Posted by Denny Williams & Jim Hisel on 9/24/2013 to[This article was first published in Late Great Chevys, February 1993, pp 14-17] One of the sought-after carburation systems for the early Chevy is the famous “348" tri-power. Deciding to build a 1958-1961 tri-power car is easy; finding and collecting the parts is another story. Many members don’t even know what to look for at swap meets. This article is intended to help those of you who want to build a 348 tri-power. It is said that “a single picture is worth 1,000 words!” Well, here is a “37,000 word” article to help you with your 348 tri-power quest!
There are two basic tri-power systems: the 1958 and the 1959-1961. The two main differences are in the air cleaners and the fuel inlets at the carbs. The main differences and even some minor differences are pointed out below.
Two excellent sources for learning about the tri-power systems are the Assembly Manual and the Shop Manual. Look in the Assembly Manual in R.P.O. 573 and the Shop Manual in Section 10. The Assembly Manual lists the GM Part #'s for the carbs. Like most other Rochester carbs, the complete part number was stamped on the tag. For the 1958 carbs, there is some confusion as to what are the correct part #'s for the carbs. The Assembly Manual, the 1929-1958 Parts Book, the 1929-1959 Parts Book, and actual tags from a couple original cars do not agree on the front and rear carbs. They all agree about the center carb: 7011952 (turboglide) & 7012503 (3-speed). The conclusion? The numbers for the forward & rear carbs may be wrong OR there may have been two front carbs and two rear carbs used.Source Front Center Rear 1958 Assembly Manual 7012851 7011952 7012853 1929-1958 Parts Book 7011951 7011952 7011953 1929-1959 Parts Book 7012851 7011952 7012853 Original Tags 7011951 7011952 7011953
We certainly hope this helps your pursuit of the TRI-POWER system for your Chevy! You may want the guys at Southeast Chevy Parts to help you with those hard to find parts or a complete system, all you have to do is call.Parts Description For a 3x2 Setup
Pump-to-carb Fuel Lines(single diaphragm pump) 3/8" Fuel Pump Hose Kit Pump-to-carb Fuel Lines(dual diaphragm pump) 3/8" Fuel Line Hose Kit Fuel Filter Manifold Water By-Pass Fitting Air Filter By-Pass Hose Fuel Pump (Double Diaphragm) Intake Gaskets Fuel Pump Spacer & Shaft Air Cleaner Top Carb Stud Kit Valve Cover Gaskets Carb Rebuild Kit Road Draft Tube Carb Linkage Bushings & Grommets Throttle Rods & Clips 1958 Complete 3x2 set-up. (Right side) 1959-1961 Complete 3x2 set-up. (Right side)
1958 Intake: Casting #3749948 - Cast October 6, 1957.(Notice large double X's.) 1959-1961 Intake: Casting #3749948 - Cast November 5, 1958. (Notice no double X's.) 1958 Complete set-up. (Left side) (1959-1961 Complete setup, left-side will be the same.) 1958 Air Cleaner Top (Notice "star" pattern.) Overall diameter is 17.5-inches. 1959-1961 Air Cleaner (Notice no star pattern. Overall diameter of top Is 17 5/8-inches. 1959-1961 Air Cleaner Lower Assembly. Carb "stack' pointed out is just over 5/8-inch high. (1958 carb "stacks" are approximately 1-inch higher.) 1958 Left-side 348 Valve Covers: 3x2 cover is in the foreground. 4-bbl cover is in background. Short bracket (for plug-wires) allows clearance of 3x2 air cleaner.
Right-side Valve Covers. One basic difference is the cut outs for
the valve rover gasket in the 1959-1961 cover. (See arrows.) Early 1958 Dual Diaphragm Fuel pump. Lower part pumps fuel: upper part provides vacuum to carb assembly. The use of this fuel pump may have lasted through January 1958 or longer. The items cast in the top of each carb is the same for all 1958-1961 Tri-power carbs. Rochesters of course! Made specifically for GM.
1958 Choke/Choke Tube Assembly. (Nottcc “exit" is out the right-side. Fuel line bends under and around choke tube.) 1959-1961 Choke/Choke Tube Assembly. (Notice "exit' is out toward the rear. Choke tube goes under a fairly straight fuel line.) A basic difference between the individual carbs is the fuel line inlet. (See arrows.) 1958 earl) has inlet in the front. 1959 1961 carb has inlet in the right side. (Rear carbs are pictured.)
1958 Fuel Line Assembly. (Right-side) Notice external bowl-type fuel filter at front carb. 1959-1961 Fuel Line Assembly. (Right-side) Brass fitting pointed out in photo is a 4-way fitting, fuel enters fitting from the bottom. Notice: No external fuel filter. Filters are built in at carb inlets. Throttle rod connecting front and rear carbs operates 1st and 3rd carbs simultaneously. Vacuum diaphragm operates forward carb & throttle rod operates rear carb. 1958 is pictured, but would be the same for the 1959-1961 system. Vacuum Valve Assembly (See arrow.) Exits rear of center carb. 1958 in photo, but valve assembly for 1959-1961 almost identical. The vacuum hose being held is connected to “slider valve" on center carb. Other end of hose connects to diaphragm. (See arrow.) Return spring is connected to bracket on diaphragm. 1958 is pictured, but is the same for 1959-1961 system. Short hose connecting the “slider valve" to the top of the forward carb "dumps" the vacuum after the throttle returns, that way vacuum does not remain at the diaphragm. (1958 is pictured, but is the same for 1959-1961 systems.)
Forward carb with diaphragm attached. Left-side is pictured. 1959-1961 is pictured, but left-side for the 1958 forward carb assembly would be the same. Forward c arb with diaphragm attached. Front/right-side view of a 1958 cart). Diaphragm on 1959-1961 forward carb would be the same. Center carb with mechanical vacuum switch (slider valve) attached. The left-side of a 1959-1961 carb is pictured, but the 1958 center carb assembly would be the same. 1958 Center carb. Right-side view. Vacuum Diaphragm. It attaches to front of 1st carb by two slotted screws. (Backside is pictured.) Vacuum Diaphragm. (Right-
side is pictured.) Diameter is
4-inches across. Slider Valve. It attaches to front, left side of 2nd carb. (Left, front view.) Slider Valve. Is secured to center carb by two slotted screws. (Left side is pictured.) 1958 Rear Carb. (Left, rearview.) Carb linkage bushings and grommets. Secondary carb linkage rods & clips for 1958 tri-power 348.
Secondary carb linkage rods & clips for ’59-'61 tri-power 348. Later 1958 fuel pump-to-carb line kit. (For 1958’s with single diaphragm fuel pumps.)
1959-1961 fuel pump-to-carb line kit.
1958 Complete 3x2 (Tri-power) setup. (Left, front view.) 1959-1961 Complete 3x2 (Tri-power) setup. (Left, front view.)