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Unread 06-09-2009, 05:50 PM   #1
swatson454
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Exhaust Project Part 2

Well I got it back from the exhaust shop this afternoon and, aside from the bill, I'm pretty pleased. To recap, it's a Hedman single header into a 2.5 inch pipe that's 20 inches long; giving the collector a total length of 24 inches. Then into a resonator and out from there at 3 inches into a 3 inch center in/center out Hooker Aero-Chamber muffler.

I was a little concerned about how loud it would be but it's not at all. It has a deep, throaty rumble and sounds a touch like a freight truck with a Flowmaster, if you can picture that. It actually has a crispness that makes it sound like the engine's had some work done to it. Sounds really impressive though and I'm quite picky with those things.

I've done this exact set-up on a high performance 383 Chevy before and the results were the same; more power everywhere. The bottom end, just off idle is definitely increased and the gains get better and better with rpm. Obviously it's limited by a tiny cam, carb etc. which makes these engines so good at what they do but the bottom end was defiitely improved and it now has a pretty snappy throttle responce. I was expecting to see an increase in idle vacuum but it stayed at 19 inches.

All in all, I'm really pleased with how this turned out and would definitely recommend this combo to anyone interested in a new exhaust.








The box can be smaller as long as it displaces 360 cubic inches. This one was d*mn near too big.



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Unread 06-09-2009, 06:10 PM   #2
Totallymetal
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First of all, it looks great!
I am curious to know where the resonator (research) came from and why. I want to replace my V8 exhaust with something optimal. Do you have any recommendations? Stock 304 2bbl.
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Unread 06-09-2009, 07:08 PM   #3
swatson454
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David Vizard has done some pretty extensive and very technical research on virtually all aspects of performance. I built and installed these boxes first on a fairly mild 350 I had in a P.O.S. Blazer and was really impressed. All I did there was cut out a spot in the existing dual system and weld them in. No other changes and a pretty impressive difference. Fortunately, in 2003 and again in 2004 I had the opportunity to test them on a dyno with a pretty radically built 383. The results were an average gain of 20ft/lbs throughout the entire power curve without a single down side! As wild as that engine was, it broke the 400ft/lb mark at 2750 rpm and carried its 482ft/lb peak from 4000 to nearly 4750 rpm. Headers with a 4 to 6 inch collector just don't do that. You need a long collector to keep the velocity up so there's a good vacuum behind each exhaust pulse to help pull the exhaust from the next opening valve and also the crucial, although minimal in our engines, time during valve overlap.

Think of an aftermarket exhaust for a two-stroke dirt bike. They use different size, taper, volume etc to tune the exhaust for peak power at a given rpm. Not just overall flow but pulse (pressure wave) tuning. Same thing.

Luckily for us, this works just as well on our stock, low rpm Jeeps too. Most improvements are a trade off i.e. more top end but a little sluggish down low. This one works everywhere otherwise I probably wouldn't mess with it on the Jeep.

The box just displaces enough volume, roughly eight times the volume of one cylinder, to make the pressure waves react as if they've reached open air. If you spent two days on a dyno and found the perfect collector length for your desired torque peak, took it home and bolted on the rest of the exhaust, you would have defeated the whole purpose without something in there to separate the tuned collecter length from the rest of the system. That's what that box does.





After that, just dump into the least restrictive system as possible and thats pretty much it. Trust me, the only acceptible backpressure in an exhaust is that that's caused by a turbocharger! lol

Anyway, I was mostly just curious to see if I'd have the same results in a stock I-6 so I tried it. I just got back from another quick drive and the results just kept me grinning. In my mind it's well worth the effort because there's no trade off. Plus it sounds neat as sh*t! Have fun
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Unread 06-24-2009, 12:59 PM   #4
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Swatson,
Do you have to worry about the axle hitting the tail pipe with that set up?
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Unread 06-25-2009, 01:45 PM   #5
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No, I'd be pretty hard-pressed to get the axle to articulate that much. Especially with the 4 inch lift.
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Unread 08-20-2010, 11:55 AM   #6
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At the risk of necroposting... are these customer made resonators or are they an off the shelf deal?
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Unread 08-20-2010, 06:33 PM   #7
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Necroposter! Lol.

No, I welded 'em up myself. Here's how the parts lay out before welding.



The inlet pipe extends into the chamber by at least an inch and the outlet is flared inside the box before its exit so as to ease flow back into the pipe. For what it's worth, the box I built for the Jeep is larger than it really needs to be. If I were to do it again, it would be 5.5 inlet X 4 outlet X by probably 16 inches long. This will look more like the chamber in the Blazer photo than the one on the Jeep. The 3 inch outlet is up to you but I sure like it.

These things work really well.

Shawn
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Unread 09-30-2010, 02:25 PM   #8
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Would the use of a resonator like this benefit in a 360 application? Heres what I was thinking of trying. In frame headers (probabley Dougs or Hedman elite) , two into one with a full 3" exhaust and a flowmaster 40 or super 44 series. If I uses the resonator box I could have both pipes come into it then out to single muffler and exhaust.

I work in a machine shop so building the box wouldn't be too much trouble, probabley use your dimensions and specs from previous posts. Was thinking on going the stainless route on the box also to prevent any rust thru. I suppose if this is ok and will work out I could possibley make several of these if there is any interests?

Thankyou,
Kevin
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Unread 09-30-2010, 02:32 PM   #9
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Thanks for the reply Shawn! Haven't been on the forum for awhile and I missed. I'll have to have my fab person stitch one up for me.

Thanks again!!

(another) Kevin
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Unread 10-01-2010, 08:47 AM   #10
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Quote:
Originally Posted by kmm View Post
Would the use of a resonator like this benefit in a 360 application? Heres what I was thinking of trying. In frame headers (probabley Dougs or Hedman elite) , two into one with a full 3" exhaust and a flowmaster 40 or super 44 series. If I uses the resonator box I could have both pipes come into it then out to single muffler and exhaust.

Thankyou,
Kevin
Hey Kevin,

I've never done this with a single exhaust but it appears as though the same benefits can be had.

The idea is to size the shorter side, drivers' side I'm assuming, to the correct length, probably around 20 inches, and then the passenger side secondary will be some multiple of that 20 inches. So say 40 or, God forbid, 80 inches. If you can't get it perfect, don't sweat it. It'll still be better than having no box at all.

How they dump into the box will be up to you. I guess if you have room you can run two pipes into the box or maybe plumb the single, 3 inch out of a y-pipe into the box. I dunno, unfortunately space will likely have a bigger say in it than we will.

One thing I forgot to mention before is that these boxes need to be welded up really well or they'll separate. It's quite impressive how much power those pulses have in them and it's a shame not to use it.

FYI, if you leave plenty of pipe out of the inlet end, your exhaust guy will appreciate it



Be sure and let us know how it turns out.


Shawn
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Unread 10-01-2010, 03:24 PM   #11
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Thanks for the reply. You kind of lost me on the size when you say multiples of 20, 40, or even 80? I was planning the box ,like the layout you had, that was 5.5" square and taperd down to 4" square and 16" long. Was just going to use one box on drivers side with the other exhaust pipe coming from collector to same box, then from there to single and muffler. Is this wrong , will it work, or should I ditch this effort?

Once again Thankyou!
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Unread 10-01-2010, 03:51 PM   #12
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Sorry, I didn't mean to throw you off. I was referring to the length of the passenger-side collector. If the best length for the collector is 20 inches, any multiple of that length will work pretty well too. Since you can't cross over to the other side of the Jeep with a 20 inch pipe, the next best length would be a 40 inch pipe, savvy?

Running duals, you'd have a 20 inch collector on each side going into separate boxes. With a single set-up, you'll have one 20 inch pipe and one 40 inch pipe going into a single box. The box size doesn't need to change as it only sees one pulse at a time anyways.

That's the 'ideal' way to skin the cat in a perfect world. The box dimensions don't change, it's just the best way to get the optimum wave reflection.


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Unread 10-02-2010, 09:50 PM   #13
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Waiting on the sound clip!
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Unread 11-05-2010, 06:41 PM   #14
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I finally remembered to do this when I had someone around to help. The audio on my phone apparently isn't the best so you'll probably have to turn it up quite high on your end. The exhaust note is pretty mellow too.









There's 115 fire-breathing horsepower!


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Unread 11-05-2010, 07:46 PM   #15
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Swatson ...
Not trying to Hijack but,
Have you run into any "start" / "warm-up" issues with having headers? I have a 258, with headers, my mech keeps telling me that the slow warm-up & (seasonal) carb adjustment issues are mainly due to my having headers on it (slow / lack of heat getting into the intake manifold to help atomize the fuel), especially in the wintertime. I note that you're in ID, I'm in PA, & here comes another winter ...

Basically, it chokes, stutters, stalls until warmed up (approx 5 min's) at which time, it runs fine. These are my first headers, so, it's new to me (LOVE the feel of extra power once it's running). I think it's already in my Prof, but:
84 CJ7, '83 motor, T-176/D300, Davis DUI Dissy, (I rebuilt) MC2150 w/1.14 (forget which jets), De-smog, minimal Vacuum lines

I don't expect any kind of full diagnosis, you obviously know your way around the powerplant, and just looking for your experience with a 258 with headers. Thanks.
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