Testing the 273 on the dyno....

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Comparing my 200 horsepower 277 poly "power pak" of 1956 with the 235 horsepower 273 "power pak" of the mid-60's, I'll note that the 277's compression ratio is only 8:1, and the cam only has .380 lift. Raise the 277's CR to 10.5 to one and give it a .415/.425 lift cam, and I think it would easily make another 35 hp.
 
As for comparison between the hi-po 273 and the 340, in the spring of 1973 I replaced the blown up 273 in my 65 Barracuda (long story) with a 340, and all I can say is that it sure felt to me like the 340 was way more than 40 hp stronger.
 
I think if you compare the HP & torque curves for a 273-4 and a 318-2, you will see a radical difference. Based on factory info, the 273-4 has an extremely flat torque curve with a peak at 4000rpm. The HP peak is at 5200rpm. This leads to an entirely different driving experience. Really, it's hard to take advantage of it unless you have a 4 speed.
 
mvh said:
I think if you compare the HP & torque curves for a 273-4 and a 318-2, you will see a radical difference. Based on factory info, the 273-4 has an extremely flat torque curve with a peak at 4000rpm. The HP peak is at 5200rpm. This leads to an entirely different driving experience. Really, it's hard to take advantage of it unless you have a 4 speed.
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Haven't drove a automatic but I have rowed my 4 gear quite a bit.

100_4689.JPG
 
Jealous... mine is a column-shift auto. It flies once it gets up there, but there is too big a gap between 1 & 2, and 2 & 3.
 
mvh said:
Jealous... mine is a column-shift auto. It flies once it gets up there, but there is too big a gap between 1 & 2, and 2 & 3.
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A higher rpm governor in the trans will narrow the "gap" by raising the shift points at both full and part throttle.
 
I have a direct comparison from back in the day. I replaced the 318 in my 68 cuda with a 273 commando I rebuilt to stock out of my 66 Formula S race car. Both cars ran exactly the same times in the quarter mile. The 318 was all low end torque and the 273 was top end power.
 
65 Cuda 340 said:
Oops, didn't see Mattax's post before posting mine, but yeah, "power packs" weren't Chevy only. That term was common in the mid-fifties to refer to engines with optional four barrel carbs and dual exhaust. Below is Plymouth literature from 1956. Per Mattax, looks like Plymouth still used the term "Power Pak" as late as 1965.

View attachment 1715833973
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I had a'56 Dodge Sierra wagon with the Power Pac. I was able to outrun my buddys 5.0 Mustang in the early 90's with it, can still picture his face!!
 
i had a 68 convertable Dart GT WITH 293 4 BARREL it smoked the tires with ease always like that 273 , of course the 340 that replaced it was even better
 
RustyRatRod said:
I thought "Power Pack" was a version of the Chevy 283.
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Yep, a Late 50's head you would see in the belairs. Like '58
Brick with a point in the middle is the boss on the ends. Lol they right up there with them ram horn manifolds..lol novelty but junk for power
 
My memory is that net hp was first widely used in 72.

However, in 1955, Chevrolet posted both gross and net figures for its new small block 265 inch V8 (gross and net figures are both at the crank, not at the wheels, but gross used cold intake air, cold carburetor via blocked heat riser, no fan or other accessories, dyno exhaust, etc, while net was hp at the crank in production trim with production timing, carb heat, intake air heated to typical underhood temperatures, all accessories including fan, water pump and generator hooked up, etc.).

The two barrel motor was rated 162 gross, 137 net. The power pack motor (4-barrel carb and dual exhaust) had 180 gross, 160 net. These figures are from the January 1955 Issue of Hot Rod Magazine, article entitled "Analyzing the Chevrolet V8" by Racer Brown, tech editor (yes the same Racer Brown of camshaft fame).

55 chevy dyno chart.JPG
 
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The Poly 318 2 bbl certainly made 230 hp. And with just 9:1 CR.
They were sold here for many years in Dodges & Plymouths & judging by the performance figures from road tests, they might have been under rated at 230 hp.
 
from what i have seen on dynos of total stock rebuilds mopar were underated most of the time , the gm engines never made what they claimed stock and some 318 back in the day made more than others . had 2 318 darts one was always faster no matter who was driving it both 318 2 doors 1972 's
 
forphorty said:
Examples of stock 318s on the dyno : 318 Engine Buildup & Dyno Test - Mopar Muscle Magazine Engines: 318 Street Recipes 318 Long Block Bolt Ons - Tech Articles - Mopar Muscle Magazine
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i had a similar 318 build in the 1970's , car held it's own with 400 firechickens and camaros that little 318 has always been underrated with the parts available today no reason not to build one . just does not sound as good as 340 . if a 318 was all i had i'd build it up for sure . in fact when people ask what i;m running i always say 318 even if it's a 340 or stroked 360
 
Mattax said:
Net peak, per J245
https://www.hamtramck-historical.co...alershipDataBook/1972/72_Plymouth_Specs_4.jpg

Gross peak,
https://www.hamtramck-historical.co...DataBook/1967/67_Plymouth_Engineering0007.jpg
https://www.hamtramck-historical.co...DataBook/1967/67_Plymouth_Engineering0008.jpg
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hard to believe those 440 numbers , my father had a 440 new yorker in 1972 and it would smoke the tires no problem cruise at 120 mph all with 280 hp and 375 tq ? sure felt like more back then , car was fast for a heavy boat
 
Bewy said:
The Poly 318 2 bbl certainly made 230 hp. And with just 9:1 CR.
They were sold here for many years in Dodges & Plymouths & judging by the performance figures from road tests, they might have been under rated at 230 hp.
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It's all in the heads! LOL

poly-318-valve-train.jpg
 
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