Spreadbore Carburetor for Big Block Chrysler (383)

Just in case you're not following along with my thread about building a family hauler out of a '66 Town and Country, I wanted to ask some advice about getting a spreadbore carburetor. I decided to toss the stock factory 2 bbl Stromberg. It's old and worn out, leaks through the throttle shafts, and I just like the concept of a spreadbore carb- tiny primaries for economy and huge secondaries for when you romp on the loud pedal.

Chrysler did use some Rochester Quadrajets in the 80's on their 318 and 360 pickups, I'm wondering is one of these will work with my accelerator and auto trans linkages? Or is there another option? Unfortunately, most QJ's out there got installed on GM vehicles, so the linkages aren't right. Chrysler did use some Thermoquads in the 70's, but I'm concerned about the plastic in those carbs disintegrating with today's fuels.

Holley did allso build some spreadbores, but I don't know much about them, or Holleys in general, other than they leak at the float bowls.

Thoughts on the spreadbores for my Chrysler 383? Oh, and yes, since you're wondering, I already bought a spreadbore manifold for the engine- an old Edelbrock unit.

Aren't the older Edelbrock carburetors basically Q-jets? I think the new ones may be based on the Carter Thermoquad based on the looks. Should be easy to get a Chrysler adapter for one if you want to go that route Link to Edelbrock carb page

Edelbrock did offer Q-Jet carbs at one point, but the majority of their "Performer" carbs are based on the Carter AFB.

A Q-Jet with a proper setup is a great carb. They are often overlooked because they are very complex and not as easy to tune compared to your typical Holley.

The Thermoquad plastic body should hold up to ethanol just fine, I wouldn't worry about it. As long as the carb is in good condition (not warped or damaged), any thermoquad, Q-jet or Holley will work quite well, with a bit of tuning.

I think people would be yelling by now if the thormoquad couldn't handle E10.

Efi. I hate carbs.

My thermoquad was great for the one week it was actually right.

Also, you might consider tossing the old school linkages for cables, a bit safer and lets you use generic hot rod brackets.

Big block Mopar?

So I told the teachin' lady, the only three letters I need to know are A, F, and B.

Edelbrock makes a little adapter bracket for the carb that puts the mopar linkages in the right geometry, and it will work for Holley carbs too. I've used the edelbrock part with a Holley economaster on a 413 and was pleased with the performance.

That said, I always start out with a Stromberg WW 2 bbl as my baseline on a mopar. Tough carb to beat for performance when you stomp on it and economy when you don't.

Hit the pick'n'pull for a mid 70's fullsize with a 400, and pull the Thermoquad and all the linkage off it. They work fine.

Note: This advice would have been much easier to follow about 20 years ago.

In reply to Streetwiseguy:

Nah, you still see them occasionally, you just need to go to pick and pull yards on the bad side of town. Hell I found a (albeit extremely rough) flat top 60 Cadillac in a Detroit pick and pull (not parts galore) once.

Which Edelbrock intake did you find?

I'd go with a Thermoquad, but I'm partial to them. The plastic body is phenolic and is fine with ethanol. You'll need the throttle stud off the Stromberg. You are going to need to modify the kickdown linkage too, but it's not difficult.

In the late '80's Chrysler switched to Quadrajets when Carter stopped making carbs. Those are all the mutant ones with the assorted solenoids hanging off them. You would be better off with an earlier Q-jet. I think the Edelbrock throttle lever adapter might bolt up to one. I haven't tried it, but the aftermarket carbs are based off the GM throttle arms so I suspect the adapter would work.

The Holley spreadbores are out there. Most of the used ones I've come across are double-pumpers I'd rather see you use a vacuum secondary on there.

If you want a modern take on a spreadbore, Demon released their Street Demon that's more or less a descendant of the Thermoquad mixed with a little bit of Holley 3bbl DNA. It's designed to fit a squarebore intake by making the secondaries one big single barrel. It's a nice piece.

oldopelguy wrote: That said, I always start out with a Stromberg WW 2 bbl as my baseline on a mopar. Tough carb to beat for performance when you stomp on it and economy when you don't.

That's the carb that's on there now, but it's old, the throttle shafts are sloppy, and it's already been (poorly) rebuilt once prior to my ownership of the car.

I had a 440 with an AFB on it. Performance was good, but it did like some gas. I had a Q-jet on an old 350 Chevy in a Suburban, and that was a great carb.

Rob_Mopar wrote: Which Edelbrock intake did you find? I'd go with a Thermoquad, but I'm partial to them. The plastic body is phenolic and is fine with ethanol. You'll need the throttle stud off the Stromberg. You are going to need to modify the kickdown linkage too, but it's not difficult. In the late '80's Chrysler switched to Quadrajets when Carter stopped making carbs. Those are all the mutant ones with the assorted solenoids hanging off them. You would be better off with an earlier Q-jet. I think the Edelbrock throttle lever adapter might bolt up to one. I haven't tried it, but the aftermarket carbs are based off the GM throttle arms so I suspect the adapter would work. The Holley spreadbores are out there. Most of the used ones I've come across are double-pumpers I'd rather see you use a vacuum secondary on there. If you want a modern take on a spreadbore, Demon released their Street Demon that's more or less a descendant of the Thermoquad mixed with a little bit of Holley 3bbl DNA. It's designed to fit a squarebore intake by making the secondaries one big single barrel. It's a nice piece.

The manifold is a DP4B, supposedly one of the better ones to get, no longer in production.

Definitely want vacuum secondaries. My understanding was the QJ/ Thermoquad was like an 800 CFM carb, but they could use it on anything from wheezy 305's to big blocks, it was so versatile.

I'd read about the silly electronically-controlled QJs, but I thought the truck QJs were simpler. Either way, it sounds like a TQ is the way to go- basically the same as a QJ, but with cooler fuel.

The street Demon is nice, but...man, $470!

So....TQ's all seem to use the factory style choke liftoff. I suspect this will not be possible with the Edelbrock manifold. How hard is it to adapt an electric hoke, or are there any sold that had electric hokes?

Some Demons left the factory with major quality control issues. Tunachucker Matt can tell you about those; he bought one on my advice and regretted it based on those. They probably got better, but I don't know which lines nor when.

Either factory spreadbore choice is probably going to be great, but I don't know anything about Thermoquads. Stay away from the computer controlled Quadrajet versions mostly for lack of tuning support for all of the ancillaries.

I thought it was pretty easy to strip the computer controlled bits from a later Q-Jet. If you just have to go carb on this, a Q-Jet seems like a great option, and I'd pick that over a Thermoquad.

But honestly an EFI setup using GM truck TBI parts seems a lot smarter if you really want a driving experience closer to that of a more modern vehicle. To do it really nicely will cost some money though.

volvoclearinghouse wrote: So....TQ's all seem to use the factory style choke liftoff. I suspect this will not be possible with the Edelbrock manifold. How hard is it to adapt an electric hoke, or are there any sold that had electric hokes?

The DP4B has a provision for a GM style choke on it. I haven't tried adapting a GM choke to a T-quad, but it probably could be done. I've also heard of guys adapting the Edelbrock electric choke kits to a T-quad, but haven't seen it. I've been toying with trying it just for kicks.

Carter did offer a line of aftermarket 9000 series T-quads in the '70's and into the early 80's. They were based off the OE carbs, not the earlier race T-quads. The aftermarket ones were available with electric choke.

The Edelbrock Performer intake is setup for a Mopar style choke stove. They have been in production for 30 years or more so plenty of used ones floating around.

tuna55 wrote: Some Demons left the factory with major quality control issues. Tunachucker Matt can tell you about those; he bought one on my advice and regretted it based on those. They probably got better, but I don't know which lines nor when. Either factory spreadbore choice is probably going to be great, but I don't know anything about Thermoquads. Stay away from the computer controlled Quadrajet versions mostly for lack of tuning support for all of the ancillaries.

Yea Demon had some quality control problems. Holley bought them out last year. The new Street Demon was built and released under Holley's ownership and is labeled as a Holley Street Demon on the box. The few I've brought in were very nice. Just as it should be with a new carb.

pres589 wrote: I thought it was pretty easy to strip the computer controlled bits from a later Q-Jet. If you just have to go carb on this, a Q-Jet seems like a great option, and I'd pick that over a Thermoquad. But honestly an EFI setup using GM truck TBI parts seems a lot smarter if you really want a driving experience closer to that of a more modern vehicle. To do it really nicely will cost some money though.

From what I understand the later carbs can be converted over, but it's usually easier to find the earlier non-electronic version.

I think it was the late '80's / early '90's Chevy/GMC trucks with the throttle body 454s had the throttle body mounted to an adapter plate and used a regular Q-jet intake manifold. That adapter and throttle body probably could be swapped over to work on the 383, but all the supporting systems would need to be upgraded. The 383 would have had a 36-65 amp alternator, mechanical fuel pump, and no sensors for the EFI to piggyback off of.

In reply to Rob_Mopar:

Yeah, I was thinking 454 TBI and an adapter. Perhaps a home made plate adapter could be made to get this a little easier. Then a Megasquirt, all the changes you mentioned, and a swap to headers with an O2 bung on each side. My brain keeps saying this would be a thousand bucks pretty easily so it may not be worth it.

I have an Edelbrok carb on our LTD Landau LeMons car with the 460. I could borrow the electric choke off that and see if it works. If it does, I'll just convert the Edelbrock to manual choke, because racecar.

In reply to pres589:

Yeah, I picked up the DP4B for $135 and the carb should be pretty cheap- even a brand new TQ is under $300. I know the GRM hivemind loves it some EFI but part of the attraction of these old beasts to me is the fix-it-with-a-hammer simplicity. A carburetor has never left me stranded.

volvoclearinghouse wrote: Definitely want vacuum secondaries. My understanding was the QJ/ Thermoquad was like an 800 CFM carb, but they could use it on anything from wheezy 305's to big blocks, it was so versatile.

I don't remember all the CFM ratings for the Q-jets, but the T-quads were essentially either 800 or 850 CFM. The secondaries are the same on either. The primaries on the 850 are a little larger to get the extra 50 CFM. The throttle plate is a mechanical secondary operation, but the air valve over the secondaries is spring loaded and opens with engine demand, similar in concept to a vacuum secondary. The linkage on the carb will block the secondary throttle blades from opening until the choke is fully open. Pretty slick setup.

The street Demon is nice, but...man, $470!

Wow, where are you getting your prices? I sell them for around $347 + shipping (and/or tax for PA residents) for the #1904 (750 CFM) and $313 for the #1901 (625 CFM). If I could get $470 for them I'd be able to run a bigger ad in GRM!

Wait... you can buy brand new Thermo-quads??