therm quad size

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swingingdart

swingingdart

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Is there a way to tell the cfm of a thermo quad? I'm getting ready to start shopping for one either on here or around where I live and would like to get one thats for an early 70s 318 or 340, anybody know?
 
measure the front throttle bores..... 1 3/8 is 800 cfm

1 1/2 is 850 cfm
 
Primary size

big 1.50 inchs rated at 850 cfm while the smaller 1.38 is good for 800 cfm.

Use a 800 on a stock 360/340 and any 318 for the most part. You'll need a mighty 318 for more really.
 
thanks guys! this is going to be a little bit of a hot runnin' 318 but I don't think it'll ever need a 850 I think 800 is pushing it! thanks!
 
The real question is, what size engine and what is the intended purpose behind the build. To state you'll never need a 850 T-Q based on CFM ability and what you normally understand about cfm size and operation doesn't exactrly apply to a T-Q like a square bore carb does.
 
well, you'd know better then me, I like the spread bore idea better then square, more jump in acceleration (thats the most fun I'd think) lol
 
Set up properly, it'll only supply what the engine can draw through it. Total cfm isn't nearly as big a deal as a Holley double-pumper or similar.
 
simple math and logic=318 engine at 100% efficiency (55-70% likely if naturally aspirated,i.e. no super or turbo charging) will require a mere 836.1111 cfm of flow @ 8,000 r.p.m.Any more carb than required results only in unnecessary de-tuning and jetting to correct a/f ratio to best possible calibration which will still be unattainable as min. jets and alterations are still better suited to hungrier engine.In other words big bog.these carbs were only installed to satisfy necessary new car production requirements to run on specially sanctioned event cars that were altered from their stock versions.youll be much happier and snappier with the appropriately sized bore for your efficiency and r.p.m. requirements.
 
First of all, the 318 didn't come with a TQ until '78 so you'll want to find an earlier one so you don't have to hook up some the smog features that the later ones have and need to work right. Many of the '77-up cars had the Lean Burn ignition systems too which should be avoided for the same reason. They made TQ's all the way up to a 1000 CFM and they seem to work on any size engine with only rejetting and minor adjustment needed to make them work good. I've seen 800 CFM's on a 440 and 1000 CFM's on a slant 6 and both performed fine. Naturally if this is going to be a drag car and seeing 7000+ RPM, you'll want the higher CFM carb to handle the flow. The rejetting and adjusting is mainly needed for mileage and to prevent a secondary bog in some cases. Usually the secondary air door adjustment will cure the bog.
 
A note on the newer T-Q carb is that the leanburn systems used with the T-Q takes care of spark advance. That means the T-Q dosen't have a port of the vacuum advance for the distributor. Find an earlier T-Q but not the first year of the carb, there metered differently.

LeDawg sez;
Any more carb than required results only in unnecessary de-tuning and jetting to correct a/f ratio to best possible calibration which will still be unattainable as min. jets and alterations are still better suited to hungrier engine.In other words big bog.
Click to expand...

Any carb used will need to be tuned. The later year T-Q's will have smaller jets and larger rods for there leaner air fuel mixture needs of the smog years. You'll likely need to rejet the carb for anything your doing. But that is also a wait and see.

I really don't understand his post entirely. A leaner mixture will probably be needed then what the stock jetting offers. How it is unobtainable is beyond me and how it is better suited to a hungrier engine is also beyond me. While it is true that lean is mean, taking your time to set up the carb is what you and everyone needs to do.

In otherwords "BOG" is really how the carb is set up, or how well it is set up.
these carbs were only installed to satisfy necessary new car production requirements to run on specially sanctioned event cars that were altered from their stock versions.youll be much happier and snappier with the appropriately sized bore for your efficiency and r.p.m. requirements
Click to expand...
These carbs )T-Q's) were first made as racing carbs making an appearance in 1969. IIRC. Since they were on production cars, they became the only carb possible to run in certain classes of racing where you HAVE to run a stock carb.
The proper sized carb is allways what you'll want to run, however, the T-Q is very flexable in it's applications and will cover a wide verity of applications and engine sizes and engine power requirements.

The squarebore carb will have to be size properly or suffer in performance somewhere. This is where the application of size is soooo important. To big or to small, there could be an issue somewhere.

The T-Q will need none of that but has it's own cave eats due to design of being a spreadbore itself. If you use the small primary version on a hot engine, your leaving alot of driveabilty on the table. Acceleration will be weak and feeling like you need to really lean on the gas pedal. A large bore version on a small and mello engine will also have poor driveabilty and gas mileage. It'll feel muddy down low.

Snappy acceleration is a combo of proper carb size, a well tuned carb and well tuned/timed of the engine at the distributor and cam timing should be where it needs to be. It's the whole package that needs to be right!
 
Rumblefish is right. Any TQ will need tuning, BUT they are more forgiving than most other carburetors. It is true that you can remove a TQ from a 440 and run it on a 318 with GREAT success. this is one reason Chrysler used them. They can be used on a wider variety of engines than most carburetors. This doesn't mean that 440 TQ will be tuned properly for that 318. Now, on a wramed over or hot 318, that stock 440 TQ would probably be a frikkin tire roaster. Also something else to keep in mind. If you're gonna run a warm or hot 318, use the 850. Here's why. The two carburetors while similar, have a very different fuel curve. What that means is, the 850 TQ will have MORE available fuel all the way up to the max it will flow on an engine. In other words, it's a richer carburetor throughout the RPM range, not just in total CFM flow. These points are all what makes the TQ such great carburetors. although they have many adjustments and can be daunting to figure out, once you see and understand what each adjustment does, you wanna beat yourself upside the head because they are so dead simple. If carter would start making the old Strip Kits for them again, I think you'd start seeing more of them in serious competition and perhaps eclipsing some of the Holleys. They are that good.
 
(Thanks Stroker Scamp)
Every once in a awhile, I see a car listed as the winner running a T-Q.

I have a electric choke T-Q @ 800 cfm. It's designed as a stock replacement carb. This one I have even has a Chevy arm on it. It was a bit weak on the 400 and probably best siuted to a daily driver 318 or 360 with little to no fan fare on the engine.

I'm tuning (Today) a big T-Q on the 400. The lack of rods and jets can be semi solved in two ways, Purchase used T-Q's for the rods and jets or visit FABO member Demonsizzler @ http://www.thermoquads.com/ for a kit to tune it up.
 
If your looking for a t-quad dont worry about the cfm size, buy the one that looks like its in the best condition, and has nice tight throttle shafts, most of these t-quads have been kicked and dragged around and have a lot of small problems like bent or wrong linkage, rusted throttle plates, stripped or broken idle screws, warped or cracked bowls ect..ect..
 
what's the number on that TQ? wanna sell it?
 
rumblefish360 said:
(Thanks Stroker Scamp)
Every once in a awhile, I see a car listed as the winner running a T-Q.

I have a electric choke T-Q @ 800 cfm. It's designed as a stock replacement carb. This one I have even has a Chevy arm on it. It was a bit weak on the 400 and probably best siuted to a daily driver 318 or 360 with little to no fan fare on the engine.

I'm tuning (Today) a big T-Q on the 400. The lack of rods and jets can be semi solved in two ways, Purchase used T-Q's for the rods and jets or visit FABO member Demonsizzler @ http://www.thermoquads.com/ for a kit to tune it up.
Click to expand...

or you can send me you jets and i can drill them on my precision lathe. i had to drill the ones on my hot 360 to .159 and that is still small
 
Just the combo I want to run next. I have the Holley Strip Dom and a T-Q just awaiting time to fool with it.
 
Wow a lot of different opinions on TQ carbs. Take the time if you buy a used carb and check for cracks in the phenolic. Unfamiliar people will miss a screw and crack them trying to pry them apart. If it doesn't fall apart with the screws out you missed one.
I thought the sizes for TQ were 780,880, & 980. I have all of them on my shelf, different years and options. 980 was from police interceptors and is streetable on a warm 440. (Works great with a Crower 'Hot Street Beast".)The 780 is what came on my 78 Diplomat.Don't be afraid to build your own TQ. Most kits have great instructions.
Take your time when you rebuild, inspect every part carefully, if it's suspect reject.
Most bog on my cars was air door adjustment (On older TQ's). Have fun, there's nothing like the howl of a TQ at wide open throttle to put the fear of Dodge into bowtie or blue oval types.
 
Welcome aboard JC.

The rated/listed/given CFm ratings by Carter were 800 and 850.
Actual wet flowed numbers they may not be, IDK for sure. But that's how they got listed and go by. Good enuff for me.

Anybody got a bench with that flow abilty?

I've used alotta different carbs with great results and truly, thers nothing more truer than "It must be tuned and tuned right!" for any carb used. Bar none. I've had good results with the T-Q.

FYI to new guys on a T-Q, JC made a point thus far forgotten, theres 2 screws down in the center of the carb on the / in the primaries throat, in the center. The carb will not come apart of you forgot to take them out!
 
Hey, EL5, your T-Q's idle screw are at an angle and the rearward on is straight. What years are those angled units?

On the intake, was the opening worth anything?
Did you take away the floor damns?
 
Only sizes for the TQ are as follows. 950 and 1000 both in 1969 and 1970 only. these were the competition carburetors from Carter. All the rest were 800 and 850. there was the aftermarket competition version in the late 70s and early 80s called the Superquad. They were all 800 CFM. I have one on the shelf. Their numbers were 9800S for the Ford and Chevy apps and 9801S for the Chrysler. I have the 9800S.
 
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