hey guys, i looked all over the net and couldn't find the CFM for a stock rochester carb. I know I gotta rebuild, replace or upgrade but I'm wondering where my carb stands to begin with.
Thanks
Scott

http://elcaminocentral.com/modules.php?name=Forums&file=viewtopic&t=2575

Scott, the best answer that I can come up with is the Rochester is good for at least 650cfm, and can be modified to about 850. Q-jets catch a lot of abuse from detractors, but I have loved mine.

The Qjet is a good carb with more than enough air flow for a smallblock Chevy however I think that some of the aftermarket performance carbs are better from the standpoint of cost, ease of adjustment and performance.

you say the stock qjet can be made to perform at close to 850??

i have an 82 conquista w/ the 305 and i feel like i am driving a fiesta with sandbags...

flooring the car is embarrising

i dont know what to do but i looked under the hood and the idle screw wasnt touching the linkage, and if floored in park the #3 and 4 barrels dont open but the engine barks/snaps/cracks.

when you shut it off w/ 87 gas it deisels.

a buddy said "timing" and turned the distributor a bit and i idle at ohh say 1rpm. so he tightened the idle screw to bring it up to near 3-4.

in park the car now idles at the 10 mark w/ no further adjustments... but in drive idles at 2rpms.

im getting a timing light to time the engine very soon

but anyhow, i want the stock qjet to accelerate like a beast, if it cant i was going to purchase a full linkage holley instead of the rochester vacuum controlled setup...

any help at all would be super. thanks guys

i just bought this 82 or maybe its an 83.. the guy sat it for 4 years, it came from cali...

thanks! --newbie

Well, Newbie, trying to get your carb to an 850 is a waste of time and effort for your elc. About the most the stock 305 needs is about 500cfm.I strongly suggest to you a good tune up first--spark plugs, wires, cap, and a rotor. Make sure all your vacumn hoses are in good shape, the pcv valve works. Is the check engine light on?? If it is repair the faulty parts setting the code. Yes, check the basic timing, probably should be set on"0." Trying to cause the secondaries to open by winging the throttle may not necessarily open them. The basic stuff must be in correct operating condition before attempting to go into the Q-jet. After you get that done let us know.

The standard Q-jet it 750 cfm. I replaced with an Edelbrock 600 cfm performer series and see no difference. Except for smoother starting, and running.

I just got tired of rebuilding an old and tired carb.

Elky77

Depending on the year of the application and the engine size. You can end up with either a 705, 750, 795 or 805 CFM Q jet and the only way to tell is to dig up the carb number which can either be on the fuel bowl casting near the throttle linkage or on the front of the fuel bowl again near the linkage. THat or you could try to measure the jets and the metering rods which should have a number or a code on them at least.

See, now it's all clear as mud.... 8O

:-D

If you turn over a Q-Jet and look at the baseplate you can see why it was used successfully on a wide range of engine sizes. The primaries are very small and the secondaries are very large. On a stock 305 which needs only about 400 cfms at WOT the secondaries hardly open at all. Going to a large mechanical Holley in a relatively heavy El Camino with an auto trans and a stock 305 engine is exactly the wrong thing to do. Save yourself a lot of grief guess&check and get what you got working correctly. If the size of a carb were the secret to high performance than Chevy would have installed 98 ci 4 cylinder engines with 2000 cfm double four barrel carbs in all of its performance cars.

a buddy said "timing" and turned the distributor a bit and i idle at ohh say 1rpm. so he tightened the idle screw to bring it up to near 3-4.

in park the car now idles at the 10 mark w/ no further adjustments... but in drive idles at 2rpms.

im getting a timing light to time the engine very soon

thanks! --newbie

Unless it is a 1 cylinder Tractor (Massy Ferguson or something like that) it idles at way more than 1 or 2 RPM. It's curb idle is or should be between 600 and 800 RPM w/o AC. Around 9 to 1200 RPM with AC. Best I can remember.

Your 305 has only 140 something horse power and never will have any more than that unless you change a bunch of stuff on the engine. Quadra Jets are good all around driving carbs but over the years they wear out and start leaking. There are bushing on the throttle plates front and back that go bad and need to be replaced every now and then. Floats go bad etc.... Nothing remains the same for ever.

Take it to someone that does that for a living and they will fix it back to new specs, you should get better performance from it then. Q-jets are funny creatures with a potential of being outstanding carbs but require someone who is very familiar with them and their quarks to work on them.

The heads on your hotrod are just barely sufficient for the 305 they don't flow well and in lots of cases the heads will heat up bad around #8 plug and even burn the valve stem where it starts sucking oil. The heads are a very poor design and made to top out at or around 5000 RPM after that they are no good. They flow around 140 CFM at best the springs are small and probably need to be replaced also. It would be best, if you keep this power plant to exchange them for some new style VORTEC heads and intake and replace the cam too. Or you could build or have built a 350.

I am running a Edelbrock 500cfm 4 barrel w/ vacuum secondaries on my car. And it runs great. better performance and mileage. however I took off all of the emissions stuff as well. if you are looking for a replacement and you don't have to have tailpipe checks done, then that would be the way to go.

and btw, i got my stock q-jet in my hand. were does it give me the cfms?

and btw, i got my stock q-jet in my hand. were does it give me the cfms?

It doesn't, you will only know by either getting out your trusty flow bench :-) or maybe a micrometer to measure venturis and then do a bunch of math or by cross referencing the carb number with a suitable reference such as an old GM overhaul manual or possibly a haynes or chilton manual although your mileage may vary.

:D :cool:

maybe a micrometer to measure venturis and then do a bunch of math

like that is ever gonna happen :lol: :lol: :lol:

I really like the "Demon" carbs. I think they are the best aftermarket carb on the market. Befor anyone starts with the Edelcrap garbage, a BG Road Demon is priced at $339.00 . If you have the stock spreadbore intake manifold, adaptors are avalible for under $20.00, but I think a nice aftermarket intake manifold like the Sportsman 2 from World Products would really help wake your engine up.

I gotta disagree with you. My 500cfm edelbrock was $269 and it works really well on the 305. better mileage and performance . the matching intake was only $100 more. everyone I have talked to who have used them say adapters do not work very well.

Maybe you had some tough luck with an edelbrock product, but that doesn't mean they are all crap.

I gotta disagree with you. My 500cfm edelbrock was $269 and it works really well on the 305. better mileage and performance . the matching intake was only $100 more. everyone I have talked to who have used them say adapters do not work very well.

Maybe you had some tough luck with an edelbrock product, but that doesn't mean they are all crap. Only 25 years of building hot rods, and I do call Edelbrock Edelcrap for a reson !!! Sence the mid 80's thier quality controle has gone to sh_t !!!!!!!!!!!!! There is NO WAY I will ever bolt on anything with thier name on it.