# How much power would I gain from a bigger exhaust on my VRT



## WeeZFan69 (Aug 3, 2003)

So this is my setup : 









My 12v is slightly built, the head is ported very nicely on the intake and exhaust side, the head is matched to the turbo manifold and its got autotech 262s. The turbo is a precision t3/t4 60 trim with a .82 AR exhaust side. I have a 2.5" downpipe, going to a 2.5" TT throughout the car with one magnaflow muffler, 2.5 test pipe also. I'm pretty sure that might be my restriction at this point. The car put down 330whp at 15psi and put down close to 370 at 17-18psi. On C2's OBD1 #36 software also. But I'm wondering would I see a good power increase with a bigger exhaust?


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## TBT-Syncro (Apr 28, 2001)

i'd guess atleast 60hp, if not significantly more.


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## WeeZFan69 (Aug 3, 2003)

TBT-Syncro said:


> i'd guess atleast 60hp, if not significantly more.


 
wow . Now.... Would I be best off leaving the 2.5DP and putting an electric cutout after it? Or try and run a full 3" inch through the car? I'd rather keep my 2.5" its in pretty nice shape but I don't know a cutout might be too loud. Now would it be very important to adapt the 2.5" on the turbo to 3" on the downpipe and run a full 3 inch downpipe to either a cutout or the rest of the exhaust?


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## huichox4 (Nov 8, 2004)

WeeZFan69 said:


> wow . Now.... Would I be best off leaving the 2.5DP and putting an electric cutout after it? Or try and run a full 3" inch through the car? I'd rather keep my 2.5" its in pretty nice shape but I don't know a cutout might be too loud. Now would it be very important to adapt the 2.5" on the turbo to 3" on the downpipe and run a full 3 inch downpipe to either a cutout or the rest of the exhaust?


 3" dp to a 3" cutout then the 2.5" exhaust could be left like that for less sound when you dont need the extra power. 


send me a PM I have a couple of vacuum actvated cutouts that could be easily added to your setup and will be kept closed untill you get on it


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## PjS860ct (Dec 22, 2002)

I think I already told you the answer to this  

I wish I have a boost activated cutouts like what ATP has but always sold out... but I cant complain about my 3"electric cutout... it serves its purpose when I want more flow out of the exhaust and more power at the same psi level... :thumbup:


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## TBT-Syncro (Apr 28, 2001)

any of those 90 degrees cutouts do little more than make noise. if you want all the benefits you need to go full 3inch system. 

dynomax does have a back pressure activated muffler though that has a built in flapper.


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## jity86 (Sep 6, 2002)

I'm running stock compression and 8psi on my vrt when I went from 2.5" to 3" exhaust I saw a 18hp gain and I made full boost 200-300 rpm sooner. It was worth it. My vrt putting down 250whp. Your car putting down 350+ you should see a much bigger gain than I did.


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## PjS860ct (Dec 22, 2002)

oppsss sorry I was talking about the flapper with the boost switch and not their 90deg pipe... Mine is a Y pipe :beer: and their flapper assembly will basically eliminate me from pressing on the switch when I want it open:thumbup: 

anyways I like my cutout cus it makes my car sounds very angry


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## WeeZFan69 (Aug 3, 2003)

PjS860ct said:


> I think I already told you the answer to this
> 
> I wish I have a boost activated cutouts like what ATP has but always sold out... but I cant complain about my 3"electric cutout... it serves its purpose when I want more flow out of the exhaust and more power at the same psi level... :thumbup:


 ya you did, and everyone else agrees :laugh:. Just not sure if its worth going to a 3" DP.


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## Jeebus (Jul 8, 2001)

It's worth doing a 3" dp over anything else in the exhaust system, however I'd be swtiching to full 3".


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## WeeZFan69 (Aug 3, 2003)

I'm also wondering... would a bigger DP and exhaust bring down EGTs? Because it can get that hot air out faster or no not really because EGT is just dependant on what the engines doing?


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## dubbinmk2 (Jan 15, 2008)

i think 3 inch DP is what makes the different


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## WeeZFan69 (Aug 3, 2003)

TBT-Syncro said:


> any of those 90 degrees cutouts do little more than make noise. if you want all the benefits you need to go full 3inch system.
> 
> dynomax does have a back pressure activated muffler though that has a built in flapper.


 uhh seriously?? whys that. And your telling me if bolted one on I'd see no gains on teh dyno?


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## TBT-Syncro (Apr 28, 2001)

WeeZFan69 said:


> uhh seriously?? whys that. And your telling me if bolted one on I'd see no gains on teh dyno?


 you'd see some, but not as much as with a full 3inch system, nor would you even see as much as one that was optimally placed (better, but not best). 

think about it like this, if you put a garden hose vertical, and put a fitting 90 degrees out of flow, do you think as much water would come out that fitting as if it was 10 degrees out of flow ? of course not. 

i know that on my friends car, after he removed his 2.5inch system with cutout, and put in a 3inch system, he had to re-adjust spring pressure, as the freer flowing setup was allowing the old settings to make more boost than expected.


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## AAdontworkx3 (Oct 1, 2002)

I saw a 32whp gain between dyno runs with an electric cutout. It wasn't a 90, more like a y-pipe integrated into a 3" DP. Not a bad gain, but more could be done tweaking angle and placement.


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## DannyLo (Aug 2, 2006)

i'm psyched because i just finished my full 3" setup on my 24v running 10psi on a precision 6765 

I had a 3.5"-3" Downpipe (C2 Motorsports' design) coming down to a 2.5" because it was all i had. Now i'm full 3" mandrel bent as of tonight  

Next is to do a new clutch so i can up the boost some more.


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## PjS860ct (Dec 22, 2002)

Lieutenant Dan said:


> i'm psyched because i just finished my full 3" setup on my 24v running 10psi on a precision 6765.


 what size exhaust housing are you using on your 6765? where dop you see full boost? BB or journal? 

thanks:beer:


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## kevhayward (Mar 13, 2007)

dubbinmk2 said:


> i think 3 inch DP is what makes the different


 Agreed. 

I run the same TT 2.5" exhaust as the OP, but with a 3" DP and 3" Cat and mine makes 350whp at 11psi. I know of one or two other GT35 specials pushing 500whp through the same exhaust. 

I'm open for experimentation though and will be trying a 3" cat back to see what the fuss is all about. I'll expect a small gain at full throttle and maximum revs, but I'm more interested in what happens below 3000 rpm on part throttle.


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## huichox4 (Nov 8, 2004)

kevhayward said:


> Agreed.
> 
> I run the same TT 2.5" exhaust as the OP, but with a 3" DP and 3" Cat and mine makes 350whp at 11psi. I know of one or two other GT35 specials pushing 500whp through the same exhaust.
> 
> I'm open for experimentation though and will be trying a 3" cat back to see what the fuss is all about. I'll expect a small gain at full throttle and maximum revs, but I'm more interested in what happens below 3000 rpm on part throttle.


 you will most likely loose a bit of tq, maybe not noticeable due to less back pressure but due to the fact that there is already a lot of flow with 2.5" exhaust 

I had a 3" DP to the stock Catalytic converters dual 2" pipes which in cross sectional area are closer to 2.5" pipes than a 3" one and dynoed with a huge torque number 460AWTQ, after I put the Straight pipes and bigger I felt the loss of tq down low but it pulled way harder up top and might save your tranny from exploding. all in an R32 turbo


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## vr6chris (May 26, 2003)

or you could just buy my 4" exhaust.


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## rod_bender (Apr 14, 2007)

Who starts with anything less than a 3" downpipe/exhaust??


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## WeeZFan69 (Aug 3, 2003)

hahah apparenlty I do. I made that whole thing myself too... figured the outlet on the turbo was 2.5 and the rest of my EX was 2.5 so why not. I never knew itd be such a restriction.. 

It got the job done though and maxed out c2's software...


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## kevhayward (Mar 13, 2007)

huichox4 said:


> you will most likely loose a bit of tq, maybe not noticeable due to less back pressure but due to the fact that there is already a lot of flow with 2.5" exhaust
> 
> I had a 3" DP to the stock Catalytic converters dual 2" pipes which in cross sectional area are closer to 2.5" pipes than a 3" one and dynoed with a huge torque number 460AWTQ, after I put the Straight pipes and bigger I felt the loss of tq down low but it pulled way harder up top and might save your tranny from exploding. all in an R32 turbo


Yeah that's what I was thinking. The gains would be more noticable up top than down low. 

At the end of the day, pressure differential and gas flow inertia decide where the exhaust goes, more so than pipe diameter alone. To properly tune an exhaust and see how restrictive it really is at max revs and throttle, you need a pressure sensor in the tailpipe 

As you have an R32, do you know if the injector connectors on it are USCar and fit Bosch EV14 52lb?

Working on an R32 T myself :thumbup:


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## AAdontworkx3 (Oct 1, 2002)

Pressure sensor? I don't have a degree in fluid dynamics, but an old trick we used to tune exhaust with:

Spray paint the entire exhaust system. Drive it hard until the paint peels. Where it stops peeling, cut if off and throw on muffler for noise suppression. Anything past this point is 'extra weight' . . .


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## huichox4 (Nov 8, 2004)

kevhayward said:


> Yeah that's what I was thinking. The gains would be more noticable up top than down low.
> 
> At the end of the day, pressure differential and gas flow inertia decide where the exhaust goes, more so than pipe diameter alone. To properly tune an exhaust and see how restrictive it really is at max revs and throttle, you need a pressure sensor in the tailpipe
> 
> ...


I have those injectors, you will need the pig tails. are you going with C2 software?? they fit the fuel rail perfect without modificaiton

they have the whole fueling kit for it with software. what are your power goals?


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## cabzilla (Jan 3, 2000)

kevhayward said:


> Agreed.
> 
> I run the same TT 2.5" exhaust as the OP, but with a 3" DP and 3" Cat and mine makes 350whp at 11psi. I know of one or two other GT35 specials pushing 500whp through the same exhaust.
> 
> I'm open for experimentation though and will be trying a 3" cat back to see what the fuss is all about. I'll expect a small gain at full throttle and maximum revs, but I'm more interested in what happens below 3000 rpm on part throttle.





Expect a huge gain everywhere there is boost, along with a drastic drop in spool rpm. I picked up over 60hp almost everywhere with a full 3" at about 13psi.


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## Big_Tom (Aug 19, 2007)

3" duh! done... :beer:


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## kevhayward (Mar 13, 2007)

huichox4 said:


> I have those injectors, you will need the pig tails. are you going with C2 software?? they fit the fuel rail perfect without modificaiton
> 
> they have the whole fueling kit for it with software. what are your power goals?


I'll be using the standalone from my 12V T. 

Shame about the pig tails, I don't like them. I'm going to have to find some USCar connector kits from somewhere then. They seem to be impossible to get for some reason. R32s must use the older EV6 connector then. My engine didn't come with injectors or a loom, so I can't check.

Power goals, haven't got one at this stage but probably start off with 400hp as it's going in a FWD Corrado. I'll turn the wick up a bit once the 02M is in!


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## kevhayward (Mar 13, 2007)

cabzilla said:


> Expect a huge gain everywhere there is boost, along with a drastic drop in spool rpm. I picked up over 60hp almost everywhere with a full 3" at about 13psi.


Interesting..... I'm currently seeing spool + a little boost at 2500rpm (GT35 0.82) so doesn't sound like I'll lose much.

For quiet 3", Borla or Magnaflow? With or without resonators? By quiet I mean no louder than my Techtonics, preferably quieter actually. I don't have forgiving neighbours.


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## cabzilla (Jan 3, 2000)

kevhayward said:


> Interesting..... I'm currently seeing spool + a little boost at 2500rpm (GT35 0.82) so doesn't sound like I'll lose much.
> 
> For quiet 3", Borla or Magnaflow? With or without resonators? By quiet I mean no louder than my Techtonics, preferably quieter actually. I don't have forgiving neighbours.





You will see earlier spool. I ran a 3" with two resonators and a magnaflow last time. This time it will be magnaflow only.


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## kevhayward (Mar 13, 2007)

Are resonators to allow for gas expansion, or just purely for toning the exhaust note? Not really sure what they do. I was originally planning on 2 mufflers and no res.


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## TBT-Syncro (Apr 28, 2001)

kevhayward said:


> Yeah that's what I was thinking. The gains would be more noticable up top than down low.


it'll help down low as well, but its a lot harder to gain 100 hp down low, than it is 100 hp up top. (and pointless in a fwd car). any dyno i've ever seen, the 3inch car reaches 'full' spool 300-500 rpm sooner than the 2.5 car.

(i can build positive pressure below 2000 rpm with my gt35).


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## kevhayward (Mar 13, 2007)

Thank you Misters Syncro and Cabzilla, and the other guys who've provided whp gain numbers.

I am pretty much convinced 3" is the way to go now. Next step is to decide on what mufflers to use. 

How do you guys with 3" get on with the over axle piece? Do you get any contact with the rear beam over bumps?


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## SoFarKingFast (Jul 9, 2003)

I had a custom 3" setup put in by a local muffler guy. He fashioned a bend over the axle that decreases diameter a little bit, and I get a little bit of knock when I have a lot in the trunk, but other than that, it is great. 

I used some hose clamps to hold the muffler against a hitch I have (yes, I tow a trailer with my VRT  ) so it doesn't knock around on those crappy rubber hangers. 

Magnaflow 3" generic muffler, sounds good.


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## WeeZFan69 (Aug 3, 2003)

So I'm finally about to upgrade my exhaust. Question is, since I'll be making everything from scraatch should I go, 3" dp to 3" turbo back, or go straight to a 3.5" dp and go 3" dp back. Or should I go 3.5" dp and turbo back. Or is 3.5" tooooo big?


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## Norwegian-VR6 (Feb 6, 2002)

WeeZFan69 said:


> So I'm finally about to upgrade my exhaust. Question is, since I'll be making everything from scraatch should I go, 3" dp to 3" turbo back, or go straight to a 3.5" dp and go 3" dp back. Or should I go 3.5" dp and turbo back. Or is 3.5" tooooo big?


3.5" DP and 3" should do the job.
I have 3" dp and straight 3" with one Vibrant muffler. http://vibrantperformance.com/catalog/product_info.php?cPath=1022_1031_1110&products_id=29
I see 29 psi off boost at 3800 rpm with a GT35R T3 1.06.
Car is not loud when driving off boost. Very deep idle sound, and when boost hits.... its loud.


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## dubbinmk2 (Jan 15, 2008)

i think for a daily car 3" DP and 2.25" is good... other wise it's a cop magnet


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## TBT-Syncro (Apr 28, 2001)

dubbinmk2 said:


> i think for a daily car 3" DP and 2.25" is good... other wise it's a cop magnet


please keep your stick on the ice.


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## PjS860ct (Dec 22, 2002)

My cousins mk2vr6 with 2.5" full exhaust with 1 muffler is louder than my friends rb25 240 with 4" turbo back exhaust... 

Im going with 3.5 downpipe to a cutout then to a 3" exhaust for my new build for next year... :beer:


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## dubbinmk2 (Jan 15, 2008)

PjS860ct said:


> My cousins mk2vr6 with 2.5" full exhaust with 1 muffler is louder than my friends rb25 240 with 4" turbo back exhaust...
> 
> Im going with 3.5 downpipe to a cutout then to a 3" exhaust for my new build for next year... :beer:



nice :thumbup:


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