Hello all I got a completely rebuilt stock 98 vortec 350 for a daily with a summit stage 2 intake. Question is what carb do I go with?
OLDSOUL84
What carb would you choose?
If you like to constantly fiddle with things to make them work right then Holley is your answer. Otherwise look into Edelbrock.
For a driver? Edelbrock AVS2, or one of those bolt-on TBI setups. Dark horse? The Summit version of the Thermoquad
What is this going into?
I ask as going into 96 up Vortec pickup going to a carb is not as simple as taking the EFI off and putting a carb on.
Setting that concern aside in my experience for a stock 350 L31 engine the 650 CFM Edelbrock AVS 2 is the simplest to use. It is very tunable inside the range you need.
The stock L31 is basically a return to the 250-300 horse pre SMOG 350. Power dependent on how the engine is dressed. Back then it was a flat tappet cam that is uses about 195/205 on timing which is about the same as the stock L31 roller cam. The difference between 250 and 300 SAE gross power was lower compression with a 2bbl to a little more compression and 4bbl. The L31 is rated around 255 SAE net which is typically about 50 horse power. So it’s reasonable to consider that to the old gross horsepower test if applied to the L31 would result in 300 horse rating give or take. Since the L31 heads make more power on less compression ratio they would add about 50 horses to the low compression 250 horse 350 so that again is an indicator that the L31 to the old gross power test would make about 300 horses. At this power level 650 CFM is plenty.
The Edelbrock doesn’t like being cooked so a half inch composite insulator between it an the intake manifold is quite help full. It also likes about 6 psi max fuel pressure, since the L31 requires an electric fuel pump it’s likely to need a pressure regulator. If you’re going to put this into a formally EFI vehicle your going to have to use a bypassing regulator to get injection pressures of 20-60 psi depending on the EFI used down to something a carb will live with.
Bogie
I ask as going into 96 up Vortec pickup going to a carb is not as simple as taking the EFI off and putting a carb on.
Setting that concern aside in my experience for a stock 350 L31 engine the 650 CFM Edelbrock AVS 2 is the simplest to use. It is very tunable inside the range you need.
The stock L31 is basically a return to the 250-300 horse pre SMOG 350. Power dependent on how the engine is dressed. Back then it was a flat tappet cam that is uses about 195/205 on timing which is about the same as the stock L31 roller cam. The difference between 250 and 300 SAE gross power was lower compression with a 2bbl to a little more compression and 4bbl. The L31 is rated around 255 SAE net which is typically about 50 horse power. So it’s reasonable to consider that to the old gross horsepower test if applied to the L31 would result in 300 horse rating give or take. Since the L31 heads make more power on less compression ratio they would add about 50 horses to the low compression 250 horse 350 so that again is an indicator that the L31 to the old gross power test would make about 300 horses. At this power level 650 CFM is plenty.
The Edelbrock doesn’t like being cooked so a half inch composite insulator between it an the intake manifold is quite help full. It also likes about 6 psi max fuel pressure, since the L31 requires an electric fuel pump it’s likely to need a pressure regulator. If you’re going to put this into a formally EFI vehicle your going to have to use a bypassing regulator to get injection pressures of 20-60 psi depending on the EFI used down to something a carb will live with.
Bogie
Thought bigger was for built motors minesjust a stock motor besides intake,shorty headrrsand hei distributor
The larger carb will work fine. Bogie is the guy best able to make a huge long post about venturi velocities vs fuel burn in on/off throttle activity. He will also explain higher velocity vs fuel draw from jets etc. eric 32 will argue the converse
no
750 vs like Edelbrock or Q-jet if you have spread bore manifold. You will lose 3mph with X carb
750 vs like Edelbrock or Q-jet if you have spread bore manifold. You will lose 3mph with X carb
My recommendation was and is to use around 650 CFM carb that minimizes tuning options and uses an adjustable secondary and if if you can get it an annular boost venturi on the primary side.
The reasons for this are:
- A stock L31 is not cammed enough to make use of a larger carburetor, it simply is not going to make enough air flow demand with the original cam. Actually the factory would use a car of about 500 CFM or less. The smaller capacity carb has higher air flow velocity through the venturies which sharpens the metering making it easier for the carb to make and maintain correct AFR to small throttle changes at typical street cruise RPM’s.
- In the case of a mild stock cammed engine there is no need for getting into the complexities of air correction jets and emulsion tube tuning which adds a lot of initial cost and user complexity to where if you’re not well versed on how a carburetor works at these detail levels gets you into trying to solve often simple problems by using these complexities and quickly getting lost in trying to tune the thing rather that using it to get from point A to B and back.
- The Edelbrock AVS 2 is about as close as you can get to the street performance (as in overall utility) of an old Rochester Q-Jet. The Q-Jet has been out of domestic production for a long time finding a good one at this point used is difficult and expensive so it’s just off my list especially if you need to bolt one on and go. A charter is tic of tge Q-Jet is the very small primary side with a double or triple stepped boost venturi which does a super good job of fuel metering at low through cruise speeds the root of this goodness is keeping the primary air flow high which results in very discrete meter changes with small changes in air flow (the doing of this gets sloppier as the ratio of venturi size gets bigger as to flow volume which relates to velocity through the venturi, the further the venturi gets in size from the flow the sloppier the metering gets with under and over runs. This gets you into screwing with main metering jets and the ever present air correction and emulsion jets of high performance carbs or just living with poor fuel mileage and hesitations if you can’t solve these technical problems.
- The Edelbrock AVS 2 uses an annular boost venturi which occupies a lot of space in the primary venturi so similar to the Q-Jet primary boosters it speeds up the air flow which sharpens the metering response to minor throttle changes at cruise so the AFR stays tighter to the demand. As with the Q-Jet primary metering is done with rods in the jets. This allows for very fine tuning as not only can you change jet sizes but there is a host of metering rods and springs that change the working size of the jet and the timing of those size changes. Additionally like the Q-Jet the secondary uses an adjustable air valve allowing tuning the secondary tip in and how much rate of tip in on the secondary side a simple screw driver adjustment. Unlike the Q-Jet it doesn’t use meter rods on the secondary side the reason being the very small primaries of tge Q-Jet result in the secondary side coming on sooner in the demand cycle so they designed in a bit more discrete fuel flow for the likely hood of high speed cruise demanding some secondary mixture flow. The larger primaries of the Edelbrock are not as likely to get into this transition zone in high speed cruise.
Getting away from Edelbrock but keeping annular boost venturies is the Summit M2008 series. This a simpler carb derived from the Ford 4100 design of the late 1950’s through the 1960’s. My basic dislike of this design has to do with FOD in fuel and fuel systems that gets past the filters as it settles to the bottom of the float bowls where it gets into the Holley style power valve resulting in fuel leaking into the metering system. This quickly washes into the engine. This is otherwise a decent carb but you must use fuel injection quality filters and keep up on their maintenance.
Basically I arrive at a point that your stock crammed L31, 350 just has no use for a carb bigger than 650 CFM. That a xpcarb in this size range will prove to deliver better fuel mileage as it is closer in size to what the engine will demand most of the time. Frankly from time spent sweating over hot engines in a dyno room a 650 with enough cam, way more than you are using, high compression, headers, high flowing intake and a stable valve train a 650 will support about 380-390 hp from a 350 while a 750 will support about 420 hp. But these are power numbers far away from what you’re proposing to build.
Bogie
The reasons for this are:
- A stock L31 is not cammed enough to make use of a larger carburetor, it simply is not going to make enough air flow demand with the original cam. Actually the factory would use a car of about 500 CFM or less. The smaller capacity carb has higher air flow velocity through the venturies which sharpens the metering making it easier for the carb to make and maintain correct AFR to small throttle changes at typical street cruise RPM’s.
- In the case of a mild stock cammed engine there is no need for getting into the complexities of air correction jets and emulsion tube tuning which adds a lot of initial cost and user complexity to where if you’re not well versed on how a carburetor works at these detail levels gets you into trying to solve often simple problems by using these complexities and quickly getting lost in trying to tune the thing rather that using it to get from point A to B and back.
- The Edelbrock AVS 2 is about as close as you can get to the street performance (as in overall utility) of an old Rochester Q-Jet. The Q-Jet has been out of domestic production for a long time finding a good one at this point used is difficult and expensive so it’s just off my list especially if you need to bolt one on and go. A charter is tic of tge Q-Jet is the very small primary side with a double or triple stepped boost venturi which does a super good job of fuel metering at low through cruise speeds the root of this goodness is keeping the primary air flow high which results in very discrete meter changes with small changes in air flow (the doing of this gets sloppier as the ratio of venturi size gets bigger as to flow volume which relates to velocity through the venturi, the further the venturi gets in size from the flow the sloppier the metering gets with under and over runs. This gets you into screwing with main metering jets and the ever present air correction and emulsion jets of high performance carbs or just living with poor fuel mileage and hesitations if you can’t solve these technical problems.
- The Edelbrock AVS 2 uses an annular boost venturi which occupies a lot of space in the primary venturi so similar to the Q-Jet primary boosters it speeds up the air flow which sharpens the metering response to minor throttle changes at cruise so the AFR stays tighter to the demand. As with the Q-Jet primary metering is done with rods in the jets. This allows for very fine tuning as not only can you change jet sizes but there is a host of metering rods and springs that change the working size of the jet and the timing of those size changes. Additionally like the Q-Jet the secondary uses an adjustable air valve allowing tuning the secondary tip in and how much rate of tip in on the secondary side a simple screw driver adjustment. Unlike the Q-Jet it doesn’t use meter rods on the secondary side the reason being the very small primaries of tge Q-Jet result in the secondary side coming on sooner in the demand cycle so they designed in a bit more discrete fuel flow for the likely hood of high speed cruise demanding some secondary mixture flow. The larger primaries of the Edelbrock are not as likely to get into this transition zone in high speed cruise.
Getting away from Edelbrock but keeping annular boost venturies is the Summit M2008 series. This a simpler carb derived from the Ford 4100 design of the late 1950’s through the 1960’s. My basic dislike of this design has to do with FOD in fuel and fuel systems that gets past the filters as it settles to the bottom of the float bowls where it gets into the Holley style power valve resulting in fuel leaking into the metering system. This quickly washes into the engine. This is otherwise a decent carb but you must use fuel injection quality filters and keep up on their maintenance.
Basically I arrive at a point that your stock crammed L31, 350 just has no use for a carb bigger than 650 CFM. That a xpcarb in this size range will prove to deliver better fuel mileage as it is closer in size to what the engine will demand most of the time. Frankly from time spent sweating over hot engines in a dyno room a 650 with enough cam, way more than you are using, high compression, headers, high flowing intake and a stable valve train a 650 will support about 380-390 hp from a 350 while a 750 will support about 420 hp. But these are power numbers far away from what you’re proposing to build.
Bogie
I'm a hardcore Qjet fanboi. No carb, factory or aftermarket, is more accurately metering than a Qjet. Tuned right, they're my absolute go-to for street. Incredible throttle response, better MPG, great carbs.
I also gasp disagree with Bogie. You can't throw a rock in a junkyard without hitting 200 perfectly viable Qjets for $25-50 each. They are everywhere. They were used from 1965 up until 1990 on everything from a 3.8L V6 up to an 8.2L Caddy 500 and everything in between. Carbs are chunks of aluminum with parts in them. They don't just suddenly become bad because they're old. If you're worried about tuning it, send it to Jet Performance with your engine specs. They'll tumble clean it, set it up, and send you a like-new Qjet that is an actual bolt-on. I have never had to adjust anything other than idle speed and maybe 1/8 turn on the idle mix screws. For the price of buying a brand new carb that will likely need a bunch of tuning, you get a custom-built carb for your application.
But I'm guessing your intake is a squarebore. AVS is likely your huckleberry
I also gasp disagree with Bogie. You can't throw a rock in a junkyard without hitting 200 perfectly viable Qjets for $25-50 each. They are everywhere. They were used from 1965 up until 1990 on everything from a 3.8L V6 up to an 8.2L Caddy 500 and everything in between. Carbs are chunks of aluminum with parts in them. They don't just suddenly become bad because they're old. If you're worried about tuning it, send it to Jet Performance with your engine specs. They'll tumble clean it, set it up, and send you a like-new Qjet that is an actual bolt-on. I have never had to adjust anything other than idle speed and maybe 1/8 turn on the idle mix screws. For the price of buying a brand new carb that will likely need a bunch of tuning, you get a custom-built carb for your application.
But I'm guessing your intake is a squarebore. AVS is likely your huckleberry
Depends on where you live, around here just finding a junk yard carb is hard let alone a Q-Jet.
Looks like new ones are being made in China?
Bogie
Looks like new ones are being made in China?
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Bogie
CARBURETOR? JUNKYARD? Man I haven't seen a carb in a junkyard in upstate NY in 20yrs.
But, Cliff Ruggles is the man with QJ's if you go that way. They are great carbs when you get em right
But, Cliff Ruggles is the man with QJ's if you go that way. They are great carbs when you get em right
I guess I'm just lucky in PA. My closest yard has hundreds. There is an old Ford Van near the front that is stacked full of them. Easily 500 Qjets, 2-jets, Varijets, and other carbs. Not to mention the 150 acres of cars sorted by brand, and everything from the 30s to today, most of which have carbs on them.
In the beginning you stated it was a daily driver stock L 31 Vortec simply converted to a carb which also means your going to need a conventional distributor I assume to be an HEI. This needs to have a Melonized gear to run with the factory roller cam.
So unless your anticipating turning this Into a high performance hot rod, I’d just stay with the original plan, get a simple carb that pretty much works out of the box whether that’s a Holley or Holley clone like the street warrior, Classic, Street Avenger or a Demon which is kind of Barry Grant’s idea of what the Carter/Edelbrock should be or and Edelbrock or a functional Q-Jet.
My recommendation is keep it simple and get it up an running.
Your going to have to do an electric fuel pump unless the Vortec block you have has a finished mechanical fuel pump or can be finished but the Vortec cam unless the marine/industrial version does not have the cam eccentric lobe to operate a mechanical fuel pump. It’s really easy to make this into a much bigger job than you originally planned.
bogie
So unless your anticipating turning this Into a high performance hot rod, I’d just stay with the original plan, get a simple carb that pretty much works out of the box whether that’s a Holley or Holley clone like the street warrior, Classic, Street Avenger or a Demon which is kind of Barry Grant’s idea of what the Carter/Edelbrock should be or and Edelbrock or a functional Q-Jet.
My recommendation is keep it simple and get it up an running.
Your going to have to do an electric fuel pump unless the Vortec block you have has a finished mechanical fuel pump or can be finished but the Vortec cam unless the marine/industrial version does not have the cam eccentric lobe to operate a mechanical fuel pump. It’s really easy to make this into a much bigger job than you originally planned.
bogie
If your running a pretty much stock engine and you want a Holley carb that would be pretty close out of the box and only need some basic adjustments and would want a Holley carb then I can recommend a Holley Street warrior carb which is a 600 vacuum secondary and there are no changeable air bleeds or anything else fancy on it and just a front metering blocks that you can change jets on and on the rear a metering plate that you can't change anything on it.
The model 1850 is a manual choke and the 80457 is the electric choke model. If you want to save money look for a used one of the above models on ebay and be careful though as sometimes folks can sell junk on there and say its good condition and there is some things too look out for but at times for just over a $100 plus shipping you can get a good condition one and put a rebuild kit in it and your good to go.
The 600 vacuum secondary Holley 1850 and 80457 are 4160 models with side hung fuel bowls and for stock motors or rv cams they pretty much work out of the box and don't run fat rich at all with a good ignition system and proper timing. I bought a used one many years back and it was the way it cam factory from Holley and it ran on a bone stock 305 small block chevy from the late 80's and it ran fine and replaced an old worn out Qjet. It ran good and fuel mileage was still good and spark plugs looked good and tan. Just have to make sure the mixture screws are adjusted well.
Now in some cases it might be on the tad rich sides but it depends on the build and timing etc but on my few builds I had and worked on and some others it always just need mixture adjustments and jetting changes as needed and that is about it along with putting in a different secondary spring to open up the secondary side for the optimal setting.
The best is a Quick fuel pod which allows you to adjust the rate on how fast and responsive it will open in relation to the air velocity coming in from the front of the carb. Just like the AVS 2
The chevy caprice it was in ran well and good. When I first bought my truck a long time ago it had a stock 350 vortec and I mean the L31 real vortec from top to bottom and I put a 600 Holley on it and only had to adjust my mixture screws and set my idle and it was spot on and ran fine. I had a dual plane intake with just a standard Hei distributor and it ran like a champ minus the rod knock lol. I eventually replace the engine with a new rebuild but reused the carb.The edelbrock AVS 2 would be better slightly wise for mileage but either carb would be a simple bolt on.
The Quick fuel carbs are nice but they are calibrated for engines and way bigger cams and unless like I and others have said unless you know your way around them and changing idle feed restrictors in the metering blocks and in rare occasions the air bleeds its a very tricky thing and you can get lost pretty fast without taking time and knowing what your getting into.
Good luck on your decision.
The model 1850 is a manual choke and the 80457 is the electric choke model. If you want to save money look for a used one of the above models on ebay and be careful though as sometimes folks can sell junk on there and say its good condition and there is some things too look out for but at times for just over a $100 plus shipping you can get a good condition one and put a rebuild kit in it and your good to go.
The 600 vacuum secondary Holley 1850 and 80457 are 4160 models with side hung fuel bowls and for stock motors or rv cams they pretty much work out of the box and don't run fat rich at all with a good ignition system and proper timing. I bought a used one many years back and it was the way it cam factory from Holley and it ran on a bone stock 305 small block chevy from the late 80's and it ran fine and replaced an old worn out Qjet. It ran good and fuel mileage was still good and spark plugs looked good and tan. Just have to make sure the mixture screws are adjusted well.
Now in some cases it might be on the tad rich sides but it depends on the build and timing etc but on my few builds I had and worked on and some others it always just need mixture adjustments and jetting changes as needed and that is about it along with putting in a different secondary spring to open up the secondary side for the optimal setting.
The best is a Quick fuel pod which allows you to adjust the rate on how fast and responsive it will open in relation to the air velocity coming in from the front of the carb. Just like the AVS 2
The chevy caprice it was in ran well and good. When I first bought my truck a long time ago it had a stock 350 vortec and I mean the L31 real vortec from top to bottom and I put a 600 Holley on it and only had to adjust my mixture screws and set my idle and it was spot on and ran fine. I had a dual plane intake with just a standard Hei distributor and it ran like a champ minus the rod knock lol. I eventually replace the engine with a new rebuild but reused the carb.The edelbrock AVS 2 would be better slightly wise for mileage but either carb would be a simple bolt on.
The Quick fuel carbs are nice but they are calibrated for engines and way bigger cams and unless like I and others have said unless you know your way around them and changing idle feed restrictors in the metering blocks and in rare occasions the air bleeds its a very tricky thing and you can get lost pretty fast without taking time and knowing what your getting into.
Good luck on your decision.
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