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350 and 305 Chevy what's The Difference



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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

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's small block

family externally if you were to look at

these engines on an engine stand

i've got 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 pulleys and belts

so there's really only one difference

well 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 three

inch 760 bore size which is

right uh right at about three and three

quarter inches

right next to this we have and i want

you to make a note of the

the bore spacing here all the meat

that's between these cylinders

and the size of that cylinder right next

to it here i have a 350 chevy

which has a four inch 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 four inches 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 board 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 and a little

bigger board but it still wasn't four

inches

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 on 3.480 just a little bit less

than three and a half inches 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 heads 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 76 cc 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 a 1 5 exhaust

which is the same

valve that's in this head but we ran

this head on the dyno

and this 58 cc chamber head

went on to a 350 and it made

about 11 and a half 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 air 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 to 1 with the 305 heads so it

was 11 to 1 compression

and it has big valves in it and it had

absolutely no horsepower gain over the

open chamber 350 head because

the valves were shrouded so badly in the

chamber

and also the portflow 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 a 350 but

they run okay

i i've 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 hear let me because oh 305's 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 they're kind of

disappointed and they're like man this

thing's 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 real big fan of these

guys

uh steve dulches dolcek that's what

freiburger calls him

david freiberger from hot rod magazine

mike finnegan they do a show called

roadkill

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 finnegan and david freiberger

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 rodder 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

rodders out there because 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 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've got a 305 out there

you know a lot of people get 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 build

one

go for it so

hopefully that helps you i mean really

the only difference is the bore size

the 305 has a smaller board 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

bunch of comments from people telling me

that 305s are actually absolute garbage

and

you should never build one i'm sure i'm

going to get that but yeah

you know you got to be open-minded to

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

i'm trying so uh i'll talk to you soon

and i appreciate you watching thanks