I am not extremely knowledgable about the mechanics of the engine, and its operating procedures so I will give this a shot.

From what I understand the Z's engine is too high a compression engine to "safely" run FI systems with stock internals. In order to take a FI kit currently available, lets say the Greddy for example, and run it "safely" what would need to be done and what is the approximate cost?

I do realize that there are many different routes available, and different price points can be used, but I am just trying to learn and get an idea of what it would take. I am not looking to run 900+ whp, just enough maybe to run in the high 12's or so, I guess around the 400+ crank level we are seeing now with relative reliability(so far anyway) from these "new" kits. Essentially take a kit out of the box and use the preset levels.

Also would simply reducing the compression ratio help these kits that are now out, or would everything have to be retuned from the ground up again? And would there be any difference in choices for a SC compared to a TT? Would you change different parts, or the same ones?

Thanks in advance for answering such an open ended question.

-Joe

 

In order to acheive your goal, you will not need to build the motor up as you suggest. You can use the Greddy TT or other turbo kits to get there. You can also use a supercharger. The problem right now with reliability at the 400 HP mark is effectively retarding the timing although it appears that this is becoming less of a factor now that people are beginning to use measures to control this aspect. I would check out some of the threads on FI and see what equipment people are using to maintain reliability at what HP level and go from there.

Timing, Air:Fuel ratio, compression and boost are the four main factors that play into the FI equation.

Air:Fuel is quite obviously the ratio of air to fuel that is combusted in the combustion chamber. This is where the spark plug lights the fuel and makes the pistons force the crankshaft to turn and create power to propel the car. Most people think that about a ratio of 12 parts air to every 1 part of fuel is sufficient for a safe running FI motor. Getting more air (ie. 14:1 ratio) can mean too little fuel in the chamber and will create a "lean" condition which means increased heat and possible melted pistons. This is also a cause of detonation where the heat caused by being lean will ignite the fuel before the spark plug does and this will also ruin the pistons.

Timing refers to the moment when the spark plug lights in relation to the piston location in the cylinder. If the timing is off this can also create a lean condition (too much timing, too high) or can reduce performance by being too low (or too little).

Compression ratio is most easily altered by changing pistons. Look at www.sgpracing.com at the pics of the pistons with 8.5:1 ratios compared to the 11.5:1 ratios. You can see how the 8.5s are sort of dished to reduce compression and the 11.5s are raised to increase it. So much that recesses have to be made for the valves to fit into so they do not slap the pistons when they open and the piston is in the "up" position. The valves open to let air and fuel into the combustion chamber to be exploded and then open again to let the resulting byproduct out into the exhaust. This is all done through the head as that is where the valves are. Anyways, a higher compression ratio will compress the air/fuel mixture in to a smaller space (raised piston) and create an effectively larger explosion (same explosion/smaller space). This will in turn create more heat being that its a smaller space. You know what that does from the AF ratio paragraph. Lower compression will make less power.

Boost refers to the measurement of the air forced into the motor by your choice of FI. Boost makes more power than compression ratio, timing, or a leaner AF mixture. It is large amounts of air forced into the motor by an external machine be it turbo or supercharger. This provides an overabundance of what lights in the air that is in the combustion chamber (oxygen). Same principle as nitrous. Nitrous is an oxygen rich gas. Another topic.

So lowering timing, compression, and richening the AF mixture will allow a person to force more air (higher boost) into a motor and make more power at a safer level. The cheapest and easiest to do is to retard timing and richen the AF mixture. It is way more expensive but way more effective to lower the comression ratio. Altering timing and AF ratio has proven effective at the 400 HP mark in the Z to be reliable. However, altering one and not the other has proven to be engine destroying. Changing pistons and lowering compression will allow larger amounts of boost and as a result, larger amounts of HP to be made. This is more or less unchartered territory with the Z right now though because at those levels of power other things are necessary to maintain the integrity of the block. Again, that's another story.