Default 4 stroke muffler outlet too small? Whats inside?

[go you good thing]

Hi,

I have just received my Grubee Skyhawk 2 kit with the standard pipe and muffler for my 4 stroke.

The muffler looks similar to the one in the 2 stroke kits even to the small exhaust outlet.

The outlet looks alot smaller compared to the stock Honda GXH50 box.

The stock inlet and outlet on the Honda muffler are about the same size giving it a balanced flow, I guess.

Has anyone tried to make the outlet bigger in the kit pipe and if so does it improve performance?

I'm not actually, at this stage, trying to improve performance beyond standard but trying to keep it as standard.

Also their is no longer a screw on cap at the base of the kit muffler so I can't see what type of baffling is there. Is it like the 2 stroke inside? If so I would maybe have to take out some of the internals also.

Cheers.

gygt.

[likearock111]

I think you've got the wrong forum, bud. You might have better luck in "4-Stroke Engines." Good luck!

[go you good thing]

I think you've got the wrong forum, bud. You might have better luck in "4-Stroke Engines." Good luck!

OOps. You are spot on. It was late when I did this one so I will contact a mod to move it.

Seeya,

gygt.

[MotorbikeMike]

Hello, yes it is wrong! I dunno if what they were smoking was not agreeing with them, OR if they cannot tell the diference between a 2-stroke and a 4-stroke?

The exit (stinger?) of your 4-stroke should be at least as big as your exhaust valve, and that one certainly is NOT.

I will be addressing this soon myself.

Mike

[go you good thing]

Hello, yes it is wrong! I dunno if what they were smoking was not agreeing with them, OR if they cannot tell the difference between a 2-stroke and a 4-stroke?

The exit (stinger?) of your 4-stroke should be at least as big as your exhaust valve, and that one certainly is NOT.

I will be addressing this soon myself.

Mike

Maybe they had their mouth over the end of the exhaust pipe drawing back the fumes for a buzz! and found the hole was better off being smaller.

I was thinking that someone may have put one of those longer pipes (poo poo I think they call them) on and was able to cut up their stock pipe for research.

gygt.

[Irish John]

Someone here said to drill an adjacent hole 5/16" just above the pea-shooter outlet and so I did. It certainly improves the throttle response and the 4-stroke burble on my full length motorbike-type exhaust but there is no noticeable increase in power.

[go you good thing]

Someone here said to drill an adjacent hole 5/16" just above the pea-shooter outlet and so I did. It certainly improves the throttle response and the 4-stroke burble on my full length motorbike-type exhaust but there is no noticeable increase in power.

Irish John, do you remember who said that they had drilled the hole?

I would like to know whats inside the muffler as it may have the same setup as the two stroke and have similar small size holes inside.

Making a bigger hole should surely improve power and speed.

That is making me think that something else in there is stopping the flow.

GYGT.

[Irish John]

Irish John, do you remember who said that they had drilled the hole?

I would like to know whats inside the muffler as it may have the same setup as the two stroke and have similar small size holes inside.

Making a bigger hole should surely improve power and speed.

That is making me think that something else in there is stopping the flow.

GYGT.

I can't remember where I read it but it was on this forum. I tried it and I liked the result. Nicer noise, bit better throttle response and no extra power.
I can tell you exactly what is inside the silencer - nothing at all. My long silencer comes off and I can see down it and there's nothing there. The smaller one is the same otherwise we'd be able to undo the end. I don't think you can improve the power and speed of a Honda 4-stroke cos it's pretty highly tuned to start with. It's too small to start making a bigger piston head and making high lift cams etc. Too hard and not worth the effort. It is not as easy to soop up like a HT engine and I'll bet if you could do it as a special project for free at a Technical College then you could probably increase the revs to about 10,000 rpm but the engine would break cos it's not designed for those limits.

[bubbatgs]

I have cut into my stock pipe!!! I will post some photos soon. for the explaination!
The back 5 inches of the pipe is made to be a sparkarrester! There is a 1" input pipe with eight 5/16s holes drilled into it. (not deburred) The exhaust then traveles through the open area into the tailpipe.(the one you can see at the end of the muffler) This pipe has 6 5/16s holes drilled into it . this is how the manufacturer has created this!
I purchased the long delux pipe. as soon as I seen the inside of the muffler. I took a long 3/8s drill bit and drilled right through the plate in the end of the out put. I added a little bit of bottom end to the preformance. I don't believe I lost anything on the top end either! The sound only increased by about 7db.
I will post photos as soon as I can take some.

[Old Bob]

I can't remember where I read it but it was on this forum. I tried it and I liked the result. Nicer noise, bit better throttle response and no extra power.
I can tell you exactly what is inside the silencer - nothing at all. My long silencer comes off and I can see down it and there's nothing there. The smaller one is the same otherwise we'd be able to undo the end. I don't think you can improve the power and speed of a Honda 4-stroke cos it's pretty highly tuned to start with. It's too small to start making a bigger piston head and making high lift cams etc. Too hard and not worth the effort. It is not as easy to soop up like a HT engine and I'll bet if you could do it as a special project for free at a Technical College then you could probably increase the revs to about 10,000 rpm but the engine would break cos it's not designed for those limits.

It depends on which Honda. The GXH50 is rated for 7800 from the factory, its no wise to increase rpm above this, how ever power gains can be had in the lower rpm range.
The GX35 and GX31 are fairly easy to hotrod, I've been making cams for both since for many years, increasing compresion is fairly easy with either engine, depending on the cam you boost power anywhere in the rpm range and especially in the 12,000 -13,000 rpm range.