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800 cfm QJ on my 300

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F-250 Restorer
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800 cfm QJ on my 300

Post #1 by F-250 Restorer » Wed Oct 31, 2012 12:33 pm

I should begin by saying that the QJ is a variable cfm carburetor. My carb came off a 301, and was set up for a 301 by GM. That means the flow was severely limited with a stop on the air flaps that prevents them from opening more than 1/4th of their potential. So, what could be a 800 cfm carburetor, is designed to flow far less by GM.

That is why I targeted a 301 carb. Not only are the air flaps and secondary butterflies limited, GM designed this carb for a smaller displacement engine ... like a 300. Most people don't realize that QJ's are set up by the factory specifically for each engine. People see them and think that b/c they all look the same, one carb fits all engines. Not the case. GM tailors each QJ to the engine it is to be used on by installing different size fuel restrictions in the passages inside the carb where the fuel travels. Along with those restrictions they drill various size air bleeds to smooth the flow, and tailor the amount of idle by pass air.

For quite a while I struggled to understand how air bleeds work. I read Cliff Ruggles' book about Qj's several times, but couldn't get it. Then, one morning as I was pouring milk from a waxed carton, and it was chugging as it came out, I thought that if I poked a little hole in one end of the carton the milk would pour smoothly. Bingo. A light went off, and I realized what the air bleeds in the QJ do: they allow the fuel to flow smoothly. Size is determined by desired flow! That's why the racers open them slightly.

One thing to be careful of with QJ's is to find one w/o the tell tale rebuild sticker. Many of rebuilders mix and match the three parts of the QJ, air horn (top) float body, and throttle plate, making them nearly impossible to tune. That is why I sought out one with the oem protecting tubes still in place around the mix screws. Those protective tubes told me the carb had never been rebuilt. I struck gold. (I also wanted one designed for use outside of California. All QJ's later than 1975, when they were redesigned to address the leaking plugs beneath the float bowl, begin their serial #'s with 1705. The next number shows the year it was made. The sixth digit should be a 1 or a 2, which means a federal application. A 4 or 5 here means a lean running California emissions carb).

To tune it I wired the secondaries closed. Using a .072 main jet with a Cliff Ruggles .044 custom m.rod and one of the stiffest power booster springs produced remarkable results.

Once I found that combo, I unwired the secondaries. I also removed a bit of the air flap stop to allow them to open more. I also adjusted the linkage so the butterflies open 90 degrees. With my C6 the secondaries only open if I stomp on it from a stop, and then only the last second before it shifts. Still, I had to dial them down. I chose a about the leanest s.rod: a CH, with is about the size of a birthday candle. Along with that I toned down the hanger too. You see, QJ secondary hangers are gauged in .005" increments, A being the richest, and Z the leanest. Right now I am at 'N', and that seems about right.

I should buy a a/f tester so I can tune the cruising mix.

*Trick: When pulling the air horn (top) off the QJ to change jets or m.rods, etc, you have to drive out the pen that holds the accelerator pump arm in place, and then pry it back through with a screw driver, all the while trying to hold the arm in the exact spot to allow the pen to go through. If the carb is on an engine it can be a PIA. What I now do, after many a try, is put the arm in place and insert a punch or nail or drill bit (whatever you used to tap the pen out) in the opposite side and use it to feel the hole. Once you find the hole with the punch, push it through the arm to hold it, then pry the pen back through. That trick really saves a lot of time.

One of the nice things about the QJ is that there are parts available everywhere. There are sites that sell everything you could ever need. For example, the 301 Pontiac QJ fuel supply fitting sticks straight out the front of the carb, and runs right into my v.cover. A quick visit to the hardware store for a 90* fitting, or a a google search produces sites with the exact fitting needed. That is quite different than finding parts for an Autolite 4100.

There is one other thing I should mention: If you are using an Offenhauser DP manifold, go online and buy one of the 1/4" base gaskets that isolates the primaries from the secondaries. All the kits I've seen have the open type base gasket. When you buy your kit, make sure the needle and seat, and the accelerator pump skirt, are designed to withstand the modern fuels, or else you will be replacing them shortly.

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Re: 800 cfm QJ on my 300

Post #2 by MechRick » Wed Oct 31, 2012 1:05 pm

I'm curious to see the results.

I wanted to do this to my Bronco, with one change...I would have used the feedback version complete with a GM V6 ecu and harness. Six inch tree through the roof ended those plans...
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

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Re: 800 cfm QJ on my 300

Post #3 by CoupeBoy » Wed Oct 31, 2012 2:15 pm

Interesting.. I read your first Q-jet on 300 thread..
QuadraJet on a 300
And I was intrigued by the 4100 Autolite thread
1"Sleeve a 1.12 Autolite 4100
So what draws you back to the q-jet? The last 'word' on the original q-jet thread was a little disheartening..
F-250 Restorer wrote:Summary: Had I known how long it would take, how much it would cost, and how much studying it would require, would I have proceeded with the QJ project? heck no!
I like the q-jet, had one on an old 283 (no idea of its origins) that when coupled with a powerglide used to get me 22-24mpg at 80mph (absolutely NO low end take off though) it was in my early years and paying attention to gear ratios seemed 'silly'.

The autolite thread seems interesting, still not entirely sure how the 1" reduction works in place of the factory venturi, but I like to learn new things.

I look forward to reading this thread as well.
-ron

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Re: 800 cfm QJ on my 300

Post #4 by F-250 Restorer » Wed Oct 31, 2012 3:36 pm

CoupeBoy wrote:Interesting.. I read your first Q-jet on 300 thread..
QuadraJet on a 300
And I was intrigued by the 4100 Autolite thread
1"Sleeve a 1.12 Autolite 4100
So what draws you back to the q-jet? The last 'word' on the original q-jet thread was a little disheartening..
F-250 Restorer wrote:Summary: Had I known how long it would take, how much it would cost, and how much studying it would require, would I have proceeded with the QJ project? heck no!
I like the q-jet, had one on an old 283 (no idea of its origins) that when coupled with a powerglide used to get me 22-24mpg at 80mph (absolutely NO low end take off though) it was in my early years and paying attention to gear ratios seemed 'silly'.

The autolite thread seems interesting, still not entirely sure how the 1" reduction works in place of the factory venturi, but I like to learn new things.

I look forward to reading this thread as well.
-ron


Thanks for mentioning those other posts. Regarding the first QJ post: I was trying to make a QJ designed for a 350 sbc work on a Ford 300. With fledgling skills, it, quite simply, got out of control when I started drilling fuel restriction orifices. I was lost. So I targeted a QJ designed for equivilent ci engines. All I did was hot tank it, and throw a kit on it, and rebush the throttle shaft. I learned a lot with that first one. I left everything oem and it was a lot cheaper. A kit can be had for about 25. Metering rods are found on Summit racing for the Edelbrock QJ. They interchange. They cost about $15 a pair, delivered. With the first one I used many parts not used on #2. I was inexperienced and didn't know that certain things weren't needed.

It is a complicated carb though. It took, and is still taking, a lot of experience and reading to dial one in. What I have now is a nice little carb that purrs nicely and performs like a killer dream.

The Autolite 4100 thread: I think I must of gotten some needles now designed for modern fuel, b/c they started leaking badly after just a short while. The sleeve was simply set in place with the primary boosters removed and reinstalled. It worked great. I will run it again once the new needles arrive, and should I tire of the QJ.

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Re: 800 cfm QJ on my 300

Post #5 by CoupeBoy » Wed Oct 31, 2012 3:47 pm

I was kicking parts bins at a local swap meet last weekend. I could have bought 5 or 6 q-jets for about $2530 each.. numerous butterfly plates. I would like to get one for my 300 Clifford Intake, but I remembered that original q-jet thread and decided against it.

I have a Holley 600, but I'd like something with smaller primaries and q-jets have those.. And when those secondaries open you can hear/feel the air rushing through the open flood gates...

good to know on the second carb it was much easier. I will keep looking for a 301/305/307 q-jet..

-ron

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Re: 800 cfm QJ on my 300

Post #6 by bubba22349 » Wed Oct 31, 2012 5:31 pm

*Trick: When pulling the air horn (top) off the QJ to change jets or m.rods, etc, you have to drive out the pen that holds the accelerator pump arm in place, and then pry it back through with a screw driver, all the while trying to hold the arm in the exact spot to allow the pen to go through. If the carb is on an engine it can be a PIA. What I now do, after many a try, is put the arm in place and insert a punch or nail or drill bit (whatever you used to tap the pen out) in the opposite side and use it to feel the hole. Once you find the hole with the punch, push it through the arm to hold it, then pry the pen back through. That trick really saves a lot of time.


Good detailed write up! For an even faster air horn (top) removal, you can also just drive the pin with a punch only far enough back (the width of arm) so as to lift the accelerator pump arm out, no need to remove pin completely from the cover.
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: 800 cfm QJ on my 300

Post #7 by F-250 Restorer » Wed Oct 31, 2012 7:34 pm

Good detailed write up! For an even faster air horn (top) removal, you can also just drive the pin with a punch only far enough back (the width of arm) so as to lift the accelerator pump arm out, no need to remove pin completely from the cover.[/quote]

Thanks. I guess I left that detail unclear. I did not mean to remove the pin. I just meant, as I have always done, to tap it enough to remove the acc. pump arm. The pin stays in place, but trying to pry the pin back into place, after a rebuild or just a quick jet/m.rod change, while holding the acc. pump arm, with tension on the acc.pump, is quite a hassle (for me). It is difficult to tell or see when the pin is aligned with the hole, so I insert a punch on the opposite side of where the existing pin is, and get it through the arm. That way the arm is held perfectly in place why I pry the pin back through the arm. Cheers.

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Re: 800 cfm QJ on my 300

Post #8 by bubba22349 » Wed Oct 31, 2012 11:02 pm

:oopsie: Every so often I do get some brain fog well actually it's ........ :bang:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: 800 cfm QJ on my 300

Post #9 by F-250 Restorer » Wed Oct 31, 2012 11:13 pm

bubba22349 wrote::oopsie: Every so often I do get some brain fog well actually it's ........ :bang:


bubba, I've gotten some good mechanical information from you in the past. It's all good, friend.

I got on the freeway yesterday, and after making the changes recommended by Cliff Ruggles, I wanted to try geting on it hard. I had adjusted the s.flaps to open 90* by changing a piece on the shaft linkage, and I also ground off a bit of the air flaps stop, enabling them to open much more than the oem 1/4. I got to hit it right with my mod c6 for the secondaries to open, but when they did it was a sweet moan that made me laugh. To feel that acceleration was a blast. That's why we all alter these engines. It was more like a small v8 than an inline 6. I wonder if there will be more power once I change the cross drilled s.nozzles and replace with solid one for better fuel dispersal, as Cliff Ruggles recommended.

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Re: 800 cfm QJ on my 300

Post #10 by F-250 Restorer » Sat Nov 03, 2012 11:12 am

I copied this great photo from a member at another forum. It is an I6 Pontiac with a QJ. Sweet.

http://i659.photobucket.com/albums/uu31 ... print1.png

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Yet another Carter AFB possibility...

Post #11 by 1986F150six » Fri Nov 30, 2012 7:18 am

Last night, I was going through some old photos of cars I have owned and ran across one of a 1962 Pontiac Tempest. The engine in it was literally 1/2 of the then popular and potent 389. Mine was equipped with a 1 barrel carburetor and was rated @ 110 HP [8.6 compression ratio]. Another variant was the 1 barrel with 10.25 compression ratio rated @ 120 HP. One could also order this engine with high compression, what was rumored to be the high performance 421 head as well as a 4 barrel carburetor.

This morning, I "Googled" this and read that this version was rated @ 166 HP and the carburetor was a 480 cfm Carter AFB. This might be a good fit for our beloved Ford 300!

As I think back, Pontiac really did delve into some interesting concepts. Imagine, having an independent rear suspension car [Tempest] 2 years ahead of the Corvette. This little car had a rear transaxle, too. And then, Pontiac came out with the 215 OHC six with 1 and 4 barrel carburetors.

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Re: 800 cfm QJ on my 300

Post #12 by F-250 Restorer » Sat Jan 05, 2013 1:43 pm

I'm laughing b/c I think it's been more than a year since I started playing with the Quadrajet(s).

I'm posting b/c after umpteen tries with jets and m.rod changes, I've finally hit a combo that I like. As with the rest of my truck, it is a mix of two carbs!

No matter how I tweaked and prayed to voodoo gods about the 850 cfm QJ, which GM originally put on a 301, I just couldn't get it right. The idle circuit was was lean for my engine. If the idle tubes are changed to .037 orifice, and the down idle restriction is opened a few thousandths as well, the 301 QJ, 17058272, or 17059272, will work well on a 300.

But I was lazy. So, rather than put in the work to replace the idle tubes and enlarge the idle down restriction, I went back to 750 cfm body, from a sbc, with smaller primary bores. I also inserted restrictions in the main air bleeds since it was a Cal. emissions carb, and I wanted to enrich it. With that middle main body, I used the base plate and air horn from the 850 cfm because it was set up for a small ci engine, metering the air/fuel for a small 301 engine. Coupled with the smaller primary bores its a marriage made in heaven, like rum and coke. It idles so smooth, purring like a fat, well fed cat.

I ended up with .072 main jets, #44 metering rods.

Every time the secondaries open with that long, low moan, it cracks me up. I really like it. I just wish it hadn't taken so much work and money to get here. Ultimately, that it took so long and was so complicated, speaks volumes about the carb and its poor reputation. It is not a bolt and go carb. But I wanted to pass along a simple recipe for a QJ to Ford 300:

A sbc QJ Is the easiest and cheapest way to go. Block the idle by pass. Use a $24.99 kit from A.Z. and rebuild. You'll need to install main air bleed restrictions from Cliff Ruggles:

http://i659.photobucket.com/albums/uu31 ... 010552.jpg

and two in the air horn:

http://i659.photobucket.com/albums/uu31 ... 010553.jpg

Then start with #72 main jets, with Cliff Ruggles #44 m.rods. The only other mod you need is to 'slightly' bend the acc. pump arm, so you don't get such a large shot. The outer hole for the linkage is too lean. Set your APT at 2.5 turns from seated. Start your mix screws at one turn out from seated. Away you go.

With post 75 QJ's you don't need to worry about the float bowl leaking through the oem plugs beneath. Adjust and away you go. With the tiny primary bores it is quite peppy.

http://i659.photobucket.com/albums/uu31 ... 010566.jpg




I'm still waiting to see how the mpg is. The throttle response is better.

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Re: 800 cfm QJ on my 300

Post #13 by F-250 Restorer » Sat Jan 05, 2013 1:50 pm

ADJUSTING THE APT (ADJUSTABLE PART THROTTLE, or cruise): This adjustment on the QJ lets you determine where the metering rods are in the jets while you are cruising the freeway.

Easy method to adjust the Adjustable Part Throttle: (This is to adjust how far up or down the metering rods sit in the jets at cruise speed.) 1. Adjust a fully warm idle screw to 2k rpm.

2. Start at 2.5 turns out from seated. Place your hands loosely over the primary choke air flap, as though to choke out the engine, but don't kill the engine. By doing this you are giving the engine less air, making the A/F mix richer. If the engine increases rpm, the mix is lean. If the rpm goes down or stays the same, the mix is rich to start with. Pull off a vacuum line. If the rpm goes up, you're giving the engine more air, changing the mix to one a bit leaner. When the rpm goes up with the v. line off, you've confirmed a rich condition.

3. Depending on what you determined from the previous step, adjust the APT screw. Clockwise is lean--you are dropping tapered m.rods into the jets; counter clockwise is raising the rods, and making the mix rich. You want to find the point where the rpm goes up about 100-150 rpm when you loosely put your hands over the top of carb. That is on the edge of lean. That is where your best mpg/performance will be.

When I started working with the QJ I thought it scary and way complicated. Now I think its a snap--easy as pie. Amazing what four or five rebuilds, 20 or so m.rod and/or jet changes will do for a person.
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Re: 800 cfm QJ on my 300

Post #14 by nightwatchman59 » Sun Feb 10, 2013 5:00 am

I ran an 800 cfm quadrajet off a 1975 Cadillac 500 ci. on my 307 ci. Chevy small block for four years street / strip and nver had to mess w/ it.Best 4bbl I ever stomped on!! :thumbup: My only regret is that I Don't have it (the carb) to bolt on my 300 like you did. Please keep me updated on your project... especially cam choices and pwer / mileage figures. I feel smarter because you took an idea I'd thought up and beat me to it!! THANKS!!!!

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Re: 800 cfm QJ on my 300

Post #15 by F-250 Restorer » Sun Feb 10, 2013 4:12 pm

I have it about where I like it now. I wanted to try the 750 cfm main body, the middle section of the carb, with the smaller primary bores, with the throttle plate and air horn of the 850 cfm carb. That way I got the main air bleeds GM set up for a 305 v8.

I do like it better. I get a better throttle response, and nothing lost with power.

I'm hoping to do some more head work, and am curious how that will affect performance. I have strange ridges in the c.chamber that shroud the valves considerably. That change, along with a C type intake, should make quite a bit of difference. Although my runners were left oem, I did pay to have the bowls cleaned up, and when the head is off I plan to clean up the runners with 110 grit, along with removing the ridges, polishing the chambers.

This is a 1981 head. I've never seen these ridges in this year head:

http://i659.photobucket.com/albums/uu31 ... 010114.jpg



I run an Isky 256 cam, with the larger 1.94 intake valves and 1.6 exh.

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Re: 800 cfm QJ on my 300

Post #16 by BIG 6 farmer » Mon Feb 11, 2013 10:06 am

You sure the head is cast as a 1981? My guess is, it could be an early type High swirl chamber? Pre E7T EFI Head. Been a while since i looked @ a Carb. type Head, dont recall seeing that. Leave Intake Runners as cast. put your work into the Exhaust port Roofs. Using a Q-Jet on a 300 six is very interesting, and should perform very well. Not my favorite Carb., had worked on a lot of them years back. If you have a good one,(not warped or a leaker) they can do every thing very well. I have a complete 75 Cad 500, Carb. too. Doubt i will use the OEM Q-Jet on anything.
83 F 150 SB 4x4 300 six NP 4speed - - 1950 IHC L162 (1&1/2 ton?) - 87 & 88 T-Bird Turbo Coupes - 2000 Triumph Tiger , 76 Honda GL 1000 , & other toys and parts (& junk) -

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Re: 800 cfm QJ on my 300

Post #17 by nightwatchman59 » Wed Feb 13, 2013 9:56 pm

I'm gonna read it every time I see it. I'm a little bothered Ford didn't copy it better, and toss in annular discharge....there's a lot of Buick/ Pontiac loyalists who know the secret well....

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Re: 800 cfm QJ on my 300

Post #18 by jamyers » Thu Feb 14, 2013 3:51 pm

F-250 Restorer wrote:I wanted to try the 750 cfm main body, the middle section of the carb, with the smaller primary bores, with the throttle plate and air horn of the 850 cfm carb. That way I got the main air bleeds GM set up for a 305 v8.
...

Glad you got it dialed in! :beer:

By main air bleeds, are you referring to the Idle Bypass Air Passages, like these? If so, I wouldn't worry about having them on any engine under 400+ cid.
James - '62 Ranchero (200cid), '71 LeSabre (464cid)

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Re: 800 cfm QJ on my 300

Post #19 by F-250 Restorer » Fri Feb 15, 2013 10:53 pm

By main air bleeds, are you referring to the Idle Bypass Air Passages, like these? If so, I wouldn't worry about having them on any engine under 400+ cid.[/quote]

No, the airhorn and baseplate are from a Pontiac 305 (I get the 305 and 307 mixed up), so there are no idle bypass passages in the throttle plate. Most QJ's have two pair: One main air bleed is close to the screw that holds the air horn to main body, the other is in the main body. Here is a photo.

http://i659.photobucket.com/albums/uu31 ... 010552.jpg

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Re: 800 cfm QJ on my 300

Post #20 by F-250 Restorer » Thu Mar 07, 2013 7:06 pm

I've been dealing with QJ's too much. Bought a new travel coffee mug, but could hardly get a sip out of it, so I drilled out the air bleed .100, and now it flows ample. 8)

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Re: 800 cfm QJ on my 300

Post #21 by E4ODnut » Thu Mar 07, 2013 9:51 pm

Ha Ha! Good one! I can relate to this. Now, if you were using programmable EFI you could have re-calibrated your coffee mug with a click of the mouse. (sorry, I just couldn't resist).
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Re: 800 cfm QJ on my 300

Post #22 by bubba22349 » Thu Mar 07, 2013 10:37 pm

LOL :rolflmao: Mechanic guys just can't help moding everything
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: 800 cfm QJ on my 300

Post #23 by Harte3 » Fri Mar 08, 2013 9:39 am

LOL :rolflmao: X2!
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

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Re: 800 cfm QJ on my 300

Post #24 by 78merKri6 » Fri Mar 08, 2013 2:27 pm

Right on Restorer! Loved your thread. Keep your mind,keep on going!
sVehicles: 93 F150 4x4 300BB,stock w/dual outlet Clifords ; 78 Mercury Bobcat w/250SB andC4 auto 2800 stall,milled head, Holman- Moody cam,Offy,3 singles (Holley), port divider, homemade headers; 65 Mustang coupe 200 6 w/C4,stocker--driven&shown.

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Re: 800 cfm QJ on my 300

Post #25 by F-250 Restorer » Tue Aug 05, 2014 1:13 am

I'm sorry to revive an old old thread, but I came across some information that eluded me before and I thought I'd pass it along to those who may be looking for a carb and find this interesting:

First off, I didn't know that Quadrajets came oem on some fords.

GM put an 800 cfm QJ on a 231 C.I. V6. (The cfm of the primary side of an 800 QJ flow around 210 cfm. The primary side of a 750 cfm model is around 180 cfm.)

I recently found one of the 231 carbs, and can't keep away from it. I find the .067 primary jets and .045 metering rods combo intriguing. The mpg of my Summit/autolite 600 is killing me, and I'm bored. :D I'm dying to find out what mpg this will produce. My Summit carb came with .067 primary jets. The same as the QJ, but the QJ has .045 rods stuck down them.

It should be quite a bit different to tune now that I have a AFR gauge!

motzingg
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Re: 800 cfm QJ on my 300

Post #26 by motzingg » Tue Aug 05, 2014 10:51 am

Awesome!

Don't be sorry at all, this thread is excellent, i've had the same thought that the q-jet might be the perfect carb for a 300-6, but i don't know much of anything about them.

If you have the time, and i know this might be asking a lot, but after all this trial and error, could you list the whole setup and all the mods that you've performed to get a well running carb?

Your posts in this thread have been awesome, but its a bit tough to follow what you've changed and figure out the final setup you've settled on.

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Re: 800 cfm QJ on my 300

Post #27 by F-250 Restorer » Tue Aug 05, 2014 12:38 pm

My problem with the other QJ's I tried to tune was that I didn't have an AFR gauge to do it properly. Now I do. You might want to pick up Cliff Ruggles' book about the QJ, used on Amazon is the least expensive.

http://i659.photobucket.com/albums/uu31 ... 010547.jpg

That little guy is the essence of the primary system. Those rods are tapered in stages and sit in the primary jets. The 'tower' sits in a cup like holder with a spring under it. At idle and cruise the tower is held down by strong v. Mash the pedal and v. changes and spring pushes tower and rods up, supplying more fuel, and boost. The Edelbrock carb uses the same system, in different configuration. With the 76, 77, 78, and 79 QJ's you can adjust minutely up or down the power piston for cruise, dialing in the perfect afr for highway cruising, and do it w/o taking the carb apart.

If you get a QJ, get those years, and get one for nearly the same or smaller engine. Google the GM models and get the numbers for a 301 or 231. It is easier to enlarge holes .002 than it is to reduce them. You see, GM tuned QJ's to each application by changing the restrictions with in the carb. In those years they also solved the prob of leaky plugs below the bowl. k

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Re: 800 cfm QJ on my 300

Post #28 by herosandwich » Wed Aug 06, 2014 1:17 am

not entirely positive it's relevant, but throwing a 25 dollar thermoquad with a spreadbore adapter was on my list of doggie doo to try with the 300. it's just too cheap to not be curious, given you have a four barrel manifold

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Re: 800 cfm QJ on my 300

Post #29 by F-250 Restorer » Mon Aug 11, 2014 9:54 pm

Another thing that made to rethink the QJ: I found my 'new' (about what, six months old) Summit carb was leaking fuel from the throttle shaft. The Summit tech laughed and said 'some of the early ones had that problem. Holley,' (and I'm quoting), 'who builds them for us, didn't press in the seal properly, and we replace them for free.' Ahhhh, no thanks. A refund will be better.

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Re: 800 cfm QJ on my 300

Post #30 by jamyers » Mon Sep 15, 2014 1:10 pm

Any updates?

Just a fyi, I highly recommend Mark Northcutt, lives near San Antonio TX. http://www.quadrajetpower.com is his website, he does really nice work at VERY reasonable rates, and he's easy to talk to and deal with. His stock rebuild is $225, you get a lot of work for the $ I had him built me a performance carb, it runs terrific on my Buick 455.

Even if yours doesn't need going through, if you have questions about jetting or getting the idle right, give him a call. :beer:
James - '62 Ranchero (200cid), '71 LeSabre (464cid)

The ONLY safety device we need is a 6" sharpened steel spike bolted to the center of the steering wheel of EVERY vehicle.
Emergency Rooms and Funeral Homes will be busy for a week or so, then I predict a dramatic drop in vehicle accidents.

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Re: 800 cfm QJ on my 300

Post #31 by F-250 Restorer » Wed Sep 17, 2014 9:25 pm

Thank you for the link. I'm a writer and working on a novel, trying to get it finished, so carb time has been cut to the bone. I should be beginning the rebuild soon, and will post another vid on youtube about the project. I did see a good ebook about quadrajets on Amazon, The quadrajet mpg secret.

I'm really looking forward to this build because of the size engine the QJ came from. It should be very close to the optimal tune for a 300. Cheers.

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