hey guys i am trying hard to find the best possible exhaust setup for my 2.0 and am hesitant of running a couple different combinations. if any of you are running this particluar setup please let me know how the car changed down low in the RPM range, and up top. this is an expensive investment to get into if it is not worth it so i really need your help, thanks in advance.

GMPP extrude honed manifold (95% sure i will be going with this no matter what), XTC catless 2.5 DP, into a custom fabbed 2.5 inch catback with a dynomax oval style muffler. i am worried that without the cat i will be too free flowing, yes that is possible, and will lose a noticeable amount of downlow power, anybody running this setup yet?

 

If you stick with 2.5" piping, even without a cat, your low-end power should be fine. Now 3" with no cat, say goodbye to the low-end

 

good to know, thats what i was thinking, now that im running dr's at the track im not worried about spinning the tires so i want as much down low as i can get, and hopefully quite a bit more up top. you can verify how much power the ol' flowmaster hurts up top...

you think this is a good setup?

 

I'd say if you ran a header (real header not crappy GMPP manifold) a catless 2.5" DP and 2.5" exhaust with a straight through muffler, you would have a pretty damn good setup. Do you have the stock stage 2 pulley or a 2.8?

 

If you tune the car properly with no cat you won't lose any low-end. When i took off my cat i lost alot of bottem end but once we tuned for it i got it right back and made more top end. So as long as you tune your car its highly benificial to remove the cat. I have a 3" manifold back exhaust and love it. Why would you put on a 2.5 downpipe?, The stock pipe from the manifold to the cat and out the cat is 3". I think they put a 3" for a reason.

 

The stock DP is 2.75"

 

Ok then even a 2.75, why would you make it smaller when your adding more power.

 

it shrinks down in size at the cat. there is also a dimple there that resticts flow. check out INTENSEs site for a better description.

 

Your right, I totally forget about the DP diameter. Yeah if you ran a real header, a 3" DP and 2.5" exhaust you would have a really stout setup. My car has no bottom end, prolly never will. Even with tuning the bottom end still just isn't there, from the 3" collector of my header to the exhaust tip my exhaust never goes smaller than 3" and the absence of a cat put the final nail in the coffin of my low-end power. Oh well it breaks the tires loose in second gear so whatever I lost in low-end was made up in the top-end

 

I thought it was smaller then that. Either zzp or ca have a pic of the stock downpipe at one point shrinks to 2".

 

Ok but my point is that if you have a 3" downpipe and not cat with proper tunning you won't lose any bottem end power. When i tuned my car i gaind all that was lost and some back from removing the cat.

 

You will gain all your bottem end back if you tune properly, I only have a 2.7 and also a 3" all the way back and alot of bottem end.

 

Yeah but you have the stock manifold with a restrictive 2" collector, i have a mid-tube header with 1 3/4" primaries and a 3" collector. HUUUUGGGGE difference in flow and back-pressure there.

 

im thinking if i ever put anymore mods on my car that it will be the gm ext. manifold and the xtc downpipe. no cat would be no no for me since this car is going to be a strict daily driver so paying it off is going to take priority instead of tuning

 

You know here in AZ cars don't have to pass emissions for 4 years?

 

You will loose some low-end power with a header not a GMPP manifold.

It's all about the header when it comes to loosing some bottom end. The top end is off the hook though.

 

how much did your header and downpipe end up costing you? I have never been at a loss for money but with saving for closing costs and downpayments and buying points off of loans then the ps3 to top it off im for the first time low on cash

 

I got a pacesetter ceramic coated header for $168 and full 3" mandrel exhaust for $350

 

Where'd you guys get 2.75 for the stock downpipe? This is straight off of ZZ performance's website. 1st is their dp, 2nd is the stock dp

 

yeah i didnt think the stock dp was any bigger than 2.5 either. here are the answers to your questions towards me-

1. i wont be tuning it, because i dont have hp tuners, and want a setup that wont need to be tuned becuase i choose the right parts for my mods
2. i am on the stage 2 belt
3. i think 3 inch will be overkill for anything bigger than 2.7 pulley, especially with no cat
4. the 2.5 inch dp will be much more freeflowing than the stocker with no cat, look at the bends in the stock one around the sensor

 

i think 3" is overkill unless your pushing over 600hp if 2.25 is good for around 300 then 2.5 would be something like 400 and 2.75 is something like 500 no? Im sure this is way over simplified and flow rate would dictate alot of that but i mean is people are nearing 300 right now and are using the gmpp exhaust and pro's are starting to move away from 3" exhausts it makes sense

 

i have heard/read in some exhaust company catalog that for a v-8 pushing 500 hp dual 2.5's are adequete (sp?), and that would make a single exit 2.5 system for a 4 banger pushing roughly 250 hp just right

 

Eric, I know you wouldn't be promoting 2.25" exhaust if you didn't have the GMPP exhaust. Why do you think you make 17 psi with only a 3" pulley? 2.25" is good for around 235-240 hp, 2.5" exhaust is good for 265-270, and 3" is good for 300+. Yes smaller exhaust works good for scavenging gases, when gasses need to be scavenged (N/A or N20) when exhaust scavenging isn't that important (on boosted motors) you want volume, the gases are already pressurized so they are pushing to get out, if you impead flow (small piping) all the gases just back up and in the exhaust system and cause basically a traffic jam and not all the exhaust gas is evacuated from the cylender so when the intake stroke comes, there is still remaining cylender pressure from the previous exhaust stroke. Thats why you make 17 psi when you should be making 15, and why I make 18.5 when with 2.5" exhaust I would be making 19.5 - 20 psi. I would rather have lower boost thats mostly air and fuel, over higher boost that is air and fuel mixed with left over exhaust gasses.

 

your talking a big engine vs a small engine though so it isn't directly half of one equals the other especially when dealing with boosted engines since what works on a NA doesn't mean it will work on a turbo or supercharged ride.

 

actually dude after installing the exhaust im back down to a lil over 15 so that doesn't apply to me. I'm not promoting anything at all just pointing out that there is a large discrepancy on what people are reporting over what people 'think' should happen without tests really proving anything for a larger exhaust being 'needed' at a certain hp level. I mean if it really follows along those lines you mentioned then if I wanted 800hp i would need like a 10" exhaust no?