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Stock cat-back good to 300whp??

MeanGrn99GTP

MeanGrn99GTP

New member
So I have read on ZZP's website that the stock cat-back is not restrictive until the 300whp mark.

Is there any dyno proof of this?

I replaced my cat back due to rust with and SLP powerflow. Comparing them side by side, looking at the bends, diameter, Y-pipe, mufflers etc. I find it hard to believe that there is 0whp to be gained even on a stock set up.

Has anyone done a before and after dyno replacing the cat-back?
 


Nobody said there was a ZERO gain, the assumption would be based on "why spend $500 for 5-10hp where the money could be spent elsewhere"

That being said, more flow can achieve greater horsepower, always
 
Just for a comparasion, think of it this way, the GM 6.2 V8 with 420hp only has 3in pipes off the manifolds into a 3.5in single catback exhaust. Thats plently of pipe size for the power output.


The 3800 has 2 less cylinders and way less cubic inches, it's really not flowing that much air at one time. The bigger the exhaust really means nothing when there is no back pressure there already. 2.25in piping for 300-350whp is just fine on a 6 cylinder. The 3in is technically overkill for just about all power levels that most run, but it's what they sell so people buy it. Once the exhaust is past the downpipe, it's not really a problem for the stock exhaust size.
 
I'm actually interested in seeing if there is a noticeable gain with a larger catback on my own car. I've been debating getting one and getting a quick dyno before and after. I haven't been to the dyno since switching back to 93, so it would be a good excuse. If I do so I'll post up the sheets before and after.

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chrsmi1 said:
I'm actually interested in seeing if there is a noticeable gain with a larger catback on my own car. I've been debating getting one and getting a quick dyno before and after. I haven't been to the dyno since switching back to 93, so it would be a good excuse. If I do so I'll post up the sheets before and after.

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That would be great!
 
What is the point of a 3" down pipe if shortly after that it gets choked by a poorly bent 2.25" catcack? I could be wrong but I feel a good after market catback is not given enough credit on this platform compared to others.
 


ITHurtzinmybutt said:
Nobody said there was a ZERO gain, the assumption would be based on "why spend $500 for 5-10hp where the money could be spent elsewhere"

That being said, more flow can achieve greater horsepower, always
Click to expand...

This


Nobody says there's no gains.. But there minimal gains when you think what a typical catback cost vs how much more power your going to gain back. Usually catback is one of the last mods when your trying to squeeze everything you can out of the SC.

Usually the restrictive part is the ubend.. So a downpipe will improve that quite a bit.. Going beyond that.. Ehh depends on what you want and what you have to spend.

Never dyno'd mine but when I went from the stock 2.25 exhaust to 3" I dropped damn there 2 psi so the flow improved. Now who knows how much of a difference you'll get let's say going from 2.5" to a 3". Plus with the vendors 3" exhaust it's 3" to the Y and then 2.5" since after that point your just adding more weight.


Only reason I went 3" instead of 2.5" was because I got a hell of a deal on it and was cheaper then what the 2.5 piping would of cost me. The stock exhaust started to crack and needing welding so I figured why not.


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REDCRAPGP said:
This


Nobody says there's no gains.. But there minimal gains when you think what a typical catback cost vs how much more power your going to gain back. Usually catback is one of the last mods when your trying to squeeze everything you can out of the SC.

Usually the restrictive part is the ubend.. So a downpipe will improve that quite a bit.. Going beyond that.. Ehh depends on what you want and what you have to spend.

Never dyno'd mine but when I went from the stock 2.25 exhaust to 3" I dropped damn there 2 psi so the flow improved. Now who knows how much of a difference you'll get let's say going from 2.5" to a 3". Plus with the vendors 3" exhaust it's 3" to the Y and then 2.5" since after that point your just adding more weight.


Only reason I went 3" instead of 2.5" was because I got a hell of a deal on it and was cheaper then what the 2.5 piping would of cost me. The stock exhaust started to crack and needing welding so I figured why not.


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Thank you for some data. You dropped 2PSI getting rid of the stock cat-back.

What other mods did you have done at the time? Obviously the more mods you have the bigger difference it will make.
 
No other mods were done at the time.

Still on a 3.6, Vs cam, SDs, overkill tune.. Blah blah.. You know the other typical mods


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FWIW, I went from a 2.5" SLP cat back to a 3" cat back and lost 20-25 hp (on the dyno). Track times dropped from 13.0 to 13.3-13.4. Also upgraded to a Gen V while having the 3" on. Same track times (even going to a 3.0 pulley) (was on a 2.8 when I went 13.0X on a Gen 3 blower).

I put a 2.5" cat back back on but haven't been to the dyno or the track yet. Now I'm on a 3.0, gen v and 2.5' cat back.
 


Before with the ported Gen 3 and 2.5" SLP exhaust (Single pipe)

Dynopull03regalSeptember12_zpsbe690326.jpg


After with the 3" exhaust and same Gen 3.

CAM00810_zpsol5l46rn.jpg


well looks more like 17-20 WHP. I have a graph somewhere of 258 (difference was I upgraded to 105 valve springs).

When I changed the valve springs (3" exhaust, gen 3)...

20140810_144824_zps0c54115d.jpg
 
I dont see how a 3" vs 2.5" the 3" would cause horsepower loss, unless you went from a straight through to a turbo choke style.

Because if thats the case a open dump you would lose 50hp which isnt the case at all.

And just for reference I ran stock and 2.5" on a 3.4 pulley, now run 3" on turbo.
 


I'm not sure how you could lose power switching to a larger diameter catback... Were the atmospheric conditions the same when it was dyno'd? Was there any KR? Are they both corrected WHP?

Any power loss other than a small amount on the low end would defy all logic. Thank you for posting graphs! That's what I'm looking for.
 
The flow velocity and scavenging of the exhaust are the biggest things you want to look into. Bigger is not always better with exhaust, you need to have a good balance of both to make the exhaust work correctly for whatever application it's in.
 
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