I am getting ready to drop a forged 402ci in my vehicle and need advice on how to make headers quiet. I like a sleeper/stealth concept and don't want the typical header ping sound. I figured ceramic coating should help a little but what else would make them quiet as cast iron headers? Maybe heat wrap?

Just looking for ideas.

 

I would have to say that the thickness of the header material has the most to do with it. Some nice thick stainless headers with heat wrap would probably be the quietest. Maybe Kooks?

 

....don't get headers then. If you want you car quiet get a Prius.

 

not gonna happen, its science

 

This.

 

Quiet down headers....thats funny. Even if you get the thickest ones and wrap them with heat wrap....they will still stand out like a header does. Just get a full exhaust with a godd muffler, thats as stealth as you're gonna get.

.

 

You're going to need some type of exhaust silencer. it will take out some the low pitch and just make it higher pitched a somewhat quieter.

Whats the intention behind this mod?

 

Coating is a start, but headers allow more valve clatter to be heard; its hard to change that other then by softening the exhaust lobe. The rest of the exhaust nosie can be handle with mufflers. On my Camaro, I used the SLP dual-dual which flowed better than stock and was quiet. When the cats were off, I used dynomax race bullets in their place to take the edge off and it dropped the volume by several db with no impact in performance.

 

Have you stood next to a 638 hp LS9 Corvette lately? And I don't think those are cast iron. I think they are double wall hydro formed pieces.

Not so funny. There are new spray coating technologies (similar to Ceramic coating) like HVOF that can arc spray up to 12mm thick in various metals. The only issue would be weight. There is also a way to open up OEM cast iron headers by flowing a 'grit slurry' through them. I am just saying there are ways, albeit probably cost prohibitive.

Do you guys remember some of the OEM cast iron headers of past? I do.

Max Wedge Hemi:


Or maybe this Ford 4-2-1 Y-pipe header:

 

The process you are describing is extrude honing, but it was for polishing. It didn't really port or enlarge the passage way.

 

Incorrect. Yes it can polish but it is also used for enlarging ports whether it is an intake, heads or exhaust manifolds. Heavier grit and longer time processing results in larger openings. If you run it long enough, it will wear right through anything. That technology was pioneered by the stock class cheaters back in the 60's. Do a Google and you will find what I am talking about. Examples:

>>By enlarging and uniformly polishing internal air and fluid passages, flow velocity is maximized.<<

>>Results have demonstrated that such increases can exceed 30 percent on aluminum intake manifolds and 25 percent on cylinder heads.<<

Just saying.

 

I had my LS6 exhaust manifolds extrude honed. I asked for their maximum level process. The result was a nice brushed apperance, but at the bottom of the brush marks there was still evidence of the rust that was there before. In other words, the depth of the material removal was about the same as the depth of normal rust penetration on the inside of a cast iron manifold. Based on my experience, extrude honing was not cost effective ($800).

 

Extrude hone is ridiculously expensive for what it is. And, I would never send anything to them unless we agreed ahead of time what the final flow results are going to be. Otherwise, you will get back the equivalent of a polish job.

 

I had my headers sitting in the corner of the garage for a while, they were quiet as could be

 

Wow, sounds like you sure got a bad job.

I agree totally!

LOL

 

standing next to a 638hp LS9? That's 636 hp of S/c power. Put the factory headers on your 402 and then be done with it. You sound like those camaro5.com members.

 

Being a little anti-social tonight Zeke? LOL

The LS9 was just one example of some pretty high horsepower engines that use factory manifolds. There are many more that are NA.

Thanks for your fabulous input.

 

I looked into doing this too and your results were typical of what I've seen (except for rust remaining workmanship issue). The amount of metal removed isn't going to take say a 1 5/8" I.D. pipe and open it to 1 7/8". 1/16" would be in this example what I would expect. They might be able to do more, but this is closer to expectation than expecting that extrude honing is going to turn a stock manifold into a free flowing monster.

 

LOL no sir not at all, I'll take the camaro5 member back!

Now keep the headers, put a bullet muffler after each header collector, one in the I-pipe and keep your catback. Just an idea.
What do you think?

 

Whew! That's good. You had me worried for a minute. LOL

Oh, I am definitely going with some LT Clear Image 4-2-1 headers. I went off on a tangent about the cast iron headers and honing crap. My generation didn't have many off-the-shelf performance products. We did a lot of experimentation back then and most didn't work!

So replace the cats with bullets? No issues with that here in Florida since there is absolutely no vehicle or smog inspections. But what is involved in tricking the PCCM?