SlakkerRacingDev

We had the opportunity this past week to test 3 different intakes on a Slakker Hartech 4.1L 997.1S engine with X51 heads. The X51 heads flowed about 4% CFM more than the 997.1 heads and provided roughly 8-10hp in additional peak power with the 997.1 3.6L intake. By swapping in the 3.8L intake, we saw an additional 6-8hp and the X51 intake and plenum added another 5hp from there. For grins, we did another series of pulls using the ebay plenum with the 3.8L intake and it hung with the X51 intake right up until the end.

However, I think the X51 intake and plenum won the beauty contest by a pretty good margin.

Ob917

Thanks for this post. I’d love to see more posts from the community with actual real world results, super helpful. The other popular 997.1 engine builders say the 9a1 3.6 heads have more potential than the x51 heads on the .2 cars if I remember correctly. 🤷🏻‍♂️
I’m ready to build a 9a1 when you guys get the new sleeves to allow a 4.2 build.

Prairiedawg

Ok, now do a 9A1.

SlakkerRacingDev

Soon. Still lots of interesting M97 builds to do first though. But as soon as Hartech releases their 9A1 replacement cylinders, we will start machining/ building them. Baz is daily driving what we think is the final design so it shouldn’t be long now.

hexagone

I think it's great there's this data - but in real world terms...

It feels probably impossible anyone would notice single digit horsepower gains from the butt dyno, no?

SlakkerRacingDev

if you added a louder exhaust with it they would.

It’s a very subjective question but a great one nonetheless. From about 3500-7000 is where the NA 997 is really good which is one of the reasons they make such great track cars. Increasing torque 3-4% in that range is enough to feel a little bit quicker. But peak HP is how we generally understand a motor this country. So if you assume that peak HP is a curve and not a spike, then somewhere around added 15hp is usually enough for people to feel the difference.

The displacement upgrades are awesome because they improve the entire rpm band. From there, we look for incremental gains in the mid and high rpm bands that stack/compliment each other. Once there is enough air flow to meet the engines demand, it comes down to resonance waves, cam
timing events, and tune.

SlakkerRacingDev

Here is a great example of resonance waves that we stumbled onto. We were tuning a 4.1L (987.1 Cayman) with a stock 997.1S intake system on a chassis dyno (measuring rear wheel horsepower) and it wasn't making the power we thought it should. It turned out that the solenoid for the resonance flap in the intake distribution tube wasn't bleeding off properly and the flap was staying closed. So we did a pull while I was in the back holding the flap open with a pair of vice grips on the flap hinge (admittedly a little dicey). With the resonance flap open, peak power jumped 21hp and so we got a replacement solenoid and continued tuning the next day.

The interesting part was we ended up with back to back runs with the resonance flap closed and open and got to see exactly how big of an impact it was having. With the flap closed mid range power was 21hp higher, mid range torque was 25lbs higher and peak torque increased by 12 lbs.

platinum997

So why not just remove the flap all together or is that what is causing the power drop at the higher rpm? So open at low rpm, closed at high rpm is the right operation?

SlakkerRacingDev

The redline is with the flap open. The blue line is with the flap closed and provides the most power up until about 5250rpm. By set the flap to close a little before that (to allow for delay) and get the best of both worlds.

Resonance waves are essentially pressure waves that bounce back and forth in both the intake and the exhaust. If a high pressure wave hits the intake valve while it is open, it will force more air into the cylinder and create more power. Exhaust side works the opposite way in that the engine doesn't have to work as hard to scavenge the exhaust gasses out of cylinder when the wave is moving away from it. The speed of the waves can be calculated based on RPM (and temperature) and travels through the intake runner to the common plenum (overly simplified for explanation purposes) and then bounces back towards the valves. So the length of the runner determines what RPM band an intake is tuned for. The Varioram system, which has 1 flap for the 997.1 and 997.1S, allows the intake to essentially tune itself for two different RPM bands.

Porsche continued to build on this principal with 2 flaps which I believe was first introduced in the 987.1S Cayman, 1 in each tube. Here is a picture of a 991 GT3 RS4.0 plenum which is similar to the 997 x51 plenum (no flaps) except that they have added two flaps to it for tuning the resonance waves all the way to 9200rpm. (Not really relevant to this conversation but I just think it's interesting).