Poseur

I've been pondering this for a few days. Why is it that rotary engines are configured upright, like an eight? Wouldnt it allow you to have a much lower center of gravity if it were configured on its side like the symbol for infinity?

I was thinking it would have something to do with the placement of spark plugs. Are the plugs on one rotor housing on the opposite side of the plugs on the other housing? If it were, I could see why placing the engine on its side would pose a problem with acces. But other than that, I can see on reason, from an engineering standpoint to have the engine the way it is.

Project84

Have you seen a rotary engine before? Spark plugs are on the same side on both housings.

And the engine is not upright, you have a front rotor, rear rotor, and a shaft running through the middle. The block itself is so small and sits so far back in the engine bay that it gives the car a low center of gravity. The car has 50/50 wieght distribution stock from the factory too. I don't know what year RX-7 you have, but mazda spend much money on wind tunnel testing and they have ten (10) patents on the 2nd gen suspension alone.

I don't know what you mean by "why is the engine upright" but the way the engine sits in the car, its longer from front to back then it is top to bottom, so it isn't standing up, its laying sideways. If you want to see an engine, click on the link in my signature, or go to www.howstuffworks.com and do a search for rotary engine.

kyle@insight

If you want to lower the center of gravity to increase handling it's not going to happen. I'm going to guess you're new and not aware of the cars performance. These cars rivaled ferrari up until the later models came out. The possibilities are endless but it's pretty much as good as it gets as far as motor placement goes from the factory. The weight balance is 50/50 and it's got a front engine mid-ship design.

Project84

The 2nd gen also has a suspension feature that will allow the rear wheels to steer into a turn. Thats right, rear wheel steering. Some people like me like it, others buy a kit that will allow you to eliminate the rear wheel steer, but that is the kind of inginuity that when into these cars.

Also, you can get aftermarket spings and shocks that will lower the car from 3/4" to 1"

Poseur

I do not mean upright in the sense that the eccentric shaft is pointing up and down. I know what a rotary engine looks like, I dont think you understand my question. I wish I had pictures to explain. I'm not completely educated on all of the terminology, further increasing confusion.

Due to the military, I am forced to live in the panhandle of Florida (hicksville) so I do not see that many great cars, however I'm taking a power mechanics course in my high school where I got the opporitunity to se a rotary engine. My time with it was brief and was in the process of being rebuilt. I didnt happen to note the plug locations so please escuse me for my error.

Now, let me try to draw in words what I was saying.

You've got your rotor housing. It is in the shape of an oval which kind of indents in the middle. Everything I say, imagine we're looking at the engine straight on, in its mounted position directly at the housing so we can see the shape that the housing makes around the rotor. The oval is upright like a zero: 0. What if we were to put the 0 on its side? Instead of the spark plugs pointing to the side, the point upwards. All of the weight of the engine would be around 20-30% closer to the ground. The rotational mass of the eccentric shaft would be much lower than it currently is.

Even if the RX-7 already handles as if it were on rails, wouldn't a lower center of gravity make it better, even if it is slight? It certainly couldn't hurt.

I just wanted to know why the Mazda engineers opted for a tall oval instead of a wide, lower CG oval (rotor housing). I don't know everything about the mechanics of a rotary engine, but I dont see why this would have any adverse effects on the opperation of it.

I'm a big RX-7 fan am well aware of the cars performance, its 50/50 weight distribution, and nimble handling. Although I wasnt aware it had rear-wheel steering. Is it similar to Nissans Super HICAS?

I don't have an RX-7 I just came to this forum to see if someone could answer my question (but I do love the car).

Project84

I see what you are saying now. If you lay the the motor on its side so the spark plugs point up then the oil pan would be on the side of the motor and the intake manifold would be close to dragging on the ground. The block would have to be total redesigned around having a horizontal eliptical path versus the current vertical one. Also, if the engine sits lower (lets say 6 inches), then the entire drive train would have to be lower. So either the tranny would hang down away from the car or the whole car would have to be lower. I don't know if there is a height to where once you get that low, you lose the practicality of driving the vehicle. I guess the ground is the limit as long as you keep the oil pan off the floor. That is a good question though. I have know definate answer as to why it is the way it is, just speculation. I'm kinda interested to see why myself, so I will ask some people on here who I think might know and I will get back to you.

What base are you at? Is one of your parents in the military? I'm in the Air Force.

Poseur

I don't mean what would happen if some one were to put the current engine on its side. But why the Mazda people decided not to. I'm sure if the engin was designed like that from the start, the oil pan, transmission, etc. wouldnt be a problem.

My dad's retired from the Air Force, he's Civil Service now at Tyndall AFB in Florida, near Panama City.

Project84

Cool, I'm station at Ellsworth AFB in South Dakota. My cousin is at Hurbert Field in FL. I asked someone about any problems with having the engine designed to sit sideways. He will send me a PM after he thinks about it.

If you want to check out my car, click on the link in my signature. I got the engine out and sitting on a stand.

Poseur

Kool, I'll check it out.

Isn't it spelled Herlbert or Hurlbert or something with a L?

Poseur

Love the car. Good call taking the bra off .

About how long does it take to rebuild a rotary from the time you open the hood to the time you start it up again?

BTW, is that a Lancer I spy?

kyle@insight

That's impossible to say. All depends on teh skill level and experience of the builder, plus wether or not any modifications will be made such as a port. Also varies on wether or not its a 1st, 2nd, or 3rd gen.

Poseur

Was asking Project84 how long it takes him.

Project84

Thats a new Lancer Evo. My neighbors car. The white escort a little further back is my wifes and I have a Ford Explorer you can't see in the pics.

It takes me about 3 days to pull the motor, clean it, tear down and rebuild, and put it back in the car. I kinda take my time, and I don't work sun up to sun down. This motor took a lot longer cause I had it almost back together and I dropped something down one of the holes where the tension bolts go. There are long bolts that go from the back end all the way to the front and holds the block together. I had to take it apart to get the piece out of the hole and when I did, one of the water seals came out and wouldn't go back in. They have to be stretched a bit to fit in there. I had to order the seal, and then my in laws came out to South Dakota from the east coast with nearly no notice, so I haven't worked on it much since I got the block back together. I got the front cover and water pump on. I have to put the intake on and put it back in the car after they leave.
I'll get more pics of it without the bra after I roll it out of the garage again. It a lot easier to work on without the emissions control system. It takes longer to pull an engine with all the emissions stuff cause there are more vaccuum hoses and electrical connectors to label, and more stuff to pull off. There are no emissions here just like in Florida.

Project84

I talked to someone about your idea for the rotary engine. They said that if you look at where the rotor creates the most compression against the housing, its right where the spark plugs are. So your plugs would either have to point straight up or straight down. Point straight down isn't cool cause you would have to jack the car to change them. Plus the oil pan need to be on the bottom so you can't have the spark plugs in the oil pan unless you have a dry sump oil system like racing cars do. With the plugs on top, he says the intake/exhaust setup would be in the way and he doesn't know if the torque vector would cause excessive vibrations or not. I don't have a clue about that last one, but I know he knows his ****. He did say that any car can benefit from having the engine lowered, even an RX-7.

Poseur

Makes sense to me. Thanks for your response, that clears up most of the confusion.