Sweet5ltr
Well-Known Member
Here is my bench racing question;
What engine makes more average power?
Before looking at results, choose what you'll go with;
(a) 500ci with 600 ft/lbs @ 3,500-5,000
(b) 400ci with 500 ft/lbs @ 4,500-6,000
(c) 300ci with 400 ft/lbs @ 5,500-7,000
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performance being the only goal for given range
Torque x RPM / 5252 = HP (we see the relative advantage of displacement here)
500ci, 600 ft/lbs @ 3,500-4,250-5,000 (399HP-485HP-571HP) 485 average HP
400 ci, 500 ft/lbs @ 4,500-5,250-6,000 (428HP-499HP-571HP) 499 average HP
300 ci, 400 ft/lbs @ 5,500-6,250-7,000 (418HP-476HP-533HP) 476 average HP
Formula 1 engine, lets say 250 ft/lbs @ 18,000
(833HP, that's why they have brutal acceleration when in the power band)
All things equal, that's why there is 'no replacement for displacement' when building a street engine in typical street friendly power bands, but at the same time, acceleration of a larger displacement engine is favored at low speeds vs a smaller displacement engine (making less torque/higher RPM) at high engine speeds.
Using strictly static measurements, what engine would produce more -inertia/power- at the tire (during launch) giving its initial torque peak ;
(torque x rear gear x 1st gear ratio of 727 transmission x stall converter matched @ torque peak) *final numbers indicate acceleration value*
500ci- 600 x 3.55 x 2.42 x 3500 (18,041)
400ci- 500 x 3.55 x 2.42 x 4500 (19,330)
300ci- 400 x 3.55 x 2.42 x 5500 (18,900)
'wildcard' 450ci- 550 x 3.55 x 2.42 x 4000 (18,900)
How street gearing and a typical 3,500 converter affects the outcome;
600 ft/lbs x 3.55 x 2.42 x 3500 (18,041) <--- no replacement for displacement!
500 ft/lbs x 4.30 x 2.42 x 3500 (18,201)
400 ft/lbs x 4.56 x 2.42 x 3500 (15,449) Even with 4.56 gears, this car will not launch very hard. Install a 4,500 converter and it will hit substantially harder (19,863)..
Results are surprising right? It would take a stock 440 wedge making 500 ft/lbs @ 3,500 RPM, 4.30 gears to run with a larger engine making 600 ft/lbs with 3.55 gears (HUGE difference). This is why choosing the correct torque converter and gearing is SO IMPORTANT! Proving why a car with lots of torque requires less gearing to have identical acceleration as a car with less overall torque.
Real world through average limited power bands, a slightly smaller engine favoring HP (torque at higher RPM) will out accelerate a larger engine favoring torque (torque at lower RPM) if setup properly, this was some of the math behind my decision to go with a smaller displacement engine and turn higher RPM:
Looking at these two numbers, peak torque, what made more peak horsepower;
512ci making 650 ft/lbs @ 3,500 (RPM range 3,500-5,500)
470ci making 600 ft/lbs @ 4,500 (RPM range 4,500-6,500)
470 making 600 @ 4,500 x 3.55 x 2.42 x 4500-600 ft/lbs (23,196) 5500-575ft/lbs (27,169) 6000-550 ft/lbs (28,350) 6500-525 ft/lbs (29,317) -wildcard- 7000-500 ft/lbs (30,068)
512 making 650 @ 3,500 x 3.55 x 2.42 x 3500-650 ft/lbs (19,544) 4500-625 ft/lbs (24,162) 5000-600 ft/lbs (25,773) 5500-575 ft/lbs (27,169) -wildcard- 6000-550 ft/lbs (28,350)
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470ci 525 x 6500 / 5252 = 649 HP (7000 RPM = 666HP) +17 HP
512ci 575 x 5500 / 5252 = 600 HP (6000 RPM = 628HP) +28 HP
That is why it's VERY important to think about all these aspects during a build, a 512ci stroker making peak torque @ 3,500 RPM (650 ft/lbs) will get beat by a 470 engine making peak torque @ 4,500 RPM (600 ft/lbs) in acceleration (if correct torque converter is used WITH IDENTICAL GEARING). Most engines make peak HP 1,250-1,500 RPM away from Peak TQ. What all this pretty much says is, pick the largest displacement engine possible that can run the highest reliable engine speed, if a large engine is bottlenecked by small camshafts and poor-flowing heads; it will not perform optimally.
Look at the graph of this 440 Six Pack, 441 ft/lbs @ 4800 RPM and 403HP. (441x4800/5252=403HP)
http://www.hotrod.com/articles/rest...f/#032-440-mopar-six-pack-dyno-test-chart-jpg
Move the peak torque up 1,000 RPM with a larger duration camshaft, properly matched intake manifold, carb, and longtube headers, and if it makes 441 ft/lbs @ 5800 RPM; it will make a 487 HP peak.
Brute acceleration, what converter would be 'overall' better in this application, going off the dynograph?
2.5k rpm (12,650 w/ 4.10 gear)
3k rpm (15,150 w/ 4.10 gear) ?? what, engine makes more torque here right!? but it does not have optimum acceleration at this RPM.
4k rpm (19,208 w/ 4.10 gear)
5k rpm (20,538 w/ 4.10 gear)
5.3k rpm (20,561 w/ 4.10 gear)
5.5k rpm (20,190 w/ 4.10 gear) *lower acceleration while dropping off power band, makes sense now right?*
Now lets say the engine drops 500 RPM per gear change (2nd gear - 1.45)... It looks like 5.3k is around the perfect shift point (all things being equal)
5k - 4.5k (12,546)
5.3k - 4.8k (12,584)
5.5k - 5k (12,306)
That is why sometimes slightly smaller displacement engines 'run better than they should'. Build for slightly less torque at a higher RPM, with an engine that allows higher engine speeds (N/A engines).
100% bench racing, 100% gearhead discussion, yalls thoughts? Kind of interesting right?
What engine makes more average power?
Before looking at results, choose what you'll go with;
(a) 500ci with 600 ft/lbs @ 3,500-5,000
(b) 400ci with 500 ft/lbs @ 4,500-6,000
(c) 300ci with 400 ft/lbs @ 5,500-7,000
-
-
-
-
-
-
-
-
performance being the only goal for given range
Torque x RPM / 5252 = HP (we see the relative advantage of displacement here)
500ci, 600 ft/lbs @ 3,500-4,250-5,000 (399HP-485HP-571HP) 485 average HP
400 ci, 500 ft/lbs @ 4,500-5,250-6,000 (428HP-499HP-571HP) 499 average HP
300 ci, 400 ft/lbs @ 5,500-6,250-7,000 (418HP-476HP-533HP) 476 average HP
Formula 1 engine, lets say 250 ft/lbs @ 18,000
(833HP, that's why they have brutal acceleration when in the power band)
All things equal, that's why there is 'no replacement for displacement' when building a street engine in typical street friendly power bands, but at the same time, acceleration of a larger displacement engine is favored at low speeds vs a smaller displacement engine (making less torque/higher RPM) at high engine speeds.
Using strictly static measurements, what engine would produce more -inertia/power- at the tire (during launch) giving its initial torque peak ;
(torque x rear gear x 1st gear ratio of 727 transmission x stall converter matched @ torque peak) *final numbers indicate acceleration value*
500ci- 600 x 3.55 x 2.42 x 3500 (18,041)
400ci- 500 x 3.55 x 2.42 x 4500 (19,330)
300ci- 400 x 3.55 x 2.42 x 5500 (18,900)
'wildcard' 450ci- 550 x 3.55 x 2.42 x 4000 (18,900)
How street gearing and a typical 3,500 converter affects the outcome;
600 ft/lbs x 3.55 x 2.42 x 3500 (18,041) <--- no replacement for displacement!
500 ft/lbs x 4.30 x 2.42 x 3500 (18,201)
400 ft/lbs x 4.56 x 2.42 x 3500 (15,449) Even with 4.56 gears, this car will not launch very hard. Install a 4,500 converter and it will hit substantially harder (19,863)..
Results are surprising right? It would take a stock 440 wedge making 500 ft/lbs @ 3,500 RPM, 4.30 gears to run with a larger engine making 600 ft/lbs with 3.55 gears (HUGE difference). This is why choosing the correct torque converter and gearing is SO IMPORTANT! Proving why a car with lots of torque requires less gearing to have identical acceleration as a car with less overall torque.
Real world through average limited power bands, a slightly smaller engine favoring HP (torque at higher RPM) will out accelerate a larger engine favoring torque (torque at lower RPM) if setup properly, this was some of the math behind my decision to go with a smaller displacement engine and turn higher RPM:
Looking at these two numbers, peak torque, what made more peak horsepower;
512ci making 650 ft/lbs @ 3,500 (RPM range 3,500-5,500)
470ci making 600 ft/lbs @ 4,500 (RPM range 4,500-6,500)
470 making 600 @ 4,500 x 3.55 x 2.42 x 4500-600 ft/lbs (23,196) 5500-575ft/lbs (27,169) 6000-550 ft/lbs (28,350) 6500-525 ft/lbs (29,317) -wildcard- 7000-500 ft/lbs (30,068)
512 making 650 @ 3,500 x 3.55 x 2.42 x 3500-650 ft/lbs (19,544) 4500-625 ft/lbs (24,162) 5000-600 ft/lbs (25,773) 5500-575 ft/lbs (27,169) -wildcard- 6000-550 ft/lbs (28,350)
**************************
470ci 525 x 6500 / 5252 = 649 HP (7000 RPM = 666HP) +17 HP
512ci 575 x 5500 / 5252 = 600 HP (6000 RPM = 628HP) +28 HP
That is why it's VERY important to think about all these aspects during a build, a 512ci stroker making peak torque @ 3,500 RPM (650 ft/lbs) will get beat by a 470 engine making peak torque @ 4,500 RPM (600 ft/lbs) in acceleration (if correct torque converter is used WITH IDENTICAL GEARING). Most engines make peak HP 1,250-1,500 RPM away from Peak TQ. What all this pretty much says is, pick the largest displacement engine possible that can run the highest reliable engine speed, if a large engine is bottlenecked by small camshafts and poor-flowing heads; it will not perform optimally.
Look at the graph of this 440 Six Pack, 441 ft/lbs @ 4800 RPM and 403HP. (441x4800/5252=403HP)
http://www.hotrod.com/articles/rest...f/#032-440-mopar-six-pack-dyno-test-chart-jpg
Move the peak torque up 1,000 RPM with a larger duration camshaft, properly matched intake manifold, carb, and longtube headers, and if it makes 441 ft/lbs @ 5800 RPM; it will make a 487 HP peak.
Brute acceleration, what converter would be 'overall' better in this application, going off the dynograph?
2.5k rpm (12,650 w/ 4.10 gear)
3k rpm (15,150 w/ 4.10 gear) ?? what, engine makes more torque here right!? but it does not have optimum acceleration at this RPM.
4k rpm (19,208 w/ 4.10 gear)
5k rpm (20,538 w/ 4.10 gear)
5.3k rpm (20,561 w/ 4.10 gear)
5.5k rpm (20,190 w/ 4.10 gear) *lower acceleration while dropping off power band, makes sense now right?*
Now lets say the engine drops 500 RPM per gear change (2nd gear - 1.45)... It looks like 5.3k is around the perfect shift point (all things being equal)
5k - 4.5k (12,546)
5.3k - 4.8k (12,584)
5.5k - 5k (12,306)
That is why sometimes slightly smaller displacement engines 'run better than they should'. Build for slightly less torque at a higher RPM, with an engine that allows higher engine speeds (N/A engines).
100% bench racing, 100% gearhead discussion, yalls thoughts? Kind of interesting right?
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