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I've heard a bunch of people say you have to feel a rotary engine to understand. I've never had the opportunity to drive an Rx7. So what's the big deal? Is there a noticable diffence between the feel of a piston engine vs. a rotary? How does it feel different?
The only thing I can think of is that most of power comes in a higher RPM right? But that's not really any different than a lot of 4 cyl VTEC/VVT engines.
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Speaking of sound...does anybody know of a site with samples of what a rotary engine sounds like? I've done some searches and visited the sites that came up in the results, but the samples I found weren't very good.
The sound of the engine is important to me when considering a car purchase, and I've been told rotaries have a very distinctive note that I'm curious to hear. Any suggestions of sites I could visit would be appreciated.
There is no real powerband "hit"(turbos excluded). It spins like an electric motor to the structural limits of the rotors and housings themselves. The feel(vibration or lack of?) is similar to most modern V-6 engines, only it never falls off the powerband. As the rpm climb, the more efficient and more power it makes, with only 3 moving parts. It loves and lives to rev.
This is the 1991 LeMans winning 4-rotor taking it easy at Laguna Seca.
by no torque, I mean that there is little power when the engine is under 4,000 RPMs. The engine isn't highly responsive until the engine revs are up high... as opposed to my Impreza now, with a 2.5L boxer 4, the thing can be at 2,000RPMs, and have almost as much power as there is at 5,000RPMs
I'm trying to attach a file like you did for the sound and dyno tests, but can't figure out how to do it. I have an RX-7 dyno test that will blow you mind. Can I email it to you, and have you post it on the forum?
No it's not. The LeMans car - even in qualifying trim - had a max redline of about 7500rpm with a race redline of either 6750 or 7000 (cant remember) it did not rev high, I imagine because of ecc. shaft flex. It sounds cool because:
a) It's a 4 rotor
b) It's a PP
Originally posted by rpm_pwr No it's not. The LeMans car - even in qualifying trim - had a max redline of about 7500rpm with a race redline of either 6750 or 7000 (cant remember) it did not rev high, I imagine because of ecc. shaft flex. It sounds cool because:
a) It's a 4 rotor
b) It's a PP
Well, it's 8500 - 9000 rpm, I stand corrected. Sorry about that, I just automatically think of race rotaries (13b) reving to 11k +, and failed to remember we're talking about the 26b here.
Rotaries are revvers. If you want to short-shift it like a Mustang GT or something, you'll be disappointed with the performance. Torque is supposed to be around 155 ft lb., 90% available between 3000 rpm - redline.
Originally posted by eelkmoore it better have lots of torque...
Ok. I can see that this is going to come up a lot. So I'm just going to cut-and-paste. If I have to use it too much I'll do up some pretty pictures/graphs to go with.
As probably the only person on the forum with a dual-axis accelerometer kicking around I think I should clear a few things up that some people (buger etc) have touched on:
Your accelaration graph is *PROPORTIONAL* to your torque graph for in gear acceleration
The proportionality constant is
= (tyre radius * gear reduction) / mass
The important factor here is gear reduction (diff ratio * current gear ratio). In other words you can double your acceleration (wind resistance ignored) by doubling you diff ratio. But by doing this you can detract from the usability of the car by reducing the max speeds in each gear.
Now here is the important bit:
ENGINES WITH HIGHER OPERATING RANGES CAN USE HIGHER RATIO DIFFERENTIALS FOR THE SAME AMOUNT OF DRIVABILITY. THIS MULTIPLICATION EFFECT GIVES MORE GROSS TORQUE AT THE REAR WHEELS GIVING MORE ACCELERATION END OF STORY.
Torque spread only affects how wide you can spread the gear ratios. It does not matter where in the RPM range the spread is because this can be traded with diff ratios rather it is the RPM range that affects how close you can make the ratios. So a car with power from 5000rpm to 8000rpm can have ratios just as wide as a car with power from 2500 to 5500 with the added advantage that it can run a higher diff ratio to increase acceleration.
car a makes 200lb.ft from 3000 to 6000 with a 4.11 rear (FD?)
car B makes 150lb.ft from 5500 to 8500 with a 5.82 rear (rx8?)
car a has 822rw lb.ft GROSS
car b has 873rw lb.ft GROSS
but here's the catch - both cars have identical speeds in each gear! It gets better the higher torque numbers give a higher top speed as well!
With all this messing around with mulitpliers, dividers, NET torque gross torue isn't there an easier way? Yes. It's the often neglected POWER curve. Power at the flywheel = power at the wheels - gear losses. So you can simply overlay two RWHP graphs with shift points marked to figure out which will accelerate harder. It's a lot easier. That's why we can't bench race the rx-8 yet - because there is no power graph yet. Although if the torque spread stays that good then it will be ONLY the diff ratio stopping the rx-8 from being an FD rx-7 killer.
The feel of a rotary is like no other. First there is no vibration, in my old 1st gen RX, when it was properly tuned, you could hardly tell when the engine was on. There is no vibration whatsoever. As far as torque, I never felt like it lacked it. By no means is it a big block V8 from Detroit, but it has enough. Also, Mazda always does a great job with the gearing.
I cannot wait to get one.....