Two Questions

[conquezzy]

Whats the difference between the 88-89 igniter mod vs the one hose 3 port wastegate mod?

 

What is the max psi on a 12a before it runs out of its efficiency range?

[Indiana]

There were two reasons for that 88/89 ignitor change, one was to allow higher boost pressures but not for manual transmission cars at lower rpms so that was one reason and the other is if you used regular unleaded fuel and not premium your max boost was lowered. There's ZERO reason to do that "ignitor mod" when you get rid of that little solenoid on the air can and just use the outer chamber on the three port wastegate actuator.

 

The "efficiency" of a turbo can be defined differently by each person you ask. Will it continue to make boost increase if the shaft spins faster? Sure it will until some physical limit prevents that. What does happen is that past a certain boost pressure, and this can also be changed from one car to the next EASILY, the temperature of that charged (boost pressurized) air goes past point "X" or where you or someone else says no its just too hot and this can also be different for every one you ask. Two things your motor uses to put in more fuel and air, pressure and flow. Pressure is that air exiting the turbo built up to X psi in your intercooler system and this can be changed by different size tubing and intercoolers. CFM flow rates are effected by intercooler tubing size, shape and the "efficiency" of the intercooler core. Say you have a 12a on a 100% stock setup and another guy has a stock turbo but on his car he has a larger intercooler, he has a cam with increased duration, lift or overlap and he has a ported head, header and large open exhaust. You think 15psi on your car and 15psi on the other car is the same? Sure, 15psi is 15psi just like a 15lb sack of potatoes is the same weight as a 15lb sack of feathers. BUT the shaft speed required by your car to make 15psi in your car is MUCH LESS than the shaft speed required for the other guys car. That shaft speed being higher in the other guys car means he is producing more HEAT in his turbo. He says that his "efficiency" of a stock turbo is 15-18psi and you say oh no you are wrong on my stock car its 18-20psi and you have this argument that has gone on for years. What you'll find is that one car with the higher boost pressures and smaller intercooler plumbing is flowing air faster for the same pressure than if the tubing was larger. Given the same shaft speed that smaller tube setup is better because it keeps the air flowing quicker and that can carry in more fuel. If you add more pressure this effects something else not related to CFMs and that's your compression ratio. The higher your boost goes, the more your compression ratio is increased. This is why now some of those high hp cars with high boost are running lower compression ratio pistons not higher CR ones. That gives them a larger tuning window and room for greater error and for higher boost levels. If you really want to know you have to get one of those sensors that read turbine shaft speed otherwise those compressor maps and boost pressures are all BS crap and mean nothing and no two cars can be compared and you are only talking about turbine shaft speed and not the rest of the car. For your purposes and a stock car, your turbo can easily push 20psi but you should be aware that this is more heat than 12psi being made for the air and the oil and water running through the cartridge and if your turbo isn't in the best of condition it might not like that and you might end up having to rebuild it sooner than later. CFMs flow in air and carry fuel with it, PSI packs in the air and fuel that was carried in. These two things are both going on in your motor and again no two cars are exactly alike unless they were built to be that way, as in both are 100% stock.

Edited May 13, 2010 by Indiana

[conquezzy]

^ Thank you!