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3IN EXHAUST UPGRADE
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The Theory
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Originally, the factory set up the 2.8 cars with 2.25 inch exhaust. So I got to thinking once I got the 3.4... I had a 2.5in Flowmaster installed with a high capacity 2.5 inch catalytic convertor and 2.5 inch cut out, but the rest was 2.25. The 3.4s stock got 2.5 inch systems, and alot of stock 3.4 guys upgrade to cast off v-8 2.75 systems. They all have gains and no problems with the exhaust being too unrestrictive. So I'm thinking my 3.4 is modified, bet I could go larger still. After some research on the Dyno, & thanks to the cut out, we found my non-mandrel bent 2.25 inch exhaust system was infact too restrictive!

I might have gone 2.75, but when have you heard of a flowmaster 2.75 in system? Plus with us going turbo eventually its best to only do the exhaust once if you can manage it! Esp when you tally up the cost of a custom mandrel bent sys! Yikes! I would not want to do it twice!

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The Layout
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The exhaust on my car was replaced from the collectors on the headers back! Nothing smaller then 2.5 was installed.

The layout is this... PF&E headers to a custom 2.5 to 3in y-pipe flowing to a 3in Flowtech cut out...then you move to the 3in Magnaflow high flow catalytic convertor, which joins the Flowmaster American Thunder series 3in madrel bent cat back system...topped of with dual 2.5 inch custom madrel bent quad exhaust tips!

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The Results
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What did the custom 2.5 inch (primaries) mandrel bent y-pipe to a single 3inch also mandrel bent pipe with 3in cut out to 3in Magnaflow convertor to Flowmaster's American Thunder mandrel bent exhaust system do for RAIF's performance (3.4l)????

Well some said it would kill the torque...
>>>WRONG!

Others said the exhaust system is too long from the start and a 3in would cause too much backpressure loss causing reversion & a lack of the proper scavaging effect...
(hence my old 2.25 crimp bent system initially gaining HP and torque when the cut out was opened. See an ideal system would see no difference with the cut out removed because it is flowing optimally!)
>>>WRONG AGAIN!

And others said is would sound like crap...
>>>WRONG! WRONG! WRONG!
(The car's sound impressed a VIPER guy with a 1000HP VIPER. Heck, the whole dyno shop thought I swapped in an V-8!)

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Dyno Comparison: 2.25in to 3in
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Check out the gains yourself...

The graph is comparing my best pull with the cut out closed with the old crimp bent 2.25in system with the cut out closed!

Max Power = 141.3 @ rear wheels (+20%) = 169.56hp @ the fly wheel
169.56hp compared to 160hp from the factory.
Max Torque = 221.3 @ rear wheels (+20%) = 265.56ft-lbs @ the fly wheel
265.56 compared to 200 from the factory...nice!

This puts me at 9hp over stock 3.4 numbers...
(Granted the 2.8 plenum probably is more restrictive then the 3.4's & my heads are 160,000 miles w/o a valve job!)
My torque is 65.56 over stock 3.4 numbers!

My gains with the 3inch exhaust over the 2.25...

Horsepower gains...15.4HP
Torque gains...18.2ft/lbs

And when the car was uncapped...I had instead 140hp and 222TQ...so esentially the same...meaning the system is very efficient!

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Dyno Comparison: 2.5in to 3in
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Someone asked... I went from a 2.25 crimp bent sys to a 3in mandrel how do I know what would have happened if I had gone with the 2.5 mandrel bend system?

Reply:
Well I have PF&E headers and their mandrel bent y-pipe was 2.5 at its exit (2in primaries into 2.5in)...it flowed to a 2.5 inch pipe then to a 2.5 inch cut out. So it was effectively a 2.5 inch system to the open cut out. I opened the cut out on a run not listed on the above dyno sheet...it is what gave the indication that I was in need of a better exhuast system.

I pulled on that run...

134HP and 207 TQ At the wheels... so if I had only gone to a 2.5 inch system and it was as effective as the cut out, I would have flowed just that on a 2.5 inch system!

So my dyno difference from a 2.25 crimp bent sys to a 2.5 decent system...
9hp gained
4ft/lbs tq gained!

So my dyno differences from a 2.5 inch system to a 3in mandrel bent sys with custom 2.5 inch primaries to a 3in (y-pipe)
7hp gained
14ft/lbs TQ gained!

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Further Questions
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Another question was raised about my TQ curve:
***Q:redraif this is a purely honest question, what did that do to the torque curve?
***A:The above dyno chart is the best way to compare what it did to my curve...basically the curves trend was the same...the difference in the numbers increased a bit more the higher the rpms...as did the hp... So basically to summarize the Car gained even more TQ and HP the higher the RPM then before. Though the peak readings were in about the same place RPM wise!

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As I said before... with the 3in sys I can run open with the cut out and there is essentially no difference. See a near perfect exhaust system will actually have little to no difference with a open cut out!!

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Well I also had a straight pipe made to replace the cat so I would not ruin it while getting the custom programing ironed out! I just bought this one and I passed emissions with flying colors, was not going to toast another one due to running rich!

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How it sounds!
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Here is Raif reving up with my full mandrel bent 3in exhaust system closed. Cat back is a 3in Flowmaster American Thunder system.