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I saw Crane’s sells a progressive mechanical linkage set up for the 427 3x2 set ups. Says that’s what racers were doing back in the day. Has anyone had experience with this set up or tried it? There is a YouTube video demonstrating it.
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You will probably get many comments "against" the mechanical linkage and "for" the factory vacuum controlled setup. Back in the day my daily driver was a 68 L89 that had the mechanical linkage. Once I learned how much throttle to give at what RPM's I had a TON of fun with it on the street. I never had it bog but was always judiciously applied throttle mainly because of lack of traction. Headers, 3.70 rear, skinny tires- i would break the rear tires loose just by breathing on the gas pedal.
Last edited by pltmgr; Mar 3, 2021 at 11:59 PM.
Reason: extra word
You will probably get many comments "against" the mechanical linkage and "for" the factory vacuum controlled setup. Back in the day my daily driver was a 68 L89 that had the mechanical linkage. Once I learned how much throttle to give at what RPM's I had a TON of fun with it on the street. I never had it bog but was always judiciously applied throttle mainly because of lack of traction. Headers, 3.70 rear, skinny tires- i would break the rear tires loose just by breathing on the gas pedal.
Yes I was curious about those experiences. How did you have the mechanical linkage hooked up?
The biggest issue with covering the stock Corvette Tri-Power carbs to mechanical linkages is the lack of accelerator pumps on the secondary carbs. Not so much of issue on a race car that is full throttle all the time, but definitely needed for street use.
Now, the best way to do mechanical "Tri-Power" is to find a set of old Mopar Direct Connection mechanical secondary setup over the counter which consisted of the Holley 4782 (center) and 4783 (end) carbs. All the carbs had metering blocks and accelerator pumps. Big difference was choke linkage. They were also had side hung floats with driver side fuel inlets. The side hung bowls were used since they were shorter due to clearance issues with the metering blocks. Now, the linkage has to be different for this setup. The stock linkages is just to ensure the end carbs close since they are opened by the vacuum pods. The mechanical secondary setup needs a progressive linkage to open. I had a setup for a while and you can see my pics below.
I ran this setup on my 496 for a year. Had to have custom 1/2" phenolic spacers made to fit between the manifold and the carbs so the front carb would clear the thermostat housing. This was with a 68/69 manifold, probably not required with the taller 67 manifold. Fabricated the linkage. Swapped the Mopar choke for the Corvette choke and fabricated a longer rod. Clearanced the air cleaner base for the forward carb float adjustment. Modified the throttle cable bracket for clearance on rear carb pump arm.
Ran like the proverbial r****d ape. I ended up swapping to EFI to improve part throttle performance and to solve the issue of the engine wanting to die on hard braking due to fuel slosh.
Here are some pics:
Some pics of the Mopar Direct Connection setup on my Corvette: Driver's side Passenger's side Better view of linkage Air cleaner base mod Throttle bracket mod
Mechanical linkages were done specifically in the day for quicker response when stomped from stop to WOT. There will be zero advantage on the street using a mechanical setup and without a progressive linkage you would be shooting three squirters every time you crack the throttle.......not ideal. The progressive linkage is better but still from a tuning standpoint on the street.....it would be a nightmare. The setup above on the members 496 probably worked well because there are so many cubes......lots of good engine vacuum and signal.
The stock vacuum setup when sorted works fine and when all three carbs are open.....that is all you need!
Mechanical linkages were done specifically in the day for quicker response when stomped from stop to WOT. There will be zero advantage on the street using a mechanical setup and without a progressive linkage you would be shooting three squirters every time you crack the throttle.......not ideal. The progressive linkage is better but still from a tuning standpoint on the street.....it would be a nightmare. The setup above on the members 496 probably worked well because there are so many cubes......lots of good engine vacuum and signal.
The stock vacuum setup when sorted works fine and when all three carbs are open.....that is all you need!
Jebby
Jebby,
Mine was a progressive linkage and boy, would it hit when the secondaries opened up if flooring it above 3k. However, driveability and other issues drove me to an EFI conversion and I am really happy with that.
Another beef I have with progressive linkages is that if you give it just enough....you can now be into three carbs when you really don’t need them....so it can be fat and blubbery at say....90 mph.....where as the original vacuum carbs won’t pull unless the demand is there....it depends a lot on how the progressive linkage is adjusted of course but most pull the ends prematurely.....
Just a thought....
Most progressive linkage systems on tri-power sets do not open the secondaries until the throttle is 2/3 to 3/4 open. That is much more throttle than needed during normal driving...even if you have a "heavy" foot. My experience with Chevy and Pontiac tri-power systems is positive with progressive linkage systems on manual transmission cars; vacuum linkage is smoother and less jarring with automatic trans cars. In fact, all Pontiac tri-power systems were vacuum actuated until 1964, when manuals got progressive and automatics got vacuum actuation.
Tri Power Mechanical Linkage
