Sweet5ltr
WellKnown 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 @ 3,5005,000
(b) 400ci with 500 ft/lbs @ 4,5006,000
(c) 300ci with 400 ft/lbs @ 5,5007,000








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 @ 3,5004,2505,000 (399HP485HP571HP) 485 average HP
400 ci, 500 ft/lbs @ 4,5005,2506,000 (428HP499HP571HP) 499 average HP
300 ci, 400 ft/lbs @ 5,5006,2507,000 (418HP476HP533HP) 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 3,5005,500)
470ci making 600 ft/lbs @ 4,500 (RPM range 4,5006,500)
470 making 600 @ 4,500 x 3.55 x 2.42 x 4500600 ft/lbs (23,196) 5500575ft/lbs (27,169) 6000550 ft/lbs (28,350) 6500525 ft/lbs (29,317) wildcard 7000500 ft/lbs (30,068)
512 making 650 @ 3,500 x 3.55 x 2.42 x 3500650 ft/lbs (19,544) 4500625 ft/lbs (24,162) 5000600 ft/lbs (25,773) 5500575 ft/lbs (27,169) wildcard 6000550 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 1,2501,500 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 poorflowing 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/#032440moparsixpackdynotestchartjpg
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 @ 3,5005,000
(b) 400ci with 500 ft/lbs @ 4,5006,000
(c) 300ci with 400 ft/lbs @ 5,5007,000








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 @ 3,5004,2505,000 (399HP485HP571HP) 485 average HP
400 ci, 500 ft/lbs @ 4,5005,2506,000 (428HP499HP571HP) 499 average HP
300 ci, 400 ft/lbs @ 5,5006,2507,000 (418HP476HP533HP) 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 3,5005,500)
470ci making 600 ft/lbs @ 4,500 (RPM range 4,5006,500)
470 making 600 @ 4,500 x 3.55 x 2.42 x 4500600 ft/lbs (23,196) 5500575ft/lbs (27,169) 6000550 ft/lbs (28,350) 6500525 ft/lbs (29,317) wildcard 7000500 ft/lbs (30,068)
512 making 650 @ 3,500 x 3.55 x 2.42 x 3500650 ft/lbs (19,544) 4500625 ft/lbs (24,162) 5000600 ft/lbs (25,773) 5500575 ft/lbs (27,169) wildcard 6000550 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 1,2501,500 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 poorflowing 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/#032440moparsixpackdynotestchartjpg
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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