Small block carburation

[Alan Collins]

Work on my 1972 350ci 200bhp small block convertable is finally progressing. I am now putting my engine back together following a bottom end rebuild.

The previous owner fitted a higher lift, but relatively mild, Summit 1102 cam. The car is fitted with the original Californian Qudrajet carburator but the airpump and all associted emissions hardware have previously been removed. I have been getting poor mpg and having difficulty setting up the carb. I am planning a new exhaust system, possibly with Summit long branch headers. I had a recent conversation with a fellow enthusist who advised the carb. was too restrictive & recommended I replace it with an Edelbrock or Holley 750cfm carb. I have read from another source that 600cfm is best for 350ci road engines, 750 would be too large. This book also recomended an Edelbrock manifold being "far supperior to the standard one".

If I can simply and relatively cheaply gain power, economy and efficiency through period upgrades then I would like to. I am sure there are many club members with tunning experience, could you please offer me your wisdom and is there anyone with suitable parts for sale?

 

[Roscobbc]

Replacing your inlet manifold with an aftermarket high performance dual plane Edelbrock unit will certainty help to maximise other changes you may make. However you will need to.do some calculations relating to the reduced height/underhood space you'll have. Quadrajet carb if working correctly is a good unit but of a different mounting pattern to Holley and Edelbrock carb. Edelbrock carb is OK - its just that the Holley is perhaps a little simpler to re-jet and adjust and parts are easier to come by. Only buy a vacumn secondary carb (if you have an auto transmission) and perhaps avoid sourcing one of the cheaper versions that have fewer adjustment points. Some of these tend to be optimised for use with later 'emissions' type engines and will run quite lean.

 

[Chuffer]

I have just picked my C3 up this very day from specialists who really know their stuff about Chevy V8 engines and very high end rebuilds and drag racing . I had a tired old Holley 750cfm on my C3 as bought and knew it was way over size for a small block . They recommended the Edelbrock 600cfm now fitted . It has made a massive improvement now it is properly set up and the timing reset . 750 cfm is better suited to big capacity engines and wild cams . Why someone fitted a 750 on mine is anybodies guess . Probably the usual misconception of big carb , big power !!

 

[BobbyV8]

I have just picked my C3 up this very day from specialists who really know their stuff about Chevy V8 engines and very high end rebuilds and drag racing . I had a tired old Holley 750cfm on my C3 as bought and knew it was way over size for a small block . They recommended the Edelbrock 600cfm now fitted . It has made a massive improvement now it is properly set up and the timing reset . 750 cfm is better suited to big capacity engines and wild cams . Why someone fitted a 750 on mine is anybodies guess . Probably the usual misconception of big carb , big power !!

Glad to hear you're happy with your new set up

 

[mickn]

I have just picked my C3 up this very day from specialists who really know their stuff about Chevy V8 engines and very high end rebuilds and drag racing . I had a tired old Holley 750cfm on my C3 as bought and knew it was way over size for a small block . They recommended the Edelbrock 600cfm now fitted . It has made a massive improvement now it is properly set up and the timing reset . 750 cfm is better suited to big capacity engines and wild cams . Why someone fitted a 750 on mine is anybodies guess . Probably the usual misconception of big carb , big power !!

As I keep telling the wife, size isn't everything.

 

[Vetman]

I have an Edelbrock 2-plane alloy manifold no longer needed. This was fitted to my 1975 L48 350. Ok for my hood clearance. 75’s may have slightly higher hood than 72. This manifold is 1/4” lower than the performer air- gap I replaced it with.

Needs a clean up but otherwise working well when I removed it.

Where are you?

 

[Chuffer]

The new Edelbrock Performer carb is mounted on the Edelbrock Torker 2 single plain inlet manifold that was on the car when I bought it , but in hindsight maybe I should have swapped that out for a dual plain inlet at the same time for optimum performance all round . Having said that , the new set up has transformed the car beyond belief so I am well happy for now . As Ross said , vacuum secondaries are best suited to auto trans but early impressions of my new set up with mechanical secondaries and an auto trans are very pleasing .

 

[Roscobbc]

The Edelbrock carb is a much updated version of the 1960's carb, the Carter AFB which was used by a number of OEM's on performance type cars (and later bought-out from Carter). I think you'll it find works a bit like the Quadrajet in as much that it features mechanically operated secondaries but there is an 'interlock' that prevents the secondary chokes operating when there is insufficient vacuum to activate - this also obliviates the requirement for a secondary 'squirter' - wheras the Holley's mechanical secondary carbs (double pumpers) do not have that feature, requiring perhaps restraint from the driver when 'mashing' the gas pedal (and not such a good choice for and automatic)

 

[Roscobbc]

Work on my 1972 350ci 200bhp small block convertable is finally progressing. I am now putting my engine back together following a bottom end rebuild.

The previous owner fitted a higher lift, but relatively mild, Summit 1102 cam. The car is fitted with the original Californian Qudrajet carburator but the airpump and all associted emissions hardware have previously been removed. I have been getting poor mpg and having difficulty setting up the carb. I am planning a new exhaust system, possibly with Summit long branch headers. I had a recent conversation with a fellow enthusist who advised the carb. was too restrictive & recommended I replace it with an Edelbrock or Holley 750cfm carb. I have read from another source that 600cfm is best for 350ci road engines, 750 would be too large. This book also recomended an Edelbrock manifold being "far supperior to the standard one".

If I can simply and relatively cheaply gain power, economy and efficiency through period upgrades then I would like to. I am sure there are many club members with tunning experience, could you please offer me your wisdom and is there anyone with suitable parts for sale?

Hi Alan - nice to see that you are using a 'mild' cam for your engine. Too many people think that if little more is 'good' -then even more is 'better' still and wonder why they have drivability issues. There is nothing wrong with a Quadrajet carb - however it could be knackered and needing replacement. You can get refurbished ones I believe. The issue you may find is sourcing a wide range of aftermarket inlet manifolds as the Quadrajet has differing choke sizes for the primaries and secondaries and a differerent bolt pattern. Holley and Edelbrock share the same bolt pattern. Me, I'm old school and prefer the simplicity of tuning the Holley - nothing wrong with Edlebrocks carb - some people love 'em. Headers with help performance in conjunction with the other modifications. You may want to consider the expense of buying a pair of aftermarked cylinder heads.......and given the funds........Edlebrock's ProFlo4 is getting some great reviews Edelbrock.com: Edelbrock Pro-Flo 4 EFI Systems

 

[antijam]

.......There is nothing wrong with a Quadrajet carb - however it could be knackered and needing replacement.......

I had all sorts of running problems on my sbc fitted with a quadrajet - popping and banging on the overrun and severe bogging as the secondaries opened. Despite rebuilding the (non original) carb myself, the problems persisted. Finally in desperation I bought a properly rebuilt Quadrajet - correct for my year - and after some rejetting the car now runs beautifully. The humble old Quadrajet is somewhat looked down upon by Holley and Edelbrock afficionados, but properly set up and maintained it's just as effective.

 

[Roscobbc]

I had all sorts of running problems on my sbc fitted with a quadrajet - popping and banging on the overrun and severe bogging as the secondaries opened. Despite rebuilding the (non original) carb myself, the problems persisted. Finally in desperation I bought a properly rebuilt Quadrajet - correct for my year - and after some rejetting the car now runs beautifully. The humble old Quadrajet is somewhat looked down upon by Holley and Edelbrock afficionados, but properly set up and maintained it's just as effective.

Potentially best of both worlds - small primaries for good low speed operation and economy (relative) - 'kin big secondaries for top-end stuff. Those Quadrajet have a lovelly 'howling' sound when hitting the gas pedal hard using an open air cleaner element

 

[Chuffer]

The Edelbrock carb is a much updated version of the 1960's carb, the Carter AFB which was used by a number of OEM's on performance type cars (and later bought-out from Carter). I think you'll it find works a bit like the Quadrajet in as much that it features mechanically operated secondaries but there is an 'interlock' that prevents the secondary chokes operating when there is insufficient vacuum to activate - this also obliviates the requirement for a secondary 'squirter' - wheras the Holley's mechanical secondary carbs (double pumpers) do not have that feature, requiring perhaps restraint from the driver when 'mashing' the gas pedal (and not such a good choice for and automatic)

You also don`t get the power valve `blow out ` problems caused by back fires with the Edelbrock as there is no power valve .

 

[Roscobbc]

You also don`t get the power valve `blow out ` problems caused by back fires with the Edelbrock as there is no power valve .

 

[Roscobbc]

The higher spec' Holley snd generics tend to have power valve 'blow out' protection these days. Holley vs Edelbrock? Do you prefer fiddling with needles and things - or - replaceable jets? Buyers choice. Ideally I'd prefer the idea of self learning injection like ProFlo4 as I can see all operating parameters (like a/f ratio, timing etc) on 'the fly' and adjust/override if I want.....