I have a few thermoquads laying around and was wondering if I can put a 400 or 440 thermoquad on a 318? If so is there modifications needed to prevent too much enrichment?

I have found that they are better anchors...

Thanks. No I didn't find that helpful. Anyone else?

I don`t see why it wouldn`t!
Small blocks i think around 800 cfm and the big blocks run 850 cfm..just check the butterfly bore size to make sure it does hit the intake!

Have a thermoquad on mine that Demon Sizzler rebuilt and love it!

The bigger ones should work fine seeing how I think it's only the primary bores that are bigger. As long as nothing hits other then that the carb itself is the same size.
It MIGHT be a bit overjetted for your engine, but they are pretty easy to adjust if you understand how they work and what to adjust.
I run a aftermarket 9800 800cfm on my 318 with either 92 or 95 jets, the metering rod adjustment has been tweaked just right and I did the air door as well. It has a electric choke with the round dial for adjusting so it's easy to get to run cold and I think the smaller primaries give it a bit better MPG and bottom end grunt.

is basically a plug and play job in relation with phisical fitment.

then some diff are in between, cfms, jetting, vacuum tees, linkage adjustments and maybe the most "important"... gas INLET needing to match with your car setup, due some are on rear of the carb instead at a side.

ON a 318 ... you would want the smaller 400 carb. And it would need to be "tweaked" ...especially on the secondary side. The air-door will have to be closed down BIG TIME and the jetting on that side would also have to be reduced A BUNCH.

some 318s were factory installed down here in Venezuela with TQs and AVSs

and 70s 340s were TQ factory...( not a GIANT diff )

too much BS about they can't be on a 318s... simply fit, tune and voila!

Down here is a tipical "upgrade" without ANY problem

BTW not a such difference between 400 and 440 carbs beside just the jets and some more tweak, but same bore diameters so same cfms

thermoquads are cool.theres a guy on ebag selling nos ones,i got a 73 with the big bores for under 200 bucks,its more than 3 times cheaper than a holley -1850 600 cost in sweden anyway.its gonna be fun to fiddle with when i get tired of my holleys,worth to try anyway,and if its easy to recalibrate its perfect for what im going to do,str-15 with the thermoquad lid.heck im gonna try all the lids, and then some.i dont know much of thermoquads yet,but if you buy a new/used i think the types made before -77 is preferable,something with bowlvalve and egr stuff.of course i might be wrong.im sure they are ok to swift over,try it youll like it

They just don't understand how they work or how to tune one.
I liked the theories of operation behind them and the spreadbore concept in general so I found one, rebuilt it, and loved the way it worked on my 318 so I've stuck with them.
I tried a AFB, AVS, and a Holley and it just ran smoother, got more power, and better MPG then anything else I tried.
If you get a bad one that's cracked or completely messed up they can horrid, but a good one will make you happy on a street engine.

Next best thing to fuel injection. On second thought, in many ways they're even better!

The larger of the TQ's were actually OEM on 318's in some applications. I have to say I disagree with the recommendation to heavily adjust the air door; that simply should not be required even on a high-geared 318. It might need tuning, but you can't just assume it will need a bunch less jet. Even off another application, like a 440 carb on a near stock 318 the jetting might be OK, you will need to check it with a lambda to be sure, or zero in on the jetting and rods the old fashioned way. Carbs meter by airflow, and mix in the fuel in proportion to the air, not to the cubic inches of the engine.
-dulcich

And the deep throaty sound when the secondary's kick in is way cool!!

Sorry for such a slow response. I went ahead and fabbed up the linkage and fuel lines using the 440 carb just to get the motor ready to accept a thermoquad and after I got done I decided to fill it with fuel and turn the motor over just to see what it'd do. Now realize I bought this carb at a swap meet about 15 years ago and it's been sitting on a back shelf since with dust collecting on it. The motor fired right up and idled smooth! took er out for a spin and it ran really well! The only thing it's doing is it seems to have about a 1.5 second delay between the time I step on it and when it starts to accelerate. The accelerator pump is operating smoothly so I'm wondering if I need to turn in the metering rod adjustment screw a little (I initially set it at 3/4 turn out from bottom) or maybe check the metering tree spring to see if it's sticking in the bore?

A few years ago I had an 86 Ramcharger with a 318 2 bbl. I bought a wrecked Cordoba with a 400 TQ. I put on a factory cast intake and the TQ from the 400 on the 318 and loved it. It did have some rattling upon acceleration and messing with the timing did nothing. I found that if I ran a little higher octane fuel in it, the 318 ran perfectly. I was getting 14 mpg with the 2 bbl and got 16.5 mpg with the TQ and better fuel.

Well I have some tuning issues to resolve. when gently accelerating I still get the initial surge then kind of a lag before speeding up and if I punch it it bogs and backfires. Any suggestion?

Your pump-shot sounds weak and/or the air-door is not properly adjusted.