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 Qjet setup for a 400 performance build 
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 21
Hi, another Qjet fan here. I have a 70 Camaro with a 17057502 Qjet on a 9:1 stock 350/350. I was planning on using that same carb for my 400 performance build. I don't know the specs on the carb as it is right now but the car was bought original and everything else was original so I assume the carb has a base setup/spec. It runs good on that 350 but I don't think it has more than 250hp in it. Has a small secondary delay. Runs a hot air choke.

New engine is setup for about 500hp with a 4.125 bore and 3.75 stroke. . Full list:

Dart SHP 400 from Shafiroff (they call it a 402 real street)
6" rods
10:1 static compression, cam should give around 8.0 dynamic compression, 13.5hg vacuum
Cam is a hyd roller 232/232 @ 0.050, 108lsa, .529I/.540E lift
Intake is a Weiand 8004
Heads are AFR 210cc 2.08/1.6
Hooker Comp 1.75/3" headers

Any opinions on what I should begin with doing to the carb is very welcomed. I'm not a novice to engines or carbs in general but a place to start is where I need help with this Qjet carb.

Here's how it looks on the original engine, or exactly how it looked like when I bought it:

Image


Sat Mar 12, 2016 8:45 am
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Joined: Tue May 06, 2014 5:34 pm
Posts: 42
Well I'm glad to see another quadrajet lover, welcome aboard.

I'm also kind of new here but I must say that it's here that I've learned the most about Qjets. Tuner (he owns this site I think ?) is extremely knowledgeable and if you read thru all the other posts, you'll find great info.

I am myself currently building a street 406 with AFR 195 heads, dual plane intake and Quadrajet. I'll be using the same type of Qjet as yours, that is a late seventies Chevy unit with .120 main air bleeds. I've played with quite a few of those carbs and they are real good candidates for a performance street engine, and you'll get fuel economy as well, compared to a Holley.

As of now, I've converted quite a few of those carbs to Tuner's idle recipe and it works GREAT ! Reduce the size of the lower idle air bleed to around 1/16" (.061"-.062") from the current .075-.077 size, block the upper idle air bleed that is in the main body and relocate it in the air horn and make it adjustable from outside with 6-32 brass set screws. That is just the tip of the iceberg, read thru all the other posts and let us know about your progress. I like the fact that you'll be running a dual plane intake.

Frank.


Sat Mar 12, 2016 9:10 pm
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Joined: Tue May 06, 2014 5:34 pm
Posts: 42
Also, don't forget to reduce the size of those two main air bleeds (both actually at .120") to between .046 and .070 with a bushing like that one: http://quadrajetparts.com/bleed-restric ... p-314.html

That will allow you to run main jets in the .070-.073 size. I personally like Cliff Ruggle's custom full taper .044" primary metering rod that has a constant taper from the .044 to the .026 power tip. Also go with his custom accelerator pump, you won't regret it.

Hope others will chime in.

Frank.


Sat Mar 12, 2016 9:21 pm
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 21
Thank you, that looks like a great start. I have read a few different recipes but most say "more more more" of everything.

Yes I will use a dual plane. I will gladly sacrifice some power up top in exchange for driveability and mileage. Not looking for a super low mileage car but it's going to be driven everywhere. I have heard you can get ok mileage with a small single plane as well but then I reckon I'd have to sacrifice the divider and good carb signal. I think a dual plane is the best option for my intended use. I picked the Weiand 8004 based on recommendations that it has a higher rpm capability than the typical performer from Edelbrock. Also contemplated the Edelbrock RPM 7104 but that might be a bit too tall for my stock hood and most say it's about the same manifold as the 8004.


Sun Mar 13, 2016 5:28 am
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Joined: Tue May 06, 2014 5:34 pm
Posts: 42
kimosabi wrote:
Thank you, that looks like a great start. I have read a few different recipes but most say "more more more" of everything.



I hear you. I used to follow that way of thinking before I learned about Tuner's way of doing things in a Qjet. I've built a 17059217 (same basic characteristics as your carb) for a friend's 400 sbc (mild street) with a Isky 270 (221@.050, 108 LSA) and my idle recipe ended up being smaller than some factory stock 305s. It now has .025" idle tube, .043" down channel restriction, .043" upper idle air bleed, .061" lower idle air bleed. Gets better mileage than before when I was using another popular recipe that called for larger everything. And the beauty is that I can now tune the entire idle/off idle curve just by replacing the upper idle air bleeds by just removing the air cleaner (3 minute job !). Fact is, we tried this carb on a very stock 350 the other day and all I had to do was replace those 6-32 air bleeds with larger ones, and playing a bit with the mixture screws...voilà !


Sun Mar 13, 2016 8:01 am
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Joined: Wed Oct 23, 2013 8:01 am
Posts: 108
Kimosabi, I assume you have read through Tuner's post on the secondary mods too.
They work!


Sun Mar 13, 2016 10:15 am
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 21
Thank you guys, I looked over both the primary and secondary recipes on here. With my limited experience with the Qjet it seem like good stuff. I do also have Lars Grimsrud's tuning papers to read. Maybe I'll find a decent core for spare parts just in case I screw things up.

Now time to head over to Quadrajetparts.com!


Sun Mar 13, 2016 1:31 pm
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Joined: Wed Oct 23, 2013 8:01 am
Posts: 108
I've bought a few cores from Ebay lately, if I can get it cheap.
You can get your brass set screws & drill bits here. http://www.mcmaster.com/#


Sun Mar 13, 2016 2:48 pm
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Joined: Sat Mar 12, 2016 8:07 am
Posts: 21
I actually forgot I already have a couple cores. One is a ebay "500hp" type of deal the other is a BOP with the straight inlet. Have never run them.


Mon Mar 14, 2016 4:42 pm
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Joined: Tue May 06, 2014 5:34 pm
Posts: 42
Be careful, a BOP Qjet may interfere with the thermostat housing on a sbc.


Mon Mar 14, 2016 9:45 pm
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