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You will have a hard time getting to 250 with an intake, exhaust and chip even if your exhaust includes headers. without the headers (muffler only), my guess would be 242 or so. in fact, i would get the headers before i got a muffler (it's a larger constraint in the case of these cars).
BTW, per my last post, here is what THESE mods would do:
Muffler / Intake:
increase thermal efficiency of motor by reducing volumetric air losses due to friction
Headers:
same as above PLUS:
increase thermal efficency of motor by balancing relative output of each cylinder
ECU:
1. increase rev limit (remember, hp=torque*rpm/5252 so same torque at higher rev=higher HP
2. increase lamda value to provide 12.6:1 stoichiometric ratio
3. adjust spark map to account for #2
4. adjust fuel / spark map to account for #1
So how do these pan out on paper?
ECU:
Just increasing lambda for a 12.6 ratio would yeild 225 HP at 6000 rpm (using the dyno graph in this thread for locations of peak values).
This equals 197 lb-ft of torque.
If we move our HP max from 6000 to 6800 rpm and estimate a torque loss of 20 for 177 lb-ft at 6800, we now have:
229HP
Intake / Exhaust:
Intake: static pressure losses can account for at most about .25 psi manifold pressure. in our case, if we say we get the entire .25 psi, we now have:
236HP
Exhaust: In order to get the .25 psi manifold pressure that we gained above (from the intake), the exhaust would have had to be tuned to the itake in order to apply the full .25 psi.
We do, however, gain efficiency from the headers.
it's a lot of math, but here goes:
with the changes we've made, we are now burning .94 kg per minute of fuel at our 6800 rpm HP peak.
this translates into about .12 gallons per minute.
our friend gasoiline contains about 46MJ (yes, MEGAjoules) per kilo of fuel.
since we are burning almost a kilo a minute, that means we're cranking out 717 kilowatts of power.
this translates to, believe it or not, 962 HP available from the fuel we're burning. We're only making 236 HP, so we are 24.5% efficient *at this RPM*. The rest is lost to heat, friction, etc.
A tuned header can decrease compression effects at the manifold. this means that the exhaust exiting the engine can more easily expand (it's HOT!) due to reduced interference with other cylinders.
the more easily that this can expand, the cooler it is upon exit of the motor AND the lower its pressure. this does a few things:
this removes some of the load necessary for the pistons to PUSH the exhaust out of the motor in addition to the exhaust gas transfering less heat to the motor.
per newton, it also reduces pressure of gas against the pistons due to heat expansion.
finally, it transfers less heat to the engine.
all of these in our case will add up to about a .5% increase to our thermal efficiency AT THIS RPM (again, we start to get inefficient at the upper limits of our rev range). .5% of our 962 gross HP yeilds about 5HP.
We are now at:
241HP
So, the SHORT answer to your question "can i get 250HP from exhaust / intake / ecu" is: Not on pump gas. :-) you're looking at 241/242 tops (unless you live someplace that's freezing cold and at sea level).
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