It's no surprise that we all want as much power as possible, but sometimes the smell of unburnt fuel can get overpowering, make you stink like you've been at a gas station all day and infects the upholstery in your car... So we have always wondered just how much power we would be gaining if we decided to run NO CAT at all..
This is a tricky one because from factory, cars typically come with quite a restrictive catalytic converter, so the real question here is - how does a completely gutted or removed cat compare to a decent sports exhaust with a high flow cat?
We hit up XForce Performance and GT Auto Garage to help us answer this one.
Our JZA80 Supra makes around 850whp on 33psi of boost, so this was going to be quite a demanding task on the catalytic converter, since at those power levels, we are probably getting to the region of maybe needing to look at a 4in system instead of a 3.5in. So even the mufflers and resonators are going to be giving some restriction, let alone a 100 cell cat.
But, there was only one way to find out just how much power a cat robs, and that was to throw it on the dyno.
With the assistance of MDSFab, we got a 3.5" "test pipe" made up, and a direct bolt in 3.5in cat on some matching flanges so we could easily swap out the test pipe for the cat and run some back to back tests.
We did 3 runs for each setup, with the results being quite consistent and within a few horsepower of each other.
It should be noted that the real difference only comes into play at the very peak power levels. Average punters with 500-600hp cars will see absolutely no gains in removing their cat, while people with 1000+ hp cars will probably see a further improvement by going a bigger exhaust all the way through.
Now that we have answered this, let's see what we can do with a 4" system!
For anyone interested in the T51 sound mod, hit up / turbomodpro
Engine specs:
Stock 2JZ VVTi block
Kelford Cams V202-D 272/278 10.2mm lift cams
Kelford valve springs to suit
Hypertune 100mm intercooler & plenum
Turbosmart 60mm gate, BOV & RR-FPR
GCG Turbochargers Pty Ltd GTX3584RS-2
Turbomod.pro compressor housing modification (T51mod)
6boost exhaust manifold
Haltech Elite 2500 ECU
PWR Performance Products radiator
Southam Engineering R35GTR ignition coil conversion
Hardrace Suspension Australia engine and trans mounts
Wiring by Whitey's Wiring
Boomslang engine harness
2200cc Bosch injectors
ARP head studs
XForce exhaust with 100 cell high flow cat
Tune by GT Auto Garage