Everything happening downstream of the turbo should be consider similar to a supercharged application IMO. Both are opened to atmosphere and are trying to get rid of an X amount of burned air fuel mixture (all other factors being equals such as EGT's).

 

Yes, but supercharged cars are not as sensitive to exhaust back pressure as turbocharged cars. Like ItalianJoe said, the main restiction on the SS/SC is in the exhaust ports of the cylinder head, and the exhaust manifold. Which has been known for a long time (and I'm sure u know).

Giving an example of a turbocharged regal gs is not a clear indicator that a 3" exhaust will make more power on the SS/SC (which is what this thread is about). Like I've said before, I agree that a 3" exhaust will make more power on some applications, but a 2.5" exhaust will still provide optimal flow and exhaust gas velocity for most setups on the SS/SC.

 

good example of a 2.5" exhaust is my m62 2.7 pulley dyno up above...


notice the curve...

 

I wish the lnf guys knew this. They all say a 3" is a waste of $$

 

it is.

 

No offense mr Powell but do u have proof there's no gains? I don't see how a 2.5" could support my power level.

 

One individual recently dyno'd their LNF on a stock LNF muffler and then with a cut out. The gain was around 30-40whp...

Though, his setup was on a larger turbo if I recall... None the less, turbo'd balts would benefit much more from a open dp or opened up exhaust relative to the CFM of their setup.

 

i build my 2.2 motor running 8:9.1 wisco piston with a TVS and 2.5 pulley 3'exhaust i feel like i lost power with the 3' set up

 

throw a 5" from a diesel on there just to be safe... hahaha

 

why don't we race for your car

 

this is an LSJ thread. i run 320 whp on the lnf cat back. I dont publish my dyno sheets, area47 has done the work with the car and thats all i need.

so yes thats the power level. I took off the 3 inch. I did not make less power. you can look at the flow numbers already published and see unless you are trying to get above 350 with an LSJ the 2.5 is fine. LNF are different, but make over 380 wt all day on stock exhaust. the rear muffler is straight through, so replacing it is just a means of making noise not power.

I guess WS Frazer is the dyno king around here with 348 whp on an LSJ , ask him.

http://www.******************/forums...lsj-parts.html

put in red line forums.com to make the link work.

 

thanks that's what i needed to hear , it's guys like you that i like you are a big help !!

 

Thank you for posting this John.

This is what I have been trying to make clear the whole time.

 

I understand. Lnf is different platform so the same can't be said. I guess ecotecs are just kinda weird. I know with the k-series honda, you need something close to a 3" when your near 300whp. My friends m62 SI sedan gained 15 whp moving from 2.5"-3"

But that's a diff car completely.

 

and the head its self flows a hell of a lot better than the ecotec head.

 

Pretty much the fastest LSJ/SC car here is zrated89.

Whelp, he's only running a "straw" exhaust.... 2-1/4 GMPP.

Does that tell ya'll ******' sumptin??

 

yup 117 trap, prettydamnstout I would say. But then with a 1.7 60 ft he can drive it as well.

this 3 inch thing will eventually run its course.

 

pif 3" new hawtness is 4pipers =p

 

Haha, I sure hope so....

I feel like we are going in circles in this thread.

 

i never knew there was a 3inch vs 2.50? this thread fails

 

I put an new magnaflow 14326 and at wot sounds horrible. When I installed it, it didn't have an tip and sounded deep, and now I have an tip welded on it sounds raspy. Im using jbp header, 2.5 catless dp, stock CB to the new muffler. What's an good resonator to put on? And should I replace the new res with the stock res? Or keep the stock and weld in new one on the dp?

 

Figured I’d post this graph here. Was having trouble getting anymore power than 408 out of my car with the 2.5” exhaust w/resonator and gutted cat due to having too much back pressure which ended up causing my resonator to explode (pictures on twincharged thread) Ended up putting on a 3” exhaust from where the cat was gutted straight back and reduced to 2.5 a foot and a half or so before the turbo to create some velocity. Also we eliminated the resonator. Car is now extremely loud and first run on dyno (not on graph) made about 350hp and lost 4psi or so. So right off the bat with the same tune I lost about 58whp just from switching to a larger exhaust. After some tuning we were able to get a best of 384hp which was AFTER we turned the boost up to 28psi. (which was 1psi more than I had before on the 2.5” exhaust making 408hp) The tune was very rich so he leaned it out a bit and lost more hp bringing us into the 360’s to 370’s as where it stand now. So the car is still at the shop til he can figure out whats going on. The only benefit shown on graph from the 3” exhaust is the power band up to 4500 rpm. After 4500 power is lost and we have no idea why.

 

You're comparing apples to oranges here.. Of course you're resulting higher horsepower with a 3".. On a turbo car. Less backpressure, faster spool.. Power comes on faster. End of story.

As Staged says below it varies from application to application, but, easily, more than half of the M62 LSJ's on this site are not making enough power to warrant a 3", it's just not realistic, and not needed. I still have friends who drive LSJ Cobalts that will argue to the death that they need a 3".. I just let it go and carry on usually..

 

Troof. kill the thread.

 

Your AFR on the 408whp run is much leaner than the rest of the runs.

There is no way you are losing that much HP at your level with a 3" exhaust over a 2.5" exhaust. Something else is wrong there...its not the exhaust.


Hell my car runs 20" of 3" pipe (3" collector) and then it dumps to atmosphere, my car is all-motor and makes 193whp. TQ was nearly 160wtq at 3000rpm as well, peak 179wtq at 4800rpm.

No loss in low end TQ or power for me.

Everyone should just run 3" cutouts and then this won't be an issue, they make more power than any exhaust combo.