How to install an Under Tunnel Exhaust on your 4-Stroke!

I started out reading Katchess's thread about his mod sled and thought the exhaust was a good idea.
Only problem was, every exhaust they had made was slightly different and none of the parts were standard or easy to find.

Wanted to lower the overall weight, and physically lower any weight I can on the sled for a lower center of gravity (CG).
A cooler sound, more throaty, NOT necessarily louder, is what I wanted.

With the Under Tunnel Exhaust, I ended up cutting about 6+ pounds from the sled. Also lowered the CG in the process.
The sound is cool! Definitely has more of a street bike sound to it.

This is what was used and how I did it.

Most all the part numbers are NAPA part numbers, that way most anyone can easily get the parts.

1 Hush Thrush Glass Pack 1-3/4" ID in & out, 3" OD, NAPA# 24210 (0907215)
1 Adapter NAPA# 735-7103
1 Adapter NAPA# 735-1626 2-1/4 ID x 2" OD
1 Adapter NAPA# 41943
1 Exhaust clamp that will fit over the Chrome tip
1 Exhaust Baffle (Any Harley/Bike shop should have this, about $10)
1 Chrome Exhaust Tip NAPA# 735-1615
1x1x1/8" Aluminum Angle Home Depot 2 foot or more.

Only the input to the glass pack and the nut inside the baffle needs to be welded, very minor.
Welded it myself, but any muffler shop can do it.

Remove the seat, rear taillight Assembly, and gas tank.
Remove the exhaust shields and mounting points.
You only have to really remove from the 2 into 1 Y pipe back, however now is a good time to replace those pesky exhaust donuts.

Need to cut the 2 into 1 Y pipe here.



This is the part you will no longer use, save the rubber mounts/bolts etc.


The larger end of the 735-1626 adapter will be made oval to fit the Y pipe.
Slowly clamp it in a vise until it fits perfectly over the Y pipe.



Once oval, this and adapter 41943 go together onto Y pipe and glass pack.
Pic of the test fit.



After proper fitting, these joints are prepped and welded.
The Grey "paint" is actually a high zinc galvanizing spray on coating to help prevent rust.



This completes the input end of the exhaust.

Output end of exhaust.

Cut adapter 735-7103 as shown here. You will use the small end as a spacer.
Welded a 1/4" SS nut inside the mount hole in the baffle.




Drill a 5/16" hole in glass pack outlet & spacer to mount baffle.



Use a 1/4" grade 8 bolt, lock washer, and blue loctite to mount baffle.


The chrome exhaust tip simply slides onto the glass pack for now.



Notes: Notice the jagged edges of the tunnel frame?
The rear tunnel frame is very thin, weak potmetal.
It was already broken and I broke that off with my bare hands, literally!
You can use a file/grinder, etc to clean up the edges.

Notice the 2 lower 1/4" stainless stop nuts. (There are 4 total.)
The original rivets that held the tunnel protectors on were worn, wobbled out, and ready to fall off.
Drilled out the rivets, (THAT was fun since the rivets wanted to spin! Had a friend hold the rivets with vise grips and a screwdriver), replaced with 4 flat head 1/4" SS bolts as shown in pic. Draw them tight until flush on bottom (track) side.




I made more room for the exhaust (just in case) by raising the center of the tunnel a bit.



A body tool would probably work good for this, but I had a hand sledge handy.




Cut a piece of 1x1x1/8" aluminum El to fit across the rear as shown to make the rear mount bracket..
You will use the original rubber mounts and bolts from the muffler to mount the bracket.
Drill the two center holes to match the muffler u clamp.
Drill the two outer holes to match the rubber mounts.



Note that the mount uses the original muffler mounting holes also.
The mount also adds strength to an otherwise pretty weak piece, as does the original muffler.

In addition to loctite and locknuts, I peened the threads on the muffler clamp to make sure it couldn't come loose.

Underside view.



Note the heads of the mounting bolts for the tunnel protectors are drawn in flush.

Tighten everything down, re-assemble, and you are finished!




I added the following piece to add strength and to close off the rear of the tunnel to keep debris out from under the seat.
Also want to add storage under the seat, but that's another project! lol

You can see the gasket around the edges to seal the tunnel.







The cover uses all original mounting holes/hardware.



Note the 1/4" SS bolts on the crossover tube.
These replaced more loose and rattling rivets.

Great write up and pics, would be easy for those going this route with your how-to, nice

Please post this in the TY4Stroke Garage or Engine & Clutching mods as well.

rxrider

You're welcome!

I did change the baffle to a Samson baffle, it had a cooler sound and even was slightly quieter.
Both pluses!

Moderators?

Is it ok to post in another place also?

What was your total money investment?

It was less than $100 easy.
The muffler was the most expensive part at $30.

It looks real good! How loud is it?

It is louder than stock, but more of a sound change than an increase in sound level.
Sounds more like a street bike now.

I didn't want it really loud and am happy with how it is.
Doesn't give you a headache or annoy others!

Im not that far from you, are welcome to check it out!

looks great!!!!!!!.

custom exhaust

What kind of metal was thepipe you cut & welded ? Would 2-mufflers fit side x side ?

The metal adapters are galvanized steel.
Muffler was alumanized steel.
Factory pipe is stainless steel.
All welded well, no problem using mild er70s wire.
(Have to weld outside, welding galvanized makes a poisonous gas.)

I don't see any way to put 2 mufflers in side by side.
Why would you want to?

There really isn't any noticeable increase in power, only a lowering of total weight and lowering of the existing weight to lower the center of gravity of the sled.

A 4-stroke is different than a 2-stroke. On a 2-stroke, exhaust tuning makes a major difference in the power. However on a 4-stroke, as long as it isn't majorly restrictive (backpressure), it doesn't change the power much.

Would think 2 mufflers would add to the weight overall.

Edit: It might make seriously cool sound though!!! Stereo, kind of like a V-8 engine does with a dual exhaust!

custom exhaust

Did your exhaust work help the droning issue?

rockmeister said:

You're welcome!

I did change the baffle to a Samson baffle, it had a cooler sound and even was slightly quieter.
Both pluses!

Moderators?

Is it ok to post in another place also?

Click to expand...

You may post the link only, that would be OK as far as I understand the site ruels.

Re: custom exhaust

fortynine said:

Did your exhaust work help the droning issue?

Click to expand...

Some, but the issue is still there somewhat.

Think alot of the drone is from the track on mine.
Will be changing the track soon and will let you know how it effects the drone sound.

Looks great I know another guy that did something very similar , the only problem was the tunnel built up with ice really fast , ( same issue as the Venture Lite and some Phazers ) ...The hot exhaust melts the snow and the snow dust kicked up from the track ..it was a real pain in the #*$&@ ....You can get a couple hundred pounds of ice built up under there .....Hopefully you don't have the same issue ...His solution was to extent it and bend it out the side of the tunnel...........