Hey guys, I've got a Power FC but this goes for pretty much any stand-alone or piggy-back.

We all know that FDs can be... "fragile" if not properly tuned. I know of a lot of people that have caused some serious damage by not tuning after doing some seemingly simple mods.

This was a big fear of mine when I first bought my FD, and I still worry about it when planning any future mods. Since I am hours away from any decent tuners and I don't have the proper gauges (yet) to tune myself this is a big issue.

To the best of my knowledge, tuning becomes VERY important under 2 key conditions;

1) A change in boost or boost pattern (i.e.; new turbo, going single or sequential, higher boost)

2) A change in fueling (bigger injectors, higher fuel pressure, etc.)

There are some mods that don't have much of an effect on tuning at all, such as;

-Intake
-Cat-back exhaust
-plugs/wires (mild changes)
-non-power mods (Oil coolers, rad, etc.)

They either don't affect the air/fuel into the engine or affect them very little.

That leaves a few mods that I'm not so sure about and would love some clarification...

downpipe/midpipe; These mods affect the exhaust flow of the engine. However, if the turbos are properly ported to stop boost-spike, and the boost level is NOT changed, is there any need for a re-tune? There will be less back-pressure and slightly quicker spool of the turbos from the exhaust mods, but shouldn't the ECU tables be able to account for that?

Intercooler: Obviously the main goal of most people with an intercooler upgrade is to be able to crank up the boost. However if the boost level is not increased, all you will see is lower intake air temps and possibly a slight (.5lb?) drop in boost. Is a re-tune needed? I am mainly asking since I would love to be able to install the I/C myself, then drive the 4 hours to have it tuned without it exploding on me.

Twinpower/Ignition: As far as I can tell, upgrading the spark should really have little effect on the tune of the car, provided that the timing of the spark isn't changed. Am I wrong?



*I am by no means an expert on tuning. All of this could be very, very wrong. I'm just looking for some clarification on what exactly should be done when, and to possibly start a discussion on what most people do.

Obviously tuning after any mod would be ideal, but a lot of us don't have the money or access for such a thing. This all boils down to what absolutely needs a re-tune, and what can get by without.

Thoughts anyone?

-Devan

 

Every time you do a larger mod you need to tune it. For example removing the cat, adding a midpipe and cat back. That is a huge change in flow that the engine sees. If you have a good tuner who has done a lot of FD's then you can tell them where you are headed mod wise and they can set it up accordingly but its best to get it right. Why chance it?

Changing plug wires doesn't matter. Thats maintainence.

A good rule of thumb is that if you are adding HP you need to have the tune looked at or adjusted.

 

Anything that would change the fuel or timing requirements. Even changing injectors for the same size, I'd retune to be safe, since minor tweaks in flow could be major changes when it gets into the engine. Exhaust, intake, turbo or any other intake changes... definitely. Timing only changes when you modify the engine ports.

 

IMHO the only boost change would be between the turbo output and the intercooler output; that pressure should drop slightly if there is more cooling from the new intercooler. The reason is that cooler, denser air in the manifold requires less work from the turbo, if boost in the intake manifold is kept constant.

Someone correct me if that is wrong, please!

 

Technically, since the ECU is a speed density system it is tuned for a certain volumetric efficiency for a given engine speed and load. The ECU can not compensate for changes in volumetric efficiency because it does not know how much air is entering the engine. In a perfect world you would re-tune your vehicle each time you install something that increases intake or exhaust flow because you have changed the volumetric efficiency of your engine.

 

This. Even an intercooler will change the shape of your airflow to the engine. Maybe not significant to the point of blowing the motor or any noticeable impact, but it could swing it away from peak performance.

 

It also depends what level you're at and how extreme your current tune is. If you're running 10 psi on stock twins with a conservative tune, then retuning is not as big a deal as a big single running 25 psi tuned on the edge. It's all relative. I re-tune my car all the time, but I have the knowledge and proper equipment so it's not a big deal.

 

The MAP sensor should respond to changes in air density in the intake manifold, yes? And that info is fed to the PCME? Although there is no airflow meter, the MAP sensor is actually a better measure of how much air is incoming, since it measures the actual pressure. Or not? Please elaborate!

 

Air pressure is not the same as air volume. A large single turbo fd at 10 psi has much more air volume then the twins at 10 psi. Which is why it makes say 80 more horsepower and will require much more fuel even though the map sensor is reading the same pressure.

Put another way imagine a 1 inch pipe and at the end of the pipe it has 10 psi of water flowing out. Now imagine a 6 inch pipe at the same 10 psi, which do you think has more water coming out?

 

as everyone else has said any mods that change the AFR a retune should be redone.

that means no different size turbos (you are drastically changing the CFM), fuel rails, injectors, or increase in boost including spikes and/or creep.

 

Yep, I understand that. But let me carry that analogy a bit further. Suppose I cap the end of that pipe with a closed chamber of, say, 1000 cc. Now measure the pressure in the pipe, or if you like, weigh the water in the chamber. I submit that the pressure with either size pipe will be 10 psi, and the volume in the chamber will be 1000 cc in either case. If the analogy is changed to a gas like air, the same weight of air and same pressure will be present in the chamber. Increased volume will only make a difference if the air (or water) is transferred away faster than it can be supplied. So at higher rpm more volume is needed to maintain 10 psi.

Since A/F ratio needs to be relatively constant for all air flows, the best measure for the PCME of how much fuel is needed is the weight of the air entering the engine. Unfortunately measuring pressure alone does not account for differences in temperature, i.e. of course cooler air is denser and weighs more, thus requiring more fuel. That's why the PCME needs intake air temperature as well as manifold absolute pressure. But given those two parameters, I must disagree with you that

 

But the rotary engine, or any engine for that matter is not sealed. It has exhaust ports, exhaust system, and an intake tract that restrict how much air is allowed to enter and exit. Also known as volumetric efficiency. When you add an exhaust system, or a high flow intake you're changing how much air can enter and exit the engine. You raise the VE and it will require more fuel. A higher VE engine will make more power at the same boost level as a lower VE engine. This is why tuning is required. Air is key in making power. If you add something to your car that gives it power, it is consuming more air.

 

I am having trouble with this analogy also.I can see this being accurate if you measure the pressure AT THE DISCHARGE of the turbo(s).

If you measure the pressure in the stock location,that is after the throttlebody,the HOSE PIPE becomes the same size because it is the throttlebody.All other aspects of the engine being the same.

Or am I missing something?

 

The hose analogy is a comparison of the whole engine from the air filter to the the tailpipe. Maybe it will help to move the pressure gauge in my anaolgy to the middle of the 1inch and 6inch pipe. The point is that pressure does not = volume and volume is what determines fuel requirements.

 

Now I am confused.I always thought it was the mass of oxygen(ie no of molecules of oxygen) which determined fuel requirement,and the mass of oxygen is determined by pressure,volume and temperature of air,so how can volume of air alone determine the fuel requirement?

 

Your missing the point...
Firstly, when I say air I'm using the simple term that most people use in the automotive world. It is Air / Fuel ratio after all. And with more air comes more oxygen, along with everything else that makes up air... nitrogen, argon, Co2 etc..

Yes temperature changes the density (mass if you like) of air but it's not really needed in this discussion or in my analogy. For 1 the ECU has it's own tables just for air temperature, and 2 the analogy assumes all atmospheric conditions are equal. The same effects on air mass can be achieved by changes in altitude, but we don't need to consider that either.

Maybe I shouldn't have used the term volume, I'm not a scientist so when I think of volume I think how much of something, but since air can be compressed it wouldn't work out the same, so yes weight or mass would be the correct way to measure the amount of air, but then again my analogy used water which would indicate a total amount of something.

Now, the point is that pressure is not a valid measurement for total amount of air (oxygen if you like). As mentioned by many people, when you change anything that effects how easily air can get into, or out of the engine (VE) the resulting air pressure will no longer be an indication of how much fuel is needed. Why? Because there is now more (or less) air going into the engine. This can easily be seen by comparing 2 cars with different mods, making different amounts of power at the same boost level.

 

Now suppose you did a test with the SAME engine,same intercooler and appropriate air cleaner---first put your single turbo on it.use factory MAP sensor in factory location,run the engine and it measures say 10psi and your fuel map delivers enough fuel for say an AFR of 11.0.
Then you take the single turbo off and install your twin turbos,no other changes are made and run the engine so that the MAP reads 10 psi----what will the AFR be 11.0 or something different?

 

It's more accurate to think of volume as the space occupied by something. "How much of something" generally refers to its mass, or as Six Rotors wrote, the number of molecules. It's the molecules of air that combine with the molecules of fuel, and the A/F ratio is the relationship of those two quantities. Cooler air is denser, i.e. contains more air than the same volume of hot air at the same pressure, so cooler air requires more fuel at the same pressure than hotter air, because there is more of it.

 

replacing your intercooler can cause a drastic enough of a change to blow an engine.

any change that affects the power output of your engine means you should do a retune on the engine, enough small changes will result in the maps not being sufficient to support the mods done.

on my car for example i hadn't touched anything on the car itself and hadn't remapped it for 3+ years and it was fine for that timeframe but i would suggest just having your maps touched up about every 2 years to be on the safe side.

there is no change too small once you get to a certain point that the car shouldn't be retuned. for example, a nearly stock car that is on the rich side can support a few modifications like downpipe and intake but a single turbo FD pushing 17psi should be remapped even when changing the catback, because small changes once higher in horsepower/boost are much more drastic than when near stock power levels. small changes on high horsepower engines turn into large mods very easily.

 

^^ that only applies to agressive tuning. If the tune is conservative all of that is not needed.

 

it's still better to be safe than sorry, but that generally only applies to the more highly modified cars.