Carb choice for 350

[streetstar]

[QUOTE=gchemist;2359185]Welcome to the site.
Edelbrocks 1406 is my choice. No more than 650 CFM for a SB. http://www.centuryperformance.com/vacuum.asp[/url]

Why only 650cfm? A stock Q-jet is 750cfm. The carburation needs to be tailored to the demands of each particular engine.
---a 350 is well suited to a 750. A smaller engine like a 305 or 307 can make use of a 600 or 650 --- but a 383 stroker, or a built 400 might be fuel starved with a 750 even. A friend's 383 makes close to 600 hp's on the dyno with a Holley 930dp, and could use more so he is going to a 1050 dominator .

A 750 quadrajet has small primaries for good torque and efficiency on the street, but has large secondaries for full throttle performance-- that is why it is made on a spread bore, whereas the Holley primaries and secondaries are externally the same size .

GM engineers are relatively smart-- they wouldnt spec the 750 qjet if it was a total dog

[piecesparts]

[QUOTE=streetstar;2361267]

Originally Posted by gchemist

Welcome to the site.
Edelbrocks 1406 is my choice. No more than 650 CFM for a SB. http://www.centuryperformance.com/vacuum.asp[/url]

Why only 650cfm? A stock Q-jet is 750cfm. The carburation needs to be tailored to the demands of each particular engine.
---a 350 is well suited to a 750. A smaller engine like a 305 or 307 can make use of a 600 or 650 --- but a 383 stroker, or a built 400 might be fuel starved with a 750 even. A friend's 383 makes close to 600 hp's on the dyno with a Holley 930dp, and could use more so he is going to a 1050 dominator .

A 750 quadrajet has small primaries for good torque and efficiency on the street, but has large secondaries for full throttle performance-- that is why it is made on a spread bore, whereas the Holley primaries and secondaries are externally the same size .

GM engineers are relatively smart-- they wouldnt spec the 750 qjet if it was a total dog

You are absolutely right in your assmptions that an engine has to be fed according to the demand. However for everyday street driven vehicles, the overcarburetion of a 750 will (and believe me, I have seen it) cause a slobbering problem at the stoplights. Your top end will be EXCELLENT but your daily drivving will be poor. The Q-Jet has small primaries and then transition to the secondaries which gives the 750 effect on them. Where a Holley, Edelbrock or Carter square bore four barrel has a slightly larger primary when it is a 750 and that is detrimental to daily driving.

This all depends on a couple of other factors 1) weight of the vehicle--a truck is heavier than a Camaro, so it will respond more sluggishly, unless really geared low. 2) the gear ing is the next thing---people of today are trying to get the gearing high enough to keep the RPMs down, that does not work well with a larger bore carb. 3) The 750 will plate out residue on the intake valves as it works in daily driving and cause more sluggish response as time goes on (seen the effects in a machine shop atmosphere.

Holley and Edelbrock corporations; both will tell you to stay at or below a 650 CFM on a 350 motor and even a 383, if it is street driven; to keep the air flow up and the efficiency of the carb working for you, that way the high velocity will make up for the heavier vehicle weight. Granted, my 383 ran hard all the way up to 6000 RPM with the 750, but I could not get the thing to work right on the street--I had to make a decision, so I did not go to the Edelbrock performer carb, which is a 625 CFM carb, but went with the Edelbrock Thunder AVS--which is actually just over 650 CFM---best of both worlds.

The Q-jet is a great choice, if you have a solid one to start with.

[slugish]

[QUOTE=piecesparts;2361365]

Originally Posted by streetstar

You are absolutely right in your assmptions that an engine has to be fed according to the demand. However for everyday street driven vehicles, the overcarburetion of a 750 will (and believe me, I have seen it) cause a slobbering problem at the stoplights. Your top end will be EXCELLENT but your daily drivving will be poor. The Q-Jet has small primaries and then transition to the secondaries which gives the 750 effect on them. Where a Holley, Edelbrock or Carter square bore four barrel has a slightly larger primary when it is a 750 and that is detrimental to daily driving.

This all depends on a couple of other factors 1) weight of the vehicle--a truck is heavier than a Camaro, so it will respond more sluggishly, unless really geared low. 2) the gear ing is the next thing---people of today are trying to get the gearing high enough to keep the RPMs down, that does not work well with a larger bore carb. 3) The 750 will plate out residue on the intake valves as it works in daily driving and cause more sluggish response as time goes on (seen the effects in a machine shop atmosphere.

Holley and Edelbrock corporations; both will tell you to stay at or below a 650 CFM on a 350 motor and even a 383, if it is street driven; to keep the air flow up and the efficiency of the carb working for you, that way the high velocity will make up for the heavier vehicle weight. Granted, my 383 ran hard all the way up to 6000 RPM with the 750, but I could not get the thing to work right on the street--I had to make a decision, so I did not go to the Edelbrock performer carb, which is a 625 CFM carb, but went with the Edelbrock Thunder AVS--which is actually just over 650 CFM---best of both worlds.

The Q-jet is a great choice, if you have a solid one to start with.

Ithink you are right on the money peicesparts with your carb knowledge . I have a mildly built 400 with a holly 650 doble pumper. In your opion , is this agood choice. Also having continued problems fouling plugs. Take out & they smell of gas with black sooty tips. Person that built engine thinks by pumping the gas to get it started (no choke ) maybe gas fouling the plugs. Have put new hot plugs in now & keeping an eye on , & not pumping as hard when trying to start . Any feedback would be great .

[piecesparts]

[QUOTE=slugish;2393011]

Originally Posted by piecesparts

Ithink you are right on the money peicesparts with your carb knowledge . I have a mildly built 400 with a holly 650 doble pumper. In your opion , is this agood choice. Also having continued problems fouling plugs. Take out & they smell of gas with black sooty tips. Person that built engine thinks by pumping the gas to get it started (no choke ) maybe gas fouling the plugs. Have put new hot plugs in now & keeping an eye on , & not pumping as hard when trying to start . Any feedback would be great .

The 650 Holley Double pumper is a good choice--all manufacuteres make a quality product--Holley is in there, also. I have been to their factory and they are great people to work with. However over the years each individual found things that one brand or another had to take issue with--Holley had the problem of leaking and also the diaphragm breaking issues, but it's reputation is solid. Now for your discussion on the choke--if you have to pump the thing when starting --EVEN on a normal day then I would bet the choke is NOT the issue. A carb does not need choking at ALL times and the gas fouling is probably due to two things 1) leakby in the carb, or 2) overjetting of the carb. Where does your engine run it's best (at what RPM). If it is a poor sl;oppy performer on the city street, then you are probably over fueling.


A couple of questions that are kind of outside the discussion---1) What cam design are you running? 2) Does your truck pull at a stoplight, while you are sitting waiting for it to change? REASON for questions---If you put in a cam that is rather healthy, then your truck is probably working itself against the torque convertor and tranny (I am guessing you have an automatic--I may be wrong). This bad idle and the torque convertor lends to loading up your engine with raw gas (due to having to set the idle high on the carb to overcome the bad idle conditions). This is primarily due to the idle adjustment is NO LONGER in the idle circuit on the carb ---it is now in the transition area. If so, then a change to your torque convertor's STALL is necessary to get your idle screws back where they belong (JUST A GUESS). I had to take my stroker motor's tranny to a 2400 stall to get a better run and idle response. The change was tremendous.

[slugish]

[QUOTE=piecesparts;2393440]

Originally Posted by slugish

The 650 Holley Double pumper is a good choice--all manufacuteres make a quality product--Holley is in there, also. I have been to their factory and they are great people to work with. However over the years each individual found things that one brand or another had to take issue with--Holley had the problem of leaking and also the diaphragm breaking issues, but it's reputation is solid. Now for your discussion on the choke--if you have to pump the thing when starting --EVEN on a normal day then I would bet the choke is NOT the issue. A carb does not need choking at ALL times and the gas fouling is probably due to two things 1) leakby in the carb, or 2) overjetting of the carb. Where does your engine run it's best (at what RPM). If it is a poor sl;oppy performer on the city street, then you are probably over fueling.


A couple of questions that are kind of outside the discussion---1) What cam design are you running? 2) Does your truck pull at a stoplight, while you are sitting waiting for it to change? REASON for questions---If you put in a cam that is rather healthy, then your truck is probably working itself against the torque convertor and tranny (I am guessing you have an automatic--I may be wrong). This bad idle and the torque convertor lends to loading up your engine with raw gas (due to having to set the idle high on the carb to overcome the bad idle conditions). This is primarily due to the idle adjustment is NO LONGER in the idle circuit on the carb ---it is now in the transition area. If so, then a change to your torque convertor's STALL is necessary to get your idle screws back where they belong (JUST A GUESS). I had to take my stroker motor's tranny to a 2400 stall to get a better run and idle response. The change was tremendous.

No does not pull at a light / has similiar stall in it as yours/ can power brake to aroud 2200rpms /

Cam is pretty mild 048 lift - 224/ 230 duration

the guy that built engine said to check for leaking while running (havent done that yet ) what do you do , just look inside carb while running .

Was talking today to another friend who builds race cars . He said double pumpers are for racing , not really good street carbs & probably dont have enough lift for the amt. of gas a double punper puts in .

Ived been advised by him & others to get a quadrajet or eldobrock for the street & occasionaly the strip 750 cfm quadrajet or eldebrock with a vacuum secondary & electric choke

also I put truck in neutral most of the time at stoplights

Actually runs well in most all rpm ranges. its a 408 cube sbc with reworked stock heads.

What would be your choice of carbs/ thanks for your help by the way

[piecesparts]

[QUOTE=slugish;2396155]

Originally Posted by piecesparts

No does not pull at a light / has similiar stall in it as yours/ can power brake to aroud 2200rpms /

Cam is pretty mild 048 lift - 224/ 230 duration

the guy that built engine said to check for leaking while running (havent done that yet ) what do you do , just look inside carb while running .

Was talking today to another friend who builds race cars . He said double pumpers are for racing , not really good street carbs & probably dont have enough lift for the amt. of gas a double punper puts in .

Ived been advised by him & others to get a quadrajet or eldobrock for the street & occasionaly the strip 750 cfm quadrajet or eldebrock with a vacuum secondary & electric choke

also I put truck in neutral most of the time at stoplights

Actually runs well in most all rpm ranges. its a 408 cube sbc with reworked stock heads.

What would be your choice of carbs/ thanks for your help by the way

OK, so it is a slightly bored motor that has a little cam to it, I had a 2200 stall converter on my 383/700R4 combo and was experiencing the rough idle circuit mess at a stop. It cleared up when I went to neutral. I stepped up to a 2400 stall and solved many of my problems. I would support some of the thinking that a double pumper is more of a higher RPM carb and if that appears to be the issue then you need to go to a different design. As you can see, EVERYONE has an opinion which is best for an engine. Some like Quadrajets, some like Holleys, others like Edeldbrocks. I am presently running an Edelbrock AVS carb--mostly due to the CFM rating of that carb and the fact that the intake is made for a square bore carb. If your intake is designed for a spreadbore, then look for a Quad, it would be better than trying to modify with an adapter and loose volumetric efficiency. I have worked on the Quadrajets in my past--haven't lately and they work great--once adjusted and set. I had some bad early experiences with Holleys, but they supported anything that I did in those days just the ruptured power valves. You will read a lot of trashing on the Edelbrocks, but for the money they work really well--if you spend a little time adjusting them.

Before I purchased my carbs, I talked to the reps at Holley and the reps at Edelbrock (I do like going on the Hot Rod Power Tours--just for that reason). Of course, they all push their own items, but they also quote a lot of info and most say the same thing. For a truck being driven on the street, you want to keep the airflow velocity up, so that it will not lag behind the motor. That means running a slightly smaller CFM carb. The heavier weighted vehicle will respond better to that thought process. (Example run a 625 or 650 CFM carb rather than a 750 CFM and the response will be better) A lighter weight car, such as a Camaro will work better with the 750 CFM carb. The Holley people support a vacuum secondary actuated carb is better, they say the feathering of the secondaries is smoother. I have found that the Edelbrocks that I have run work just as well without the vacuum actuated diaphragm design. (I have adjusted my springs, needles and jets to what I like)

Did you know that the Edelbrock AFB design carb and the Carter AFB design carb is the EXACT SAME carb. (both carbs are made by Magnetti-Marelli) The parts are interchangeable---even if the parts distributors say that they aren't. I have a Carter in my basement that is full of Edelbrock parts (Edelbrock is cheaper than Carter on parts)

You still need to make sure that you are getting your carb adjusted to where the idle is in the idle circuit part (butterfly relationship to the venturi)and not in the transition area---gas smell and bad mileage is normal there. Where do you have your idle mixture screws set at? I set mine using a vacuum gauge instead of by ear, however both methods work . I am also going to ask, where do you have your intial timing set at? Maybe it is set to low.

If you think that your carb is leaking gas, try closing down on the idle mixture screws and see if it runs with them closed off. There is a possibility that it might with the gas leaking into the intake.

[slugish]

[QUOTE=piecesparts;2397436]

Originally Posted by slugish

OK, so it is a slightly bored motor that has a little cam to it, I had a 2200 stall converter on my 383/700R4 combo and was experiencing the rough idle circuit mess at a stop. It cleared up when I went to neutral. I stepped up to a 2400 stall and solved many of my problems. I would support some of the thinking that a double pumper is more of a higher RPM carb and if that appears to be the issue then you need to go to a different design. As you can see, EVERYONE has an opinion which is best for an engine. Some like Quadrajets, some like Holleys, others like Edeldbrocks. I am presently running an Edelbrock AVS carb--mostly due to the CFM rating of that carb and the fact that the intake is made for a square bore carb. If your intake is designed for a spreadbore, then look for a Quad, it would be better than trying to modify with an adapter and loose volumetric efficiency. I have worked on the Quadrajets in my past--haven't lately and they work great--once adjusted and set. I had some bad early experiences with Holleys, but they supported anything that I did in those days just the ruptured power valves. You will read a lot of trashing on the Edelbrocks, but for the money they work really well--if you spend a little time adjusting them.

Before I purchased my carbs, I talked to the reps at Holley and the reps at Edelbrock (I do like going on the Hot Rod Power Tours--just for that reason). Of course, they all push their own items, but they also quote a lot of info and most say the same thing. For a truck being driven on the street, you want to keep the airflow velocity up, so that it will not lag behind the motor. That means running a slightly smaller CFM carb. The heavier weighted vehicle will respond better to that thought process. (Example run a 625 or 650 CFM carb rather than a 750 CFM and the response will be better) A lighter weight car, such as a Camaro will work better with the 750 CFM carb. The Holley people support a vacuum secondary actuated carb is better, they say the feathering of the secondaries is smoother. I have found that the Edelbrocks that I have run work just as well without the vacuum actuated diaphragm design. (I have adjusted my springs, needles and jets to what I like)

Did you know that the Edelbrock AFB design carb and the Carter AFB design carb is the EXACT SAME carb. (both carbs are made by Magnetti-Marelli) The parts are interchangeable---even if the parts distributors say that they aren't. I have a Carter in my basement that is full of Edelbrock parts (Edelbrock is cheaper than Carter on parts)

You still need to make sure that you are getting your carb adjusted to where the idle is in the idle circuit part (butterfly relationship to the venturi)and not in the transition area---gas smell and bad mileage is normal there. Where do you have your idle mixture screws set at? I set mine using a vacuum gauge instead of by ear, however both methods work . I am also going to ask, where do you have your intial timing set at? Maybe it is set to low.

If you think that your carb is leaking gas, try closing down on the idle mixture screws and see if it runs with them closed off. There is a possibility that it might with the gas leaking into the intake.

really appreciate your feed back . dont really understand how I can check idle in the idle circuit part vs. the transition area. Also dont know how to check idle with vacuum guage. thinlk my timing is at 36 degrees . Am going to track this weekend . wil let you know what happened. obviously im not a mechanic , but will run your ideas by mechanic friends . thanks again for your input.

[Pyrotechnic]

Originally Posted by streetstar

Why only 650cfm? A stock Q-jet is 750cfm. The carburation needs to be tailored to the demands of each particular engine.
---a 350 is well suited to a 750. A smaller engine like a 305 or 307 can make use of a 600 or 650 --- but a 383 stroker, or a built 400 might be fuel starved with a 750 even. A friend's 383 makes close to 600 hp's on the dyno with a Holley 930dp, and could use more so he is going to a 1050 dominator .

A 750 quadrajet has small primaries for good torque and efficiency on the street, but has large secondaries for full throttle performance-- that is why it is made on a spread bore, whereas the Holley primaries and secondaries are externally the same size .

GM engineers are relatively smart-- they wouldnt spec the 750 qjet if it was a total dog

Yes the typical Q-Jet CAN flow up to 750 CFM. The way the secondaries are designed though, that doesn't always happen. The secondaries and secondary metering rods on the Q-Jet are designed to flow only as much air and fuel as the motor needs. A 305 or 350 will not pull 750 CFM through the carburetor. They went with this design so a single carb body could cover a large range of displacements and power levels.

[lurch115]

i've messed with / rebuilt just about any and every carb. you could think of and as long as you know a few tricks you can rebuild the stock q-jet and have one heck of a carb. the biggest "problem" with them is that if you leave them sit long enough to dry out the accelerator pump (which is made of rubber like material) also dries out and cracks. Allowing fuel and pressure to get through it....which is why you get the big flat spot in acceleration when you put your foot down quick.... the other issue is with the automatic chokes... edelbrock 1406 is also a good choice