Thermo Quad

Got one but not sure what I should do with it. Pro's / Con's ?

 

Depends on which 1 you have. :Brow:
When they work, they are Great. Just have to find out which you have. Competition Series or the one that came from the small MoPars, or ?
JR

 

have no idea. Is there a place to run the casting numbers through. All I know is it was represented to be a 850.

 

My experience with TQs is pretty bad. If I got one again, for whatever reason, I'd toss it in the trash. YMMV.

 

the 72 to 74 850 are the best stock units so ive read and competition series of course there was a Universal 850 that a lot of the guys ran ,had a GM throttle arm I think. ive had a 1000cfm unit throttle response was AMAZING but I had trouble with it on the secondary side

 

From what I have heard 1000 Thermo Quads were after market only. They didn't come on passenger cars. I had real good luck with a 1000 on my bracket racer. Jim Bell had nothing but good to say for the 1000.

Bob H.

 

I'll have to post a few pics later.

 

the Thermoquad is nothing more than a Qjet with a little more cfm, perimeter fuel bowl with 2 floats and needle valves, and plastic center to cool the gas and charge. I had a ton of Qjets 750/800's and built them for my own cars and customers. when I got to 470 CID, tunnel port heads, tunnel ram, a single 800 cfm Qjet could not feed it, even with 2 fuel pumps. it would run out of fuel at the top of 3rd gear. (electric pushing into mechanical). the Qjet builders say now that 1/2" or 9/16" fuel line from tank to carb will fix that, but the needle in the Qjet is small and too much pressure just blows it off the seat, the ones I ran can't hold more than 6.5 psi. at 7psi it starts to flood.

Carter made Qjets for GM as a contactor, Qjets have been around since 1966. Carter having this close relation with Qjet, improved it.

this is why the 2 carbs perform so similar, they are the same design.

the Qjet was around 3 years before the Tquad. If you hear someone raving about how great a Tquad is, it's really a testament of how good the original Qjet design was.

 

Id forgotten all about this. I might have a treasure instead of a turd sitting on my bench.

 

I have one (850 cfm) and love it. Smaller primaries than a qjet for better drivabilty and response but bigger secondaries than a qjet

 

the 850 TQ has larger primaries than a QJ, and the TQ 1000 has only one booster venturi on primaries.

the TQ and QJ have same size secondary throttle plates 2-1/4" IIRC

I plopped a 1000cfm TQ CS series w/screw in jets on my car today for first time ever. I'm in the process of tuning it, it runs and reacts exactly like the 800 cfm Qjet I had on the engine years ago, only slightly bigger primaries. I think the TQ primary side on the CS series is noticeably richer than the Qjet. I say this because, I was able to run the QJ without metering rods on my engine, and drive it around. I can't do that with this TQ as it will give a rich backfire through the exhaust while idling. it must have a really big fixed idle jet restriction. the primary jets in the TQ certainly are a lot bigger in size than any Qjet.

the idle circuit on the TQ 1000 cfm has 2 air bleeds in the primary idle circuit. One in the top angled backwards near the primary rod hole, and one in the primary barrel entrance in the front wall facing backwards. it's either an air bleed or a high speed enrichment nozzle that pulls from the idle circuit at high rpm tip in. it looks almost like a nozzle ? above the main booster venturi in front wall- because it sticks out into the primary barrel. air bleeds usually are nearly flush with the casting.