Rebuild or replace?

Still having issues with the cooling on my 67 Dart GT convertible, 273 4bbl, 904, 7.25 3:55. Still getting way too hot on 20+ mile runs, and burning oil. Pretty sure there is corrosion in the block that’s preventing flow, and likely a head gasket issue (some oil in the coolant).

Torn between seeing about having the 273 rebuilt (to the 273 Super Commando 275 hp specss) or getting a 408 stroker with about 400 hp.

I assume a pull, rebuild, and reinstall will run me around $3.5-4K ish, while prices on crate strokers seem to be right around 6k for just the engine, no labor.

Car is just a weekend cruiser, but is also dreadfully slow as is. My mechanic described the engine as “tired and worn”.

Guess the big question is whether the rest of the components will handle a stroker, and if changing to the bigger engine would increase or decrease the value of the car?

Depends on the budget
A 408 will torch that 904 and shred the 7.25

So, if you can afford the 904 rebuild and a 8.75 then my choice would be the 408 dressed up like the 273

Turning a car into a hod rod usually takes more money than just fixing what you have.

So, at the very least, you can try to maintain what you have in a driveable state for as long as possible & start saving some money & locating parts.

With that in mind, one of my pals LOVES this stuff - https://www.amazon.com/dp/B00R74I5UY/?tag=joeychgo-20

He has used it on his cars without any cooling issues & is always amazed at the amount of stuff that flushes out.

No , they can't handle the stress . Upgrades are essential if you go with a crate . Remember the factory equipment was "just good enough" when it was new .

383Scampman said:

No , they can't handle the stress . Upgrades are essential if you go with a crate . Remember the factory equipment was "just good enough" when it was new .

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Oh yeah, you need another grand for brake upgrades

Exjouster said:

Still having issues with the cooling on my 67 Dart GT convertible, 273 4bbl, 904, 7.25 3:55. Still getting way too hot on 20+ mile runs, and burning oil. Pretty sure there is corrosion in the block that’s preventing flow, and likely a head gasket issue (some oil in the coolant).

Torn between seeing about having the 273 rebuilt (to the 273 Super Commando 275 hp specss) or getting a 408 stroker with about 400 hp.

I assume a pull, rebuild, and reinstall will run me around $3.5-4K ish, while prices on crate strokers seem to be right around 6k for just the engine, no labor.

Car is just a weekend cruiser, but is also dreadfully slow as is. My mechanic described the engine as “tired and worn”.

Guess the big question is whether the rest of the components will handle a stroker, and if changing to the bigger engine would increase or decrease the value of the car?

Click to expand...

Your call on that one. Been there, done that. I rebuilt my HP 273 in my 66 Dart. I have no regrets but I have a healthy sum wrapped up in it. It runs good but a stroker would be more fun for about the same money. Buy an engine and park the original in the corner. It could always be freshened up and put back in if need be. Use your valve covers and air cleaner to make it look like the ol' 273. FYI there was never a "Super Commando 273". The 275 horse engines were built for the 1966 D Darts only.

I’d just get a good running Magnum 5.2/5.9 they make gross hp of around 300 hp. And put the rest to rear end brakes etc..

Or even start fresh with a decent 318 rebuild and mild hop up.

Personally, and just my opinion. Magnum. Either or. Odds are can pick up a good motor for around the same price as a 318 or 360 core. I'm not sure of all the details of what has to be swapped, I know intake, distributor, if you want v belts the timing cover and pulleys. But you have all that, other than intake. Unless you get lucky with a 318/360 core and find one with very little ridge, you are up to having to have it bored and honed, new pistons and rings. Go to junkyard, get a 5.2/5.9, just about guaranteed not to have any ridge, pistons and rings still in good shape, can hone and change rings for peace of mind if wanted... But new bearings and timing chain, like $200 or so for the intake, use the timing cover and pulleys you have, carb? And distributor you have and call it a day. Take it easy until you get the rearend upgraded. Oh, you will need a flexplate balanced for the engine as well, at least for the 5.9... Again, just my 2 cents

I love 273's. I'd build it with 2 barrel pistons and bore and hone with torque plates. Get a set of file to fit Speed Pro rings or a good set of Perfect Circle chrome rings. Have the heads checked for cracks. Mill the heads .020 and .019 on the intake side of the heads. Get a competition valve job from someone who is good. Call for a custom cam from Racer Brown, Isky, or someone that will grind a small, .450 lift and 260-268 duration, solid lifter cam. Blueprint it, I mean find true TDC, centerline the cam, measure the piston depth from the block deck front to back and side to side, measure your combustion chambers. Balance the rotating assy. Get a set of stainless steel exhaust valves, 340 valve springs or equivalent, viton seals, double roller timing chain, brass freeze plugs. I assume it is a Commando motor? Those early 273's did not need much to bring them back to new. The forged crank may just need to be polished. Resize those light rods. Add a windage tray. Do you have the Commando single exhaust? I typically recore the radiator with a 3 row core. Adjust the bands and pressure in the 904, reseal it and and replace the filter and fluid. Worry about the 7 1/4 when it goes.

Exjouster said:

Still having issues with the cooling on my 67 Dart GT convertible, 273 4bbl, 904, 7.25 3:55. Still getting way too hot on 20+ mile runs, and burning oil. Pretty sure there is corrosion in the block that’s preventing flow, and likely a head gasket issue (some oil in the coolant).
Torn between seeing about having the 273 rebuilt (to the 273 Super Commando 275 hp specss) or getting a 408 stroker with about 400 hp.
I assume a pull, rebuild, and reinstall will run me around $3.5-4K ish, while prices on crate strokers seem to be right around 6k for just the engine, no labor.
Car is just a weekend cruiser, but is also dreadfully slow as is. My mechanic described the engine as “tired and worn”.
Guess the big question is whether the rest of the components will handle a stroker, and if changing to the bigger engine would increase or decrease the value of the car?

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First;
Weekend cruiser, to me, implies put it in drive, sit back, enjoy.
So 50 hp will do that.
How did you get to 408stroker/400hp from there?
The 67 273/904/355s , with 4bbl added, and the 3.55s, should make a very nice weekend cruiser;
if you can get rid of the cooling problems, and get the ignition timing sorted out, which may be partly to blame for ... Both the heating and the dreadfully slow,
and maybe the carb is responsible for the oil-burning, possibly.
So before you spend a ton of money, how about doing a few tests to see just how tired that 273 is.
I mean it is entirely possible she is worn out,IDK, but the tests will prove it.
The First test is a Compression Test. in if the numbers are even then that speaks to a good thing. If the numbers are 150 or better then the engine is NOT worn out. If the numbers are 110 or lower, she's toast. From 130 to 145 is a bit of a crapshoot. So;
the next test is a Cylinder Leakage Test. Numbers less than 4% are excellent They say over 20% is worn out, but the truth is over 10% is already lazy, in your 9/1 Scr 67 2bbl 273. At 9/1 the factory pressure was 135 +/-15. .
Overheating on a 20 mile run could have other sources than the cooling system. And those same sources could be what's making her so lazy.
Obviously , oil-burning is usually a symptom of a tired engine, but every once and a while, it ain't rings. And when you combine all of your symptoms, you might have to do some digging.
In any case a fresh 273 could be about 190Plus hp , which is plenty for a weekend cruiser, with 3.55s; at 50 odd ft above sea level. If you gotta get inside it, a lil boost in Cylinder pressure might be all it takes.

This is not to negate anything anybody else has said thus far. There have been lots of good ideas presented.

Like has been said, the 275 HP 273 will end up costing you more or real close to the 408.
Either way additional upgrades(brakes, rearend) will be in order.
Enjoy whichever you decide.

I would consider brakes, suspension, better tires, and subframe connectors (times 100 because 'Vert) a must have even if there is no engine in the car.

So what to do really want to do with the car and how much to you realistically want to spend?

With the given info I'd vote 5.2 Mag, 4bbl, Doug's or TTI headers and enjoy. Or lube the Visa Platinum and go balls out Hellcat swap.

Rebuilding the 273 should cost between $1,000 to $2,000 and make around 265 horsepower and pull to 6,000 rpm.

Ima thinking as a cruiser, low rpm performance might take precedence over absolute power, and so torque at ~2050 stall (about the factory rating) is what's gonna make you smile.
A nice number for this 3.55 combo, might be .060 to .070 foot pound per pound of vehicle weight. So for a 67 GTconvertible at say 3100 plus driver and at least one passenger, cuz who cruises alone ( I mean besides me, and I ain't really cruising, perzactly) so say 3450 loaded with a bit of gear, that would be a minimum of 207 ft lbs at the factory stall of ~2050. Can the 273 do it?
If less than that, it's gonna be lazy.
The number I'm favoring for this combo is a minimum of 1800 ftlbs @ stall, divided by the Torque Multiplication. So with 3.55s and a 2.45low, that makes 1800/(2.45x3.55)=8.70.
And 1800/8.70=207 crank ftlbs. This will squeal a pair of street tires, but not spin very far. However, it won't be dreadfully slow.
Sticking with this method, the next step Ima thinking, is 10% more. This could be done;
by engine;so 273x1.1 equals 300 cubes; or
by increased torque,so 207x1.1=228ftlbs crank at 2050stall
by stall;so 2050 plus an easy 200=2250,or
by gears; so 3.55x1.1= 3.91s
At zero mph;
of these, the gears at zero mph are the least effective.
Unless you have killed the low-rpm torque with too big a cam you can't do much to increase the torque at 2050 rpm.
That leaves cubic inches and stall. if you can buy a good used bigger engine for the same price as a good convertor, that is the better choice. But if you want to stick with the 273, then a higher stall is your only choice.

If you continue this way in 10% steps, pretty soon your stall is gonna run off the scale.
But engine wise; the 318 is 16.5% bigger, and the 360 is 31.9% bigger, and both will pull that 2050 TC very nicely.
The 318 will be happy with 3.23s and the 360 with 2.94s, both to make the 1800minimum ftlbs at zero mph.
The 318 would need 1800/(2.45x3.23)=227 crank ftlbs at 2050, which is a piece of cake for it.
The 360 would need 1800/(2.45x2.94)=250 crank ftlbs, which is also a piece of cake for it.
But notice that in each case of reduced rear gears, the hiway cruise rpm goes down about 9%.. So with 27 inch tires, and at 65mph,, the 3.55s will cruise at 2870@ zero slip, the 3.23s at 2610, and the 2.94s at 2370. That last one is 500rpm down.... yet with the 360,takes off with the same performance as the 273 with 3.55s. In a weekend cruiser, at least to my way of thinking, this is a good thing.

Finally if you have to freshen your engine, it costs about the same no matter what SBM you start with.

Ok waitaminit, I once installed a complete 318 top end and cam onto a 340 bottom end, with nothing but headers and dual exhaust. The 340 was the early hi-compression variant. That 2bbl made a smoking hot cruiser.

66fs said:

Rebuilding the 273 should cost between $1,000 to $2,000 and make around 265 horsepower and pull to 6,000 rpm.

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Can a 273 be made to be a strong runner , sure it can, but for most they would be better off going with 318/360 even for a mild engine.

For most setups a 250hp 360 or even 318 will walk away from a 250hp 273. A stock magnum 5.9 with 4bbl and headers dynos 320 hp @ 4800 add a mild hydraulic roller cam and be at 350+ hp @ 5000-5200 rpm max.

Be very street friendly get away with any gears or stall, even though a step up in both would help. Little reason to build anything less then the need to be different.

I’m all for people doing /6 273 could arguably throw 318 into the mix. But for most a even if power isn’t a huge concern would be happier with even a dead stock 2bbl 360 over anything less.

Lots of opinions... Here's mine -
It's a convertible. That means it's got structural issues from the ground up. It also means the usage is more about cruising and enjoying than racing around. You want a little more pep - did you ever had a well-built 273 in it? Probably not if it's original and tired. 273s are not cheaper to rebuild properly. Especially the 4bbls. I would spend the money on the engine you have. Do it right, with an eye towards a little more grunt than it had new. Keep everything else original. Maybe change the rear axle ratio to 3.23 if you have a 2 series. While the engine is out have the engine bay refinished in the factory color if it has also been left original. Then enjoy the car.

What I would recommend is look for ant 318 car that runs good that has a shot body. That is what I do for guys that can't afford a motor. Complete Gasket kit paint and your good to go. There are some low mileage cars and trucks out there with good 318's and rusted beyond repair. I just did a 34k 318 runs like new. Total cost was around $500 with 4bbl intake ,carb , parts and paint . I also installed he trans. I put Valve seals in without removing the heads also. Should have taken the heads off but to late now. I pulled it from this 67 Barracuda. it was originally out of a 73 charger. Cost of the motor was free. it was left over from Todd's car we took the clip off of for his fast back. I alway see free motors on the web go get one. This is the same motor. The first thing I did was put it together and got it running good . Then removed it and painted everything.

The 67 wasn't designed for dual exhaust. the trans cross member is not cut away for exhaust pipe on right side. when you reach the rear of this car her single fuel tank strap is in the path.
All that is after you accept the headers in a-body headache.
Bone stock 2brl and single exhaust has got her from point A to B for more than 50 yrs.
Regardless which route I took, I would invest in a new radiator.

The 67 I pulled this motor out of had duals and tips on it from a 72 340. I also had a 67 here with a 383 with duals.

273 said:

Can a 273 be made to be a strong runner , sure it can, but for most they would be better off going with 318/360 even for a mild engine.

For most setups a 250hp 360 or even 318 will walk away from a 250hp 273. A stock magnum 5.9 with 4bbl and headers dynos 320 hp @ 4800 add a mild hydraulic roller cam and be at 350+ hp @ 5000-5200 rpm max.

Be very street friendly get away with any gears or stall, even though a step up in both would help. Little reason to build anything less then the need to be different.

I’m all for people doing /6 273 could arguably throw 318 into the mix. But for most a even if power isn’t a huge concern would be happier with even a dead stock 2bbl 360 over anything less.

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Not to get into "Bench Racing" but A 360 with 250 HP would be a low rpm tractor motor. A 250 HP 273 would be a High Performance motor. The 273 would win no problem. Plus by changing motors, the OP is replacing everything in the drive train when he does not need to.

66fs said:

Not to get into "Bench Racing" but A 360 with 250 HP would be a low rpm tractor motor. A 250 HP 273 would be a High Performance motor. The 273 would win no problem. Plus by changing motors, the OP is replacing everything in the drive train when he does not need to.

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I'd build a 318 , they're cheap. Stick the 273 in the corner of the garage.
That way you dont have to update everything else. Though I might do a street convertor, like the 200 kind, while you're there...

66fs said:

Not to get into "Bench Racing" but A 360 with 250 HP would be a low rpm tractor motor. A 250 HP 273 would be a High Performance motor. The 273 would win no problem. Plus by changing motors, the OP is replacing everything in the drive train when he does not need to.

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I was going by the fact that most don’t want to run gears stall etc..

Stock gears and stall or even mild step up will be closer to what a 360 needs than a 273.

The OP was talking about 275 hp 273 or 408 which either gonna need a complete drive train upgrade to match.

You already have the 273. I know people are suggesting a 318 or a 360 but that's gonna cost $200-300 and then you'll have an engine you know absolutely nothing about. You know your 273 burns oil and such? Pull it yourself and disassemble yourself. Have it tanked and maybe a freshen of the bores. Have the crank polished and use all your original parts. Hot tank and polish shouldn't be more than $200-250 and then new rings will set you back another $50.
Clean everything else yourself. Maybe throw in a new chain and for less than $500 you have a completely brand new 273 which you know your convertible can handle.
You'll be surprised how much you'll probable enjoy it. Good luck.

MOPAROFFICIAL said:

I'd build a 318 , they're cheap. Stick the 273 in the corner of the garage.
That way you dont have to update everything else. Though I might do a street convertor, like the 200 kind, while you're there...

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Unfortunately, I think the 67 904 trans has a different input shaft and convertor hub. I'm not sure what convertor is available for a 67 down 904.