richo

355HZ

CID x RPM / 3456x VE %=CFM

Sooo 253x 5000 (max for a crap 308 cam) /3456 x .75 (approx ve for an old engine)
This gives us a very rough calculation of intake flow: 274.5 cfm

350 will be fine tho saying that i had a 253 with just a few more goodies than urs (plus it reved to 6800rpm) and that ran fine with a 600 vac seconds and didnt use as much fuel as i would of thought.

richo

cheers 355hz i'm heading to the shed to fit the 350 and maniflod.thanks

ahk068

I'm leaning towards the too big, too small theory. Factory 2 barrell manifold isn't real special. Quady or a vac sec 465 on a stock 4 barrell manifold would be the go but i'd definately run the 350 first. As a temporary measure you could put the 350 on the 4 barrel manifold. redline make an adapter. I've done it before and it isn't perfect but its better than the two barrel manifold

BossHoggett

Took the words outa my mouth.
i dont endorse 350s for a start....Carter ! least they have metering rods, so you do get more than 1 dimention of tune. and theyre rated closely at 410.

wabbit

throw the 2 barrel manifold

2barrel and 4 barrel Holleys are measured differently. using the same pressure drop as a 4 barrell, a 350 measures about 270cfm.
the 350 has the same size throttle plates and venturis as a 450 or 465, but the 4 barrell has the secondaries to help things along at higher revs.

a 600 flows more in the primary side than a 350 does, so is less responsive at lower revs....



NOW,
let's throw all that out the window, because Edelbrock (MAY) use a different baseline for measurement. I'm not sure.
Is the edelbrock squarebore or spreadboreÇ

355HZ, that calculation really is only a baseline. it works for grandpa in his Statesman, but lighter cars and prescribed usage willo change that.
remember that Holley recommends a larger carb for a lighter body, such as a Mustang.
that calculation is designed for 4 barrel carbs on a 3500 pound car

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greenhj

changed my mind

400HPONLPG

Spot on wabbit , that calc is for 350 Chevs with 23 degree heads , and not all statesman owners are Grandpa's

wabbit

not yet, 400

not yet

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GTR308

a 600 is too big a mech sec 450cfm 4 barrel 4360 series holley is the go, they will bolt straight up to a std 4 barrel manifold.

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308 performance centre, perth

rodrat

yes for both....

the ideal CFM carb will be for a 4.2 litre = a 450 unless your pulling high revs find a 500CFM...but a 450 and no higher will push that torque to ideal levels..Yella Terra will help but seeing it is a 253 you wont need huge ammounts of flow..bear in mind.

wabbit

I disagree a lot

Keeping mind that I'm not a fan of double pumpers, anyway.
a 450 would be near perfect for a 253.....with vacuum secondaries.

it really depends on proposed usage. except for strip work, I can't think of ANY situation where a DP would be better on a 253........unless it was grossly worked.....
like a stage 5 cam and stuff, man

I'm pretty sure that I've read that you build engines for a living, GTR308, and I'll respect your opinion, but IMO a proper street 253 won't handle a DP, even a 450.
a driver that can adjust to the shortcomings would make it so, but if my MUM can't drive it, it's not streetable. I don't mean that she has to enjoy it, she just has to be able to drive it.
I'm being generous there,too. My mum is a better driver than my wife and 2 eldest kids.

EvL253 wll have a lot of arguments on this subject, too.
his 253 has a new generation 750DP. i like them. i like annular boosters

whoops.....might be nearly time to pull the old head in......what's a 4360, GTR308Ç

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GTR308

its not a D/P, its mech sec but not a double pumper, it has a very sensitive secondary booster and therefor does NOT need a acc pump on the rear barrels. they work extremely well when set up properly on a good 253, yes i am a engine builder and yes i have tried them many times, and yes they work well. my old 253 did 13.7 qtr in my LH torana 14 years ago with that carb and it got 26mpg open road and 23pmg around town with 3.55 gears. i scalped many 308s and a few chevs with that combo on the street.

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308 performance centre, perth

wabbit

i stand corrected

so the 4360 that you speak of is one of the new generation Holleys(insert Q mark..etc)

thay all have the annular boosters (insert Q etc)

BUT, they are a mechanical secondary, without a secondary accelerator pump (Q. etc)

that does change things quite a lot.
I understood these carbs even less than I thought I did

over to you, GTR308

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GTR308

they are called a 450 economaster series they were designed as a direct replacement for a rochester they even look a bit like one, they are also a slight spread bore design, they are not the same as the new gen holleys no annular boosters either. they are brilliant carby if you know how to make them work. problem with the 465 vacs is they wont open much till 4500+ rpm even with the lightest secondary spring. thats why the 450 is a better option

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