20+ Horsepower from exhaust

[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.

[Fletcher]

I have heard that Porsche is trying to milk these engines in small incriments due to the logical ceiling with the 997's 3.8L mill. They will spread out the h.p. and displacement to allow small steps just as with the original 986 the cap being 225 on my 04 2.7 (series 1 let's call it). Now with the 2nd gen motors they have upped the hp a bit. Like you said moving the obvious graph up a few hundred rpm and thus power and a bity of torque. My motors redline is 7200 and yet max power is at 6450 I think (but it really goes flat above 6k).
Ultimately if I could move that graph up to say max power at 7000 while adding headers, intake etc should get me close to 250. It would be more enjoyable to drive (pulling to redline) as apposed to falling flat at 6k. If all goes well it will be fun trying anyway.
I love tuning chat
P.S. I found out that contrary to what I thought before, Remounting the first o2 sensor to the cat (in the case of a high flow system, the one that WAS at the pre-cat) is not good. You have to extend the harness leads to the o2, that's bad. And by leaving it very close to it's original position but now on the headers (just past the collector) is the best shot and for no cel. Header wrap/jethot coating would probably help in this regard as well keeping the inside HOT for proper o2 reading. Neil @ Orton said he does this all the time with no cel's.

[insite]

if you had a set of headers tuned for 7000 revs made, programmed ecu to match, added a larger throttle body / smooth intake, then you'll see 270HP IF the valves are large enough (not sure what the stock diameter is).

that assumes 150F manifold intake temp, .25 psi manifold pressure increase, no thermal efficiency increase, lambda=.8. Just the RPM increase alone, if the ecu has enough play to tune to this RPM, would give you 253. Add everything else and you get your 100HP / L.

[insite]

Does anyone know the valve diameters or port areas for these cars? If we can find those, we can calculate the theoretical and most likely HP limits of these cars (without doing any serious engine work first).

[Lux]

Insite,
Good stuff, man.

Fletch,
Custom mapping will yield the highest gains for sure. But even then it's still minimal gains. Dyno charts are great and all but you need to know the facts behind the numbers. Showing gains on 94 or 104 octane gas means nothing since we only have 91 in CA.

[Automon]

Why only 91 in CA? I live in $hit hole USA (MI) and I can get octane up to 110, which I run in my bike but not my Porsche
Automon

[Fletcher]

You just have to look for it. You can blend to get 93 or 94. Try this blend chart if you need it.http://members.aol.com/SteveL1994/public/OctaneChart.xls

[Lux]

Originally Posted by Automon

Why only 91 in CA? I live in $hit hole USA (MI) and I can get octane up to 110, which I run in my bike but not my Porsche
Automon

Well, I can get 104 octane down the street at the local 76. But at almost $5/gallon I'll pass. I'm just suspicious of tuning for OBDII cars. Even Jim Conforti of BMW tuning fame said that OBDII is a ******************** and that getting 5-6hp is about it. Of course he's talking about a different car (E46 M3) but since all cars since '96 have OBDII I'd guess that we're in the same boat.