So I have noticed a lot of posts asking this very question. It got me to thinking that there really isn't a single source of info on this that is really readily available. So, being as I have a pretty decent working knowledge of the S197's PCM, and some experience with tuning it, I spent some time making a Crazy Al/TacoBill style review/writeup on what does need a tune, what does not, and the why's for each. If you feel this is useful to the community as a whole, feel free to ask to make this a sticky.
Anyway, without further intro...
Mod: Flash Tuner Tune: this is what makes it all possible Why: In the “Old Days” if you wanted to add or retard timing, you gave your distributor a twist or changes out a spring. If you wanted slightly more or less fuel, a small screw on the Carburetor was all you turned. If you needed a lot more fuel, you swapped out the carb altogether. These and dozens of other things were all handled by mechanical devices that made up a car. Now, everything is controlled by a computer. No more screws to turn or springs to add. Now, if you want to add more timing or change your fueling, its as simple as a few keystrokes for those who have the skill and know how. Basically, what a flash tuner does is it takes a pre-created program (made either by the tuners manufacturer or by an aftermarket tuner) and loads it into a flash type memory in the cars computer. The car then uses this program to tell it how to operate the vehicle. This program is pretty complex and controls thousands of sensors and servo’s at once, but it basically boils down to a few things; Timing, Fueling, Shifting for an automatic trans, and emissions. Popular Brands: SCT Livewire and Excal and the Diablo Predator seem to be the most popular, in that order. There are others, such as Granatelli’s Fuego, Sniper Special Forces, and even more tuner shop aimed products such as HP Tuners.
Mod: Cold Air Intake (aka. CAI) Tune: Sometimes, depends on manufacturer Why: The long and the short of it boils down to MAF size. If an intake is made with a MAF size that is the same or very close to stock, then the computer will not need to be recalibrated. If the size of the MAF is increased, the computer will need recalibration. MAF’s are calibrated so that it samples a tiny section of air as it comes into the intake. The exact volume of air is known to be a direct proportion of the total volume of air flowing in the intake. By making the MAF larger, you are changing that proportion and you have to let the computer know about this change or else it will be getting a lot more air than it thinks it is. Popular Brands: No Tune: K&N, AEM Brute Force Tune: C&L, JLT, Modular Depot, Demolet
Mod: Under Drive Pulleys (aka UDP’s) Tune: No Why: By changing the size of the Crank pulley, you are effectively changing the “gear ratio” of the crank pulley to the rest of the pulleys it drives. You are both slowing them down and giving the crank more mechanical advantage over those other pulleys. More mechanical advantage means it takes the pulley less work to turn everything. The end result is that there is less parasitic drag on the crankshaft and more being send to the wheels. Popular Brands: Steeda, BBK, Granatelli
Mod: Charge Motion Control Valve Deletes (aka CMCV Deletes or just Delete plates.) Tune: ALWAYS, Car will go into limp mode without one. Why: The intake manifold of the S197 has a second set of butterflies in them, placed just before the intake valve. The goal of these plates is to increase the velocity of the air as it moves into the combustion chamber. Increasing the velocity of the air as it enters (also called port velocity) helps the engine build torque and maintain fuel efficiency. In Theory, as the engine speed increases, these butterflies are supposed to open (between 1500 and 3000 RPMS based on engine load) and allow the air into the cylinder without restriction. In function however, these plates do still end up providing some small restriction to the intake. As their name implies, the CMCV Deletes remove these butterflies completely. When you remove these plates however, you must tell the computer that they are no longer on the car. The computer has entire strategies of timing, cam phasing and fueling that it applies based on these plates being closed. If there are no plates to close, but it thinks that there are… I think you can see where the problem comes in here. Popular Brands: Steeda, Ford Racing Performance Parts (these are no longer available new and are identical to the Steeda Economy Plates)
Mod: Gears Tune: Always, especially important on Automatics Why: On a Manual trans, recalibrating the computer for gears is mostly for two reasons; your speedometer and odometer. There are a few other things that come into play, but they are pretty minor and really would not effect drivability. On an Automatic trans however, it’s a completely different game. Road speed plays an important factor in the auto trans deciding when to shift and how to shift. Without updating the auto trans for the new gears, your car will shift funny and sometimes even not shift at all in extreme cases. Popular Brands: FRPP and Motive.
Mod: Long Tube Headers (aka Long tubes) Tune: Yes Why: Long tubes relocate the O2 sensors further downstream in the exhaust. This causes two issues. The first is, it will take the sensors longer to get hot enough to be in operating temperature range. This is because even self heating sensors rely somewhat on the heat from the gases to help heat them. The second problem is cause by the same thing as the first; the sensor is relocated down stream further. The computer knows the volume of air it has to push out of the cylinders for that air to reach the O2 sensor, so it knows that after it sprays fuel now, it can read it X amount of time later to see how accurate it was with it’s predicted volume of fuel. By moving the O2 sensors further away from the motor, your increasing the volume of air between the cylinder and the sensor. Now the computer will be expecting to see a change in X time, but in fact, that change will be arriving at the sensor much later. Popular Brands: Kooks, American Racing
Mod: Short Tube Headers (aka Shorties) Tune: Not usually, tho sometimes minor fuel corrections are needed Why: Unlike Long tubes, shorties just replace the exhaust manifold itself. All emissions gear and O2 sensors remain in the stock locations, so all the factory calibrations are close enough. Sometimes to make up for the extra scavenging that Shorties have over the stock log style manifolds, a slight adjustment in fueling may be needed (usually with forced induction or very radical N/A motors.) Popular Brands: BBK is the only one I know of. If you know others, post them and I will update.
< Message edited by GT Bob -- 2/6/2008 8:40:27 AM >
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"Vera" '07 GT. Manual, 3.55's, Spohn Adj LCA's, Hurst Shifter, GT 500 Rear and chin spoilers, GTA's, Steeda UDP, Roush rear springs, ProFab CAI #6, BBK Shorties
"Dyno's Rarely Lie, but E.T.'s and Trap speed say so much more."
Mod: One Piece Driveshaft Tune: No Why: Same idea as UDP’s. The extra power is gained by reducing rotational mass and reducing parasitic drag on the power being put into the rear tires. Less things eating up power before it gets to the rear wheels, means more power gets there, Popular Brands: Spydershaft, shaftmasters
Mod: Axleback exhaust, Catback Exhaust, Mid Pipes (X, H or Prochamber) Tune: See below Why: The stock exhaust flows pretty well on the S197. Well enough in fact that with the exception of moving to an Offroad style midpipe or headers, there are no real power gains to be had by changing out the exhaust. Headers I have already talked about so I will not go there again here, but with the exception of midpipes with no Cats (aka offroad pipes), none of these will require a tune. This is basically because the parts they are replacing are not measured volumes. Once the exhaust gases pass the rear O2 sensor, as far as the Computer is concerned its gone and the computer could care less about it. Now, if you replace your mid pipe with an “Offroad” type pipe (which is illegal in most states, and hence the name), you will need to disable the rear O2 sensors. It is the only exhaust Mod behind the headers that will require a retune Popular Brands: Almost too many to list… FRPP, Borla, Pypes, JBA, Flowmaster, Dynomax… these are only a few of the many.
Mod: Cams Tune: Yes Why: If you think of your car as a human body, the Cam is the brain. It tells everything when to happen. As the cam turns, it pushes open the valves, which then tells the PCM to pump blood…errr… spray fuel into the cylinder. It then closes the valve and a sensor on the camshaft then tells the coilpack when to send a spark into the chamber to light the fuel on fire. It then turns more, and opens the exhaust valve, so the piston can push all the spent fuel charge out. Now, while the Cam controls when these things happen, the computer has an exact model of what the cam is doing and knows what to expect. By changing the cams, but not changing the model that the computer is working with, it’s going to be out of synch with whats going on. Popular Brands: BBR and Comp
Mod: Throttle Bodies Tune: By model. Why: The why on this is very similar to what I talked about in CAI’s. The computer has a pretty specific model of how much air the throttle body can flow based on how open the butterfly’s are. This measurement however, is not as important as the MAF’s, but it still plays a part in everything. These values can be updated in a tune, but as anyone who has run a BBK or even a JDM kit that uses a GT500 TB, it’s not 100% needed. I’ve seen a few articles that have tested TB’s and they all follow one general theme. Without an aftermarket tune, the gains for the TB were in the 8 to 15 HP range at the rear tires, depending on other mods done to the car. Once an aftermarket tune updated for the TB is added to the mix however, things change considerably. The difference between having the TB and not drop to as little as 1 hp and 3 ft/lbs when the tune is updated for the Throttle Body. Now, while no one ever made any hints as to why, I have an idea on this. Please keep in mind that this is purely speculation on my part and I haven’t done any testing to prove this, it’s just me following what seems like logic. It strikes me that that without updating the tune for the TB, the airflow model is going to be expecting less air than the larger TB will flow. By having more air and the same amount of fuel, it’s going to lean the AFR’s out a bit… which is exactly one of the things that tuners do since the stock commanded AFR’s at WOT are in the 12.0 to 12.4 range. However, once you update the airflow model to accurately reflect the amount of air that is flowing past the butterflies, the AFR’s go right back to what is commanded. As a side note, most say (and I tend to agree) that the stock TB’s are good enough to support airflow to horsepower levels that are well past what the stock bottom end can handle and the only time that a TB is really worth it is in radical NA builds (i.e. “Cammer 5.0” engine, 298ci Strokers and the like) or in forced induction setups in the 450+ RWHP range… tho there are examples of people using the stock TB’s to the 600 horsepower range. Popular Brands: BBK, Grantelli, and JDM’s GT500 adaptor kit.
Mod: Electric Water Pump Tune: No Why: Same idea as the Underdrive pulleys, just taken to the next step. Instead of increasing the mechanical advantage that the crank has over the pulley, you eliminate the drag on the pulley altogether. No drag on the pulley means that there is no power used up to drive it. Popular Brands: Meziere
Mod: Tires other than factory size Tune: Yes Why: The computer uses the height of the tires to help calculate the speed and distance traveled. If you change this height, then your speedometer and odometer will be off. Popular Brands: You name it…
Mod: Coil Pack (a.k.a. COP’s) Tune: No Why: The computer just tells the coils when to discharge. How much they discharge, how fast they do it, and how fast they recover are all a function of how the coil is made. Popular Brands: Granatelli, Accel, MSD, and Summit Racing.
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"Vera" '07 GT. Manual, 3.55's, Spohn Adj LCA's, Hurst Shifter, GT 500 Rear and chin spoilers, GTA's, Steeda UDP, Roush rear springs, ProFab CAI #6, BBK Shorties
"Dyno's Rarely Lie, but E.T.'s and Trap speed say so much more."
Throttle body......I have yet to test any larger (aftermarket/GT500) yet. The only things I would think that may need changing is effective throttle angle and open loop throttle angle tables
The table in particular for the Throttle bodies I am talking about is the Effective Throttle Area-Vaccum vs Throttle angle table (or at least thats what the HP Tuners software labels it). My understanding is that it is used by the PCM to calculate the amount of air passing the throttle plate based on engine vaccum and Throttle angle.
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"Vera" '07 GT. Manual, 3.55's, Spohn Adj LCA's, Hurst Shifter, GT 500 Rear and chin spoilers, GTA's, Steeda UDP, Roush rear springs, ProFab CAI #6, BBK Shorties
"Dyno's Rarely Lie, but E.T.'s and Trap speed say so much more."
I have been running the GT500 t/b for a few months now and you can get by without a retune but it does make some dead spots at times by not having the correct values loaded for it. it's nowhere near the issues others have experienced using aftermarket t/b's but you should still have a retune just to get the correct values loaded. There is very little to gain on N/A cars with this mod anyway. I imagine a KB,whipple or saleen s/c car would see decent gains making it worth the expense to purchase install and retune for this item. FYI on a simple at track mod: Power Steering Delete Belt= No reflash
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leonardracing.com 11.89 @ 114.77 stock longblock n/a auto
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THANK GOD FOR THIS THREAD!
