I can't imagine anyone here not aware of exhaust mods performed on STR's. Those interested in an exhaust mod and those who have already implemented re-pipeing may recieve some insight from this thread prior to cutting up and welding in their masterpiece of pipes or re-pipe: Obviously when coupled to a 112 cu. in. Eaton design positive displacement supercharger (PDS), the little 4.2 DOHC 32 valve belts out power (400 hp @ 410 lb/ft torque). The PDS effectively increases engine displacement to nearly 6 litres but with a much more dense air and fuel mixture forced down her gullet...creating power rivaling the 6+ litre GM metal. Some of us would love to enhance this process and the most common methods that may come to mind is increasing air intake and out-take (exhaust) that compliment the areas of the power curve that matters the most in street or track competition. The STR can definitely handle improvement in both air in and and air-out departments...we installed low restriction air filters and smaller blower pulleys, and await Mafioso's "Big Suck" air intake tube. My recent experience with my 03 STR's air-in-air-out modding has taught me the lesson of: "Don't over do it" in the air-out department. The Magnaflow hi-flow cats? Wow! Definitely do this...huge improvement in throttle response and cylinder scavenging, allows the motor to suck more air in (this likely lowers block temperatures too +++). Magnaflow X-pipe? Wow! again...the engine loves this; as it evens out and smooths exhaust impulses, again allowing much improved cylinder scavenging. Continue with either 2 1/4 or 2 1/2" pipe to the muffler. Your choice of muffler is what I believe to be critical at this juncture. If not using a pulley smaller than 1.5 lb., you may make the mistake of welding on a flow through muffler and lose noticeable and mucho needed low end torque. I wouldn't be writing this if the STR was blessed with an LSD differential sporting 3:25:1 or lower cogs. At the present I have the above full exhaust mod but with 12" Dynomax glass packed tube (flow through) pre-mufflers leading to Dynomax Super Turbos (14", glass packed, two-chamber with full throttle by-pass tube), low temperature thermostat, K&N filter, and a 1.5 lb pulley. IMO this combo is perfect because it: breaths, maintains low end trq., and emits a combo of rasp and growl without filling the cabin with annoying resonance while at cruise. From a stop my STR launches harder than when it was stock and with flow through mufflers. The balance of exhaust noise to blower whine is perfect. The launch growl is just "Right" and when "off it" cruise noise is comfortable with just a little more than subtle deep exhaust groan. Without pre-mufflers the Dynomax Super Turbos emit annoying interior resonance, most notable when climbing a hill in high gear. When I had the Magnaflow mufflers there was a noticeable loss of low end torque (trq.)...sounded real mean but definitely some low end trq. missing. With a 3 lb. pulley (which i'm still hedging on) and Mafioso's air intake tube perhaps some or all of that missing torque will come home with a flow through muffler. Otherwise, the s/c 4.2 is a good breather out of the box but stands to be improved. "Over-improving" the air-out dept. may emit impressive sounds albeit at the cost of "another" showin ya his butt whilst ya wondering "Where have all the low end grunt gone". Happy to answer questions and Happy Holidays.

 

Great post.

Of course your advice brings up the question of whether you can get similar results with just changing the mufflers (and perhaps resonater delete). If one keeps the stock cats and piping and swaps mufflers for magnaflows straight through I wonder what results one would see. I seem to recall the guy you talked to at EuroTek suggesting this course of action.

 

Hi Chris, We understand in order to build more power we need to increase air in and air out without sacrificing too much torque. There is a way to have your cake (hp) and eat it too (more torque). The stock cats are way too restrictive, especially when introducing more air (includes increasing air intake, blower speed, and/or porting/polishing). Allowing the spent gases out faster builds power by increasing cylinder filling and disposal, plus may lower block temperatures: Pented up hot exhaust gases that have to squeeze through narrow passages increase friciton thus raising engine temperatures= hotter intake charges= ECU pulling back fuel and timing= loss of power. An x-pipe facilitates the same whilst balancing the banks and smoothing exhaust impulses. The stock resonator has an adequate core and incorporates a cross over channel but is not up to the task when filling with more exhaust gases then their disposal. I agree with you on the stock mufflers. These may be retained for both their maintenance of back pressure and noise quality. I remember when no mods were performed except removing the resonator. The immediate increase of exhaust pressure from the muffler tips and increase in noise was surprising. With a blown engine torque can either be maintained or dramatically increased. Take the M5 for example: Normally aspirated 5 litre V10 with an 8 grand redline. It belts out 507 hp but only generates 368 lb/ft torque. IMO, a savy driving STR owner with a decently modded car (460+ hp @ 480+ lb/ft) torque can concievably take out an M5 in the 0-60 and 1320. I know of a few here (including myself) who otherwise feel they can or have already performed this feat. In the final analysis all this talk brings us back to our eagerly awaiting curiosity for "ttwotees" dyno run on his new motor, full exhaust mod, and "Snake Bite"....

 

dynos are better judges of loss than seat of the pants

 

And track times are better judges than dynos!!

 

haha, very funny!

Seriously, only if the same driver does tests under identical circumstances. Fairly rare.

 

Dyno shows HP, TQ gains.....1/4 mile times shows results.....but what do I know

 

We all can agree on one thing...Regardless of dynos and track times, a well modded and piloted Jaguar STR is a formidable predator.

 

for a daily driver

 

LOL, hee hee...ditto. Was my daily "hunter", I meant "driver" till the road salt and sand was laid down.

 

I drive mine in the winter here in Chicago....It gets a hand washing detail every week.....My paint still looks just a new....and will prob put some southern cars paint to shame.....

It is all about taking care of it....and turning the traction control off and going sideways down the road loud and proud!

 

Riski, would you know the widest rear rubber one could fit with H&R Sport Lowering Springs? Can we fit 285's?

 

295's should clear maybe a thin 305 like a nitto

 

Riski, you have any vids from you at the track? I'd like to hear that exhuast under full throttle.

 

I thought we could stuff wider than 275's...just chickened out on that they would rub a bit. Anyone want a pair of September 2010 low mile (approx. 4k) Michelin 275's? They cost $350/each. Will let go for $250/each, OBO.

 

No I dont have any around that I want to put on the net.....I have a few people that keep tabs on what I do on here, and will get scared and not race

 

Riski, can ya post a clip featuring just exhaust note?

 

Ill see if I can edit some of it.......I raced a GN so i dont think I qas louder than that tubed out race car.....

I shall put the GoPro camera on the side/back one day and take her out for a spin when it is less snowy....

 

How'd ya do against the GN? Was it modded? There's a lot of aftermarket for the GN.

 

It was a tubbed out race car, that ran clocks off pick a 8-9 race car to run your car with and it is hard for people to figure out your times