273/4 -318 debate

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stock 2bbl, 1978 4bbl if you think it rates, whatever you got. time slips and weight a plus for some base HP calculations or dyno sheets. Sure, 79 TQ's and 81 on plus TB roller cams. Problem with later posted numbers is the net HP rating.
 
I guess I posted my stock 318 2bbl times. 15.9's at 84 mph. Never weighed the car, guess about 3500 lbs.
 
pishta said:
post 'em up! What do those 5.2's run?
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I have a friend that’s big into four wheel drive seventies power wagons and eighties Rams. His strongest build, aptly monikered The Ill 318, was an early block with forged crank, Icon domed pistons, 1’st gen performer rpm, edelbrock carb, 2.02 valved 308 heads, comp .480 lift cam and roller rockers. Put it in a 33 inch mud tired, manual trans, 4.10 Dana ‘88 model W-250. Sadly, he never got to take it to the track (truck totaled by oncoming elderly driver jumping median) but it it was able to top out at around 130 miles per hour at about 5500 rpm. At least that’s what the speedometer of the vehicle pacing his speed read. Not bad for 5000 plus pounds of rolling thunder bouncing down the road. Still thankful I was not involved in that speed trial, I imagine it looked like a state trooper’s worst nightmare...
 
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B.T.W., he is presently building Ill 318 version 2.0 with another 70's 318 block, ported 318 magnum heads, air gap intake, 800 Holley spread bore double pumper, and matching cam. It's going into a mid nineties Dakota 4X2 with 4.10 gears. I'll let you know what it runs, should be a lot of fun!
 
the 273 doesn't make 425 hp, more like 306 hp. =1.25 hp per CI. matte steens 273 super stocker runs 10. 30 @ 130 MPH, 1.65 HP per CI. = 450 Hp. taken from mopars orginal tables.
 
pishta said:
Thats ok, its in Metric.....Its a Euro data site. Maybe if we figure out what a Nm is to ft/lb
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Your 460 Nm computes to 339 Ft/lbs, sound about right?
The conversion factor is Nm = ft/lbs divided by .73756
 
stixx, you ever see a dyno sheet like this that doesnt intersect at 5250rpm? I thought it may be a Euro measurement thing....yeah. I believe I see where they set it up differently by not making the lines intersect. The values on the left dont line up that way. We just have to mentally move the power curve as well as its data points up to meet the tq curve. So this graph is correct, it just doesnt follow the ASE standard of lining the tq and HP values on either side to force an intersection at 5250. if we start the Tq values at 100Nm on the left , then the graphs intersect at 5250. Good data, bad practice.
 
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pishta said:
stixx, you ever see a dyno sheet like this that doesnt intersect at 5250rpm? I thought it may be a Euro measurement thing....
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You're spot on pishta ! (5250 rpm)
I've seen this kind of thing before, in the 80's with HR Magazine. They would do an engine build with their beloved 350, then brag, brag, brag about how much power it made..
But I noticed they were puffing the numbers above the 5250 mark. (curve looked suspect)
They weren't smart enough to bring up the torque values with it, so when I did the math, they were actually 45-50hp short of their claims.
 
AJ/FormS said:
Wait, I think there is something wrong with the calibrations....the lines should cross at 5250.
And how many 318-2s make 460 ftlbs
And if they did that at 2750 the HP would be 240....... not 180ish
I'm confused,lol
View attachment 1715247228
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the TQ side should start at 100, not 25. That would align the points SAE style. Just drag the TQ lines down 75 points and realign the values on the left. Id do it as a transparent overlay but Im not that good at GiMP, anyone know photoshop that can do this?
 
maybe this is better, disregard the higher TQ lines as they are the old scale, the new lines are to the new scale...thats still in Nm :(, mult by .7375 to get Ft/lbs...
new.jpg
 
pishta said:
stixx, you ever see a dyno sheet like this that doesnt intersect at 5250rpm?
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No. I hadn't even looked that closely on the dyno graph. It is a pastime of me to redraw dyno curves (in order to be able to compare them),
and they ALL intersect at 5250 rpm. :)
In your thread I just googled up the conversion from newton-meters into foot-pounds.
 
pishta said:
the TQ side should start at 100, not 25. That would align the points SAE style. Just drag the TQ lines down 75 points and realign the values on the left. Id do it as a transparent overlay but Im not that good at GiMP, anyone know photoshop that can do this?
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And then you would have to run a few calcs here and there to prove they are the same curves
 
stixx said:
No. I hadn't even looked that closely on the dyno graph. It is a pastime of me to redraw dyno curves (in order to be able to compare them),
and they ALL intersect at 5250 rpm. :)
In your thread I just googled up the conversion from newton-meters into foot-pounds.
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Here's from the horses mouth, the website creator!
"...It’s because the torque on the charts is in Nm (newton-metre) and power in PS (metric horsepower), both belonging to the SI system (International System of Units). I assumed that it would be more universal around the world than FPS system… In that case the lines intersect around 7100 rpm..."
 
It's just a formula

(torque times rpm)/5250=horsepower

5250 is just a constant comprised of factors related to the conversion. Because it is the devisor, the lines cross;
(425 ftlbs at 5250rpm)/5250=425hp@5250 rpm
(425x5250)/5250=425

If they cross somewhere else then it ain't horsepower the way we measure horsepower, or the scales on the graph are staggered or mislabeled , and that would just mess everybody up. So if it comes from Europe, they can keep it along with driving on the left side, and euros and all kinds of other nonsense,lol. I ain't willing to learn another formula just to be able convert their junk to our junk.

You can't just shift the left side calibration, they both have to start at zero at the same spot, else you cannot compare them directly, cuz they are no longer proportional. You have to expand or contract one scale or the other until they cross at 5250 and then the scales will be directly comparable.
Otherwise you have to do the math.
Below is a nice simple curve using the same scale for torque and horsepower.
and an example; go to 3750 rpm and pull 420 ftlbs off the graph. Then (420x3750)/5250=300hp, check the power curve to verify.
You can now clearly see what to expect from this engine in terms of take-off performance by the expansion of the power curve that can be read off the torque curve. If instead, you only had the power-curve, and had an overlay from another cam on it, it might be difficult for simple guys like me to be able to determine a performance difference down there, between them.. the torque curve just expands that nicely for a visual ah-ha!
This becomes very important the smaller the engine is on account of 20 or 30 ftlbs is the difference at 2250rpm of one rear gear size, or one cam size, or a compression boost requirement just to maintain the 2250 stall. Not everyone wants 4.10s or 2800s.
And 25ftlbs is easily seen on the torque curve, whereas 10.7 hp doesn't look like much; (25x2250)/5250=10.7; yet the performance difference is exactly the same.

xr270.jpg

graph pirated from google
 
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I have owned both and ran both in my 1967 Dart. I can vouch for the 15.9 with a dead stock 318 2bbl. I have seen it go as quick as 15.7. 273 4 bbl ran 16.2. Both with stock stall speed 904 torqueflight. Now the 273 I did have was a low compression 2bbl short block with a ldf4b manifold and 600 CFM AFB. The 273 had more horsepower at a higher rpm but had no low end torque. I did get the 273 into high 14s one time using a scary neutral drop. In reality the 273 with a 4speed should be a mid to high 14 second car. Low 15s at minimum. With an auto the 318 would be extremely close. I used to shift my 273 at 6500 rpm. Oh and just for fun that same 273 with headers and 100 horse shot of nitrous went 13.78 at 105 with a stock converter and 3.23 gears.
 
Real easy to sum up. NHRA stock eliminator would have a 67 273 4bbl B-cuda and a 68 318 2bbl B-cuda in the same class and theoretically they finish the 1/4 at the same time
 
pishta said:
Were having a discussion on the merits of the 273-4 engine compared to the 318-2 of the following years, sometimes even the same year. Sure the 273-4 was a hot motor back in 65 when it was the best thing between the fenders of the early A's but you just can't deny that a 20% larger motor is going to make a difference. Performance test are all over the board, depending if the dufus can drive or if the dyno is set up properly, yadda yadda...but I found a site that has a lot of info on cars in general and has generated graphs (from factory data) on performance specs. So I tried to match 2 like cars (in weight, gear and transmissions) with our 273-4 and the 'new' 318-2. Results? Well, I think it would ultimately come down to the reaction time between these 2 motors as they are pretty close. You can see the shift points are higher on the smaller higher winding 273 and the torque advantage goes to the 318 down low. Theoretical top speed goes to the high winding 273 due to the cam profile and possible higher RPM potential of its heavier valve springs and forged crank.

1965 273-4 Barracuda
reference weights: shipping weight 3029 lbs base curb weight: test weight 1430 kg / 3152 lbs
how fast is this car ? top speed: 126 mph (©theoretical);
accelerations: 0- 60 mph 6.9© s; 0- 100 km/h 7.3© s (simulation ©automobile-catalog.com); 1/4 mile drag time (402 m) 15.6
View attachment 1715247101







1968 318-2 Barracuda
reference weights: shipping weight 1363 kg / 3005 lbs base curb weight: 1430 kg / 3152 lbs
how fast is this car ? top speed: 178 km/h (111 mph) (©theoretical);
accelerations: 0- 60 mph 6.8© s; 0- 100 km/h 7.3© s (simulation ©automobile-catalog.com); 1/4 mile drag time (402 m) 15.4© s

View attachment 1715247102



overlaid


View attachment 1715247103

<<<lower 75 from tq curve points to align 5250rpm intersection>>>
<<<the tq graph should start at 100 so the data points align SAE>>>

and the overlay of the HP/torque curves from factory data. increased displacement really shows in the torque curve but the smaller 273 can hold its HP peak longer. This is due to camshaft differences. Put a similar cam in a 318 and its curve would change.



Bottom line: in a 1/4 mile race all things being somewhat stock on these 2 cars, the 318 would edge it by .2 seconds..theoretically. Now on the highway having some fun with your buddy, the 273 would probably walk away after 4500 RPM. Now put the 4bbl cam in the 318 and it would probably be a 20% increase across the board on the 318 data. To say the 273-4 would walk a 318-2 in a drag race is not supported in this data. All data is from blueprint specs and we all know how well those are kept in production, especially compression ratios.
Food for thought...or to fling?
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"All cranks were forged" is a encompassing statement. Maybe not. I had always heard that Mopar used forged cranks up to 72 in the small blocks. I don't know about the slants and big blocks without looking it up.
 
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