The above shows a recent dyno run I did for my 997S. As illustrated, there's a flat spot of torque delivery at around 3000rpm, which is noticeable while driving.

So what can we do to smoothen out the flat spot? Any thoughts?

 

I have AWE cats, works very well and my car pulls very hard through the power band. I haven't dyno'd it so I can't tell you if it is there or not on my car.

 

Is the car stock? Is that the factory map?

 

It's the resonance flap that is flattening the curve. Just like the drop you have around 5100 rpm when the flap opens.

 

need more info on mods and what ecu tuning is involved

 

Thanks guys for the inputs!

The car has got Europipe and that's all. There's no mod to the ECU nor air intake, just the exhaust.

For those who's not familiar with Europipe, it involves a set of X51 headers, 100-cell cats and mufflers. See below:



The dyno was done right after the exhaust installation.

For this, anything we can do about it?

 

i have the same mods on my 997s, with no mods to the intake or exhaust. i recommend a ecu flash "giac" ie. also what gear did you do the dyno pull in?

 

Not sure which gear, but I would presume it's the 4th.

Why GIAC? Any good?

 

the reason i ask what gear is because, i dynoed my car in 3rd and 4th....my car made 317 rwhp on the 3rd gear pull, which was about 4 hp higher than in my 4th gear pull.

i am about to get the giac upgrade, and i to wanted to hear some more feedback from members. wanna know if its worth the upgrade.

-jason

 

i have heard giac is the best software. my brother is running giac software on his turbo and it was a significant hp and torque increase. i am not sure if the non-turbo cars react as well to the upgrade. anyone with some 1st hand experience?

 

For the dips at 2600 and 5200rpm on this engine - absolutely nothing unfortunately. They're a characteristic of the engine produced by the resonance effects in the intake system. The 2 points in the rpm band where the dips occur also correspond reasonably closely with the points at which the resonance valve in the inlet opens and closes so I'm guessing they represent the crossover points of the torque curves produced by the open valve condition and the closed valve condition.

Having seen the full throttle mixture and timing maps for these engines, you can see where Porsche has already added a little timing and slightly enrichened the mixture at these points to try to compensate for the dips - it's already been done in other words.

This is where a single throttle plate per cylinder like the BMW 'M' motors would help. I've seen some Porsche Motorsport GT3 engines with this arrangement but don't know if a) it's ever been standard on any production Porsche engine (it certainly hasn't on the Carrera engine) or b) if anyone offers this level of tuning for a Carrera motor. Could get mightily expensive if they do......!

 

Thanks Ian.

So you are saying Porsche has done what they could cost-effectively to address the issue/characteristics of the engine? And any kind of ECU flash might shift the entire curve upward a bit but not change the curve pattern, i.e. those two dips would still be there.

Unless a custom ECU program....

 

The tuning flap in the back crossover tube is controlled by the electric changeover valve which recieves it's vacuum supply from a reserve canister on top of the engine.

The tuning flap is normally open and operates as follows:

Open from 700 to 3120 rpm and from 5120 rpm .

Closed from 3120 to 5120 rpm , if the throttle is also more than 30% open at the same time.

You can modify it to stay open at all times or closed at all times or open and closed at different times. All changes will effect performance and move the power band around. In effect, you would be modifying the size of the intake.

 

I agree with this entirely. One tuner here in the UK I've spoken to and who's experimented at length with this on the dyno with 996s and 997s tells me the torque curve can be changed quite markedly. He also said that in the end however, Porsche's own solution always seemed to be 'best fit' for general use.

It would be interesting to see if you could use this flap to optimise top-end power (at the expense of lower-down torque) for use on the track.

 

Any change to the intake system will determine where PEAK torque is located. Its effect on flow due to the change in the sound waves and frequency of the air’s movement.

Most people think of an engine as an air pump, which it is, but intake air can and is FORCED past the intake valve, depending on the design of the intake system and the sound wave it produces. When the intake valve is open, this wave, traveling at the speed of sound, passes into the cylinder. When the valve closes, the wave bounces off the valve and back into the intake, again traveling at the speed of sound. When it hits the intake, the air is compressed before bouncing back towards the valve again with a different frequency and with a positive pressure.

Therefore, it is important that this positive wave to get to the intake valve at the exact time the valve is opening in order to maximize the benefits of the positive pressure. This allows for greater cylinder filling than you would otherwise have.


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