Basic 305 build

[lukieg]

 Im woking on a 305 build for mileage mostly.. lg4 with vortec heads and a 4bbl intake, small cam and such.. I searched far and wide locally for decent qjets... all were mostly old rugged and beat.. I have yet to find someone I trust to rebuild one and Im not at the stage currently where i wish to learn.. I was looking at reman ones but they are really quite costly.. it seems edelbrocks and holleys are a bit cheaper even new. Would a 390 holley or 500 edelbrock be able to get similar mileage to a quadrajet? Thanks

[bake74]

  No, the quad will get better than both of those if tuned right.

[lukieg]

or even a holley 2300.. I know the q-jet is the best available.. but for new and slightly less.. will any of these options come close??

[bd]

Just remember, with any given engine, fuel mileage is inversely proportional to horsepower, the size/weight of your foot, and how much stop-n-go driving you do.      Actually, you can nurse any correctly sized carburetor bolted to a mild engine to get reasonable mileage.  It's largely about how you drive it.

[bake74]

     If you are looking for mileage only, any of those carb's will work, just get the smallest size that will be rated for your H.P. Output of the motor you are building, and keep in mind that you got a carb. For mileage, not for H.P. and drive accordingly.

[TexasRed]

What transmission will you be running?

I think only edelbrock has a 500 or sub500 cfm carb that's not high.

Will you be using aftermarket intake? If not, you'll have to factor that into your cost equation (adapters),

Holley makes a new spreadbore for less than $400.

Summit also sells their squarebore carb: http://www.summitracing.com/parts/SUM-M08600VS/
While it is a 600, it should be ok for that engine and its cheap and comes with annular boosters.

[lukieg]

 I was kind of leaning towards the smaller holley 2bbl or perhaps smaller demon 2bbl.. party because I always wanted to try one..  I hear they are worse on gas for just putting... but in the real world is it?? I use a fair amount of throttle from time to time daily driving... I just think the secondaries kick in alot more then i even realize..

[TexasRed]

you'd be better off disconnecting the secondaries then. Remember that a two barrel has to flow enough air and fuel to satisfy the engine's full capacity.

[lukieg]

a 350 cfm 2bbl wont supply a slightly built 305?

[gto109]

I've found that a stock cam for a 350 and a 600 cfm carb get better milage in a 305.  I had an 85 Olds Cutlass years ago with that set up plus headers and duel glass packs out the side of the car.  It had more power to push it with less throttle.

[gto109]

here is a build i found one day on a guys pontiac with a chevy 305.  the cam he is giveing the part number to is a stock 350 cam.  this guy used to race this car.
Baseline: Stock 1977 305 2v................17.30s and 12mpg
Performer intake w/ Holley 600 carb........16.50s and 17mpg
Recurved stock HEI and added Supercoil.....16.30s and 17mpg
Headers w/ turbo mufflers dumped at axle...15.70s and 20mpg
Mufflers removed, 3ft tubes on headers.....15.50s and 21mpg
TRW #274 cam, new chain, flex fan..........15.00s and 23mpg
Full duals from headers Dynomax mufflers...15.10a and 23mpg
K$N stub stack, softer secondary spring....14.90s and 22mpg
Magnum roller tip rockers, 1.52 ratio......14.80s and 24mpg
Magnum 1.6 rockers on exhaust side.........14.80s and 25mpg

[lukieg]

 Ok so the mroe i milled around the idea the more I kind of want to try a 2bbl build... everything from this point due to fuel prices will likely be at least tbi injected ah well... Im kind of young and carbs were out when I started wrenching... what are the advantages to a 2bbl  if any.. i know the cfm is rated different.. would I want a 500 cfm or the 350 version.. what about demon carbs?? Just holleys built a little better? Any input would be helpful.. would a stock 4bbl or after market dual plane intake with spacer be ideal? Everyhting else is single plane high reving stuff.

[muddpuppy01]

you defiantly want a dual plane. if you want a 2 bbl you need a 2 bbl intake. To me a motor is only going to take in as much or little fuel as it want with proper tuning of the carb.

Running to little of a carb might use more fuel do to you have to overcome decreased power and it may not even run correct off idle

4 barrel you can make it suck down fuel like no ones business but lightly using the thottle will solve that

for the most mpg you can get you would have to get a direct injected motor which are more efficient motor all the way around ( all the car that get 40+ are direct injected )

it has to do with weight to power ratio with aerodynamics and efficiency of the motor
(proper tuning). take my jetta tdi for example motor is putting out around 220hp I and get around 40 - 45 mpg with it. my k20 factory stock was 160 hp. throw on a bunch of miles I think I would be lucky to get 110 at the wheels right now if that. I could swap in another motor to give me more power in the k20 and I am sure I would get better mpg out of it.

for me I would spend the money on getting the qjet rebuilt completely in and out. then adjust the carb to the motor either through dyno session or pulling the pulling plugs and reading them correctly. to me a dyno session is the better way to go due to being able to see the graph and get more information. there you can adjust the timing and curve to get the motor what it wants. then adjust fuel rods to finely tune it. running lean on the motor will hurt the hurt the motor and create less power due to lean mixture in the combustion chamber creating inefficient burn. to rich and you are using more than it can use in the and burning to long . which can be compounded by to little timing ( atdc ).finely tuned motor will give more power and burn efficiently.

the qjet with its spread-bore design will give you better low end response with the smaller primary and the bigger secondaries will only open as far as it needs to.

[lukieg]

 Thank you for your reply however I am fairly set on a 2bbl at this point.. i have played around a bit with 4bbls and now i want to try at least one 2bbl because unless im going resto on something.. im likely going to get into injection.

[muddpuppy01]

injection would be better for mpg than a carb unless you plan on playing with it all the time.