Graphs: torque in gears / rpm per mph in gears. 2.5L 6-speed auto trans.

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Guest2019C20

Thought these graphs might be interesting to some of you. The dyno numbers are from the stock curve shown on the Racing Beat dyno for the 2.5L engine.

This first graph shows the lb-ft available in each (6-speed automatic) gear, vs the vehicle speed. It visually shows how acceleration drops in higher gears. In this case, I'd downshift to 3rd for a quick pass starting at 65 mph.


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This graph plots engine rpm vs mph, in each of the auto's 6 speeds.

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In 24 hours, I'll be able to experience this first-hand. I'm a little anxious for the time to pass... ;)
 
welcome to the forum!
Looks like an interesting post, but unfortunetly your images aren't showing up.
 
looks like it's definitely good to wind out every gear to the rev limiter (or higher if tuned) for max acceleration with the 2.5L

It would be really cool to overlay the 2.0L (with both the 6MT and 6AT) on there!

other than the pics not embedded I gotta say this is my favorite first post on this forum lol.
 
Yes and an intakentune and exhaust make it better apparently the 2.5 has a big restriction on the exhaust cam. There is an aftermakret one but I'm trying to wait a bit before ai decide if i want to get it.
 
I got 3 HP from a RoadsterSport Q and a tune in my MX-5, too, but stock mine produced ~8 HP more than typical, on a stingy dyno. I'm told the same factory makes the Racing Beat and RoadsterSport mufflers. I no longer think it's worth the money to change the exhaust. It's not the '80s anymore.
 
And your point is?

LOL! The gaps in the gears are too wide. Max. acceleration occurs when the shift is made at the intersection of the wheel torque curve of one gear and the next higher. The next higher gear has more available RPM *and* at least the same wheel torque.

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Unsurprisingly, this H-D only needs 3 gears (1,3,5), but 5 or 6 sells bikes.
 
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Max accel occurs with the system that has the MOST AREA under the curves. You posted a graph for an engine whose torque falls off massively with rpm. A poorly designed engine.

A perfect engine would have a torque curve that was perfectly flat, horizontal. A million gears still wouldn't make those curves intersect.
 
Max accel occurs with the system that has the MOST AREA under the curves. You posted a graph for an engine whose torque falls off massively with rpm. A poorly designed engine.

A perfect engine would have a torque curve that was perfectly flat, horizontal. A million gears still wouldn't make those curves intersect.

Looks like you need a Tesla P100D be happy with torque curves. No tranny either to worry about gears.
 
Looks like you need a Tesla P100D be happy with torque curves. No tranny either to worry about gears.

Can you imagine 500 HP at each wheel, with rotation speeds controlled by the millisecond? Talk about torque-vectoring cornering!

I'd really miss the engine noise, though. I love the way my CX-5 sounds.
 
Max accel occurs with the system that has the MOST AREA under the curves. You posted a graph for an engine whose torque falls off massively with rpm. A poorly designed engine.

A perfect engine would have a torque curve that was perfectly flat, horizontal. A million gears still wouldn't make those curves intersect.

No. Acceleration is determined by wheel thrust (F=ma). Thrust is determined by wheel torque and tire friction.

The "area under the power curve" describes the quantity of *work* done, power times time.

You may want to call the H-D engine poorly designed, and I would fully agree, for other reasons, but its torque curve is typical for auto engines. The perfect engine you theorize cannot exist. Fixed ports in the head will necessarily cause a roughly arc shaped torque curve with torque falling once RPM causes flow to become high enough to be restrictive. The point where pressure drops below atmospheric at the intake valve, for instance. Variable intake ports/systems can help, but just make step changes and perhaps an M-shaped torque curve.

So, a real engine, will make the maximum thrust (acceleration) through all the gears when the torque curves intersect below the redline in the lower gear.
 
So, a real engine, will make the maximum thrust (acceleration) through all the gears when the torque curves intersect below the redline in the lower gear.

What you are literally saying here, is that the CX-5 would accelerate faster, if it's torque was LOWER than the dyno actually measured it. That's insane.

You could argue that if mazda put more, closer gears in the tranny, that the curves might intersect. Or if they put a turbo on the engine, and drastically improved low-rpm torque, that the curves might intersect. But you didn't do that. I guess you just don't have anything better to do?
 
Did you guys the article on the new external combustion rotary in development by mazda?
 
What you are literally saying here, is that the CX-5 would accelerate faster, if it's torque was LOWER than the dyno actually measured it. That's insane.

You could argue that if mazda put more, closer gears in the tranny, that the curves might intersect. Or if they put a turbo on the engine, and drastically improved low-rpm torque, that the curves might intersect. But you didn't do that. I guess you just don't have anything better to do?

LOL. I bet he had closer transmission ratios in mind when he made his statement.

A small gap between gears might actually be better than the gears intersecting for acceleration (especially in an automatic) because the momentum of the engine as it spins down during an up shift.
During a shift, the momentum of the engine gives the car a little extra torque kick, effectively moving the wheel torque up slightly on each up-shift.
 
What you are literally saying here, is that the CX-5 would accelerate faster, if it's torque was LOWER than the dyno actually measured it. That's insane.

You could argue that if mazda put more, closer gears in the tranny, that the curves might intersect. Or if they put a turbo on the engine, and drastically improved low-rpm torque, that the curves might intersect. But you didn't do that. I guess you just don't have anything better to do?

I did not say anything like that. You fail to understand the concept.

What I said, in effect, was that the car would accelerate harder if it did not have an extra bog/pause at each upshift because there was a large step down in thrust (wheel torque) in each higher gear.
 
You can reduce the bog/pause that Colt is talking about by #1 getting a tune. Your car will return throttle much quicker than stock. IN fact you can get WOT shifts with a minimal drop in RPM, and almost no delay if you want to. The other thing is to upgrade to a hardened rubber (hardrace) or Poly (JBR/Corksport) trans mount. The amount of movement during a shift on the OEM mount is bad, especially during hard acceleration or high rpm downshift. Then change out the oem geoturds for some stickier rubber for less slip after a hard throttle on shift.
 
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