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Discussion Starter #1
I am currently running a 750 Holley 3310 carb with vaccuum secondaries on my mildly built 400 big block. I am wondering if it would be worthwhile to swap to a rebuilt 800 cfm thermoquad, or if it would be unncecessary.

My combo:

-'77 400 big block
-~9:1 compression
-performer rpm intake manifold
-windage tray
-summit cam 282/292 advertised, 224/234 @ .050, .465/.488" lift, 114 lobe separation angle
-stock exhaust manifolds
-dual 2.5" exhaust with glasspacks


Thanks!
 

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DO NOT FEED THE TROLLS!
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I really like the Thermoquad in principle, but in practice I had a whole lot of trouble with them.

A buddy of mine has a Carter AVS (now sold as an Edelbrock Thunder) on 496 stroker and it apparently works quite well. If you don't need to pass an emissions underhood inspection you might want to look into some of the other carbs out there.
 

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The Thermoquad can be modified to run like crazy, but finding the right guy to do it might be tough. My 360 Trailduster came with one. After tuning by an expert, it was very very capable. I do not like the Edelbrock, mostly because it is more difficult to tune. In my mind, you have the right carb and CFM for your cam. I currently run a 750 Demon on my 360, and I am very satisfied.
 

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Which thermoquad are you talking about? The Rochester or Carter style? I like the Mopar spreadbore style thermoquad, not the Rochester so much. The 750 is actually a pretty good match for your 400, secondary opening with the proper spring pressure (spring adjustments), are usually pretty decent, but I am kind of partial to the Holley carbs anyway.
 

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Discussion Starter #5
If I were to swap on a thermoquad, it would be a remanufactured version of the one originally offered on the 400 HP. I basically was wondering if I would gain anything in terms of performance over my Holley, since there is only a 50 cfm difference between the two. I probably won't go through with the swap unless I can expect a performance gain, since the Holley i have works fine.

Off topic; some of you guys might recall me posting a lot about the cam in this car. FWI I did end up swapping the milder Summit cam back in and it made a huge improvement in throttle response and torque below 3,000 rpm. I also can idle the engine between 600 and 700 rpm now, whereas with the Comp cam and Rhoads lifters it wanted to idle more like 800 rpm and with the Comp cam and standard lifters it was really unhappy at anything below about 900 rpm.
 

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Thanks for the updated information. It's kind of like the six pack I have for my 440 Charger. 1350cfm is more than the engine could ever suck, it is more the image of owning it, whereas 750cfm is still a little more than what the engine can ever pull in, especially on the street, so for the money, 50cfm is almost impossible to experience or know it is there.
 

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Discussion Starter #7
Good to know. I will probably leave my Holley alone, then. Like I said, it works fine and at this point I have just about perfected the tuning.
 

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DO NOT FEED THE TROLLS!
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I can tell you from my TQ experiences, when they ran right, they were absolutely awesome. Mild mannered in stop-and-go traffic and in parking lots, but when those secondaries opened you could hear the gaping maw hungering for more... Muahaha!

I guess I'm personifying a little too much here.
 
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