rxspeed87

click me

kinda a log one but if you have nothing else to do you might get a kick out of it
all about backpressure and if it is good for your car or not

and some of the things this guys says I am sorry but makes me laugh

Maxthe7man

Ummm, I hate to break this to you, but that guys right, when you lose velocity in a large exhaust system, you stop the exhaust from scavenging the motor, and wipe out the reason for having overlap in a camshaft. Car Craft did a full dyno test on this last year, they ran a motor with different exhuast system and then no exhaust systems, the biggest mufflers and pipes did not make the most power, nor did having no muffler at all. Exhaust system sizing is a balance, there is to small and there is to big, and then there is tuning the motor to the exhaust which has to be done afterward, most people that add headers and high flow pipes to your average carbed v-8 actually end up with less power, because they failed to rejet the carb afterward, when you hit the magic point of your exhaust system, it will lean out the motor, requiring more fuel..Max

jarrod

yep

Node

iTrader: (1)

unless you're running a turbo then less exhaust is better.

rxspeed87

rx7speed = rxspeed87



well on of those guys is me
i'm the one saying that you need to have velocity there is another guy name chevyluva3. he is the one who says stuff like

BACKPRESSURE IS THE CAUSE TO CREATING TORQUE'S EFFECT.
Thats the only way to overcome backpressure is to increase torque, if you get rid of backpressure, you lose torque. (thats right thats a period, finally)



I had nothing to do so I wanted to stir up some trouble on the camaro forums
though I think qwktrip explained it the best

Cameljoe

Here is my question. would a 2.5" system be more suit for street use with the occasional "spirited race" than a 3" system, for example on a TII?

Scott 89t2

well for electric motors, the more resistance stoping it from turning, the more torque it has. if you slow a drill bit at half the speed, the drill will work twice as hard producing twice the torque, but also heat up twice as much, and use twice the electricity.

I don't think you can compare them... just more info to throw into the topic.

rxspeed87

on most drill bits I have seen though that is done through gearing
like a high and low setting
when you put it on the high setting it is going to use a taller gear so it will spin a lot faster and when you put it on a low setting it will switch over to use a shorter gear so you will multiply the torque that the drill bit is making

Aaron Cake

iTrader: (1)

Scott 89TII is right about electric motors producing more torque closer to stall speed, but it really has nothing to do with a gasoline engine.

rxspeed87

I admit I know jack about those type of motors

just have seen that a lot of them the motor doesn't changespeed but through the gearing you can make the bit turn slower


how do they do it though?

RX7boy

hey rx7speed how far away from moscow is caldwell?

rxspeed87

I'm about 30 miles away from boise

Cap'nWankel

Maybe these links will help you to understand the negative effects on backpressure.


http://personal.riverusers.com/~yawpower/jantech.html
http://personal.riverusers.com/~yawpower/febtech.html

rxspeed87

I understand the bad effects of backpressure

the guy I was debating it with on the camaro forum said that you need to have backpressure


though thank you I was looking for that site while trying to explain it to him

rxspeed87

well looks like that one is now finished

oh well

CosmicButtHairs

hmm
I don't really agree with that. Sorry Node.
But from what I know (and I hope to be enlightened)
I think a stock exhaust or a restrictive one would be better on a turbo because you can control the boost better since boost controllers can only increase the boost and you can't lower it.
For me, I kinda like the idea of being able to run stock boosts rather than having a car 'naturally' run 15 psi's without a controller.

Maxthe7man

Not quite, I have a few more things on my mind..
Many cars are tuned via the efi to have a certain amount of charge dilution via the EGR valve, the egr dilutes the charge and tends to (contrary to popular belief) cool the combustion chamber somewhat, which also reduces the engines tendency to knock or detonate, on most vehicles today that are designed to operate on the razors edge with poor fuel, disabling the egr or having it not operating will make the engine ping as the combsution chamber starts to run hotter, having said that, with no back pressure on todays vehicles, the egr flowrate decreases or becoms non existant, when excessive pinging is heard, the first thing people tend to do, is pull timing out of the motor, which pulls the rug out from under it and it starts to make less overall power, and makes the engine run ragged at low rpms because all of a sudden the mixtures are off and the timing is wrong..
Now Node says except on turbo cars, which is gernerally true except for cars that use integral or smaller wastegates, when the path and flow of the turbine are open up, it becomes harder to get the gasses to flow through the wastegate, its just as easy to get it through the turbine, so boost creep becomes a problem. Also on factory turbo cars, their is a tendency for the turbo to overspeed with a large non-factory exhaust system which is detrimental to turbo life.
Backpressure, while certainly not wanted in all engines, is in most cases a neccasary evil for most cars on the street, also on carbed vehicles, the exhuast is directed underneath the carb through a passage to warm the carb, aiding choke action, and stopping the carb from icing in cool weather and aids in fuel vapourisation, with no back pressure you get no flow through the passage. with efi they do not have chokes, and the fuel is atomized in the intake port to the throttle blades see no evporating fuel, the tendency to ice is eliminated, therefore the intake does not have to be heated by the exhaust..Max

rxspeed87

I dont really think that the EGR is needed to run a car

to this date my rx-7 is the first car I have ever owned with a EGR system
I had a setup like that on my other cars but it as either taken off or was not working to start with
they have not had any problem with pinp at all... nor did I have to run top grade gas
also though all these cars are carb and my rx-7 is the first FI car I have owned also

I dont think auto makers would put there car on the verge or performance/long lasting.... if anything I would think the auto maker would pull some performance to make sure the car last a little longer...
in removing the EGR yes I admit you might come up with some problem with ping. thing is most the time you come through with ping is under load I think. and from what I udnerstand a lot of EGR systems are made to not run under heave load like WOT or such.
kinda why there is not much to be gained from removing the EGR of my rx-7 under light cruise/load the egr is in effect to reduce comb temps in an effort to lower specific emission from the car that will happen when your exhuast temps are higher. but again it does this only under load
and if you make it to where you NEED to run egr under load you are going to lose power as it is. granted you want cooler intake charge to make more power but when for the comb chamber to make max power you want it to run as hot as you can without pre-det. you pull exhaust gas you will lower your intake temps yes but also you are not diluting the fresh intake charge which is also going to lower power output.
best case would to run that performace edge would be to build the motor so you do not need to have the EGR in there. that way you have a higher VE and by pulling in more fresh intake rather then a already used crap.
oops just notice you were talking normal driving not under load
I would still think under load though you would have more of a problem with ping then under cruise. and under load the EGR will be shut off so you get max power so you aer not not getting that cooling intake charge.
so I would think if you need that egr to run right due to pinging that you might have something wrong with the car are not running low grade when the manufac has even told you that you need to run premium in which case when you put the car under load you are goin to have even more problems with ping

and with the exhaust being right under the carb? I have not had that on any of my cars my celica the exhaust was on the other side
my camaro and mav have the exhaust on either side of the carb
nor do they have any kind of tube that will bring heat up to the carb
even if they did you do not need backpressure to carry heat
that will happen by convection since the exhaust will be lower then the carb the heat will rise. the pressure inside the exhuast can not and will not have an effect on that

sorry If I'm wrong please tell me. had a party so kinda shnocked at the moment
but give me a little bit of time and I will see what I can come up with for reference for what I was saying.

Maxthe7man

Actually removing the egr will most likely produce ping at throttle tip in more than any other throttle position as the engine sees vacuum advance start to drop off ignition timing while transitioning to straight mechanical advance. The egr is put in their to make the vehicle capable of running on pretty shitty gasoline, by diluting the charge , it also knocks down oxides on nitrogen somwhat..
On any carbed v-8 with a stock intake and some 4 an 6's, or a moderate performance intake, you will see a passage running from one head to the other through the intake manifold, some relied on water heating of the intake, but that meant extended warmups, newer efi engines have egr to, but there is now no reason to heat the intake for the reasons I stated earlier. Hp numbers sells cars, and the automakers will do anything they can to boost numbers and still retain driveabiltiy, emmisions, and longevity, hence the reasoning for egr, and other like devices, such as knock sensors and what not, they could al build 7:1 engines that would run on crap gas, but the first oem to move to 8:1 and offer 20 more hp would sell more cars.

rxspeed87

the EGR was put into play to reduce NOx emission. it is a device that is used under part throttle operation under high load/throttle the EGR valve will close and allow as much fresh intake charge into the system
between this and what you said about ping more apt to happen at throttle tip in I think it has been established that the EGR does not help a car produce more peak power since it will not have any effect through WOT which gives peak power

here is something I found about the EGR valve also

"When optimal air/fuel mixture is attained (14.7:1), the combustion process creates several different nitrogen oxides (NOx) because the combustion chamber is operating at over 2000° F . To reduce the NOx emission, the combustion chamber temp must be lowered. So the Exhaust Gas Recirculation (EGR) valve recirculates the now inert exhaust gas back into the combustion chamber to lower the total volume of combustable mixture. This results in a slight loss of power."

or here http://www.innerauto.com/innerauto/text/exha04.html

http://www.motorage.com/edindex/129614.htm




I admit you can get some ping problem with crappy gas that will cause ping if you do not have a EGR but if the car is in tune and you are using the right grade gas (i.e no 87 on a FD but instead 92+) with the timing set right you should have no problems with ping.

and also the tube you were talkign about that goes from on top of the head to the intake sounds like the PCV system which will reduce your blowby emissions. that does go into your intake yes. though a lot of ppl again want to have a higher amount of fresh intake so they will instead just put a breather on it and vent it to the open air.
the EGR should be somewhere lower near your exhaust manifold to pull spend emissions out of there.


so far again only under light load it will open up so will not help produce peak power, and when the EGR is open it will lower power.
will help lower NOx by quite a bit since it will lower your temps
there is a chance that it will help you reduce the chance of ping though most ppl I have seen have no problem with removing the EGR valve as lon as everything else is in tune.

and if you have a computer/ vac control EGR that you still have no need for backpressure in your exhaust system also

Maxthe7man

Nope the Pcv tube is totally different, on a carbed v-8 you have to acutally pull the intake off to see the egr port that travels underneath car, on a efi v-8, you will see a steel tube about 3/4" diameter going to the egr which is usually located on the back of the intake on a EFi v-8.
The egr can be tossed and backpressure reduced , if youhave enough control of the engine parameters, with a carb/distributor engine or a an efi engine with standalone eif, yes you could tune the engine out of the need for egr, but on an oem computer controlled vehicle, its next to impossible in most cases, because of the tendency to detonate and feedback from the knock sensor, 9 times out of 10, fooling with the exhaust and egr on a efi vehicle without any tuning measuers will net you poorer driveabiltiy, and less performance..A rotary is a different in that it is not as detonation prone by means of combsution chamber design, and ignition setup.
If you want to see the effects of backpressure and egr first hand on a computer controlled vehicle, check on pinging problems in 5.9 litre dodge rams and 4.3 litre chev trucks. both oem's thought it was combustion chamber coking, and or poor fuel at first, after much head banging, they discovered that half of the pinging problems were bad egr's from a 3rd party source, the other half were caused by having aftermarket exhaust systems installed.. Not all owners had this problem though, the efi computers in both of those vehicles have learning computers, which records sensor feedback during driving conditions to tune the engine to the enviroment it sees in reguard to driving style,fuel and alititude, the people that continued to drive their trucks with a pinging problem, had the problem dissappear over time, it was found that the computers had stored enough knock sensor feedback to drastically pull back the timing in order to prevent ping feedback from the knock sensor, this was discovered after those same owners had taken their vehicles in becuase of soggy low end power and bad fuel economy. The ends do not justify the means..
In an all out power effort engine, egr is not neccesary, but you have to have control over ALL engine parameters to do it, in most efi engines you have no control over spark timing, advance curve, mid throttle mixtures or even idle mixture in some cases, and changing the parameters of the egr and back pressure, will usually bring about a change in engine performance, in a negative way.
Its funny you know, my neighbour is a GM driveability EFI mechanic, even though he likes horsepower and speed, he refuses to put headers or big cats on his suburban, the only thing he has done is a set of flowmasters, he says that is all you can do on a factory tuned v-8, is a set of mufflers, anything more will actually slow it down, because the oem computer will see the leanness and the pinging and pull timing back, most people equate louder with more power, which is simply not the case.
I do run headers, no egr, and a very short exhaust system on my 440, but I also have re-jetted the aftermarket carb, recurved my distributor and added a bigger cam to bleed off low speed cylinder pressure to avoid detoantion on 10:1 compression with premium gas..Max

rxspeed87

well seems like we agree on one thing
modern EFI can be a pain in the ***

not trying to be an *** or anything with this. if i'm hey I learned something so that would be cool. just trying to put my view forth and if it gets proven wrong then that's cool to me as long as I know why I'm wrong



also what else do you know that will kill a few min of my day

though with regards to restriction an the EGR.. still say dont need it
most EGR do not need it to open up. also with gas will try to flow from a high pressure zone to low and so when the EGR opens up wouldn't that draw the exhaust gas into it?

with headers or cat-backs on a modern EFI I have seen that at times that can cause some problemswith drivabilty but that is not always due to the EGR but mor of getting better flow and some of the computers do not see the change and still only give the same amount of fuel causing a lean mixture which will make the motor to ping.
though I have heard many stories from ppl (hey I am the node of the thirdgen camaro forum) about ppl putting headers,high flow cats, lots of aftermarket stuff for that matter and have no problem with there computer freakin out... though to get best performance you do need to modify the PROM cause the stock timing and fuel curves are not the greatest when you put mods in there... but... if you go to far like a big cam or something you can put things in trouble with the computer and start to run like crap, like a big cam


though I think we have the wrong forum for this, this is a rotary forum man not the piston place
if you want also we can talk about it on AIM

NZConvertible

Getting back to the original topic, when talking exhausts on turbos, bigger is always better. Yes, a bit of backpressure is required, but you already have a huge backpressure-creating device hanging off the side of the engine. It's called a turbo! It creates all the backpressure the engine needs. The larger pressure difference across the turbine caused by a less restrictive exhaust increases flow and power.

NZConvertible

Getting back to the original topic, when talking exhausts on turbos, bigger is always better. Yes, a bit of backpressure is required, but you already have a huge backpressure-creating device hanging off the side of the engine. It's called a turbo! It creates all the backpressure the engine needs. The larger pressure difference across the turbine caused by a less restrictive exhaust increases flow and power.

Maxthe7man

Yes the turbo does make backpressure, but thats not really the topic at hand..
By dropping the pressure differnce across the egr, you decrease the flow, if you had 2 psi of back pressure, even with a vacuum on the other side, if you decrease the pressure to .5 psi, its not going to flow as much through the valve..Max