Thermoquad on a 318?

Engines, Exhaust and Fuel Systems

  1. The Director

    The Director Active Member

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    Well, this may sound stupid, or it may actually have been done before, but since I'm curious, here goes:

    I found a 4 bbl carburetor in my locker in the garage that went on a 1982 Dodge Travco Motorhome we used to have. (A 440 powered that thing.) Anyway, I was flirting with the idea of seeing if it was possible to get that onto my 318 in the Fifth Avenue I have. It would definitely need a new intake manifold, but other than that, I don't know if this is feasible. (I would also have to remove the lean burn, inherently, because this carburetor does not support that.) I think the carburetor is a Thermoquad, because if I remember right, it's got that black piece of plastic that is known on the bottom.

    Any thoughts?
     
  2. Camtron

    Camtron Well-Known Member

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    Going to be pretty big on the 318 and make your exhaust smell like a chemical fire, lol. It will run though (assuming it doesn’t need a rebuild). As tempting as it is, don’t slap an intake and carb on the car before you have headers and a duel exhaust system on the car.
    I have a two barrel that works without the lean burn if you want it, it’s yours for free.
    I’d delete the lean burn, get headers and exhaust on the car and then worry about intake and carb.
     
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  3. AJ/FormS

    AJ/FormS Well-Known Member

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    I ran the big TQ on my 318 for years and years and years.
    The only thing you have to do is limit the secondary some and get the tip-in timing right. In 20 minutes you can have a BB stomping mighty 318,lol. I would bolt it on in a heartbeat.
    I will add tho, that I found a small-port, cast-iron, spreadbore intake, to bolt it onto. This crispyed up the response nicely. I have no idea what that intake came off tho.
    Since then, I have obtained an Offenhauser Dual-Port, from a member on FABO, I want to someday try.
    My combo includes headers, a clutch and 3.55s, but is otherwise stock 1973. If you do not have a high stall or bigger than stock gearing, your results will vary.
    But hang on;
    With the hiway gearing these cars come with, the Rs take forever to build, and the teen may not like the secondaries until after 2400rpm. And the problem with that is; if she don't spin the tires, then with 27" tires and a 2.74 low gear, 2400 is;
    30.5 mph with 2.20 gears and
    27.5 mph with 2.45s,and
    24.5 mph with 2.76s,
    versus (see note #1below)
    In which case, the primaries, being smaller than the factory 2bbl, you might, actually lose performance below that magic number where the primaries run out of flow.
    If you need off-the-line grunt, you will have much better results with a hi-stall Torque Convertor, followed by gears.
    Your factory lo-stall TC may be limiting your engine to a place on it's power curve where the power might be something like 60hp. If you had a hi-stall, it will allow the rpm to climb up to a higher part of the curve, where the power could be close to double as much.

    Following, is a MAGNUM 5.2 power curve for your perusal. Look at the power difference from 1800 to 2800, and you will see what I mean; I see ~90hp versus ~155.
    The 4bbl cannot touch this power increase, limited at the factory stall.
    (note #1) versus; in my combo; 17mph with 3.55s. But the clutch allows for reving it up to whatever it takes to break the tires loose, and then;
    POW!
    the secondaries open.

    power-318.gif
     
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  4. volaredon

    volaredon Member

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    I've had vehicles from the factory with a 318 and TQ. Most notably my 1981 W150. I still miss that truck. Huge power from a 318 and unbelievable mileage. I love the 318 in general and if you have a tq that is set up right, you will love it.
     
  5. The Director

    The Director Active Member

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    Thanks for the information guys - out of what it seems, I think I'll try out that carb. It'll be nice to get rid of the lean burn as well on that. (Now just to figure out how I'll work the exhaust and header upgrades without making the car too loud.)

    The power I'm looking to get out of it is when I'm actually moving, and not so much in the case of being off the line. (I'm comfortable enough with my off the line power, and, it can spin tires.) Oh, and since I'm thinking about transmissions, one day, if I'm ever crazy enough to do it, I'd do a manual swap. Probably to a 4 speed setup. It's a deep rabbit hole that I'll jump into once I actually get serious about that.
     
  6. BudW

    BudW Moderator Staff Member

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    I rank the Thermoquad's into three different groups. Ones that run excellent right out of the box (ie: the early ones), those that ran OK but some fine tuning is needed (the mid-year TQ's) or the later ones which are a royal pain in the you know what (which is what came on all FMJ's.

    On the drivers side rear of the TQ baseplate there will be numbers stamped. The top number is the model number the lower number is date it was made.
    Example:
    TQ 9046s.jpg
    This one is model 9046s. Made the 351st day of '74.

    If you could tell me those numbers, I can give you my opinion for that carburetor. IMO, all of the TQ's made after 1980 are not worth the trouble to use. Many of (but not all) of the ones used from '72-75 are excellent – but there is no real set date to when they changed. A person needs to use the model number.
    BudW
     
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  7. The Director

    The Director Active Member

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    My thermoquad reads "9275S" on the top row, and "243 9" on the bottom row. Below is an image of the actual carb's numbers.
    DSC07648.JPG

    I'm not sure if this is original to the 1982 Dodge Travco motorhome that it was originally on, but I know that was the vehicle I got it off.
     
  8. Mikes5thAve

    Mikes5thAve Well-Known Member

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    That's 78-79 360 truck.
    Motorhomes and coach built stuff is strange. Sometimes parts can be from older years of they had bought in bulk from the vehicle manufacturer and had stock to use up but they usually leave the engine the way it came.
     
  9. The Director

    The Director Active Member

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    That's strange for it to be intended for a 360.... because the motor it powered was a 440. And, if anybody's wondering why this carb is off the motorhome, it's because we replaced it with a different carb, but this one still ran the thing. I'm pretty sure it just needs some rebuilding or something to make it better. Can't really remember, since this was about 5 years ago now. I'd like to make it useful, since it's already in the house.
     
  10. AJ/FormS

    AJ/FormS Well-Known Member

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    I've put old 440 TQs onto teeners. AFAIK,there are just two sizes of TQs, the principal difference being in the primaries. IIRC the two sizes are 1.50 and 1.375 bores, which are typical 2bbl sizes. The secondaries are all the same from the few that I have seen; 2.25ers if I remember.
    To match the carb cfm to the engine, you just adjust the max air-door opening.
    Then you make the usual fueling changes as may be necessary.
    All the important stuff happens in the primaries. The three-step metering rods is where the magic happens.
     
    Last edited: Apr 4, 2020
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  11. BudW

    BudW Moderator Staff Member

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    Well put @AJ/FormS.
    @Mikes5thAve is correct, this TQ came from a 78-79 360 pickup. It has the smaller primary's and also has an electric Bowl Vent - which will need something done with it or carburetor will not work correctly (send me a conversation for instructions about the Bowl Vent).

    Bowl Vent aside, I rate this TQ as a yellow (Green is the early ones that work great, no matter what, and Red is the late ones - that I wouldn't use if someone paid me (aka, what was used on FMJ's)).

    This particular unit was made on 249th day of '79. It is very possible this unit is correct for this vehicle for motor homes were done differently than cars/trucks were. I have a '79 360 motor home engine that came out of a '80 or '81 motorhome. The engine came from a different manufacturing plant as the cars/pickups came from.
    I believe the motorhome companies will place an order for say 10,000 engine/transmission assembly's. Chrysler will build them on the spot, then wheel then into a warehouse for the motorhome company to pickup (when needed?). Sometimes they will load them onto train cars for shipping and the train cars could take months (or years) before opened to unload.

    About 99% of all engines made by Chrysler (in late '79's to early '80's) were made at the Mound Road engine plant. Your block will have an EIN (Engine serial number) in addition to the VIN stamped on it (in different locations). the EIN number is stamped just under the Left cylinder head gasket surface on front side of the block - on small blocks.

    It will read something like "9M 360 1111 0001". The first digit is year made; 9=79, 0=80, 1=81, etc. Second digit is plant made; M= Mound Road, W= Windsor, T= Trenton (big blocks) and K= ??. The next is engine size (this case 360). The next four digits are month and day (November 11). The last four digits are engine built that day.

    My '79 360 Motorhome engine is very odd:
    20170710_003508a.jpg
    Block was cast on May 4, '78
    20170710_003408a.jpg
    20170710_002922a.jpg
    EIN number is "9K 360 1221 59019". Engine was assembled on December 21, 1979, at "K" engine plant (Kokomo ??). The last four (five, in this case) is 19th engine made that day and I suspect "59" might be the motorhome contractor. Most blocks are cast a week to a couple of months before assembly date - not 19.5 months later.
    I also suspect your 360 might have similar details (maybe).
    The TQ number I got was 9126s ('78 360 truck California) - which is one my "red" carburetors.
    This motorhome had a '80 or '81 build date (can't remember and didn't take a picture of it).
    BudW
     
  12. volaredon

    volaredon Member

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    I have 2 either 1979 or 80, 360 truck TQ's, both same carb # as each other. Redone by Demon Sizzler, only reason IO sent em in was to have him rebush the throttle shafts but he played with jet sizing as I remember while he had them..... haven't looked at em in a while but as I remember the only issue with them were they had idle stop solenoids, which I no longer have.... (no electric bowl vent jazz) was just gonna make a throttle stop out 1/8" flat stock at the time...… one will be going on my 78 Sport Fury's 318 this spring, the other will be going on one of my son's trucks, not sure which...…. BTW what ever happened to Demon Sizzler?
     
  13. BudW

    BudW Moderator Staff Member

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    Bermuda triangle?
     
  14. kkritsilas

    kkritsilas Well-Known Member

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    My two J bodies both have factory TQs. I think the 4 barrel 318s were only available in Canada and California.

    TQs only came in two CFM sizes: 800 CFM (small block) and 850 CFM (big block). The change was due to a 1/8" diameter difference in the primaries, secondaries were the same size (i.e. huge). It looks like the one you have is for the 360, so should be fine on the 318. It may be need to to be adjusted to get the idle speed/mixture right.

    I think they used a small block TQs on a big block to maintain flow velocity and to improve throttle response and fuel economy. After all, its not like motor homes get floored all the time, or drag raced (at least, not out of the factories).
     
  15. Mikes5thAve

    Mikes5thAve Well-Known Member

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    A mopar buddy of mine bought a factory 4bbl 1982 New Yorker. I found the car and still kicking myself for not getting it myself. It also has the Mirada wheels on it. But it was about 6 hours from here and was for sale for a while from a seller who didn't know anything about the car so I didn't want to make that trip out it was junk or a slat 6.

    I don't know if an RV builder would really know or care about differences in carburetors. They probably had a stack of engines and thermoquads and threw whatever they had in there not knowing what part went with what.
     
  16. The Director

    The Director Active Member

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    Funny enough, now it looks like I have the perfect excuse to throw that Thermoquad on, being that my factory carb just started to leak some gas, and I'd rather just replace it.

    But yeah, I doubt that the motorhome guys cared as much about the carb difference. That Travco was 32' and I doubt that a small difference in carb will really be noticable on a 6 or 7+ thousand pound vehicle. (Or, does it?) I appreciate all the information guys, it really helps!
     
  17. LSM360

    LSM360 Well-Known Member

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    Remember, the M body Police cars with 318 four barrels came with a thermoquad through 1984 until they switched to the Rochester Quadrajunk. The police 318 did have 360 heads and exhaust manifolds too though.
     
  18. The Director

    The Director Active Member

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    I never knew that Rochesters were put into M-Bodies.... good to know.

    I'll definitely change the intake and open up my exhaust to support the 4 barrel setup, but I'm curious if I need the 360 heads, or if this is just a performance option. I've heard of someone doing that actual mod on a car before, but I've never heard of it being a factory installment.
     
  19. Mikes5thAve

    Mikes5thAve Well-Known Member

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    No you don't need to use the 360 heads. If you want to get into changing them there are better ones out there anyway.
    The factory 4bbl intake has bigger intake ports then the 318 heads do. You would still get a performance gain but not as much as if the ports actaully matched.
    Edelbrock performer intake has smaller ports that are a bit better matched 318.
    A lot of it comes down to how much work you want to do and what you want to spend.
    What year 5th aevnue is it? If it's 85 or newer it already has the swirl port 302 heads that are better then the older 2bbl ones. At one point some people were actually using those heads on their 360s.
     
  20. The Director

    The Director Active Member

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    My Fifth Avenue is a 1988 model from Jersey. As far as I know, Jersey models don't have any special configurations, unlike the California/ High Altitude cars that I've read are setup differently.

    And being that the heads aren't required, I think I'll leave them alone then. I'm looking to spend up to $800 on the high end of this idea. The exhaust setup would probably be the hardest to fit into that constraint, since an intake manifold is about $340 or so, and I might have to rebuild that carb, and that's probably another $60 (just a guess.) The exhaust would be nothing loud or fancy, but just enough to improve the flow enough for the setup.