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Specific Cat-back HP Gains

5K views 13 replies 7 participants last post by  plemon61 
#1 ·
So it seems like most are in agreement that a cat back on an otherwise stock G8 should add approximately 10 hp give or take. I want to know how much hp gains can be had from any full cat back on my engine over the stock exhaust system.

I’m doing a dod delete on my 09 g8 gt. Cam specs are 218/226 .595 lift on 114+3 lsa. Already have a specter cai. I will also be adding kooks mid lengths with high flow cats. And a mail order tune from one our vendors.

Now with the motor set up like this, how many hp will a full cat back give me over the stock setup ? This is my dd car. Any info is much appreciated. Thanks Patrick
 
#2 ·
Every one of these G8 GT are different. Catback, intake, cam swap, tune, headers, cats or not, etc etc..... You can do the same mods to 2 identical cars and get different results.
 
#3 ·
If specific numbers in regards to gain are your goal, you need to dyno the car and get a baseline. If my memory serves me correctly, most stock G8’s are 280-290 rwhp. If you dig deep enough here on the forum, there’s probably a thread on this.
You mention using Kooks mods and high flow cats. Whose cats? What catback are you considering, and what diameter? Whose tune?.
Been my experience to strap it down and spin it to get a baseline. Do your mods, and get it dyno tuned with the same dyno, then you’ll get your number.
 
#4 ·
Do it right the first time. Get Kooks long tube headers, a better CAI and a street tune customised to your car and driving conditions. I think canned tunes of any kind suck, but that's my opinion. Get a tuner to drive your actual car and adjust everything on the go.

Like the others said all our cars are unique. It depends on a lot of factors, including the parts you use. I recommend the Solo exhaust system.
 
#5 ·
I get what you all are saying but I think you’re missing my point. I’m just wondering if anyone can give an approximate hp increase from any cat back ( Solo, Corsa, Magnaflow ) say 2.5” diameter when hooked up to our 6.0 L engine that already has good exhaust flow out of the heads (Kooks mids with their high flow cats) has a relatively small cam, but much larger than stock and a good tune ( Pat G or RCR) Gotta be more than 10 hp I would think.
 
#6 ·
Let me put another way. With the above mods, how much hp am I leaving on the table with a stock cat back ? Specifically the mid pipes and 3 resonators.
 
#7 ·
Let me put another way. With the above mods, how much hp am I leaving on the table with a stock cat back ? Specifically the mid pipes and 3 resonators.
 
#8 ·
I live in a complex and have yet to hear a cat back that's quite enough on cold start. I leave for work pretty early every day so trying not to be that ***hole neighbor. I have Magnaflow axel backs on now just for a bit of sound. I like it the way it is and I think it will be a bit louder with the Kooks mids and HFC's. Adding them to get rid of the biggest exhaust restriction.
 
#9 ·
Like others have said. Everyone of these cars reacts differently. I have however done very similar mods to what you are looking for. I don’t remember exact cam specs but it has very good street manners. I have K&N CAI, Borla cat back, kooks mids with high flow cats and custom tune. Dyno read 386hp to the wheels. Again as others have said. Get a custom tune, remember all of them react different and good luck!!
 
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