about two years ago i was talked into replacing my 3" cat back with a 4". did i go to big? it sounds great and when i had the work done i had other engine mods done as well and im not sure if such a big header back system is hurting or helping my performance.
its a stock cube motor and my other mods are an f14 cam, ported heads, headers pulley ewp and all the bolt ons.
i know its more than i need but is it dragging down my overall setup?

 

4 inch is fine and no it's not hurting your setup one bit.

 

quoting JRP:

A 2.75” (stock) single system is good for a 310hp engine with zero loss…
A 3” Single system is good for a 370hp engine with zero loss…
A 3.5” Single system is good for a 503hp engine with zero loss…
A 4” Single system is good for a 657hp engine with zero loss…
A 2.25” dual system is good for a 457hp engine with zero loss…
A 2.5” dual system is good for a 513hp engine with zero loss…
A 3” dual system is good for a 812hp engine with zero loss…

 

my macks got dual 8" stacks and only makes about 360hp bout 590ft lbs so screw it put 6" exhaust on that beast

 

Cool, I've been looking for exactly that info, so thanks for posting it.

NOW - Does anyone know for sure if it's fairly accurate or not?? Sounds like a 3.5" setup would be the way to go for the system I have planned... (I could go to a 4" setup, but that's a slight bit more weight, as well as being more difficult to route...)

 

You don't have to go 4" all the way, you can get a 4" cutout and place it just before the axle, then route whatever you can over the axle. And coming off the headers you can use 3", then a merge to a single 4", then cutout, then back to 3" over the axle. Just an idea...

 

You probably don't need a 4" though with a stock cubed motor. 3.5" would be plenty big enough...

 

i had a 3" header back system on before with a custom y-pipe but after a bunch more mods the y-pipe was too small so since i was replacing my headers i was gonna have my exhaust guy bend me up an all new system in 3 1/2" when we got to talking about it he talked me into a 4" set up going into a spintech muffler with dual 3" outlets. at the time it sounded cool so i said yes without thinking it through to much.

according to the chart i could have gotten away with a 3.5 " setup but at least this way ill be good when i install my FAST direct port 125 shot.

 

I am going to get a 4" Y pipe merge put in today that will reduce to 3" for my hooker catback. At a later date I will put a 4" cutout in. One 4" pipe flows roughly 11% less than two 3" pipes.

 

Just some experience I had.....My last car (the 2000 in my sig) had the Cartek Stage 3LS6X H/C/I package with an LS6 shortblock. With my Hooker headers, mufflex 3 inch ORY and mufflex 4" exhaust into spintech into dual 3" outlets the car made 417 rwhp and 395 rwtq. The guys were like WTF? They dropped the mufflex 4 inch and put on a loudmouth (I ended up buying a TSP rumbler which is just the same) and the numbers jumped to 460 rwhp and 417 rwtq. This may sound unbelieveable but call Dave and he will tell you (this setup was done in spring of 2004). My advice (since I learned the hard way) bigger isn't always better.

 

you saw a gain of 23hp and 22ft lbs going from 4" back to 3" with no other mods at all?

 

It was actually 43rwhp and 22rwtq. I know it's unreal and I'm sure some BS flags will be flying but that's why I said to call Dave at Cartek to confirm. I just wanted to tell you my experience with a 4" system.

 

These numbers are for NORMALLY ASPIRATED combos.


Nitrous, forced induction combos are not as sensitive to exhaust size.


As far as the car in this thread picking up RWHP going smaller. The muffler in that combo is what was killing you. A Magnaflow or Borla single in/out muffler would have made the same or more power than what you have now with the 4 inch on the car.

ANY and I mean ANY crossflow muffler cannot flow with a straight through muffler. Spintech mufflers are known to kill power. Even the single in /out ones.

David

 

the whole reason i bought the spintech was because of all the good things ive heard about them. now your saying that spintech was a bad choice?

what makes them so bad?

does anyone else have any experience with these mufflers?

 

yup im with that guy ^^^. i had my custom built three inch exhaust until the dyno numbers read to low and i cut it off to make it open headers and picked up almost 70rwhp. but the muffler is so important, that guy above changed to many things at once to really say it was just the size. i now run a full 4"system all the way back to a race flowmaster single in and out and love it. i know everyone says flowmaster sucks, but this is not a normal 40 series muffler either. i will get new dyno numbers to see what this exhaust does against open headers.

 

1999 SS.....I'm not saying a spintech is a bad choice, just probably not the best choice (at least it wasn't for my application). Again, I just wanted to give you my experience.