Reciprocating versus rotary engines
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Re: Reciprocating versus rotary engines
Originally Posted by OldSStroker
New, I beg to differ.
The LS series (GenIII and beyond) engines required completely new tooling as well as design and development. GM could have gone SOHC or DOHC as Ford chose to do with their Mod, but after lots of R & D, they decided that a new OHV V8 engine was a BETTER way to go for both cars (minority) and trucks (majority) that it would be used in. Better meaning lots of things including performance, cost, durablility, etc. Whether or not the LS engines do a better job than the Ford Mod is another discussion. I don't think torque/power output is a problem, nor is rpm.
I loved it when the pushrod CTSV racers had their rpm limit dropped from 7900 to 7000 after the cleaned up at Sebring in '04. Of course they had a major advantage over the DOHC rev machines from the competition; they made 5.7 L the good way by using the block form the not-then-released LS7 with a 4.8L crank and the LS7 heads. Nice beta test for the LS7.
GM's DOHC engines, the 12 year old Northstar and the Vortec 4200, 2500, 2800 family do pretty much what they are meant to do. The 4-5-6 family makes just about the same hp/cube and torque/cube as the LS2. They have 90% of max torque from converter stall to WOT upshift which makes them very driveable. The Blown 'Star makes 469 hp from 268 cubes which is about 15% better in grunt/L than the 500 hp Blown Ford GT. The problem is that DOHC 4V V8's not only have more parts than OHV pushrod 2V, but they are heavier and have a higher center of gravity. Every pound slows acceleration, but also decreases lifetime fuel economy. I find it ironic that the current Cadillac Northstar runs on 87 to save the 'wealthy' Cad buyer $.20/gallon or so. Same power as when it used 91.
Some of the reason for DOHC is marketing. If German high-end cars (BMW, Merc, Audi) have DOHC 4 and 5-valve engines, you need the same to entice their buyers to buy your non-German, non-Japanese "Bimmer". Or so goes the logic. Of course the pushrod CTSV grabbed a few who actually wanted to go fast.
DC could easily have gone DOHC with their new V8s. They have tons of Mercedes experience and $ behind them, but they, too chose to use 2V pushrods in the Hemi. Here's a marketing case where "Hemi" blows OHC out of the water, and is cheaper to build & maintain over it's lifetime than an equivalent DOHC. DC did a great job there. Well, maybe more C than D.
How about this: by using larger displacement, with DOD thrown in, you can get the fat, flat torque curves as well as good mpg and have a lighter, cheaper-to-build engine that's just as technologically advanced as a DOHC which spins higher. Nice for trucks, and not all that shabby for a car. I really like 70 mph cruising below 2000 rpm, and the boot in the rump from 6 L. When they are looking at my tail lights, does the DOHC really matter?
Sometimes simpler can be better, sometimes not. It depends on how well you do it.
The LS series (GenIII and beyond) engines required completely new tooling as well as design and development. GM could have gone SOHC or DOHC as Ford chose to do with their Mod, but after lots of R & D, they decided that a new OHV V8 engine was a BETTER way to go for both cars (minority) and trucks (majority) that it would be used in. Better meaning lots of things including performance, cost, durablility, etc. Whether or not the LS engines do a better job than the Ford Mod is another discussion. I don't think torque/power output is a problem, nor is rpm.
I loved it when the pushrod CTSV racers had their rpm limit dropped from 7900 to 7000 after the cleaned up at Sebring in '04. Of course they had a major advantage over the DOHC rev machines from the competition; they made 5.7 L the good way by using the block form the not-then-released LS7 with a 4.8L crank and the LS7 heads. Nice beta test for the LS7.
GM's DOHC engines, the 12 year old Northstar and the Vortec 4200, 2500, 2800 family do pretty much what they are meant to do. The 4-5-6 family makes just about the same hp/cube and torque/cube as the LS2. They have 90% of max torque from converter stall to WOT upshift which makes them very driveable. The Blown 'Star makes 469 hp from 268 cubes which is about 15% better in grunt/L than the 500 hp Blown Ford GT. The problem is that DOHC 4V V8's not only have more parts than OHV pushrod 2V, but they are heavier and have a higher center of gravity. Every pound slows acceleration, but also decreases lifetime fuel economy. I find it ironic that the current Cadillac Northstar runs on 87 to save the 'wealthy' Cad buyer $.20/gallon or so. Same power as when it used 91.
Some of the reason for DOHC is marketing. If German high-end cars (BMW, Merc, Audi) have DOHC 4 and 5-valve engines, you need the same to entice their buyers to buy your non-German, non-Japanese "Bimmer". Or so goes the logic. Of course the pushrod CTSV grabbed a few who actually wanted to go fast.
DC could easily have gone DOHC with their new V8s. They have tons of Mercedes experience and $ behind them, but they, too chose to use 2V pushrods in the Hemi. Here's a marketing case where "Hemi" blows OHC out of the water, and is cheaper to build & maintain over it's lifetime than an equivalent DOHC. DC did a great job there. Well, maybe more C than D.
How about this: by using larger displacement, with DOD thrown in, you can get the fat, flat torque curves as well as good mpg and have a lighter, cheaper-to-build engine that's just as technologically advanced as a DOHC which spins higher. Nice for trucks, and not all that shabby for a car. I really like 70 mph cruising below 2000 rpm, and the boot in the rump from 6 L. When they are looking at my tail lights, does the DOHC really matter?
Sometimes simpler can be better, sometimes not. It depends on how well you do it.
I was NOT trying to argue that DOHC engines are better, or have more potential, or anything like that. What I was trying to say is that companies tend to stick with what they know, which you essentially proved by your statements. Even if GM re-tooled to make a new OHV motor, the fact is that is what they had the most experience with and what they had proven variables to work with. Companies don't like to change when what they have is working. Heck, look at how many teething pains the mustang went through when they went OHC.
Again, this thread was not meant to be a "this" is better than "that" thread. Although the title does lead one to believe that, the first post clarifies it a little more I think.
So let's see if we can bring this thread on-topic. It's not a debate as to why a OHV piston engine is better than a rotary, or DOHC, or vice versa. It's a question about the current weaknesses/strengths of the rotary engine, and what could/should have been different with more development time/money.
So I'll start. If someone like GM would have stuck with the rotary, here are some things that I think may have been resolved:
1. Sealing surface materials. Mazda has made some great strides on their own with coatings for the housings etc, but I think with more minds looking at it there would be even better coatings available today.
2.Weight. Although the rotary is pretty light, mazda still uses iron end and center housings with aluminum rotor housings. I think with more R&D coming from different companies, those iron parts could be aluminum or something else more weight-effecient, bringing the HP to weight ratio up more.
3.Intakes. One of the effects intake air has in a rotary is very strong return pulses once the intake port is closed by the rotor. Mazda uses this as an almost "supercharging" system to force air into the ports that are open at the time. With more R&D, I think a variable-lenght intake track would be possible, as well as more effecient design for increased throttle response and fuel economy.
I'll start with those.
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Re: Reciprocating versus rotary engines
Originally Posted by newby
Again, I think you're misconstruing my point.
....
If someone like GM would have stuck with the rotary, here are some things that I think may have been resolved:
1. Sealing surface materials. Mazda has made some great strides on their own with coatings for the housings etc, but I think with more minds looking at it there would be even better coatings available today.
2.Weight. Although the rotary is pretty light, mazda still uses iron end and center housings with aluminum rotor housings. I think with more R&D coming from different companies, those iron parts could be aluminum or something else more weight-effecient, bringing the HP to weight ratio up more.
3.Intakes. One of the effects intake air has in a rotary is very strong return pulses once the intake port is closed by the rotor. Mazda uses this as an almost "supercharging" system to force air into the ports that are open at the time. With more R&D, I think a variable-lenght intake track would be possible, as well as more effecient design for increased throttle response and fuel economy.
I'll start with those.
....
If someone like GM would have stuck with the rotary, here are some things that I think may have been resolved:
1. Sealing surface materials. Mazda has made some great strides on their own with coatings for the housings etc, but I think with more minds looking at it there would be even better coatings available today.
2.Weight. Although the rotary is pretty light, mazda still uses iron end and center housings with aluminum rotor housings. I think with more R&D coming from different companies, those iron parts could be aluminum or something else more weight-effecient, bringing the HP to weight ratio up more.
3.Intakes. One of the effects intake air has in a rotary is very strong return pulses once the intake port is closed by the rotor. Mazda uses this as an almost "supercharging" system to force air into the ports that are open at the time. With more R&D, I think a variable-lenght intake track would be possible, as well as more effecient design for increased throttle response and fuel economy.
I'll start with those.
You say that if GM or others helped out the rotary could be the engine of choice now. Could be, but noone thought it was the correct move, or at least they were not willing to commit the money, which is the thing that drives it.
You say it's because they stick with what they know. I say it's because they didn't see a future for the rotary that was even equal to that of the recip, given all the restraints.
You don't appear to be an engineer, Newb, but you point out some of the inherent problems with the rotary, and you think they could be fixed. Yep, they probably could, but would that make it a better, or even equal candidate than the recip? Again, those folks who make the decisions and spend the money evidently don't think so.
If Ford went thru teething pains with the MOD, it wasn't because it was an OHC. Any new project has teething problems. Some folks just resolve them before they start selling them. Case in point would be the Vortec 4200, or the Hemi.
Explaining why someone else did or didn't decide to do something is difficult for folks not directly involved in the decision making. I wasn't involved in the rotary decision making process by any stretch, but I was a little closer than perhaps other posters were, and some of my friends were even closer. The same applies to the LS engines. The decision to keep the cam in the block wasn't that "we've always done it this way" but rather that they decided it was better overall for their goals. Nine years into selling them, that seems to have been a fairly good decision.
Obviously we disagree, but I appreciate your position. No offense intended, but I think that it may be a bit naive.
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Re: Reciprocating versus rotary engines
Originally Posted by OldSStroker
Newb, almost anything is possible given enough time and money. The question boils down to why or why not do it. I say that all the OEMs save Mazda decided rotary wasn't and still isn't the way to go. Mazda won't commit more than a car or two to rotary, not the whole line. They even tried a Miller-cycle engine for a short time in one model.
You say that if GM or others helped out the rotary could be the engine of choice now. Could be, but noone thought it was the correct move, or at least they were not willing to commit the money, which is the thing that drives it.
You say it's because they stick with what they know. I say it's because they didn't see a future for the rotary that was even equal to that of the recip, given all the restraints.
You don't appear to be an engineer, Newb, but you point out some of the inherent problems with the rotary, and you think they could be fixed. Yep, they probably could, but would that make it a better, or even equal candidate than the recip? Again, those folks who make the decisions and spend the money evidently don't think so.
If Ford went thru teething pains with the MOD, it wasn't because it was an OHC. Any new project has teething problems. Some folks just resolve them before they start selling them. Case in point would be the Vortec 4200, or the Hemi.
Explaining why someone else did or didn't decide to do something is difficult for folks not directly involved in the decision making. I wasn't involved in the rotary decision making process by any stretch, but I was a little closer than perhaps other posters were, and some of my friends were even closer. The same applies to the LS engines. The decision to keep the cam in the block wasn't that "we've always done it this way" but rather that they decided it was better overall for their goals. Nine years into selling them, that seems to have been a fairly good decision.
Obviously we disagree, but I appreciate your position. No offense intended, but I think that it may be a bit naive.
You say that if GM or others helped out the rotary could be the engine of choice now. Could be, but noone thought it was the correct move, or at least they were not willing to commit the money, which is the thing that drives it.
You say it's because they stick with what they know. I say it's because they didn't see a future for the rotary that was even equal to that of the recip, given all the restraints.
You don't appear to be an engineer, Newb, but you point out some of the inherent problems with the rotary, and you think they could be fixed. Yep, they probably could, but would that make it a better, or even equal candidate than the recip? Again, those folks who make the decisions and spend the money evidently don't think so.
If Ford went thru teething pains with the MOD, it wasn't because it was an OHC. Any new project has teething problems. Some folks just resolve them before they start selling them. Case in point would be the Vortec 4200, or the Hemi.
Explaining why someone else did or didn't decide to do something is difficult for folks not directly involved in the decision making. I wasn't involved in the rotary decision making process by any stretch, but I was a little closer than perhaps other posters were, and some of my friends were even closer. The same applies to the LS engines. The decision to keep the cam in the block wasn't that "we've always done it this way" but rather that they decided it was better overall for their goals. Nine years into selling them, that seems to have been a fairly good decision.
Obviously we disagree, but I appreciate your position. No offense intended, but I think that it may be a bit naive.
As for being "equal" to a recip, I don't see why not. There's a reason so many sanctioning bodies don't have a class for 3-rotor motors, there's just no way to fairly match them up with an "equivalant" recip motor.
You could even fix fuel economy issues (and some are experimenting with this) and increase power output by going to a direct-injection type engine. With a direct-injection type system, you wouldn't have to saturate the intake charge as much as current rotaries have to, so you'd improve fuel economy, and there would be no gas being pulled into the exhuast out of the intake port so emissions would also improve.
I take no offence to you saying I may be a bit naive, but I also think you (although you obviously are very smart) are also being slightly naive. You're only reasoning so far that the rotary CAN'T do something or couldn't be equal to a recip is the fact that the big automakers decided not to research it. Basing your argument on a decision made 30 years ago with technology not even close to what we have today is not really fair.
Again, if you have an engingeering issue with the engine, I can understand that. But just saying that because 30 years ago automakers decided it wasn't feasible at the time doesn't sit well with me, I guess I always just have to question why. If you look at what mazda by themselves have done in the timespan they've had the rotary, then you look at how much more time piston motors have had, why wouldn't the rotary be equal with the same time investment? And again, not basing it off a 30 year old decision made mostly for financial reasons, but from an engineering standpoint.
And again, I don't take anything personal, I have no vested interest in this conversation as I don't own any mazda stock or anything like that
I just like playing the devils advocate I guess 
And this discussion has been very good so far I think.
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Re: Reciprocating versus rotary engines
I've exhausted my ammo on this one, Newb. I guess Mazda is backed into a Catch-22. They can't fix the problems because there is not enough volume to find the "easy fix", and there is not enough volume because of the problems. I'm not convinced that is how the world works, but it may.
How about we go on to transmissions, like why not use CVTs on everything and not waste money on developing 6 speed automatics with the same old planetary gearsets that pre-date the model T Ford? I know, we've always done it that way.
How about we go on to transmissions, like why not use CVTs on everything and not waste money on developing 6 speed automatics with the same old planetary gearsets that pre-date the model T Ford? I know, we've always done it that way.
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Re: Reciprocating versus rotary engines
Originally Posted by OldSStroker
I've exhausted my ammo on this one, Newb. I guess Mazda is backed into a Catch-22. They can't fix the problems because there is not enough volume to find the "easy fix", and there is not enough volume because of the problems. I'm not convinced that is how the world works, but it may.
How about we go on to transmissions, like why not use CVTs on everything and not waste money on developing 6 speed automatics with the same old planetary gearsets that pre-date the model T Ford? I know, we've always done it that way.
How about we go on to transmissions, like why not use CVTs on everything and not waste money on developing 6 speed automatics with the same old planetary gearsets that pre-date the model T Ford? I know, we've always done it that way.
lol Was that a shot at me? Come on now....
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From: Las Vegas/Pahrump, NV
Re: Reciprocating versus rotary engines
Originally Posted by newby
1. Sealing surface materials. Mazda has made some great strides on their own with coatings for the housings etc, but I think with more minds looking at it there would be even better coatings available today.
Originally Posted by newby
2.Weight. Although the rotary is pretty light, mazda still uses iron end and center housings with aluminum rotor housings. I think with more R&D coming from different companies, those iron parts could be aluminum or something else more weight-effecient, bringing the HP to weight ratio up more.
Originally Posted by newby
3.Intakes. One of the effects intake air has in a rotary is very strong return pulses once the intake port is closed by the rotor. Mazda uses this as an almost "supercharging" system to force air into the ports that are open at the time. With more R&D, I think a variable-lenght intake track would be possible, as well as more effecient design for increased throttle response and fuel economy.
1. Stricter smog regulations.
2. Low sales numbers.
Those 2 provided the ultimate catch-22 for the development of the rotary. Fortunately for the rotary it was given a 2nd chance a few years ago, but once again the current incarnation is still in the "let's test it and see how it does" stages.
If the RX-8 sales do well then Mazda will be able to devote more time/resources into resolving the issues with the rotary. As for the big three ever resuming their development on the rotary, I doubt it. They will see more gains for the dollar in alternative fuel development.
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From: Jacksonville, FL
Re: Reciprocating versus rotary engines
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From: Virginia beach
Re: Reciprocating versus rotary engines
Well since this topic is going south, let's move onto what is rotary-inspired: the QUASITURBINE ENGINE
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From: Redmond, WA
Re: Reciprocating versus rotary engines
Originally Posted by RussStang
I have heard a 5 rotor engine in a drag car in a video I saw. That thing sounded quite nasty, and made 500 hp all motor.
If you think (or know) about how a rotary engine is assembled, you'd understand the difficulty of joining three eccentric shaft sections to build a 5-rotor engine.
Originally Posted by JakeRobb
A two-rotor makes SIX pulses per revolution of the crank. Three from each rotor. That's the same as a V12, not a V6.
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From: Redmond, WA
Re: Reciprocating versus rotary engines
Originally Posted by Maldo
Check out this web site about Rotary engines
http://www.rotaryengineillustrated.com/re101.php
Thread Starter
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From: Exton, Pennsylvania
Re: Reciprocating versus rotary engines
Originally Posted by jimlab
I think you mean 3-rotor, since 4-rotor engines are as rare as honest politicians and in 8+ years of owning an RX-7, I've never yet heard of a 5-rotor engine... not even from the rotary crazies in Puerto Rico or Australia.
No, I mean a 5 rotor engine. It was in a purpose built drag car though, nothing the resembled an Rx-7. I think I may still have the video on an old hard drive, but it is definetly going to take some searching for it. I may have been wrong on the HP figure though. Come to think of it, I think the thing ran in the single digit speeds down the track.
Last edited by RussStang; Oct 23, 2005 at 01:46 AM.
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From: Redmond, WA
Re: Reciprocating versus rotary engines
Originally Posted by RussStang
No, I mean a 5 rotor engine.
The fastest rotary drag cars in the world are only running 3-rotor engines (with a huge turbo, of course).
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From: Las Vegas/Pahrump, NV
Re: Reciprocating versus rotary engines
Originally Posted by jimlab
I think you mean 3-rotor, since 4-rotor engines are as rare as honest politicians and in 8+ years of owning an RX-7, I've never yet heard of a 5-rotor engine... not even from the rotary crazies in Puerto Rico or Australia.
If you think (or know) about how a rotary engine is assembled, you'd understand the difficulty of joining three eccentric shaft sections to build a 5-rotor engine.
Actually, a 2-rotor engine fire as often as a 4-cylinder piston engine. It takes 3 revolutions of the eccentric shaft to fire all 6 rotor faces, not one.
If you think (or know) about how a rotary engine is assembled, you'd understand the difficulty of joining three eccentric shaft sections to build a 5-rotor engine.
Actually, a 2-rotor engine fire as often as a 4-cylinder piston engine. It takes 3 revolutions of the eccentric shaft to fire all 6 rotor faces, not one.
Now granted the Australian's and Puerto Rican's are crazy there are some Brit's that are even further out there!!
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Re: Reciprocating versus rotary engines
Originally Posted by 04toy
Hate to rain on your parade here but you are incorrect. There have been 1, 2, 3, 4 and 6 rotor engines built
5 was the number of rotors under discussion, and the fastest rotary drag cars in the world still run 3-rotor engines.
I've seen pictures of the 6-rotor engine, but I've never seen it installed in anything. Considering that a 3-rotor engine is longer front to back (not to mention heavier) than an LS1, a 6-rotor engine would easily be the length of a V16. Ever seen one installed in an actual car? How about the 5-rotor engine in question?