I have been kinda been putting off this question for fear of being laughed at but here goes.
I have a 170 in my dart that I have already converted to a super six setup that also has been upgraded to 2 inch ex. and a msd ignition and recurved distributor.
I am thinking that the 170 may actually run better with a smaller 2bbl carb,possibly increase throttle response and mileage.I can tune the Holley 390(I already have the carb and Offy intake) with power valves and tune the secondarys to open whenever neeeded or not open at all if need be.
Am i stupid or would this work.
HyperValiant

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1960 Hyper-Pac Valiant(rolling test-bed)
1963 Valiant V2OO(Son's summer project,- he just turned 15 )
1972 Valiant 4dr(Daughter Kelly's repair in progress)
1974 Valiant (v8) daughter Kelly's work in progress

I think it would work.

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Official Cookie and Mater Tormentor.

I don't know whether it would work or not, but it's unlikely anyone would laugh at you for posing a serious question, especially if you've thought it through as it appears that you have.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

I've used a 600 double pumper on a stock Slant long block. It was not the best choice, but with tuning you can make any carb work. A 390 with vacuum secondaries is a way better choice than a double pumper too.

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Official Cookie and Mater Tormentor.

I installed the 390 and Offy intake Saturday,I installed the carb with the primaries towards the fender.It started right up and actually ran better than I thought it would.
I have put about 60 miles on it and noticed that it accelerates quicker than the bbd did and getting up to hiway speed with the family in the car is no longer a problem, torque seems much better.I cant say much about mileage yet as I never get good mileage during a tuning process.
The engine is idling at 750 rpm and holding 19-19.5 inches of vacumm at idle but shows rich on the air/fuel guage.The plugs 2 thru 5 look good with a light to medium tan color while 1 and 6 are little rich looking.The engine is pulling slightly higher vacumm numbers while being driven now.
The carb is stock except for a vacumm secondary quick change kit and has 51 jets and a 6.5 power valve and I am thinking of 48 jets and a 5.5 or 4.5 power valve.
There will be more updates as I go along but I am open to any suggestions or advice.
Thanks
HyperValiant

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1960 Hyper-Pac Valiant(rolling test-bed)
1963 Valiant V2OO(Son's summer project,- he just turned 15 )
1972 Valiant 4dr(Daughter Kelly's repair in progress)
1974 Valiant (v8) daughter Kelly's work in progress

i ran a 390 on my street 225 and in my case 49s primary and i replaced rear meter plate with a block and used 52s, i liked the carb on the street untill i raced it then i found 600cfm was faster, but you will be fine

A couple of things:

Is your secondary a plate or have you installed the conversion block for the 4160 to use replaceable jets? The plate that comes on the 8007's was impossibly rich on my application. The conversion block makes things much easier to deal with.
A 4150 Secondary Block will not work on a 4160. Get the conversion block if you don't already have one.
Does your 390 have the PV Blow out protection? Do you have the Chrysler throttle conversion bell crank? Your primary won't open completely without it.

Have you checked the secondary idle setting? Spec is 1/2 to 1 turn after contact. Too far closed, and your primary idle mixture screws will have no effect. Too far open and you will be bleeding raw gas from the secondary transfer slots. This takes a lot of fiddling around.

The secondary idle circuit may be what's pushing you into a rich condition. It could also be the secondary plate position.
The 390, by the numbers is too large for even the 225.
The wildest Rabbid imaginings allow the stock 225 a VE of maybe 80%. 70% would be closer to the mark. It doesn't breath very well in stock form.
When I did the math I came out with 370 CFM. That was complete with an impossible engine speed, a VE straight out of a Fairy Tale, and an insane desire to make it work anyway.
My engine won't run over 4100 RPM. Punch that in, along with a more realistic VE, and the two barrel looks pretty attractive.

With extensive engine mods that all goes out the window.

With a stock engine, you will spend your time patching the various circuits of the carburetor by masking with pump cams, shooters and PV's.
Smoke and Mirrors. Everything is a compromise.

What secondary spring are you running? The Black, Brown and Plain will all likely lock the secondary out with your engine size. That will be handy while tuning the primary circuit. I stick the black spring in during primary tuning.

I think your PV will open too late. The rule of thumb is to run a PV 2" HG below your loaded idle vacuum. High-Beams on, in gear w/ A/C on etc... For us that means a 9.5 or 10.5" PV, unless we have some humongous cam.
There are also some non-performance dual stage PV's out there that are designed to start opening at the higher number, say 12.5 and fully open at the lower number, of, for instance, 5.5. They also do a good job of emptying your wallet via high purchase price.

I haven't tried NAPA's PV's, so don't know how well they function.
But!
A Holley is like a Honda car. Use OEM parts, or you will encounter problems.
Once I learned that, my carbs started working much better.

I've been playing with mine on the 225 for a couple of years. If I get it figured out, I'll let you know.

CJ
'74 Valiant 4dr Tuna Boat
52 Primary, 54 Secondary
10.5 PV ~22 MPG Freeway

Soon to get a highly modified engine with a Humongous cam...

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Part of Tyrde-Browne Racing

Thanks for the tips Ceej,I will be tuning this weekend and using this info plus some more tips I have procurred.I am driving the car daily and it actually runs well but on the rich side according to my a/f gauge and I currently have the purple spring in the secondaries.
I think that the idle circuit needs to be leaned out.
I also have an insane desire to make this work and am stubborn and hardheaded to boot .
Thanks again
HyperValiant

_________________
1960 Hyper-Pac Valiant(rolling test-bed)
1963 Valiant V2OO(Son's summer project,- he just turned 15 )
1972 Valiant 4dr(Daughter Kelly's repair in progress)
1974 Valiant (v8) daughter Kelly's work in progress