273 Commando

[67BELVSLEEPER]

Hi guys,

New to the forum. I know there are probably tons of threads about the 273 Commando, I’m just trying to get few notes.

Picking up a 67 Belvedere 4D. Has a 273 Commando, Holley 4BL, 3 speed auto, unknown gearing. I know these cars are fairly light. Does the 273 have any power at all. I read the Commando has a little hotter cam, are they lopey in stock form with exhaust? I’m looking to build a 4 door street sleeper. Mid to low 13 second 1/4 mile capability would work for me. Can this be accomplished with the 273 without a whole bunch of $$.

Thanks for your help.

 

[1967coronet440]

Probaly have a ways to go, I think those were 235 hp from the factory which would probaly put you in the 15-16 second range in the 1/4 mile. As for building them I can’t speak to that I’ve never built one, I’m sure someone who has will chime in though.

 

[67BELVSLEEPER]

I agree, I’m thinking I would need 300 or so at the crank to dip into the 13’s. If I researched right I think they are about 3200 lbs?

 

[1967coronet440]

Ya probaly right around there

 

[Dibbons]

Maybe I can be of help 12.72 @ 108 mph attained with a '65 four door 273 Valiant (4-speed, 4.56 rear end, 10 inch slicks, full race camshaft--stock cylinder heads and 600 CFM Double Pumper). But it only weighed 2960#.

 

[67BELVSLEEPER]

Maybe I can be of help 12.72 @ 108 mph attained with a '65 four door 273 Valiant (4-speed, 4.56 rear end, 10 inch slicks, full race camshaft--stock cylinder heads and 600 CFM Double Pumper). But it only weighed 2960#.

View attachment 526532

Nice run!! A lot it gear there. I’m basing stuff off my Foxbody Mustang. I tracked it a few times, but not sense I built and dynoed it. It is similar in weight to the Belvedere, dynoed at 302rwhp/328rwtq. I would expect mid to low 12’s as the suspension is done as well. If I can get 13’s from a 4 door and keep the original motor I think that would be fun.

 

[Kern Dog]

The 273 by nature is a poor performer at high rpm. The intake valves and ports are small, the intake manifolds fitted to them are restrictive as well. The Ford 302 had a 4 inch bore that allowed for larger valves. The 302 make power by spinning some serious rpms. The 273 was, as odd as it seems, a low rpm "torque" engine. They can be made to run but that will surely make it unlikely to be much fun to cruise.
A stock rebuild of a 360/5.9 from a 1993-2002 truck with the Magnum heads can get you into the 14s easily while getting decent mileage and lower rpm freeway cruising.
The 67 B body is likely in the 3300-3500 lb range. Only a scale knows for sure.

 

[67BELVSLEEPER]

The 273 by nature is a poor performer at high rpm. The intake valves and ports are small, the intake manifolds fitted to them are restrictive as well. The Ford 302 had a 4 inch bore that allowed for larger valves. The 302 make power by spinning some serious rpms. The 273 was, as odd as it seems, a low rpm "torque" engine. They can be made to run but that will surely make it unlikely to be much fun to cruise.
A stock rebuild of a 360/5.9 from a 1993-2002 truck with the Magnum heads can get you into the 14s easily while getting decent mileage and lower rpm freeway cruising.
The 67 B body is likely in the 3300-3500 lb range. Only a scale knows for sure.

The engine will be the last piece. Going to build it from the bottom up. Sounds like a swap may be smarter performance wise and for have better streetability.

 

[67BELVSLEEPER]

Going to be a bit if a re learning curve. The last carbureted car I had was in 2011, 1979 Camaro 350 4 bolt. The Foxes are pretty much plug and play....pulled the motor/trans, built them in my basement, put it back in, fired first try. Set the fuel pressure, timed it, no tune needed.

Wednesday this new rig will be mine and I can’t wait. My neighbor growing up had a 70 Challenger. It’s still in the garage today with the vintage “thrush” and “High Jacker” stickers on it lol. That’s what got me into the Mopars. My wife thinks the Belvedere is ugly which makes me like it even more!!

 

[Dibbons]

Kern Dog is right about a 360/5.9 being a better cruiser, but I thought the goal was to pump up the factory stock motor? I don't agree the 273 is a poor performer at high rpm, when my motor was screaming through the trap area at 6,400 rpm it was still pulling strong--and like I said, these were stock heads and valves.

 

[Kern Dog]

I don't agree the 273 is a poor performer at high rpm, when my motor was screaming through the trap area at 6,400 rpm it was still pulling strong--and like I said, these were stock heads and valves.

Really? No porting at all? That is impressive. Most were tapped out by 5000 rpms!
Dibbons...Didn't you come by my place awhile back? Are you the guy that bought some 71 Road Runner bumpers or something?

 

[Dibbons]

Regarding the 273 cylinder heads, on the kitchen table using a Dremel tool I matched the ports with the 340 Edelbrock Tarantula manifold gaskets and the Cyclone fenderwell headers gaskets. I also polished the combustion chambers and the intake 1.78"/exhaust valves 1.50". Used a steel shim head gasket. Standard valve job I did myself at the Community College auto shop class I was taking. Of course, the Isky 312 advertised duration/.580 lift cam was made to spin (4,500 - 8,000).

 

[Kern Dog]

Holy crap..That is a huge cam! I have a smaller cam in my 440/493!

 

[62 Dart Convertible]

If your goal is low 13's in a B-Body in street trim, more cubes will make it so much easier. A 273 or 360 shortblock look the same. Plenty have built stroker LA engines (like 410 cubes based on 360 and 400+ HP) with the Commando chrome air cleaner and black crinkle rocker covers. Tada - sleeper.

Years ago I had an A-body with mild 360, 727 and 3.23 open rear that went 14.0 @ 100mph with no traction. (9.5CR, pocket ported and port matched J heads, Crane HMV278, Edelbrock Performer and Holley 750 VAC, Tri-Y headers.) I let my Mum drive the car too, it was mild but lots of fun.

 

[JimKueneman]

I put a RV cam, 2 1/4" dual exhaust on stock manifolds, Edelbrock Performer with FiTech EFI on my Coronets stock 318. After I got the timing set where it wanted to be vs where the tag said to put it I am completely happy as a cruiser in my Coronet. Will it spin the wheels, no (stock 2.94 posi) but it will pull nicely once you get it off idle (gearing is too high for launches). Gets about 14 MPG. It would be much more fun with lower gears but I spend 50% of my time at 75MPH+ on the interstate to get from my house to town and shows and the 2.94s are really nice for that. Someday I will take it to the strip and see what it will do and back calculate HP from that to get an idea.

 

[YY1]

Let's get our terminology straight-

A 273 is not automatically a "Commando".

A 273 Commando is a 10:1 engine with a solid lifter cam, adjustable rocker arms and a 4 barrel carb.

They were only (yes I said only) installed in Dart GT's and A body Barracuda's.
(yes, you could get a Commando 273 in a non-Formula S Barracuda)

A normal 273 is a 9:1 engine with a 2 barrel.

 

[67BELVSLEEPER]

I ran the ID plate and it said 273 2 BL. It has the “Commando” air cleaner assembly and what looks to be a new style Holley 4 BL. Maybe somebody just put the Commando cleaner on it.

Looks like a non commando 273 to me, original red painted valve covers?

 

[67BELVSLEEPER]

I would still consider doing the 273.

My 302 makes the most HP around 5200. The car goes like a bastard. I just don’t know what to expect from these 273’s.

 

[67 GTX]

I agree, I’m thinking I would need 300 or so at the crank to dip into the 13’s. If I researched right I think they are about 3200 lbs?

I believe the two doors are closer to 3400, maybe a bit lighter with that engine. But the four door should be nearer to 3400-3500.

 

[JimKueneman]

I would still consider doing the 273.

My 302 makes the most HP around 5200. The car goes like a bastard. I just don’t know what to expect from these 273’s.

View attachment 526586

This is very close to what I did to the 318



283 HP @4900 RPM, 355 TQ @ 3800 RPM.

Note the torque number in the range where you are most of the time. That is what the 273/318 do the best once you let them breath.