Frisson

I want to do a stage 3 package (Heads, Cam, Intake, tune) to increase and change the car's power delivery. What I DO NOT want is a louder car.

I have heard the stock manifolds flow pretty well. Would it be harmful to leave them? (vs headers)

I am okay with sacrificing some HP if there are no other side effects.

SPDKLZ1

Harmful? No. Maybe leaving 15-25 hp on the table.

Z.06

Passing on the long tube headers also decreases the heat aging/failures on your starter and wiring harness.

97TAWS6

Same thing here, promised the wife that I was not going to turn this car into a smelly car that gasses us in traffic like my TA. (right away). Will prob do it after I put the catted y pipe on my TA and show her a catted system will not stench us out.

jayyyw

15whp and 30wtq is what headers were worth for me. I did heads, cam, air intake, and e85 first go around. Then headers alone. Then ported MSD and NW102

niphilli2

it really depends on the size of the cam. The stock manifolds are great up to about 550 whp beyond that they become a restriction.

with this said, I can’t say I’ve ever seen a big HC car on stock manifolds; you should do it and let us know the results!

monsoon725

I did long tubes on my supercharged SS sedan. I hated it. I hated the smell. Even with cats. Not for me.

I just got my car back from Katech. Stock exhaust. Love it.

97TAWS6

I just put Magnaflow bullet cats on my LS3 Trans AM. Smell is much improved, but still willing to give up a little for awhile.

OhhhApieceOfCandy

Not sure what year your car is but longtubes with cats and a pre '09 Z catback would be pretty quiet. Something to consider if you don't want to give up any power gains. I ran that setup for a while before going to an '09+ stock catback.

NA FURY

What's the biggest cam you think you could get away with on stock manifolds? I'm looking to keep the stock manifolds as well but would like some chop.

Cordes Performance Racing

depends on the cam, but it can be worth a lot of power. I won't do it as timing can be so low on pump gas exhaust temps get really hot and can melt OEM cats. Do headers w/ high flow cats, and leave OEM mufflers. In closed mode if you think that is loud than get an old carolla.

grinder11

Brian Thomson made over 1,000 crank hp using an LS9 blower on an LS7 running stock exhaust manifolds. They are very good. Research Thomson Automotive 1000hp LS7 article in Motor Trend in 2015.....

Gearbhall

Catted headers with stock NPP isn't loud at all. Hell catless headers with stock NPP is quiet when the valves are shut, but to avoid the smell go catted. The only problem is stock NPP drones pretty bad when the valves are open.

Gearbhall

Headers have no impact on the size of cam you can use. You can put as big a cam as you want, its just you won't benefit as much as if you did headers also.

niphilli2

id give the TSP stage 1 v2 a try (1.2)

97TAWS6

I looked at it this way, if I am choking the cam a bit, I can swap headers easy... if I have to swap a cam because I chose it for stock exhaust and I upgrade to headers.... not so much. Really do not want to redo installs, so choosing the cam to fit my goal of a great street cam based on Tony's suggestion. No buck under 2k etc.. Choking it a bit with stock manifolds for sake of my current goals.

niphilli2

this is a really good point. The TSP 1.2 is not a small cam by my standards (I think it has 6 degrees of overlap). I was thinking someone who cares about noise might also hate the shake and cam surge that comes along with a big camshaft with lots of overlap.

the reality is the reason the LS7 loves big camshafts is because the overlap creates exhaust scavenging that helps with the rather anemic exhaust port flow. Overlap is certainly not going to hurt the stock exhaust if you are willing to deal with the driving manners.

449er

The LS7 manifolds do flow well, in my opinion unless you are building a max effort car, it's not worth the cost ( roughly $2k for Kooks or ARH) plus the x pipe that will need to be changed & you will also need a tune