Thermoquad jets

[QuickDart360]

I am debating whether to run .101 primary jets or .104. 850 thermoquad on a 360 modded motor. Removed choke door/flap. Engine consists of 292 mopar cam. Kb107 pistons, 340 X-heads. 3.91's out back.

 

[ACME SS]

Its a simple swap. Try it each way or if you want to have fun, take it to a dyno.

 

[Bewy]

If it came with 98 jets, try 101. As a test, if you get any surging at high speed cruise [ 60 mph or over ], screw IN the screw in the rod hangar, 4 turns. This will richen the cruise without stripping the carb. Reset the screw & go to a larger pri jet.

This combo will almost certainly need three things, because of the cam:
- a lot of timing at idle, up to 40*. Use MVA to add to the static timing. This gets done FIRST.
- increase in IFR, 0.003-5"
- more idle air so that you have 0.020-0.040" of T slot below the blades at idle, in gear. Later TQs have bypass air in the choke air horn that can be enlarged. Earlier models should have the blades drilled; drill the sec blades. Drilling the pri blades encourages nozzle drip because you are pulling more air past the nozzles.

 

[QuickDart360]

If it came with 98 jets, try 101. As a test, if you get any surging at high speed cruise [ 60 mph or over ], screw IN the screw in the rod hangar, 4 turns. This will richen the cruise without stripping the carb. Reset the screw & go to a larger pri jet.

This combo will almost certainly need three things, because of the cam:
- a lot of timing at idle, up to 40*. Use MVA to add to the static timing. This gets done FIRST.
- increase in IFR, 0.003-5"
- more idle air so that you have 0.020-0.040" of T slot below the blades at idle, in gear. Later TQs have bypass air in the choke air horn that can be enlarged. Earlier models should have the blades drilled; drill the sec blades. Drilling the pri blades encourages nozzle drip because you are pulling more air past the nozzles.

Good morning Bewy! I have some 1996 or 1998 metering rods in it now. But I also have a set of 1966 rods and another set of 2005 rods. Which is the best choice?

 

[Bewy]

Have a look on the mounting feet for the model number. It will be 6xxx or 9xxx. You can then find the original specs for that model on line. If the rods you have are not correct for that model, pick the thinnest rods as a starting point.
1966 67/52/45
2005 65/55/40
1996 69/48/35 [ very rich power step ]
1998 70/57/40

Bear in mind that the engine is now 'modded', so original rods/jets are unlikely to be optimal, but a good starting point.

What has been done to the engine?

 

[QuickDart360]

I do have a single plane intake. The 340 Victor to be precise. Using an adapter to run thermoquad. Heads are stock unsorted 340 X-heads with 2.02 intake valves. Also the big hydraulic 292 mopar purple cam. 727 and 9.5" FTI 3400-3600 stall converter. 3.91's out back.

 

[Bewy]

What I said in post #3 is going to apply, particularly ign timing.
You get the idle timing dialled in first before touching the carb [ centri timing curve & WOT timing comes later.]
Idle timing is realllllllly easy. Set initial to about 12* BTDC, not critical. Disconnect & plug VA. Adjust carb for best idle.
Warm up engine, in gear, engine running/idling, turn dist slowly to advance timing. Idle rpm will increase; keep advancing dist until you get the highest rpm; toggle dist to make sure you have highest rpm. Idle WILL also be smoother. Now check the timing. If it is 45* [ more likely in the 30s ] , then that is what the engine wants for best idle/tip in response/cool running/avoidance of a flat spot. The easiest way to do this is using vac adv connected to manifold vacuum. A dist with an adj vac adv is reqd for this. Most adj VA units have about 30* of travel. So any combination of init + VA can be used to provide the # you got in the test. The reason the rpm increased in the test is because the engine was making more hp from the extra timing.
I suggest you do the above testing & report back with the #s.

 

[QuickDart360]

What I said in post #3 is going to apply, particularly ign timing.
You get the idle timing dialled in first before touching the carb [ centri timing curve & WOT timing comes later.]
Idle timing is realllllllly easy. Set initial to about 12* BTDC, not critical. Disconnect & plug VA. Adjust carb for best idle.
Warm up engine, in gear, engine running/idling, turn dist slowly to advance timing. Idle rpm will increase; keep advancing dist until you get the highest rpm; toggle dist to make sure you have highest rpm. Idle WILL also be smoother. Now check the timing. If it is 45* [ more likely in the 30s ] , then that is what the engine wants for best idle/tip in response/cool running/avoidance of a flat spot. The easiest way to do this is using vac adv connected to manifold vacuum. A dist with an adj vac adv is reqd for this. Most adj VA units have about 30* of travel. So any combination of init + VA can be used to provide the # you got in the test. The reason the rpm increased in the test is because the engine was making more hp from the extra timing.
I suggest you do the above testing & report back with the #s.

One other detail I forgot to mention is I advanced the cam @ the crank by 4° to get better low end response and it helped. Also my timing is set @ 16° initial and car has been running well like that. This carb that I want to rejet is a carb I bought from a guy on ebay. His name is Steven Sills. He did it well but jetting is different from the old carb I took off. Old car was set up with. 101 jets and .149 rear jets. Also this old carb had the 1966 metering rods. Only reason I took it off was because it started to give too much fuel. Nozzle drip that is. Caused car to stall out after some driving.

 

[QuickDart360]

Eventually I will rebuild that carb since it ran so well!!

 

[Bewy]

QD360,
OK, one thing at a time:
- that engine will always be 'doggy' down low because of the cam duration & the Victor intake. Advancing the cam, by whatever amount, will only minimally improve low end TQ.
- TQs had different size primary air bleeds; larger ABs were used with larger main jets. Same applies to secondaries. You need to find the model # [ post #5 ], post it here & then original jetting can be given
- not surprised to hear it has nozzle drip. What you have here is a 'sequence of events'. Big, rough idle cam, needs a higher idle speed.......which needs pri blades open further for more air to idle....which then causes nozzle drip from the additional idle air passing through the boosters.
- 16* initial is nowhere near enough. Did you read post #3 #7?????
With the proper idle timing, the blades can be closed slightly. Once the idle timing is done as above, remove the carb & check how much T slot shows below the blades, at idle in gear. If more than 0.040" showing, more idle air is needed. Drill the sec blades, NOT the pri blades. Start with one 3/32" hole in each blade, & enlarge in 1/64" increments until you have 0.020-0.040" of T slot, 020 preferred.
- all this will be a waste of your time & my typing finger unless you do as above.