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Just sitting here and thinking about engine designs. I decided to compare a Renesis to "ancient tech" Chevy LS6 engine.
.................................................R enesis Specs...........................LS6 Specs
Dressed Weight (lbs).............................303............. ..........................458
Max Power (hp)............................238 @ 8,500 rpm....................405 @ 6,000 rpm
Power/Weight (hp/lbs)..........................0.78................ ......................0.88
Specific Power (hp/lbs/1000 rpm)...........0.094.............................. ......0.147
Max Torque...................................159 @ 5,500.........................400 @ 4,800
Torque/Weight (ft-lbs/lbs)......................0.52.................... ..................0.87
Specific Torque (ft-lbs/lbs/1000 rpm)........0.095................................. ...0.182
Please excuse my formatting. That aside the LS6 "ancient tech" engine stacks up quite well.
This thread has been edited to reflect the "new" 238 hp spec. Sheesh, we have gone from 260 to 250 to 247 and now 238. It is unknown if Mazda will fess up about torque levels.
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I'm not quite sure I agree. RX-8 tops the LS8 in the hp/weight figure. The rest neither accounts for gearing nor for rev ranges, of which the RX8 has 50% more than the LS6.
You're comparing apples to oranges. The best piston comparison for the renesis would be the s2000 motor. If you're going to compare the LS6 to a rotary, compare it to the R26B.
I think what babylou really is saying is essentially a defense of what he sees as GM, or possibly U.S., engineering. While I don't like entering into nationalistic arguments, I'd have to argue against him anyway. GM's V8's are 'ancient tech' and have less inspiring numbers not because of faulty engineering, but because quite simply economics. Pushrod V8's are cheaper to make = higher profit for GM. There are also peripheral benefits such as cheaper maintenance due to widespread penetration of this particular V8, or in other words, it is traditional.
If you want to point to an example of quality GM engineering, then use the Corvette GTS LeMans race cars as an example.
Sheesh, you guys sure can make some far reaching assumptions out of me posting some simple data. I just thought it was an interesting comparison and am backing neither nor am I making any kind of nationalistic or corporalistic (new word) comparison.
Keep in mind that the average Vette purchaser does not like to run at high engine speeds. If they did an LS6 can be made to run another 900 rpm in street trim for about $100 additional build cost by GM. This would up the power to weight to 1.01, which exceeds the Renesis.
FYI I am not even a power guy rather I am an "add lightness" guy.
yeah, your "Specific Power" metric really well illustrates the difference in the design philosophies: the wankel type is definitely a rev motor, whereas the LS6 has tons of force on tap at all times (as one would expect)...
if we looked at this dimentionally however, (despite the fact that the pushrod V8 is a really compact design) we'd REALLY see how the wankel comes through...
... but as m477 was saying, this is not the BEST comparison of the two technologies: i'd really like to see GM's pushrod V6 (that's in all of their mid-size sedans, like the Grand Prix, Alero, Malibu, etc etc etc...) compared with the wankel... the boys on the Autoweek forum seem to love it to death (i have NO idea why), so i'll see what i can scare up a bit later... i'm at work :D!!
I was thinking that a comparison to a comparable power engine would be good. Here is a comparison with the "super high tech" Honda S2000 engine (F20C):
.................................................R enesis Specs...........................F20C Specs
Dressed Weight (lbs).............................303............. ..........................326
Max Power (hp)............................238 @ 8,500 rpm....................240 @ 8,300 rpm
Power/Weight (hp/lbs)..........................0.78................ ......................0.74
Specific Power (hp/lbs/1000 rpm)...........0.094.............................. ......0.089
Max Torque...................................159 @ 5,500.........................153 @ 7,500
Torque/Weight (ft-lbs/lbs)......................0.52.................... ..................0.47
It seems to me that the S2000 engine does not look as impressive as it used to or the Renesis looks a real sweet. Of course there are a few other metrics that I have not compared that the Renesis would be strong or weak in because I do not have the data. Things like cost, fuel efficiency, CG, size, durability, NVH, reliability, emmissions, etc.
This post was edited to reflect the once again new found (yeah right) power deficit.
Here's a question:
Do torque and horsepower grow exponentially or lineally relative to displacement/size? If it's exponentially, then the comparison doesn't make sense.
Originally posted by vipeRX7 Here's a question:
Do torque and horsepower grow exponentially or lineally relative to displacement/size? If it's exponentially, then the comparison doesn't make sense.
neither... it's not something you can just project so easily: there are more factors to it than just displacement, althought if you're keeping the fundamental design the same, just a little longer stroke/wider bore, then it's linearish...
regardless, there are more than just two factors (hp and torque) to compare regarding engines: dimensional size and "dressed" mass are both also extremely important, i'd say more important than a displacement comparison.
Originally posted by babylou It seems to me that the S2000 engine does not look as impressive as it used to or the Renesis looks a real sweet. Of course there are a few other metrics that I have not compared that the Renesis would be strong or weak in because I do not have the data. Things like cost, fuel efficiency, CG, size, durability, NVH, reliability, emmissions, etc.
:D the Boogdawg and i (i just jumped on his bandwagon) have been saying the same thing for months. :D
Another reason the pushrod V8s aren't going further up the rev range is because at higher RPMs they can experience valve float due to the inherent design of pushrods. A piston hitting a valve is a VERY bad thing!
Originally posted by Supercharger
Does anyone has the spec's of a normally aspirated 20B 3-rotor engine?
If you're trying to make a direct comparison, use the 26b data which I posted to compare to a V-8. A 3-rotor would be a better comparison for a 6-cylinder.
Originally posted by m477
If you're trying to make a direct comparison, use the 26b data which I posted to compare to a V-8. A 3-rotor would be a better comparison for a 6-cylinder.
heh heh, actually, the firing frequency of a bi-rotor means it's the best to compare with a 6 cylinder, and a 3 rotor actually fires similarly to a 9 cylinder... and yeah, the quad rotor is very close to a 12 cylinder.
so a 2.0L 3 rotor'd be very close to a 4.0L V8 in the amount it breathes per revolution, but we shouldn't limit ourselves to displacement alone: it will certainly be short on torque next to the ultimate American V8 the LS6, but could be made equal in power no matter the tune, by revs alone.
in any case, the major advantages in this case would still be the unbelievable compact and light package all that power comes in, more than the inherent simplicity which really takes newcomers to the engine.
Just a reminder, but *in defense of the R26B* the Chevy engine is brand new. Remember that the R26B is 12 years old, so as far as current engines go, we don't know whether a new rotary engine would be superior. After all, how many piston engines 12 years older than the R26B compare with the rotary?
About redlines, I don't know whether Le Mans requires any limit on revs, but the R26B could probably go higher than it does. See the "only 9000 rpm redline" thread for more info about why the Renesis/R26B don't have higher redlines. Remember that wankel himself tested a rotary up to 25000 rpm!
Also, indy engines (as far as I know) would not be as reliable as the R26B. N/A rotaries are renowned for their reliability, especially in racing.
But you're right , at least from those statistics, that the Chevy engine is superior in the ways you mentioned. I just had to give some background to prevent a n00b from reading that and thinking that rotaries are hopelessly inferior :p :D
...remember too that the R26B was an engine designed and tuned to run for 24 consecutive hours around a pounding circuit, with tons of acceleration and deceleration, whereas an Indy track engine runs for what, 3 hours?? (i have no intrest in oval racing, and thus pay little attention to the length of the races)...
now, it's not easy to get a motor to run at those kinds of rpms for any amount of time, but the general cruising of the engine at the highest rpms for most of the race doesn't require the same KIND of tune that the R26B did, where driveability is certainly an issue throughout most of the track... the Indy engine would be optimized for running at max rpm constantly, with the volumetric efficiency peaking right at the highest rpms possible, almost regardless of the engine's behavior at lower rpm.
Even though this thread is basically dead I saw a few errors in my original numbers posted so I have corrected them. The Renesis weight increased from 273 lbs to 303 lbs (according to R&T special RX-8 edition). I also had the Renesis at 260 hp instead of 250 hp. The last error was I had the F20C at 250 hp instead of 240 hp.
Maybe the new F22C numbers will be available soon and we can see if it stacks up better against the Renesis.
Don't knock pushrods as "ancient" technology. The LS6 is seriously one of the most powerful engines for its size. When weight is considered it becomes even more of a masterpiece.
Everyone seems to believe DOHC is the "best" way to do an engine. However, make the LS6 a DOHC design and theres NO WAY it would even come close to fitting inside the hood of the Corvette.
Look at the Cadillac Northstar DOHC V8 side by side with the LS6 (I have) and the LS6 is much much smaller than the Northstar.
Rumor has is General Motors is capable of tuning the LS6 to reach 500hp. Remember, as of now the engine has no variable valve timing, which is what they're working on. When that happens the horsepower should jump significantly.
I used to naively believe that pushrods = old junk. After studying and dissecting several different motors in a lab, I've changed my position. Pushrods are cheaper, more compact, and really don't give up anything but revs and some smoothness to OHC designs.
The LS6 is one of the best motors in the world. No doubt about it.
Originally posted by Jerome81 Don't knock pushrods as "ancient" technology. The LS6 is seriously one of the most powerful engines for its size. When weight is considered it becomes even more of a masterpiece.
Rumor has is General Motors is capable of tuning the LS6 to reach 500hp. Remember, as of now the engine has no variable valve timing, which is what they're working on. When that happens the horsepower should jump significantly.
I used to naively believe that pushrods = old junk. After studying and dissecting several different motors in a lab, I've changed my position. Pushrods are cheaper, more compact, and really don't give up anything but revs and some smoothness to OHC designs.
The LS6 is one of the best motors in the world. No doubt about it.
Precisely why I put the word ancient in quotation marks.
Though I am an admirer of the LS6 engine I doubt GM can make 500 hp with the current displacement and still be production feasible (cost, durability, etc). I bet if 500 hp were easily achievable GM would go ahead and do it.
Also, VVT is only gonna give about 4-5% more power. However, there will also be incremental gains in power throughout the entire rev range, improved fuel efficiency and reduced emmissions due to VVT.
:D!!
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