trimming rear bumper exhaust cutout

[tiFreak]

anyone have any tips on doing it, how to measure, what tool to use, etc.?

just wondering because I have a Borla that's been in my basement all summer, it's a dual tip and while I have no problems about chopping up my bumper I am scared about screwing it up

[pdxmotorhead]

When I mod fender flares, or other plastic stuff I use a 4" angle grinder, tape the area with masking tape and draw what I want to cut.

Dave

[cooljess76]

Just like Dave said, I'd mask the area with tape, then draw the outline of what you want to cut. Just take a bunch of painters tape and block off the whole area. Then use a sharpie and sketch the outline on the tape. An angle grinder will work just fine, but might be a little difficult to control. Definitely cut on the inside of the outline just in case it starts to get away from you, you'll be able to stop and correct it before you cut too much material off. You might also consider a die-grinder, rotozip or dremel tool with a cutoff wheel for easier control. For the interior corners(if you want them round, they look better) use a drum sander on your rotozip or dremel tool. Make sure you leave a little material because the final step will be filing the edges down by hand with a flat file. The interior corners will require a rounded hand file.

As for measuring and positioning the muffler, well obviously you'll want your cutout to be slightly larger than the muffler tips. So measure the width of the muffler tips and just make sure your outline is wide enough to give a little clearance so the tips don't contact/melt the bumper. Positioning the muffler should be decided BEFORE installation. So with your old muffler off, look at the rear bumper from a distance and decide exactly where you want the new muffler tips to rest. Do your cutting, then hang the muffler and position it as necessary. You might have to get creative when it comes to bending, shortening or lengthening the muffler hangers, but in the end, the muffler should hang securely exactly where you want it to. Don't let a stubborn muffler hanger keep you from positioning the muffler where you want it to be. Once you're comfortable with the muffler's positioning, then you can come up with a plan of attack towards welding it to the piping. Most auto parts stores and muffler shops carry a wide variety of different diameter tubing in various bends and angles. Sometimes you'll need to cut a section out of one and weld it to another etc, just try to do it in as few sections as possible in order to keep it looking clean and neat.

[jwm]

Dunno how picky you are, but when I had my Supersprint exhaust installed, I wish I had kept the cut pieces so I could look into having a body shop plastic weld the "returns" back onto the rear valence.

In other words, so the part of the valence that surrounds the exhaust tips (if that makes any sense) could be put back in place to restore the factory appearance. That way the opening in the valence would look like it was "supposed" to be that large.

[tiFreak]

I don't have a rotozip or a dremel, just a pneumatic angle grinder, which like Jess said, isn't a very precise tool another problem I have, the muffler is stainless steel and has hangers on it that won't work on my ti, can you even weld to stainless?

this is still making me nervous, do most muffler shops know how to do stuff like this? I'm thinking maybe I could have them do it

[Pursuit]

I'd be worried to let an exhaust shop do it, maybe if they are very performance oriented and comfortable doing that sort of thing.

It's not hard, just go very slow and methodically when setting up for it.

Take some measurements of where your current exhaust sits (relative to bumper opening) and then when you have the new exhaust mounted compare the position of the tips to the original exhaust and opening.

Clean the bumper (you want the tape to stay on through the entire process) and tape off a generous margin on the bumper where you'll be cutting, then measure and mark the tape.

Figure your corner radii by measuring off your exhaust tips. Find a piece of pipe, or make something yourself, with that or a close enough radius. You'll use this as a sanding block to tidy up the corners.

Using the largest drill bit you have that's close to the corner radius, drill holes where the corners will be. Since these holes will be quite clean, you can take them right to the edge of your marked line. Or, experiment on the inside of the line and work your way closer.

Now you just have to connect the drilled holes with straight lines. If you're really nervous, you can just use a hacksaw blade. Grinders are actually okay as they tend to not melt the plastic as badly as dremels etc. I would cut a 1/4" or so inside the line initially and then if you're comfortable take it closer. Think about the rotation direction of the grinder and don't let it grab and run off on you (for example, going with the rotation of the grinder, cut from the corner holes downward to the bottom of the bumper, and from the corner holes to the middle of the flat bit stopping each cut so that they meet in the middle - this way if it does run away from you it either runs off the bumper or you have some room for error). Use both hands and rest a forearm against the bumper to hold your position. If the bumper is off the car you really need someone or something beside yourself to keep it from flopping and kicking around, just in case.

Leaving the tape on, use your corner radius sanding block and a normal sanding block to take the trimmed bits right back to your line. I don't use a file as it has a tendency to grab and pop paint chips.

For a really clean look, use a hot piece of metal to melt the edges smooth with a quick pass over.

Don't take the tape off until you're totally done, this way you never lose your reference lines.

-OR- get the exhaust mounted and take the bumper to a decent body shop, they'll be able to do it in no time but make sure you specify exactly how you want it before they start cutting.

[tiFreak]

the hacksaw blade idea makes me a little less nervous, might give this a try at work one day, eventually, of course I've had all the parts for a vented brake conversion sitting around for a while and still haven't done it so who knows how long it might take me