So I see many have good experience with the Holley 390, Demon Jr 525, & the Edlebrock 500's. Opinions vary of course, but generally I am seeing positive results with these. Should I worry that I will outgrow the 390 & wish I would have gone with one of the others? The Demon Jr gets a lot of praise, but I also see some saying they needed to modify the vacuum port for proper distributor advance & also will need to hog out the B intake to match the large carb throats. That sounds a bit scary. Also I worry the Demon Jr being so physically large it wont fit under my T-Bird hood.

Those of you that have been down this path before, if you had to do it again, what would be your choice? For rebuilt carbs, the price differences don't appear to be a huge difference. E'brocks could save me some, but not if it isn't the right choice. I am thinking electric choke & block off the intake's center exhaust passageway with thin sheet metal.

I value your thoughts!

390 - goo dcarb, easy to adjust, had a n assy defect new out of the box that was a bugger to track down.  Once sorted out, it provided good throttle response, and started very easily - much easier than the edelbrock, especially after sitting for a few days.

500 - Carb is good, but feels a little "sloppy"... by that i mean the throttle response isnt as crisp as the 390.  However, carb pulls noticeably harder at WOT.  The 390 feels like it runs out of breath quickly, but the 500 pulls much harder through the rev range.

Both carbs required a bit of tuning for my application, both are pretty easy to tune.  after running both carbs back to back over several days, the decision to stay with the edelbrock was pretty easy...just plain ole more power, but the 390 worked well.  I think a 600 would be too big (and the math says so too).  Ill probably sell the 390 and try a Road Demon Jr 525.  Rumor has it they have very good throttle response compared to the edelbrock......not sure how much bigger they are than the holley or edelbrock though...

Let me know if you need any other info.

Also, you can get intake manifold gaskets with the exhaust heat passage mostly blocked off - those work fine too to keep the paint on the manifold.

The Demon jr sounds like agreat carb too. I'm just worried about having to hog out the manifold bores to match the large carb primaries & also I have heard they are physically very large. I want my T-Bird hood to close! I also hear with the large primaries & a Ford-O-matic, second gear starts are somewhat difficult. Anyone with direct experience with this carb on a 312 T-Bird?

   I have a 1955 Tbird with an aircooled FOM and a 1957 312 engine. I have used a Holley 1850 AAS ( 600 CFM, vacuum secondaries ) for over 25 years and have never thought of changing it for something else. I did add the electric choke.

   You are right to wonder if you get the 390 or 465 if you may regret it as you probably will. The vacuum secondary carb is self regulating in that the airflow through the venturies draws the amount of fuel out of the fuel bowl that it needs.

 That makes it very forgiving and docile in normal driving.

 Most of the time you are only using it as a TWO BARELL carb in normal everyday driving. Then you want to go fast and you stand on it. At this point you are still on two barrels until your engine RPM and manifold vacuum cause the second two barrels to open and add power. Ask yourself do you want a 390 or a 465 or a 600? Let us know what you decide and if your happy with whatever you choose. Pete

  Pete you are right.....but there's a catch. With a smaller engine, 272 or 292, you'll want a carb with small primary venturii's for better throttle response and mileage at the lower RPM's and Throttle openings  you use on the street. the 390's and 465's have those. you'll only need the 600 cfm part at full throttle and higher revs. Maybe someday Ted or John will get a chance to do back to back carb tests on a mild 292/312. It would be an interesting duno run.  

Cheers

Richard

I’ve a low opinion for those carb calcs as internal circuitry on a particular carb makes all the difference.  I’m currently in the process of dynoing a 312 that has unported G heads with a multitude of carbs on a variety of intakes including a dead stock intake with the original ½” spacer.  Fifteen different carbs have so far been tested.  The best overall players so far are a pair of 600 Holleys and a L1848 465cfm Holley.  The original L1273 (ECZ) Holley (410cfm?) and the original ECZ-AA Carter (400cfm) were the worst of the lot.  The star of the show on the stock intake is the 1.08 Ford (480cfm) and while it was down on upper end horsepower, the lower end torque numbers were out of sight.  An 830cfm vacuum secondary Holley was also tried on the stock intake and was found to perform the same as the 600’s on this particular engine while idling characteristics and low end reponse were just fine.  The problem with all this testing is it’s primarily associated to this particuar engine combination and as head porting and better intake manifolds come into play later, much of what’s learned here may not be very applicable.

What makes vacuum secondary carbs very nice to work with is that engine demand will only permit the secondaries to open by the amount that the engine wants if the carb is properly tuned.  It's difficult to overcarb an engine with a correctly tuned vacuum secondary carb but selecting the correct size double pumper carb is difficult in this regard.

In searching anything to do with this carb, I don't see much mentioned with having to change jetting or secondary springs on the Demon Jr. Anyone with personal experience with the need for tuning out of the box Demon Jr?

this came from this chart.

http://www.mustangtek.com/4100/ford4100.html

I think my carb may be hacked. its a 6A-E which shows to be 4 speed but mine has auto kickdown linkage. the jets in mine are 49 and 67. my good deal may have bit me in the butt.

I now have my '57 B style intake & ported the bore size to match the larger 1/2" phenolic spacer. I filled up the valley areas where the remaining lip was real thin with JB weld, & filed everything flat. Took a long time, but I think it came out OK. Received the rebuilt 525 Demon Jr yesterday & will start to put it all on.

On this intake manifold (vs. my previous '56) there is some vacuum port hole at the rear. My previous intake didn't have that provision. What is that for? Should I just plug it & run the various vacuum lines needed from the carb ports? Anybody know the right size plug for this if that is the way to go?

That port has a 3/8" pipe thread.

Also - be watching the float stability - my outfit had Viton needle and seat assemblies that just didn't care for the local gas - very sticky and a pain in the a$$ while trying to tune. I changed them out for steel needle and seat assemblies and that finished off the problem immediately.  From Summit a pair of .130's is P/N 6-515-2 about the best price you will find mail order. 

I'll buy the 3/8" plug for the manifold & also the 0.130 steel needle & seat. I have to buy a fuel inlet fitting anyway (didn't realize the reman ddn't come with one). On your T-Bird did you stick with stock primary jets & secondary spring?

The Demon internal throttle return spring is not well suited to the Fordo "kick-down" springs in the throtttle assembly - still working on that one.... It needs a better set-up altogether - but I haven't gone there yet. Finally, to get it out on the road - I stuck a bolt, nut and washers in the slot to stop over-travel for now.  

I'm having a problem with this computer this am - will try to get you a picture

this is with the old 600 Holley - but shows the filter and pressure gauge

I put a bigger 428 fuel pump on there - with no vacuum pump so that part of the plumbing changed

Set idle mixture with vacuum gauge - I think its best not to have the open style of carb spacer on a street motor - so it will "answer" the screws side for side.

I used the Holley "Black" secondary spring - stiffest in the pile. The Demon primary is a huge hole with nice boosters and from what I can see - tends to act like a big two barrel most of the time. It doesn't even need the seccondaries to feed a 312 with standard gearing for most use.

Primary jets went down one - needle and seat set-up as above.

The float level on a Demon is a wonderful tool - it changes rich/lean very nearly linear across the scale. Because the bird auto starts in second - you've got to creep it up until she accelerates cleanly - otherwise bogs a bit. 

The live vacuum makes the idle speed come up - but the idle water temp goes down. It also provides for some very high vacuum readings at idle - that you won't get when you are hooked up to the ported. Wise men have told me  - whatever works best for you  - use.

Keep in mind that when the engine comes off idle - both systems will behave the same........

Running live manifold vacuum and no exhaust crossover valve has made my outfit run pretty cool - in fact I'm about to go up to the 180° thermostat (factory spec is 157°). I don't like the wide swing from winter to summer and I'm trying to narrow it down.

Brian - Bend some nice lines for your fuel set-up - its time well spent. I found that a lot of the brass fittings are poorly ported on the inside and had to (judiciously) drill out bigger passages for fuel to flow through. On the pressure side of the pump, it isn't as critical as the suction side.

I don't have pictures of it - and its not on the car right now - but I've been trying to design and build a clamp on extension for the lever where the kickdown rod attaches to the linkage. By making the lever longer it should be able to operate the kickdown pressure control rod - to move it downward a bit more than where its stopped now. The "springy" throttle linkage has given me more than a few headaches -and they ain't over yet.

I may attempt to bend some tube & see how that goes. I also am intrigued about your comments on running cooler. I would like some of that.

Be careful closing the hood on the Demon if you use the factory style air-cleaner - I never tried to use that part, just fitted the aftermarket open element style units. The small oval style fits the bump in the hood perfectly - but you may have to adjust your "steady rests" to center the carb/engine under the scoop. It was leaning one way about a half inch......