Ok its time to buy something else should I get a header or exhaust system. I have a 98 lude I know the headers on there could be better. I can not afford both, so its one or the other I am either getting dc sports 4-2-1 header or greddy evo cat back, what do you think?
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MSN Online messanger: fastluder1
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My take on it is, it's not worth it, unless you are going to do the whole package...i/h/e..why? because you can make one portion of the system as wide and free flowing as possible, but if the exhaust is still going to have to go through a constricted area or bottle neck at some point, all your efforts are fruitless...my opinion would be, if this is all you could afford, to go with the cat back exhaust..im sure the headers on 5th gen ludes are not as restrictive as the exhaust, and since the exhaust is the last part that the....exhaust (hehe) would see, i think it would make the most sense overall..
if you're as confused as i am right now, i'm saying go with the exhaust
PTER, I have skunk2 coils with tokico blues, got some rims on the way, and an apr wing on the way, 8mm wires, vacum lines, cai, plugs, short shifter, pedals, gauges, shift knob, 12% tint. pretty much all i want to do now is oem body kit, headers and exhaust, clutch and flywheel.
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MSN Online messanger: fastluder1
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HiTech header (better than anything else, if he ever makes one)
Custom 2.5" exhaust
Do everything out of stainless, and you will make power and save weight!
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Billy - 98 Prelude
#27 H2 NASA TX HondaChallenge
#27 PTB NASA TX Performance Touring Racing makes heroin addiction seem like a vague wish for something salty. -- Peter Egan
Header over exhaust anyday I wouldnt want to lose torque for racing...and everyone sees your headers in your engine bay before tech if you are worried about that
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If you only knew the power of the Lude...
'92 Porsche 968 - National PCA HPDE Instructor
'98 Red Base Prelude - 02 & 03 DSP Champion - Sold
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
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Billy - 98 Prelude
#27 H2 NASA TX HondaChallenge
#27 PTB NASA TX Performance Touring Racing makes heroin addiction seem like a vague wish for something salty. -- Peter Egan
Still, personally, I do not feel that the stock exhaust is THAT restrictive.... You are still going to be pushing a lot of exhaust out.... And think of the backpressure created also that will be beneficial with lots o gases in front of the exhaust.
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If you only knew the power of the Lude...
'92 Porsche 968 - National PCA HPDE Instructor
'98 Red Base Prelude - 02 & 03 DSP Champion - Sold
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
Darth isn't too much back pressure, bad...you want very little back pressure...that was my understanding anyways...i think the stock headers are less restrictive than the stock exhaust also..just my thoughts
Originally posted by prelude_driver Darth isn't too much back pressure, bad...you want very little back pressure...that was my understanding anyways...i think the stock headers are less restrictive than the stock exhaust also..just my thoughts
You get do need some backpressure for torque and I am sure you will not create enough to be a problem.
__________________
If you only knew the power of the Lude...
'92 Porsche 968 - National PCA HPDE Instructor
'98 Red Base Prelude - 02 & 03 DSP Champion - Sold
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
Even though it is a Pontiac, we can relate the basic ballpark figures learned to the Lude. Keep in mind that our stock exhaust will not be this restrictive as we still did buy a performance car from the factory... So the 2-3 HP gains people usually get from a Lude exhaust would probably be right. Also, many people find this after having the "whole system" of intake, header, exhaust. Couple this with the larger price for a louder coffee can exhaust, the header wins hands down. Not to mention that since you, like me have a 98, we need to "catch up" with our headers as the 99+ guys already have a leg up on us
__________________
If you only knew the power of the Lude...
'92 Porsche 968 - National PCA HPDE Instructor
'98 Red Base Prelude - 02 & 03 DSP Champion - Sold
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
You get do need some backpressure for torque and I am sure you will not create enough to be a problem.
That's a misnomer. It's not the back pressure but the velocity of the exhaust gasses that affects torque. Backpressure has nothing to do with it.
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Billy - 98 Prelude
#27 H2 NASA TX HondaChallenge
#27 PTB NASA TX Performance Touring Racing makes heroin addiction seem like a vague wish for something salty. -- Peter Egan
Actually, backpressure does have something to do with it. I did some reviewing in my internal combustion engines book and some other research and am now refreshed on the subject.
Ok, first, backpressure is not good for peak horsepower. The engine must use some of its power to pump the spent exhaust gasses out, and the more backpressure, the more power is lost this way. The best exhaust systems can even reduce the backpressure to below atmospheric at a certain RPM. They do this by taking advantage of the fact that exhaust flow is not continuous, but occurs in pulses. When the exhaust valve opens, a high pressure pulse comes out the exhaust port and into the header. The pulse then travels down to the collector, where it hits the expansion into the larger pipe and is reflected back - only the pulse that heads back is a low pressure pulse, not a high pressure one. If this low pressure pulse arrives at the exhaust valve just in time for the valve to open, it'll help pull the spent exhaust gasses out. So the lower backpressure pulses can help create power.
This low pressure wave has another benefit besides making it less work to pump the spent gasses out of the engine. If the intake valve opens before the exhaust valve closes (this is called cam overlap), the speed of the exhaust gasses can help pull the air and fuel mixture into the cylinder. If the cam, intake manifold, cylinder head(s), and headers are well matched, it's possible to push the volumetric efficiency of an engine beyond 100%. Some racing engines even run a line from the crankcase to the headers to let the exhaust suck out the crankcase fumes.
You're probably asking what this all has to do with torque. As you may have suspected, the effects I listed all sound like they should increase torque and power throughout the rev range (remember, hp=torque*RPM/5252, so if you increase power at a given RPM, you increase torque too.) In fact, they do. I've seen quite a few dyno graphs where an engine made more low RPM torque after a freer flowing exhaust was added. Sometimes, an exhaust mod added low end torque but moved both the peak torque and peak power up a little in the rev range, making the engine feel like it had comparatively less low end grunt - even when it was really pulling harder at low low RPM too. However, I've also seen graphs where the engine definitely lost low RPM torque after restriction was removed from the exhaust, so I know this isn't an illusion. Low end torque loss is a possibility, but not a given.
As you may have guessed, there's a second effect here at work. Remember what I said about camshaft overlap and low backpressure letting the exhaust gasses pull in the air/fuel mixture? Well, at low RPM with a cam with large amounts of overlap, the momentum of the exhaust doesn't just pull the air/fuel mixture into the cylinder; it can carry it straight out the exhaust port if the pressure at the exhaust port is lower than atmospheric (or lower than your intake pressure, if you're running forced induction) and the exhaust valve's open long enough (either low RPM or way too much overlap). Obviously, this reduces the amount of air and fuel that do anything useful.
Usually, the more aggressive the cam, the more likely you are to lose low end torque. Some engines will gain torque at almost all RPM when you reduce backpressure. Others will gain peak power but loose low RPM torque. Our cams with a VTEC engine have low overlap on the low cam, a benefit of the VTEC engine.
So I guess it depends on the exhaust you get. However, most dynos that I have seen of a Lude with an aftermarket exhaust show that the torque at the low rpm's still show a loss in torque over the baseline. If anyone knows of another exhaust that gains all around, maybe not as much at top end than low end but still gains some low end, PLEASE list it because then you might get me thinking about an exhaust. It still has to look good like a stock and not sound like a pissed off bumble bee...
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If you only knew the power of the Lude...
'92 Porsche 968 - National PCA HPDE Instructor
'98 Red Base Prelude - 02 & 03 DSP Champion - Sold
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
We could write a book about the subject, but here's quick reason why larger diameter exhausts kill low end power...
If you have a certain volume of gas that you are trying to move through a pipe, you can adjust the velocity at which this gas moves by varying the diameter of the pipe that the gas is traveling through. Small pipe diameter = high gas velocities. i.e. the larger the pipe the slower the gas will move for a given volume.
Now, the problem is that exhaust gasses don't move uniformally, they move in pulses as the exhaust is pushed out of each individual cylinder. This creates exhaust pulses, or areas of high and low pressure. Now, the larger you make the exhaust pipe, the slower the -average- velocity will be. Also, the gas will be heavier since there is more volume. That's what causes the problem. Instead of the gas flowing though the exhaust pipe, it "stacks up", and the engine has to work to pump the exhaust out. This stacking up causes MORE backpressure, and kills low end power. Now you ask, what about high end power??? Well, on the top end, the gasses are moving much quicker since the engine is turning faster, so there is less stacking up of the exhaust pulses.
So why not make exhausts all 1.5" in diameter???? Well, now you run into the problem of restriction. A piece of tubing can only flow a certain amount of gas before there is a pressure drop (restriction). i.e. you couldn't flow 500 CFM though a 1/4" tube with no pressure drop, but you could flow 500 CFM through a 4" tube with very little pressure drop.
So, you have to balance exhaust gas velocity vs. restriction.
Any type of restriction is BAD for power. If backpressure were a good thing, why not make an exhaust that uses 5" tubing but with a restrictor plate to increase back pressure? If backpressure is what helped low end torque, wouldn't that help?
The ultimate would be a variable cross section exhaust, but that's another topic.
To be truthful, an exhaust just needs to be long enough to complete the scaveging effect in the cylinder head. Anything after that is a waste because you're pushing the exhaust through the pipe, it's not traveling down the pipe using it's own inertia.
Whew...hope there's no typos in there! I know there is probably a few, so don't flame me over some mis-spelt word, okay?
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Billy - 98 Prelude
#27 H2 NASA TX HondaChallenge
#27 PTB NASA TX Performance Touring Racing makes heroin addiction seem like a vague wish for something salty. -- Peter Egan
However, I've also seen graphs where the engine definitely lost low RPM torque after restriction was removed from the exhaust, so I know this isn't an illusion. Low end torque loss is a possibility, but not a given.
You should check the diameter of the aftermarket exhausts to make sure that the tubing isn't so big that the engine is working to push the exhaust gasses out the exhaust at low RPMs. That could also be what's causing the problem, not just lack of backpressure. The larger tubing could be causing MORE backpressure than the stock exhaust.
As you may have guessed, there's a second effect here at work. Remember what I said about camshaft overlap and low backpressure letting the exhaust gasses pull in the air/fuel mixture? Well, at low RPM with a cam with large amounts of overlap, the momentum of the exhaust doesn't just pull the air/fuel mixture into the cylinder; it can carry it straight out the exhaust port if the pressure at the exhaust port is lower than atmospheric (or lower than your intake pressure, if you're running forced induction) and the exhaust valve's open long enough (either low RPM or way too much overlap). Obviously, this reduces the amount of air and fuel that do anything useful.
There are other ways to tune this besides adding backpressure, like decreasing overlap, retuning the header, etc.
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Billy - 98 Prelude
#27 H2 NASA TX HondaChallenge
#27 PTB NASA TX Performance Touring Racing makes heroin addiction seem like a vague wish for something salty. -- Peter Egan
Originally posted by 71dsp However, I've also seen graphs where the engine definitely lost low RPM torque after restriction was removed from the exhaust, so I know this isn't an illusion. Low end torque loss is a possibility, but not a given.
You should check the diameter of the aftermarket exhausts to make sure that the tubing isn't so big that the engine is working to push the exhaust gasses out the exhaust at low RPMs. That could also be what's causing the problem, not just lack of backpressure. The larger tubing could be causing MORE backpressure than the stock exhaust.
You left out the sentence before that one: Sometimes, an exhaust mod added low end torque but moved both the peak torque and peak power up a little in the rev range, making the engine feel like it had comparatively less low end grunt - even when it was really pulling harder at low low RPM too. It is just a matter of how good the design really is. With a smaller diameter pipe, you get greater velocity of gases with some added pressure at the beginning of the pipe. With a larger diameter pipe, you get a slower moving velocity, but there is lower pressure drawing more air out of the cylinder which helps the engine work.
As you may have guessed, there's a second effect here at work. Remember what I said about camshaft overlap and low backpressure letting the exhaust gasses pull in the air/fuel mixture? Well, at low RPM with a cam with large amounts of overlap, the momentum of the exhaust doesn't just pull the air/fuel mixture into the cylinder; it can carry it straight out the exhaust port if the pressure at the exhaust port is lower than atmospheric (or lower than your intake pressure, if you're running forced induction) and the exhaust valve's open long enough (either low RPM or way too much overlap). Obviously, this reduces the amount of air and fuel that do anything useful.
There are other ways to tune this besides adding backpressure, like decreasing overlap, retuning the header, etc.
But who in the world is really talking about adding backpressure??? I am not saying, go and add more backpressure by getting a smaller exhaust.... Are you refering to the jokingly comment I made by saying "imagine all of the backpressure..." or whatever... True there are many ways to tune everything... You are not going to add more back pressure by adding a freer flowing header, come on, give me some credit here. I mean, in the next paragraph or something I said that a VTEC engine already has very little overlap in the lower rpms...
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If you only knew the power of the Lude...
'92 Porsche 968 - National PCA HPDE Instructor
'98 Red Base Prelude - 02 & 03 DSP Champion - Sold
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
I read your sentence, and I understand what you are talking about.
A larger diameter pipe -can- add backpressure. Remember, we are dealing with pulses, not a steady stream of exhaust gas flow. Moving gasses in pulses becomes increasingly difficult at low velocities if you increase the diameter of the tubing because you are increasing the volume of the gas you are moving (not to mention that increasing diameter already decreases velocity). Think of it this way, if you increase diameter by 25%, you increase volume by 56%!!! That's a lot more exhaust gas to move, especially when the gas is moving in pulses.
Also, I never referred to "adding" backpressure. My comment is that backpressure is generally not a good thing, no matter how much you have (there are cetain exceptions with header design, but we are talking about exhausts here).
Now, let's not turn this into a pissing match, okay?
Besides, I won't be dealing with cams, valves, overlap, and all that business soon.....
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Billy - 98 Prelude
#27 H2 NASA TX HondaChallenge
#27 PTB NASA TX Performance Touring Racing makes heroin addiction seem like a vague wish for something salty. -- Peter Egan
[quote]Originally posted by 71dsp I read your sentence, and I understand what you are talking about.
A larger diameter pipe -can- add backpressure. Remember, we are dealing with pulses, not a steady stream of exhaust gas flow. Moving gasses in pulses becomes increasingly difficult at low velocities if you increase the diameter of the tubing because you are increasing the volume of the gas you are moving (not to mention that increasing diameter already decreases velocity). Think of it this way, if you increase diameter by 25%, you increase volume by 56%!!! That's a lot more exhaust gas to move, especially when the gas is moving in pulses.
Yeah, I can see the pulses of gas creating pressure as the pulse in front of it slows creating pressure that way, but it still would be a lower pressure than that coming from the engine which would make it flow into the lower pressured pulse easier. But yeah, it is more gas with the larger cross sectional area...
Also, I never referred to "adding" backpressure. My comment is that backpressure is generally not a good thing, no matter how much you have (there are cetain exceptions with header design, but we are talking about exhausts here).
I never said you were adding backpressure, I thought you were saying I was. Its cool
Now, let's not turn this into a pissing match, okay?
I guess........but I still say I can piss farther...
Besides, I won't be dealing with cams, valves, overlap, and all that business soon.....
__________________
If you only knew the power of the Lude...
'92 Porsche 968 - National PCA HPDE Instructor
'98 Red Base Prelude - 02 & 03 DSP Champion - Sold
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
[quote]Originally posted by Darth Luder
[b][quote]Originally posted by 71dsp I read your sentence, and I understand what you are talking about.
A larger diameter pipe -can- add backpressure. Remember, we are dealing with pulses, not a steady stream of exhaust gas flow. Moving gasses in pulses becomes increasingly difficult at low velocities if you increase the diameter of the tubing because you are increasing the volume of the gas you are moving (not to mention that increasing diameter already decreases velocity). Think of it this way, if you increase diameter by 25%, you increase volume by 56%!!! That's a lot more exhaust gas to move, especially when the gas is moving in pulses.
Yeah, I can see the pulses of gas creating pressure as the pulse in front of it slows creating pressure that way, but it still would be a lower pressure than that coming from the engine which would make it flow into the lower pressured pulse easier. But yeah, it is more gas with the larger cross sectional area...
Also, I never referred to "adding" backpressure. My comment is that backpressure is generally not a good thing, no matter how much you have (there are cetain exceptions with header design, but we are talking about exhausts here).
I never said you were adding backpressure, I thought you were saying I was. Its cool
Now, let's not turn this into a pissing match, okay?
I guess........but I still say I can piss farther...
Besides, I won't be dealing with cams, valves, overlap, and all that business soon..... Oh well, at least we got a lot of good info out to these folks, good discussion...
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If you only knew the power of the Lude...
'92 Porsche 968 - National PCA HPDE Instructor
'98 Red Base Prelude - 02 & 03 DSP Champion - Sold
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
Originally posted by Darth Luder I guess........but I still say I can piss farther...
I think I will take your word on that one....
Besides, I won't be dealing with cams, valves, overlap, and all that business soon.....
I am turning my Prelude back into a daily driver, and looking into an RX7 for the future. Probably won't actually buy something until early next year, though. Rotaries don't have valves, cams, overlap, pistons, etc. Scaveging doesn't even matter, from what I can tell!! Exhaust is still in pulses, though, although not as rough!
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Billy - 98 Prelude
#27 H2 NASA TX HondaChallenge
#27 PTB NASA TX Performance Touring Racing makes heroin addiction seem like a vague wish for something salty. -- Peter Egan
