What would you rather have? (Dyno chart content)

Two engines, similar WHP. Similar power curves, actually.

Versus

(top power/torque curves)

The one with more torque.

Those curves don't look similar at all. One's a highly modified N/A engine or a centrifugal supercharger, the other is either a big engine or positive displacement supercharged. yes?

I'll take the one with the blower

The one that revs higher, because I'm a kid on the inside.

The one with more area under the curve. Peak numbers get too much attention.

The one with no rust.

Commuter? #2

Fun only car? #1

9000 rpm = more broken parts than 7000rpm, unless be are comparing a B16 Honda and a 502 Chevrolet.

I don't enjoy broken parts.

What are you planning on doing with it?

I'm with Keith, those 2 curves don't look anything alike. I'm guessing displacement vs revs.

Top curve looks a lot like a Honda engine... is the bottom curve a 2.5L NC Miata swap? Am I close?

Oh, and to answer the question: torks. I've been down both roads. I like torks, especially if you're not giving up any horsepower to get there.

Fix the low rev limiter on the top one.

Did something break at 9000 rpm?

Bottom engine, definitely.

Keith Tanner wrote: Those curves don't look similar at all. One's a highly modified N/A engine or a centrifugal supercharger, the other is either a big engine or positive displacement supercharged. yes?

One's a 208whp rotary and the other is a 200whp 2.5l MZR.

I'm seeing a mostly flat torque curve across about 70% of the rev range. The 2.5 has more torque, but since it only revs to 7400 instead of 10,500 it would need 25% taller gearing, so the torque benefit is canceled out. (Horsepower is horsepower)

ProDarwin wrote: Did something break at 9000 rpm?

At 9000 I have the computer add something like 20-25% more fuel so the flywheel and clutch don't come up and say "hi" when it gets slippery. You do not put a rev limiter on a rotary unless you enjoy broken stationary gears.

More info: It would cost me about $3000 to get to point B factoring in the engine, computer, trans, and re-gearing the rearend. But it would be far more emissions friendly (even without a cat, and I'd probably hang a cat on it anyway) and probably easier to quiet down. Fuel economy would probably be a wash.

Rotary counts as "highly modified N/A" I should have assumed rotary given your predilections :D

Whichever chassis is easier to LS swap

It really depends on the application but all else being equal I'd happily give up about 5% in peak HP to gain about 40% in peak torque if the torque curves are both relatively flat. Of course, all else is rarely equal and it's hard to beat a rotary for power density.

patgizz wrote: Whichever chassis is easier to LS swap

My life goals involve driving home and not blowing engines up

I have seen waaaay too many people blow up their LS-swapped RX-7s, or Corvettes or CTS-Vs, at track days, to ever want one of those things in a car that I expect to drive home. Besides, I think they drive like poo, very "numb" power that isn't very modulable. Now if you could maybe make the engine make 300hp but no more than 175-200ft-lb of torque... probably a way to do it in torque management, actually. But then that crank weighs like 45 pounds, need to cut half that weight out so there isn't so much engine inertia.

I think that probably makes the decision for me. There are things you can do to make the Duratec engine's timing chain setup more reliable but in the end, you have a lot of parts in there that are going to want out, and the prospect of holing the block three-six hours from home is a dealbreaker.

Knurled wrote:

Keith Tanner wrote: Those curves don't look similar at all. One's a highly modified N/A engine or a centrifugal supercharger, the other is either a big engine or positive displacement supercharged. yes?

One's a 208whp rotary and the other is a 200whp 2.5l MZR. I'm seeing a mostly flat torque curve across about 70% of the rev range. The 2.5 has more torque, but since it only revs to 7400 instead of 10,500 it would need 25% taller gearing, so the torque benefit is canceled out. (Horsepower is horsepower)

Yeah, once you re-gear the car so that it's got the same redline with the MZR, there's not going to be much difference. That's why the power curve is on there.

Personally, I like turbo motors with a big healthy slug of torque in the midrange. Something like this:

I kinda like this shape

I should have figured this was a test to see if we were cool enough to pick the rotary

I disagree that the LS engines are numb and difficult to modulate, I have no difficulty dealing with the above torque in a 2400 lb car and 225 series tires. They do always sound understressed instead of ready to explode, but that's just aural. Put a good cam in it and the throttle response is nice and sharp. You also have to take care of the oiling (a problem with a bunch of stock applications), but every engine needs some attention to be 100% track reliable when it's outside the normal scope.

But they aren't weird enough to be cool

I'll take the one that handles better, since they both have sufficient power and tq..

I can't get to image hosting, because work.

I just excel-mathed both of those curves. I changed the gearing so they have equivalent top speeds in the 2nd gear. I then graphed acceleration.

The MZR powered car will out-accelerate the Rotary car by a significant margin across the entire gear, except for about a 10mph span where the rotary offers a tiny advantage. In the meat of the curve, the MZR advantage is substantial (>10% accel).

edit: google photos working temporarily...