I have a 55 Thunderbird that has the original carburetor and distributor. The car has been upgraded to 12 volts and I was told the engine was rebuilt at "some point".   I rebuilt the carb and fuel pump.  The vacuum advance can was also rebuilt. I plan to spend a couple of more weeks trying to optimize what I have before I make a decision.  My goal is to get the car to be more responsive, I am not looking to smoke the tires :-)
I am considering upgrading to a more modern carb and a distributor with mechanical advance.   Is it worth the expense to do these upgrades?

Define "more responsive." Does your car have a Fordomatic? Gear ratio? If you have the original 55 distributor, upgrade to a 57-up distributor. If you want to retain the mechanical tach drive, get an aftermarket CRT Tbird distributor. If you want to keep the Holley 4000 Teapot carburetor, read Ted Eaton's article (eatonbalancing.com) on modifying the Teapot carburetor for compatibility with 57-up distributors. 

If you have a Fordomatic, have you tried starting out in Low by manually shifting into Low? It's more responsive than leaving it in Drive and starting out in 2nd. If you manually shift from Low to Drive and then immediately shift back to Low once it's in 2nd, it will hold 2nd gear; it's a technique that might require some practice to master. 

"rebuilt at some point" - I would highly suggest a compression test of each cylinder. Those readings would tell you a lot. Beyond that like blacktie says a distributor upgrade would be very helpful. Y Blocks tend to like a lot of initial advance, at times much more than what is posted in any shop manual. Blacktie is spot on for the recommendation on the Fordomatic shifting

Daniel Jessup

Lancaster, California

aka "The Hot Rod Reverend"
check out the 1955 Ford Fairlane build at www.hotrodreverend.com

When I say "more responsive", when I step on the gas hard, I don't feel the car pulls enough.  It has a slight hesitation when starting from a full stop and I floor it.  I am going to start a new post about my carb issue.  I also need to check the adjustment of the transmission kickdown (I don't think this would affect starting from a full stop).   When I got the car the trans kickdown didn't work at all.  I got it to work by trial and error but I recently found the instructions how to do it correctly.

Yes it's an automatic.  I read somewhere that it's not a good idea to start in low and push it hard (not sure if this is true).   So I haven't done much with 1st gear

I've seen the article about modifying the carb for the 57 style distributor.   I am still dialing in the carb and timing.   I bought the car 11 months ago, but I've only been able to drive it for 3/4 weeks this year, so I'm still learning about the idiosyncrasies of the car.

If you're looking for it to be more responsive off idle, stick with a 4-barrel carburetor with small primaries. You probably read Mark R's post on VTCI. He went from a 570 cfm Holley to a 390 cfm Holley. He's quite pleased with the performance and his mpg has improved. If you're not particularly concerned about improving the performance at higher rpm, your 55 intake with an adapter for a 57-up carburetor should do the job and save some money. However, you probably won't have enough hood clearance for an adapter and a carburetor spacer. 

You could also consider having numerically higher ring & pinion gears installed, but you probably won't like them on the highway, and they won't improve mpg. The stock gear ratio behind the 55/w Fordomatic is 3.31. 

The original Holley model 4000 carbs (Teapots) are sensitive to ethanol laden fuels.  I have found that upping the primary jet sizes by two numbers helps with the hesitation issues caused by the 10% ethanol laden fuels.  Also keep in mind that simply switching to the premium grade (91-93 octane) gasoline may also help as the premium grades typically have 3-5% ethanol versus the full 10% found in the 87-89 grades.

Lorena, Texas (South of Waco)

Bigger primary jets may be one of the reasons my PONY teapot performs so much better than the rebuilt original that came on the car (?).  That, and the advance limiter I installed (weaker LOM spring settings) burns way more 93 octane though.

6 VOLTS/POS. GRD. NW INDIANA

Rossi… when you say you floor it from a stop it should go into low or first gear. If it doesn’t you should try what Blacktie suggests and if there is a difference, the link/rod from the carb linkage to the trans is not adjusted correctly.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

It seems better when I start in "Low" but still not 100%.   Are you saying Starting in Drive aggressively is the problem?

I tried 93 octane fuel and #54 primary jets (my carb had #52), I might have noticed a small improvement.   It's very difficult to find non ethanol fuel in NJ.   Any other suggestions?