Basic 273 tech tips/advice

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273 Commando

273 Commando

mooser's dad
Joined
Dec 27, 2008
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San Jose, CA
Hi guys, I'm new to the site. I'm mooser's bank (dad) trying to help him build up his '74 slant six Duster into something more fun, so here's where we're at. I got him a running '72 Swinger donor car (bad body) that was going to be some kid's racecar project that failed. I think we did ok for the money as it has a 4.5" bc 8.25 differential, a reman tranny, fairly new Hedman headers with full exhaust and Flow Masters, 625 cfm Comp. Series Carter AFB, Pertronix ignition and an Eddy 318 2P-SP intake. Now, here's the kicker. That 318 turned out to be a early '66 273 pushing 160 psi cylinder pressure. It still has the solid cam in it. I dont know much about small blocks,especially this one, except that the intake bolt angles are different and someone machined the Eddy intake accordingly.

My buddy and I want to tear it down and do a rings and bearings budget job on this guy, give it a fresh coat of paint and pretty it up to look real nice in the "Moose Mobile". I would welcome any advice,tips,comments, or anything else that may help.

I'll be using Schumacher mounts, the Duster has disc brakes already and I got new leaf springs and .87 torsion bars already to go. Most of my help is with the engine tips. Thanks in advance!
 
If you're just going to use it to drive around with the 273 is fine. Stock 2 barrel motors make their peak torque at something like 1800 rpm (I might be a bit off on this, I'm old), so they're good for a street driver. They're not a powerhouse but I can speak from experience that they can make enough power to break parts. If you want to go that far, somebody here can probably recommend a cam to juice it up a little. If you change cams, keep it mild. Otherwise, you'll have to turn it pretty tight to get anything out of it. My 273 once saw 7000 rpm when my eyes strayed from the tach.
 
273 Commando said:
Hi guys, I'm new to the site. I'm mooser's bank (dad) trying to help him build up his '74 slant six Duster into something more fun, so here's where we're at. I got him a running '72 Swinger donor car (bad body) that was going to be some kid's racecar project that failed. I think we did ok for the money as it has a 4.5" bc 8.25 differential, a reman tranny, fairly new Hedman headers with full exhaust and Flow Masters, 625 cfm Comp. Series Carter AFB, Pertronix ignition and an Eddy 318 2P-SP intake. Now, here's the kicker. That 318 turned out to be a early '66 273 pushing 160 psi cylinder pressure. It still has the solid cam in it. I dont know much about small blocks,especially this one, except that the intake bolt angles are different and someone machined the Eddy intake accordingly.

My buddy and I want to tear it down and do a rings and bearings budget job on this guy, give it a fresh coat of paint and pretty it up to look real nice in the "Moose Mobile". I would welcome any advice,tips,comments, or anything else that may help.

I'll be using Schumacher mounts, the Duster has disc brakes already and I got new leaf springs and .87 torsion bars already to go. Most of my help is with the engine tips. Thanks in advance!
Click to expand...

Gee, it sounds like a real solid engine as is. 160psi is pretty good, for a 2 barrel engine. I'd look in the cylinders to see if you possibly scored a gennie 4bbl Commando motor. If it runs good,ie, no smoke, no funny sounds, I'd leave it alone, give it a Krylon rebuild (read : paint 'er up) and stick 'er in.

Just my take...
 
I think the SP2P is a 4bbl intake, but one designed for fuel economy. If you dont want to sepnd, it's fine the way it is and 160psi is fine for pump fuel. If you wanted to spend a litttle, I would suggest adding a set of re-drilled magnum heads and an Edelbrock Performer 318/360. You can get some money for this by selling the rockers, pushrods, and intake off the 273. Otherwise, clean, paint, and run it.
 
On the 273, they allready hae a bit of compresion when made IIRC. You should be good there and 160 psi is nice. I'm not that familar with the Edelbrock intake you have now. My first instinct was to say Performer.

Being a solid cammed engine, it shouldn't be to hard to do a copy of the early D-dart engine. 275 hp. The cam is no longer available. It was speced at 284 duration. MoPar offers a purple shaft at this advertised duration, but I do beileve it duration @ .050 is larger.

The D-dart also came with a 600 Holley and headers stock.

As for performance upgrades, I'd swap out the heads for 318 heads and then move to the performer intake. A good head preping would be it.
Dependent of the target goal of the car, I'd choose a cam that would match the RPM driving range and gear ratio.
 
Just curious Rumble. Why switch to 318 heads? Is it for the later style manifold choices (assuming he has early 273 heads) or hardened seats? Those are the main advantages I can think of. I think the valve size & combustion chambers are the same.
 
The best reason for going to the 318 heads would be to get the hardened valve seats (73 & later). The 302 (85 & later) heads would still be small valve, but would have the smaller combustion chamber. Both would be compatible with the existing intake. I run 302s with a Performer, 625 AFB, and a mild cam. Throttle response is good. It has never been raced, so I have no idea what a ¼ mile would be like.

If magnum heads would fit without having to notch the bores, that would be my second choice. I think these have larger ports, so a Performer RPM or Air Gap would be better intakes. 360 heads would be my third choice, again if the block doesn't have to be notched. Ditto intake choices.
 
If it is a 66 273 the intake bolt angles are the same as the later motors. Sounds like you have good cylinder pressure. 273's lack low end brunt. If you decide to swap out the cam, hyd or solid, stay in the 268-272 duration range. A 340 oem cam or the 268 comp are good choices. I put the 340 cam in a tired 273 2bbl with new valve seals and springs and 4bbl intake,600 holley, really woke the motor up. I did try the 280 mopar cam, sounded cool, but no bottom end.
As for a head swap, newer heads,non magnum, have larger chambers which will drop your compression, 2bbls only 8.8-1 to start. 2.02 valve head need the block notched to clear the valves...
My 2 cts

Good find and good luck
Bob
 
Thanks for all the input guys! It does have the '65 273 heads on it and the block is dated Dec. 65. I know that Edelbrock is a low rpm intake, it's runners are real small. If I remember right, the SP-2P was a 70's 318 upgrade for mild street use and to gain 4 bbl power over stock 2 bbl and the LD 340 was all the rage for 340/360's. I'll try to find a used Performer to run with the AFB. How can I tell it this engine is a real Commando when I tear it down? If it is, I figure the stock cam would be fine at 248 duration and .425 lift (Chrysler advertised figures) One web site that specializes in the 273 recommended the Comp Cams 270S as a great solid street cam with an auto trans (again, it's the money...Christmas bills, argh!) Oh, one more thing. The rear main is leaking, hence the tear down. I dont know anything about this engine's previous life, so I'll play it safe and regasket everthing and paint it Chrysler red as it should be. My buddy want to do the rings and bearings as a present for my son.
 
A real Commando engine will have domed pistons that are specific to each side of the motor & a dual point distributor. The version of the LD 340 for the early 273 heads was called a D 4B, the one for late 273 & 318 heads was called an LD 4B, then came the LD 340. I have one of the dual point distributors, but I'm not sure I'd want to part with it. I'm sort of a packrat. I'd definitely stick with the small valve sizes on the 273 to keep velocity up. I had a 273 with a single plane Offy manifold, a .474 284 cam, domed pistons & headers. It was gutless at low rpm but was a real screamer when you wound it up.
 
'64 Cuda said:
Just curious Rumble. Why switch to 318 heads? Is it for the later style manifold choices (assuming he has early 273 heads) or hardened seats? Those are the main advantages I can think of. I think the valve size & combustion chambers are the same.
Click to expand...

The hardened valve seats are a plus, but the main idea I had in my head was for the intake angle. A modern intake would be a plus for sure.
The 1.78 intake valves are find with a good head prep. 1.88's might be a bit much. (Build dependent of course) I'd bet the 1.60 exhaust valve would be good to use over the 1.50.


BobsDart His intake was milled to fit the odd angle.

273 Commando, I think that Comp 270S cam would be great with the more than likely modest gears that are in the car. What are they? Do you know?
 
rumblefish360 said:
but the main idea I had in my head was for the intake angle. A modern intake would be a plus for sure.

BobsDart His intake was milled to fit the odd angle.
Click to expand...

The bolt size and bolt angle are different between early and late 273 intakes, not the gasket surface angles. They are the same.
 
I don't know the gear ratio yet. I tried doing the spin test on this peg leg, but still I couldn't get an accurate reading. I'm planning on 3.55's for the Moose Mobile. As far as the heads go, my buddy has a Performer he'll give me and machine the bolt holes to the early 273 configuration, and I guess a budget valve job with springs appropriate to the cam if we change it.
 
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