Thread: three deuce help

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I'm putting three deuces (rochesters) on a chevy 350, what size gas lines run into the individual carbs? I want to make them out of metal, possibly brake lines, but don't know what size they should be. And, when I get around to putting everything back together, and start to set the carbs, at what rpm do I set it up, so the front and rear carbs start to be activated? Thanks much for the help!!!!! kbyounger

Either 5/16" or 3/8" line would work equally well.

With mechanical linkage I set my end carbs to start opening at a certain MPH (on a level section of road). The personal preference is that they usually will start tipping in at 80-85 MPH.

OK, I'm a little confused. I assume that you're saying, you run on the center carb until reaching 80mph, and at that speed, the first and last start to kick in. But, depending on the tranny you have your rpms at 80 will vary. If for example, at 80 you're turning 3000 rpms, then it stands to reason, that any time you hit 3000rpms, the first and third carbs will begin to open. Thus, they open for hard excelleration when getting to 3000 rpm, right? How did you decide on 80 mph? I know that I very seldom if ever run that fast. Thanks so much for you patience.... kbyounger

Rather than "80 mph" he meant, above your usual cruising speed. You don't want the end carbs opening up until well past cruise, that way they can be jetted for power at WOT without worrying about economy. The only time the end ones are needed is wide open. Some guys used to put a Chev starter solenoid working them and a switch under the gas pedal, step on it hard and CLICK! Everything open but the windows!

You'll find that the cruising speed in a hotrod or custom with 3 deuces is a lot less than your daily driver with FI. Considering the amount of fuel those 3 babies can swallow, you'll be wanting to keep your foot out of it as much as possible.

I normally cruise to work in my daily driver at 80+ mph. In my 3 deuce car, not a small block, I usually cruise at 55 to 65. If I have to stomp on it I can actually see the gas guage drop. Not a pretty picture, especially not with gas at $3/gallom and mileage at 8 mpg at cruising speed. My outbound carbs usually kick in at about 75, anything faster would be in a stroke range.

speed and rpm have nothing to do with it. throttle position is what opens them. you set them up to open just past normal driving. just like a 4 barrel.

“…You'll find that the cruising speed in a hotrod or custom with 3 deuces is a lot less than your daily driver with FI….”

Not necessarily true Bob …….it depends on the car and how it’s set up. My Tri-Power Plymouth is normally driven at 75-80 (Interstate) and 65-70 on most 2 lane roads around here. It also got 19-21 MPG at 75 MPH while on vacation last year (yeah, surprised the he!! Out of me too . )

I am the first to admit that I got very lucky with the cam/gear ratio/tire size selection and happened to hit a sweet spot at 2600 RPM (cruise RPM at 75 MPH) with my engine. My particular combination is a 354 (365 Ci with overbore) 10:1 compression hemi, and 4 speed (OD) transmission with 4.10 rear gear set (with the OD trans the rear end ratio is effectively 3:00).

My comment about the outboard carbs kicking in at 80-85 MPH is based on the way I drive my car. I set the Tri-Powers up to so that the under MY normal cruising conditions I am only running on the primary carb. As I mentioned I set this on a straight flat stretch of road and set it a bit higher than 75 so that when pulling small hills it doesn’t start opening the outboards every time. The springs on the end carbs are also stiff enough that the cruise control will not overcome them which is also a nice feature in that it allows me to choose when the outboards open.

Shine's comment about throttle position is correct. It’s the reason I set mine on straight level ground.

i bet when you got fetch them other two on that hemi they're home that's just almost scary.