strange idea for my tri power

what if i had my center carb hooked up to a cable throttle and have the secondary carbs put on some sort of electric actuator that would engage off of a vaccume switch or perhaps a microswitch mounted to the center carb some way and use a manual bypass toggle, that way i can shut off the outer carbs when i want to

I'd have a couple concerns, would the center carb be able to carry the car on a fuel/airflow basis? And also could air seep through the outer carbs lean out the outer cylinders?

other than that, I'd go electric solenoid, and that would be fun to do. Have it activate the stop on the progressives via a cable.

if all carbs are idling i think it would be ok, i was thinking of useing a power door lock solinoid or somthing like that

Many of the early tripower V8's use a vacuum actuator to control the outer carbs. This gives you a light throttle pedal (only have to push against one carb), and the outer cars are progressive according to load. Kind of like the vacuum secondaries on a 4bbl.

It wouldn't be too complex to set one up that way. A single diaphragm could be used to pull both carbs open. Pick up manifold vacuum from the log, maybe use a thermo vacuum switch so that it would be disabled until the engine warms up. By sizing the diaphragm and return springs you could tune the opening rate, again much like tuning a vacuum secondary by swapping springs in the secondary carb diaphragm.

You need a mechanical limit linkage between the primary and the secondary carbs. That ensures that the secondaries are pulled shut when the primary is closed and that they can't go to WOT unless the primary is full open as well. Again, similar to the limit link on a vacuum secondary 4bbl.

In a nutshell, you have a vacuum actuator pulling the secondaries open. The center carb and a return spring on the secondaries are pulling them shut. By sizing the return spring, the size of the actuator, and the vacuum orifice to the actuator, you can control the opening rate to match load.

It's simpler than it sounds and worked pretty well on all those old Cadillacs, Pontiacs, Chevys, and Mopars.

The pedal pressure for typical Offy Tri-Power as mine is set up is heavier than I would like when the outers engage. The outers are entirely programmable with the simple Offy slide rods. I like your idea of relieving the pedal pressure especially since the outers basically snap to WOT at a pre-set center carb throttle position. A solenoid activated setup could work from my view. As mentioned, until they open the outer "leakage" of vac and idle mixture does factor strongly in the overall tuning and drivability.

The additional pedal effort when the outers engage is an indicator of the kick in the pants threshold and keeps me somewhat reserved with the right foot.

Have Fun

im going to experiment with some servos and try to come up with something

Its very, very easy to do, and it would work. I think is was possibly the fact that 1904 carbs leak if there is no fuel through them, that probably was why Edelbrock and Holman Moody didn't do it first in 1960. The technolgy was certainly there.

It would essentially be like a vac sec 3-bbl carb, using the port vacum differential between the centre carb air velocity signal and outer air velocity signal to trigger actuation.

The Holley The Rochester triple 2G "6-bbl" 1957-1958 J2 Oldsmobile, and all Holley 2300 series Mopar 340 and 440 six packs ran that way, with no cable control to the outers.

Peak power was on par with the best single plane manifold with an optimised 4-bbl 850 to 950 cfm Holley 4150/4500 series carburation on those V8's.

There is only one reservation I have with vac sec carbs, and that applies to the best setups Detriot used ( in my opionion, the 630 cfm 5.0 Mustang and 7.5 F250 series 4180 series), to any other vac sec setup ever used. There is always a fuel conserving flat spot, and that's why early 2-bbl Jap cars and all 4-bbl vac secs, and especailly, every Mopar and Olds six pack showed awesome economy on little throttle, but heavy fuel use on wide open throttle. It is a good thing, and if there is heavy dampening so you feel a flat spot, it'll give you great power and good economy. Take it from the greatest vac secondary car racers....Don't waste your time trying to dial out a flat spot, it'll hurt your fuel economy, and won't help your performance.

i bought this type of servo setup, i think i can adapt it somehow http://www.youtube.com/watch?v=KSmRWhTQ ... re=related

I'm all for innovation, but a word of caution.

I personally wouldn't ever use Servotronic accelerator cable actuation even for secondaries unless it is a factory set up. Too many issues over the recent Toyota/Lexus failsafe Nipondenso and American made equivalent electronic throttles have gone under the bridge. BMW's M5 first used a fully electronic set-up in 1986, and there were a spate of over centre throttle jambs at MIRA in the UK (by Wheels Magazine, at 145 mph in a 3.5 liter Bemmer), and documented failures elseware...this on a West German TUV approved set up, the great grannies of all conservative legislators.

When Ford made fly by wire standard on Explorers and Falcons in 2003, and on Toyota diesels in 2002, I realised that creating a vacum secondardary or fly by wire system was possible to take load of the accelerator pedal.

Use prudent judgement, but I wouldn't want to ever aid and abbet working with any servo system like that unless its got an armload of SAE degree engineers to help me out. You can pick up a smashed remote control plane when a servo fails, but there would need to be some subsidary failsafe measures before I'd ever use one of those on my tripower.

thank you for your words of caution, i will also install a fail-safe of some sort, maybe i can rig it so that if one servo malfunctions, it will force both secondaries shut, this is just an experiment

i just got what you were talking about xctasy, i can use a vacuume relay that would be connected to the manifold vacuume and have the signal sent by the ported vacuume from the center carb, it does sound like a way more reliable way to go, maybe i can use something like this http://www.ebay.com/itm/1968-1982-Corve ... es&vxp=mtr and maybe http://www.ebay.com/itm/310373164925?ss ... 1423.l2649

Yep, the last one is a real good one. You could link both outer carbs to one or link both outers and use two.

Other option is two of the the vac canister used in the Australian dual path "BBM" OHC/DOHC 4.0 Ford i six on 1994 to 2007 Fords. See one canister in the foreground


http://media.photobucket.com/image/Ford ... 974734.jpg

It allows the second shorter path to come in at 3800rpm by a vacuum switch that goes to a pin on the EEC V. It is dependant on the vacuum switch to open the butterflies and then the ECU gets a signal to adjust the timing too.

Just the vac canisters could be used. It could then be like a mechanical secondary at a certain rpm point.

You'll note that the total port area open is equal to three 390 cfm vac sec 4bbl carbs for just a 243 cube engine. Max power doesn't increase at all with the Bi Butterfly Manifold, but low speed torque goes up 37 lb-ft at 2800 rpm with half the runners shut on this set-up. Its total area is three times that of three 1.3" holes on an Offy three carb manifold, so I'd bet you'll find running three carbs all on at once is a better Idea, but you don't know till you try!

thanks for your help, this is a much better idea then the whole electric servo thing

i just got the vacuume actuator in the mail today but my center carb needs a new economizer, i think that is what it is anyway, it will not idle, i rebuilt it twice, it is adjusted properly

http://s1028.photobucket.com/albums/y34 ... age029.jpg its almost done, i just have to have the carb adaptors milled a little to make it work