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 Q-jet vs Thermoquad 
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Joined: Fri Oct 23, 2015 8:43 am
Posts: 33
Since this forum is dead, I thought I'd post up a topic for discussion. I've build a lot of Q-jets, but I've never been inside a Thermoquad. It would appear that Carter used the Q-jet for "inspiration" when designing the TQ. Does the TQ have any inherent advantage over the QJet? Is there anything that makes the Q-jet more efficient or "better" than the TQ? Interested in hearing thoughts from the carb experts.

Fri Feb 26, 2016 9:53 am
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
I've done a lot of them over the years, but not near as many as QJets, and not so much in the last 10 years. I don't think there is any significant advantage or disadvantage other than the obvious, two inlet valves and there is a larger bore version. I think the QJet is more surgical with the wide selection of secondary metering rods and the hanger, plus air door spring tension. The TQuad has only spring tension and jets ... and air door opening limit but the QJet has that too (door limit). The problem with TQuads is the limited availability of metering parts relative to the QJet because there are 100+ Qjets in the bone pile for each TQuad. I think they are a good carb except for an occasional headache with the "X Rings" which seal the primary main well in the lid to the bowl. On of my old pals who is a real Mopar guru showed me SBC valve stem square cross-section O-rings can replace the X-ring.

Sun Feb 28, 2016 1:14 am

Joined: Fri Oct 23, 2015 8:43 am
Posts: 33
Thanks. I don't hear much about TQ carbs, and I've never played with one.

Sun Feb 28, 2016 12:08 pm
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
I like them. It is nice to be able to change the primary metering rod so easy.

Sun Feb 28, 2016 6:15 pm

Joined: Wed Oct 23, 2013 8:01 am
Posts: 113
What was the CFM range on them? Too bad they are so homely.
Dual floats may offer a bit more resistants to fuel starvation in some situations.

Mon Feb 29, 2016 6:15 pm

Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
77cruiser wrote:
What was the CFM range on them?

According to this page at The Carburetor Shop, 520 to 1000 cfm advertised flow.

A few month's ago Paul Ceasrine posted that Carter rated flow based on a calculation using throttle bore, venturi size and estimated volumetric efficiency (VE). He also wrote that when tested on a flow bench, they found the 800 rated versions flowed 735 and the 850 flowed 787cfm.
ref.: Carter Carburetors ~ Advertised CFM Ratings and Corrected CFM Flow Ratings ~ at forabodiesonly

Sorry can't help on the fuel control question. No personal experience or good references on that. Curious myself.

Wed Mar 02, 2016 10:29 am
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