carb questions

Can I put a holley 750 W/ vaccum secondaries on my 84 caprice? I just bought the edelbrock cam, valvesprings, lifters, intake and roller rockers for the stock 305. I really don't want an edelbrock carb because I have had some bad personal experience using them. if a holley won't fit, what other options do I have? would the throttle cable bracketry work with the holley? would the vaccum lines even hook up to it? Any help would be great.

on a 305 a 750 holley is going to be too much carb. You'll do much better with a 600, or I think they even have a 480 or 500cfm. That said you'll probably still need to play around with the jet sizes cutting them back to .055 or possibly smaller. If I remember correct my 350's holley 600 is running .060 jets down from the .067's that it came with and it's still using a little too much gas.

If the Holley Spreadbore is still available, they are direct replacements for the QJet. I believe that they were offered as 600 and 750 cfm. I've used them on pre-computer applications with great success.

Bob

Can I put a holley 750 W/ vaccum secondaries on my 84 caprice? I just bought the edelbrock cam, valvesprings, lifters, intake and roller rockers for the stock 305. I really don't want an edelbrock carb because I have had some bad personal experience using them. if a holley won't fit, what other options do I have? would the throttle cable bracketry work with the holley? would the vaccum lines even hook up to it? Any help would be great.

Keep in mind that factory E4ME Qjet is the only carb that won't require you to disable the car's computer system and install a distributor with a vacuum advance...

on a 305 a 750 holley is going to be too much carb. You'll do much better with a 600, or I think they even have a 480 or 500cfm. That said you'll probably still need to play around with the jet sizes cutting them back to .055 or possibly smaller. If I remember correct my 350's holley 600 is running .060 jets down from the .067's that it came with and it's still using a little too much gas.

Umm, Not to start any arguments, but you DO realize the E4ME Rochester flows 780 SCFM @ 28" H²O, right? The beauty is that with proper AV spring windup and pull-off adjustment, the Rochester will tailor flow to load more appropriately than the Holley, which most likely comes out of the box more closely tuned to a 350 CID engine. It will work equally well on a 283 or 502 BBC.

What's more important here is that the E4ME has a far better vacuum signal than most out-of-the-box 4150s or 4160s, and unless you are willing to spend a week exchanging venturi pods in the Holley, rejetting multiple times, adjusting the float every time, tweaking idle mixture rates, adjusting to compensate for the poor (too rich) transition circuit in the Holley for a 305, swapping power valves and secondary AV springs, etcetera, you'd be better off staying with the Rochester.

This doesn't even consider the fact that the E4ME already has the necessary TPS so the ECM can operate, and the MC solenoid to enable the Rochester to maintain correct emissions AND get better fuel mileage. If you want to out-power the Holley, switch to a different secondary metering rod hanger and DR rods in the Rochester. It's a lot easier, and a lot more sophisticated design tha the generic 4150.

Just my 2¢

Thanks for all the good info. I think im going to stick with the rochester after hearing how good it is. maybe I will get a holley for when i finish rebuilding the 350 I have for it.

Frankly, unless you're going all-out race, and don't care about part throttle mixture, the typical Holley is not a good choice. I "race mode" the 4160 Holley (or its offshoots and clones) can be adusted further to accomodate different power valve vacuum ranges, have two accelerator pumps adjusted to just the right volume for best launches, meter the full-flow mixture quite well, and deliver a richer secondary flow faster than the Rochester. That's all great so long as your throttle only ever sees two positions - Idle or wide-open - Nothin' in between.

For a street carburetor, even a Carter ThermoQuad or AFB would be a better choice, although inferior to the QuadraJet. Despite the marketing hype and low price, they're not "all that."

i have a 600 edlebrock on my 350 i get good gas milage and performance, im happy with that . this was the recommended carb for a 350 so i dont see how a 780 is gonna be better for a 305 a agree with bzr77 . im sure it will work fine on a 283 or a vbb but your not gonna have it matched very well, you will loose performance , maybe not much , but some, unless the engine is built to handle that size carb. i'd go with a 600

i have a 600 edlebrock on my 350 i get good gas milage and performance, im happy with that . this was the recommended carb for a 350 so i dont see how a 780 is gonna be better for a 305 a agree with bzr77 . im sure it will work fine on a 283 or a vbb but your not gonna have it matched very well, you will loose performance , maybe not much , but some, unless the engine is built to handle that size carb. i'd go with a 600


A misconception about the Qjet is the flow characteristics - granted, it will flow 780CFM on demand - but the air valve functions in a way that the engine is never over-carbed.

A properly tuned Qjet will provide the proper flow characteristics for a 305, 350, or a 454 - and it has the ability to breathe on the high end when called upon. Most other carbs can't do that. Another thing the Qjet has over other carbs on C3 or OBD cars is that you need not disable the computer to run it. The PROM on an ECM can be programmed in such a way as to deliver tailored advance curves and more accurate mixture control for any specific condition via the computer - you can't get that on a mechanical setup and it is this reason why I now prefer to run the OBD system as opposed to fully mechanical advance and mixture control. You can only do this with the E4ME Qjet - others need not apply.

A misconception about the Qjet is the flow characteristics - granted, it will flow 780CFM on demand - but the air valve functions in a way that the engine is never over-carbed.

A properly tuned Qjet will provide the proper flow characteristics for a 305, 350, or a 454 - and it has the ability to breathe on the high end when called upon. Most other carbs can't do that. Another thing the Qjet has over other carbs on C3 or OBD cars is that you need not disable the computer to run it. The PROM on an ECM can be programmed in such a way as to deliver tailored advance curves and more accurate mixture control for any specific condition via the computer - you can't get that on a mechanical setup and it is this reason why I now prefer to run the OBD system as opposed to fully mechanical advance and mixture control. You can only do this with the E4ME Qjet - others need not apply.


learned somethin new , interesting !

If the Holley Spreadbore is still available, they are direct replacements for the QJet. I believe that they were offered as 600 and 750 cfm. I've used them on pre-computer applications with great success.

Bob

The Holley spreadbore is available through Summit racing in the States as well as many speed shops here in Canada. I put one on my Camaro (may she rest in peace) and I loved it. GREAT CARB!

Cheers