Thermoquad or Holley?

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Mopar-Mitch

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I have been having a lot of trouble out of my holley double pumper, since I bought the car last year. It has a oversized cam and I don't know any of the engine spec's. My intake is the old Torker 340 and the car needs a stall converter really if i keep running the current setup. I have no low end torque. I keep getting gas in the oil from the Holley its old and been rebuilt several times. A good buddy of mine gave me a New rebuilt from Chrysler thermoquad, it's for a 1977 400 HP engine. I can pick up a intake from another buddy, he has a stock 340 cast iron intake 71 casting he also has a wiand spread bore he'd sell me, I'm leaning toward the original cast iron because I can use the choke, what do y'all guys think, should I just buy a new holley or switch to a dual plane and use the thermoquad and maybe gain a little low end torque?

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Mitch, I really like TQ’s. But I’d the cam is so big you need a high stall converter to keep it running & it came with a single plane intake, your probably going to like the Holley better. Knowing how big the cam is would be really good. You make it sound large. You may want to try a 4 corner idle 4150.

The benefit you think you will have with the choke in the Thermoquad will probably not pan out.
 
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FYI that 9103 carb is off of a 77 400 HP, That being said I would go with the Holley.
 
The problem with the TQ (or any metering rod carburetor) is that with a large camshaft the vacuum drops to the point that the metering rods "jump" and the idle mixture is very tough to get right. The Edelbrock style carburetors are "better" at combating this, but "I" have never been able to tune that out of a thermoquad. Maybe somebody else has and will chime in with the magic secret.
 
Mitch I've always had luck with the Holley as well. Like Rumble said to bad you don't have the spec's off the cam so you could match up a converter.
 
Hate to sound like a broken record...but a lot carb problems is not the carb...but ignition problem.

Where is your timing at.....initial timing that is....big cams want a lot of initial timing....
 
Hate to sound like a broken record...but a lot carb problems is not the carb...but ignition problem.

Where is your timing at.....initial timing that is....big cams want a lot of initial timing....
Yep, I need to recheck the timing, the Holley keeps getting gas in the oil, float's seem to be right, it seems to be leaking off after I shut it down.
 
Yep, I need to recheck the timing, the Holley keeps getting gas in the oil, float's seem to be right, it seems to be leaking off after I shut it down.

It could be that it's running rich because it doesn't have enough initial. It's a very common issue. Good luck! If you were local, I'd say come help me put some sound deadener in and I'd tune on it for you....and have a few beers.
 
It could be that it's running rich because it doesn't have enough initial. It's a very common issue. Good luck! If you were local, I'd say come help me put some sound deadener in and I'd tune on it for you....and have a few beers.
Yep, now that sounds like my kind of a good time, sure wish I was closer!
 
The problem with the TQ (or any metering rod carburetor) is that with a large camshaft the vacuum drops to the point that the metering rods "jump" and the idle mixture is very tough to get right. The Edelbrock style carburetors are "better" at combating this, but "I" have never been able to tune that out of a thermoquad. Maybe somebody else has and will chime in with the magic secret.
I spent years trying to combat oscillating metering rods on Carters. The cure is switching to Holley.
 
No expert here , wondering about the rest of the combo when you mentioned lack of low end torque . Rear end gear ratio etc. Are you sure about the size converter that's in there etc.
 
Holley floatvalves rarely leak. I'm guessing your PV is ruptured and gas is getting pulled back thru the vacuum circuit.. Pull the front bowl off carefully so as not to disturb the metering block. Then place a pan under the block and pop it off. If gas runs out from the cavity, there's your main problem. Put a 10.5 in there.
 
Holley floatvalves rarely leak. I'm guessing your PV is ruptured and gas is getting pulled back thru the vacuum circuit.. Pull the front bowl off carefully so as not to disturb the metering block. Then place a pan under the block and pop it off. If gas runs out from the cavity, there's your main problem. Put a 10.5 in there.

There is a hole in the base plate so there might not be fuel in the cavity.
 
One thing to add that I dont see anyone else mentioning that thermoquad is a later carb most of them after 75 were lean burn carbs and dont have the port for the vacuum advance for the distributor. I don't see the port in the pic you posted I'm pretty sure that's a lean burn carb!
 
I'm pretty sure some fuel will remain in there at shut-down at least long enough for this test. I know for me it has.
This would help explain the gas in the oil as well, as the float bowl is constantly draining.
 
One thing to add that I dont see anyone else mentioning that thermoquad is a later carb most of them after 75 were lean burn carbs and dont have the port for the vacuum advance for the distributor. I don't see the port in the pic you posted I'm pretty sure that's a lean burn carb!

Actually, that's not quite correct. That port was never used for the distributor from the factory. It was used for the EGR valve. But you ARE correct in that it DOES make the perfect port for the distributor vacuum advance.
 
One thing to add that I dont see anyone else mentioning that thermoquad is a later carb most of them after 75 were lean burn carbs and dont have the port for the vacuum advance for the distributor. I don't see the port in the pic you posted I'm pretty sure that's a lean burn carb!
That port is easy enough to add, and you can even customize the cut-in point.
 
My vote is for the Thermoquad. The TQ was free.Going to a dual plane will help bottom end torque with a automatic.Sounds like you can get the factory intake easy,and a 71 was the best TQ factory intake to have. I ran that set up on my Duster 340 with a 320* duration Crane cam. It idled at 1500 RPM. Granted my car was a 4 speed and had 5.13 gears But I would give it a try.You didn't say what gears you are running.
Rusty,Help me out here ! I know you believe in the TQ's :drama::usflag:
 
love the thermoquad but unless you get the tun right on it for your application its not really going to help you. a 77 440 was a smogger.

i'd redo the holley on it and be done.
 
The rear end is a 1973 8 1/4 I don't know the ratio, its a sure grip but seems like awfully high gears, the whole drivetrain is from a 73 duster 340.
 
My vote is for the Thermoquad. The TQ was free.Going to a dual plane will help bottom end torque with a automatic.Sounds like you can get the factory intake easy,and a 71 was the best TQ factory intake to have. I ran that set up on my Duster 340 with a 320* duration Crane cam. It idled at 1500 RPM. Granted my car was a 4 speed and had 5.13 gears But I would give it a try.You didn't say what gears you are running.
Rusty,Help me out here ! I know you believe in the TQ's :drama::usflag:
I never used the TQ, but ran plenty of AFB'S and AVS's on many combos.
Idling at 1500 rpm, tells me your TQ wasn't optimum on your combo.
My vote is for the Holley and a dual plane. save the TQ as a collectable. and some headaches.
 
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