Carburetor Question for a 70 Cutlass Supreme
October 10th, 2023, 11:25 AM
#1
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Join Date: Sep 2023
Location: Wisconsin
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Carburetor Question for a 70 Cutlass Supreme
What is the best bang for your buck carb for a 4 barrel olds 350. I’ve tried the Holley calculator, which gave me some ideas, but I’d really to get a good idea through the actual experience of others…
October 10th, 2023, 01:01 PM
#5
Out of Line, Everytime😉
Join Date: Dec 2006
Location: Melville, Saskatchewan
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On a completely factory motor, the factory Quadrajet. Now it is modified then whatever brand of carb you prefer tuned with a wideband to your particular motor. Something like the Steet Demon 750 cfm will bolt right to your factory intake but may be way off for a factory stock 1970 Olds 350. Now with a cam change and headers, it might be very close. See what I am getting at?
October 10th, 2023, 03:27 PM
#8
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Join Date: Nov 2008
Location: Central Fl
Posts: 7,881
This is like asking what’s the best cookie available today.
Buy whatever and tune it with a wideband as mentioned. However be prepared to spend a considerable amount of time tuning a Qjet or todays Brawlers. They’ll most likely be all over the place.
October 10th, 2023, 05:46 PM
#12
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Join Date: Sep 2023
Location: Wisconsin
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On a completely factory motor, the factory Quadrajet. Now it is modified then whatever brand of carb you prefer tuned with a wideband to your particular motor. Something like the Steet Demon 750 cfm will bolt right to your factory intake but may be way off for a factory stock 1970 Olds 350. Now with a cam change and headers, it might be very close. See what I am getting at?
don’t quote me on that though I still very new to this all…
October 10th, 2023, 06:14 PM
#14
Out of Line, Everytime😉
Join Date: Dec 2006
Location: Melville, Saskatchewan
Posts: 8,994
The big thing with the stock Quadrajet is condition. It may need all the throttle shafts bushed as well as a rebuild with a new float. It could be corroded inside and who knows what else, it is 50+ years old. The later 800 cfm are the best Quadrajet carbs but are also lean emissions carbs, unmodified. As said, the stock carb may be a little off but should be close but only a wideband will truly tell you. Do you have a carb preference?
October 10th, 2023, 08:59 PM
#15
CH3NO2 LEARN IT BURN IT
Join Date: Jul 2010
Location: Land of Taxes
Posts: 4,917
Hello, Mr Dingus allow me to be long-winded,
A properly tuned QJet won't need to be touched with a screwdriver until it's ready for a rebuild in 10-20 years. A Holley on the other hand comes with a screwdriver.
Buy a QJet from a custom builder....not a big box supplier.
The correct QuadraJet will bolt right back into the same spot without any modification to the linkage or air cleaner.
The 1900 series Edelbrock is easy to tune. The rods, jets, and springs can be swapped without taking the carb apart. You will need throttle and trans kick-down linkage mods.
Demons are supposed to be good, I don't have any experience with them. You will likely need the same linkage mods.
You will never find a carb out-of-the-box tuned and ready to go. It may run but not to its full potential. No carb will.
Carburetor tuning is a lost art. It's an analog metering device in a digital world.
If you are willing and able to be patient and have a good tinkering skill set. and basic tools, go for it.
You can get it close with a good understanding of how a carb works. You will need a vac gauge, tac/dwell meter, a timing light, and know how to read spark plugs. A wideband A/F meter is even better.
The bottom line, any carb will work if properly tuned.
Option 2 find a good QJ rebuilder that tests the carb on an engine before shipping it back to you. It will still need basic tuning.
Option 3 buy a new carb and find a person who knows how to install and tune it.
Man, I need to open an old-school shop!
A properly tuned QJet won't need to be touched with a screwdriver until it's ready for a rebuild in 10-20 years. A Holley on the other hand comes with a screwdriver.
Buy a QJet from a custom builder....not a big box supplier.
The correct QuadraJet will bolt right back into the same spot without any modification to the linkage or air cleaner.
The 1900 series Edelbrock is easy to tune. The rods, jets, and springs can be swapped without taking the carb apart. You will need throttle and trans kick-down linkage mods.
Demons are supposed to be good, I don't have any experience with them. You will likely need the same linkage mods.
You will never find a carb out-of-the-box tuned and ready to go. It may run but not to its full potential. No carb will.
Carburetor tuning is a lost art. It's an analog metering device in a digital world.
If you are willing and able to be patient and have a good tinkering skill set. and basic tools, go for it.
You can get it close with a good understanding of how a carb works. You will need a vac gauge, tac/dwell meter, a timing light, and know how to read spark plugs. A wideband A/F meter is even better.
The bottom line, any carb will work if properly tuned.
Option 2 find a good QJ rebuilder that tests the carb on an engine before shipping it back to you. It will still need basic tuning.
Option 3 buy a new carb and find a person who knows how to install and tune it.
Man, I need to open an old-school shop!
October 11th, 2023, 05:54 AM
#16
BBQ
Thread Starter
Join Date: Sep 2023
Location: Wisconsin
Posts: 12
Hello, Mr Dingus allow me to be long-winded,
A properly tuned QJet won't need to be touched with a screwdriver until it's ready for a rebuild in 10-20 years. A Holley on the other hand comes with a screwdriver.
Buy a QJet from a custom builder....not a big box supplier.
The correct QuadraJet will bolt right back into the same spot without any modification to the linkage or air cleaner.
The 1900 series Edelbrock is easy to tune. The rods, jets, and springs can be swapped without taking the carb apart. You will need throttle and trans kick-down linkage mods.
Demons are supposed to be good, I don't have any experience with them. You will likely need the same linkage mods.
You will never find a carb out-of-the-box tuned and ready to go. It may run but not to its full potential. No carb will.
Carburetor tuning is a lost art. It's an analog metering device in a digital world.
If you are willing and able to be patient and have a good tinkering skill set. and basic tools, go for it.
You can get it close with a good understanding of how a carb works. You will need a vac gauge, tac/dwell meter, a timing light, and know how to read spark plugs. A wideband A/F meter is even better.
The bottom line, any carb will work if properly tuned.
Option 2 find a good QJ rebuilder that tests the carb on an engine before shipping it back to you. It will still need basic tuning.
Option 3 buy a new carb and find a person who knows how to install and tune it.
Man, I need to open an old-school shop!
A properly tuned QJet won't need to be touched with a screwdriver until it's ready for a rebuild in 10-20 years. A Holley on the other hand comes with a screwdriver.
Buy a QJet from a custom builder....not a big box supplier.
The correct QuadraJet will bolt right back into the same spot without any modification to the linkage or air cleaner.
The 1900 series Edelbrock is easy to tune. The rods, jets, and springs can be swapped without taking the carb apart. You will need throttle and trans kick-down linkage mods.
Demons are supposed to be good, I don't have any experience with them. You will likely need the same linkage mods.
You will never find a carb out-of-the-box tuned and ready to go. It may run but not to its full potential. No carb will.
Carburetor tuning is a lost art. It's an analog metering device in a digital world.
If you are willing and able to be patient and have a good tinkering skill set. and basic tools, go for it.
You can get it close with a good understanding of how a carb works. You will need a vac gauge, tac/dwell meter, a timing light, and know how to read spark plugs. A wideband A/F meter is even better.
The bottom line, any carb will work if properly tuned.
Option 2 find a good QJ rebuilder that tests the carb on an engine before shipping it back to you. It will still need basic tuning.
Option 3 buy a new carb and find a person who knows how to install and tune it.
Man, I need to open an old-school shop!
October 11th, 2023, 07:49 AM
#17
Running On Empty
Join Date: Jul 2018
Location: Earth
Posts: 18,708
Find the model # of your carb, order a rebuild kit. Very easy to rebuild the carb. Tons of videos if you want visual tutorial assistance. Grab a new filter, gasket & spring while you’re at it. Model # located on driver side of carb towards rear with numbers running vertical.
October 11th, 2023, 01:05 PM
#18
Registered User
Join Date: Feb 2013
Location: Phoenix, AZ
Posts: 14,068
That has not been my experience. I started driving with a 1970 Cutlass Supreme then moved to the current 1971 Cutlass Supreme convertible. Over the past 40 years the QuadraJet on each of them has worked very well. As said above it's very easy to rebuild and keep running well.
October 11th, 2023, 04:58 PM
#19
BBQ
Thread Starter
Join Date: Sep 2023
Location: Wisconsin
Posts: 12
On a completely factory motor, the factory Quadrajet. Now it is modified then whatever brand of carb you prefer tuned with a wideband to your particular motor. Something like the Steet Demon 750 cfm will bolt right to your factory intake but may be way off for a factory stock 1970 Olds 350. Now with a cam change and headers, it might be very close. See what I am getting at?
October 11th, 2023, 05:34 PM
#20
Out of Line, Everytime😉
Join Date: Dec 2006
Location: Melville, Saskatchewan
Posts: 8,994
As is maybe not, depends on the size of the aftermarket cam. The idle passages need enlarged to provide enough fuel with increased duration. The 1970 carb is better than say an unmodified 1980 Qjet. Once modified correctly, 1980 carb will make more power due to the extra 50 cfm on the primary side.
October 11th, 2023, 07:19 PM
#21
Registered User
Join Date: Feb 2013
Location: Phoenix, AZ
Posts: 14,068
My 350 has a 217/221 cam, Performer RPM intake manifold, headers, and a 2500 RPM stall converter. And the original QuadraJet carb.
October 11th, 2023, 10:27 PM
#22
Registered User
Join Date: May 2009
Location: Northern California
Posts: 1,705
I have street motors mildly warmed over, nothing loud or lumpy, but fun.
I can recommend carbs from SMI (Sean Murphy Induction) in SoCal. They do good work and when you do the order they ask good questions about your engine so they can jet it right. I’ve found they jet it a bit rich which is the right side to err on, but I only second guess them because I’m using 02 sensors on both tailpipes to really dial in the jetting.
Tell ‘em what you have and I’m sure they’ll build something good for you.
Chris
I can recommend carbs from SMI (Sean Murphy Induction) in SoCal. They do good work and when you do the order they ask good questions about your engine so they can jet it right. I’ve found they jet it a bit rich which is the right side to err on, but I only second guess them because I’m using 02 sensors on both tailpipes to really dial in the jetting.
Tell ‘em what you have and I’m sure they’ll build something good for you.
Chris
October 12th, 2023, 08:37 PM
#23
CH3NO2 LEARN IT BURN IT
Join Date: Jul 2010
Location: Land of Taxes
Posts: 4,917
With every change to the engine, the carb will need to be retuned to optimize performance.
A 750 CFM QuadraJet is good up to 375-400 hp without major modification above simple rod springs jets and AVSD adjustments.
The cam, timing curve, trans type, and rear-end gear ratio all need to be considered as a system and tuned accordingly.
Anything above stock cam profiles will require advanced modifications and are for the advanced tuner, not a novice. If you consider yourself a novice carb guy buy and understand these books:
and
https://www.ebay.com/itm/15563387539...kaAuYuEALw_wcB
A 750 CFM QuadraJet is good up to 375-400 hp without major modification above simple rod springs jets and AVSD adjustments.
The cam, timing curve, trans type, and rear-end gear ratio all need to be considered as a system and tuned accordingly.
Anything above stock cam profiles will require advanced modifications and are for the advanced tuner, not a novice. If you consider yourself a novice carb guy buy and understand these books:
and
https://www.ebay.com/itm/15563387539...kaAuYuEALw_wcB
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