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The goal was to remove a torque hole between 4200-4700 RPM, that appeared when moving from a VICS manifold to the Skunk2. The idea was that the squaretop would be the best of both worlds. Here was the plot that made us move to the squaretop:
BLUE – Skunk2 (Muffler) – More Torque after 6250
RED – Skunk2 (No Muffler)
GREEN – VICS (Muffler) – More Torque 4200-4700
After moving to the squaretop we are down power EVERYWHERE.
Blue: Racing Beat, Kooks Exhaust, VICS Intake (Pre-Flat Floor)
Red: Modified JDM Tri-Y for Side Exhaust, Skunk2 Intake Manifold, 14" Intake (smooth 90)
Green: Modified JDM Tri-Y (Larger secondary runners and 2.5" exhaust) , Squaretop Manifold, 21" Intake (smooth 180)
Removing the 21" Intake and going straight TB was 2hp and 3ftlbs lost.
Removing the muffler was 0hp and 1ftlb lost.
Wheels and tires are about 1-2lbs heavier.
Fluids are all the same and new.
Fluids are not overfilled.
The engine has 2% leakdown
There was an endurance race in-between where the flexpipe shrunk during the race and eventually blew out. This would have built up excessive backpressure, but I would assume we would see any engine issues with the leakdown, right?
Has anyone seen this behavior when moving from the squaretop to the Skunk2? It appears the squaretop is performing worse than the VICS.
Its possible that all or some of this is also exhaust related since we moved our secondaries from OE size (1.1ish) to 1.38ish. However it was a cleaner version of the custom mid-pipe. We also changed the 20" of pipe between the final collector to the muffler from 2.25" to 2.5", What made us want to go larger was the fact that the muffler going to a shorter muffler and removing the muffler resulted in more power.
If I understand correctly you modified the header and exhaust at the same time ("Larger secondary runners and 2.5" exhaust")?
Maybe the primaries are too big and killing power
Primaries are the stock JDM Tri-Y
Secondaries were increased from stock sizes (1.1") to 1.38" ID
At the same time we changed the final collector from 2.25 to 2.5" and there is about 20" of tube and a 90 degree that also changed from 2.25 to 2.5".
That said, the 6-8ftlbs across the entire range is a big change and I would expect that torque up top would have increased if it was related to this change, but its a valid question.
Too many variables to judge.
Ambient change? Intake temps differ? If stock ecu then it pulls timing very quickly once past 35c of iat.
Greg's upcoming video should be same-day mani swap on the dyno (with a squaretop I sent him), all else being equal.
That intake tube test is pretty interesting. Bigger changes than I would expect. That filter directly on throttle run with the big torque hump at 3.5k rpm is pretty amusing.
02-26-2021, 08:33 AM
Dyno - Squaretop vs. Skunk - Odd Performance
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