Exhaust/Stack Ideas

Thanks buddy, all i need now is some better front tires haha. I had to do some welding to the elbow at the top because the pipe wasn't threaded. Everything fell into place though (I don't say that too often haha )

A much better setup than mine for sure. Yeah, get some knobby front wheels on that sucker and you'd make anyone's heads turn.

I don't know man, I dig the Craftsman in your picture, it looks like the one in the banner at the top of the page lol

How'd you get those front tires to work? I tried to use rear wheels on my mower but the little axley thingys were too small lol

Extended the spindles and put Honda 250 front hubs on. Worked alright, but the sloppy front end was not working well with em, so I put the golf cart axle on. Looks a tad different now.

Thats a good lookin exhaust, you may want to add a support on the backside of the u bolt to give better support.

Remember that the engine is vibrating, and moving, so don't fasten ot down solid. All you need to do is support it so it doesn't put extra stress on the engine.

Thanks for the pic Jeff, I'll look into that. I'm thinking about putting the stock rear tires on the front if no other problems come up. And sorry I don't quite get what you're saying Chopperhed, think you can explain it a different way?

you need to support the weight of the stack without limiting movement too much, You have a u bolt setup restricting lateral movement, but it doesn't actually do anything for support. A flexible mount is required.

Over time something in that setup will break from metal fatigue, and it won't be a long time.

You have a solid pipe bolted/threaded to a vibrating tengine. A solid mount will fail within minutes.
a bracket solid mounted to the stack, with a rubber/ flexs/ spring mount to the tractor would fix your problem. This keeps exhaust heat away from any rubber parts.

The trick is to support the weight of the stack, without limiting movement.
'
An un supported stack could break your cylinder head .

Yeah, good idea. One good thing with an OHV is if it breaks, you just get a new head. With a Flathead, you'll total the block. You can use old automotive exhaust hangers I'm sure.

Hmm, i think its going to take some trial and error to find the best way to figure this out. Thanks for the idea, i'll mess around with it next time i'm in the garage haha.

will straight piping it to the back of the mower have enough back pressure to not burn the valves on an older 11horse flathead briggs?

Thecrazyoldcraftman wrote:

will straight piping it to the back of the mower have enough back pressure to not burn the valves on an older 11horse flathead briggs?

as long as you have at least 18 " your fine

Funny thing about opinions- we all have 'em... I'ma go ahead and disagree. You don't need 18" to keep from hurting something. Much less will be fine.

thank you all for your opinions and I have one more question? what type of pipe ( material) makes the best sound

I agree with Doc's comment about the 18" not being important. The reason people say the motor needs backpressure is because the jetting needs to be richened up when eliminating the backpressure. If you change the exhause and don't adjust the jetting accordingly, you could burn a valve. Now, depending on the RPM's you're running, there are certain lengths that will work better or worse, but that needs to be determined by trial and error. (or a lot of math that sometimes doesn't work anyway).

Also, Chopperhed makes a very important point which I will expand on: Black Iron Pipe is heavy, very heavy. There is really no need to use such thick-walled tubing. The weight of this stuff alone can break the exhaust port right off your motor. Whenever possible, use thin-walled exhaust tubing and make a good strong brace for it.

As far as Exhaust tone goes: I don't think anything ever sounds better than a glasspack. A cherry Bomb or whatever you call it in your area. An open straight pipe can sound good, but gets annoying to the rider and anyone nearby too!

Awww- we don't wanna get started on the whole backpressure thing again, do we?

Back pressure is bad, mmkay? We're just gonna leave it at that. Now- the reason you often need to re-jet when you fab up a better exhaust- better flow. Better flow? More fuel. More fuel? More power. That simple. Now- if the exhaust is TOO big, you lose some velocity, much like if your carb is too big. Keep the pipe to maybe 1 1/4" diameter maximum, and you'll be fine.

As for the burnt or cracked valve thing-

There are people out there that will SWEAR on their not-yet-dead mother's graves that it is a problem. I'll tell you what- On many of my projects present and past, I have run open pipes as short as 4" for extended periods, on multiple engines. I have closely and repeatedly inspected the valves. I have had zero issues. With pipes that short, I HAVE had exhaust velocity problems, but no valve issues.

Google 4 stroke and back pressure! Google knows everything   

We gained 1000rpm on our 2-stroke engines when we got the pipe in tune with the engine, that's kickass. Like a non-moving supercharger.

Agreed: Both 2-stroke and 4-stroke engines will benefit from a tuned pipe. Obviously the 2T pipe is more complicated with Divergent cone, belly, convergent cone etc... The 4T pipe that works best is the Dual Cone Megaphone, but that is extremely loud! So, I like to just eliminate the muffler and go with a class packed straight through muffler. Sounds great and I'm not out to win races.   
Almost anything you do to the exhaust will require jetting changes if you plan on running hard though....

If y'all have some free time and a beverage or two- here's some good related reading- http://www.diygokarts.com/vb/showthread.php?t=22264

Ummm, yeah. I think we're all in agreement here LMAO!   

I've studied exhaust building and tuning for many many years. Math can get you close, but it's still not an exact science. I use the 80-20 rule: 80% of the gain will take 20% of the time, then its 20% to 80%. This is why I'm not getting crazy about a tractor exhaust.

Lose the restrictive muffler, build a pipe, then jet accordingly. And try not to make enemies out of the neighbors!   

Yup- that pretty much sums it!

I've been waiting for a while to get the time to build an exhaust.  The stack I had on the 6hp Quantum motor isn't going to cut it for the 12+ flatty, so I've been looking around for ideas...

Here's what I just bought for $20.60 and free shipping...
Heartthrob aluminized glass pack


Not a Cherry Bomb brand but the same thing and I've got red paint.  

The design criterion for the new system are these:
-1" pipe from the port to curl under the frame and turn back towards the rear underneath.  10"-15" length.
-Slip-fit section to allow adjustment of header length from 15" to 20+"
-Gradual cone adapter to the Glass pack.  Possibly creating some negative wave effect for better scavenging.

The 1 3/4" Glass pack will give a deep throaty sound and have no back pressure.

That's the plan.  Let's see how long it takes me to make it come true!  

T-Dub13 wrote:

I've been waiting for a while to get the time to build an exhaust.  The stack I had on the 6hp Quantum motor isn't going to cut it for the 12+ flatty, so I've been looking around for ideas...

Here's what I just bought for $20.60 and free shipping...
Heartthrob aluminized glass pack


Not a Cherry Bomb brand but the same thing and I've got red paint.  

The design criterion for the new system are these:
-1" pipe from the port to curl under the frame and turn back towards the rear underneath.  10"-15" length.
-Slip-fit section to allow adjustment of header length from 15" to 20+"
-Gradual cone adapter to the Glass pack.  Possibly creating some negative wave effect for better scavenging.

The 1 3/4" Glass pack will give a deep throaty sound and have no back pressure.

That's the plan.  Let's see how long it takes me to make it come true!  

let me know how this does,i might buy a set for the mini deuce

Well I was interested in trying to tune the exhaust for my Murray / 12+hp Flatty, but it doesn't look like it's worth it.  I did some calculations and for an exhaust tuned for 3500RPM, it wants to be 6-7 feet long (Depending on how I calculate it).  That's fine for a car, but my tractor is not long enough for a system like that.  so, I guess i'll continue with the above plan and see what happens.  I will continue contributing to this thread if I find anything out.

EDIT: After re-reading an old favoritebook on 4T tuning, I was reminded about the Cam timing and exhaust tuning relationship. On the stock cam in my 28 series 12+hp flatty, the cam doesn't have enough overlap to take advantage of a tuned exhaust anyway. So I guess I'm open to building whatever sort of exhaust will flow well and sound good. Reversion is something that I will try to eliminate by having a header pipe that's about 20" long.

I guess that's good news, sort of...