# Shop said items will reduce output



## x47544F (Apr 11, 2012)

Shop says many items in the list will reduce the power of bolt on GTO if installed???

Kooks ss headers
Kooks street screamer catback
Kooks midpipes w/ cats
LSXr 102mm manifold
NW 102mm DBW TB
SNL 4" CAI w/ 102mm MAF


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## x47544F (Apr 11, 2012)

I realize that the 3" exhaust isn't needed at the moment but once heads and a carefully selected cam is installed it should be efficient according to David Vizard's book. (Unless I totally misinterpreted something...) I don't claim to know a whole lot about engines I am learning like everyone but I am fairly confident the items won't reduce power... Perhaps they might be trying to sell me something? In the end, it is important to remember places are businesses... What are peoples thoughts?


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## time3777 (Oct 11, 2010)

I installed everything on your list on my car except the intake and my power increased tremendously. The shop must be trying to sell you something.


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## BearGFR (Aug 25, 2008)

Going with larger than needed exhaust WILL reduce low rpm torque. This happens because with the larger tube, flow velocity is less (the bigger diameter means you don't need as much velocity to move the same volume of gas), and the decrease in flow velocity means you lose some of the scavenging effect from the inertia of the flowing gas to help evacuate the cylinders, so the engine has to expend some energy to "push" the exhaust gasses out -- energy that would have otherwise been available to send out through the crank. Mr. Vizard does talk about the importance of flow velocity in his books.

Bear


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## svede1212 (Nov 1, 2005)

A large exhaust helps peak HP/RPM but is less effective than a smaller one at mid-lower RPM. You're moving less gas then. The shop must have idiots or con men. Those parts (except the intake of course ) will add 30-40 RWHP after tune. The Screamer will only change sound. I always advise everyone to put on their LTs before they proceed with more exhaust work. Often it's the only thing you need for more power and sound.


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## x47544F (Apr 11, 2012)

@Everyone
Thanks guys for the responses I appreciate it. 

@time3777
Thanks that gives me confidence in my choices.

@BearGFR
I agree it is velocity not back pressure that you want. David Vizard's book mentions 2.2-cfm per hp of flow is required to keep the loss % to less than 1%. Then I read a 2.5-in pipe will flow ~560-cfm. 
So I just sort of did:
560*2=1120-cfm
1120/[email protected] (With optimum mufflers)
So I said well I know whatever muffler attached will flow less so I
went with a 3-in pipe diameter since I figured the mufflers would flow more.

Although, now that I read it again. Perhaps a 2.5-in pipe w/ a 3-in muffler would have been the best for NA with the LS2. Although, since I wasn't sure about going FI or not I went with a 3-in diameter. In FI scenario more air is being pushed into cylinders so I figured a larger diameter would be better. 

Also selecting parts is a lot harder when you are trying to look into the future as well . I figured if I went NA I could get away with the 3-in pipe.

@Svede
I would have gone with a Svede OTRCAI but at the point in time I wasn't sure which direction I was going to go (FI or NA) so I just sort bought the SNL due to the 102mm MAF that came with it. I didn't know if I was going to remain NA or not and the Texas speed 102mm MAF was like $200ish so I was like well I will just pay the extra and get a CAI. Perhaps one day I will get a Svede OTRCAI ;-). 

Also since I know you just installed a 102mm LSXr intake ;-),
1.) 
Are LS2 MAP sensors threaded? When I drill the hole for the MAP sensor is it a friction fit or are they actually threaded? The manual mentions there is a bolt that holds it in place but looking at the image of the MAP I was like that totally looks threaded but maybe they don't mention threading?


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