bambam

2 cars - same car, same driver, same weight, same gearing, same dyno....now for the fun part...

Both engines are naturally aspirated and dynoed on the same day, same time ...only variable is the engine.
Engine #1: makes peak hp at 8400 rpm, 268whp.
Engine #2: makes peak hp at 9600 rpm, 253whp.

In the 1/4, who wins? Consider everything else about suspension, weight, gearing, chassis, and driver are the same.

Lets hear who wins, and your theory on why.

Takabell

Obviously the car making more power earlier, all else being equal...trq, gearing etc

raverx3m

iTrader: (1)

the one that can carry out RPMs longer with same gearing . beeing at peak power.
while the other one shifts dropping it to the begining of powerband.

raverx3m

iTrader: (1)

LS vs gsr motor ls power band is almost similar to GSR and then it has to shift. gsr has another 1000 rpm to go before shifting

ddd4114

Which engine makes more average power in the powerband?

SHRUGS*

iTrader: (1)

really

raverx3m

iTrader: (1)

the one that chuck norris drives lol

bambam

The higher you rev, the furthered distance the vehicle covers in the same amount of time. People are so hung up on peak numbers all the time.

ddd4114

For the same gear, not the same time.

An engine that revs to 9000 rpm but only makes 200 whp will be a lot less capable than one that only revs to 7500 rpm but makes 300whp.

All else being equal, the engine that makes more average power in the powerband will be faster. If the average power numbers are close, then things like transient response and inertia come into play.

GhostAccord

Saying that the higher rpm engine covers a longer distance in the same amount of time is a bit much. What about the 6500 rpm that it has to go through before it hits it's power band? Your not going very far very fast with the engine spending time out of it's power band. Without the lower end power, using longer gears isn't really of any benefit to a high rpm engine.

There is a reason that the higher RPM engines usually have shorter gearing. It's so they can get to there peak RPM ranges quicker and not get left behind.

This could be a reason why so many people tend to dwell on peak numbers and power bands so much! They tend to be important when deciding what gear ratios would suit the engine/chassis the best.

bambam

In the 1/4 your car should never see below 6500 rpm though...but maybe a fraction of a second on launch.

bambam

Rpms are important. One full rotation of your overall tire height will cover X distance. If X distance is being covered at a faster rate (rpm's), where does that leave you?

ddd4114

That's just gearing differences. The engine is still responsible for accelerating the wheels to that speed. The more powerful the engine, the faster that speed can be achieved.

What would be faster, a stock RX-8 or an LS1-swapped RX-8? The LS1 makes more power but is heavier, has more inertia, and has a much lower redline than the rotary engine, so do you think it would be slower?

bambam

In that case no...but for the example i posted above? Same everything, but engine 1: 268@8400 or engine 2: 253@9600?

bambam

My money would be on engine 2. My point is, people get so hung up on peak whp numbers and forget application.
Rpms do have an impact on how fast you can cover the 1/4. Forget my engine comparison...bad example.
Lets go with both engines make same peak whp but one at 8400 and the other at 9600, all other factors identical, who crosses the finish line first and why?

ddd4114

Physics doesn't change with the scenario. All else being equal, more average horsepower with the same weight means the car will be faster. It doesn't matter if peak power occurs at 3000 rpm or 9000 rpm. You just gear the car appropriately.

If all else is equal and the general shapes of the torque curves are the same, my money would be on engine 1.

ddd4114

If all else is truly equal, then it would be a pretty close race...

97mm_EH3

Without knowing gear ratios and tire diameters, you have squat.

Which ever car goes through the traps at peak RPM's has the best chance to win.
Both those engines would want different gear box ratios.

GhostAccord

My money is on engine 1 as well.

bambam

acceleration = engine_torque x 2 x pi x engine_speed / (velocity x mass)

Excellent article:
http://vettenet.org/torquehp.html

raverx3m

iTrader: (1)

so does anyone actually know who won?

mike703

car 3 mine!!

bambam

This answer is right. Gearing and tire sizes (theoretically an extension of the transmission) would need to be known. It would be a close race. Also, the full usable rpm range graph would need to known (6500rpm+).

My point was to establish a thought process on how rpms can positively affect 1/4 mile times and that less power at higher rpm CAN make for a faster car, which can be seen in the formula i posted above....i just failed at creating a viable example.

NAH2B

any drag racer who is good at what he does knows rpm=et

i will take the car making peak @ 9400rpm

alot of people with limited experience theorize making peak power earlier @ a lower rpm is better because you reach your peak power sooner. sounds good on paper but its wrong.

97mm_EH3

Would that be with a Prelude gear box, a LS box, or a 4.9 "R" box? How about a stock Accord box, 15 inch wheels, and peak @ 9400? Maybe an automatic?