20+ Horsepower from exhaust

[Fletcher]

I spoke with a tuner in Sacramento today. They have a dyno and tune european cars and the like. They sell the unichip. He said he can make hp in my car. Custom mapping after my mods are installed. I also found this interesting dyno chart on Unichips website. They have a great rep. Maybe my goal of 250 is doable (I am starting with 225).

[Fletcher]

I am awaiting verification of which model yesr this is. On their website unichip.us you can see all the numbers. This was with an scargo intake. Not too shabby. This is of course bhp.

[insite]

Facts: To get 20HP out of the boxster (2.7L), you need to do one of the following:

1. Decrease manifold air temp by 4% absolute (about 50F)

2. Increase manifold air pressure by 9% absolute (about 1.1 psi)

3. Increase overall thermal efficiency of engine by 10% abs (3% of fuel heat val)

4. Increase lambda number by .08 (to 12:1 stoicheometric rato [13.1 is stock])

which one of these does a muffler do? or an intake? discuss.

[spgribben007]

I have a couple of questions with this subject:


One is gas mileage. Would a muffler like the kind mentioned improve or hurt your gas mileage? What if you would include a power flow kit, would that enhance the performance and compliment those mufflers? With a limited budget which end should I concentrate on (intake or exhaust)?

And now the stupid question, how do you read a dyno chart? Do I compare the blue lines with red lines or the dotted line with the solid line? Sorry, but since I came aboard not too long along I have dffinitely learn a lot from this forum. Thanks guys.


spgribben007

[Brucelee]

If you add a chip, intake and exhaust mods, I can see getting to 250. I assume this would all be emissions legal? That is a big deal in many states.

[insite]

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).

[insite]

spgribben007:

exhaust / intake will improve your fuel efficiency under normal driving conditions. with a limited budget, i wouldn't do anything at all to these cars since gains are marginal at best.

the most bang for the buck short of a supercharger would be your ECU program, but you only get the most of it if you also do your air intake (muffler really not necessary on this car) and headers, all of which equals the price of the supercharger (almost).

as for the dyno charts, you are graphing torque and HP vs. rpm at the same time. torque is your flatter curve (for our purposes). hp always = 0 at 0RPM, so the HP curve starts very low. the torque curve is showing you, at each rpm, what your torque value is. the HP curve is showing you your HP output at each rpm. horsepower is derived from torqe (HP=torque*RPM/5252).

in the above chart, the dashed lines are torque and the solids are HP.

the colors usually illustrating before / after some type of mod.

[spgribben007]

Insite

Thanks for the suggestion and quick response.

[Fletcher]

But I would disagree about the ultimate gains acheivable. The current model has 240hp and I believe 197 tq. They did not change the internals of the engine, including cams. They did enlarge the throttle body, add factory manifold (header style) and ecu changes, as well as intake manifold changes (how much I do not know since my 04 has the flapper style intake as well). I believe it is made of plastic now which may help the intake temp a bit.
All relatively subtle changes for 240 h.p.. Is this the last evolution of this motor power wise (no way). But remember Porsche does not want to spend a fortune on exclusive parts and tuning for just this mill and they have noise regulations and blah, blah you know to deal with. Can you make it smog legal sure. The headers will delete the pre-cat but if you use dual o2 cats that are at least 200 cell and get the ecu tuned properly a/f ratio. You should be fine. The pre-cats are for some tailpipe bag test only (not sure what that's about). Ultimately the sniff test on the dyno tells the tale.
I also think unichip is pretty reliable so there dyno numbers along with the cold air intake from scargo should be very close. Of course we all know about the power range of these motors from the factory right (they differ) some are stronger than others. Perhaps the best combo is Intake, Headers, ECU.

P.S. I think this is a great topic and Boxster tuning is just getting it's feet wet. I hope we can someday get a reliable supercharger kit or a less expensive turbo kit 24k is ridiculous. Don't get me wrong the Boxster is a great car but I noticed recently how the power really flattens out past 6k and we have 7200 to work with

[Pilot2519j]

I doubt very much the claim of 20 hp plus. Neil from Orton Motors who specializes in doing performance mods for 986's mentioned that changing the headers from the more restrictive factory model will result in a freer reving engine. He did not mention anything regarding hp additional for doing the mod.
He does do the engine swaps which new engine costs are prohibitive. 16K for the 3.4L and 18K for the 3.8L

[insite]

Fletcher -

good points. i think that in addition to the changes that you mentioned, the majority of the gains in the 987 have to do with RPM and nothing more. i think some revisions to the intake have allowed them to maintain good driveability in the low rev ranges while further expanding the top end's spark map / fuel map / variocam program to move the torqe peak further up the ladder.

if you look at the dyno curve on the previous page, all it would take is moving / extending the flat part of the torqe curve (190 lb-ft in that graph, blue curve) from 6000 RPM (peak HP of 217) to 6630 RPM and you now have 240HP. if you go to porsche's website, you will see that indeed, peak power now occurs at 6400 RPM. this isn't the full 6630 that we needed, so they have added 7 lb-ft of torque; easily realized with the larger throttle body and new headers.

i have LONG believed that they drastically underrate the rev limit capabilities of their cars. think about this: my 1986 toyota celica was a 2L 4-cylinder. it redlined at 6900 RPM. It did this with cylinders and valves that were LARGER than the boxster's (2.0L / 4-cyl = .5L / cyl vs. 2.7L / 6-cyl = .45L / cyl) and connecting rods that were longer. from a force perspective, the new box generates 33.33 ft-lb of torque per cylinder; the celica generated 31.25.

considering the fact that a) the inertial mass of the reciprocating parts weighed more and b) this was a massed produced TOYOTA and c) that was 1986; one gets to wondering why that would be.