Re-Doing Exhaust Anyway.... A Few Q's

[boy&hisdogs]

After lifting my truck I need to change the crossover pipe to clear the driveline. And... well the rest of the exhaust is a rusty, leaky, sloppily clamped mess that I put together when I was a teenager. Since I'm going to be getting the welder out anyway, I might as well make any other exhaust mods all at once before sending off for a tune.

The truck is a 98 K1500 with a stock 5.7 Vortec. I have 37s and 4.88s and spend most of my time cruising between 2000 and 2500 rpms so that's where I want the engine to run best. I like a choppy, thumpy, old muscle car exhaust sound more than a smooth drone if it matters.

1) Do X/H pipes matter if I have a 2-1 muffler? Or would a y pipe and single in/out muffler be better?
2) Are shorty/mid headers worth it?
3) People say that the headpipe between the manifold and cat is the biggest choke point on these trucks. Could I go to a (slightly) bigger one and keep the stock cats? I live in CA and don't want to mess with smog stuff too much since my truck has passed every smog check free and clear so far.
4) Are stock sized pipes (with the 2-1 muffler) ok for a stock engine? Most headers I've seen have a 2.5" exit, will that cause problems with the stock 2.25" pipes?

 

[Frank Enstein]

1) Not really. And if the merge is placed too close to the engine bottom end torque can be lost. dual mufflers and an "H" pipe will give a more "Throaty Muscle Car" sound. I do not believe the exhaust after the cat/O2 sensors is subject to emission testing but check with the local smog station. California emission laws regarding aftermarket parts have changed several times lately. I'm not trying to be Mr. Doom and Gloom I just don't want you to have any hassle at your end after you do all this work.
2) Usually worth 10-15 horsepower depending on the rest of the system. Ten with stock exhaust 15 with a cat-back system. Make sure they have an CARB E.O. number for your vehicle.
3) Maybe but in The People's Republic of California I wouldn't change it. Unless it has an E.O. number of course!
4) The stock pipe size is generally on the small side but going a bit bigger (one size larger not 5 sizes!) can help flow some and may deepen the tone. The farther away from the engine the smaller the pipe can be without hurting performance. A larger exhaust tip can deepen the tone. I don't recommend exhaust tips until the system has been driven a couple of weeks. If you're happy with the tone the size is fine. If you want it deeper go with a bigger tip.

 

[Erik the Awful]

4) The stock pipe size is generally on the small side but going a bit bigger (one size larger not 5 sizes!) can help flow some and may deepen the tone. The farther away from the engine the smaller the pipe can be without hurting performance.

I'm from the school of thought that your exhaust should always increase in size the further you go from the engine. Yes, you lose exhaust velocity, but the exhaust is not inclined to squeeze back into a smaller space, so you avoid reversion. I violated this on my own exhaust because I didn't realize there were 2.5" outlet headers for our trucks.

I come from the land of no inspections, so I can't speak to meeting California's rules. I have Hedman long tubes, 3"-2.5" reducers, Walker cats (that are melting), a Jones x-pipe, and Cherry Bomb Salute mufflers, dumped behind the cab. It's a bit too loud for me, and I have some more tubing to eventually extend it out to the bumper. Other than the headers, it's all 2.5". Everybody says it sounds bad ass (the Lunati cam helps). It's more thunder-y than choppy, but not fake-boomy like a stock cam with Flowmasters.

 

[boy&hisdogs]

Essentially the way it works here is that a manufacturer has to pay an exorbitant fee for the state to "approve" their part. If the part doesn't have the California approval number on it, it's not legal for use, regardless of how much smog it actually does or doesn't put out.

You can fail a smog check before they even put the sniffer in your tailpipe of they can't see the numbers stamped on your smog related parts like cats and headers.

So no cheap ebay parts for me, at least not headers. And CA approved aftermarket cats are like $800 minimum, most are over $1000.

 

[Supercharged111]

Could you run bigger pipes to the cats and just waller out the body? I'm sure you can get some CARB legal shorties for it, but a 2.25-2.5" head pipe will wake the thing up. You could use the back of the exhaust as a jig to open up the front and vice versa. This would keep your stock cats in their stock locations.

 

[boy&hisdogs]

Could you run bigger pipes to the cats and just waller out the body? I'm sure you can get some CARB legal shorties for it, but a 2.25-2.5" head pipe will wake the thing up. You could use the back of the exhaust as a jig to open up the front and vice versa. This would keep your stock cats in their stock locations.

I was thinking about that, make everything before the muffler 2.5". For what a cat costs here I wouldn't want to mess with it, but I figure it's a choke point anyway, might as well just do what I can everywhere else around it.

I can get lots of legal, direct bolt on shorties but that's it. There's not really any legal long tube, mids or tri Y for the Vortec 5.7. I have heard of people buying CA legal TBI 350 headers and just adding the Vortec sensor hookups themselves, but that's still technically not legal since you 1) are not supposed to modify smog parts in any way and 2) It wasn't certified for the engine that its actually on.

 

[Supercharged111]

I was thinking about that, make everything before the muffler 2.5". For what a cat costs here I wouldn't want to mess with it, but I figure it's a choke point anyway, might as well just do what I can everywhere else around it.

I can get lots of legal, direct bolt on shorties but that's it. There's not really any legal long tube, mids or tri Y for the Vortec 5.7. I have heard of people buying CA legal TBI 350 headers and just adding the Vortec sensor hookups themselves, but that's still technically not legal since you 1) are not supposed to modify smog parts in any way and 2) It wasn't certified for the engine that its actually on.

8 lug Vortec head pipes are big FYI.

 

[boy&hisdogs]

8 lug Vortec head pipes are big FYI.

That's something I've had in mind, since but I'd still have to modify it to clear the front driveline.

 

[Supercharged111]

That's something I've had in mind, since but I'd still have to modify it to clear the front driveline.

Yep, but the cats are bigger too so if you can find one it's a good start.

 

[boy&hisdogs]

Yep, but the cats are bigger too so if you can find one it's a good start.

That I did not know... the only thing is that reselling/using used smog parts is also illegal, so it's not as simple as going to the pick n pull. I'll have to find one being parted out by just some guy, and hope he will sell them to me for a reasonable price, and that they are still good.

It's worth a look since they are bolt-on, I can put them on the truck whenever.