350 and 305 Chevy what's The Difference

hey everybody welcome back today I want to talk to you about the difference between a 305 Chevy and a 350 Chevy these are both small block engines and there's been a lot of confusion I've had a lot of questions um there's a lot of disinformation about these two engines out there as to what the differences are first of all the 305 and the 350 Chevy are both part of Chevrolet small block family externally if you were to look at these engines on an Eng stand and I've got um a 305 and a 350 behind me here I'm going to show you the difference here in a minute but if you were to look at these engines fully assembled on the engine stand you would not be able to tell the difference because dimensionally on the outside of the engine they are identical they're virtually the same a lot of the parts are interchangeable the heads the intakes the exhaust manifolds a lot of the pulley and belts so there's really only one difference well there's there's more than one but there's one basic difference between a 350 and a 305 and that is the bore size so this is a 305 Chevy and if you'll notice that I wrote the size on here the 305 has a 3in 760 bore size which is right at right at about 3 and 3/4 in right next to this we have and I want you to make a note of the the bore spacing here all the meat between these cylinders and the size of that cylinder right next to it here I have a 350 Chevy which has a 4in bore and if you look at the meat between the cylinders here it's a lot thinner and it's a much bigger bore to give you some contrast let me grab some calipers so this is a set of dial calipers and what I've done here is I've set the ID gauge for the bore size on the 350 which is 4 in so you can see that's sitting right in there now if we take this over to the 305 you can really see the difference here if I try to get this into the 305 bore yeah it's it's not happening that's how much smaller that bore is so we got quite a difference if I put the edge of this here you can see the difference in bore size so the 305 is a significantly smaller bore it's about a quarter of an inch smaller Chevrolet did have some other small blocks like the 307 and so forth that had a shorter stroke a little bigger boore but it still wasn't 4 in so the bore size is one of the major differences that we have here but the reality is 350 Chevy and 305 Chevy have the same crankshaft and they have the same connecting rods the only difference between these two engines is the bore size they have the same stroke crank which is um 3.48 just a little bit less than 3 and2 in so you can actually interchange the crankshafts on these engines as long as you get get you know get them rebalanced um the heads are also different now what they did with the 305 is the head's identical as far as the physical dimensions of the head but what they did is they changed the combustion chamber size is a 350 head and it has a 76c combustion chamber here so this is what they use on the typical 350s and right next to it we have a 305 head which has a 58cc chamber so if you look at this chamber you can see this is a much smaller chamber and what they did is they made a smaller chamber because they had less cylinder volume and so they had to make a smaller chamber to get the compression ratio where they needed it one of the things that a lot of guys do is they take these small chamber heads and they put them on a 350 to bump the compression up which does work the problem with that is is that the port flow on the 305 is pretty poor They Don't Really flow very well and they have smaller valves now this head has actually had bigger valves put into it so this head this 305 head actually has a 350 valve in it it has a 194 intake and A5 exhaust which is the same valve that's in this head but we ran this head on the dyo and this 58cc chamber head went onto a 350 and it made about 11 1/2 to one compression so we bumped the compression of the motor up by putting the smaller chamber head on it with the big valves in it you know what the result was the result was we gained no horsepower the the engine virtually made the same horsepower it did with the open chamber 350 head and the big valves because a lot of it is about airf flow so a lot of times guys will sell these 305 heads on the Internet or whatever and they'll say Hey you know close chamber heads 305 heads with big Chevy valves and they they tout those heads like it's some kind of a performance thing don't fall for that believe me we had to run 106 octane fuel in this motor because it was over 11:1 with a 305 heads so it was 11:1 compression and it has big valves in it and it had absolutely no horsepower gain over the open chamber 350 head because because the valves were shrouded so badly in the chamber and also uh the port flow they don't flow air so 305 heads on a 350 yes you can put them on yes you can bump your compression up but quite honestly you're wasting your time and your money doing that you don't really want to because you're not gaining anything so hopefully that makes sense I hope you guys uh you know you can glean some from this because and you know 305 heads they the or 305 engines rather they have kind of a bad reputation 305s um you know they're it's not a 350 I understand that and it's probably not going to make the power of 350 but they run okay I i' I've I've had some customers that built 305s because they wanted you know they just wanted a small cubic inch motor they wanted the economy if you build them right get the right piston and head combination get a good intake and a good exhaust on it they run okay they're not bad um you know they they I I hear a lot of people oh 305s are just absolutely garbage and junk well a lot of that comes from the fact that people have taken 305 heads and put them on a 350 and and they're kind of disappointed and they're like man this thing is really a piece of junk but the reality is is that 305 engines they're they're okay I mean they're not bad you can make a little bit of Power with them um I was watching a show there's a show on the internet called engine Masters and you may be familiar with it um I'm a a real big fan of these guys uh Steve dolz DOL that's what fryberger calls him David fryberger from Hot Rod Magazine uh Mike finnean they do a show called roadkill um absolutely the best Hot Rod shows ever on any media TV internet or whatever if you really want to get indoctrinated to become a hot rod guy watch every episode of roadkill with Mike fenegan and David fryberger fantastic I love them I don't I never miss an episode and it's because I can relate to these guys so basically what happened with those guys was when when they took over hot rod many many years ago they turned it into something that the average hot Roder out there can relate to because before they were there Hot Rod Magazine was basically you know bikini girls and show cars and what they did is they took it and they brought it down to the real world where we're thrashing on the car you know in your garage or in your backyard or wherever trying to build your own hot rod and they've really what the reason that they are so successful is because they have really touched on a nerve with hot roders out there because we're we're able to relate to what they're doing on roadkill and they do a lot of comparisons on engine Masters but anyway they took a 305 on engine Masters if you get a chance watch it and they put nitrous into it well they ended up blowing the motor up but that's because because it had stock pistons and stock ring end Gap had they opened up the rings on that motor and gave it more clearance it probably would have kept running and made a lot of power but that 305 made really good power on the dyno for what it was so it was it was pretty impressive so you know if you got a 305 out there you know a lot of people going oh that's a piece of junk just get rid of it they're okay you know if that's all you got and and you want to run one or or build one go for it um so hopefully that helps you I mean really the only difference is the boore size the 305 has a smaller boore it has less cylinder volume the crank and the connecting rod and the stroke is exactly the same so if you have any questions or comments make sure you post them below I'm sure I'm going to get a B bunch of comments from people telling me that 305s are absolute garbage and you should never build one I'm sure I'm going to get that but eh you know you got to be open-minded this stuff so post any comments or questions you have below I'll do my best to get back to you I know I don't always respond right away I get 300 emails a day man um I'm trying so uh I'll talk to you soon and I appreciate you watching thanks

Channel: Myvintageiron7512

Views: 701,398

Keywords: Mouse, Rat, GMC, Chevrolet, Mopar, Rat Rod, Hot Rod, Roadkill, Shop, High performance, Turbo, Boost, Blower, supercharger, Ford, Camero, Impala, Nova, Chevelle, Corvette, LS, 283, 307, 327, 383, 396, 427, 454, Olds, Buick, Pontiac

Id: 0K1yGXct_sg

Length: 9min 47sec (587 seconds)

Published: Tue Nov 22 2016