Stock spec v times

keep in mind I said extended cab, because I know a non extended cab can take a 350z

lol i was going to say, i thought the SS silverado was built to contend with the lightnings and srt-10 ram, didnt think there was any competition there..........i DID beat a srt-10 at the track once, my 9.85 to his 9.97........he didnt know how to drive though.....hahaha

!!!!!!!! DAMN WTF WERE YOU DRIVING? But I think the SS silverado runs a lower 14 in the 1/4.

lol my bad zach, that was in the 1/8th mile here at jax raceway park, i was driving the spec of course

i have yet to see any proof that backpressure is needed at all for power...
http://www.supertrapp.com/technology/index.asp

I had a friend who was very serious about atucrossing and used a supertrapp muffler to tune his car at a dyno. He didnt just use the muffler, but when he had the car tuned to his liking, he would get a few extra ponies here and there by tuning the muffler.

http://www.supertrapp.com/technology/index.asp

I had a friend who was very serious about atucrossing and used a supertrapp muffler to tune his car at a dyno. He didnt just use the muffler, but when he had the car tuned to his liking, he would get a few extra ponies here and there by tuning the muffler.


I'm not sure i completely understand the concept of the backpressure in this case, and how it will cause you any gains? Can someone explain that to me?

I'm not sure i completely understand the concept of the backpressure in this case, and how it will cause you any gains? Can someone explain that to me?

Honestly I dont even understand very well myself, it is actually more complicated than I care to understand. But I believe its something like this. suppose you have a mass of air coming out a 2.5inch pipe. and the same mass of air coming out of a 3.5" pipe. For the same rate of air, there will be more volume on the 3.5" but more speed on the 2.5" pipe. And at low rpm you want the air to move quicker than at higher rpm.... I dont know exactly, the first part is true about volume and speed, thats simple physics. the other part... Im not even sure if that is true but so Ive heard. maybe you should do a search to see if you find something. a have seen different explanations and they all make some sort of sense. I guess its actually a mistery and people make up their own conclusions :screwy:

I have heard other explanations like if you have ever run in one of those bikes at the gym that you can adjust friction. you can pedal pretty fast with the right amount of friction, two much friction and you get tired, not enough friction and it just doesnt feel like your doing your best. I DONT KNOW!!! WHY DO YOU MAKE ME THINK ABOUT THIS!?!?:banghead:

At high or low rpm the flow size is the same, but the backpressure is created if the outlet size is too small, and at higher rpms is trying to force the air out. That creates back pressure. What i"m not sure about is why you want back pressure. I guess i'm not to understanding of the optimum exaust size all together. I'm in a physics based engineering program, and have done some physics labwork on some of the issues. Like with that tornado thing.

Someone explain the reason why you want the backpressure please!!

cuz the backpressure will 'press' you 'back' into the lead.....i guess that wasn't a good explaination :)

you want backpressure because it forces your NA engine to work, turbo cars want no backpressure because they get enough of it from the turbines and anymore would create lag, but a NA car wants backpressure because it will keep the exhaust speed constant, if it free flows then the exhaust speed will vary, causing a change in vaccum in the exhaust tubing which will cause power to fluctuate, it does this due to wave scavenging, which is where a vaccum in the exhaust tubing pulls the exhaust out of the cylinders on their exhaust stroke, this frees up some of the enigines energy to make power in the combustion chamber and not have to spend it expelling exhaust gasses. so there you have it, backpressure will not create a huge difference but as a previous poster mentioned, it will help tune a few extra ponies out of an NA car.

you want backpressure because it forces your NA engine to work, turbo cars want no backpressure because they get enough of it from the turbines and anymore would create lag, but a NA car wants backpressure because it will keep the exhaust speed constant, if it free flows then the exhaust speed will vary, causing a change in vaccum in the exhaust tubing which will cause power to fluctuate, it does this due to wave scavenging, which is where a vaccum in the exhaust tubing pulls the exhaust out of the cylinders on their exhaust stroke, this frees up some of the enigines energy to make power in the combustion chamber and not have to spend it expelling exhaust gasses. so there you have it, backpressure will not create a huge difference but as a previous poster mentioned, it will help tune a few extra ponies out of an NA car.

Actually backpressure is always a bad thing. What you want is exhaust velocity. If you go too large on the exhaust, you exhaust velocity suffers. I would go find the physics formula for all this stuff, but I am lazy, and unless anyone contests me, I will not spend the time. But at low RPMS you are putting out less exhaust, that is why if you go with the max recommended size exhaust (lets say 2.5 inch on a Spec-V) you gain HP at high RPMs where the velocity is at its max, but lose a little bit of low RPM power.

Plus, exhaust systems with no backpressure sound TERRIBLE. Just think of all those 1.5 liter Civics with 3.5" tubing. The air is practically falling out of the car making a farting noise.

Plus, exhaust systems with no backpressure sound TERRIBLE. Just think of all those 1.5 liter Civics with 3.5" tubing. The air is practically falling out of the car making a farting noise.
ahahahhaha :rofl: :rofl: :rofl: :rofl:
my new sig

rofl holy shite, beat me to it slideways

Actually backpressure is always a bad thing. What you want is exhaust velocity. If you go too large on the exhaust, you exhaust velocity suffers. I would go find the physics formula for all this stuff, but I am lazy, and unless anyone contests me, I will not spend the time. But at low RPMS you are putting out less exhaust, that is why if you go with the max recommended size exhaust (lets say 2.5 inch on a Spec-V) you gain HP at high RPMs where the velocity is at its max, but lose a little bit of low RPM power.
So the optimum exaust tubing is dependent on where you want your power curve? Like a smaller tube for more low rpm power, and bigger for higher rpm curve. So midrange will optimize high and low end power?

So the optimum exaust tubing is dependent on where you want your power curve? Like a smaller tube for more low rpm power, and bigger for higher rpm curve. So midrange will optimize high and low end power?

Speaking in general, yes, but I can only really answer that if I was able to dyno test all sorts of different sizes, but I can guess that 2.5 is going to be the best for a Spec-V. You might lose a little bit off your bottom end, but for your powerband you are getting the optimal size, and you could go bigger and probably get a better top end, but lose too much low to mid power to make it worthwhile.

I forget what car it is right now, I think the new Corvette, but there is one that has baffles that restrict the exhaust at low RPM's to maintain exhaust velocity, but open up at higher RPMs, so you get optimal exhaust size and velocity for the entire powerband.

so i should take my whole exhaust off including my header and ill see maximum top end right? or do i need that backpressure to make my car run right? :owned:

the only car you dont need backpressure on its a forced induction car, like i said they get enough from the turbine, but mild backpressure keeps exhaust velocity CONSTANT, which creates a continuous vaccum of exhaust leaving the pipe which pulls the exhaust out of the cylinders, if you use too big of an exhaust piping to eliminate backpressure exhaust velocity will actually be slower because of the volume of the exhaust piping, which is why you should'nt go too big, try removing your entire exhaust system and get back to me and let me know if you need a little backpressure or not. what you really want is the perfect size, just like fugiot said, that will create the greatest exhaust speed and lowest amount of backpressure, but you dont want zero backpressure because that will cause slower exhaust speed, catch 22 huh?

so i should take my whole exhaust off including my header and ill see maximum top end right? or do i need that backpressure to make my car run right? :owned:

It seems like you just want to argue with me here, but your not going to win, seeing as how you would still have backpressure, from a little thing I like to call THE ATMOSPHERE.

You can search it and every time you will see, the ideal exhaust has maximum exhaust velocity and ZERO backpressure. The reason a car runs shitty with a 3.5 inch pipe is because there is less exhaust velocity as well as zero backpressure. Lets say for a given car 2 inches is perfect at 3000 RPM's(since no exhaust is perfect at all engine speeds), it would have maximum exhaust velocity and no backpressure. If you were to decrease the exhaust size to say 1.75 inches you would get backpressure which WOULD PUSH THE EXHAUST GASES BACK TOWARDS THE CYLINDERS! and you would lose exhaust velocity. If you would go to say 2.25 inches, then you would still have no backpressure (GOOD!) but your exhaust velocity would suffer do to the larger exhaust size. You can use Bernoulli's equation to figure out why this happens. I haven't taken physics in 2 years now so I can't quite derive it out, but if you search I'm sure it can be done for you.

*edit* I should say however that all of this is in theory, in the real world you cannot eliminate all backpressure(ie atmosphere, pipe bends, etc...), but the ideal exhaust has the lowest possible backpressure possible (lets say 3-4PSI as apposed to 20-25PSI stock).

all exhaust is going to squeeze the gas some, unless you either remove your tubing or go with something like you see on a honda, you will have SOME backpressure, you just dont want a lot of it, i dont think this discussion is going anywhere though :useless:

all exhaust is going to squeeze the gas some, unless you either remove your tubing or go with something like you see on a honda, you will have SOME backpressure, you just dont want a lot of it, i dont think this discussion is going anywhere though :useless:

Your right, all exhausts are going to have some backpressure, but your argument that you WANT backpressure is flawed, which I was pointing out to help inform other board members that it is not backpressure, but exhaust velocity that is important.

but is it not true that SOME backpressure will actually increase exhaust velocity, its the perfect match of exhaust size and engine flow

you guys are just confusing me...i think imma pick up "cars for dummies" i get the backpressure thing, its just dumb to be arguing about....but w/e

but is it not true that SOME backpressure will actually increase exhaust velocity, its the perfect match of exhaust size and engine flow

Actually backpressure will never increase exhaust velocity, but having too small of a pipe for your top end will increase exhaust velocity for your low end, not because there is more backpressure, but because the exhaust velocity at low RPMs is better suited to a smaller pipe. But at high RPMs when your flowing much more exhaust, you will get more backpressure, which will hinder the velocity and give you less HP.

I looked into it and it is the new Corvette with the baffles in the exhaust that restrict the exhaust at low RPMs, this is not to cause backpressure, but to give it a small pipe at low RPMs to have maximum exhuast velocity, and when it opens up at high RPMs it is to minimize backpressure as well. Some Ferraris and Porsches have this as well, but I can't name any specific model.

I am not trying to argue here, its just a point that many people are confused on. Even I used to be confused on the relationship between exhaust velocity and backpressure, from growing up with people that worked on muscle cars, they tend to be the ones that spread the myth about backpressure.

Actually backpressure will never increase exhaust velocity, but having too small of a pipe for your top end will increase exhaust velocity for your low end, not because there is more backpressure, but because the exhaust velocity at low RPMs is better suited to a smaller pipe. But at high RPMs when your flowing much more exhaust, you will get more backpressure, which will hinder the velocity and give you less HP.

I looked into it and it is the new Corvette with the baffles in the exhaust that restrict the exhaust at low RPMs, this is not to cause backpressure, but to give it a small pipe at low RPMs to have maximum exhuast velocity, and when it opens up at high RPMs it is to minimize backpressure as well. Some Ferraris and Porsches have this as well, but I can't name any specific model.

I am not trying to argue here, its just a point that many people are confused on. Even I used to be confused on the relationship between exhaust velocity and backpressure, from growing up with people that worked on muscle cars, they tend to be the ones that spread the myth about backpressure.



almost...
everything is right except that
but because the exhaust velocity at low RPMs is better suited to a smaller pipe.

is sort of backwards. when gas at a constant volume and velocity is fed through a smaller pipe, the gas is compressed by the pressure from behind, speeding up the flow of the gas. sort of like squeezing a water baloon. it will try and flow out both ends but since there is more exhaust coming from the engine the only way to go is out the back. the analogy is more for effect and not for cause, since gas is highly compressable and water isnt. but compressing gas will build pressure, and the high pressure will want to go to the low pressure area behind the exhaust.