I guess that's why the TII's came with lower compression than the NA's? Does the intake manifold change effect the longevity of the 89+ motor?

 

Lighter rotors have everything to do with stress.
For example, take a bicycle wheel and turn it, easy? Ok, now jack up the front of the car and turn the front wheel. Alot harder isn't it?
Now take the bicycle wheel and turn it for say, 100 rev's per minute and do it for 3 mins. Should be a piece of cake right? Now do that with the front wheel on the car. Alot harder and your arm gets more tired doesn't it. This is because it takes more force to turn the front wheel than the bike wheel because the front wheel is heavier. Same concept applies to the apex seals. More force = more stress.
Newton proved this already. Force = mass X acceleration.
Since the wheels(rotors) rotate, they have a constant angular acceleration, lets call this A.
Let M1 be the mass of a 86-88 rotor and M2 be the mass of a 89-91 rotor.
Let F1 be the force to turn a pre 89 rotor and F2 to turn a 89+ rotor.
So we have F1 = M1 X A F2 = M2 X A
Let A be arbitary be 1 (doesn't matter what you set it as)
we have F1 = M1 and F2 = M2
since M1 > M2, F1 > F2
Therefore, more force must be applied to turn the early rotors then the late rotors. Which means the lighter rotors will impose lesser stress on the apex seals then the heavier rotors.

BTW, why do you think the lighter flywheel will rev faster? Because less force is needed to turn it. The eccentric shaft don't have to work as hard (read as less stress) to turn it. F=MA again.
Lets say M is 1 and F = 1 to simplify stuff
F=MA is 1=1*A, A = 1
say M is now 0.5 since it's a lighter flywheel
F=MA is 1=0.5*A, A = 2
Acceleration faster = rev faster.......

We are having a wonderful discussion. Keep it coming.

 

Of course a lighter flywheel is going to turn easier. It's common sense(which I don't have much of these day). You don't see putting 25lb. flywheels in their RX-7's now, do you? lol....not flamin' on you dude.

 

That's all fine and good in neutral, but once you let the clutch out the biggest stress on the motor is moving the car. Now you have a heavier car to push... which would should offset any advantage that you get by having slightly lighter rotors.

BTW- I think the biggest reason that the 89+ cars (including 3rd gens) don't last as long is because of the electric oil metering pump. I have the feeling the old mechanical one would dump a good bit of oil, and the 89+ is probably trying to use as little as possible. (Increasing wear on the motor)

 

well, because MAZDA is constantly working on the motor, a newer engine will be better (always, durability and power-wise) than an old one, since all MAZDA rotaries share the same base. The new Renesis motor may have some teething problems, like the L8A or L10A did before it, but they will be solved very soon, considering that MAZDA has no big problems to look after like they did originally. Apex seals are not a prob.

 

That's nice in theory, but lets look at what has actually happened with the RX-7s:

1st gen 12A: No power, VERY RELIABLE
1st gen 13B: decent power, RELIABLE
2nd gen 13B: decent power, RELIABLE
2nd gen 13BT: good power, Fairly Reliable
3rd gen 13B-REW: great power, Not Reliable

Do you see the pattern? The newer the engine, the less reliable it has proven to be. I agree that the motor SHOULD be more reliable in the new cars, but it just doesn't seem to be working that way.

 

Is the hearsay or it's actual fact from personal experience?

 

HA! Show me a 40A that can run for five minutes without catastrophic breakdown... Poor lubrication, no sealing, blows smoke always when in good condition and all. Hell, the motor was such a piece of crap Toyo Kogyo never tried to put it in a car (well, they did (r360) but it has since been remouved). Pretty good for the first rotary Toyo Kogyo ever made tho.

 

It is from everyone's personal experience. Sorry there haven't been any scientific tests done like you are looking for. Sometimes things are a certain way & thats just the way it is.

 

I am not looking for any scientific test or anything, just some simple facts to back your arguements. Like, most milage from a 88 car compare to the most milage gottehn from a 89 car. Just stuff like that. It's really hard for me to believe some opinion someone saids or someone's hearsy when no evidence is present.

Dumping oil in the engine does not make it better. Last time I heard, the engine burns gasoline and not oil. There is an optimal level of oil need to inject to lubricate the apex seals. Too much would bog the engine, and too little will make the seals wear out. The electric pump using as little as possible while getting the job done is a good thing and not a bad thing.

 

I believe that I made it clear that I was speaking about the engines used in RX-7s. Not early pre production motors, or engines used in the RX-2, RX-3, REPU, or any other rotary for that matter.

 

More oil is better up to a point. More lubrication = less wear, I guess what I am saying then is that I don't think the electric one injects enough oil. Less oil combined with higher compression would contribute to more wear and less life.

 

Well... the power is based on personal experience. I've driven all of them. (Except GSL-SE, which I have only ridden in) The reliablity is based on the experiences of the people that I know. I have friends with 1st gens in the 200k range, where as most of the 13B guys are blowing up ~150k miles... Turbo II's seem to go a little less than that. And 3rd gens seem to go 60 - 80k typically. There are exceptions to all of these... but I'm just going off of what I've learned to expect after being involed with RX-7's and the local RX-7 Scene for the past 5 years. Also this is experience is echoed by some of the local reputable Mazda service facilities.

 

Well you are talking about the most ever, meaning like a damn record. Lets say 1 series 5 engine lasted 350k(not even close, but lets pretend) & the longest a series 4 lasted was 250k(don't think so either). That makes the series 5 last longer? Because of one single engine? I am talking about in general, not the longest 1 engine of a certain type lasted.

 

maybe we should setup a thread where ppl would list their milage

 

I don't see that working too well... I mean most people have rebuilds or new engines whether or not they know it or not.

 

With the ppl with the original engine, we can how much they have on it.

With the ppl with blown engines, we can see how much mileage they had it before it went dead.

2 separate categories.

 

Hey go for it

 

You are partially correct in what you are saying in reliability of the car. However, we were referring to the reliability of the engine. The reason the 13BT and 13B-REW are less reliable is because of the Turbos, extra wiring, and vacuum lines. The engine themselves were just as reliable as earlier model NA's.

 

The best turbo engine would be a combination of all 3.
The low compression of the series 4.
The rear housing of the series 5.
The intake of the series 6.

 

My co-worker drives an '88 SE with 239K miles on the original motor.

There have been mileage polls before and the 86-88's had shown longer lifespans than the 89-91's. Of course, there were more Series 4's made and they have had 1-3 years more time to accumulate more milage.

 

Well we aren't talking about JUST the block. We are talking about a specific car - the 89-91 N/A. This includes the electric oil metering pump and the whole package. If you are talking about shear block strength, then yes... the 3rd gen motor is probably the strongest. I'm talking about the implementation of the engine... the end result of Mazda's efforts.