273 commano on the dyno wooooow

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MoparAnglia said:
All dyno results are dependant upon atmospheric conditions, Correction factors are used to standardise the results at a set air temperature, altitude etc.

This is my local engine builder. He's not a Mopar guy as such, but that 273 had some good tricks in it. He also did a 500 horse 349 (318-based) stroker for a circuit car, and doubtless a few more.

I had him balance my 318/390 rotating assembly, and it will go on his dyno when I get around to firing it up.
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moparanglia.............Thanks for explaining corrected bhp .:supz:
 
I loved my 273 that I built originally for my dart. It had 8:1 compression, a .510 cam, 1.88 J heads, single plane intake, 650 DP, backed by a 727 with a 10 inch converter that stalled 2000 (that's all it would go supposed to be a 3500) and 4.56 gears. It ran high 13s at 97 IIRC and it would not spin the tires but come 5k up it would pull pretty hard to 7200. I was pretty impressed with it but the 360 that replaced it was real similar in build specs (same compression same cam) was way torquier and was light years faster. I would love to revisit the 273 again and build it all out and see what it runs.
 
replicaracer43 said:
Its real simple, a smaller engine has to turn more rpm than a bigger one to make the same power.. a equally built 340 or 360 would stomp all over that 273 anyday.....
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Yea, people don't wanna spin their 340 to 7,500, then claim they need a stroker engine....nah, you need a solid cam and 4.56 gears

rpm scares people but the short stroke engines are built for rpms

One benefit of the 273 is fuel economy--even with steep gearing if you keep the speed down and drive with a light foot on the gas, it still can pull some decent mpg

..

Can I vent.... its too bad the 70's had to be so screwed up with smog regulations..things were moving along so well in the 60's, who knows what the 70's would have brought if the car makers didn't get all those regulations shoved on them. Best part is, after we got done with the 55 mpg to save fuel, we got gas hog SUV's going 75 mph

Now we are to get 55 mpg cars in ten years to make up for it, this is bull....
 
I agree ! and that 273 really revs fast to 7K.


back in the 70-80's they had cars with 40 mpg and now you'd be lucky if they get 30 mpg. and with 8 speed automatic transmissions..
 
The extra smog gear and safety gear kills the mileage. Some cars were 1,800 lbs.

One small car that wasn't all that bad was a 1980 Charger..think that was it, was a tiny front wheel drive car with a 2.2 turbo 4 banger. It got that 40 mpg driven lightly and had pretty good pick up, wasn't no 13 second car but an honest 15 before mods and DC had performance stuff for it, could easily get in to the 14's with a few mods

Car wasn't so safe in a crash thou, these new cars today are safer in a crash and today's cars hold the road better and brake better. When I think of safe cars, its those full size 70's cars that I feel hold up better in a crash but todays cars do steer and brake better to avoid crashes
 
The heads dictate the HP, the displacement dictates where that power comes in. 360 will produce 450 HP at alot lower RPM than a 273. same in a slant, same head over 3 sizes, more or less where the power was RPM wise was up to the displacement.
 
pishta said:
The heads dictate the HP, the displacement dictates where that power comes in. 360 will produce 450 HP at alot lower RPM than a 273. same in a slant, same head over 3 sizes, more or less where the power was RPM wise was up to the displacement.
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Problem with the 273 is that it has a long stroke and small bore which hurts cylinder head flow and you can’t run a 2.02 intake without notching the bore in the block. Even then the bore is so close to the valve that it hurts flow by a lot. An all out motor with really high compression and huge camshaft will have trouble making 450 even if your able to rev it to 8k.
 
Who needs 2.02 valves? 1.88 360 intake valves would do just fine. Its only 50 thou bigger (on each side) and I dont think it will hurt anything. If you feel it is shrouding, you can notch the bore as the most head gaskets today are 4.08 fire ring bored unless you get dedicated 273 or 318 head gaskets.
 
pishta said:
Who needs 2.02 valves? 1.88 360 intake valves would do just fine. Its only 50 thou bigger (on each side) and I dont think it will hurt anything. If you feel it is shrouding, you can notch the bore as the most head gaskets today are 4.08 fire ring bored unless you get dedicated 273 or 318 head gaskets.
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Well, if you want 400+ hp from your 273 you will need 225 cfm at minimum and small block mopar heads won’t get there without a 2.02 valve. And it’s .140” difference. Or 7% difference in size and actually circumferentially it’s more like 14% which which will cost you 30cfm. Notching the bore works, it’s actually a poor practice, if you piston is down in the bore. Also on a wedge head the notch isn’t the same as a canted valve motor where the valve is moving away from the bore. Also the head gaskets are 4.100. A 400+ hp 273 needs to be a perfect specimen and putting bandaides on it will come up short on power. Like I said before I would like to prove my theory. However, I have been around the block a few times with the small Chrysler and I do my own head Porting and set up as well as my own engine building. This is a great discussion because it inspires us.
 
turbodart68 said:
Problem with the 273 is that it has a long stroke and small bore which hurts cylinder head flow and you can’t run a 2.02 intake without notching the bore in the block. Even then the bore is so close to the valve that it hurts flow by a lot. An all out motor with really high compression and huge camshaft will have trouble making 450 even if your able to rev it to 8k.
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LOL, 3.31" isn't in the "long stroke" category, and it's still an over-square engine. Try to get sympathy from a slanty racer 3.5" hole & 4.125"swing !!! SB Mopars have a
nearly ideal placement of valves in the chamber/bore for an inline-valve arrangement. True small bores can restrict flow, but are more resistant to detonation, so You take
advantage of every little gift each particular build offers to the max. It is also not 100% true that heads that flow enough to make 400hp, will do so no matter what the
displacement, there are frictional losses that go up exponentially with RPM, as well as the inertial loads/losses Energy=Mass x Velocity sq. it's not a free ride to 10K just
'cause the heads say they can take You there!! In this sense, You're correct. To obtain that output at the needed R's, a reduction in stroke would be needed to offset the
new demands of such an increase in inertia, and help slow the intake velocity for a given RPM as well.
 
Killer6 said:
LOL, 3.31" isn't in the "long stroke" category, and it's still an over-square engine. Try to get sympathy from a slanty racer 3.5" hole & 4.125"swing !!! SB Mopars have a
nearly ideal placement of valves in the chamber/bore for an inline-valve arrangement. True small bores can restrict flow, but are more resistant to detonation, so You take
advantage of every little gift each particular build offers to the max. It is also not 100% true that heads that flow enough to make 400hp, will do so no matter what the
displacement, there are frictional losses that go up exponentially with RPM, as well as the inertial loads/losses Energy=Mass x Velocity sq. it's not a free ride to 10K just
'cause the heads say they can take You there!! In this sense, You're correct. To obtain that output at the needed R's, a reduction in stroke would be needed to offset the
new demands of such an increase in inertia, and help slow the intake velocity for a given RPM as well.
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Lol, I’m not looking for sympathy. The reason I mention stroke is that 3.31 is the same as the 340. Granted it’s not much but if you spin it 9k you’ll need a light rod/piston package. The reason I mention the small bore is that a 2.02 valve won’t fit. It hits the block. And if you want the big flow to make max power for the displacement you’ll need that 2.02 valve. I raced a 273 for a few years so I have some background on this particular motor.
 
For a streeter,I wouldn't spend a nickel on a 273 that power peaks at 5000, never mind one that power peaks at 7400. Wait, let me take that back; I wouldn't spend a nickel on a 273 period. Even if I had a lightweight early-A. I don't care how fast it revs.
Well, if it was the last engine on earth, and I had quarter section of prairie sod to bust, I guess I could figure out a way to marry those two, cuz at my age a shovel would probably kill me........
 
you are forgetting that that car in question has to run a period 273 for FIA European events. it's not like they had a choice and chose to run a 273. if caught cheating it'll not get invited back to the Goodwood Revival etc.

you are also forgetting that the owner of that engine isn't set to a budget so it probably cost more than a few mint '65 Formula S's would set you back.
 
[QUOTE="dodge freak, post: 1969824389, member:
Can I vent.... its too bad the 70's had to be so screwed up with smog regulations..things were moving along so well in the 60's, who knows what the 70's would have brought if the car makers didn't get all those regulations shoved on them. Best part is, after we got done with the 55 mpg to save fuel, we got gas hog SUV's going 75 mph

Now we are to get 55 mpg cars in ten years to make up for it, this is bull....[/QUOTE]


Yes, our government and insurance industries really did one on us in the 70's. But what was coming? I walked into Ostrich Racing, who did a lot of R&D for Chrysler back then. He had two sets of Westlake heads, you know the ones that John Buttera put on his 32 3-window back in the 80's. What Gary told me was that mother mopar wanted something like that for the small block, so that this would be the hemi of the late 70's. After the the Ball stud hemi had run it's course, which was suppose to come out in 73 but didn't, in 78 or so this 340, downsized to 301 was going to be the monster of the boulevard after those. Of course, these were suppose to go into the F bodiy Volares and Lil Red Wagon. What would have been.

Wonder if anyone has done the 4" stroker on a 273 block and what, or how that works out.
 
273's don't rev to the moon because of their short stroke. They have fairly light pistons because of the bore size, the lighter weight rods the same as the 318 has but they have/had a solid lifter cam, a dual point distributor, a open plenum intake, and a 4 barrel that all could go to 6000 r's without much of an issue. and another interesting note: the 235/273 has the highest hp/cu.in. ratios of all Mopar small blocks. Now, that is using rated horsepower numbers of course.
 
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Yeah that's it.
My 69 FSM lists the "autothermic alloy tin coated" 273pistons at 549 gms, while the 318s are 592, and the 340s are a whopping 719. The 69 conrods are all listed as 726 gms, but I've seen the earlier lightweight 273rods.273 pins are about .180 shorter than 318/340s, and that might make them 8gms lighter
The 360 has the same 726gm rods, just press fit instead of floating. The KB107 360 pistons are listed at 502gms, thus about 10% lighter than 273 pistons.
The smallport top-ends seem to rev up PDQ, as well.
But I was surprised by the Edlebrock heads/AirGap combo. My 360 buzzes up to 7200 (with those KBs) in a heartbeat.I can't say faster than a 273 cuz I've never had a built one. But I did have to get a rev-limiter after I saw the tach needle coming down from 8000 on a missed powershift.I thought that might be a little much,lol. It's been set to 7200 since then, but I try to shift below that..................It revved even faster with the 292/108 cam
 
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The reason a 273 is a revver like the 340 is because of head flow per cid. Any size engine can turn 7500 if you have enough head.

The main difference is 273 so small it's pretty easy to get the heads to flow enough especially compared to 408 plus.
 
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