New topic,
exhaust planning... Again looking for a forum sounding board/sanity check.
Earlier I mentioned that I want to run my exhaust down the boat sides on either side of the frame rails. There’s not a great deal of space but I’m optimistic I can wedge something in there. Been playing with the idea of making some custom triangular shapes but that’s just an option.
The first trick will be how to get headers of any kind of a decent length to package on the engine side of the firewall. I can't see the bundle of the tubes running through the triangular hole just under the footwell on each side so it’s going to take some creative routing. The good news is that my stance is so wide that I do have quite a bit of space at the sides of the motor and that opens up options. Best possible conceptual run I've found was done on the 2013 Miller Motorsports KOH Rig.
Super simple, super clean. Credit to the guys at Liquid Iron Industries who made this on behalf of Erik Miller (epic build thread here if anyone is curious):
2013 Miller Motorsports Ultra4 Car - Pirate4x4.Com : 4x4 and Off-Road Forum
I'd basically plan to route my headers as a mirror of what Erik did (running up and forward instead of up and back). Miller's car was about 18" primaries. I'd love to get mine north of 30" if I can. Instead of the merges exiting pointing downward, I’ll also make mine turn horizontal again to gain some length (merges point toward firewall).
I’ve also been reading about merge collectors. I ran across some folks who should know (Joe Sherman of Engine Master’s fame was one) who claim they don’t do much except possibly down low.
MERGE COLLECTORS,WHEN TO USE,HOW BIG A CHOKE AND WHY • Speed Talk But that’s the thing, I care a great deal about torque down low for this rig so I’m still planning around merge collectors.
Note: my last set of merges I bought from Burn Stainless who spec’ed them for my RX7. They were (are) rad but budget constraints rule Burns out this time. Instead I’m going to spec my own and trust that they’re close enough… From lots of history on here (with a dash of David Vizard theory thrown in), I pretty much think that 1 ¾ primaries with a 2.5” dual exhaust is about optimized for a stock displacement LS1. That said, you can just as easily do 1 7/8” and 3” duals not leave a lot on the table and still have room to grow. That’s my plan, so I basically just need to spec the merges and components to make it happen.
I’m looking at:
• 1 7/8 primaries (a touch oversize for an LS1, but I could easily see this growing down the line
• 15 deg merge angle
• 2.5” choke diameter (more on that in a second)
• 10 deg transition
• Just enough length running straight for 02 bungs.
12 deg merges have a reputation for making the most power but they’re just too long and 15 degree merges are notably shorter but not that far behind. The hardest bit to spec out was the choke point diameter. I didn’t have a great grasp of what the choke point does (still don’t fully get it, but the most helpful description I ran across was the following from the Speedtalk thread linked earlier:
The principle that is at work in a merged collector is this. The smaller the choke the longer it takes for atmospheric pressure to equalize into the back door of a given engine. It protects your power curve the same way as shorter cam timing and longer primary tubes. Just slipping a collector on with a smaller choke will usually show more power at the bottom of the curve. (which Joe points out)..
The secret is that you can now shorten your header which is how you can make more power upstairs.
Header length is always relative to rpm band but also the size of the choke. Most headers have to be long because the collectors are so large. The longer tubes keep the reflected wave "back" at the lowest point on the power band that the engine has to pull from. Change the collector choke and shorten the tubes and you will see the power. If you can't shorten the tubes, do not blame the collector, and if you need shorter headers, call me...
I am using Joe Sherman's example as what will happen just installing on a existing header. If you can not shorten your header or get one shorter for your application, Joe is absolutely correct, they are expensive and are not a solution in themselves.
Calvin Elston
Elston Exhaust Inc.
Matthews, NC 28104
704-443-8088
Web:
www.elstonheaders.com
Blog:
www.exhausting101.com
I also ran across a decent cheat sheet on this particular topic.
www.coneeng.com/pdf/Area_Calculation_Table.pdf
Screen cap cribbed here:
Short story: picked 2.5” choke based upon the chart and goal of focusing on low end torque. If anyone has better resources please chime in. Note, one cool thing at the
www.coneeng.com site I ran across is a DIY merge collector of sorts that still lets you weld it around 100%.
Slip On Collector, Conical Merge Collector, Slip On Collectors
I never liked that there’s no way to 100% seal my slip on collectors on the RX7.
So that leaves the rest of the exhaust. I’ll run a V-band off the header and then duck under the floorboard into the boat side.
I might be able to snake an H-pipe across but I'm not sure. I do want to try to keep this rig relatively quiet but that may be a challenge given the lack of internal insulation. That basically means I want as much sound deadening material in the muffler can as possible. Even using a triangular shape I don’t have a huge space to use but I can make the muffler pretty long. It also needs to be held relatively rigid in space because clearances aren’t going to be much. So that brings me to the next question. How flexible are flex pipes? I used one on my jeep but that’s my entire experience with the things. I think I may need one on each side before I run under the firewall, which eats up space I’d rather use for header primaries. I assume the interlocking style flows better, but I’m guessing the double braid is actually more flexible as I would think it can do a bit of in/out motion (Chinese finger trap style) Anyone know for sure?
That brings me around to considering engine motion and clearances similar to the train of thought on AC and accessories. I could run this solid mounted (or nearly solid). There’s nothing I can do about thermal growth but does anyone have opinions on whether I could get away without a flex pipe?
What style of hanger would you use in extremely close quarters?
I’m planning to dump this in front of the rear and point it slightly downward. Am I dumb for even thinking that an exhausts that exits under the vehicle can be tamed enough to be livable?
If that’s too boomy I may have to figure out how to snake it over the rear axle which isn’t trivial but doesn’t look impossible either. I just need to duck to the inside of the frame rails. The upside of taking the exhaust all the way back is that I could work out a Porsche style crossover exhaust.
Something like this internally, but with perf core and a case around the bulk. This is about as close to an X-pipe as I think I'll be able to pull off.
That might let me just run simple glasspacks or similar down the side and save the effort with the crazy triangular mufflers.
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