How much HP 2.5 exhaust?

[grocerygetter]

What you guys need to watch when testing exhaust gains is the maf reading. If you see increases in maf values vs before, it flows better and makes more power.

[Iam Broke]

I log almost every cruise & pull, as DA changes I may lose a tenth or two but MAF freq remained the same at 10,050 peak, boost remained the same with just the exhaust swap. Not saying ~5 whp may have been lost but not enough to affect real world performance and the drone was unbearable on the 3" system I had. Even replaced the MBRP x-pipe with the MBRP L99 chambered H and it was still deafening. YMMV.

Since replacing the K&N kluge intake I had on the SC with a CAI inc. system MAF flow is up at 10,350 hz but I suspect the ID is a bit different causing the shift. I had to adjust the fueling a bit with the new intake to maintain .78 PE lambda.

As was posted before a smaller exhaust increases the velocity of the system. I know if it's too small it may reach a choking point with backpressure but I don't see it here. Perhaps if I had a radical cam I would have noticed more. Stock LS3 internals.

[grocerygetter]

And that's how u compare!
I could totally see the CAi brand intake picking up hp over the other. That type of blower would like a bigger tb too.

[Iam Broke]

...and a blower cam...and a Melling oil pump ..and new chain & sprockets...then I'd need forged pistons...a clutch...axles...diff..squash...and so on and so on. lol.

[Bo White]

Originally Posted by BlaqWhole

Question: Does anyone have a video or a link to a thread that shows before and after dyno testing of a 2.5 > 3 inch exhaust? Because I keep reading people say that it doesn't make a difference. But I have yet to see any hard evidence. Its like someone one day decided to say this and it just caught on.

Having said that, I personally would not use any 2.5 inch exhaust on any application producing more than 500 whp. I don't think a dual 2.5 inch exhaust is enough at that point. You might be able to make X amount of power, but I think upping to a 3 inch at that point would provide worhtwhile gains. But still, I'd like to see some dyno results because word of mouth isn't enough for me...no offense anyone.

I feel the same way which is why I'm running a 3" OBX cat back now. I'm going back to the dyno hopefully this week and I'll post up like I said earlier. I know I gained because my wideband shows I'm leaner(to the point of needing a retune).

[BlaqWhole]

Originally Posted by Bo White

I feel the same way which is why I'm running a 3" OBX cat back now. I'm going back to the dyno hopefully this week and I'll post up like I said earlier. I know I gained because my wideband shows I'm leaner(to the point of needing a retune).

I can't wait to see your results. I'm just getting tired of reading people repeat something without any actual proof. There are too many unproven statements about modifications being passed around like they are facts.

[Bo White]

Wed. at 2 is when I'm going to the dyno. I may have to go up on injector. My 60lb'ers were already at 95% the last dyno session.

[camaro500]

I had a 3 inch cat back and I ended up putting my stock cat back(h pipe L99)on with mangaflow competition axle back and saved at least 25 pounds. My 2-3 hp gain from my cat back does not make up for the 25-30 pounds extra weight. Don't make the mistake I did by spending 1400$ on a 3 inch cat back when you can get a nice axle back for $450-500 and save weight. If you plan on running a blower cam with a supercharger, then go with the 3 inch. Anything less than that go with an axle back.

[BlaqWhole]

Originally Posted by camaro500

I had a 3 inch cat back and I ended up putting my stock cat back(h pipe L99)on with mangaflow competition axle back and saved at least 25 pounds. My 2-3 hp gain from my cat back does not make up for the 25-30 pounds extra weight. Don't make the mistake I did by spending 1400$ on a 3 inch cat back when you can get a nice axle back for $450-500 and save weight. If you plan on running a blower cam with a supercharger, then go with the 3 inch. Anything less than that go with an axle back.

Which cat-back was it? Corsa? I heard that one cat-back was extremely heavy but I can't remember which one it was. The OBX exhaust seemed lighter than the stock one but I didn't weigh it.

[Bo White]

Its either a touch lighter or about the same.

[Unobtainium]

Gained 6whp going from factory L99 exhaust to custom 2.5" with 2 short resonators(basically straight pipes).
I'm going to test 2.5" vs 3" on the car after turbo install.
Should be 550whp. I'd be surprised to see anything more than 10whp.

[grocerygetter]

for 5 or 10 whp it may be worth keeping the 2.5" for no drone on the interstate. My car sounds awesome at low rpm and wide open. It actually gets quieter inside the car at cruise rpms.

[Irnwkrkev]

Originally Posted by BlaqWhole

I can't wait to see your results. I'm just getting tired of reading people repeat something without any actual proof. There are too many unproven statements about modifications being passed around like they are facts.

A little research will net you all kinds of h.p. figures for exhaust diameters based on flow ratings.

That being said sometimes theory doesn't always prove to accurate, like how bolt on 6.2l respond well to 2" primary headers (although some will say it's due to the small 3" collector).

The stock system seems to be great for handling drone and does a good job of managing airflow with the rear diffuser. They do weigh a ton though.

[VADER SS L99]

Originally Posted by Unobtainium

Gained 6whp going from factory L99 exhaust to custom 2.5" with 2 short resonators(basically straight pipes).
I'm going to test 2.5" vs 3" on the car after turbo install.
Should be 550whp. I'd be surprised to see anything more than 10whp.

Turbo? I bet you gain more than 10RWHP on a turbo setup. Turbo applications benefit greatly from bigger exhaust (way more than NA and SC anyway). If your downpipe is 3" and you have no neck downs, I bet you gain at least 10RWHP. Added benefit will be better spool. Get before and after dyno results same day same dyno and I bet you will see the gains.