. 283 and 307 were the same engine. 2 barrel, 1.72" intake *****ty heads, small cam. Just a 1/4" stroke. Get a 350 4 barrel and you already gain 100 Horsepower right off the bat. As 305 goes, it is no different.The motors are the same family. 350 is just cost effective. 350 are a dime a dozen in junk yards.

Last edited by lg1969; 11-10-2012 at 09:24 PM.
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Old 11-10-2012, 09:13 PM
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off subject a bit but the 69 dz 302 was a little screamer. course today its no big deal but in its day it took little to get that sucker really runnin.out of the box they were dang tough to beat in two bits.
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Old 11-11-2012, 10:26 AM
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pre 1967 the 307 was popular as a stroker 283. in 1967 GM brought out the 350 and even the 327s popularity went down
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Old 11-11-2012, 12:00 PM
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yep, the 327 was the street choice in them days. then the 350 took its place. and did it well.if i had a 305 or a 307 id run em. no prolem. but a street car dont have to be all that fast for me. i dont care for a dog but even a 300 hp build is plenty to push one along.most folks never experience 300 hp. any engine can be improved in power. the 350 is proly the cheapest power out there. i like em but i aint gona use one in my chevy. maby a big block. im not a cookie cutter guy. hahaha..nothin wrong with the 350 at all. i just dont want to raise my hood and see the same engine in most hot rods.
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Old 11-11-2012, 12:55 PM
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Anything you can do to a 283 or 327 you can do to a 307.
But the stock 307 cylinder heads got to go. Once you bolt a high performance small chamber
cylinder head onto it, it becomes a high perf , high compression motor just like a 283 or 327 or 302 for that matter.

These 307 engines make a great low cost base for a supercharged motor using the 142 weiand blower. Replace the stock 307 heads with (the good) large chamber 76cc heads with large 1.94" x 1.60" valves and you are blower ready. Preferabily ported heads. The resulting low engine compression ratio is just right for generous blower boost and power on pump gas.
A low cr 7.5:1 307 with 10-12 psi boost makes a ton of power. (2.33:1 blower drive ratio)
Such a 307 SBC with a blower friendly moderate solid lifter street cam Crane Mechanical Flat Tappet Camshafts 113841 - SummitRacing.com will rev up 7000+++rpm and make well over 450 supercharged hp.
Be prepared to go fast.

The 305 is much the same story. Just cause the factory didn't hot rod these motors does not stop you from hot rodding them.

Last edited by F-BIRD'88; 11-11-2012 at 01:17 PM.
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Old 11-11-2012, 02:03 PM
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Just for interest some circle track associations require the 305 to keep performance and expense more equal and costs down..

Sam
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Old 11-11-2012, 02:41 PM
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I have always thought that Chevy either had and abundance of 283 blocks left over or an abundance of 327 cranks or they needed to keep running either or both of those parts to pay out tooling costs.

As far as the 305, it was obviously a mileage motor using the 3.48" stroke crank to bring torque readings up a little to move the heavier cars/trucks and still get decent mileage.
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