piston vs rotary engines!!??

[Neutrino]

Originally Posted by Moppie

A little tip, try changing gear

well very often those autocross courses have very very tight turns and changing gear would mean putting it in first at speed...and i'm not gonna do that in my daily driver


and disco 192 if you would ever had raced before you would know that torque is as vital as horsepower....why do you think honda engineers raised the torque in the new s2000 because they are stupid?and don't say marketing ploy because most people when they buy cars don't even know what torque is

[disco192]

I realize that it is important to have a flat torque curve and power in the bottom of your powerband.

They gave the s2000 more torque so they could have more power in the lower end of the power band. They also lowered the redline, but they didnt do it so much for performance, they did it for driveability. They both run very similar 0-60 and quarter times, but the new one is a hair faster.

And acceleration equals the area under the torque curve, which is essentially the average HP. Top end HP isnt the only factor, but due to gear ratios it is a large one.

And yes, i know that torque is important but it just seems like everytime someone says the T word people cream their pants. Most people dont even truely understand what it really is.

[Moppie]

Originally Posted by Neutrino

well very often those autocross courses have very very tight turns and changing gear would mean putting it in first at speed...and i'm not gonna do that in my daily driver

Then learn to heal toe

I certianly never had a problem getting my SiR into 1st at 40kmh, you just have to give the throttle a little blip, and it, being a Honda, had one of the worst gear boxs Iv ever used.



But Rotorys do not have a problem with a lack of torque, thier extremly succesful history in rallying is proof enough, its always been regarded as a sport where who has the most torque wins.
And it shouldnt be that hard to find a picture of an old RX3 or something lifting its front wheels in the air at a strip, which should require at least a small amount of torque.

[Polygon]

I was not generalizing that Mazda makes bad cars when I said that the RX-7 had reliability issues. I was focusing on the fact that the 13B isn't the best engine and is very high maintenance. What I am about to post are facts that have been admitted by the engineers that designed the 13B.

The engine had a pesky port overlap problem. This meant that exhaust gases were allowed into the combustion chamber during the intake process. This caused a few problems like excessive heat, which contributed to bursting apex seals. The turbo also contributed to that problem. This meant that N/A RX-7s were less prone to that problem. This also caused the RX-7 to have poor gas mileage and emissions. It also caused the car to stall at idle which increasing the engine speed at idle solved. These problems can't be completely negated by meticulous maintenance or better cooling systems. The problems will still exist and will still cause these reliability issues. Don't argue with me that the RX-7 wasn't very reliable and call me ignorant, because that is proof enough that it wasn't reliable compared to the other sport compact cars of the time.

As for the torque issue. Torque is VERY important in any kind of racing. Horsepower sells cars but torque wins races. In the simplest terms I can think of to explain it horsepower is how fast you can go in a gear and torque is how fast you get there. That isn't exact, but it is as simple as I can get. As for rotary engines and torque I stand by statement. They do not produce the rotational force that a piston engine does so the ratio is way off and the maximum torque is produced much higher in the power band. The specs on the 13B Turbo show that it has 255HP and 214 ft/lbs of torque. It has a descent amount of torque but ideal would be an even amount or more torque than horsepower. Also the maximum torque is produced at 5,000 RPM. In racing and especially drag racing it is very important to have that torque produced in the low end of the power band and hold strong throughout. However, this same pattern can be seen in some piston engines like engines using variable timing and lift systems. Remember that it is easy to increase horsepower but torque is quite another story. In racing that is just more important. I am also not saying that you can't get a good amount of torque out of a rotary I am just saying I don't think that you can't get as much.

As far as the Renesis goes, reliability will remain to be seen but I feel that they have fixed all the problems that the 13B had. They have removed the turbo and gone N/A. There is also no more pesky port overlap.

[lietuvis91]

good stuff ya'll! this definately taught me alot! I'm no expert either, but i drive a 1991 sentra SE-R and those of you who know, it has one of the torqiest 4 cylinder engines ever made. i have driven many 4 cylinders to compare, and off the line my car pulls the best I think. This I definately attribute to the amount of torque it has!

[kfoote]

Originally Posted by Moppie

A little tip, try changing gear

In many autocrosses, there ARE turns that are tight and slow enough that they're 15-20 MPH. This drops the car out of the powerband, and most cars have a lockout that makes it very difficult to get the car into 1st gear with the car moving. Heel-toeing does not help. Even on a road course, coming out of slow corners the SCCA ITS Mazda RX7's get pulled by cars with similar power but less torque (Porsche 944 8v comes to mind).

Physics lesson: HP = Torque x RPM x (constant). If the RPM is low, the torque number is more indicative of the acceleration of a car. What this multiplication results in is the elimination of one degree of time as a factor in HP calculation, where it is a factor in the torque calculation. Higher HP = higher top speed, but for a lower torque and a constant period of time, it takes a longer period of time to get there. Fast lap times are about fastest times, not how fast you're going at the end of the straight. In my example, even though a slightly higher HP (or HP:weight ratio in SCCA ITS trim) Mazda RX7 may be going the same speed at the end of a straight as a Porsche 944, the Porsche will take less time to get down the straight because though the acceleration has begun to trail off, it has already made up the time at the beginning of the straight with its torquier engine and steeper acceleration curve. This is all assuming the same exit speed for the two cars, same shift points (at a higher RPM for the RX7 than the 944), and same length of time in gears. (In reality, the shift points of the 944 and RX7 are very similar, but due to the lighter minimum legal weight of the RX7, their cornering speeds are usually higher and entry speed onto the straight is higher as well. Because of this, the RX7's are usually a bit faster on most tracks than the 944's) I know someone who runs a 91 Sentra SER in ITS as well, and the top end speed is usually about the same as the 944's and RX7's, even though they have less power and are slower in the corners. That's probably better than the example I gave, though the dynamics of the SE-R is totally different than the 944 or the RX7.

[mcdoink]

there shouldn't be any debate over whether torque or horsepower is more important. fact is, they're both equally important in a fast car. thats the reason why diesel powered semis with loads of torque couldn't burn cars on a regular basis, even if they didn't have a huge trailer behind them. think of it like this...if torque is the force behind your engine, then horsepower is the ability of the engine to gain speed. that's the closest i can get to the proper explanation of it now... im kinda out of it.

rotary powered cars are cool, get over it

[nelson583]

hy i have a mazda rx7 1980 13b 1/4 9.047 the diference is if you put the two motor together for race the mazda rotary you spend $5000 in the motor to run in the lows 10 second 1/4 but to put the piston motor to run lows 10 second 1/4 cost you 15,000 to 20,000 because you has to built all motor. for the rotary only you need a good compresor to port the plates and 2 or 3 trucos. in rpm my car easee touch 15,000 rpm wen i race i take my car at 10,500 rpm 0 to 60 in 2 second the 1/4 at 156.65 miles



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[nelson583]

Originally Posted by lietuvis91

Did anyone read this dec issue of turbo mag? They started a series on rotary engines and they explain how they work and some issues with them in detail. I'm seriuosly considering an RX-7 now. I just wanted to know does anyone think that maybe rotary is the best way to go for drag and just high speed driving in general. They do have much less moving parts it seems so less shit that can brake! It just spured my interest in rotary and want to know if any of you guys have any experience with them, or can anyone compare from experience cylinder vs. rotary angines reliability and race potential!? What are some of the advantages or better yet biggest disadvantages of rotary engines??? And how hard are they to work on for the do-it-yourselfers as compared to piston engines???

http://www.rotaryengineillustrated.com/animations.html

[AreaT51R]

Ok...short and simple. Torque gets you off the line and HP gets you down the road. Nuff said. The thing that impresses me about the rotary is its efficiency. Think rotational mass vs. recipricating mass. In a piston engin the piston/rod mass has to go a cirtain direction and suddenly come to a complete dead stop and change direction-recipricating mass. In a rotary engine the mass is rotating in one direction and never has to stop-rotational mass. Put a ball on a 3 ft. string and try to get it to go up and down the distance of 30 ft. then use that same set-up and swing the ball in a circle the diameter of 30 ft. what's more efficient? Duh. Also...the design alone of the rotary enging is responsible for the tremendous gains in power by adding small performance parts that would normally give the average Honda 3Hp. Rotaries Rule!!!

[Polygon]

Originally Posted by AreaT51R

Ok...short and simple. Torque gets you off the line and HP gets you down the road. Nuff said. The thing that impresses me about the rotary is its efficiency. Think rotational mass vs. recipricating mass. In a piston engin the piston/rod mass has to go a cirtain direction and suddenly come to a complete dead stop and change direction-recipricating mass. In a rotary engine the mass is rotating in one direction and never has to stop-rotational mass. Put a ball on a 3 ft. string and try to get it to go up and down the distance of 30 ft. then use that same set-up and swing the ball in a circle the diameter of 30 ft. what's more efficient? Duh. Also...the design alone of the rotary enging is responsible for the tremendous gains in power by adding small performance parts that would normally give the average Honda 3Hp. Rotaries Rule!!!

1. You want to talk about efficiency? I don't think that allowing exhaust gasses in on the compression stroke is efficient. I also don't think running rich at idle is efficient. Suddenly, rotaries aren't sounding very efficient.

2. In a piston based engine, while the engine is running none of the pistons EVER come to a stop. If they do you have a VERY serious problem. Not even under severe detonation do they come to a stop.

3. You can't compare a rotary to a piston-based engine, size for size, when adding mods. Displacement isn't the same between the two.

[quaddriver]

Originally Posted by Polygon

1. You want to talk about efficiency? I don't think that allowing exhaust gasses in on the compression stroke is efficient. I also don't think running rich at idle is efficient. Suddenly, rotaries aren't sounding very efficient.

2. In a piston based engine, while the engine is running none of the pistons EVER come to a stop. If they do you have a VERY serious problem. Not even under severe detonation do they come to a stop.

3. You can't compare a rotary to a piston-based engine, size for size, when adding mods. Displacement isn't the same between the two.

actually each revolution the pistons come to a stop - twice

iirc, the problem with rotaries (besides having too little rotating mass to apply the clutch smoothly) is with emissions. after each 'fire' the volume of the chamber gets rather large rather quickly with respect to crank angle. Because of Mr Boyle, the resulting mas rapido loss of pressure cools the currently burning mix, slowing/stopping the autoignition of the advance reactions. This results in a rather large HC output. Correct me if I am wrong, but it was the inability to meet tier 2 emissions is why mazda/ford pulled the rotary for a number of years - I have not bothered to read up on how they solved this problem.

[Polygon]

Originally Posted by quaddriver

actually each revolution the pistons come to a stop - twice

iirc, the problem with rotaries (besides having too little rotating mass to apply the clutch smoothly) is with emissions. after each 'fire' the volume of the chamber gets rather large rather quickly with respect to crank angle. Because of Mr Boyle, the resulting mas rapido loss of pressure cools the currently burning mix, slowing/stopping the autoignition of the advance reactions. This results in a rather large HC output. Correct me if I am wrong, but it was the inability to meet tier 2 emissions is why mazda/ford pulled the rotary for a number of years - I have not bothered to read up on how they solved this problem.

1. No, like I said, the pistins NEVER come to a full stop.

2. The 13B had poor emissions because of port overlap and because the engine ran rich at idle. They solved this by moving the ports.

[quaddriver]

Originally Posted by Polygon

1. No, like I said, the pistins NEVER come to a full stop.

2. The 13B had poor emissions because of port overlap and because the engine ran rich at idle. They solved this by moving the ports.

I beg to differ, in a recip motor, at TDC and BDC the piston is indeed not moving or being acted on (force applied no movement) in any direction - for an instant[1]. there is no '3 second rule'

of course they 'bottom dwell' and the tdc reversal is more violent
(leading to nasties like rod stretch etc) but they do in fact stop

notes:

[1] the sideways force to the thrust side gets to its lowest point, but I think due to angular momentum of the small end of the rod, there is at least a dick hair of force still applied, but I might be wrong....its been a few years

[AreaT51R]

The piston in a cylinder goes up and stops COMPLETELY then goes back down. What the fuck else would it do? The rod may not completely stop due to it's rotation at TDC but as far as a 180 degree change in direction it does completely stop. The design flaw, if that's what you want to call it, of the rotary enging may not be as efficient but the mechanical movement of engine parts in a rotary are. Increase the same psi in a rotary and piston engine and which one gains more power? Hmmmm? Oh...and don't give me that bull shit about increasing psi in a rotary vs. a fucking McLaren F1 V12. But then why compare the two...it's comparing apples and oranges right? So what's the point of this whole thread? Just to argue I guess. Bring it!


P.S. Don't get pissed, it's all in fun and games!