the good things about the thermoquad

[Cheapstreet_duster]

first off let me say i run holleys on my last three race cars.
and have an injected alky set up on another one right now.

my statement was about the thermoquad.
this would be "4 what its worth" Most people i hear from dont like the thermoquad,carter/edelbrock afb or even the quadrajet for that matter.
Its mostly i think because they didnt understand them.
this thread isnt intended to claim these carbs are better than today.
just so we can all have a better understanding, and move ahead.
now i am in no way a carb expert.. i have an understanding and i try to pay attention...thats all. when i learned why these carbs have atributes i said to my self man those guys were smart. (this wasnt yesterday either)
most of it started with holley's but there have been the carter wcfb then the carter afb. all before or around 68. the SUPER STOCK thing was happening. and at the same time epa zombies were starting to grumble.
the SS racers were looking to fine tune the motors to a sharp point.
this is where these carb type setups got there foot hold.
the thermoquad and the Qjet were the fruits that came of it.
why is the thermoquad platic? its not its "bakelite"polimer it keeps the fuel bowl insulated from heat.
why is there a door or plate on the secondaries. ? Ah this little feature is a brilliant find. this air door is designed to prevent premature air moving through the 2ndary ventury and bogging the motor. this is were you can have an 850-900 cfm carb on a small block street motor and not be over carburated. the door opens based on what the motor can take-when adjusted correctly no more. its a supply and demand thing. why is this good? because its adjustable and can accomodate fine tuning.
why are the primary butterflies so small and the 2ndary soo Big?
most understand this.. to run less fuel at low speed this keeps velocity and efficiency up,keeps torque at a lower rpm.
than when needed you apply throttle and the big 2ndarys open giving you all 850 cfm-ofcourse modulated and metered by the "air door"
why does it have those tricky needle/seat jet valve.? seems complicated? well this is one of the best features,possibly most miss understood... most people know how to change jets in a holley. and that the bigger the jet hole the more fuel it will supply. well the problem is most motors dont want the same fuel metering throught the complete power curve.
the needle and seat jetting/fuel metering is much more adjustable take a tapperd needle and thread it into the jet. the farther in the more the hole is restricted. slide it out and the tapped end gets smaller and alows more fuel to flow through. This my friends is how you fine tune the fuel map and get the max performance through out the power range. the air door is connected to the needle valve .As more air passes the air door this lifts the needle out of the hole and gives fuel inrichment,Brilliant i say..
now all this adjustable features makes it seem more difficult. or scares people away. this is also why holley has a large market share. the holley is better understood. or atleast is simple enough for most to get a grip on and they almost seem ubiquidous so there is usually someone pitted next to you that has one and may understand it better and can help.
but the thermoquad,carter afb, and q-jet all were designed to get better fuel inrichment and meet better epa standards. but the ss guys found they could put there 2cents in and get some outstanding features. and ended up with super good tune ups and went really fast.
i have a friend who is and old timer at heart. he builds tunes,races and sells thermo's and afb's. i learned alot because i asked and he devuldged.
i said earlier that they may not be better than todays stuff but i many cases i think it acually might just be..
cheap....

[Cheapstreet_duster]

just incase someone needs a thermo-quad done up. here is his email
demonsizzler1@cswebmail.com
ill try to get him to join maybe,,
dont post questions here please
post questions in the "mopar tech forum "section

[demon sizzler]

Originally Posted by by demonsizzler

***The message above did not show my name
-------------------------------------------------
Some good points were made in the above statements and I would like to further comment on just how good a carb Thermoquads are.

In many cases, selection is crucial because so many changes were made to the ThermoQuad over the span of the production. All 1971-1974 models were the best and were non smoger engine applications. The 74' models did include egr vacuum ports but the jetting and emulsion and bleed id's were still basically as good as the 72'-74' models. **The 1971' oem #4972 & 4973 models were different from t he 72'-up carbs and were air metered instead of solid fuel metered. In my opinion, the 72'-up
models are superior because the metering systems were much more sophistocated making these much more precisely tuneable. Also it is much easier to find a 72'-up carb and therefore the jets/other parts are much more abundant used and new.

I have tested a wide range of year and models over an 18 year period and noticed early on how increibly adaptable these carbs are. For example, I built a stock 6322(73' 440 carb)for a mild 273 build up and the carb proved to be an excellent performer and gave excellent gas mileage.
Again, the key to excellent performance is selection; stay away from the 75' up carbs in stock state, for a non smoger application. This will give you poor performance/gas mileage because these carbs tend to be very lean due to jetting/metering rod size and somger circuitry for emission purposes. These smoger carbs have excellent circuitry for modification when the smoger provisions are completely disabled and the carb is recalibrated for a specific non smoger application.

I can build a full race T.Q. for a specific 440 application, with a total flow of 1,000 cfm's and also use it on a less radical 340 application with excellent results. Again testament of the incredible versatility of a T.Q.!

T.Q's are becoming very popular with the rising cost of gas and also to restorers and class racers, especially stock ,super stock and F.A.S.T. class racers. I really like the unique features and super tuneability of these carbs and am sold on how well these carbs respond to mods.

Most tuning us done externally:
to richen each of the 3 circuits is very simple.

1)to richen the idle or to lean it, you can simply adjust the idle mix screws,
the metering rod tree height;

2)to richen the main or cruze circuit, you can simply swap metering rods and adjust the piston height:

3)to richen the wide open throttle, you can adjust the vertical stop on the air door, change the metering rods or even remove the air cleaner.

4)You can also richen/lean the accelerator pump volume/duration by linkage placement in the pump arm or by changing the stem height of the pump externally.

Then there is the air door timing:
dictated by 3 main ways; the 2ndary air door spring tension, the pull-off linkage and the vertical air door vertical stop. You can literally dictate the launch from standstill with any of the three adjustments for a tire smoking launch to a good hookup.

If you have one of these carbs, clean it up, rebuild it and see for yourself how well these big cfm carbs can perform with a little tuning!

Written by demon sizzler
********************

I have neem using an Edelbrock on my car for the last 4 months. It runs much better then it ever did with the holley. They just make great street carbs. I will probably switch back at a later date. Ive never tried a Thermoquad so I cant comment in them.

[Jason96r]

Yes David is a good guy, and a great guy to talk to. I have never gotten to sending him an email, but I am very happy with how my TQ that he built performs; the price is right too. I never have had a built holley, but people are surprised when they say why do you have that junk(TQ) on your car then they drive it and are very surprised. Anyway Demonsizzler is a good guy to deal with.

Jason Foster

[SBDart 416]

I use an 750 Edelbrock .... It run dam good too . I have a friend that live buy the old avs an afbs he run two on his car 5.60s in the 1/8 mile. this guy is good with an old carter stuff. I bought it new and john did his thing to it . the thing has not been off the car sent it when on 11.90s 1/4 all day long . just my 2cent ...............

[mopar dave]

scott brown also recommends those holley AED's, infact he recommended a 850 annular holley AED for my 408. dave

Good things ?...... the list could go on and ON .........

.....the Q should be ...what is BAD about a Plastic-Fantastic ?? !! ........a very VERY short list INDEED !!

are the Quadrajets an alright carb for street use... i am currently running an Edelbrock and love it... i have a Q-jet apart on my desk and the only reason im asking is because it has a higher cfm rating... so if i get a larger cam and such should i run the Q-jet ?

ONE very big error that alot of people make ---- it putting way toooooo big a carb on their motor.

LOOK at the Nascar restrictor plate racing........ those plates cut the effective CFM rating by a TON but they still run pretty good.

[crankshaftkid]

But a big carb is what you want on a drag engine for quick acceleration. Look how long it takes for a restrictor plate car to get up to speed at Daytona....a full lap or more. 2 1/2 miles worth. For a street performance car, you have to 'dial in' your combination to get the best possible acceleration, some sort of fuel mileage and driveability in all kinds of weather and that's asking a lot from a carb! The TQ imo, can handle it. Had good running Holleys on the street before too but imo, they do require more attention to keep em tuned.

OK...let us carry this to an Xtreme .......

Run a bone-stock GTX with a AVS down the 1/4 mile.

THEN put on a Carb/intake combo like what is on a typical Pro Stock car on that same car and see how it runs...... NOT very well.

And in many cases I have seen.....typically a 4500 Berri on a warmed-over A engine --- in a heavy car, with say a 10" converter and a 4.10 gear or so ...... way WAY over-kill.

Do you know what GM puts on its 572 crate motor ?..... a 850 carb.

It takes so long for them to come up to speed because of the gear ratio not the restrictor plate.

Originally Posted by racer_x

It takes so long for them to come up to speed because of the gear ratio not the restrictor plate.

the gear in those cars sure don't help but -OF THE TWO ITEMS - the plate hurts the worst. Somewhere I heard that the plate effectively brings the CFM rating of the crab down to 450 or so.

[crankshaftkid]

With those engines producing over 750 hp, the gear ratio don't play that much of a role in how long it takes to get up to speed. Even a 2.76 gear would get up to speed in less than 2.5 miles without the plate. Without the plate, the cars would be way over 200 mph. Heck, they broke the 200 mph barrier over 30 years ago at Daytona with unrestricted engines with less hp.

[crankshaftkid]

Originally Posted by DocFiberglass

OK...let us carry this to an Xtreme .......

Run a bone-stock GTX with a AVS down the 1/4 mile.

THEN put on a Carb/intake combo like what is on a typical Pro Stock car on that same car and see how it runs...... NOT very well.

And in many cases I have seen.....typically a 4500 Berri on a warmed-over A engine --- in a heavy car, with say a 10" converter and a 4.10 gear or so ...... way WAY over-kill.

Do you know what GM puts on its 572 crate motor ?..... a 850 carb.

Well ya...most talk about using an 850 as being too much on a mild 440. That's what I'm talking about.....

Somewhere I heard that the plate effectively brings the CFM rating of the crab down to 450 or so.

i've heard the cfm of the CRAB is like 490 or so

OK...let us carry this to an Xtreme .......

Run a bone-stock GTX with a AVS down the 1/4 mile.

THEN put on a Carb/intake combo like what is on a typical Pro Stock car on that same car and see how it runs...... NOT very well.

And in many cases I have seen.....typically a 4500 Berri on a warmed-over A engine --- in a heavy car, with say a 10" converter and a 4.10 gear or so ...... way WAY over-kill.

Do you know what GM puts on its 572 crate motor ?..... a 850 carb.

extreme???? think thats a little beyond.

The carb CFM is all based on how much air and fuel the motor can process, I have a 750 on my 318 and she runs much cleaner and better than it ever did with the 600, why because the heads flow enough and with the cam the motor can process all the fuel efficently.

[prochargedmopar]

Anyone see the article written by steve dulcich this month. It's in either mopar muscle or car craft. Very good an informative. I can now understand why people don't like the t-q but I can also understand how it is such a versitile carb.

[TheOtherDodge]

The BEST thing about a Thermoquad is that you have the option to run a Holley!

Had to do that to ya Cheap! Good write up though!

but you gotta love their sound

[Dartwizer]

well lets see 1.They are cheap,ok used to be;untill someone found out how good they can be made to run and the price went up..Go check out e-bay and see what I mean.2.They're not for everyone,just go look at the Chevy's next time your in the pits.I bet,he has the best that Holley has to offer.3.The money I could have spent on that brand new shinny Holley maybe can go on a new set of gears or new converter,slicks,etc,etc. 4.The silly looks guys give you after they see it or "Gee Daddy what kinda carburetor is that" 5.It's pure Mopar,,,,thanks Mom....6,if it could be 9[/u]

[prochargedmopar]

Mopar Muscle Aug 05 by Steve Dulcich. Some Quotes:

A $15 ThermoQuad, a $22 rebuild kit, and a little know-how can add up to a hellava $37 carburetor.

The TQ was hands down the most sophisticated of the Carter four-barrels and the most tunable.

The TQ seems to defy convention in terms of airflow relative to displacement, since the factory routinely bolted the larger of the two to smog laden 318s.

For any carb to survive as an OE unit well into the advent of fuel injection and stringent emission standards, it had to be a precise fuel-metering device. Part of the TQ's secret is in it's contoured air door, unlike the flat plate air door used in the AVS which itself was a quantum leap in technology over the afb's crude counterweighted velocity valves. The TQ's air door is contoured to create a highly effective venturi in the region of the secondary fuel discharge nozzles. The TQ's sophistication may well have been its undoing as far as universal popularity goes. Just the air door itself can be amnipulated by no less that five different settings and adjustments, all of which play a role in how the secondaries react and affect the fuel curve. Add in the tuning permutations possible with three-step metering rods, primary and secondary jets, step-up piston position and tension, accelerator pump timing, stroke and volume, main and auxiliary air bleed circuits, and you can see that the potential to really screw one up is incalculable. Compare that to the most popular carbs where tuning for most enthusiasts requires just unscrewing a jet and replacing it with one having a bigger number for more gas. Learn the TQ's secrets, however, and these dirt-cheap units can run with the best of 'em.

He goes on to show us how to tune/tweak for power and milage on the dyno. He also shows a chart of 65 or so different metering rod #'s and step sizes. What he say's is the most complete list he is aware of.

The funniest quote of the article:
"Ten screws hold the carb's three main body-components together-eight of which are visible; two of which are hidden behind the choke. If you ruin your TQ by trying to pry it apart with these two bolts still fastened and crack the phenolic housing, you can save face by claiming the plastic body is warped and needs replacing. THIS TRICK HAS WORKED FOR YEARS." LOL

Later