How free flowing should the XJ exhaust be?

[PurpleCherokee]

There were people arguing that a free-flowing exhaust system will kill torque which this can definately prove wrong. And then there are people (like you I believe) that are saying that you gain nothing, simply move your powerband, which this will also prove wrong. It's about a NET gain. And since we're arguing the relationship between backpressure and power, the cat plays a big role. And since my exhaust system has as little backpressure you can possibly have, a dyno sheet will say a lot.

 

[copbait]

There were people arguing that a free-flowing exhaust system will kill torque which this can definately prove wrong. And then there are people (like you I believe) that are saying that you gain nothing, simply move your powerband, which this will also prove wrong. It's about a NET gain. And since we're arguing the relationship between backpressure and power, the cat plays a big role. And since my exhaust system has as little backpressure you can possibly have, a dyno sheet will say a lot.

If you do two sets of runs, one without the cat, and one with, then your results will be meaningful, but they will only be meaningful with your particular setup. The gains you might see could be dependent on the engine and header mods you have done. The results won't really be useful for someone with a stock engine.

In doing both sets of runs, there should be as little time difference between the two sets of runs as possible, we're talking minutes if possible, as changes in weather conditions/temperature and dyno calibrations can have an effect on the results. So you will need to do the part swap right in the shop parking lot in between sets.

 

[PurpleCherokee]

Everything's welded up or I would. But all I'm sayin is that we know what the torque curve for a stock XJ looks like, and soon, we will know what my new torque curve looks like. Now, from the difference in the two you can assume that the differences are a result of
A. Intake
B. Exhaust
Since those are the only two things not stock. And since we can safely assume that intake isn't goin to be that significant of a factor in the results, we can assume that the rest of the difference is from the exhaust. And part of the exhaust design is the fact that it's catless, therefore, it has to be considered as part of the result of the new torque curve. Granted, we don't know how much of it was because it was a catless design vs how much of it was the rest of the design of the exhaust but it will certainly say SOMETHING. But I'm not just out to try to show something about how cats affect power, I'm mostly trying to show how overall exhaust flow (and backpressure) affects power. And no, this "experiment" isn't as scientific as I'd like for it to be, but I am looking forward to the results none-the-less. So you take Net power increase over stock - Estimated power increase from intake = Power increase from exhaust. Then you can derive all of the factors that make up the exhaust (lack of cats and lack of much backpressure) and assume that they had a fairly big impact (seeing as how the DO comprise the exhaust system) on the performance gains. Sorry, that's as scientific as I can get

 

[wolfpackjeeper]

I am not saying that you will not see an increase, I just said that it will not prove anything because the experiment assumes too much. We would be taking assumptions about assumptions as facts, which they are not. It is amazing how wildly different your results can very with 2 variables in the same equation. When I told you that you were wrong it is your method I was critiquing, not your exhaust.

 

[copbait]

yea, unfortunately you can't just compare one snapshot of test results to another set of values from a different vehicle tested on different equipment. way too many variables for it to be useful at all. it's difficult enough to get accurate information even keeping as many things constant as possible.

in fact you could take your setup to a shop one day, and then take that same vehicle to the same shop a week later, and the results could differ by several percentage points. it could show you gaining 5HP when in fact nothing had been changed at all.

it's unfortunate that this performance stuff is so difficult to get clear answers on, i guess that's why it is such a highly debated topic.

 

[BBeach]

This is gonna end up with him somehow seeing a higher number, prolly due to a fresh motor or one of the other several variables and people are gonna believe it.

 

[wolfpackjeeper]

seriously. I have seen people feel a huge difference with the Ass-Dyno and have actually lost a significant amount of power, several times actually. They are usually 4.6l mustang drivers

 

[BBeach]

seriously. I have seen people feel a huge difference with the Ass-Dyno and have actually lost a significant amount of power, several times actually. They are usually 4.6l mustang drivers

Their ass-dyno malfunction is usually related to them going into a situation already "knowing" what they'll get out.

 

[BBeach]

Someone should do a random test by changing the diameter of their exhaust tips. Assuming no exhaust leaks along the way, it should still give a ball park idea to their backpressure theory. Say if you're tailpipe is 2.5" in diameter, then put on a 2" tip, hell put a 1.5" tip on there and let us know. I know the temp of the exhaust gas lowers, changing the properties of the fluid, but you could almost assume that to be a constant before the tip whether its 2.5" or 1.5".

 

[copbait]

Their ass-dyno malfunction is usually related to them going into a situation already "knowing" what they'll get out.

and of course the degree of the "ass-dyno" effect is directly proportional to the amount of money spent on said mods

 

[wolfpackjeeper]

and the fact that an older sbc still makes more at the wheels than they do at the crank....

 

[seanyb505]

Purple, for the sake of not looking like an idiot dont come back with one dyno sheet and say it proves anything. Im not saying taking the cat off doesnt gain anything or hurt anything right now, or anything along those lines relating to back pressure. You HAVE to take into account not all engines are the same, not all dynos are the same, and its rare to have the same weather conditions which could potentially play a bigger part than your entire exhaust system. If you can, at least try to put a stock airbox on, as again, you cant estimate gains and base your conclusions on those estimations. You simply cannot compare your engine to a factory dyno sheet.

 

[PurpleCherokee]

This is gonna end up with him somehow seeing a higher number, prolly due to a fresh motor or one of the other several variables and people are gonna believe it.

Ok... If I'm not mistaken aren't the factory specs from a "fresh motor"??? I NEVER said that this is an extremely scientific test but it's the best I can do. And it WILL say SOMETHING. We SHOULD be able to draw SOME conclusions about it. Come on people, since when did dynos become useless??? :dunno:

 

[BBeach]

Ok... If I'm not mistaken aren't the factory specs from a "fresh motor"??? I NEVER said that this is an extremely scientific test but it's the best I can do. And it WILL say SOMETHING. We SHOULD be able to draw SOME conclusions about it. Come on people, since when did dynos become useless??? :dunno:

Idk much about this engine builder, but the smallest things can be possible with him vs the guy in ohio built our engines. The only way to make it even remotely scientific is to put one on before and after the test (keep it on too :moon: ). Just read sean's post above yours and you'll have an idea. Also, look up scavenging.

 

[wolfpackjeeper]

Dyno numbers mean close to nothing. ET times speak worlds. Most people will use a dyno to tune or remap a motor and get it roughly dialed in. But do to the variances it is pretty usless to prove broad spectrum claims.

 

[PurpleCherokee]

Wolfpackjeeper: When it comes to making power, dyno numbers mean way more than ET's. I however, am looking for both.

BBeach: You've never heard of MARSHALL engines??? I thought they were pretty well known. But in case you can't READ, I mentioned previously in THIS THREAD that I spoke with a tech person for Marshall and verified that their motors put out the same amount of power as stock... because they ARE stock... suprise suprise.

Also, look up scavenging

. What an arrogant asshole thing to say. So I'm assuming since you don't agree with my exhaust set up in the performance department (I'm not even gunna mention the environmental department) that you either think that:
A. Cats HELP scavenge or
B. My exhaust set-up (a straight-through design) is losing power because it doesn't have enough backpressure (that backpressure is a good thing)
Both of which is just plain false. Obviously, YOU are the one who needs to look up scavenging...
"Mufflers -- Two Golden Rules To Avoid Power Loss". "...To achieve a zero-loss muffled high-performance race system we need to work with the two key exhaust system factors in total isolation from each other. These two factors are: the pressure wave tuning from length/diameter selection, and minimizing backpressure by selecting mufflers of suitable flow capacity for the application..."
Holy shit did I just hear "MINIMIZING BACKPRESSURE"!? And that was just the first google hit I came across... oh, and here's the link in case you feel like getting educated :wave: ... dickhead.

Seanyb505: I won't say "here's a dyno sheet and it PROVES that a straight-through exhaust design due to its low back-pressure makes more power than a system with more backpressure". I don't have the means to do the test correctly. I don't have the time, or money, or will. But I will say "here's a dyno sheet with much higher numbers than a stock dyno sheet and this is the kind of exhaust set-up I'm runnin... you can take whatever you want from it".

Or you (in general, not sean) can just be an ignorant tool and make up excuses for why the results might be a little flawed and flame someone who isn't able to spend a weekend with a dyno to "prove" something.

 

[wolfpackjeeper]

dude, you are the one who came on here talking about how you are going to prove to everyone that you are right and that they are wrong. Now you come out attacking the subscribers to the thread when all they did was tell you reasons why it would not be an all inclusive test that would prove what you were trying to do.

And no dyno runs do not mean more than ET's and track performance. I have seen 300hp cars run 12's and I have seen 500hp cars run 15's. the dyno is not a useful tool for proving anything, unless of course you are trying to make yourself feel good about your car, or your are trying to promote a product(adds 15HP!!!) I saw 4 valid reasons made as to why the dyno is a tool for tuning and not for making numbers claims, and you just blow them off.

and to top it all off you come off as the arrogant jerk, not anyone else. You can take your dyno results that only apply to you and cram them up your ass.

 

[PurpleCherokee]

I'm not dyno-ing to do anything more than show how much a very free flowing exhaust system (with no cats) can help w/power. Let me say this again, just how I said it before... "when it comes to making POWER, dyno runs mean way more than et's". I'm sorry, but you must be really dumb (to say it nicely) if you think that et's say more about making POWER than a dyno...

 

[wolfpackjeeper]

try hanging around a forum with drag cars instead one with rock crawlers. a dyno gives you a rough idea, ET's are where the money is at. If you make 600hp on a dyno, you dont win any prizes, break into the 10's with your ET and you are a Hero. Too many people screw with dyno results for anyone to take them seriously. Products are tested on a barebone system to make max horsepower and marketed as a street mod. Most people, except you of course, see the dyno as a means to an end, not as the end itself.

Dynos are used to shock and awe the layman. Professionals see them for what they are...

 

[BBeach]

Wolfpackjeeper: When it comes to making power, dyno numbers mean way more than ET's. I however, am looking for both.

BBeach: You've never heard of MARSHALL engines??? I thought they were pretty well known. But in case you can't READ, I mentioned previously in THIS THREAD that I spoke with a tech person for Marshall and verified that their motors put out the same amount of power as stock... because they ARE stock... suprise suprise. . What an arrogant asshole thing to say. So I'm assuming since you don't agree with my exhaust set up in the performance department (I'm not even gunna mention the environmental department) that you either think that:
A. Cats HELP scavenge or
B. My exhaust set-up (a straight-through design) is losing power because it doesn't have enough backpressure (that backpressure is a good thing)
Both of which is just plain false. Obviously, YOU are the one who needs to look up scavenging...
"Mufflers -- Two Golden Rules To Avoid Power Loss". "...To achieve a zero-loss muffled high-performance race system we need to work with the two key exhaust system factors in total isolation from each other. These two factors are: the pressure wave tuning from length/diameter selection, and minimizing backpressure by selecting mufflers of suitable flow capacity for the application..."
Holy shit did I just hear "MINIMIZING BACKPRESSURE"!? And that was just the first google hit I came across... oh, and here's the link in case you feel like getting educated :wave: ... dickhead.

Seanyb505: I won't say "here's a dyno sheet and it PROVES that a straight-through exhaust design due to its low back-pressure makes more power than a system with more backpressure". I don't have the means to do the test correctly. I don't have the time, or money, or will. But I will say "here's a dyno sheet with much higher numbers than a stock dyno sheet and this is the kind of exhaust set-up I'm runnin... you can take whatever you want from it".

Or you (in general, not sean) can just be an ignorant tool and make up excuses for why the results might be a little flawed and flame someone who isn't able to spend a weekend with a dyno to "prove" something.

I honestly dont care much for remanufactured engines as Id rather build a stroker if mine blew...I can read last time I checked, but sometimes Id prefer not to read some of your ignorant statements. As I said before, who cares if its stock. For it to dyno at the same exact number as one from 10 years ago from the factory, id be surprised. What if its 195? Id bet you would claim a 5hp gain.

"But I will say "here's a dyno sheet with much higher numbers than a stock dyno sheet"

Now its much higher numbers...