Thermoquad race tune

-
71duster06

71duster06

Well-Known Member
Joined
Jan 23, 2008
Messages
639
Reaction score
74
Location
West Michigan (GR)
Hey everyone. I have a thermoquad that I am going to try on my 340. I have a few that I can rebuild.

6318- 73' 340 MT 1-3/8"
6324- 73' 440 HP 1-1/2"

The 340 is currently a mid 13 sec car (4 speed w/ 3.23s) with a 750 Holley Vac. secondary.
(1970 340, 10.5-1 comp, Lunati 60403 cam, LD340 intake)

I was curious if there are any tips for race prepping a thermoquad. (jets, metering rod # etc.) Any first hand insite will be great.
 
on my 340 the 750 holly dp made 13 more hp on the dyno than the tq but the tq ran 2 tenths quicker than the holly so please post your results you will love the tq if you get it right
 
i know of no company offering jets or metering rods for a tq you need to modify stock stuff if need be.that little screw on top of the metering rods isthe tricky one once you set the air screws
 
i think there is a sticky in the fourms by the banned for life stroker scamp on the tq
 
jimjimjimmy said:
on my 340 the 750 holly dp made 13 more hp on the dyno than the tq but the tq ran 2 tenths quicker than the holly so please post your results you will love the tq if you get it right
Click to expand...


Good to know. i am going to switch back and forth at the track once the TQ is dialed in...then i can get a true comparison.
 
Badsport said:
Hey Kyle, I would suggest getting a strip kit, it's going to be pricy though. I would call and talk to this guy. He has limited hours though, I believe it's listed on his homepage.

http://thecarburetorshop.com/Perfparts.htm
Click to expand...

I actually have a Carter strip kit that I got a while ago. I was just curious if anyone had good recommendations for jets and metering rods for a good baseline. Tho I know how different every motor acts...
 
jimjimjimmy said:
on my 340 the 750 holly dp made 13 more hp on the dyno than the tq but the tq ran 2 tenths quicker than the holly so please post your results you will love the tq if you get it right
Click to expand...

Did the TQ 60ft better then the Holley ?
 
AdamR said:
Did the TQ 60ft better then the Holley ?
Click to expand...
if i can remember right they were close but the tq is a great carb out of the hole when the back doors are set just right.i will look for my slips it was 98 when we raced last .
 
Use AFB/AVS rods to tune. They will need to be 3/4 inch shorter than they are now. Bend and clip the rods.

Use the bigger TQ.

The secondary air door needs to be tuned in. The opening spring rate is key. IF you do not have the "tool", it is a little tricky to do.
 
rumblefish360 said:
Use AFB/AVS rods to tune. They will need to be 3/4 inch shorter than they are now. Bend and clip the rods.

Use the bigger TQ.

The secondary air door needs to be tuned in. The opening spring rate is key. IF you do not have the "tool", it is a little tricky to do.
Click to expand...

Ordered a new rebuild kit for the 440HP TQ.

Im anxious on how it will run at the track compared to the 750 Holley....
 
There are a couple other things besides the air door spring that affect the transition to the secondaries.

One is the very small bleed hole in the front wall of the RH secondary barrel. It connects with the vacuum diaphragm that's linked to the air valve. The front edge of the secondary throttle valve blocks this hole off when the valves are closed. As soon as they start to open, air at atmospheric pressure enters the bleed circuit, and over a couple seconds this spoils the vacuum that's holding the air valve closed.

The other is the initial opening of the air valve--.040" or so. This is a little like the initial kicker opening on an automatic choke. When the secondary throttle plates first start to open, this opening allows some air to flow in past the secondary nozzles, but only a little. When the secondary plates are just starting to open, for a moment that creates a very high vacuum at the nozzles and a rich mixture.

Both these things are another way of doing what a separate secondary enrichment nozzle or a separate accelerator pump for the secondary circuit would do. They work with the air valve spring to keep the FAR from being too lean (or too rich) during the short time the valve is opening.

At least on some TQ's, the accelerator pump linkage is also designed to provide an adjustable shot of fuel when the secondaries begin to open.

So there are really three or four things that interact to control FAR during the transition to the secondaries, and not just the air valve spring. I would think that slight adjustments to any or all of them might make for more power during those few seconds of transition.
 
Noticable improvement with the TQ in power!

The TQ did loose a bit in off idle throttle response and a tad in low end power...... but the secondaries definitely makes up for that.... I forget the secondary transition compared to the Holley (which is very minimal).

Overall im impressed with the TQ again... thing revs noticably quicker too
 
Did you remove the choke plate/attaching rod? If you did and you used the 850(6324), use a 4101 or 4102 primary jet and use at least a 5149 2ndary jet. Try using a 2005 or 1998 metering rod if you have these in your strip kit, David.
 
Thanks Rob! You know the story on my mia here and I just thought I would chime-in and try to help. See you around, David.

ps a few pics of some 'trick' T.Q. internal parts for a perf gain.
 

Attachments

  • DSC00100.JPG
    79.9 KB · Views: 1,561
  • DSC00108.JPG
    92.9 KB · Views: 1,523
You will love that thermoquad. Pulled off my Holley DP and replaced with a modified 900+ cfm tq and it ran awesome ! Was on my 440, much better during light throttle operation on the streets and performed very well at the track. My buddy ran consistent 10.0's with same carb on his demon.
 
David, it is always a pleasure to see you here helping out.
 
Thermoquads are all junk, and they run like chit. Hard to keep a tune, don't do what they are supposed too when you tune them. Parts need to be made to fine tune them. A/F Meter numbers mean jack-**** when trying to tune. You have to resort to throwing fuel or air at it to see if it picks up or not. On top of all that, a six-pack picked up 3tenths in the car....
 
quadrajetparts.com Has some decent stuff for the thermoquads.
 
You must log in or register to reply here.
-

Back
Top