Thermoquad vs holley vs q-jets

[ValerianMagnum]

Hi Guys i was wondering since im doing all my research to build my ratty valiant for cheap , power and reliability :

i have 3 Thermoquads , 1x 340 72 car , 2x 440 carbs , couple of regular q-jets carbs ( one from a dodge truck / factory ) 2-3 holley vacuums and last but not least i have a 650 holley dp 4150 series

set up will be certainly a copy of my 380 hp crate engine , 5.9 with a big cam , low compression and headers ..street- strip car

your guesses ..btw they all needs to be rebuilt ! best bang for the buck ?

 

[MopaR&D]

Did you pick an intake yet? That will be your main factor, not many good performance manifolds around these days with spread-bore flanges and adapters are dumb.

I don't have experience with q-jets but I'd vote for TQ or Holley DP. I'm not a huge fan of VS Holleys seems like they tend to not work quite as well in real life as on paper. For a street car with auto and/or tall gears I prefer Carter/Edelbrock/Street Demon air-valve secondary carbs. What trans and gearing you running?

 

[Bewy]

TQ

 

[RustyRatRod]

I really love a well tune Thermoquad. Nothing really beats it on the street. Only trouble is, they have a learning curve. There used to be a Thermoquad tuning book you could find on ebay. It was a copy of the 1972 Thermoquad factory tuning manual. Better than anything out there. I don't see them on there now. I've had one twenty plus years. Very informative.

 

[Col_Steve]

440 TQ

 

[Bewy]

RRR,
Do you have an ISBN number or any other indentifying info on the TQ book? Exact name? Thanks.

 

[DFX 340 Duster]

 

[66fs]

Try the 72 340 TQ since that will be closest to your engine. May not have to touch it. 440 TQ should be richer. 650 Holley will not even be close. I also like a good Q-Jet set up right, but a choke could be problematic on a Mopar depending on style.

 

[Darter6]

^^^^^As said above,TQ if you have the spread bore manifold.
When it comes to carbs, it IS personal preference.

 

[Dana]

Big cam, low compression lends itself to a spread bore, because airspeed will be your saving grace down low. If you go with a TQ a later one would be best. They have bypass air in the idle circuit, something that cams with more overlap need because the spread bores primary boosters are so sensitive, too much throttle angle at idle will start up the primaries too soon. Same with the QJ. Bypass air will be your friend.

 

[ValerianMagnum]

Did you pick an intake yet? That will be your main factor, not many good performance manifolds around these days with spread-bore flanges and adapters are dumb.

I don't have experience with q-jets but I'd vote for TQ or Holley DP. I'm not a huge fan of VS Holleys seems like they tend to not work quite as well in real life as on paper. For a street car with auto and/or tall gears I prefer Carter/Edelbrock/Street Demon air-valve secondary carbs. What trans and gearing you running?

i have a 2002 ram ...it as a 5.9 magnum with a 46re rwd trans and suregrip 3.55 , it all be fitted with some work in the valiant , not saying its easy but can be done , i have a m1 single plane intake but might by a speedmaster dual plane intake since its a street and street project ,

 

[rumblefish360]

Big cam, low compression lends itself to a spread bore, because airspeed will be your saving grace down low. If you go with a TQ a later one would be best. They have bypass air in the idle circuit, something that cams with more overlap need because the spread bores primary boosters are so sensitive, too much throttle angle at idle will start up the primaries too soon. Same with the QJ. Bypass air will be your friend.

Is it possible to show what your speaking of on a TQ?

i have a 2002 ram ...it as a 5.9 magnum with a 46re rwd trans and suregrip 3.55 , it all be fitted with some work in the valiant , not saying its easy but can be done , i have a m1 single plane intake but might by a speedmaster dual plane intake since its a street and street project ,

I personally would not do the M1 single on that set up. The gear ratio is is numerically to low. The M1 is best suited for a big for the street cam, a good bit of converter stall & a lot more gear.

I don’t know what a “big cam” is to you and on that set up, I’d like to know, but everything else points to a dual plane intake.

 

[ValerianMagnum]

Is it possible to show what your speaking of on a TQ?


I personally would not do the M1 single on that set up. The gear ratio is is numerically to low. The M1 is best suited for a big for the street cam, a good bit of converter stall & a lot more gear.

I don’t know what a “big cam” is to you and on that set up, I’d like to know, but everything else points to a dual plane intake.

I not thinking about the m1 really its just that i have it laying around for my 76 duster with the crate engine , speedmaster intake will be the best

 

[ValerianMagnum]

Big cam, low compression lends itself to a spread bore, because airspeed will be your saving grace down low. If you go with a TQ a later one would be best. They have bypass air in the idle circuit, something that cams with more overlap need because the spread bores primary boosters are so sensitive, too much throttle angle at idle will start up the primaries too soon. Same with the QJ. Bypass air will be your friend.

its very good infos and i appreciate it ..can you show me pics or give me more details about it ? thank you

 

[Dana]

First let me say that you can add idle bypass air to an older style TQ, without much more effort. But we’re taking about carbs that carry $150 or more core charge. And once they are drilled and ground on there is no going back to original

 

[RustyRatRod]

RRR,
Do you have an ISBN number or any other indentifying info on the TQ book? Exact name? Thanks.

Lemmie grab it and I'll get you a picture.

 

[RustyRatRod]

This is the same as I have, but in print. ^^^^^^

 

[RustyRatRod]

RRR,
Do you have an ISBN number or any other indentifying info on the TQ book? Exact name? Thanks.

Here you go buddy. "I guess" the number you're looking for is 72-1. That's the only number anywhere. It's 13 pages not counting the front and back covers.

 

[Dana]

Here is the factory idle bypass air entry. This is a 9103 carb. 1977 400 AT HP.

Air then passes through the main body and out of 2 holes in the base plate. Here my .099 drill bit fits snug.

On the top side I drill and tap for a 10/32 x 1/8 brass set screw. It’s a #21 drill.

The factory.100 hole will accommodate a pretty good cam. You will sometimes notice that these later carbs will have the mixture screws out 4 or more turns or clear out of adjustment and still are too lean at idle. Then you have to enlarge the idle feed restrictors (IFR) and may even have to drill and tap the idle air bleed to reduce its size and richer the idle mixture further. On a pretty nasty 451, I’ve the idle bypass @ .128 and the IFR’s @ .052. It is a balancing act and takes a little patience to get it perfect.
I should also mention, set your transfer slots with the proper exposure before you start testing and resist temptation to compromise that setting throughout the tune.

 

[ValerianMagnum]

Oh...my thats a lot of infos , i really appreciate your infos guys and pics , never did such a thing , i have 3 tquads core 2x for 440s and 1 is a 1972 340 6139s carb !

 

[Dana]

This is the 72 340 AT 6139 baseplate. You can see it is configured completely different. No idle bypass holes. No holes in the air horn . The 9800 series Superquad uses Idle bypas in a completely different configuration than the 9103 style, that is the way we would alter this 6319 if we chose to.

 

[AJ/FormS]

If you are gonna keep starting multiple threads, you should really put the details of your combo down in your signature, so we don't have to go hunting every time. It's easy to do, only takes a few minutes, and you can change the details anytime,as often as you like, and the signature will be applied and updated to every post you ever make, and it will automatically always show the last updated one. How handy is that !

 

[RustyRatRod]

Here is the factory idle bypass air entry. This is a 9103 carb. 1977 400 AT HP. View attachment 1715871287 Air then passes through the main body and out of 2 holes in the base plate. Here my .099 drill bit fits snug.View attachment 1715871288 On the top side I drill and tap for a 10/32 x 1/8 brass set screw. It’s a #21 drill.View attachment 1715871295The factory.100 hole will accommodate a pretty good cam. You will sometimes notice that these later carbs will have the mixture screws out 4 or more turns or clear out of adjustment and still are too lean at idle. Then you have to enlarge the idle feed restrictors (IFR) and may even have to drill and tap the idle air bleed to reduce its size and richer the idle mixture further. On a pretty nasty 451, I’ve the idle bypass @ .128 and the IFR’s @ .052. It is a balancing act and takes a little patience to get it perfect.
I should also mention, set your transfer slots with the proper exposure before you start testing and resist temptation to compromise that setting throughout the tune.

I'm kornfrooshed. You say you drill and tap and install a set screw. Do you drill an orifice through the set screw? Wouldn't closing it off defeat the purpose? Educate the stupid please. lol

 

[Oldiron440]

I had a buddy that pasted in 14 that could make any of your carbs run but he's gone now so I would pick the DP Holley just on it's simplicity and availability of part's.
Any moron can make one run fairly well, hell I can.

 

[Dana]

I'm kornfrooshed. You say you drill and tap and install a set screw. Do you drill an orifice through the set screw? Wouldn't closing it off defeat the purpose? Educate the stupid please. lol

Yes you redrill. The set screw just makes it tunable. If you go too big, just screw another blank in and start over. Sorry for the confusion, I think it but don’t type it.