Quadrajet info needed!
Thread Starter
Registered User
Joined: Mar 2006
Posts: 119
From: Minnesota
Quadrajet info needed!
So I've monkeyed enough with my Edelbrock 1407 (750cfm) carb and I think based on some advice here and my own research elsewhere that I'd rather just buy a Quadrajet, but I need some definitive answers before I purchase.
1.) Will I need an adapter for the q-jet work with my Edelbrock Performer RPM Intake Manifold? I know the quadrajet is a spread-bore, but I have read both spread and square-bore for edelbrocks... does anyone know for sure? Or is there a way I can measure for myself?
2.) What is a good source for Quadrajets? Not a rebuild kit, I need the entire carb (car already had the eddy on it when I got it) I've heard you can get them pre-setup (or at least close) to your engine
2.a) I have seen them on Summit/Jegs etc. but they all say for Chevy... is there actually a difference or does that just mean GM?
Related questions
3.) Is it helpful to run a fuel pressure regulator with a Q-jet? (this was one suggestion for some of the issues I was having with the edelbrock carb as anything above 6-6.5psi can cause flooding...?)
4.) Do you guys run a fuel filter between the pump & carb? Previous owner spliced one into the metal line just using rubber line & hose clamps...
I'll probably use this opportunity to replace the line & I'd like to just run a replacement steel line hence why I'm asking about filters/regulators
...actually what I'd like to do is run braided line ('cause it looks b*tchin' lol) but I've heard both that regular steel line is better and also that the available adapters for a quadrajet don't actually work
As always, any help/info/points-in-the-right direction is appreciated!
1.) Will I need an adapter for the q-jet work with my Edelbrock Performer RPM Intake Manifold? I know the quadrajet is a spread-bore, but I have read both spread and square-bore for edelbrocks... does anyone know for sure? Or is there a way I can measure for myself?
2.) What is a good source for Quadrajets? Not a rebuild kit, I need the entire carb (car already had the eddy on it when I got it) I've heard you can get them pre-setup (or at least close) to your engine
2.a) I have seen them on Summit/Jegs etc. but they all say for Chevy... is there actually a difference or does that just mean GM?
Related questions
3.) Is it helpful to run a fuel pressure regulator with a Q-jet? (this was one suggestion for some of the issues I was having with the edelbrock carb as anything above 6-6.5psi can cause flooding...?)
4.) Do you guys run a fuel filter between the pump & carb? Previous owner spliced one into the metal line just using rubber line & hose clamps...
I'll probably use this opportunity to replace the line & I'd like to just run a replacement steel line hence why I'm asking about filters/regulators
...actually what I'd like to do is run braided line ('cause it looks b*tchin' lol) but I've heard both that regular steel line is better and also that the available adapters for a quadrajet don't actually work
As always, any help/info/points-in-the-right direction is appreciated!
Registered User
Joined: Sep 2011
Posts: 2,148
From: Plano, TX
1) The intake is a spread bore. It's easy to tell. Take off the carb - if the back of the carb opening widens to support much larger secondaries than primaries, then it's set up for a spread bore. Square bore intakes look like a square.
2) The linkage and other relatively minor bits are very different. Anything can be made to work. However, I would never buy one from an online shop or a parts store. Some folks on here may have cores or be willing to do a build. There's also well regarded folks like Sparky (Sparky's carbs) that do good work.
3) As long as you're running a mechanical pump and it's in good shape then there's no need.
4) As long as the filter is in the carb, then there's no need.
If you use a repop hard line, then you absolutely need to get the right style of qjet. The location of the fuel inlet is one of the major differences between the GM configurations.
I run braided, and it's fine. I did have to buy two different adapters to get one that sealed well - ended up with the purple one (forget who made it). There are two different inlet sizes in the QJet family, and each had two different sealing methods over their life. So it's easy to pick the wrong thing and end up with a mess.
2) The linkage and other relatively minor bits are very different. Anything can be made to work. However, I would never buy one from an online shop or a parts store. Some folks on here may have cores or be willing to do a build. There's also well regarded folks like Sparky (Sparky's carbs) that do good work.
3) As long as you're running a mechanical pump and it's in good shape then there's no need.
4) As long as the filter is in the carb, then there's no need.
If you use a repop hard line, then you absolutely need to get the right style of qjet. The location of the fuel inlet is one of the major differences between the GM configurations.
I run braided, and it's fine. I did have to buy two different adapters to get one that sealed well - ended up with the purple one (forget who made it). There are two different inlet sizes in the QJet family, and each had two different sealing methods over their life. So it's easy to pick the wrong thing and end up with a mess.
Old(s) Fart
Joined: Mar 2007
Posts: 50,803
From: Northern VA
Out of Line, Everytime😉
Joined: Dec 2006
Posts: 10,109
From: Melville, Saskatchewan
If you are set on a new carb, get a Street Demon 625 or 750 cfm carb. It is based off the Thermoquad but all new castings with a better choke and bowl options. Full tuning kits are available and mileage should equal a Qjet. If you want a Qjet, get a late 70's Olds core and find a good builder. Although most guys who do it, should have cores
Thread Starter
Registered User
Joined: Mar 2006
Posts: 119
From: Minnesota
1) The intake is a spread bore. It's easy to tell. Take off the carb - if the back of the carb opening widens to support much larger secondaries than primaries, then it's set up for a spread bore. Square bore intakes look like a square.
2) The linkage and other relatively minor bits are very different. Anything can be made to work. However, I would never buy one from an online shop or a parts store. Some folks on here may have cores or be willing to do a build. There's also well regarded folks like Sparky (Sparky's carbs) that do good work.
3) As long as you're running a mechanical pump and it's in good shape then there's no need.
4) As long as the filter is in the carb, then there's no need.
If you use a repop hard line, then you absolutely need to get the right style of qjet. The location of the fuel inlet is one of the major differences between the GM configurations.
I run braided, and it's fine. I did have to buy two different adapters to get one that sealed well - ended up with the purple one (forget who made it). There are two different inlet sizes in the QJet family, and each had two different sealing methods over their life. So it's easy to pick the wrong thing and end up with a mess.
2) The linkage and other relatively minor bits are very different. Anything can be made to work. However, I would never buy one from an online shop or a parts store. Some folks on here may have cores or be willing to do a build. There's also well regarded folks like Sparky (Sparky's carbs) that do good work.
3) As long as you're running a mechanical pump and it's in good shape then there's no need.
4) As long as the filter is in the carb, then there's no need.
If you use a repop hard line, then you absolutely need to get the right style of qjet. The location of the fuel inlet is one of the major differences between the GM configurations.
I run braided, and it's fine. I did have to buy two different adapters to get one that sealed well - ended up with the purple one (forget who made it). There are two different inlet sizes in the QJet family, and each had two different sealing methods over their life. So it's easy to pick the wrong thing and end up with a mess.
As for the line, I guess if I'm not running a filter or a regulator I'd probably just get a new prefabricated steel line (from inline tube or fusick or whoever) - though that obviously depends on getting the correct Olds carb
Thread Starter
Registered User
Joined: Mar 2006
Posts: 119
From: Minnesota
If you are set on a new carb, get a Street Demon 625 or 750 cfm carb. It is based off the Thermoquad but all new castings with a better choke and bowl options. Full tuning kits are available and mileage should equal a Qjet. If you want a Qjet, get a late 70's Olds core and find a good builder. Although most guys who do it, should have cores
Between the two, which would you say is simpler?
...or more accurately, which do you sort of "fire and forget" because that's one thing that drew me to the quadrajet in the first place is that it seems like everyone says once you get it tuned you never have to mess with it
Registered User
Joined: May 2013
Posts: 223
From: Richardson, Texas
this is a search of the Oldsmobile q-jets at Summit
http://www.summitracing.com/search/p...cending&page=2
http://www.summitracing.com/search/p...cending&page=2
Old(s) Fart
Joined: Mar 2007
Posts: 50,803
From: Northern VA
this is a search of the Oldsmobile q-jets at Summit
http://www.summitracing.com/search/p...cending&page=2
http://www.summitracing.com/search/p...cending&page=2
Out of Line, Everytime😉
Joined: Dec 2006
Posts: 10,109
From: Melville, Saskatchewan
A Street Demon will be more tunable by a non experienced tuner. I am seriously considering the 750. I have a very nice running Holley reman Qjet. I would stay away from any reman carbs. Seems they suck now, even the Holley ones. Mine I notched the part throttle adjustment, added a threaded plug to access it and upped the primary jetting to 73 from 71, has 44K primary rods. I also run the CV rods with a G hanger on the secondary. The Street Demon will match a Qjet for performance, mileage and should be just as trouble free. I liked the Thermoquad but the choke sucked and they had flooding issues with leaky O rings. Both of those have been addressed with a better electric choke and eliminating the O rings all together. They also give you an option on a polymer or aluminum main body. I never had issues with my Thermoquads with bad bodies but some did. The Street Demon is all new castings with modern polymer not Bakelite resin like the Thermoquad. Another plus is no special tool is needed to adjust the secondary air door, unlike the Thermoquad. Just use a flat screwdriver if it needs adjusted. Remember the Thermoquad was Carter's answer to the Qjet, this is an improved, non emissions version with better tuning abilities.
Last edited by olds 307 and 403; Aug 3, 2013 at 06:41 AM.
Registered User
Joined: Oct 2010
Posts: 398
From: Austin, TX
The two best resources for information on Q jets are the Doug Roe book and the Cliff Ruggles Book. Oldsmobile carbs used a straight fuel inlet while Chevrolet used a side inlet. Either would work, but the correct fuel line for an Olds will come into the carb behind the thermostat housing.
There are many carb rebuilders. I used Dean Oliver. He set my Q jet up perfectly. Only adjustment I needed was the high idle. Have not had to adjust it for years. Here is his web site.
http://www.retunedmusic.com/deano/
Dean Oliver 870-830-5470
He is a great guy to deal with. Will take the time to set it up for your application and engine build details.
There are many carb rebuilders. I used Dean Oliver. He set my Q jet up perfectly. Only adjustment I needed was the high idle. Have not had to adjust it for years. Here is his web site.
http://www.retunedmusic.com/deano/
Dean Oliver 870-830-5470
He is a great guy to deal with. Will take the time to set it up for your application and engine build details.
Thread Starter
Registered User
Joined: Mar 2006
Posts: 119
From: Minnesota
The car will stall under hard breaking or cornering so I think maybe the floats need to be adjusted...?
I know the Eddy is on the older side (at least 13 years based on my + last owner's history) and looks like it could use a rebuild... problem is, this is a TRUE daily driver (I've seen some people use that term loosely, just because they take it out once or twice a week for ice cream - nothing wrong with that, but mine is a commuter vehicle 5 days a week... In fact, I switch cars in the spring & fall, so my Aurora is in storage, uninsured at the moment) so I can't afford to have the carb off for any extended period of time
So for the money and inconvenience, it seems a better route to get one ready to go and just do a swap
I probably wouldn't get rid of the edelbrock, I probably WILL fix/rebuild it and use it on a different project
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