Experimentation with the exhaust system?

[michaelthepsycho]

If the point of installing new exhaust systems is to increase airflow / reduce pressure, has anyone experimented with perforating, drilling, or cutting the exhaust pipes (after the catalytic converter of course) to do so? Instead of spending $700, I'd like to completely perforate the cat-back portion of my exhaust system when I get the time / balls to do it (both of which may never come). Anyone else have some power tool fun on their A/Cs?

[mcheddadi]

here's a better idea, remove everything after the catback, if its too loud, just add a resonator

[mrodrig2]

OP, you are in CA, you will get reamed by the inspectors if you do this. Not to mention how crappy it will sound. Like poster above says, you may as well just remove everything rather than hack it up.

[michaelthepsycho]

Ahh but not if you do it with 1mm drill bits and only do the top side so that when inspected from the bottom, no physical differences are detected Besides, I don't really care about the sound but no one knows for certain if it sounds bad and the little holes should provide a nice exhaust shrill. The only reason I'm bringing this up is because of some wood-work I've done with power tools back in high school.

[Zerep]

it would sound like a civic with a rusted muffler but go ahead. and i think letting the exhuast gases escape directly into the undercarriage is a bad idea. tell them to build you an exhuast 3 inch tubing from the cat to the back. you have a 2.5 so regardless of what you do u are going to lose torque.(opening the exhuast less back pressure)

[LinkNuc]

This idea belches forth a massive quantity of FAIL

[Beak]

take that muffler off. and you could always put it back on once you get it out of your system. you will gain hp on wot

[vonivo]

Just remember naturally aspirated engines benefit from some back pressure where forced injection ones dont.

[michaelthepsycho]

Someone with some form of scientific explanation explain why it absolutely does not work (as some folks suggest). I'm a mechanical engineering major and although this idea may be full of fail, I'd like to further understand why. My concept in bleeding out back pressure is not unlike what performance exhaust systems are doing: larger diameter, less bends = reduced back pressure. I don't want to remove it because it's outright against the law but small modifications might not get picked up by inspectors. I'm not trying to be extreme (removing the cat-back portion would categorize as that); all I want to do is minor D.I.Y. stuff. The whole idea of course, is just like why people would add L.E.D. bulbs to their vents / cup-holders or paint their air conditioning outlets... Not too hard to understand?

[LinkNuc]

Adapted from FlowMaster, Mech Eng. huh? Well Fluid flow ain't helping ya here for that matter Heat Transfer (I'm a Nuke which is just a specialized ME)..you don't learn this crap in college.

Backpressure:

This is a condition found in virtually any engine and is largely a function of exhaust system efficiency. In a racing engine, it is an issue of particular importance in as much as it relates to valve timing, exhaust port flow, contamination of fresh air/fuel charges, and other factors pertaining to efficient removal of exhaust residue from an engine's cylinders. Because of the effects of backpressure on an engine's ability to make power (torque), it is important to understand that as backpressure changes, other areas of an engine are affected.

For example, as backpressure increases (regardless of the cause), other engine components are typically optimized to compensate (or provide a partial solution) for this loss in exhaust system efficiency.

Perhaps one of the first areas an engine builder then addresses is the camshaft. By increasing the amount of effective valve overlap (and to some extent duration), some additional time is provided to evacuate the cylinder. However, this tends to reduce lower rpm torque, which then becomes compromised by higher operational rpm levels. But the trade-off here is that backpressure continues to increase with rpm and a point of diminishing returns is established. And typically, spark timing and fuel enrichment are adjusted to this less-than-ideal set of circumstances. Given these conditions, lets examine the changes we can expect to take place as backpressure is decreased.

By reducing the backpressure, some amounts of raw fuel (and fresh air) will be "scavenged" into the exhaust system. So by reducing the amount of air and fuel in the cylinder at the time of combustion.

A degree of cylinder pressure will be lost (a decrease in available torque) Effective air/fuel mixtures will be leaner (possibly leading to parts damage). Ignition spark requirements will change. The exhaust system's temperature will rise (owing to the burning of air/fuel mixtures in the exhaust manifolding and pipes). Exhaust gas temperatures will increase (particularly notable during engine dynamometer tests). There will be a tendency of back-fire (or popping) during deceleration of the engine.

[michaelthepsycho]

I just read up about 10 pages worth of info on the Toyota Tundra site and various other back pressure discussions. They've got a few folks talking about how the reduction of back pressure is a variable in where you want your max torque at. For the daily driver, I'd say the sweet spot would be in the 3,250 ~ 4,250 rpm range to determine the diameter of your exhaust system. Smaller diameters push that max torque spot into the low RPM range while wide diameters put the max torque into RPM's that the average driver would never reach. Moral of the story: moderation. I guess perforating the cat-back portion of the exhaust would bleed off (but not hemorrhaging) back pressure in a minor way as to not push back my max torque spot too far up on the RPM range. As for the fuel-air ratio, I believe the modern ECU was invented for that reason to prevent the engine from running too lean / rich.

[mrodrig2]

Someone with some form of scientific explanation explain why it absolutely does not work (as some folks suggest).

No one specifically said it won't work, just that there are better ways to achieve the same effect.

I don't want to remove it because it's outright against the law but small modifications might not get picked up by inspectors.

Depending on state, yours included, this would classify as an unsanctioned exhaust modification for a car intended to be driven on public roads, so its illegal whether or not the inspectors catch it. I wouldn't call that a "minor DIY."

[southOC2.5]

I have an exhaust set up for you...lol 500 bucks and I will install it for you! Im in Lake Forest CA, I bought it but didnt fit my sedan.

zer...coupe

[Hussain]

idk about the 2.5 but with the 3.5 theres 2 bolts you can unbolt and push the pipe to the side and run the car with no muffler, i've done it several times and tested it at the track too... well, i got tired of getting under my car so i just installed a electronic exhaust cut-out.... an electronic exhaust cut out sounds like exactly what you're looking for...... just search for my several threads about it...... i'd post links and vids but i'm at my grandmother's house in colorado and the computer is slow as hell lol but you should really look into an E cut-out

[michaelthepsycho]

an electronic exhaust cut out sounds like exactly what you're looking for...... just search for my several threads about it...... i'd post links and vids but i'm at my grandmother's house in colorado and the computer is slow as hell lol but you should really look into an E cut-out

Oh man, you hit the spot so ON! That's exactly what I'm talking about, an exhaust mod that doesn't replace the whole thing. Thanks buddy!

[michaelthepsycho]

By the way, did you use single or dual valves? And what diameter? I don't want to change the stock exhaust too much, I think it looks fine.

[Hussain]

honestly, i've done alot of experimenting with my exhaust system.... i explain things in details with pics in my other post... i'd do the same with this post but this comp is a POS! lol so bad and laggy that it even skips letters when i type lol

well, before the cat theres flat piping and i had that replaced with 3" piping (best to just go 2.5")... i have a 3" Electronic exhaust cut-out but do NOT recomend it. 3" is bigger the what is needed and screws up ground clearence.... i assume the 2.5 has a similar set-up to the 3.5 so i'd replace the flat piping with 2.5" and a cut-out 2.5" in diameter.... should talk to a local muffler shop about it and have them lift your car up so you can see what options you have.... get an E cut-out, Stillen headers, and your exhaust set-up will be perfect