Warwick Morris

Yeah, I did hear it. Probably too loud for me, but it did sound the business.

d00d

It's a common assumption that removing a restriction such as a muffler or catalyst from the exhaust path decreases torque, but that's not true, at least for a GT3 and probably the same for a GT4.
Money2536 actually saw an increase in torque with the exhaust valves open all the time;
https://rennlist.com/forums/991-gt3-...l#post11889943

jlennox

Are there any gains when fully catless with race headers vs the catted version with race headers?

Jamie@dundonmotorsports

For a stock car, even with our race headers and tune the gains without cats in the rear muffler section are minimal. On a Spyder we recently completed with heads/cams, prototype air filter box, etc... our exhaust with test pipes installed made 5-8whp. As the engine is trying to push more air out at high RPM's the stock exhaust can become a restriction, but we're not seeing it until you're at almost 400whp...

So the short answer is yes, but unlikely to see them unless you go whole hog!.

John@Fabspeed

No offense taken, still think you are an awesome GT4 member You've been wanting a system like that for a year, plus Jamie is a cool dude lol

O5C4R

Ok so with race headers is your exhaust with the 200 cats much quieter then the stock exhaust - sorry if I've missed this somewhere above

Jamie@dundonmotorsports

At full throttle yes it is more quiet by about 10-12dB over the stock exhaust. You can hear the exhaust note a bit more than the PSE with the valve closed as our mufflers are a little smaller.

O5C4R

Thanks, I will seriously consider this, especially if you can pack the mufflers as mentioned for a little more sound deadening

i do love the race headers at full song however

Jamie@dundonmotorsports

Is that you! Super cool!

Leuz

Sub

thigos

Jamie, I saw that you can buy this on your site now. Any updates? Would like to get some db info comparing the sound levels of the different options...
Thanks,
Matt

RDCR

When you say "stock exhaust" do you mean the PSE on your headers or stock GT4 headers/PSE?

Based on my experience at Laguna the stock GT4 exhaust system at full throttle with valves open reads between 96-98 db and under 90 db with them closed. If your system is a true 10-12 db less with valves open over a stock GT4 system we could run aftermarket headers/your exhaust at Laguna without the need for a GPS based exhaust controller to force the valves closed at the sound booth.

I've heard claims the stock PSE with valves forced closed will still pass sound at LS with after market headers / 200 cel cats but have yet to actually talk to anyone running AM headers/stock PSE to directly verify.

I'd like to run AM headers someday and would love to ditch the PSE controller.

Jamie@dundonmotorsports

Hi Matt, it's on the site, we have the modular redesign finished. We're also working on a bit of drone killing between 2000-2400rpm currently. Current Beta tester is sensitive to it and we want to release the best possible product. Designing targeted frequency resonators is tricky business, with the cats in the car it's even trickier as the exhaust temps which effect speed of sound dramatically (and hence the wavelength one would be trying to phase shift). All that said we're on it, tried 1/4 wave pipes and the frequency is too low to really go after it effectively that way. Working on a helmholtz resonator now...

We're talking about PSE exhaust being stock, our headers/PSE combo is in the 105-108 range, pretty stinking loud. Our Muffler brought that down 10-12dB. We haven't tested the muffler on a stock car yet, but typically dB reduction is dB reduction. Also we wouldn't expect the same issue with resonance on the stock headers as the total volume of the system is less than our race headers/cats etc...

Car 6

You've got my attention with the drone issue. My aftermarket system has a pretty strong drone up to about 2800 rpm according to my iPhone sound app (about 140 hz). I'm working on an active noise cancellation system with a powered subwoofer, but it's not there yet and a pipe solution would be much cleaner. So I'm very interested in how your drone efforts succeed. (It does seem that at those frequencies the cabin of the car could be a tuned cavity. Corvette coupe owners complained a lot more about drone than the convertible folks.)

smmmurf

Subscribed. I need a catted system that will pass sound at Laguna Seca and stand up to extended lapping. There have been some premature failures of catalytic converters on cars that have seen extended track use.

I would be glad to help test sound levels and report back if this information would be useful to you.