Slow'86

Good morning,

One thing I'm currently working on figuring out is, what is the truth with N/A LS motors and exhaust? There are alot of basic charts, calculations, etc.

I've seen talk that a slightly smaller exhaust will net a bit more torque lower in the RPM range, while a free flowing exhaust gives more peak.

My 6.0 is going to have a 228/230 cam, 243 heads and Speed Engineering headers. I was thinking about using 2.5" or 3" pipe off the collectors and have them going into a Y. After the Y I was thinking of just using the Hooker Aero Chamber 3" catback that is available for our cars. I already have the Aero Chamber set up, but I'm not sure if it would be a restriction on the system.

Thanks!

ShiftyCapone

iTrader: (7)

You motor will be solidly in the 420+ rwhp range which will tax the 3" system. Hooker's dual 2.5" system (28% more flow are than single 3") is recommended for 450hp or less combos (per Toddkey). The car will still make power, you will just be leaving some out of the equation. How much, hard to say, but measurable. The more rearward you can place the restriction, the less impact it will have. Meaning, if you start your bottleneck just behind the headers, it will zap more power than if the 3" doesn't start till right before the muffler.

Slow'86

Whoops, I meant my cam is a 228/230, not 228/238.

My plan was to get rid of the 3" downpipe and only use the bit that goes over the axle.

I might be best off welding up my own catback system out of aluminized pipe. It's going to be a nice weather driver, so aluminized pipe shouldn't be an issue I think.

Slow'86

Also, unrelated to exhaust, are my 245 width tires going to be causing issues for me given the power level?

Slow'86

I've done a bit of research regarding 1. the aerochamber muffler and 2. 3" exhaust in relation to my horsepower level.

I found this on LS1Tech from Cody_Brooks who has the same catback: "the aerochamber in the hooker cat-back flows 900 cfm which is plenty for most motors. considering how much the exhaust has cooled (often times 150*F or more between the crossflow muffler and y-pipe) by the time it gets back there to the muffler you need the small restriction it does have to help keep the velocity up. my exhaust when I'm done will have headers, dual 3inch pipes feeding into the y-pipe and a single 3 out to the muffler and dual 2 1/2 out of the muffler which will work with the natural cooling of the exhaust to keep velocity up, restriction down, hp and tq up as well"

I don't know how much of it is 100% true, but the 900 CFM is correct. (~2.2 CFM per HP is recommended, so about 410 HP) So the muffler is just fine for the system, and the dual 2.5 tailpipes should be fine, as well. So I am just going to work on figuring out how I want to go about minimizing the single 3" part of the catback.

dixiebandit69

Yes.

ShiftyCapone

iTrader: (7)

Don't convince yourself. You won't be happy knowing a few hundred bucks is keeping you from 30+ more hp. If anything, fab a Y-pipe to a mufflex 3.5 or 4" single system. You could run the aerochamber if you are short on funds, but LS motors, especially with a cam, benefit greatly from a property sized exhaust. Also, 245 wide tires? RIP traction.

Slow'86

Alright, thats very true. I did see the mufflex system and it's pretty nice. Although I may end up building my own for cost savings.

Yeah, I figured 245mm was a bit small. What do guys with similar power levels run? I'll be sad to go without the IROC wheels, but burning tires up doesn't really sound like fun lol.

JAYDUBB

From experience, LS engines (especially the 6.0's) flow so much air with good heads that a 3 inch exhaust will become a restriction. 420whp is around 500 crank. IIRC, isnt the limit on a single 3 inch 400 HP crank?

I would say get the Speed Engineering headers and then have a custom dual 2.5 inch exhaust made for the car and make sure they tuck it well. That would be the MINIMUM starting point, IMO. OR like you said, Speed Engineering headers and custom Y to the 4 inch Mufflex system.

Slow'86

Yeah, I think a very well flowing 4" system is definitely going to be a requirement. Mufflex also makes the dual tailpipe version, which looks real nice IMO.

I think the max size inlet Hooker puts on the Aerochamber is a 3.5," so I'm thinking your correct in saying I shouldn't convince myself, ShiftyCapone.

JAYDUBB

Have you considered running the full Hooker Blackheart system or is that too pricey?

Slow'86

That system is beautiful! But, yeah, it's a bit pricey. I think if I end up doing dual, I would get one of the DIY kits from Summit or Jegs and weld one up.

JAYDUBB

I feel you 100%. I would do the Speed Engineering headers, custom Y and 4 inch Mufflex or a custom fabbed true dual 2.5 and seriously tucked up (My preference is the true dual). Ive tuned several 4th gen F-Bodies and Trailblazer SS's. The single 3 inch exhaust (YES, GM was dumb enough to put a single exhaust on the TBSS... They REALLY didnt design it for performance like Mopar did the SRT8 Cherokee) causes enough restriction that I have to pull timing due to backpressure causing detonation. SMH

Lonnie P

3" is a little on the small side.
There is probably a reason that my 2500HD with a 6.0 came from the factory with a 3.5" exhaust.

Slow'86

Now that I know 3" is too small, would it be easier to do a dual 2.5" or a single 4"? I think for a 4" I would do it same as the Mufflex system, but with a Hooker Maxflow, instead.

I was also wondering if fuel lines are the only thing in the way of doing a dual on both sides of the car? How hard would it be to route the fuel lines in a way that I could do a dual system (2.5"-3") on either side of the car? I have to redo my factory lines, anyway (factory Rochester with no electric fuel pump).

five7kid

iTrader: (14)

My personal opinion - you're worrying about this too much.

As for the "small" for torque, "large" for HP thing - that's more relevant to the header primary tube size than exhaust size. Once you get past the collector, it really won't have that effect ("torque tube" length does matter, but building a "Y" pipe into a 3" single is going to give you that function). If your exhaust is too small, it'll kill power, period.

To illustrate the small exhaust "problem": My son is running a 6.0 in a '75 Vega (don't let that fool you - at 3175 going down the track it weighs more than some 3rd gens on here). MS3 cam (238/242 @ .050, .600"/.600" lift), ported 799s, 1-3/4" primary headers into 2-1/2" duals with H-pipe, shifts at 6500 RPM. That is a relatively "small" exhaust but calculates out north of 470 HP. You didn't say what your car is going to be used for, but I think you'd be fine with your original plan (which would be much simpler than trying to go with a larger exhaust).

You might get a little more power out of a larger exhaust. You didn't say which primary size headers you're getting - the LS engines tend to like the larger primaries, and a healthy 6.0 is no exception. Really, though, taking off weight will speed you up as much as making more power, and at least to a certain point, will cost less than making more power.

five7kid

iTrader: (14)

The issue with routing duals is the torque arm. And not much room past the axles, either. Keeping the fuel lines away from the exhaust is a good idea, though.

Slow'86

Hello, thank you for the information! The amount of knowledge you all have really makes this forum so helpful.

Yeah, I am quickly feeling as if I am overthinking all the little bits of the project. I've decided to use the Speed Engineering headers. I'll likely use a 2.5" or a 3.0" Y pipe into the 3" catback. The cam is actually only a 228/230 .585/.585 112, so it's not super radical. The car is going to primarily just be a weekend cruiser and fun ride that I may take to the strip a couple days a year at most.

If I end up having an itch for more power after it is up and running, I may buy a Mufflex dual outlet. But that is something I would have to save a good amount for. I think I will end up focusing my money elsewhere in the project. If the 3" misses out on a few horsepower, that's honestly okay, seeing as how it's not a max effort track car, anyway.

Lonnie P

You overthought it to the point of doing exactly what most said not to do.
You should have 1-3/4 or preferably 1-7/8" headers, 3" pipe off the headers to a y & a 3-1/2" or larger exhaust.

At least get good headers & y-pipe... you can swap the cat back at a later date.

FYI, I have seen a .25 sec reduction with a 4" Mufflex over a 3" Borla on an 11 sec 02 LS1 car with 1-7/8" headers & 3" y-pipe.

Slow'86

Yes, the Speed Engineering headers are 1-7/8. I'm using 2-1/2 after the headers into a 3" Y, into the 3" catback I have.... for now.

If/when i want more power, I'll get a larger catback later. I'm doing it this way because of lack of funds for the Mufflex system I want.