exhaust tube sizes

[rurouni20xx]

so in other words it has 10 clamps and all sorts of step ups? thats what i call persistence as far as getting what they want.

 

[MikeInIdaho]

Both of my vehicles are straight-piped, or nearly so. My '06 b2300 has a 2 1/4" single-in/single out dynomax race bullet welded on right after the cat and is straight piped from there to right in front of the rear tire. There is a very slight reduction in sound compared to a straight-pipe (1-2db, tops) and similar performance. On my '82 VW Rabbit (N/A diesel), I'm running a dual-outlet exhaust manifold off a '91 8v (gas) GTI with a custom-built y-pipe, and then a straight-pipe from there to out in front of the rear tire (also 2 1/4'). On the rabbit in particular, there are no cats (obviously), resonators or mufflers of any kind. Both vehicles' exhaust systems are as free-flowing and loud as can be (the truck actually isn't that bad, due to the cats) and produce practically zero backpressure. I haven't experienced any engine-related issues with either vehicle and both run (and sound) great. On the Rabbit, I actually noticed a significant reduction in operating temperature after disposing of the restrictive, backpressure-building and performance-robbing factory exhaust.

 

[twinky]

so in other words it has 10 clamps and all sorts of step ups? thats what i call persistence as far as getting what they want.

no there arent 10 clamps
all welded (be me)

 

[shadetree]

What is backpressure?
Backpressure is exhaust gasses backing up in the combustion chambers/primary piping due to poor flow caused by some type of restriction in the system. This can be due to poor design, bent pipes, system too small, junk in the system.

Do I need/want backpressure?
No. The less the better. However, you can't get rid of all backpressure. You will have some, but you want to be able to manage what you have.

Will my valves burn without backpressure?
It depends on your fuel mixture. In earlier days with carburetors, changes in the exhaust system would change total system flow(as it does in all systems) from intake to exhaust. A jetting combination that works for one system, could become lean if the exhaust was changed allowing for greater flow thru the system. The leaning out of the system caused combustion chamber temps to rise, and the material makeup of the valves at the time could not handle the increased temps.

Modern engines with EFI, and better valve material adapt much better to these changes. If the flow is increased, and the system leans out, the O2 sensors will note this change and adjust fuel flow accordingly preventing high combustion chamber temps and no damage will occur. Modern engines are "lean burn" engines anyway, and the fuel mixture is more closely monitored.

Will no backpressure kill my bottom end power?
Backpressure takes away power in all ranges. When the exhaust system is changed, and some low end power loss is noted, it is not due to backpressure, but the loss of exhaust system velocity(the speed of the gasses flowing thru the system). This happens when larger piping is installed in the system. It really doesn't cause a "loss" of power, it just moves the power up higher in the rpm band. Reverting to a smaller pipe would then lower the power band.

The exhaust system is very complex, and all physics involved cannot be discussed on a forum such as this. I just tried to cover some of the points more often discussed.shady

 

[jax4bangin]

thats not exactly true i got a 5" Stack on my truck i did get that boot of torque and horsepower "altho i did lose like 1 mpg lol tho it could be my lead foot"

please post the vid. i need to hear this bad boy lol. do u got a 2.3?

 

[rurouni20xx]

u see where im coming from shady, and thanx for posting that. i remember all that from my exhaust classes during votech, tuning exhaust w/ backpressure was always an interesting factor. it was also made a point that w/o backpressure the valvetrain could fail, and i experienced such failures on efi and carb bikes in the shop. the sensor does change your a/f at cruise and idle to make up for these changes, but only slightly. during open loop circuits (accel, decel, beyond 70% throttle) the engine uses a preprogrammed chart to fuel the engines during these open loop circuits. if these values arent recalibrated you could still burn the engine out w/o knowing it.

 

[shadetree]

u see where im coming from shady, and thanx for posting that. i remember all that from my exhaust classes during votech, tuning exhaust w/ backpressure was always an interesting factor. it was also made a point that w/o backpressure the valvetrain could fail, and i experienced such failures on efi and carb bikes in the shop. the sensor does change your a/f at cruise and idle to make up for these changes, but only slightly. during open loop circuits (accel, decel, beyond 70% throttle) the engine uses a preprogrammed chart to fuel the engines during these open loop circuits. if these values arent recalibrated you could still burn the engine out w/o knowing it.

I don't know about bikes, but in automobiles going "open loop" will enrich the mixtures to sometimes as low as 11:1 under stoic. It never leans the system unless the system has been tampered with.shady

an engine w/ no cats/backpressure dumps fuel thru the valve and the valve doesnt have the leftover fuel to cool the valve. a pipe w/ cats and straight piping scavenges greater pulling the fuel thru the cat faster than normal creating the same problem just not as bad. there is a fine line of balance here to keep backpressure up to keep this from happening. most tuned exhaust systems actually use sound waves to create backpressure while still allowing the exhaust to flow.

This is a different situation. Backpressure isn't being used, but flow velocity. I know one bike mfgr who used a valve to interrupt flow during valve overlap, but it wasn't using backpressure. This wasn't a very efficient way of doing things as it was rpm specific so it was dropped.

Scavenging, over scavenging, and underscavenging can be controlled by tuning the exhaust system, if fact that is one of it's purposes. Using sound waves is part of this system, as it is an inherent by-product.shady

 

[rurouni20xx]

most 4 cylinder sportbikes and yamaha vtwins now use exups (exhaust ultimate power valves) to tune the engine w/ backpressure and flow velocity. your right it is dif and similar as it all goes hand in hand. a stock tuned trk w/ a dif exhuast and no additional tuning while in open loop does not change its map to compensate in a speed density system. ford mass air systems may actually richen up since the higher velocity throughout the system is sensed and the engine is richened, hence the beauty of mass air over speed density. i dont have much experience w/ mass air but im learning. almost all motorcycle and fourwheeler applications are speed density (ducatis i believe are mass air) and must be reprogrammed, mass air vehicles may not need to be. ill research this theory and if someone has supporting information it would be much obliged. thanks for the educated knowledge shady.

 

[MikeInIdaho]

I just wanted to say that you guys have just proven that it is in fact possible to disagree with one another and intelligently discuss our differences in opinion without resorting to name-calling and personal attacks. Thanks!

 

[rurouni20xx]

i agree to disagree all the time, its called compromise and realizing that ppl are going to do what they are going to do. i also like to intelligently discuss things, and ask questions where i may, not point middle fingers cuz i can. in the end were all human, we all share this planet, and id rather get along w/ everyone and enjoy my life however long or short it may be. i may look like im against something at times and scrutinize when actually im simply questioning it and if there is sufficient data supporting posted theories or actions i may come to try them myself one day. til then ill look around and take in all that i can that way maybe one day ill make a better informed decision based on learning from somebody elses previous expensive experience, lol.

 

[shadetree]

And, I don't know that we are really disagreeing. It has to do with different experiences, and different ways of expressing what we know. I try to make things as simple as possible for the novice reader.

ruro - speed density in autos does go to different programs at wot to richen up the mixture. It bypasses some of the sensors, hence "open loop."shady

 

[LittleHorse]

how many motorcycles out there even use speed density? I'm not super familiar with a lot of street bikes, but the motocross bikes (example-Suzuki RM450) and quads with fuel injection don't even have an oxygen sensor or map sensor or maf - it's just programmed maps, a TPS and a fuel injector. It's not much more tolerant to system changes than a carburetor, the advantage is being able to load in a program in a few seconds rather than pulling the bike apart to change jets.

I believe the Suzuki SV650 is set up this way too. I'm kindof a Suzuki guy so my knowledge of other manufacturers is limited. And I'm not much into the 4cyl bikes...

It's funny the differences between the worlds of modding cars and bikes. Anybody changing an exhaust on a dirt bike knows they have to rejet, but people goof around with their cars all the time and don't change a thing. I changed the exhaust on my DRZ400 and opened up the airbox and went from a 142.5 main jet to a 160. That's a 12% difference with no internal engine modifications!

 

[rurouni20xx]

ill let you in on some background on me, im a silver certified yamaha technician that has worked dealer level since college, and have taken the manufacturer level fuel injection classes, hence my knowledge and experience w/ such units. ive worked at 4 dealers in 3 states, one dealer had six major brands (honda, yamaha, kawasaki, suzuki, arctic cat, canam/bombardier) and i had to work on all these brands of m/c, atvs and utvs. ive also worked on ktms, been around bmw/ducati, and some polaris, and a few harleys to boot. did some trk racing in hs, have an outdoor power equipment technology degree, ran around w/ the tuner crowd, worked govt contract on humvees and 5 tons for 6 months, if it burns rubber and hauls ass, im interested. i may be well rounded but by no means an expert, always open to learn w/ new info. enuff about me, onto bike fi class. all bikes that are efi are pgm-fi (programmed fuel injection). no maf, they use the intake pressure sensor b4 the throttlebody or the map sensor on the t/b to take measurements and calibrate. there is a map sensor on some models its on the throttlebody using a direct vacuum fitting you just dont recognize what it is, and the bike system is much more complicated than you realize, yet simple at the same time. the bikes w/o this unit have a sensor on the intake tube or throttlebody that senses suction and doubles as the crankshaft/camshaft position sensor on single cylinder engines. i used to program these bikes all the time on the dyno using powercommanders and the winpep 7 program. (where i work now doesnt have such things so i use uploadable maps from dynojet.) the ones that have o2 sensors (more common on street bikes and i think they new yfz450r has one, ill have to look again) use the narrowband sensor like a car, but still depends on a preloaded map to go by. when under accel etc (open loop) it depends on this map to run, and if this map isnt modified serious engine failure will result. the bike doesnt learn like a trk/car does, it has to be reprogrammed to compensate for changes in exhaust/intake mods, cams and other work done to the bike. it is similar to speed density, but i cant tell you if it is speed density because it appears in cars speed density systems and mass air systems learn. pgm-fi is the term honda uses as yamaha says yfi etc, i have no confirmation on what it is as i only know what the manufacturer calls it, and how it operates. it MUST be recalibrated on bikes/atvs or serious problems will occur, much like changing parts on a carb bike w/o rejetting. still learning the cars, and taking notes as i go using my current knowledge as a reference. any input and conflicting opinions and experiences are a plus to help me and others grow in knowlege, thats what forums are about in my opinion.

 

[LittleHorse]

I see.

I'm more the other way around. Very familiar with automotive FI systems, especially the Bosch Jetronic systems used on Datsun and BMW's, among others. I used to be very familiar with Ford's EEC-IV systems but I haven't messed with them for 5+ years so I'm having to re-familiarize myself.

Bike FI systems I'm only as familiar with them as I have felt motivated to get, as I don't own any FI bikes at this point.

 

[rurouni20xx]

ill be looking forward to compare information w/ others such as yourself in the future. this mass air stuff is interesting to say the least, im trying to learn as much as i can so i can do the megasquirt ems thing w/ my trk. i asked the guys at diyautotune.com about a setup and they can have one setup for eec4 ford w/ the mass air sensory. id reflash the computer and do it that way w/ a tuner but a standalone is easier for the most part while going down the road, which is how im going to have to tune mine since the nearest dyno is over 200 miles away...and the megasquirt is the only ems ive found so far that supports mass air systems. i realize ill be starting w/ a blank ecm but im confident in my tuning capability and ive tuned quads in the past while running them and datalogging and this should be very similar. its time consuming i know but when you dont have access to all the right equipment there isnt much you can do. if i had a donor quad id try the microsquirt on it to get myself acquainted. i believe theres a good amount of learning and power to be made using these systems if used effectively. the way the bikes are setup reminds me a lot of the speed density systems ive been reading on thats why i am almost positive they are one in the same, just dif sensory. now to just tune one and a mass air system i could really tell the key differences.