To change or not to change...

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sparksfly121

sparksfly121

67 Dart GT Conv
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Mar 23, 2014
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Nashville, TN
My 67 Dart GT convertible has the original 273 2bbl. I’ve been considering upgrading to a 4bbl for the added horsepower, but I can’t decide. Should I keep it original, or should I beef it up?
How much extra hp should I expect? Is it worth it?
 
The 4 barrel will add a little zip but not by much. The factory 4 barrel 273's had more compression, a bigger cam, and a dual point distributor as well. It's up to you. It's work and expense for 10 horse or so.
 
just buy a 360 with a 4 barrel, and put the 273 valve covers and air cleaner on it
 
Thanks for the input. I’d like to stick with the same block, since it is original and my parents bought it new. Doesn’t sound like it will be worth it without a major overhaul. What could I do to gain hp on a 273 block? I do remember on a previous build it was bored .30 over. (Not being a mechanic, it sounds impressive, but not sure what it means to performance. )
 
sparksfly121 said:
Thanks for the input. I’d like to stick with the same block, since it is original and my parents bought it new. Doesn’t sound like it will be worth it without a major overhaul. What could I do to gain hp on a 273 block? I do remember on a previous build it was bored .30 over. (Not being a mechanic, it sounds impressive, but not sure what it means to performance. )
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Not much. Overbore is machining to remove wear and taper. It really doesn't increase performance much by doing so.
 
toolmanmike said:
Not much. Overbore is machining to remove wear and taper. It really doesn't increase performance much by doing so.
Click to expand...
but it does "force" you to buy new pistons
which is a perfect excuse to bump compression up a few points
 
I don't are about HP I just want a good Thermoquard that goes WAaaaaaaaaaaa when I mash the pedal!!!!! lol

Like said without some HP upgrades you are just getting a little more noise maybe. Lke said,flip the air cleaner lid upside down!
 
sparksfly121 said:
My 67 Dart GT convertible has the original 273 2bbl. I’ve been considering upgrading to a 4bbl for the added horsepower, but I can’t decide. Should I keep it original, or should I beef it up?
How much extra hp should I expect? Is it worth it?
Click to expand...

A couple of questions, does it have automatic or manual 4 spd trans ? Thinking it probably has the single plane intake manifold in '67 ?? If it has dual plane intake manifold then it will probably run a little nicer as a driver.

'67 273 2 bbl came factory at 8.8:1 compression ratio and made 180 horse power.

The 2 bbls can be gas leakers, and are pretty much an economy carb.

Did the 4 bbl swap on a '69 318 2 bbl with the Mr Gasket 4 bbl adapter. Granted this was the 230 horse power 9.2:1 factory 2 bbl engine, dual plane intake, so it made use of the extra fuel better. Was nice cause did not have to pull the intake manifold, and the port matching at the heads stayed correct, unlike other 4 bbl manifolds that are swapped on.

The whole tone of the engine deepened up from the added fuel it was recieving with the 4 bbl on it.

The 2 bbl was a gas leaker and a fire hazard, ran pretty crappy too. So right there
were a couple of reasons for me to do the swap, plus I wanted the added benefit of the secondaries.

1406 Edelbrock electric choke carb, started and ran real nice, that was a big improvement in it's self. No rejetting was required.

So yes I was very happy with the 4 bbl conversion and results, made a nice change to the driveability of the whole car.

Your experience may be a little less performance, but the nice starting and nice running engine could be worth your effort.

PS: If you don't have a Mopar High Torque Mini starter on it, put one on. It will start like it has fuel injection, they spin lots faster.

Also the mini starters are engineered to take way less electricity to run them, so the added benifit is that your ignition system now gets a boost to help start your engine quick too.

The big heavy original mopar starters drain a lot of juice as you are cranking them to start your car, robbing the juice from your ignition system.

Screenshot_20200807-121328_Gallery.jpg
 
George Jets said:
Your experience may be a little less performance, but the nice starting and nice running engine could be worth your effort.
Click to expand...
So are you saying I’d get less performance out of a 4bbl? Or less performance than expected? To answer your question, it’s an automatic, probably with the original intake. (I assume single plane). Would I expect more horsepower out of a 4bbl upgrade, or just better reliability and less fire hazard? Lol.
 
sparksfly121 said:
So are you saying I’d get less performance out of a 4bbl? Or less performance than expected? To answer your question, it’s an automatic, probably with the original intake. (I assume single plane). Would I expect more horsepower out of a 4bbl upgrade, or just better reliability and less fire hazard? Lol.
Click to expand...

You will get a performance boost out of the 4 bbl up grade. You will need to set up your automatic kickdown linkage and throttle cable for the 4 bbl setup as it is different than your 2 bbl setup.

4 bbl throttle cable and kick down linkages setup pictured below:

Edelbrock Mopar.jpg


Give it a try, this is what all this classic hot rod car stuff is all about. Making the best of what you got going, expermenting, and the success at the final outcome.

The nice part about using the 4 bbl adapter is that if you don't like the way things turned out you can easily go back to your 2 bbl setup without a bunch of major work.
 
A 4bbl is a modest up grade. Dual exhaust helps also. But I will say this: as the miles get up on the motor everything wears alittle causing a gradual power loss that u usually don’t notice. The timing chain gets loose and retards the timing, so u can try adding a few more degree’s of advance. Same with ur distributor. Electronic ignition is a popular upgrade. I have never had a 2 bbl carb leak gas unless dirt or some other foreign object got in the fuel, but that can happen with any carb. Holley carbs were bad with even the smallest crap making the needle and seat leak and flood the engine. It’s ur money. Spend it how u feel fit. I get it that u want to keep it original. Lots of ppl put the original engine in storage and run 1 with performance upgrades then switch back after they had their fun. Kim
 
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