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24K views 23 replies 12 participants last post by  vspinelli77 
#1 ·
I just posted on the new members listing then I saw this one.

I was lookin to maybe rebuild the carb on my eldorado when my wife said just get a new one. So since thats a option any suggestions as to what has been working best.
thanks Dave
 
#3 ·
A good rule of thumb is to use the following formula as a guideline:


(Cu/In)*max_rpm/3456=cfm.

Engine = 500cu/in
Max_rpm = 4500

formula looks like 500*4500/3456 = 651cfm carb.

Please note, I have been building engines for over 20 years and this formula is pretty close at all levels. Too much carb will cause you nothing but grief.

Good luck.
Ogier :dance:
 
#4 · (Edited)
I put a brand NEW Edelbrock Performer 1411 carb on my 69 Caddy hearse with a 472 motor. This carb is 750 cfm electric choke and I love it. Easy to install and $298.00 from Advance Discount Auto Parts. If your going new this is a great carb. you will have to buy the adapter plate for an additional $30.00 but it is well worth it. Pulled it out of the box bolted it on and started driving. Didn't need to mess with the carb in anyway as far as adjusting it. Was perfect right out of the box. http://www.edelbrock.com/automotive/carb_square.html
 

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#5 ·
AZ Dave said:
I just posted on the new members listing then I saw this one.

I was lookin to maybe rebuild the carb on my eldorado when my wife said just get a new one. So since thats a option any suggestions as to what has been working best.
thanks Dave
I would use an Edelbrock 600 on it if it were mine. I have used four of these over the last few years and, like another poster here alerady said, you just put them on and drive away. Just be careful and don't fall in to the "bigger is better" thinking that we sometimes fall in to...

Steve B.
 
#6 ·
In all the searches I did when looking to replace my carb. the 1411 was the suggested carb for the 472 motor. It has nothing to do with thinking bigger is better, this is the carb. recommended when entering the info regarding my vehicle i.e. year make and model. This is from Advance Auto Parts website.

750 cfm Carburetor with square-flange and electric choke

For 402 c.i.d. and larger Performer applications. Lean calibration for maximum fuel economy. Provides excellent fuel economy when used on 454 c.i.d. Chevrolet and 460 c.i.d. Ford Performer applications.

Includes both timed and full vacuum ports for ignition advance.Comes with the following jets, rods and springs: Metering Jets: Primary .110, Secondary .107; Metering Rods: .075 x .047. Step-Up Spring: orange (5" Hg).

As I stated before I love mine. Runs great and have never had a problem. The 472 and 500 cad motors are basically the same motor. So if it works on the 472 I don't see why it wouldn't work equally as well with your application.
 
#7 ·
Sasquatch said:
In all the searches I did when looking to replace my carb. the 1411 was the suggested carb for the 472 motor. It has nothing to do with thinking bigger is better, this is the carb. recommended when entering the info regarding my vehicle i.e. year make and model. This is from Advance Auto Parts website.
I wasn't questioning your carb choice Sasquatch. Personally I would choose the 600 over the 750 but that is just my opinion. My warning against "bigger is better" was meant to let him know to stay away from the over 1000cfm carbs like the Demon racing carbs.

600 cfm is a little bit small and 750 is a little big. I personally like the 600 best because the low end performance is a little better and thats where I drive my cars.. They never get wound out so I would never see the handicap at the top end. Your mileage may vary, tax tag and title extra.

Steve B.
 
#18 ·
I wasn't questioning your carb choice Sasquatch. Personally I would choose the 600 over the 750 but that is just my opinion. My warning against "bigger is better" was meant to let him know to stay away from the over 1000cfm carbs like the Demon racing carbs.

600 cfm is a little bit small and 750 is a little big. I personally like the 600 best because the low end performance is a little better and thats where I drive my cars.. They never get wound out so I would never see the handicap at the top end. Your mileage may vary, tax tag and title extra.

Steve B.
These 472 and 500 Cadillac engines came from the factory with an 800cfm Quadrajet carburetor.
 
#9 ·
Thanks for the input so far.
I checked out a Edelbrock #1406 today and it wasn't emmissons legal. I would need the 1400 He did have a Holley that was "pretty much the same thing" and it was legal, but I hadn't really heard to much on there product in this discuisson.

Dave
 
#10 ·
AZ Dave said:
Thanks for the input so far.
I checked out a Edelbrock #1406 today and it wasn't emmissons legal. I would need the 1400 He did have a Holley that was "pretty much the same thing" and it was legal, but I hadn't really heard to much on there product in this discuisson.

Dave
Sorry Dave I didn't even think about you still needing to pass emissions tests. What is the cut off year in Arizona (if thats where you are)?

I haven't had any experience with the Holley carbs. Hopefully someone familiar with them will chime in soon.

Steve B.
 
#12 ·
Imprl59 said:
Sorry Dave I didn't even think about you still needing to pass emissions tests. What is the cut off year in Arizona (if thats where you are)?

I haven't had any experience with the Holley carbs. Hopefully someone familiar with them will chime in soon.

Steve B.
The emisions cut off is '67 in Arizona.
It seemjs that The Edelbrock's come with more assessories and stuff. the Holley I looked at was just the carb.

Dave
 
#13 ·
Mystical_Ice said:
don't put a 600 in a 500c.i. engine... i put a 600 cfm edelbrock (model #1400 = electric choke) in my 368c.i. engine... that was what people recommended for it (mechanics i know) and it worked out fine. i can't see it working for an engine that's one third bigger than mine ;)
I was looking to get a carb for my mild .060 over 500 (514ci). The tech at Demon told me that a 725 Road Demon was all I needed.
95% of the engines out there are way over carbed (percentage just a guess but probably pretty close). A carb that's too big can lower the overall performance of the vehicle.
The formula posted by Ogier will get you really close to what you need.
 
#20 ·
Remember that the QJ uses airflow-controlled secondaries - it will only flow as much air as the engine needs at wide open throttle. The primaries are the same size on both "sizes" of QJ. It's all done with primary and secondary metering rods, secondary air valve spring wrap, and secondary rod hanger sizing. The carbs are infinitely tuneable. There are over a dozen primary metering rod tapers and over 90 secondary metering rod configurations.

Whatgever you do with a QJ, get the HP paperback book by Doug Roe - "Rochester Carburetors".

The Edelbrock is a poor copy of the old Carter AFB - Aluminum Four Barrel. A well-tuned QJ is far better. Swap meets for rods, hangers, bits & pieces.

602638
 
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#21 ·
Yes they are very tunable. I recently installed some wideband 02 sensors in my LeMans, running a Q-jet on that. Getting some smaller secondary metering rods to richen the mixture some. Showing about 12.8 on the primary side, and when I get into the secondaries it is a bit lean, running around 14-1. My APT needs to be leaner as well, but that may affect the desirable 12.8 I have. Jetting, mixture rods, etc. Fun to do now that I know exactly what the AFR is.

Cliff Ruggles is a wealth of information as well. He is very active in his forum, Cliffshighperformance.com. He recently retired from his full time shop building carburetors, he has been drag racing Pontiacs for decades. Very good advice there for all makes and models running these carburetors.
 
#23 ·
I agree the Quadrajet is very tuneable. It's also true the secondaries only allow much fuel as needed. However, most Quadrajets were 750cfm. The Quadrajets that came on the big Cadillacs were 800cfm. This is what the factory engineers believed was the best fit for the engine. The point I was trying to make is that a 750cfm Edelbrock, in my opinion, is not too much carb for a Cadillac 500, as some other poster had suggested a 600 cfm carb. Any of these engines can me made to run with almost any size carb if tuned properly. Ford and Lincoln 460 motors came from the factory with a 600cfm Motorcraft carb. I actually have both engines in cars that I own and can honestly say the 500 with an 800 cfm Quadrajet has more power and pulls harder than the 460 with the smaller carb (I replaced Motorcraft 600 cfm with a Street Demon 625cfm, as the venturis match up well with the original intake. Edelbrock carbs run well and don't require constant adjustments, like some Holley's do. However, the Edelbrock primaries are larger and may not match up well with a factory intake which has small openings matched to a Quadrajet. The solution is to either use an Edelbrock dual plane intake, open up the factory intake or use an adapter for the Edelbrock, otherwise it may not run right.
 
#24 ·
So here's my 2 cents... I have a 76 Calais Sedan - my Old Man bought it new, and it's been with us ever since. I've been puttering around with this car since the early 2000's (about 20 years), and I've learned a few things. First, if you have an excellent near mint Quadrajet - send it out for a professional rebuild and add a 1" phenolic spacer ( Canton Racing 85-250 ), with the Fel Pro Marine Q-Jet gasket above and below (one above, one below the spacer) - the Fel Pro gasket is 0.23" thick, part number 17845. You'll need the thick gaskets and spacer to combat fuel boiling in the carb. This is an issue whether you use your stock carb or an aftermarket - it has to do with the Ethanol in modern fuel causing boiling at lower temperatures. It's a real PITA. The stock Q-Jet carbs were 800 - 820 CFM (yes, I said 800, look it up). Anyway - if your Q-Jet is beat to heck, has been manhandled over the years, worked on by an idiot, or is just plain gone, then an Edelbrock Performer 800 CFM ( part number 1413 ) is the way to go. "Oh no, that's too big!" -- lies, all lies. I am assuming that we are talking about STOCK OEM intake manifolds. If you have an aftermarket manifold, then it is likely single plane, and my comments are not applicable. However, if you have a STOCK OEM manifold, then it is DUAL PLANE (there is a divider wall between the left and right halves of the plenum, directly under the carb. With a dual plane manifold, any given cylinder only "sees" 2 barrels of the carburetor (one primary, and one secondary). None of the cylinders are ever exposed to all 4 barrels. In a single plane application, all 8 cylinders individually are exposed to all 4 barrels. Our stock Cadillac 472's and 500's have a dual plane cast iron manifold. Also, keep in mind the stock Q-Jet was 800-820 CFM. So, why would GM put such a big carb on a motor that only rev's to 4,000 or 4,500 RPM ? Partly because it's a dual plane manifold. It's a massive motor, and it needs to breathe. And why do so many people struggle with aftermarket carbs on these motors ? Because they need to breathe. You need a ton of air. The traditional metering springs / rods / and jets in most carburetors are going to be far too rich for the application - which is in part why so many vehicle owners will say that a 650 or 750 "runs good" out of the box (even when it doesn't). I ran a 650 for a while 15+ years ago, and it was TERRIBLE. Non responsive, sluggish, just a dog. The 800 Edelbrock would stall out from time to time, run pig-rich, and fouled plugs right out of the box. I dialed mine in with an Air-Fuel-Ratio gauge (wide band oxygen sensor), and these are the results... -- PARTS -- -- Edelbrock 1413 Performer Series Carb with Electric Choke -- -- Edelbrock 1480 Tuning Kit ( contains primary jets / rods / and metering springs ) -- -- Edelbrock 120-407 Primary Rods and 68-47 Primary Jets ( from the 1480 tuning kit ) -- -- Edelbrock PINK ( 66-187 ) Metering Springs ( from the 1480 tuning it ) -- -- Move Accelerator Pump Linkage 1 step leaner by moving linkage to the 2nd (MIDDLE) hole ( carb ships new with linkage in the 1st hole - closest to the carb body ). -- -- Edelbrock 1425 Secondary Jets ( 0.092" orifice ) to lean out wide open throttle ( these are purchased separately, not part of the tuning kit ) -- -- Choke is set to 1/8th open at cold, per Edelbrock manual. This is slightly tighter than the carb ships when new - it's about 1/4-inch open when shipped new. -- -- Edelbrock 77280 Throttle Kickdown Switch (they call it a 'Nitrous Kit', but all it does is close a switch when the throttle linkage is near 90+ percent, which I use to trigger the electronic transmission kickdown that is stock in my 76 Calais - the OEM switch was on the driver side and won't work with Holley or Edelbrock Linkage - only the stock Q-Jet linkage). Idle mixture screws will be roughly 1-1/4 turns out. Check this with an AFR gauge preferably, or dial it in for 20" of vacuum at 800 - 1,000 RPM. I use a 2" open element 14" round air cleaner for reference. Note - a 3" tall would be better, but won't clear my hood with the phenolic spacer installed. I usually let the car warm up for 10+ minutes when it is stone cold, or 3 to 5 minutes when coming out of the grocery store. The car runs like a scaled dog. I am exceedingly happy with the carburetor and the support guys at Edelbrock.
 
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