71' 340 air cleaner, choking out my little 318. WHY??

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Dana

Dana

FABO Vendor
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Combo:73 swinger, 69 stock bore 318, 714 casting heads with stock size valves, summit 6900 cam( close to stock 340) 9.59:1 compression, 800 thermo quad, good flowing manifolds, 2-1/2 exhaust, o/d 4spd, 3.91 gear,27" tire, twin scoop functional hood. Timing 17* initial 32 total, all in by 2600.
Problem: Wind out 1st gear at approx. 4000 rpm( foot to the floor)she noses over- shift, she winds to 3500-4000, noses over shift maybe 4500, noses over in 3rd.
Attempts to fix: Took out k&n filter bolted lid back on/ no change. Then took off wing nut, thinking the pressure was somehow messing with the metering rod bridge or the air door/no change. Then took the lid off, and she pulled strong to 5500-5600.
Thoughts: There is no way this mill is hungrier than the car it came on from the factory. And even if it is, that air cleaner should support a high revving big block. Is it on a fine line of being rich in the secondaries, and no lid leans it out enough? It only has a 110 secondary jet.
I WELCOME ANY AND ALL QUESTIONS, COMMENTS, AND/OR CRITICISM. Thanks in advance
 
couple of questions !!! what is the statis of the timing gears and chain ? what does it idle at ?
Still got the old point's setup or is it petronix or msd ?
dying at 4000rpm sounds like a valve train issue, or a carb issue.
 
You can always play with the jetting & air door. But there are a couple of things, or combination of things, that could be causing the problem.

I think the air cleaner top is too close to the carb vents, causing turbulence and/or flow restriction.

Can you temporarily space the lid higher without the air cleaner? If that works, you may need a taller air cleaner.
 
win38mag said:
couple of questions !!! what is the statis of the timing gears and chain ? what does it idle at ?
Still got the old point's setup or is it petronix or msd ?
dying at 4000rpm sounds like a valve train issue, or a carb issue.
Click to expand...
New speed pro timing set, aprox. 2000 miles, same as motor. Idles @ 800-850, it's the don Gould ignition box. If I take the air cleaner completely off, it runs like a beast (for a 318)all day ,anyday.
 
LocomotioI said:
You can always play with the jetting & air door. But there are a couple of things, or combination of things, that could be causing the problem.

I think the air cleaner top is too close to the carb vents, causing turbulence and/or flow restriction.

Can you temporarily space the lid higher without the air cleaner? If that works, you may need a taller air cleaner.
Click to expand...
Good suggestion, i will try that. Did'nt this air cleaner come on TQ's from the factory? And did the 71 TQ's have different vents?
 
you are doing the right things: testing and letting your engine tell you what it wants. Right now, more air. Let it breathe... :)
 
Dana said:
Good suggestion, i will try that. Did'nt this air cleaner come on TQ's from the factory? And did the 71 TQ's have different vents?
Click to expand...
I think so and don't know.

I have very limited TQ experience but had them do weird things. One was that during a burnout, it felt like it was on a rev limiter and sounded like it wanted to die. But it launched ok and didn't run bad. Slow, but not "bad". Not sure if it was jetting and/or a too loose air door.
 
I see, the 71TQ had 3 vents. 2 smaller ones equally spaced off center in the rear, and a large cast one front and center. Mine is a single large vent rear and center. (84 truck 360 carb)
 
I'm picturing the 70's big block tq air cleaners. Bigger than the hubcaps and like 2" tall. Some of them single snorkel.
 
Dana said:
I'm picturing the 70's big block tq air cleaners. Bigger than the hubcaps and like 2" tall. Some of them single snorkel.
Click to expand...
yep. Also, the TQ is an excellent carb if tuned properly.
 
[Q8willrun, post: 1971797988, member: 32076"]yep. Also, the TQ is an excellent carb if tuned properly.[/QUOTE]
I could'nt agree more!
 
Air restriction from either the lid being too close (which I doubt) a secondaries linkage hitting the air cleaner base or the hot air door on the snorkel is closed.
Couldn't be much else.

Well, possibly a plug wire arcing to it. :D
 
fuel said:
Well, if that is true, not sure what air cleaner you have. Never had ant motor die at 4,000 rpm that did not run out of fuel, 383 or ignition HEI.
Click to expand...
Yes, and fuel is comprised of gasoline and AIR.
 
TrailBeast said:
Air restriction from either the lid being too close (which I doubt) a secondaries linkage hitting the air cleaner base or the hot air door on the snorkel is closed.
Couldn't be much els.e.

Well, possibly a plug wire arcing to it. :D
Click to expand...
I took just the lid off, and it ran great. No snorkels on this one, just two hole lined up with the hole in the hood under the scoops. In the morning i'm going to run a nut down on the carb stud as a spacer ,then screw the lid on. I thought maybe someone had run into this problem with this particular air cleaner/carb combo.
 
That air breather calls for a Fram CA305 filter, which is 2 3/4 inches tall. I found a Fram CA127 is 3 1/2 inches tall, from a 1973 Chrysler New Yorker. I've used these for years if you have enough hood clearance. It kind of acts like an unsilenced breather from the top and will let that TQ ROAR like it's supposed to.
 
lemondana said:
That air breather calls for a Fram CA305 filter, which is 2 3/4 inches tall. I found a Fram CA127 is 3 1/2 inches tall, from a 1973 Chrysler New Yorker. I've used these for years if you have enough hood clearance. It kind of acts like an unsilenced breather from the top and will let that TQ ROAR like it's supposed to.
Click to expand...
Great info. I just copied that down in ink! Thanks
 
Dual snorkel air cleaners run the same as no air cleaner on 440 Police cars. Check the linkage on the carb for interference and that the choke is open. TQ's have linkage that will not engage the secondaries, unless the choke is open. Sounds like you are close since it runs great with the base on.
 
Problem solved! Just picked up the wix equivilent of a CA127, screwed it down tight, leaving the lid 3/4" above the base, and she's running like a scalded dog to 5600. So, evidently the vents on top of a 71' Thermoquad and it's respective air cleaner were dialed in together from Detroit. Not compatible with the 84' 360 TQ. The TQ howl is definitely more prominent now. You gotta love that! Now I'm gonna start tweaking this TQ to try and compensate for the dreaded 1-2 gear ratio drop. I'll also have to start rethinking my mag headed 340 that is almost complete. It has an air-gap, and spread bore adapter. With this extra air cleaner height, it will not fit. I guess I'll be looking for a ld340. Thank you guys for all of your for your help. I believe I would still be head scratching if you had'nt lended a hand.
 
You're welcome, glad to have the right answer. I don't know everything but I've learned a few things in my 60 yrs.
 
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