Modifications for the g60 engine. This is only a basic list of posts discussing common modifications, and is not meant to be exhaustive.
Here's a great post on some "gentle" first modifications for people that want a good bump in power without going all-out:
And here are some posts on some less common modifications:
Posts on more common mods:
A few of my own notes:
1) Maintenance before Modification. Making sure your car is in tip-top shape before you go throwing modifications at it is very important. If you've got driveability problems and an engine that stumbles (or whatever) and you try to modify your engine for more power, you'll probably be very disappointed.
2) Hang out in the g60 forum. Read old threads. This is probably one of the best ways to get a handle on what's going on in the g60 world, and to get a good feel for what people are doing and what problems they are having.
And here's a basic explanation of the "stage" kits you commonly hear people discuss for the g60 engine.
-ISV reroute or check valve
-68mm pulley for the supercharger
-Low-temp fan switch and check valve
-Same as stage III with (usually) a 260 deg. cam
-Same, with a 268/260 cam and stage IV chip
Not well defined, usually all of the above and some of the following:
-Smaller pulley (62mm, 58mm and so on)
-More aggressive cam
-Porting modifications - head, intake manifold, throttle body, etc.
-Chips with different functionality
In addition, you'll see many people talking about other methods of forced induction on the g60 engine - different superchargers and turbos. Those usually recieve the same modifications as above.
And here's a basic run-down of the modifications listed above:
ISV reroute or check valve - not a direct power adder itself, a reroute or check valve is more to be certain that your ISV isn't leaking boost. The reroute kit repositions the tube exiting the ISV such that any leakage is just dumped into the intake piping and thus not lost, and the check valve simply doesn't allow air to flow "backwards" through the ISV. Basically, you need one or the other, not both.
Low temp fan switch and thermostat - Used to ensure that your engine does not overheat under the additional stress of power-adding modifications. Note though that it is very important to have your cooling system working properly before you throw power parts at your car. You want these parts as insurance, not as band-aids to hide the fact that your cooling system is in bad shape. In fact, there's been some debate as to wether or not you should even use these parts.
Smaller Supercharger Pulleys - These are key to g60 performance. Basically, the g60 charger spins at a certain ratio to the crankshaft rpm's, since it is driven off a belt from the crank. So, the size of the pulley on the charger will determine the speed the charger is spun at a given engine speed. So, if you put a smaller pulley on, you'll get a faster spinning charger, which will give you more boost. Basically, pullies are the "boost controller" of the g60 world.
(Side note about charger reliability!)But, there are limits. The g60 charger wasn't meant to be spun at crazy speeds, and doing so only stresses an already fragile charger. This has several implications - first off, you shouldn't play with smaller pullies on a charger in unknown condition. Send the charger to a reputable rebuilder and get it checked out before you notice signs of failure. BBM, ORZ, and KK all have good reputations.
The classic choice in a small pulley - 68mm - is fine to have on a daily driver car, and if your charger is in good shape and you've got a level head, having one on your car should not worry you. However, using pullies smaller than that, or running a 68mm (or even stock) pulley on a charger in unknown condition is just asking for trouble unless you know what you're doing.
Fuel Pressure Regulators - Without getting into a complicated explanation of how your fueling system works, here's the simplified version - the computer controls the amount of fuel entering your engine by opening and closing the injectors really really quickly. So, in a given amount of time, the injectors will be open for a certain percentage of that time, and closed for the rest of the time. The Percentage that they are open is called the duty cycle and helps determine the amount of fuel that reaches the engine. The other main factor that determines fuel amount is the pressure of the fuel in the fuel rail. The fuel rail is just a fancy plastic pipe that connects the four injectors together. Basically, for a given duty cycle, the higher the pressure, the more fuel will be injected. So, if you increase the fuel pressure, you'll increase the amount of fuel delivered.
It gets a bit more complicated than that, but that's basically the reason why you need a fuel pressure regulator (or FPR) upgrade when you do the basic "stage" kits discussed above. The chip(s) you put on your car to provide proper fueling are programmed with certain parameters in mind, and one of those is that there will be a higher pressure fpr on your car! The most common choice for an fpr is a 3.5 bar unit, which is half a bar higher than the stock 3.0 bar unit. Be careful though - there are scads of fpr's from other cars that will bolt on, you need to be sure that you're getting a 3.5 bar unit. For example, a common place that people get these units is from Porsche 944's - but some of those came with the proper 3.5 bar unit, and some came with a 2.5 bar unit.
Another note on fpr's for anyone who's curious. They are rated with a given pressure, but they do not maintain that given pressure in the fuel rail. You'll notice that they have a vacuum line attached to them that runs to the intake manifold. Ever wonder what that was for? Well, inside the fpr is a flexible diaphragm that sees fuel pressure on one side, and manifold pressure on the other side. This side of the diaphragm is spring loaded too, the spring determines the pressure rating. So, on one side of the diphragm you have the spring pressure and the manifold air pressure, and on the other side you have the fuel pressure. As the diaphragm flexes, it sort of uncovers an opening on the "fuel" side running to the fuel return line. (This is hard to explain without a diagram, bear with me!) This flexing is what regulates the fuel pressure - the pump is basically constantly pressurizing the fuel rail, and the diapgragm inside the regulator is flexing under the pressure created by the pump and allowing fuel to return to the tank via the return line. Thus, the pressure reaches an equillibrium where the fuel is returning to the tank at a rate such that the pressure inside the rail is held at a certain value.
Since the "air" side of the regulator is pressurized by the spring and manifold pressure, your fuel rail is pressurized to manifold pressure + the fpr's pressure rating. So, if you're at full throttle and seeing 1 bar of boost (about 14.5 psi) then you're fuel rail will be at 4.5 bar if you have a 3.5 bar fuel pressure regulator.
ECU Chips - These are, perhaps, the most important component in the modification process. Re-mapped chips allow your engine's fueling and spark systems to adjust to the higher power your engine will make with other modifications. Choosing the correct chip for your application becomes very important once you've ventured into the more extreme reaches of g60 modifications, but for the "normal" stage kits listed above, there are several good chip choices.
One additional note about chips - a chip should not be thought of as a power-adding modification. Instead, it should be thought of as a way to adjust your engine for other modifications you've made, in order for your car to operate properly and make the most power it can with those modifications.
Cams - Swapping to a more aggressive cam is pretty straightforward. One thing to note though is that with some methods of forced induction (turbos especially it seems), the really aggressive cams can make less power, since they allow more blow-by due to higher overlap.
Another note about cams - when you swap cams, it is a very good idea to put new lifters in at the same time. Old, worn lifters will kill a new cam in no time. Also, be sure to follow the installation and break-in instructions that came with your cam.
Porting work - Usually done when the normal modifications have all been carried out, porting the head and intake manifold can help to unlock quite a bit of power on the g60 engine. The counter-flow 8 valve head on these engines isn't the best flow-wise, and a correct porting job can work wonders. It is important to get the job done by someone with the knowledge and experience to do it right, though. An incorrect porting job is a waste of money.
Larger injectors - Intermittent injectors, like those on the g60 engine, control fuel delivery by opening and closing at a rapid rate. The percentage they are open in a given time interval controls how much fuel is injected. So, in a given second at idle, they may be closed 90% of the time and open only 10%. And, at full throttle and 6k rpm's, they might be open 80% of the time. Basically, when you reach a certain point modification-wise, you'll be cramming so much air into the engine that the injectors can't keep up - even when they are open as much as they can be, they won't be injecting enough fuel. So, the remedy is to swap in higher flowing injectors. When doing this, it is very important to get a chip that is matched to your injector size, otherwise you'll have problems. See section above on fuel pressure regulators for more info on helping your fueling system keep up.
One may venture to ask this question: "When I've reached the point where people are telling me to get bigger injectors, why not just slap on a really high pressure FPR?" And you'd ask that question with good reason - an fpr can be had for $45, while a set of injectors will probably run $100 used, and several times that for a new balanced set. Well, you have to remember how fpr's work - they don't pressurize the rail themselves, they basically just regulate the pressure created by the pump. So, at a certain point, the pump is the limiting factor in the amount of pressure you can have, not the fpr itself. So basically, if you threw a 6 bar FPR on (if you could find one!) then you'd be waaaay over the limits of the pump, and your car wouldn't run as you might expect. It's at this point - when you've got a higher pressure fpr and need even more fuel - that the bigger injectors make sense.
[Modified by SaabFan, 8:14 AM 12-13-2002]
[Modified by SaabFan, 4:21 PM 4-17-2003]