JosephIV

iTrader: (14)

I have a 3" downpipe from my TC78. I've been gathering up parts to finish off my build but am now ready to put an exhaust on my car. This is my first turbo car. I set aside money for either a Mufflex 4" cat back in stainless (talked to them and they can do stainless) or have the local turbo / fab guys do a full custom job. Either option is pricey IMO.

My buddy recently got an SLP LMII to put on the car I sold him. That got me thinking about simply buying an LMI or II and having the turbo fab guys build me an exhaust from the downpipe's V-band to the catback with a V-band added to the front of the catback. I'd also add a 3" cutout up front with a dump and call it good for now.

My car has a 3" DP on it now so I'm not seeing the harm in doing a full 3" or gain vs cost in stepping it up to 4" on this turbo. I've searched and found Procharger guys running a full 3" and also saw 5.3/4.8 guys with 76mm or smaller turbos doing it but didn't find anyone with my setup. There has to be someone running this.

Does anyone have any experience of their own with a setup like this? Do you guys think I'll be hitting a wall with the DP closed? My goal is 600 RWHP if that helps. Thanks!

Forcefed86

iTrader: (4)

Best of both worlds... Run a 3" cutout and stock or small diameter exhaust after. Gives you a nice quiet car that can be uncapped in seconds. Allows you to run a lighter weight full length exhaust that is easy to plumb. And not give up any power. 3" is plenty for a 600hp goal IMO.

I run a 4" DP and 4" cutout. The I run a single 2" pipe off my down pipe. With the dump closed my car is very quiet.

JosephIV

iTrader: (14)

Thank you for the reply, with the numbers in your sig I have no problems trusting your opinion. Had you responded that I'd be shooting myself in the foot with a 3" system I would be doing 4". I'll be ordering an LMII this week plus cutout. Maryland Speed is a site sponsor and just down the road. I ordered from them before and stupidly never saw that they are 10 minutes away.

RedRocketZ28

iTrader: (19)

For reference, here is my old setup...3" downpipe into a 3.5" cutout, back to crushed 3" over the axle.


Had an exhaust shop fab up the exhaust from my downpipe exit at the k-member. I had $400 or so total into that setup, including the cutout.

With the cutout closed, and boost controller off, it gave me 10 lbs. The car trapped 136 mph on that setting. Opening the cutout netted me a best of 141 mph which was 14 lbs. I loved driving the car around with the quiet exhaust.

JosephIV

iTrader: (14)

Wow, if that's the case then I should be alright. I looked at everything from 4" single to Stainless Works 3.5" catback to the setup I mentioned above. Going with an SLP LM and cutout is the least expensive solution. I considered connecting to the catback with 3.5" pipe and 3.5" cutout since everything forward of the catback has to be fabbed anyway and it's best to have the bigger diameter pipe closest to the turbo. Your setup with a decent mandrel bent catback should work for me.

LT1RAY

iTrader: (21)

My previous car had a HS turbo kit, Turbonetics 7875, and a full 3 inch exhaust system. Before the full exhaust (wastegate only) it made right at 13 lbs of boost on pump 91. Then I had a full exhaust system built using a Hooker Maxflow muffler:

http://www.jegs.com/i/Hooker-Headers...rentProductId=





It lost 2-3 lbs of boost with the exhaust but still made 600+ whp on 10lbs and sounded stock.



Shorty after this I added a 3 inch cutout right after the downpipe and loved it. Here's the car with the cutout open on 15-16lbs of boost and e85 now.



The exhaust tip is just barley visible.

TOYBOX

Forcefed86, agreed best of both street and track .

coltboostin

Run the cut out.

And for anyone thinking 3 inch is "enough" @ 600whp.......

http://www.superstreetonline.com/how...ust-test-tech/

Remember, any restriction post turbine will decrease its efficiency.

RedRocketZ28

iTrader: (19)

It certainly looks like it's "enough" at those power levels...

Could more power be made with a larger exhaust? Of course, but for the OP's goals it will work just fine.

JosephIV

iTrader: (14)

Thanks guys. These responses are what I was looking for. I really do want the best of both worlds on the budget that I have and I believe I can do that with the 3" system and cutout. I can go bigger and do it once but I also have a wife who simply can't fathom being out $1,400 or more for a 4" full 304 stainless exhaust. Best to be out less than a grand and live with it for a few years.

Mongoose350

iTrader: (1)

Lmao! I have the same thing happen with my son about every day. Even down to the "shut the door daddy". Looks like the car hobby may live on a while yet.

willizm

iTrader: (10)

I ran full 3" back on my TC78 and PT7675 setups. 3" downpipe to a 3" cutout and then to the 3" magnaflow catback. That catback keeps everything quiet. I just went to a 4" downpipe to a 4" cutout that then tapers down to the same 3" catback. My first mod on the car is the only one that has stayed on throughout the years and that is the magnaflow catback.

Attachment 723071

JosephIV

iTrader: (14)

Damn, these cars are great inspiration guys. I also was wondering about "crossflow" mufflers that are commonplace on our cars. Seems like they're not a big deal, especially with the cutout. I've only ever owned SLP Dual/Dual, TSP true duals, and the Magnaflow that came with this car but the over axle pipe is ghetto rigged and I hate the megaphone tips.

I'll have something by March 25 as that's when some sale codes end online.

coltboostin

Dafuq? The car picked up 103whp just from an increase in exhaust size!!! A 20% increase. People pay shosp 10k+ for full NA builds and tunes at hopes of that kind of increase. The 3 Inch was more than just "holding back" that car, it was inadequate.

With your logic-we should all run 2.5 inch exhaust and just keep turning up the boost until it makes the power we need.

RedRocketZ28

iTrader: (19)

Please read and comprehend what I typed. A 3" exhaust is enough to get it to 600 rwhp. I made 606 rwhp on 13 lbs. with an on3 76mm when my car was first together. It made 650 rwhp at the same boost level with the Turbonetics 7875 and trapped a best of 142 mph. For me, it was "enough". To reach the OP's goal of 600 rwhp in an LS platform it doesn't require 20+ lbs using even a mediocre turbo. I am in no way saying a larger exhaust wouldn't pick up power so don't assume that.

How are you determining what you think my logic is? I never said, or implied, to run a smaller exhaust and turn up the boost. I simply stated that at his power goals, and even beyond as other people have proven, a 3" will SUFFICE.

coltboostin

Its the internet. Everything is obvious, and serious business!

JoeNova

I plan on finishing up my 4" downpipe eventually with a cheap 2.5" rear exit. Probably with a single muffler and a cheap resonator. I'd like to run a boost activated cutout.

RedRocketZ28

iTrader: (19)

Quoted for truth! Haha.

JosephIV

iTrader: (14)

Well, after all of this I put a deposit on a full 3.5" stainless single exhaust with V-bands. A shop near Maryland International Raceway is doing the fab and I'm simply going to use a Magnaflow bullet, go over the axle, and dump before the rear valance cutout. The car should be dropped off next week for the work. After adding up the cost to fab the front half, buy a catback and cutout, I realized that someone can fab it all up and it will be a better fit to my car expecially considering the suspension bits, and BEEFY S60 rear.