What can you change internally on an S4 13B to raise the red line? I'd like to be able to rev higher than the stock red line without worrying about killing something. How farther can I push it? I expect balancing from Mazda Trix, RX-8 stationary gears, and competition rotor bearings from Mazda Trix will all raise this limit? How much farther could I go with these mods? Are there any other things I could do?

 

Is this car N/A or turbo? I'm assuming it is N/A, so in that case, start off with series 5 rotors and have them lightened and side clearanced. Those other things you mentioned (balancing, stat gears) will also help. Lighter apex seals such as carbon are reccomended as well. If you really want to go all out, you could try to get your hands on a Guru 2pc E-shaft with the center bearing.

 

how high can u rev the 86 n/a to without worry of damage...8k?.. i mean rev it there often

 

Temporarily, if everything's in good shape, probably 9500ish.

There is no point to revving that fast with stock ports/stock manifolding, however.

For extended timeframe running (like, say, track days) stock redline is probably best or slightly lower. The water pump stalls somewhat below redline.

IIRC the stock computer has a fuel cut at 7900rpm anyway, so you don't really have to worry. This is still beyond useful power with a stock engine.

 

could ne one tell me where i can find new head gaskets for an fd

 

uhh...

 

What do you have an coolant leak below your valve heads?



























Just kidding nube. Rotary's don't have head gaskets. They have what's called coolant seals that seals around the perimeter of the rotors(1 inner & 1 outer). What kind of problems are you having with your Fd?

 

Also, about the water pump thing, what do most aftermarket pulley kits run the water pump at. Rather, with an aftermarket pulley kit, where would the water pump reach it's maximum efficiency, if anyone knows with any certain kit.

 

Its kind of a common thing to think that just spinning more rpms will get you more power. But there is no need to spin the engine beyond the factory redline on an n/a if you dont have other VE mods that will keep the engine efficient at those speeds. I think even s5's make peak at 7k or close to that, with a redline of 8k.

 

i was just wondering...i like to know limits lol.. i dont plan on reving that high untill i street port and mod some more and find out where power cuts off.

 

A big enough street port is like a big enough anything port. You will not be able to rev the engine high enough, period, for any length of time.

Something else to consider. Unless you are simply dyno racing, stretching the powerband ever higher may actually be detrimental. The reason you make power, normally, is to make the car accelerate harder. The faster the engine spins, the more rotational inertia saps your acceleration. (There is almost twice as much rotational inertia at 8000rpm as there is at 6000rpm, for example, since it is a function of the square of engine speed) At some point the power gains are negated by the extra energy just to accelerate the engine at speeds that high. This is greatly aggravated by the fact that, since to take advantage of the higher RPM you need lower gearing, the same vehicular acceleration will require a higher RPM per second acceleration.

RPM sucks!

 

^damn peejay, you are well-read. I see what you are saying though. The higher you spin, the harder the engine needs to work to make power up there as efficientcy drops off. Strange that you will see your best efficientcy at peak torque, and make power after that simply becuase you are making more power cycles per unit of time.

 

I was just mainly wondering what I would need to do to run safely in the 7 - 8 k range without overheating or breaking something. So if I need to I can drive around at high RPM ranges (6 - 8 k) without killing my engine or overheating. I'm not talking about doing so to make huge power increases or whatnot. I know I won't be doing more than a street port.

 

You're wrong, the ammount of energy it takes to accelerate a mass dosen't change depending on the ammount of potential energy stored within it aka rpm. But what can make it require more energy is friction.

 

The amount of energy *does* change for a given RPM/second acceleration rate. This is because the rotational inertia is a function of the square of present RPM. The faster it goes, the harder it is to make it go faster. This is something *entirely* separate from mere friction.

Further exacerbated by the necessarily higher RPM/second rates required with the lower gearing used to take advantage of the higher RPM. (Going from 3000 to 6000 is the same speed increase as going from 5000 to 10,000rpm - the speed doubles - yet for the same vehicle acceleration the higher RPM engine must have a 40% higher RPM/sec acceleration rate)

 

For extended periods of time - slow down the water pump so it does not run into cavitation. When the pump starts cavitating, flow stalls.

Carbon apex seals. The iron ones hurt housings.

Watch your oil pressure and temperature. Try switching to a straight weight oil if you run into oil pressure problems at extended high RPM.

For dragstrip type use, stock will work just fine for those RPM levels.

 

So your saying that because I am rotating with the earth at 500mph that its going to be harder for me to walk east vs west?

 

The earth is only spinning at "500mph" at a given latitude. Angularly it is only turning at roughly .00007 RPM. At any rate, it is not in a state of acceleration. Liken it to sitting in a car driving down the road at a steady speed. You can move around just as if you were sitting still.

Speed is one thing. Acceleration is another matter altogether. Speed is the end result of acceleration, but for everything but land speed racing, we are only really concerned with accelerating the car as hard as possible.

 

Thank you for proving my point, I had a feeling that we were on the same page here. Just because the engine internals are moving at a speed doesn't mean that its harder to accelerate them. I interpreted a statement in your first post as saying, that by virtue of the fact that the internals are spinning their inertia will make them harder to accelerate a given amount then if they were stationary. I guess I read it wrong.

 

No, you read it right.

It's simple kinetics. The energy in the system goes up as the square of the speed. That energy doesn't come from nowhere, it has to be put into the system by the act of accelerating it up to that speed.

 

alpha = angular accelration
T = torque
I = moment of inertia

T = alpha*I

much like the more commonly known equation: F = m*a

Show me where angular velocity shows up in that simple equation of motion peejay...? I'm in the mood for a physics debate.

 

Moment Of Inertia dose not change based on rpm. Setting aside parasitic drag and load, a engine accelerating from 4k to 5k requires the same amount of energy as the same engine accelerating from 5k to 6k over a fixed period of time.

 

Si!!!

 

ok, the kenitic energy of a rotating object is K=(.5)I(omega)^2. I is the moment of inertia of the system, a constant. Omega is the angular speed. As speed increases, the energy increases by the square of its angular speed. so if you have an inertial constant of 1 for example, your energy at at 1000 rpm or 104 radians per second, the kinetic energy would be about 5.4 Kilo Joules. at 2000 rpm, or 209 radians per second, the kinetic energy would be 21.9 Kilo Joules. 3000 rpm is not 38.4 Kilo joules, but rather 49.3 Kilo Joules. The energy being related to the squre of angular speed(aka rpm) which will create large increases in energy requirements for a given rpm as you increase speed. These equations were taken from Halliday/Resnick/Walker Fundamentals of Physics 7th eddition.

 

I apologize for the poor grammar, but i'm mentally geared more towards science and math, not english skillz LOL rock on