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Seeking Carburetor selection advice

Old January 13th, 2019, 06:06 PM
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Seeking Carburetor selection advice

Hey folks,
I'm still in search of the perfect carb for my 455, 030 over with ported and polished J heads.
I went through a couple Quadrajets using Ruggles book but I made a rookie mistake; I was hunting for a good idle by modifying the idle circuits when, in fact, I had the preload on the lifters too tight. I had one to the point that it would break the tires loose at the 2-3 shift but it wouldn't idle well and stalled a lot. I'm a Q-jet guy and know quite a bit about them now, but the constant tearing them apart to make small changes is getting a little old.
I'm looking at the Edelbrock AVS 800 CFM 1813. Folks say bolt 'em on and forget 'em. I know that's not very true but I like the external access for swapping parts.
I'd Love to go EFI but I just don't have the cash.
Opinions?

Engine specs:
455 bored 030 over
Ported and polished J heads
Cam is .512" in and out with a 110 LSA (a bit much, yeah?) with Comp Cams roller tip rockers. I dialed it in and the heads have matching springs
9.6 -ish compression with forged Wiseco pistons with hand-filed rings, stock rods with ARP bolts
Performer intake, dual plane (I have an adapter for a square bore)
Hedman long tube headers
Carter Muscle Car HV fuel pump with a QF regulator
HEI limited to 13*, making up the rest at the crank, MSD weights and springs activating as soon as I hit the gas but not at curb idle (850 rpm)
200-4R trans with a 2500 stall converter
3.73 rear gears
It pulls a steady 14 inches of vacuum.

Last edited by Macadoo; January 13th, 2019 at 06:10 PM.
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Old January 13th, 2019, 06:21 PM
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You only list cam lift, that’s really inconsequential. Duration and lobe sep are way more important.
Not sure of your budget but I’d do a Quick Fuel SS830.
Don't use an Edelbrock carb if at all possible.
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Old January 13th, 2019, 07:02 PM
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227 intake, 233 exhaust. 110 LSA (as stated above). Sorry Mark, I should have known that. I'll have a look at the QF.

Last edited by Macadoo; January 13th, 2019 at 07:08 PM.
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Old January 13th, 2019, 07:07 PM
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Yeah, that's a bit pricey. Pretty though. Mark, what do you not like about the Edels? Because it's the old Carter design?
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Old January 13th, 2019, 08:49 PM
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I like the Holley 3310 vac secondary 750cfm Its simple and inexpensive and will bolt right on.
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Old January 13th, 2019, 09:09 PM
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I gave mac a 3310 It was barely enough for my needs on my last 355.

Mac what are you looking for in a carb ? idle still ? or off the line performance ?

I have a friend who has an 850 demon that may work for you.
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Old January 13th, 2019, 10:07 PM
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The holley Street Demon. 625 CFM model is good for 500hp, and the 750 for past there.

The only Holley style carb I like is the Quick Fuel Carburetor BR-67214 Brawler. About $385 when on sale
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Old January 14th, 2019, 06:43 AM
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Originally Posted by Firewalker View Post
The holley Street Demon. 625 CFM model is good for 500hp, and the 750 for past there.
Not sure where you get that. If you look at my big block builds they’re pulling over an inch of vacuum at WOT, and that’s with 850’s. Even a 750 is too small for any bb making any decent amount of power.
And “bolt on and go” means nothing. Virtually all of them will do that. Too many never take the time to rejet as needed however.
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Old January 14th, 2019, 05:19 PM
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As said the Street Demon 750 are good carbs but a bit on the small side but should provide decent performance and economy if tuned properly. They are basically new 3 barrel, improved version of the Thermoquad. People including Cutlassefi like the Quickfuel carbs for a Holley style carbs. Or find a 800 cfm Qjet core to build.
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Old January 14th, 2019, 07:09 PM
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Originally Posted by oldcutlass View Post
I like the Holley 3310 vac secondary 750cfm Its simple and inexpensive and will bolt right on.
Thanks for the input Eric. But Copper is correct; the 3310 didn't keep up. But to be fair, I didn't do any part swaps to get it tuned.

Originally Posted by coppercutlass View Post
I gave mac a 3310 It was barely enough for my needs on my last 355.

Mac what are you looking for in a carb ? idle still ? or off the line performance ?

I have a friend who has an 850 demon that may work for you.
I think I have the idle pretty good, finally. It was the same thing you posted to Youtube; getting the mechanical advance out of the picture at idle, but kicking in just when touching the throttle. I't s a little high in park but works well at curb idle. I read about a lot of guys talking about a "nice, crisp throttle response." I'd like to have that. Maybe it's the 200-4R. I still need to modify the governor to lengthen the 1-2 shift. And honestly, I'm tired of pulling the carb and air horn to make the slightest change in a Q-jet.

Originally Posted by Firewalker View Post
The holley Street Demon. 625 CFM model is good for 500hp, and the 750 for past there.

The only Holley style carb I like is the Quick Fuel Carburetor BR-67214 Brawler. About $385 when on sale
That BR-67214 gets good reviews for sure. Some posts say it's just a rebranded Proform. But that Proform gets good reviews too and is a little more expensive.

Originally Posted by cutlassefi View Post

Not sure where you get that. If you look at my big block builds they’re pulling over an inch of vacuum at WOT, and that’s with 850’s. Even a 750 is too small for any bb making any decent amount of power.
And “bolt on and go” means nothing. Virtually all of them will do that. Too many never take the time to rejet as needed however.
Which is why I'd like something easier to tune than a Q-jet. The Edelbrock has easy access to the rods but I think that's not true for the jets. But the airhorn comes off pretty easily.
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Old January 14th, 2019, 07:20 PM
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The Quick Fuel/Brawler/Hot Rod series carbs offer 4 corner idle and have easy to replace air bleeds as well. Toughest thing is replacing jets, which still only takes a couple of minutes.
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Old January 14th, 2019, 08:12 PM
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Mac a tight converter will pose issues you cant tune out. Keep that in mind. Your converter could not be enough for that set up or possibly was made too tight. Fwiw
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Old January 15th, 2019, 06:17 AM
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Some have luck with Edelbrock carb, many do not. One member compared the Carter to Edelbrock castings, the Carter were much better. Remember even the AFB/AVS had hot start issues back when they were factory carbs. I really think that was a big part of the Thermoquad getting the Bakelite body. Go with Mark's recommendation, especially if looking for maximum power. Personally I can adjust my part throttle on my Qjet in minutes through the air horn. I slotted the APT adjustment and added a slotted threaded plug. A flat screwdriver is used for both. A couple of turns out adds noticeable performance gains, in a couple of turns adds 2 to 3 mpg. Along with the secondary rod change, it makes a big difference. Of course an AF gauge is the only right way to tune your car. Curious, what kind of mpg is achieved with these new Holley style carbs? Can they match the Street Demon or Qjet, both with an ideal tune?
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Old January 15th, 2019, 10:36 AM
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Originally Posted by olds 307 and 403 View Post
Some have luck with Edelbrock carb, many do not. One member compared the Carter to Edelbrock castings, the Carter were much better. Remember even the AFB/AVS had hot start issues back when they were factory carbs. I really think that was a big part of the Thermoquad getting the Bakelite body. Go with Mark's recommendation, especially if looking for maximum power. Personally I can adjust my part throttle on my Qjet in minutes through the air horn. I slotted the APT adjustment and added a slotted threaded plug. A flat screwdriver is used for both. A couple of turns out adds noticeable performance gains, in a couple of turns adds 2 to 3 mpg. Along with the secondary rod change, it makes a big difference. Of course an AF gauge is the only right way to tune your car. Curious, what kind of mpg is achieved with these new Holley style carbs? Can they match the Street Demon or Qjet, both with an ideal tune?
The tuning on the Street Demons is pretty straight forward, with little to change and virtually all of that on the outside of the carbs. Very much like the AFBs or AVS or Thermoquad carbs are. You can go from thrifty gas mileage to strip tunes in a few minutes, with a few turns of screws or a swift change of rods and or springs.

Kenne-Bell racing tested the Thermoquad versus the Quadrajet versus the 850 Holley, and found the Thermoquads matched the 850 in the quarter, but with the gas mileage and driveability of the Quadrajet. This was all in the early 70s on a W30.

Parts interchangeabibility. lots of parts like rods, and springs, and floats and needle and seats are interchangeable between the AFB, AVS and thermoquads and the Street Demons. So for example, you could use brass floats and .120 or larger needle and seats in the Street Demons, if desired.




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Old January 15th, 2019, 06:45 PM
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Originally Posted by coppercutlass View Post
Mac a tight converter will pose issues you cant tune out. Keep that in mind. Your converter could not be enough for that set up or possibly was made too tight. Fwiw
As you know, this converter came from Midwest Converters so quality is not guaranteed. But I can feel it kick in around 2400 or 2500. That shouldn't be too tight for my power band if my numbers are correct. If it's in the trans, I have to get to the shift points first. I have a good article on modifying the governor (which is inside the pan) and I'm making that a winter project. And while i'm in there I'm going to get the right speedo gears in there as well.

Originally Posted by cutlassefi View Post
The Quick Fuel/Brawler/Hot Rod series carbs offer 4 corner idle and have easy to replace air bleeds as well. Toughest thing is replacing jets, which still only takes a couple of minutes.
That all sounds pretty good to me. No drilling out idle tubes and air bleeds?
Originally Posted by olds 307 and 403 View Post
Some have luck with Edelbrock carb, many do not. One member compared the Carter to Edelbrock castings, the Carter were much better. Remember even the AFB/AVS had hot start issues back when they were factory carbs. I really think that was a big part of the Thermoquad getting the Bakelite body. Go with Mark's recommendation, especially if looking for maximum power. Personally I can adjust my part throttle on my Qjet in minutes through the air horn. I slotted the APT adjustment and added a slotted threaded plug. A flat screwdriver is used for both. A couple of turns out adds noticeable performance gains, in a couple of turns adds 2 to 3 mpg. Along with the secondary rod change, it makes a big difference. Of course an AF gauge is the only right way to tune your car. Curious, what kind of mpg is achieved with these new Holley style carbs? Can they match the Street Demon or Qjet, both with an ideal tune?
Well sir, like I said, I was making some major mods on my APT Q-jet hunting for a good idle when it turned out to be the preload on the lifters was too tight. I went through Cliff's instructions for setting the APT a few times but my results were always the opposite of what was supposed to happen. When tip-in was supposed to decrease the idle, mine raised and vice-versa, lol. I never did get that nailed down. Don't get me wrong, I was determined to be the local "Quadrajet guy" but I went through three Q-jets and all of them were warped beyond repair. I thought about buying the straightening jig but lost interest at that point.
I would also be interested in know about the gas mileage of the newer Holleys. One of the reasons I like the Q-jets is because of the small primaries. Currently I'm getting 18+ mpg (highway) with the 200-4R overdrive locked.

Originally Posted by Firewalker View Post
The tuning on the Street Demons is pretty straight forward, with little to change and virtually all of that on the outside of the carbs. Very much like the AFBs or AVS or Thermoquad carbs are. You can go from thrifty gas mileage to strip tunes in a few minutes, with a few turns of screws or a swift change of rods and or springs..
I know nothing about this design. What are the springs of which you speak? Is it like the vacuum activated power piston of the Quadrajet?
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Old January 15th, 2019, 07:18 PM
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Originally Posted by Macadoo View Post
As you know, this converter came from Midwest Converters so quality is not guaranteed. But I can feel it kick in around 2400 or 2500. That shouldn't be too tight for my power band if my numbers are correct. If it's in the trans, I have to get to the shift points first. I have a good article on modifying the governor (which is inside the pan) and I'm making that a winter project. And while i'm in there I'm going to get the right speedo gears in there as well.


That all sounds pretty good to me. No drilling out idle tubes and air bleeds?


Well sir, like I said, I was making some major mods on my APT Q-jet hunting for a good idle when it turned out to be the preload on the lifters was too tight. I went through Cliff's instructions for setting the APT a few times but my results were always the opposite of what was supposed to happen. When tip-in was supposed to decrease the idle, mine raised and vice-versa, lol. I never did get that nailed down. Don't get me wrong, I was determined to be the local "Quadrajet guy" but I went through three Q-jets and all of them were warped beyond repair. I thought about buying the straightening jig but lost interest at that point.
I would also be interested in know about the gas mileage of the newer Holleys. One of the reasons I like the Q-jets is because of the small primaries. Currently I'm getting 18+ mpg (highway) with the 200-4R overdrive locked.



I know nothing about this design. What are the springs of which you speak? Is it like the vacuum activated power piston of the Quadrajet?

The springs that push the fuel rods up, on the primaries, when vacuum drops enough and you need more fuel.


Last edited by Firewalker; January 15th, 2019 at 07:22 PM.
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Old Yesterday, 03:03 PM
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Informative video, thanks man. Those are very much like the power piston in a Quadrajet. And exactly like the Edelbrock, down to the shape of the metering rod cover.
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Old Yesterday, 05:24 PM
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Originally Posted by Macadoo View Post
Thanks for the input Eric. But Copper is correct; the 3310 didn't keep up. But to be fair, I didn't do any part swaps to get it tuned.



I think I have the idle pretty good, finally. It was the same thing you posted to Youtube; getting the mechanical advance out of the picture at idle, but kicking in just when touching the throttle. I't s a little high in park but works well at curb idle. I read about a lot of guys talking about a "nice, crisp throttle response." I'd like to have that. Maybe it's the 200-4R. I still need to modify the governor to lengthen the 1-2 shift. And honestly, I'm tired of pulling the carb and air horn to make the slightest change in a Q-jet.


That BR-67214 gets good reviews for sure. Some posts say it's just a rebranded Proform. But that Proform gets good reviews too and is a little more expensive.



Which is why I'd like something easier to tune than a Q-jet. The Edelbrock has easy access to the rods but I think that's not true for the jets. But the airhorn comes off pretty easily.

Once you get the tune right there isn’t much that needs done to a Q-Jet. The metering rods are easy to change, and so is the part throttle tune.

if you provide a Q-Jet expert with your engine specifics they can come up with a recipe that will get the tune in the ballpark. Then all the fine tuning is done without major carb teardown
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Old Yesterday, 06:13 PM
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What is your trans shifting at? The small weight I grind down a lot, tap and locktight a small screw and grind the head down even with the weight. This brings the factory 4000 rpm shift points to 5000 rpm with stock springs. You might be able to increase it some with a lighter spring and it will stay in place. The Street Demon/Thermoquad was basically Carter's answer to the Qjet. Holley eliminated the Bakelite body, Aerospace polymer now, leaky O rings, divorced choke and secondaries that needed a special tool. Too bad the they don't have a 800 or 850 cfm model.
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Old Yesterday, 06:27 PM
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Originally Posted by matt69olds View Post



Once you get the tune right there isn’t much that needs done to a Q-Jet. The metering rods are easy to change, and so is the part throttle tune.

if you provide a Q-Jet expert with your engine specifics they can come up with a recipe that will get the tune in the ballpark. Then all the fine tuning is done without major carb teardown
Yeah man, I've been through a couple of modded Q-jets using Ruggles recipes. My main problem was finding a core that wasn't warped, especially the air horn but also the main body and base plate. I have four of them and all horribly warped. i'm just ready to try something different.

Originally Posted by olds 307 and 403 View Post
What is your trans shifting at? The small weight I grind down a lot, tap and locktight a small screw and grind the head down even with the weight. This brings the factory 4000 rpm shift points to 5000 rpm with stock springs. You might be able to increase it some with a lighter spring and it will stay in place. The Street Demon/Thermoquad was basically Carter's answer to the Qjet. Holley eliminated the Bakelite body, Aerospace polymer now, leaky O rings, divorced choke and secondaries that needed a special tool. Too bad the they don't have a 800 or 850 cfm model.
Yup, that exactly what I'm talking about doing with the governor. Except my shifts don't reach 4k, more like 3500. At least that's where it's at with the proper amount of preload on the TV cable.
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Old Yesterday, 06:29 PM
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With an automatic transmission and street use, shouldn't I be looking for a vacuum secondary carb? They seem hard to find above 750 cfm without BIG money.
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Old Yesterday, 06:54 PM
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Originally Posted by olds 307 and 403 View Post
What is your trans shifting at? The small weight I grind down a lot, tap and locktight a small screw and grind the head down even with the weight. This brings the factory 4000 rpm shift points to 5000 rpm with stock springs. You might be able to increase it some with a lighter spring and it will stay in place. The Street Demon/Thermoquad was basically Carter's answer to the Qjet. Holley eliminated the Bakelite body, Aerospace polymer now, leaky O rings, divorced choke and secondaries that needed a special tool. Too bad the they don't have a 800 or 850 cfm model.
I don't think Holley wants these to be known for ultimate power and going fast, so limited their CFM sizes, but that can be changed for those who dare and actually need more than 750 CFMs.

The question might be how does a 500 CFM rated at 3" 2bl carb can make over 500 horsepower, when it's only 353.5 CFM rated at 1.5 inch 4bl levels. Its because the advertised flow is somewhat meaningless on a running motor, where increased vacuum increases its CFMs. So if a 353.5 cfm carb can make 500+ horsepower, then a 750 cfm might not be that shabby.
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Old Yesterday, 07:13 PM
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I know nobody likes Ebrock's, but I've used the 1407 manual choke for over 15 years and feel it's a decent trouble free carb for street use. My question is everyone says it's a relabled Carter, but it has Weber stamped on the side. Are Carter and Weber the same?
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Old Yesterday, 07:13 PM
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I agree on a Street Motor, the 750 Street Demon would work fine.
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Old Yesterday, 07:39 PM
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Mac if you wanna try an edelbrock. I can borrow a 750 cfm from my boss and we can try it on one weekend and see how it works. He also has the tuning kit. He wants to sell one and he owes me a favor or two.
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Old Yesterday, 08:45 PM
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https://www.chevyhardcore.com/tech-s...on-carburetor/

A link on tuning a Street Demon, though this will apply to other cars somewhat.
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