Exhaust/Stack Ideas

My 1998 B & S 15.5 OHV is flanged only no threads

My 11hp briggs flathead has a 1inch outlet port with a thread and bolt holes. The 2 bolts in the muffler go into the outlet ports to hold it in and there is a bolt in the head that supports the muffler. When i pulled my muffler there was no threads on the muffler, it was just bolted to the engine, the muffler didn't have a thread. I'd guess yours will be the same since we have the same engine.

Of all the briggs motors ive seen the flatheads had threads and th OHVs didnt.

I haven't had a chance to take it off and see if its threaded or not. I like the tractor flapper idea though, sounds great. Is there any problems that i could run up on by doing this though? Like something exploding because of too much pressure or anything?!

TennesseeCowboy wrote:

I haven't had a chance to take it off and see if its threaded or not. I like the tractor flapper idea though, sounds great. Is there any problems that i could run up on by doing this though? Like something exploding because of too much pressure or anything?!

In another group I'm in they put a pipe nipple in the threads and cut it flush with the flanged surface. Seems odd to me, but they say the single makes more horsepower that way. Then they put on a flanged bolted header pipe. I read B&S took a 5hp and tried to see what could be done with it, and the largest horsepower gain came fron taking off the thread-in muffler and using a header pipe! Don at G-Team Racing has a couple videos on hopping up the flathead engines that are well worth buying.
Garry

I had a stack on my tractor for a while, but it proved more of a nuisance for several reasons. The way I did it was run it through the hood using pipe fittings.

That does look like it would get in the way being through the hood like that. I'm wanting to run mine out and up next to the hood. Does it make a big difference in sound?

The one above was pretty quiet, being a very short exhaust. My hood just wasn't shaped for a stack. It will be much easier with your tractor.

Yeah i figured lol. I want it to sound more deep like a tractor, how would i do that?

You can do it like this. Slip a piece of exhaust over the muffler. Makes it much louder. another way is to make the stack taller with the muffler at the bottom of the stack. You can also just straight pipe it.


Though I stuck this stack over the muffler, I never tried it. Looks a little silly.

Ok, so i took it off and found out that the engine part is threaded. And i found a piece of pipe that would thread into it. What should i do next? (Unless I should just leave it like this... ) Its pretty loud too, how would i make it have a deeper roar to it instead of a loud popping sound?

You can only do so much with the sound. Small engines like these ain't going to sound like a 460 V8 gasser for sure. I found making the pipe bigger makes a deeper tone. Making a longer stack will also make it deeper, but it could be detrimental if you roll the thing over. Just try a bunch of ideas and see which one gives you the deepest tone.

for deeper louder volume a megaphone is best.

you have a threaded port. Go to a hardware store or any place that sells plumbing and heating supplies and for a few bucks, you can build a system that progressively gets larger as it extends. The longer and bigger the pipe the deeper it will get.


For maximum effect, a cheapo motorcyle megaphone from motovan will add a bit of flash and some nice tones.. They have turn out styles Rat tail styles, anything you could want for motorcycle atv side by side and sled parts. They are canadian, so shipping south may be an issue. but i find I can get their parts from any serious bike shop in town. And If you look, you can find some very economical deals on go kart, dune buggy, cycle , atv, stuff.

Sorry about the plug, but i love their catalogue.

I ran shorty pipes ( temporarily) on my 18HP twin murray - thing sounded just like a harley davidson motorcycle.

how i did mine

boggo, that setup is kinda like the one i was thinking of making. How does yours sound?

it sounded really good, nice thump to it but was abit loud being a black 11hp motor. lower revs should be fine though (i had mine screaming its head off). but everyone around my area likes it, so it did get alot of attention

Not a stack, but this is my exhaust. It's 1" from the block, stepped to 1 1/4" for 24" then stepped to 2" for another 20". It's got a good, low rumble at low RPMs, with a decent bark when wide open

That there is what is called a good looking tail pipe. Well supported, and well built. Not to mention good smooth flow.

Nice job

boggo wrote:

it sounded really good, nice thump to it but was abit loud being a black 11hp motor. lower revs should be fine though (i had mine screaming its head off). but everyone around my area likes it, so it did get alot of attention

Mine has an 11 hp, think that would be a problem if i run it wide open mostly?

AcreFarm wrote:

Not a stack, but this is my exhaust. It's 1" from the block, stepped to 1 1/4" for 24" then stepped to 2" for another 20". It's got a good, low rumble at low RPMs, with a decent bark when wide open

I dig that. Looks really professional lol

TennesseeCowboy wrote:

Mine has an 11 hp, think that would be a problem if i run it wide open mostly?

Unless you remove the governor, these things are built to run wide open all day long. Removing the governor will negate that. Over revving these engines can cause severe damage.

They are built to be best around 3000 to 3500 rpm depending on the engine. Some may even go as high as 4000.

Ours put up with ungoverned over revving just fine, but we also understand that we are reducing the life expectancy of the engine. In general, valve float will keep the RPMs down enough to prevent serious issues. For liability reasons, I would not recommend doing what we do though

Certain flathead flywheels have been known to explode, and cause some pretty severe injuries. I've had a flywheel come off after the threaded section broke on the crank, and the retaining nut disappeared. Some sanctioning bodies have outlawed rear engine riders due to exploding flywheels causing severe injuries.

I've heard that, and (other than modified engines) never seen any proof it happens. B&S would have to have the flywheels tested at a much higher RPM than stock for liability reasons. If you mod the engine to make the RPMs go past the natural ceiling that a stock engine has (like the racing people do), you would definitely have a point. The magnitude of a lawsuit facing B&S would be huge if a governor failed and the flywheel detonated. Would love to see someone get video of spinning one to the point of destruction to see what it would take.


Note: edited for clarity

...and like I said, I don't recommend anyone do what we do.

Lol thanks for the tips guys but thats totally not what i was asking..I was wondering if his pipe setup would be unbearably loud if i ran wide open all the time But thanks anyways:)