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Old 05-28-2008, 12:07 PM
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Holley or Quadrajet

OK I'm sure the mileage thing has been beat around pretty well. I've seen where a Holley 4150 is not very good on mileage. I'm running one a 355 Chevy in a T-bucket. I have an old Quadrajet that I could rebuild and swap on the Chevy. Would the mileage be much or any better with the Quadrajet? I currently get 12 mpg in town and 16 mpg on the highway. I know hot rods are not about mileage but if I can do better, why not?

A rebuild kit is $85. That is for a super kit not just gaskets.

http://www.carburetor.ca/carbs/HTML/SuperKits/SK05B.htm

I'll probably also need an adapter for the carb to manifold (WEIAND). This carb has the 'divorced choke'. I don't think that will work with my manifold. My Holley has no choke. I've had no trouble even at 20 degrees. Can I just wire the choke open? A conversion to electric is like $45.

Thanks,

Bill

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Old 05-28-2008, 12:29 PM
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The milage you end up with will depend on the jets and rods and primary spring that is in the qjet. It's a crap shoot and you may need to order up a LOT of jets and rods to get it dialed in.

My thoughts on the master kit: Way too much stuff for what you need. They include an elect choke coil, which you don't have. They kindly include new brass bushings for the throttle shafts, but do NOT include the reamer, which they do offer for a mear $159.99!!! If your primary shaft is fairly snug, the bushings are not needed.
They include a new brass float. Personally, I like the phoenolic floats. I have a drawer full of brass ones!

You can get a good kit from Napa for about 20 bucks and a new float is 12.

I dunno, building a very old, unknown qjet would not be my first choice. I"d look for a newer 80's version with electric choke. Most of those are set up fairly lean and will provide a better starting point for a milage carb.

Mark
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Old 05-28-2008, 02:01 PM
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how much do you drive the t bucket ? you running what a 650 DP on yer 355 ? 12mpg & 16mpg ain't that bad except a t bucket is light weight. but sounds like the Holleys doing ok.
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Old 05-28-2008, 02:50 PM
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First clue is no trouble starting in 20 degree weather that bad boy is way rich.Need to check float level, jetting, any leaking gaskets etc. A properly set up carb will not start and run easily in that temp without a choke.
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Old 05-28-2008, 03:13 PM
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Quote:
Originally Posted by barnym17
First clue is no trouble starting in 20 degree weather that bad boy is way rich.Need to check float level, jetting, any leaking gaskets etc. A properly set up carb will not start and run easily in that temp without a choke.

Very good observation! Kinda wish i'd thought of it! LOL

It might be easier to find a basic 600 vac secondary elec. choke Holley and de-tune it some. Atleast it would bolt on and hopefully you already have lots of jets and gaskets laying around.
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Old 05-28-2008, 07:30 PM
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Quote:
Originally Posted by barnym17
First clue is no trouble starting in 20 degree weather that bad boy is way rich.Need to check float level, jetting, any leaking gaskets etc. A properly set up carb will not start and run easily in that temp without a choke.
It has #64 primary jets. I don't see or smell any obvious leaks. The floats are just at the bottom of the sight holes. With the original air cleaner ($10 flea market 10") the plugs were black. I put on a K&N and now the plugs are a dark brown. I was thinking a bit leaner might help. Are light brown correct?

Thanks,

Bill

Last edited by longt; 05-28-2008 at 07:38 PM.
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Old 05-28-2008, 07:35 PM
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Quote:
Originally Posted by Mustangsaly
how much do you drive the t bucket ? you running what a 650 DP on yer 355 ? 12mpg & 16mpg ain't that bad except a t bucket is light weight. but sounds like the Holleys doing ok.
That's why I don't want to put too much into it. I don't drive it a whole lot, 1500 miles/year of so. I just want to see if I can do better. Hot rods are never finished right?

Thanks,

Bill
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Old 05-28-2008, 09:07 PM
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You are heading in the right direction but not there yet,Is your idle mixture set correctly? best way for strret car is the lean drop method. 1.Warm the engine to operating temp,2 Verify ignition timing is correct .3 Set your base idle speed ,at this point set it as low as it will go and still idle.4. with a dwell tach hooked up adjust each idle mixture screw one at a time a.Back the mixture screw out slightly to confirm it changes idle speed and quality(leaning) then go in slowly until highest speed is reached, then turn the screw back out till the idle drops 50 rpm.Repeat for the other side. B do it again. You have just set your carb to best lean idle. Reset to your desired idle speed.If you have a radical cam we may have to do some more adjustments. Also do you have a functioning pcv system hooked up to the pcv port at the back of the carb? If not it is time to install one these carbs are designed with the airflow of the pcv in mind and if not present it will be rich at idle. The pcv flow is a controlled vacuum leak the designers allowed for when setting up the carb. You can make it work without it but it is easier when installed.See what this does and we will work on main metering, Idle transfer setting etc. this may correct the whole problem without having to get to involved,if not we will figure it out.Now having said all this a Holley will probably never get the mileage of a qjet it is simply not nearly as sophisticated .
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Old 05-28-2008, 09:10 PM
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One thing I forgot this all depends on the throttle not being open to far to get idle speed.Once you open them to far it will be idling on the main ciruit and we have to make some fixes in that case. But if turning the mixture screws changes idle characteristics we should be ok.
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Old 05-28-2008, 09:39 PM
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A Q-jet has a bit of a design advantage over a 4150/4160 Holley because of the smaller primaries.

Holley makes a 4175(?) spreadbore that will fit without an adapter ... but they are usually more money.

Holley P/N 80555C is pretty typical.
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Old 05-28-2008, 11:17 PM
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If you're really interested in getting the most from a Qjet, don't use an adapter. Take a look at one. The primaries go from the tiny Qjet size up to a huge diameter, while the huge secondaries get necked down in a similar fashion. Its not ideal, and while its possible to get them working fine it tends to remove some of the drivability and mpg for which Qjets are so famous. The real answer is to get a spreadbore intake for the Qjet.

My suggestions in order of preference are; 1- tune what you have, 2- change the intake and add the Qjet (which will require tuning as well), 3- as an absolute last resort I would do the adapter.

A well-tuned holley is a powerful critter. It will never have the throttle response or MPG of a Qjet in most cases, but its a fine carb and it just sounds like yours is a little off.

In my boat I tried to split the difference; I got a spreadbore Holley
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Old 05-29-2008, 01:18 PM
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ASSUMING that your Weind intake is a single-plane type with just a big square-ish opening ...


an adapter plate of this type is not too bad. (Trans-Dapt P/N 3220)
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Old 05-29-2008, 01:37 PM
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First off, a 355 will run just great on a 550-600 cfm carb. But what besides a .030 350 do you have? Manifolds, intake and exhaust, camshaft, rear gears, transmission, ignition? Right now we are taking a 'shotgun' approach.

There are those that love the Q-jet and people like me that feel that they take too much time to "get right". IMHO - a 4150 Holley for the racers and an Edelbrock or 600CFM #0-1850 4160 Holley for the cruisers

A t-bucket, 12-16 mpg ain't all that bad. Remember - it has a barn door sized windshield, a window sized radiator, if it has a top, it just makes the barn door windshield even bigger plus the tires hang in the breeze. Now this is NOT streamlining

The 'bucket I had ran a .030 351W(356ci), a big Lunati cam, a Performer intake, a 600CFM Edelbrock, Sanderson headers and an MSD ignition with 3.40 gears with short tires. I considered myself lucky if I got 12 - and the plugs were a pale shade of tan.

JIC you feel that I don't know 'buckets -

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Old 05-29-2008, 05:13 PM
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Quote:
Originally Posted by Irelands child
First off, a 355 will run just great on a 550-600 cfm carb. But what besides a .030 350 do you have? Manifolds, intake and exhaust, camshaft, rear gears, transmission, ignition? Right now we are taking a 'shotgun' approach.

There are those that love the Q-jet and people like me that feel that they take too much time to "get right". IMHO - a 4150 Holley for the racers and an Edelbrock or 600CFM #0-1850 4160 Holley for the cruisers

A t-bucket, 12-16 mpg ain't all that bad. Remember - it has a barn door sized windshield, a window sized radiator, if it has a top, it just makes the barn door windshield even bigger plus the tires hang in the breeze. Now this is NOT streamlining

The 'bucket I had ran a .030 351W(356ci), a big Lunati cam, a Performer intake, a 600CFM Edelbrock, Sanderson headers and an MSD ignition with 3.40 gears with short tires. I considered myself lucky if I got 12 - and the plugs were a pale shade of tan.

JIC you feel that I don't know 'buckets -

Nice T!

My 355 Chevy has World heads, Weiand Team G single plane manifold, 4150 Holley with mechanical secondaries, Choke tower has been removed, 3.00 rear end gear 8" Ford, typical T bucket exhaust, TH-350 with a mild shift kit, 2500 stall torque converter (suggested by Phoenix Transmissions based on engine specs.), Mallory HEI ignition, no external ignition boxes. I don't know the cam but it is a mild Crower hydraulic. The engine was tuned on an engine dyno when built and before it was sent to me from FL. I'm in PA. It made 391 hp on the dyno.

Bill
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Old 05-31-2008, 07:56 AM
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New question

Quote:
Originally Posted by barnym17
You are heading in the right direction but not there yet,Is your idle mixture set correctly? best way for strret car is the lean drop method. 1.Warm the engine to operating temp,2 Verify ignition timing is correct .3 Set your base idle speed ,at this point set it as low as it will go and still idle.4. with a dwell tach hooked up adjust each idle mixture screw one at a time a.Back the mixture screw out slightly to confirm it changes idle speed and quality(leaning) then go in slowly until highest speed is reached, then turn the screw back out till the idle drops 50 rpm.Repeat for the other side. B do it again. You have just set your carb to best lean idle. Reset to your desired idle speed.If you have a radical cam we may have to do some more adjustments. Also do you have a functioning pcv system hooked up to the pcv port at the back of the carb? If not it is time to install one these carbs are designed with the airflow of the pcv in mind and if not present it will be rich at idle. The pcv flow is a controlled vacuum leak the designers allowed for when setting up the carb. You can make it work without it but it is easier when installed.See what this does and we will work on main metering, Idle transfer setting etc. this may correct the whole problem without having to get to involved,if not we will figure it out.Now having said all this a Holley will probably never get the mileage of a qjet it is simply not nearly as sophisticated .
This will probably sound dumb... when setting the idle mixture do you block off any used vacuum ports, like PCV and trans, or leave them normally connected? When I tried to set the idle mixture I didn't see any vacuum change. I hooked the vacuum guage up to the trans port. The only other used port was the PCV valve. I know if you don't see a vacuum change the first suspect is a vacuum leak.

Bill
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