Settings for Thermoquad 6545

[Andi Kreis]

One of our Swiss club members contacted me regarding carburettor problems with his 440 1972 Int3 (engine no. HC10261/133). He says the CO is stable whilst the engine is idling but the in mid revs there would be a lack of power. He's got a Edelbrock Performer manifold and a Carter Thermoquad 6545 and is looking for the best jet / needle setup for his application. Unfortuantely I'm not familiar with the Thermoquads so I need your help. Thanks for your hints!

[Chris_R]

The Thermoquad 6545 was original specification for the 1974-6 Dodge D-series Pickup and 1974-76 Dodge Ramcharger (roof and passenger seat were optional extras) trucks when fitted with the 440 engine.
From Richard Calvers books, the H series came with a Holley. The later J series came with a TQ, given by Richard as the 6411S so you could perhaps look up the specification for a Carter TQ 6411S and see if that can be applied in the 6545.
According to Carter documentation, the TQ6411 was a California spec carburetor used on Chrysler, Plymouth and Dodge brands.
Both the 6545 and 6411 are rated at 850cfm.

[Andi Kreis]

Thank you, Chris. Will forward your informations to our JCC member. I suspect 850 cfm is a bit over the top for a standard 440 engine...?

[thomaslk]

Thank you, Chris. Will forward your informations to our JCC member. I suspect 850 cfm is a bit over the top for a standard 440 engine...?

i also read about this surprisingly high cfm rating of the TQs - but there seems to be different measurement methods (dry/wet).
Not sure if this explains the high rating compared to current aftermarket carbs.
rgds
Thomas

[Joerg]

Ask Dave Barnett, he knew exactly what to do with this truck carb. Not uncommon on Interceptor and no big deal to set it right (they are all more or less the same).

Joerg

[ffdave]

I saw Andi's post and have been looking through my book collection to try and find details of the 6545. Some of the later truck Thermoquads had a lot of emissions kit stuck on them and they can be hard work to richen up across the whole rev range. Andi perhaps your friend could take a pic for us, i have needle pairs if required.
The Thermoquad is indeed an 850cfm carb, being a spreadbore it has small primaries for low speed responsivness and mahoosive secondaries for breaking the speed limit. Properly set up they are in my opinion one of the best carbs out there matched only by the Rochester Quadrajet. (He says with a Holley street avenger on his SP! ).

D.

[Philip Lochner]

He says the CO is stable whilst the engine is idling but the in mid revs there would be a lack of power.

It sounds to me like the engine is running lean at partial throttle. One of the wonderful aspects of the TQ is that YOU DO NOT NEED NEEDLES AND JETS TO ADJUST FUELLING!! It can be done with a small screwdriver.

I would recommend that he increases fuelling on the primary barrels by turning the primary adjustment screw by 1/2 turn at a time KEEPING RECORD OF HOW MANY TURNS YOU ARE MAKING!!

Turn the screw clockwise for more fuel (and anti-clockwise for less fuel).

Be sure to test the result of your adjustments with a LIGHT FOOT, ie smallish to medium throttle openings. Try not to engage the secondary throttles.

[Philip Lochner]

We are of course assuming the centrifugal advance and vacuum advance on the distributor is working correctly....

[thomaslk]

Hi Philip,
it is a bit off-topic but I am really impressed by your new avatar.
Did you change to 25" rims ipo 15" ?

Back to Thermoquads:
Is there any chance to "detune" the late series4 California TQ with the additional anti-smog devices to "normal" TQ functionality ?
I guess my PO switched to the simple Edelbrock aftermarket carb because the TQ exhibited some irregularities. Have to look up the TQ spec number.
rgds
Thomas

[Philip Lochner]

Hi Philip,
it is a bit off-topic but I am really impressed by your new avatar.
Did you change to 25" rims ipo 15" ?

Back to Thermoquads:
Is there any chance to "detune" the late series4 California TQ with the additional anti-smog devices to "normal" TQ functionality ?
I guess my PO switched to the simple Edelbrock aftermarket carb because the TQ exhibited some irregularities. Have to look up the TQ spec number.
rgds
Thomas

Thank you for the compliment Thomas!!! I am pleasantly surprised by how many compliments I get for it! I'm using it on my Whatsapp profile as well and the same thing happens there. Its a local chap who draws this picture off a photo that you send him. He charges about GBP100 per drawing.

The Carter TQ my '74 car came with is the 6411SA, which must be one of the most SMOG tuned versions out there. Basically, I simply plugged ALL the pipes on the carb, EXCEPT the vacuum advance port, which still has a pipe to the vacuum advance port on the dissy, and the Crank Case ventilation port, middle front of the carb.

It now looks like a porcupine with all these blocked pipes, but it works fantastic as you can see per my youtube video.

I have said it many times and will say so again: The TQ is IMHO, a Rolls Royce among carbs. The Edelbrock and Holley is in my opinion the equivalent of a Mahindra or Tata.

[Andi Kreis]

Thank you for your hints, guys!

@ Dave: I will ask our member to take a picture of the carb. Is there something he should focus on (e.g. production / casting number etc.)?
@ Philip: Would you mind takeing a picture showing what setscrew you are referring to for adjusting the fuelling - remember I haven't got a clue when it comes to TQ's...

Best regards

[Philip Lochner]

@ Philip: Would you mind takeing a picture showing what setscrew you are referring to for adjusting the fuelling - remember I haven't got a clue when it comes to TQ's...

PLEASE JUST REMEMBER THE SETTING YOU STARTED FROM !!!(So that you can turn it back to that location if you find no improvement)

Also, note that turning this screw should have very little effect if any at idle

Tuning a carb is really something that should only be done with a Wideband Oxygen Sensor and someone who REALLY knows what he's doing.

[bkbridges]

There are many articles on the interweb that describe tuning procedures for the thermoquad. heres a good one by Dulcich: http://www.hotrod.com/how-to/engine/mop ... arburetor/
heres one that tells you what was in each individual model and when: http://www.carbkitsource.com/carbs/tech ... aanth.html (6545 was oem for a 360cu in truck motor in smoggy 74, prior to catalytic converters... a bit lean for a 440 I would imagine in stock trim)
Now you can even buy them on Jegs and Summit's websites!
BKB

[thomaslk]

VERY interesting reading - thx Bruce.
Till 10 minutes ago i THOUGHT i got the original carb in a box from the PO but looking to the stamped numbers this is not the case.
Not really sure if i should be happy about it or not. So what i have is a TQ 9801S which is obviously an aftermarket version. In addition i have a spare TQ 9247S from a motorhome engine. Currently my engine runs with an Edelbrock 650 AVS -an 800 AVS is available on the shelf (i was not really happy with the 750 AFB 1411).
Subjectively the engine runs really well with the current setup - but objectively measured with the wide-band lambda sensor the world looks not as perfect - cruising is ok with AFR low/mid 15, power mode a bit too rich and WOT probably too rich with high11/low12 values.
So question is now:
1) leave it as it is - carbs are never perfect and the current setup seems to be "safe"
2) refine the Eddy tuning
3) dive into the adventure of TQ tuning incl search for a spreadbore intake (EDE DP4B?) ipo my current Weiand 8009.
Generally i agree with Philip that regarding appearance/finish/precision the TQs look much more promising than the Eddies with their "lawn mover style".
Will i really gain something by going back to TQ? I do not want to step back to the stock iron intake or to spread/square bore adaptor - even if i have both parts handy.

Feedback welcome

Sorry for hijacking your thread a bit, Felix. Maybe i should have started a new one

rgds
Thomas

[bkbridges]

The Edelbrock carb is very tunable, and your WOT AF is a bit rich, leaving some power and efficiency on the table... Id get a tuning kit for the Eddy and see if it helps any. Both of your TQs are good fodder, and might present a bigger top end when tuned properly vs. the edelbrock 650, which is just too small (I ran one on my 68 Cougar's 302 before going to multiport injection...)
BKB