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Old 05-06-2013, 04:04 PM
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Carb swap tips

I am ready to chuck this quadrajet at a high rate of speed into the wall

I am eyeballing an Edlebrock 1806 (squarebore, elec choke, air valve secondary, 650 CFM). What do I need to consider when doing the swap?

I am certain the old steel fuel line won't work.

What about the throttle cable? Right now I am having to use a Mr Gasket universal bracket and cable, can I reuse those?

Need a new squarebore plenum spacer too.

What else am I missing?

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Old 05-06-2013, 07:15 PM
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Check your fuel psi at the carb and compare to the new carb specs.
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Old 05-06-2013, 07:17 PM
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Quote:
Originally Posted by Silver Surfer View Post
I am ready to chuck this quadrajet at a high rate of speed into the wall

I am eyeballing an Edlebrock 1806 (squarebore, elec choke, air valve secondary, 650 CFM). What do I need to consider when doing the swap?

I am certain the old steel fuel line won't work.

What about the throttle cable? Right now I am having to use a Mr Gasket universal bracket and cable, can I reuse those?

Need a new squarebore plenum spacer too.

What else am I missing?
Remember where I mentioned qjets and big duration cams not being friendly without a bunch of work?
if i remember right you have good heads, an xE274 and around 10.1:1 correct?
Do this and be happy and faster, depends on gear and converter so pick your poison, but either will work
Holley 0-4779CK1 Holley Classic Double Pumper Carburetors & Kits
Holley 0-3310SAK Holley 750 cfm 4-bbl Carburetor with Manual Choke
JEGS Performance Products 15150 JEGS Billet Aluminum Throttle Brackets
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Old 05-06-2013, 07:21 PM
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Things to consider,fuel fittings,fuel line location and length,throttle cable mounting,( check that you have full throttle by having someone step on the pedal) kick down?Vacuum line re routing, air cleaner still fits, warm air feed for cold starts if it applies?,return spring fits
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Old 05-07-2013, 11:40 AM
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Quote:
Originally Posted by bygddy View Post
Remember where I mentioned qjets and big duration cams not being friendly without a bunch of work?
if i remember right you have good heads, an xE274 and around 10.1:1 correct?
Do this and be happy and faster, depends on gear and converter so pick your poison, but either will work
Holley 0-4779CK1 Holley Classic Double Pumper Carburetors & Kits
Holley 0-3310SAK Holley 750 cfm 4-bbl Carburetor with Manual Choke
JEGS Performance Products 15150 JEGS Billet Aluminum Throttle Brackets
Yes your memory is good! Some would argue that Vortec heads are not good heads though. The truck has 3.73 posi with a 4 speed manual trans.

Well I don't want to start a which carb is better thread. I really don't have too much opinion (yet) on Holley v Edelbrock, but I want to stay away from double pumpers just to keep MPG in check (this is just a street truck that won't see any track time).

I got the cam break in done on Saturday, but there was a fuel leak at the inlet on the qjet. The threads are OK, the boss is not cracked, and the white plastic seal is also present on the inlet fitting as well...so who knows why it leaks, I can't figure it out. So in the meantime I have put some ARP thread sealer on it (yes it is gasoline safe).

So long story short I have not had a chance to drive the truck yet, so as far as tuning it remains to be seen if the carb has any manners. The old cam from the PO was an older grind Crane 222 @ .050" and the carb ran well with the setup. Although the vacuum operated secondaries were rigged to open all at once, which I have since changed back...maybe that was done for a reason?

I was planning on getting a new square bore carb in the future just so as to match the Edelbrock RPM intake. Right now I have this carb adapter (http://www.summitracing.com/parts/edl-2693) which is advertised at least to overcome the problems of regular spread to square mounting.

So it looks like if I do go the Holley route I will need to get a Holley specific throttle cable bracket? No arguments as to quality, it has to be better than the POS Mr. Gasket universal one on there now! What if I go the Edelbrock carb route? Will I need a new bracket too?
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Old 05-07-2013, 12:02 PM
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I have to ask why the 1806 instead of the 1405 or 6? The AVS feature, while nice, really wonder if it's necessary on a street driven vehicle. Then, next do you really need the additional 50 cfm and for those added $50-60 bucks that could be used to get a decent Lokar cable and bracket(I have seldom found anything with the Mr Gasket label worth bringing home). Did you go though the cfm calculator that Summit posts with the carbs? VE is seldom more then 80-85% and you seldom operate the engine at peak rpm. Of course, it is your decision and money, I'm just being a devil's advocate

A better cfm formula:

Size = CID x RPM/3456 x VE
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Old 05-07-2013, 12:10 PM
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I would just fix and dial in the Q jet you got.
But if you are hell bent on using Edelbrock the 750cfm AFB or the 800 AVS thunder carb are better
for your purpose. No they are not too big.
The carb formula does not get you the right size carb for the job.
its for fools. A Qjet flows 795cfm.

If fuel mileage is a priority the Qjet is the best overall choice.
But you have to dial it in. All you are doing is trading one set of tuning,setup,install issues for another
and you already own the Qjet.
Qjet tuning and service parts edelbrock, the carb shop etc etc.

Wiht teh XE274H-10 cam and the small Qjet primary throttles you will need to use very generous idle timing in the area of 24-26deg BTDC to get correct throttle position and T slot exposure at idle.
Get the primary throttle Tslot exposure right so the idle screws are active to adjustment.
lack of idle timing results in the primary throttles too far open at idle.
Generous idle timing gets it dialed in.

Last edited by F-BIRD'88; 05-07-2013 at 12:22 PM.
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Old 05-07-2013, 12:20 PM
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carb flow

Quote:
Originally Posted by F-BIRD'88 View Post
I would just fix and dial in the Q jet you got.
But if you are hell bent on using Edelbrock the 750cfm AFB or the 800 AVS thunder carb are better
for your purpose. No they are not too big.
The carb formula does not get you the right size carb for the job.
its for fools. A Qjet flows 795cfm.

If fuel mileage is a priority the Qjet is the best overall choice.
But you have to dial it in. All you are doing is trading one set of tuning,setup,install issues for another
and you already own the Qjet.
Qjet tuning and service parts edelbrock, the carb shop etc etc.

Wiht teh XE274H-10 cam and the small Qjet primary throttles you will need to use very generous idle timing in the area of 24-26deg BTDC to get correct throttle position and T slot exposure at idle.
Get the Tslot exposure right so the idle screws are active to adjustment.
lack of idle timing result in the primary throttles too far open at idle.
mostly true,,,
why is it that people recommend small carbs and big heads?
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Old 05-07-2013, 02:46 PM
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Originally Posted by vinniekq2 View Post
mostly true,,,
why is it that people recommend small carbs and big heads?
Are you speaking in general or to my setup. I have the Mexican Vortecs which are 165cc nominal (if memory serves) intake runners. And are you saying the 650 cfm suggestion by Irelands Child is too small?
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Old 05-07-2013, 02:49 PM
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Quote:
Originally Posted by Irelands child View Post
I have to ask why the 1806 instead of the 1405 or 6? The AVS feature, while nice, really wonder if it's necessary on a street driven vehicle. Then, next do you really need the additional 50 cfm and for those added $50-60 bucks that could be used to get a decent Lokar cable and bracket(I have seldom found anything with the Mr Gasket label worth bringing home). Did you go though the cfm calculator that Summit posts with the carbs? VE is seldom more then 80-85% and you seldom operate the engine at peak rpm. Of course, it is your decision and money, I'm just being a devil's advocate

A better cfm formula:

Size = CID x RPM/3456 x VE
I am no expert. Is the Air valve system just a clone of the vacuum secondaries like the original qjet? Where as other vacuum controlled secondaries use some sort of vacuum port?
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Old 05-07-2013, 03:07 PM
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Quote:
Originally Posted by Irelands child View Post
I have to ask why the 1806 instead of the 1405 or 6? The AVS feature, while nice, really wonder if it's necessary on a street driven vehicle. Then, next do you really need the additional 50 cfm and for those added $50-60 bucks that could be used to get a decent Lokar cable and bracket(I have seldom found anything with the Mr Gasket label worth bringing home). Did you go though the cfm calculator that Summit posts with the carbs? VE is seldom more then 80-85% and you seldom operate the engine at peak rpm. Of course, it is your decision and money, I'm just being a devil's advocate

A better cfm formula:

Size = CID x RPM/3456 x VE
I can't figure out the deal between the 1405 and 1406. To me they seem to be the same carb, except the 05 is the manual choke...but the descriptions seem to indicate that out of the box the 1406 is a tad lean?

1405: Moderate street high performance, street and towing.
1406: Mild performance, calibrated for economy.
1806: Moderate high-performance street.
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Old 05-07-2013, 03:34 PM
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Quote:
Originally Posted by Silver Surfer View Post
I am no expert. Is the Air valve system just a clone of the vacuum secondaries like the original qjet? Where as other vacuum controlled secondaries use some sort of vacuum port?
I'm not an expert either, but have run many carbs over the years. I do like the Performer based carb as super easy to "play" with as far as tuning particularly on a street engine. These carbs as well as the AVS and their predecessors, the Carter AFBs all use a weighted secondary set of butterflies above the mechanically operated secondary butterflies that opens by air velocity rather then using a vacuum chamber. You can, if brave, reduce the weight on those upper secondaries as I have done in the far distant past on Carters and open them faster. It is a crapshoot though. Neither way is right or wrong as Holley and even many if not all of the Rochester Q-jet use vacuum. It seems that too many people think bigger is best and they have done it or know of someone who did - maybe but probably not. An engine can only 'intake' just so many cubic feet per minute and atomize the fuel correctly for efficiency plus economically. That formula that I gave above has stood the test of time - and is NOT my formula but one used by most engine builders for overall best operation of their product. If you are running a NASCAR 358 cubic inch engine with a VE (volumetric efficiency of 100%) and at 8-9000+ rpm, you were required by them to run an 830 cfm carb. Not bad for 8-900 horsepower at 205 mph as seen at Talladega on Sunday. The formula above holds!!! Sorry naysayers. Oh and a for instance - Ford with the carbed 460 - that OEM 4bbl was never larger then 525 cfm. A 600 cfm Edelbrock 1405/6 or Holley 0-1850 would work wonders but a 780 cfm Holly 3310-1 made it a gas guzzling dog.

That Q-jet, set up correctly and on a proper intake is as good or better as either the Performer/AVS or Holley. It just cost more in dollars and time to get to that point

Below is a 1405 being rebuilt and another to be done as well. You can see the upper butterflies in the back barrels. What you see is about all there is to the Edelbrocks.



The same carb on my SB Ford:



As a note, that is not a 1406 but a modified for electric choke 1405
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Old 05-07-2013, 03:45 PM
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Quote:
Originally Posted by Silver Surfer View Post
I can't figure out the deal between the 1405 and 1406. To me they seem to be the same carb, except the 05 is the manual choke...but the descriptions seem to indicate that out of the box the 1406 is a tad lean?

1405: Moderate street high performance, street and towing.
1406: Mild performance, calibrated for economy.
1806: Moderate high-performance street.
Out of the box is a good start point. You need the mod kit for the 1405 for the best alternatives for either. And you are 100% correct in that they are the same carb but with the 1406 being a bit leaner new, off the top of my head .003" primaries (.098 vs .101) as well as more expensive)
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Old 05-07-2013, 04:49 PM
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generally speaking

Quote:
Originally Posted by Silver Surfer View Post
Are you speaking in general or to my setup. I have the Mexican Vortecs which are 165cc nominal (if memory serves) intake runners. And are you saying the 650 cfm suggestion by Irelands Child is too small?
If the carb is minimal size then it will run out of breath.
I use 750s on 283 and bigger.My street car has a 950. The smallest Holley I ever used was a 600. I bought a car that had a 600 double pumper,it ran 13.9s when I bought it.The first thing I changed was the carb to a 750 double pumper,it then ran 13.4s. If you never race the car then the extra horse power will never be missed.I later changed the carb to an 800 double pumper then 850.It ran a best of 11.9s when it was stolen.the engine was a 355
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Old 05-07-2013, 10:59 PM
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Quote:
Originally Posted by Silver Surfer View Post
I am ready to chuck this quadrajet at a high rate of speed into the wall

I am eyeballing an Edlebrock 1806 (squarebore, elec choke, air valve secondary, 650 CFM). What do I need to consider when doing the swap?

I am certain the old steel fuel line won't work.

What about the throttle cable? Right now I am having to use a Mr Gasket universal bracket and cable, can I reuse those?

Need a new squarebore plenum spacer too.

What else am I missing?
Like you know the Q-jet fuel line won't work as-is, it comes in from the front or side, but further forward than the Edelbrock carb.

The quick and dirty way of dealing w/it is to use rubber fuel line from the existing fuel line to the Eddy fuel inlet, but I do not recommend this due to the chance of fire. It doesn't take a lot of money or work to bend up a steel line from the pump to carb. Also there are several companies who make braided steel lines that go from the fuel pump to the carb that look good and are safer than splicing a rubber line into the factory steel line. Using braided steel line from the end of the factory line is another way to go that's better than just a bare rubber line, but doesn't look as good.

What is wrong w/how the Q-jet is running? Did you change the power piston spring? There could be dozens of things so I'll wait to see what you can tell about the performance using the Q-jet. There's no reason the Q-jet cannot be made to work, although it will take tuning (and maybe re-tuning) to get it dialed in right.

The ignition advance curve has to be set right as well. You can have a perfect carb but w/o the advance curve being right for the cam, etc. the engine will still run like stink.
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