pcmhacking.net

Hi Guy's

Any ideas what size CMF carby I should get? The problem is I have no history on this engine, except it's been rebuilt for burn outs all I can tell from the outside is it has 4 barrel dual plain inlet, extractors the cam is not stock I was told (no idea of cam size/type).

Any tips or advice on how to work out best option would be great

Is the manifold a square bore or spread bore pattern? Or both?
There is a formula to calculate cfm but I would just stick with a Rochester. Pretty sure you can still get jets and metering rods for them.

here is a picture of it

Spread bore ...

500CFM = 439.236 = (253 * 6000) / 3456

CFM = (CI * MAXRPM) / 3456 ...

Technically 500CFM is a bit large.

What carby do you think would be the cheapest option but brand new? I'm on a tight budget. Been looking around not 100% sure what one to get. All the other V8's I've worked on had a carby so I just rebuilt kitted them

oh forgot what if the cam is a mild one will that make a difference to cfm? I know the cam is not stock.

Any new carby will be expensive.
Search around and you should be able to find reman ones.
I would still go the Rochester, particularly if in a VH. More so if regoed. Pick one for a 253 blue motor. Should be plug and play with the throttle cable, no electric or manual chokes to mess around with. And no power valves to sort out. Worst case might be one size up on the primary jets and new metering rods. Could be wrong but thought the PCV connection is in the base plate of the carby and Holleys don't always have this???

If going a Holley, a 450 spread bore is an option, or the 465 square bore with the adapter plate. Both of these will be more expensive than a Rochester if bought new, possibly around the same or cheaper if reman. Holley 450 would be the pick of them, but need to get one jetted to suit your engine.

Put a Rochester on it, from someone like this. https://hume.com.au/product-category/ca ... quadrajet/

Thanks guy's looks like I'm getting a Rochester it's going to be a road car when finished. The prices are what I expected to spend, so get this one don't see 253 listed

Rochester Quadrajet Holden VB Commodore 308 5L Carburettor 17059594

Hey Guys! is this the right one? https://www.ebay.com.au/itm/Rochester-Q ... SwvGteHlNM

Not sure on the ebay one. Could be the right one. But be prepared to put money into it though. Might just need a kit but its an unknown really. Could you look at it before buying?

If buying a reman carb, at least you know the secondary air valve diaphragm is good and the throttle plate wont be warped. A Rochester for a blue motor 308 would be fine too. I thought it was just the secondary metering rods and the primary jets that were different over the 253. If you have a mild cam, it could be a better start.

From the photos on the Hume website, the idle screws have also been uncovered so that will save you some work.

But what else do you need? Do you have the air cleaner, throttle cable bracket, auto choke piping etc?