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YOUR RESEARCHFor those who rebuilt to 4.0
Leading reported evidence
Replace catless x-pipe
Performed · outcome unconfirmed
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Then I swapped the catless x-pipe for top gear 200 cel cats/xpipe, no noticeable change in noise or power.
Leading evidence: 'Replace catless x-pipe' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Replace catless x-pipe' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
Then a proper dyno tune, noticed a small change everywhere.
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Suggestion
Then I did the larger GT3 IPD plenum and larger Panamera throttle body, noticeable change all over the curve.
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Suggestion · Original poster
Did anyone change to some kind of performance cams, change throttle bodies.
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Suggestion
Since we break in and test every engine we build on our engine dyno (6-8 per month), we have a solid understanding of what bolt-ons work—and which ones don’t.
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Rennlist: 1 discussions
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I'm probably going to do a rebuild in the fall after DE season ends. My question is what performance gains have been seen with goi g to 4.0 sleeving? Did anyone change to some kind of performance cams, change throttle bodies. I'm sure it will require a returne.
I'm just looking for real world data. Seat of the pants inputs welcome as well.
First part of my project was just the 3.6 to 4.0 swap. Torque and power difference was highly noticeable from the one drive I�d been on ( had bad bore scoring when I bought it ).
Then I did a tiptronic to manual swap, no difference in power obviously but changed the driving experience
In other ways.
Then I did the air box resonator delete. Noise change only.
Then I did the IPD plenum swap, felt a little bit of oomph up top, no lower loss down low.
Then I did the larger GT3 IPD plenum and larger Panamera throttle body, noticeable change all over the curve.
Then a proper dyno tune, noticed a small change everywhere.
Then I swapped the catless x-pipe for top gear 200 cel cats/xpipe, no noticeable change in noise or power. The exhaust smell diminished which is what I was after. Rest of the system is Fabspeed.
Considering cams and investigating to see if I have the larger exhaust manifolds already�..but also seriously considering selling the car for another project.
I have a thread on here which documents everything I did in detail. 😊
RapidIC, I've been through your threads and had a couple of PMs with you. I'm kind of in the same boat. Did the tip to 6 speed, Top Gun cats and mufflers. Now I'm looking for more midrange torque since it seems sluggish at DE days and lagging cars I should be keeping up with. Looking g at the awd delete next fall. Too many other projects this spring and summer to consider losing any track day opportunities.
I rebuilt my 997S from 3.8 to 4.0. The difference was noticeable but not earth shattering. I have a Tipt and did not get a tune. It was a grocery getter, no need for huge performance bump.
Our naturally aspirated (NA) 4.1L engines have been delivering anywhere from 375-415 peak HP at the crank, and boosted setups have achieved 475 HP (4 PSI) to 535 HP (7 PSI). Since we break in and test every engine we build on our engine dyno (6-8 per month), we have a solid understanding of what bolt-ons work—and which ones don’t.
Here’s what you can expect:
375 HP: Displacement upgrade with ECU adaptation, keeping everything else stock.
415 HP: Ported and polished heads, 82mm throttle body/plenum combo (not IPD—the wedge disrupts resonance wave tuning), 997.1S intake manifolds, high-flow cats, and a Motec M1 ECU.
535 HP: Xona turbo, Tial wastegate, and ported/polished heads.
Weight savings is another key to improving performance—dropping 100 lbs is roughly equal to gaining 10 HP.
Places You Won’t Find Gains:
Plenums with a wedge in the middle.
Anything that deletes the rear intake distribution flap.
Airboxes: Across the board (996.1, 996.2, 996 X51, 997.1, 997.2, BMC air filters, K&N cone filters), we’ve seen only a ~3 HP delta. On our dyno, the K&N consistently edges out the others, but just barely.
Mufflers: No significant improvements here.
Exhaust manifolds (like Soul) can improve certain rpm ranges, but the stock manifolds are remarkably effective. The challenge lies in the variability of resonance waves due to temperature changes. While intake side tuning is predictable, exhaust side tuning has far greater variability.
Note: All numbers are from our engine dyno, measured at the crank using STP correction, on 4.1L engines.
