Gone but not forgotten
- Jan 30, 2001
- Hermosa Beach, CA
- 1987 Z51 Silver Coupe
Taken from the "Performance" page of http://home.fuse.net/c4/:
Here are some things that won't really do you much good...
Throttle Body Changes
Unless you are going to replace the TPI runners with larger diameter versions, there is no point in buying a 52 MM or 58 MM throttle body.
The problem is the runner restrictions. By doing the things listed above that improve your intake air flow, you have maximized the flow as much as you can realistically expect to increase it without major (read expensive) changes.
Also, increasing the runner diameter or installing shorter runners will cost you low end torque but only slightly increase your high end horse power. As mentioned above, unless you can run your car at very high speed, you should stick with the stock runners and enjoy the torque boost they provide.
Adjustable Fuel Pressure Regulator
A high pressure fuel regulator is a waste of time unless you are putting in a custom PROM in the ECM that allows for the increased pressure. (The stock PROM will sense the increased pressure and immediately react to it so you can't get a result you can feel from your efforts).
Basically, the O2 sensor will sense the richer mixture, the ECM will read this and shorten the on time for the injectors. A custom PROM chip would react differently but the stock chip and most mass market performance chips don't address this issue.
You should however check the pressure that your stock regulator is producing. Make sure it is above 35 pounds. (A gauge to check this is available from virtually all after market suppliers for around $40.00).
Higher Output Injectors
The same "waste of time and money" logic applies to using higher output injectors. Unless you are going to change the PROM to take advantage of the increased amount of fuel, it is a waste of time and a big waste of lots of money to pump more fuel into the engine.
Cold Air Induction Systems
Lastly, cold air induction systems are not going to accomplish a great deal in an L98 engine although it does help slightly in an LT1 or LT4. The theory behind these cold air induction add ons is you get a 1% increase in horse power for each 10 degrees you lower the temperature of the incoming air.
A cold air induction system grabs the air from a point outside (or at least nearly outside) the area immediately in front of the radiator where engine heat is trapped in a stock car.
Problem is, on an L98, coolant is passed through the intake manifold after it has passed through the block (This is not true in the LT1 or LT4. It goes through the intake manifold first) and therefore, in varying degrees the intake manifold is going to heat the cylinder's input air up regardless of what you do to the air before it gets to the intake.
Also, the throttle body has coolant passed through it to guard against the throttle body blades becoming iced up during certain temperature/moisture combinations (30 - 70 degrees F and dew points at or above 50 degrees F). You could bypass the coolant but shouldn't unless you are never going to drive it when it could ice up.
Bottom line is: all of this heat is just not going to be overcome by lowering the intake's air temperature 10-15 degrees F and even if you do lower it 10 degrees, 1% of 300 HP is only 3 HP which is can be measured on a dyno but is in the noise as far as actually feeling it.