Horsepower and Displacement
 

I've been curious for a while about just what it is that makes rotaries special, the Renesis in particular. It's light but relatively powerful; it doesn't get the greatest gas mileage, but certainly not the worst; it's not a torque monster, but it's got a lot of power/weight ratio; and we like it, but maybe we're not exactly sure why.

I think one of the things that make the Renesis special is the amount of power we get for the engine displacement. I mean, 238(ish) hp out of 1.3 liters displacement doesn't come along every day. So I did a little spreadsheet magic to do some comparison. I selected a few sports/sporty cars and compared engine type, size (liter displacement), HP, EPA city/highway guesstimates, and calculated the HP per Liter of displacement. The HP/Liter is where I found a sizeable difference between engines.

Running down the right-hand column, notice that the lowest HP/Liter comes from our own Viper, that iron beast icon of American musclehood. The more popular Corvette is a bit higher on the scale, as are the benign SLK and TT and the more sporty 350Z and Boxter. Moving up the scale a bit more we eventually get to the more impressive figures of the STi and Evo.

And just where does our RX-8 fit in the HP-to-displacement lineup? At 183 horsepower per liter displacement, we're right at the top, with an 86% higher HP-to-displacement ratio than the average for the pack. Pat yourselves on the back.

But not so fast! Remember how our resident whiners constantly remind us that our mileage sucks so badly? Let's see... compared to the average EPA city and highway estimates, the RX-8 comes out ... about average among the city figures, and 2% lower than the average highway figures.

So, for the highest horsepower per liter ratio of the bunch, we get a car with marginally lower average mileage that goes around an autocross course and a track like a bat outa hell. Color me happy.

:D:

Devil's advocate: a number of people would debate that the car is actually a 1.3

I'm confused by your post. He says it's a 1.3L

Maybe I'm missing something.

yes, our displacement is 1.3 liters for one revolution of the crankshaft, whereas, for example, a honda prelude motor is 2.2 liters, but for 2 rotations of the crankshaft, so technically, to compare apples to apples, our motor is technically a 2.6 liter.

The Renesis has a 1.3 liter displacement.

If you want to compare it to piston engines you should consider it a 2.6. If you don't your spreadsheet is little more than smoke and mirrors.

Not this again :rolleyes:

Hey, at least I didn't bring up the fact that the EPA estimates are really off for the RX-8 compared to most other cars on the list and that the 238 (even 232 which is what the RX-8 is rated at now) is quite generous. It's also curious he left off the S2K from the list. :wavey:

Thats like saying the rotary is accually equal to 6 cylinder engine because of three chambers per rotor.

Yea I know, I meant 'not this thread' again. Here comes a couple pages about crankshaft revolutions.

Gotcha :)

Yes, 2.6 as it pushes that amount of volume. I do believe the Europeans consider it 2.6

I think the renesis is closer to a 6 than a 4, but in a package smaller than the 4. It's still an impressive powerplant. Without it I wouldn't have bought the rx8.

almost 800whp on a 1.3l 13b-rew with GT42/ what do you think about that?


^ oh yeah and it runs low 7's on the 1/4. and... its a RX-3 lol.

when it won the engine of the year award, it was awarded for being a 2.6L engine

not according to my mpg

Funny thing about displacements. For every revolution of the crankshaft, an RX-8 pumps 1.3 liters. However on a 4 stroke like the Nissan 350Z, every rotation of the crankshaft displaces 1.75 liters.

When we raced shifter karts we ran 2 stroke CR125's - 125cc displacement per revolution. As the later 4 strokes began to show up to achieve equal power they had to be 250cc. Both peak out at about 44HP.

Fuel mileage is still a bit weak on a rotory. That probably won't change much until someone gets clever and finds a way to recover some of the wasted heat.

Same here, 20 mostly city with a heavy throttle foot...not as bad some make it out to be.

As for the 2.6L BS, I'm still waiting for someone to show me a 2.6L 6 cylinder that weighs about 250 pounds and sits about 6 inches directly behind the centerline of the front wheels. Or show me a four that is so light and compact.

...didn't think so.

It may not be a 1.3, but it's no 2.6. Its a rotary, you won't find anything smoother or more distinctive.

Hp/L is a joke for engine comparison anyway. Hp/lb(kg) is a much more "real world" useful value for determining the "greatness" of an engine (go-go LS series :D: ). Hp/L is just there to make S2000 owners feel special... :wavey:.

The thing that makes the rotary special, is not hp/L or hp/lb, it's hp/cubic feet...its small packaging allows better placement in the car.

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And I equal or better the EPA mpg estimates on a regular basis as well.

According to the surveys conducted on this forum, the EPA estimates are about as accurate for the 8 as for any other auto. And if you're so curious about the S2000, why not post the info? It's not like it's a secret. :rolleyes:

Nope, we consider it a 1.3lt (1308cc) engine, like it's supposed to be ;)

And maybe the HP/Kg means more in the "real world", but also HP/lt or max RPMs are very strong indicators about the technology level of an engine. Take the Renesis or the F20, and compare them to the PSA 2.0lt or 2.2lt engines, or your own (USDM) equivalent 2.5lt or even 3lt engines. Guess which engines come out on top :rock:

High rev engines are great, in the right car. And high revs are the only reason you get such high hp/L values. Ever seen a 60's era cammed out V8 revving in the 9-10K range. That's hp/L. Variable intake timing makes it possible in modern cars, and that's not new technology, it's been around for a long time (first used on a JDM rotary in the early 80's, I believe). Ever notice how hp/L people always refuse to acknowledge factory forced induction cars, claiming it's not a fair comparison...

The 7.0L LS7 is pretty low on the hp/L list. But it has more R&D and technology in it than any rotary or F20/22C, K series, etc. And it's not much heavier than the Renesis or F20, and lighter than many OHC V6s. It's not nearly as tall, so sits lowere in the car (the case for all pushrod motors). Plus you don't have to rev it to the sky to get anything out of it, even though it revs to 7k+. Hp/L doesn't tell me a single thing about an engine other than whether it revs high or not (excluding FI cars).

And in the engine of the year competitions, the Renesis was in the 2.6L category, I believe.

Guys, I made a spreadsheet of redundant threads per topic and I found that there are actually only 13 original threads in this entire site. Pat yourselves on the back.

All I'm concerned with is that the Renesis is a huge step in power vs. the past 13B engines without increasing displacement. (I'm not counting porting, just OEM vs. OEM)

Also, let's take another comparison of the 3.5 Z VQ engine vs. the Renesis. This is just a laymans example, but the last 300ZX was Naturally Aspirated 3.0 liter at ~220hp or 73.3hp per liter. The last 13B was 2.6 liters at ~160hp NA or 61.5 per liter. Nissan rates the current VQ 3.5 liter at 300hp or 85.7 per liter. Mazda now rates their same displacement engine at 232hp or 89.2 per liter.

In other words, in a comparative time, Mazda has produced more per liter than Nissan and severely cut emissions in the same packaging size. To me, this is something to be very happy about.

As you said, HP/Lt and max RPMs are somewhat related (since we are not talking only about N/A in here). BUT, high RPM engines are obviously more R&Ded, and certainly have better materials, since these engines have smaller tolerances, higher linear speeds of their components, and need far better control (mechanical and electronical) of their various bits and pieces. Thus, they need a higher level of research, materials, and manufacturing, in order to be as strong as their low-RPMs siblings ;)

Compare the latest 5.0lt V10 powering the M5, and *every* 5.0lt out there (be it US, EU or JDM). The fact that this engine is among the fastest concerning piston linear speed although it's a very sizable engine (displacement) clearly shows that this engine is far superior to everything before it. Notice how I haven't even mentioned its HP/lt output.....