Rogillio

Ok, dumb question from a newbie time

i have a stock 2009 Corvette and have been proclaiming a screaming 430 Hp. But I saw a video that says if you have duel exhaust you have 436 Hp. I have 4 pities out the back. So do I have 430 or 436 horsepower? Did I not understand the video or do I have 436 Hp?

Sorry for the dimb question. Just don’t want to short change my car when people ask. :-)

RicK T

No, the NPP option (Performance Exhaust) added 6 HP to the standard 430.

To check what you have, look at the exhaust tips. If they are "dimpled" inside and if you look into the inside pipes and see valves, you have the NPP option. See pic in this thread:

https://www.corvetteforum.com/forums...post1576985331


You can also check the RPO code list on the inside of the glove box door. The codes are listed alphabetically, just look for NPP.

Rogillio

Frankie15

Look for these above your exhaust tips. If you have them, you have the NPP option with 436 HP.

Rogillio

Cherokee Nation

Less restriction in the exhaust outlet...But you will not notice any hp gain, just more noise.

Vette_DD

Several forum members couldn't find the sticker in their glove box until we insisted that it was probably there. If there, it will be on the EXTREME left side of the inside of the glove box door. It is a white sticker with black lettering. Use a flashlight.

BullittEV

also, be aware that the exhaust axleback systems from the C6 (2009-2013) are not interchangeable with every other C6 model.

There is a change in the mandrel bend for the 09+ 6.2L vettes, incase you were interested in changing it out.

therealmz

only a dyno will tell you the truth...................until then, you're GUESSING.

cgladish

the NPP exhaust option doesn't add horsepower, but when it's activated, it does allow less restriction which let's the other 6hp free.
when not activated, the exhaust goes through the muffler ( quieter & are more restrictive ). when activated, the exhaust is straight piped
( nosier & less restriction ).
if you have the standard exhaust, the exhaust will always run through
the muffled section of the muffler.


let them ponies run free!

cadyshac

The RPO code tag is not "in" the glove box, it is on the outside of the glove box door visible from the drivers seat when the glove box door is open. Sit in the drivers seat, open the glove box, the tag is on the outside part of the opened door facing the center console or shifter. Take a pic of it with a cell phone then google "RPO codes" for whatever year your vette is. You can use these and your tag to decode exactly how your car came equipped from the factory.

Rogillio

Rogillio

Where can I find the codes defined?

Null Pointer

True, unless the glove box door had the broken latch fix done where it was entirely replaced. Some Corvettes, like mine, had that warranty fix done and so I don't have the RPO sticker in the glovebox. I did get a copy of the build sheet from the Corvette museum for my car, which has most of the RPO codes that the car was built with.

buckmeister2

Not a dumb question....the person on the video probably did not actually say, "dual exhaust". They likely said "dual mode exhaust", which is what NPP is.

TorchRedFred

GM claims that the NPP exhaust option adds 6hp. The valve is there just to make them quieter at lower RPM's, but I believe the mufflers are different than the stock ones and that's where the additional claimed 6hp comes from. They are less restrictive than the stock ones and as a result are louder. GM added the valves to compensate for the increase in noise.

Corvette_Ed

Iirc, with valves open, the NPP exhaust is running at the equivalent of 80% open pipes.

nick14003

Lmao, first of all. It really makes no difference, no human will feel 6 horsepower difference...

Second of all, your talking horsepower to the crank, not to the wheels, which is a widely skewed number and really has no basis in reality... If you put your car on a dyno, you'd be in the high 300's.

Quoting manufacturer stated numbers, is really an obscure topic and talking differences of 6 horsepower, is pointless, your car would vary that much horsepower by a slight change in altitude, or if you change octane fuels.

It's kind of like, when people take a 430 stock car, add an air intake and tune, and they claim it makes 450 or 460... they can say whatever number they want really, but in reality who is going to measure the hp to the crank? no one... even with those basic mods a dyno wouldn't even bring it up to 430 hp, which is why people kind of just blurt out guesstimate numbers. So really, it's whatever you believe it is, as long as you are somewhat near reality, and don't think the exhaust is adding 50+ horsepower.

This is a norm in the car community when you are adding small amounts of power, when you add forced induction or go up in triple digit numbers, people generally switch to rear wheel horsepower RWHP or WHP when claiming horsepower, which is what would generally be measured at a Dyno, but even dyno numbers can vary by switching dyno's and based on the car, that's a whole issue of it's own.

There is no magic number, or a relative ground zero, just say whatever you believe to be true.

TorchRedFred

I think you are overreacting a bit. No one said you would notice a 6hp difference or is making a big deal about it. It is only brought up to point out that there is a difference between the stock exhaust and the NPP option other than just a valve. My guess is that most people prefer the option because of the added benefit of being able to add a Mild to Wild switch and the louder exhaust note. The NPP exhaust was a $1200 option. Not the smartest way to go if your only concern was to add 6hp.

Rogillio

I know it doesnt matter, I just didn't want to understate my car. I finally have a car that has so much horsepower that when asked about it, there is no need to lie. 430 hp is wicked powerful in such a small car. :-)

I have a 2014 Ford F150 Raptor that also has a 6.2L motor that is rated at 411 hp and weights about 6,200 lbs. My Corvette is rated at 430 hp and weights about 3,100 lbs .....she's not much good off-roading in the mud though.