Carburetor Upgrade Advice?

[MKB]

I'm considering replacing the stock carb on my '62 with a Holley Street Avenger or other aftermarket newer carb. I have a strong preference for an electric choke and may consider a different intake manifold as well. Anyone have any experience or good/bad results with Holley, Edelbrock, or Weber to share? Thanks in advance- Mike

[mike harmon]

I recently had to replace the stock cast iron exhaust manifolds on my '62 (cracks all over them, leaking everywhere) and didn't want to go thru the hassle of trying to find good '63 or later ones, surface the port faces on the heads, etc. etc., so I got a set of tubing headers that simply bolt on- but don't have a heat sink so I had to go to an electric choke. These used to be common as kits to bolt onto any stock factory carb, but no more. I instead ended up getting a Holley model 4160 from one of the catalogue suppliers, Holley part no. 0-80457S. It's 600 cfm, more than adequate for the 390 up to a mild modified- headers and a mild cam, stock or mild dual-plane aluminum intake manifold. It was a very simple bolt on, took less than 15 minutes. Most of that time was spent scraping old gasket material off of the manifold. Not included in that time was fabricating a new steel fuel line (fuel inlet on stock Autolite is in front, Holley is on the side), re-soldering a broken wire connector on the power seat relay on the firewall so that I could add the wire for the choke, trimming some sheetmetal on the throat of the air cleaner where it mounts on the carb, and cutting a very short piece of copper tubing to use as a bushing for the throttle linkage rod where it fits into the carb's bell crank. The stock rod is smaller than the hole on the bellcrank, but at least the hole is in the exact same spot as the stock, so that no adjustment has to be made of the linkage rod. That all took about 1/2 hour, but I have a tubing bender that saves a lot of time and effort. Running to a local speed shop to get a fuel line fitting that would fit the Holley's inlet and reduce down to the small 5/16 stock sized fuel line instead of the modern 3/8 size took 1/2 day. As promised in the literature in the box, all adjustments were right on, I filled the bowl using the starter (no ignition) and the float levels are exact. Only a very small idle air bleed (mixture) adjustment was necessary, and that probably was because it's an old, tired engine with over 93,000 miles on it. It starts and runs very well in both very dry 100+ degree and wet, near freezing weather, and when pushed hard runs like a striped ape! The secondaries are vacuum operated, and are very smooth. The opening of the secondaries can be altered if you wish by changing a single simple "power valve"- Holley has a wide assortment of these things to open at different vacuum levels. It doesn't have a hot idle compensator or a dashpot, but I've sat in traffic idling for a long time with the transmission in drive in 105 degree heat, and no problems. No problems with stalling on rapid stops (Autolite needs the dashpot for this), no problems with stalling in slow or idle speed turns either! If a dash pot is needed, Holley has one available. I just returned from an over 600 mile trip, and on pure freeway driving at reasonable speeds, I averaged a real 17.5 mpg... that's after correcting for a 2% odometer error. Not bad for a 4200 lb car with that large an engine, smaller-than-stock rolling diameter tires (modern radials are smaller diameter than the old bias ply, hence the 2% odo error and over 7% speedo error at 65) and an antiquated Cruise-O with a lot of inherant internal drag. Around town it gets about 10.3 mpg overall. Both these figures are better than the Autolite got, and it was a fresh rebuild. For stock or mild enhancements, I wouldn't bother with another manifold, unless you want to loose some weight and have something shiny. For such use the aftermarket manifolds are expensive, a lot of work to put on, normally won't provide any real noticable seat-of-the-pants benefit and very little measureable benefit on a dyno- unless the stocker is a very crude singleplane 360 degree (all runners are relatively short and converge into a large, single open chamber into which all four barrels dump into) and the replacement is a refined long runner dual plane 180 degree setup- one primary and one secondary feed four cylinders, the other primary and secondary feed the other four cylinders. Often times the after market stuff doesn't have all of the same threaded bosses for mounting accessories and such. I found all of this out the hard way with a small block Chevy engine after spending several hundred $$ and getting nothing in HP, torque or economy gain, using a well-known major brand that's big in racing.

[MKB]

Mike- That's the kind of help I needed! I'll look into replacing the fuel line all the way from the filter to the carb with 3/8". It might look a little cleaner and function better, too. Mike, do you know the CFM rating of the original factory 4bbl? I couldn't find it in the service manual.

Thanks for the comments on fuel economy. My car is a major guzzler. 10 mpg is about typical for mixed driving. To say it really sucks seems appropriate here. Stalling is also a random city driving problem I'd like to see go away, too.

Thanks again.

Off to the Holley store.......

[mike harmon]

Right offhand I don't know the stock carb's cfm, but I would guess it's somewhere between 500 and 600. I didn't bother to do this, but you can measure the diameter of the Autolite's bores at the baseplate to the nearest 1/32" with a good quality metal measuring tape and a pair of mechanical drawing dividers or anything similar. I believe the primaries and the secondaries are the same diameter. This figure might be also shown in the shop manual. Compare this to the bore diameters of the Holley, and calculate the difference between the two. Dividing the difference by the diameter of the stocker will give the percentage larger (or smaller) the Holley is over the stocker; this will give a rough idea of the difference in the cfm. Other factors such as the design and placement of the atomizers and the size of the venturi will determine the actual cfm figure. The proper way to do this would be to measure the diameter of the venturi, but this is hard to do without taking the carb apart, unless you have a set of long slender sharp pointed dividers that will reach into the carb body.

[GeorgeG]

Mike: The standard Ford/Autolite 4100 carb with 1.12 inch bores used on the TBird is rated at 600cfm. There is also a smaller version 4100 with 1.08 inch bores that was used on 289 A code engines that's rated at 480 cfm. -- George