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Discussion Starter #1 (Edited)
Question: Is a 3.74" bore REALLY the 305's limiting factor?

When I got my Nova almost 16 years ago now, it had the factory 305 2bbl. As a high schooler, I was mighty proud of it. Older folks always said 305's sucked and had no potential, because it had a small bore. Without a 4" bore, it would never breathe well because couldn't fit the coveted 2.02/1.60 valveset the 350 ran.

Later, the LS engines, and their domestic competitors the 3rd Gen HEMI and now Coyote 5.0s emerged. I've noticed several of these engines have < 4.00" bores and produce respectable horsepower. I realize the head technology is night and day alongside the 305, as well as the valvetrain and bottom ends.

And for the record, I've been running a 350 +0.020" for almost eight years now.
 

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I can tell you from experiance that in NHRA Stock Class racing, there are 305 engines that can make equal to, and a bit more H.P. than a 350 in cetain classes.
 

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check my you tube channel. I build 300 +hp small blocks all day. especially 305's. I love 305's. "small" bore and long stroke. really just a small bore 350. Key is not to over cam it ( like the old 283's ) and make it breathe well. 305's with good heads ( not stock) are great on the street where torque is king! and with fuel prices going up and up.... they are better on gas than a 350!!! I have a bretty beefy 305 i built in my 83 z28 and it will pull into the mid 13's with 3.42 rear and good trans. and that camaro gets over 20 mpg ( if I keep my foot off the giggle pedal...)
 

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The 305 is an OVERSQUARE engine, meaning the bore (3.736) is greater than the stroke (3.48)
 

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The small bore kills the 305 for many reasons. Sure you can make some power with it but it will NEVER equal a 4" or larger bore engine. The small bore does not allow you to run GOOD heads with LARGE valves. The small bore actually shrouds the valves and impedes the air flow. The 4.125 bore engines (400) are even better than the 4" bore 350 because the bore is big enough to unshroud a large valve head.
 

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DPack77,

What do you want to use the engine for? Racing, fuel mileage, overall good street motor? If the shortblock is in good shape then consider placing some of the best flowing heads Chevrolet has ever developed...the Vortec head, with 1.94 intake valves, and 1.50 exhaust valves. Consider using the Edelbrock Performer, or Performer RPM intake, a torquey camshaft, and an Edelbrock 600 cfm carb. It should take off quick, top out at about 5000 to 5500 rpm and get good fuel mileage. At least that has been my experience. I'm sure other SNS members will chime in with their experiences.

Food for thought,

Ed
 

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Bore diameter is not the limiting factor to the 305 engine. The limiting factors in OEM configuration are poor cylinder head design and excessive deck clearance/insufficient compression height. I've disassembled 305's that have had the tops of the pistons as much as .060"+ below deck at TDC! This eliminates all quench and makes for very, very lazy mixture motion in the chamber. Couple that with an inefficient/ineffective combustion chamber design along with lazy cam timing and that it is why the 305 is notoriously weak on power production as well as overly pre-ignition/detonation-sensitive in OEM form.

A good example are the 4.8L and 5.3L Gen-III/IV engines; 3.78" bore diameter. A crazy amount of power can be extracted from these engines without ever touching the basic long block. Why? 15-degree cylinder heads with outstanding runner design, valve placement, and combustion chamber design, as well as a vastly superior valvetrain, and improved firing order as compared to Gen-1 small block architecture.

Is it easy to build a 600 horsepower 305? Nope. It doesn't come easy in a 4.000" bore or 4.125" bore Gen-1 engine either, even though magazines and marketing departments would have you believing differently. However, if you're comparing specific output in terms of horsepower-per-cubic-inch and brake specific fuel consumption then the 305 can easily be built to rival larger displacement/larger bore engines. Properly modified small displacement small blocks such as the 283, 305, and 307 are still viable choices for the person wanting V8 performance coupled with decent fuel efficiency and good street manners.

For the "no replacement for displacement" crowd unfortunately that age-old saying has worn itself out in this modern era of efficient and affordable power adders. Add some boost or nitrous to any of these small displacement engines and you can quickly embarrass many big block combinations on the street or at the track. It is so ridiculously simple and affordable to turbocharge an engine these days that displacement is no longer relevant.
 

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Discussion Starter #11 (Edited)
Pete: Awesome feedback--thanks for the insight! (And thanks for reading the whole question).

SmoKum: You're right, my apologies. I meant less than 4.00", but got ahead of myself. Original posted updated.

Ed: I run a 350; but I appreciate the feedback. Just asking why the 305 is considered junk with a 3.74" bore, but the 5.3L is considered desirable with a nearly identical 3.78" bore.

Thanks,
Doug
 
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