Just curious, as I can't find a solid answer anywhere here.

What is the performance potential of the stock L69 aluminum intake, a mechanical Qjet carb, and L69 air cleaner on a 350? Will this induction support maybe 400hp?

 

the carb and air cleaner will, the intake should be swapped out for a performer rpm air-gap or similar single plane depending on usage

 

Well, what I have now is a RPM Air Gap, Holley 4bbl, and 14" open element. I was just wonding how the factory stuff would compare? Non-CC Qjet though.

 

So what is the stock aluminum intake capable of, performance wise?

Really what I want is street/strip performance, but something more street friendly than what I have now, and something that isn't touching the hood too. I can see a mark on the air cleaner lid where its rubbing on the hood, lol.

Thats sorta why I want to go back to the Qjet. When I had the CC Qjet on my car a few years back, it was alot easier to live with... started in the cold better, better gas mileage, etc. My double pumper drinks fuel like crazy, even with all the fine tuning I've done, and it runs quite poorly when cold. My old Qjet never had these problems... I don't know why I didn't just keep it now

I still have the aluminum GM intake my L69 came with, and if it is a good intake, I'll probably just have it bead blasted and use that with the mechanical Qjet and L69 air cleaner.

Is there anything the stock aluminum intake could use to boost performance? Anything ground down, ported, etc...?

 

should work well. Is the q-jet lower than the holley? Could always use a drop base air cleaner, and keep the superior intake manifold. Swapping to a worse manifold just for hood clearance is kinda... barely worth it.
The q-jet as far as driveability goes - I can agree with. Let me know how you get it jetted once you're done, I always like to hear others setups with that.

 

I don't know as much about tuning a Qjet as I do a Holley, so you might become my new best friend if I do it

The intake is the problem though... I've already got a 1-3/4" drop base, and it still rubs on the hood. The RPM is a really tall intake. I can't even use a wingnut on the air cleaner stud anymore... the 'wings' hit the hood!

I'm just wondering though, how much, if any, power am I going to lose by using my stock intake over the RPM? I don't really need the extra 1000rpm powerband that the Ede intake gives, because its always been fastest shifted around 5500 rpm, not 6500. I also still have 601 heads, not any aftermarket heads with huge intake ports or anything.

 

That's messed up man. My stock LG4 intake, on a non-cc qjet on a performer RPM manifold, fits fine. No weird chunks missing out of the hood.
I thought firebirds had a lower hood line too. Perhaps my power bulge is saving me? I think the air cleaner stud would hit the edge of the bulge though.
New motor mounts here too...

***oooohhhh, air gap... yea, that's tall I think...****

Problem with the stock intake is that it's short, so it forces the air to turn sharper, which makes it cut off flow at higher RPM. What do you have to lose right? Intake gaskets are like $20....

I think over 5000RPM you'll feel it.

 

I doubt the stock intake would support 400 HP without basically the equivalent of professional porting. It's got small passages and INTENTIALLY sharp corners (helps fuel atomization, hurts flow). A swap to a standard Edlebrock Performer (swap meet or ebay for $50 or less) will work a lot better than a stock intake, but not as good as an RPM. Myabe 15 HP down, give or take. Your hood clearance will be dramatically improved with the carb sitting 3/4" lower on the standard Performer. Plus a QJet is about 1/4" shorter than a Holley from mounting flange to air cleaner flange.

The QJet is certainly capable of it, especially if you file down the air door stop on the secondary side to somethign close to 90* opening. Any stock QJet is capable of 750 CFM flow, some as much as 800, depending on the casting/part number- enough for 400HP. So much depends on the tune. Richer secondary rods many be required to keep up with a heavy-breathing engine. A set of "DA" secondary rods on a G hanger won't be far wrong for most QJets in an application like yours.

I wouldn't use the stock dual-snorkel. Fine if you're running 14s or maybe 13s but it's got it's limits, too. I'd do a simple 14x3 open elemnt with a drop base. Just make sure you don't have the base of the air cleaner hitting the accelerator pump arm on the top of the QJet. Using a "thick" air cleaner gasket (Holley sells them- about 3/8" thick) can often give you the little extra clearance you need to mount a "parts store" open element to a QJet.

For cold weather, certainly feel free to use a stock air cleaner housing with it's provisions for heated air off the exhaust manifold. For summertime use "let 'er eat" with an open element.

I've run Qjets on top of standard Edelbrock Performer intakes with a drop-base 14x3 air cleaners in a 3rd gen with no hood clearance problems. I've done low 13s/high 12s like this many times.

 

Well, once I have this car in the 13's, I'll be happy. Its a low 14 car right now (although the MPH says otherwise), so I don't think I'll be outflowing the L69 air cleaner... if I do, I can always use the open element I have now.

So it sounds to me like I might be best off to use something inbetween what I have now, and the stock intake? Something like the Performer or something then?

 

i'd swap rear ends before i'd swap out intakes and carbs and everything else to pick up some ET, that open rear end can't be helping. For normal driving you can lean out the primaries more until it starts to surge at cruise then jump up 2 sizes, that should help out your mpg a bit.