Muffler modding

Posts: 39

I have a stock crossfire 150r and I want to drill out the exaust and add a uni. Could anyone help me through the process please? I just need to know what size holesaw to drill out the exit pipe. And if I am understanding right there is a plate in wich to drill about five or six 3/8 holes in? Any help is appreciated.

Posts: 3560

You drill the outlet nipple out with a 1" holesaw. To mod any further you'd have to cut the muffler open and then reweld it closed.

Posts: 39

Thanks for the reply. Is this mod worth it? Will I actually see any performance improvement? If I do this it will be with the a uni and rejetting. With this combo even help much to be worth the effort and loudness?

Posts: 114

I did the multiple hole drilling and had to take the chrome plate off the back of the muffler first. After drilling the holes (some are smaller than others so I probably haven't realized the full gain of this yet, but I was a little nervous about drilling too much...you may want to experiment and start small to see what you are comfortable with) I cut some 1 inch spacers and put the cover back on with longer bolts so I didn't restrict the air flow. If need be, I can always put the cover back on with the short bolts and reduce the noise/flow. I noticed a slight bit more power and a better sound. I'm always concerned about the neighbors but the noise increase wasn't dramatic so no prob!

A week or two later I was able to add the UNI and that seemed to help a little more, not with top end speed so much as power and a little shorter time getting to top end. (and it looks really cool! You can actually see the engine now!)

But THEN I added the new jet and WHAM! I was blown away! Top speed increased by at least 2mph (still have to check it with the GPS), mid range power is awesome and it sounds and feels great. I think I get to top speed in literally half the time I used to, if not sooner. For 20 bucks you can't beat that modification combo!

Of course I had no clue what I was doing throughout and relied on the good people from this website to guide me (even if it was rather simple in hindsight). Embarassed

Now I'm feeling that need for the 1500 spring to even out the bottom end power. It's always something once you start messing.

Best wishes!

Posts: 114

Meldridge,
I tried sending details of mods in a personal email but it's been stuck in my outbox for a while.
I guess I'll post here instead.

Here are some pics of what I did. (in reverse order)

First you can see the chrome shield that had to be unscrewed and removed.

Second, I'm showing how after I drilled holes I added spacers and longer bolts so that I could still keep the look of the cover but allow the muffler to breathe. (couldn't find the right size spacer at home depot so I had to "fabricate " them out of some metal ceiling light screw extension stuff I found lying around)

Third you see the the holes that I drilled. I just started with a very small drill bit and worked my way up to whatever size felt comfortable. You'll notice the hole sizes are not all the same. Mine is not an exact science. I'm not sure if I drilled deep enough, wide enough, etc., but maybe someone else can offer guidance on that. Perhaps I'll increase the size someday, but for now I'm satisfied with what I've done.

As someone else mentioned in another post, keep the short screws that came with the cover and if you ever need to block the holes, you can put them back on. (or probably use some JB Weld to fill the holes)

Best wishes.
Tim

Posts: 6278

Posts: 39

I got it. Lots of working for me lately but I just checked it. Thanks a bunch rubber.

Posts: 114

Outbox understood. Thanks Jabo.

Posts: 2634

I did exactly what guy48065 said you could do...Being that I teach auto shop in a high school, we have some equipment that makes the job that much easier...thanks to a lincoln mig welder, and a air powered 4" cut off wheel, and an O/A cut off torch, I was able to remove all the chrome, cut the face (outlet) of the exhaust off like removing the top of a can with the cut off wheel. I then used the O/A cut off torch to literally melt off the little baffles on the inside of the muffler...it basically looks like 1" macoroni elbos inside...3 of them I believe......After I got those melted off, I accidentally burned throught the plate they were held in place by, and I got a closer look at the actual "guts of the pipe.....basically three baffles in a radiator like pattern, and then fianlly, one comes out at the back to the exhaust..... I drew a crappy pic to better explain, but I am sure if you have a cut-off wheel or dremel with cut off wheels, or even a hack saw, you can cut the cap off at the weld, and bring it to a local muffler shop to cut the elbows off with a torch and weld it back on for 20 bux or less! I sure would do it for ya if you were close by, only for a cup of cofee and a donut! lol...

The pic is a basic representation of what I found inside, and the easiest part for me was melting the guts....just had to be careful not to burn through the side!!! when it was all done and cooling off, I gently tapped it with a hammer handle to knock out anything that may have been trapped inside....I let it cool for about an hour (had lunch and all), and sent two of my students to the MIG to re-weld the cap back on. They did a great welding job, no leaks (tested with high air pressure) and I painted it with high heat barbacue paint so that it never rusts.....Best part of the whole thing? Because nothing was changed on the outside, I simply screwed the chrome back on, and bolted it right back onto the kart as if nothing was ever done to it!!!

YES...there is a huge performance difference. So far, this is my only performance modification...It is a little louder, but climbing my hill, it is about 10 seconds faster going up, before the exhaust was cut... I had my students drive it before the mod, full throttle when warm up the hill, and it took almost 1 minute...59.88.....After the modification, 49.92 and a heavier kid drove the kart!!!

Good luck if you drill it, I am sure you will get the same results, I just chose the difficult way because I had the tools!!!

Good luck!!

John

Posts: 114

I think I found my project for the day and it involves barbecue paint! Great suggestion racemybuick. I'm sure it adds a nice look to it as well.