Will extending my exhaust on a 3hp give my engine more power?

#1
I see a lot of folks running straight pipes on their bikes rather than the stock muffler. Will this help give your engine more power or is it mostly an aesthetic choice? I'm wondering if running a straight pipe with my stock muffler attached to the end of it would make any performance difference. 115958991_10104743728432058_6229985723923130260_o.jpg
 
#2
I'm sure there is some sort of Mid Range gain from it but, Its not going to be very noticeable, If the neighbors don't mind and the noise won't drive you crazy build it as you want it.. I have a 3 hp Tecumseh with a straight pipe no muffler, it runs great, makes a little noise and is fun overall to ride..
 
#4
You first ask about extending your exhaust, and then you ask about straightening your exhaust. Those are two different things.

Removing a restrictive muffler and installing a straight pipe will improve performance in the middle and upper RPM range. It is enough to feel kind of, sort of, but not worth the anger of the neighbors.

The reason you see some of the 5HP Briggs and Tecumseh's with modified exhausts are because their owners have installed performance parts like cams, valves, carburetors and stronger internals to hold the power. For those guys, they need their engines to breathe more, with less restriction.

So far everyone who has commented is in general agreement, although I am very suspicious of my own empirical testing that I strongly suspect with stock engines, it is just like eletrathon says, "if it is loud, you must be going faster. " :)
 
#6
You first ask about extending your exhaust, and then you ask about straightening your exhaust. Those are two different things.

Removing a restrictive muffler and installing a straight pipe will improve performance in the middle and upper RPM range. It is enough to feel kind of, sort of, but not worth the anger of the neighbors.

The reason you see some of the 5HP Briggs and Tecumseh's with modified exhausts are because their owners have installed performance parts like cams, valves, carburetors and stronger internals to hold the power. For those guys, they need their engines to breathe more, with less restriction.

So far everyone who has commented is in general agreement, although I am very suspicious of my own empirical testing that I strongly suspect with stock engines, it is just like eletrathon says, "if it is loud, you must be going faster. " :)
I think I imagines maybe a more high flow air filter and and a more flowing exhaust could help the engine get some minor gains easily. Know of any simple mods worth doing to the stock muffler?
 
#7
I think I imagines maybe a more high flow air filter and and a more flowing exhaust could help the engine get some minor gains easily. Know of any simple mods worth doing to the stock muffler?
Use 3/4" threaded iron pipe to build your "pipe" to the location you want it to go. Thread on a 3/4" x 1" adaptor and then use a 1" muffler. It will have some muffling, it will be some louder. You will think it is very cool and very fast, but the neighbors will not soap up the street so you fall down.
 
#9
what i did as a kid...get a piece of pipe longer that you think you need...install it...take a crayon and make a heavy line down it the long way...run it full throttle down the road and where the wax melts cut it. it "seemed" to give more top end...again...I was a kid!
That’s awesome! Worth a shot. My bike runs way better with the filter off so I’m looking for a less restrictive air filter. Any cheap suggestions?
 
#10
There are several small air filters that can be adapted to your engine. Check through the numerous parts suppliers. The key word is, "adapted". To answer your basic question: Yes, an open intake and exhaust will, USUALLY, improve performance. You engine is a pump. it pumps air into a cylinder, mixes in fuel to make it combustible, then adds a spark to ignite it. The more air and fuel you can get in, the more performance you get out. WITH LIMITATIONS. In a perfect world, if you have an otherrwise stock engine and add on better air intake and better exhaust, you get better power. That said, by adding the open air cleaner, you have increased the amount of air in the combustion chamber, but, did nothing regarding fuel. In other words, you have leaned out the mixture. Or, another way, provided less power making fuel. The exhaust, on the other hand, really doesn't matter. As long as it is not too short or too restrictive, on your stock engine, a free flowing exhaust is, if anything, just an aid in clearing the chamber. Look at it this way. Again, in a perfect world, if the open intake and exhaust gave you a net of 10% increase in power, (that would be an amazing amount for those mods), you would then have 3.3 horsepower. You aren't going to feel it, but, you'll probably enjoy the look and ride.
 
#11
There are several small air filters that can be adapted to your engine. Check through the numerous parts suppliers. The key word is, "adapted". To answer your basic question: Yes, an open intake and exhaust will, USUALLY, improve performance. You engine is a pump. it pumps air into a cylinder, mixes in fuel to make it combustible, then adds a spark to ignite it. The more air and fuel you can get in, the more performance you get out. WITH LIMITATIONS. In a perfect world, if you have an otherrwise stock engine and add on better air intake and better exhaust, you get better power. That said, by adding the open air cleaner, you have increased the amount of air in the combustion chamber, but, did nothing regarding fuel. In other words, you have leaned out the mixture. Or, another way, provided less power making fuel. The exhaust, on the other hand, really doesn't matter. As long as it is not too short or too restrictive, on your stock engine, a free flowing exhaust is, if anything, just an aid in clearing the chamber. Look at it this way. Again, in a perfect world, if the open intake and exhaust gave you a net of 10% increase in power, (that would be an amazing amount for those mods), you would then have 3.3 horsepower. You aren't going to feel it, but, you'll probably enjoy the look and ride.
I ended up measuring the intake and buying this foam filter for pretty cheap:
https://www.ebay.com/itm/Red-Bent-Foam-Air-Filter-32MM-For-50cc-110cc-125cc-ATV-Quad-Dirt-Bike-H-P/164228946839?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Its about a mm bigger than the intake so hopefully it stays on. I see a lot of folks making or buying adapters rather than directly clamping on filters which leaves me a little skeptical. I understand that the gains will be minimal but for such a slow lil bike I really feel a substantial difference in power with the filter off. Obviously I don't want to ride around like that. Ideally the combination of a less restrictive exhaust with this foam filter will help but who knows? I appreciate all the wisdom since I've never really messed with a Briggs until now.
 
#13
I ended up measuring the intake and buying this foam filter for pretty cheap:
https://www.ebay.com/itm/Red-Bent-Foam-Air-Filter-32MM-For-50cc-110cc-125cc-ATV-Quad-Dirt-Bike-H-P/164228946839?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Its about a mm bigger than the intake so hopefully it stays on. I see a lot of folks making or buying adapters rather than directly clamping on filters which leaves me a little skeptical. I understand that the gains will be minimal but for such a slow lil bike I really feel a substantial difference in power with the filter off. Obviously I don't want to ride around like that. Ideally the combination of a less restrictive exhaust with this foam filter will help but who knows? I appreciate all the wisdom since I've never really messed with a Briggs until now.

32mm is about 1 1/4 inch. Are you certain you measured the outside rim of the carb? I don't think you will have anything to clamp onto, anywhere else. I'm thinking your measurement should be closer to 64mm.
 

cfh

Well-Known Member
#16
i only run 5hp motors, but this is what i have noticed... in a stock situation, and open exhaust seems to do nothing. i mean it *sounds* faster, but i don't believe it to *be* faster.

but if you put a slide carb on the engine, or any other performance item (cam), the weakest link does tune things down. I've really noticed a stock exhaust with a slide carb (and sometimes a cam) does hold things back, and it can be significant too. but in a stock engine situation, i don't think an open exhaust helps or hurts.

on the other hand, i end up with open exhausts on all my bikes, but largely for a different reason. stock exhaust on vintage 70s mini bikes are usually long gone. so i end up making a new custom exhaust, because i can't find (or afford) a stock exhaust. and when i make an exhaust i don't put a muffler on them. but i live in the country... no one cares how loud my crap is.
 

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