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Please elaborate.

S/C, N20 or Turbo....yes.

N/A...no need.

 
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here

also, there was a dyno of shawn hillier's car ... 213 whp, 15x wtq with a k20a, i/h/kpro/3" exhaust/hondata img ... sounds low, but the outside temps were over 100 degrees. I'd post a link to the dyno, but the source file has been taken down

 
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Exhaust thermal dynamics > one person's word on exhaust.

A 3" exhaust supports up to 500-600 WHP. 2.5" would probably be more than sufficient on an N/A K20. That motor is still a 4 CYL motor and does not put THAT much exhaust pulses out per second.

Remember exhaust gas does have a drag point, and I believe 3" actually exceeds it.

 
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well since you're already in the mindset that nothing can change your mind, there's nothing more I have to say

 
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well if you look on clubrsx.com in the N/A section they do have a discussion on there about needing 3inch exhaust and headers... basically they said that a car with ITB's,IPS-K2 stage 2 cams, and kpro will gain more horsepower with 3inch headers and exhaust that is offered by IPS... they do state hower that you will lose some power in the lower end of the powerband but will gain a significant amount in the top end.. heres the article

http://forums.clubrsx.com/showthrea...31&page=2&pp=25

and i quote some of the highlights for you..

post #26 says: Stage 3 cams don't appear to make more power than stage 2 because of the limiting factor of our induction systems.

post #36 says: to get the best out of either cam you will need ITBs, 3" race header and EMS.

post #37 says: You guys may be happy to know that there is more potential for power left in the "stage 2 class" of aftermarket cams without going ITB's! We have seen 20hp and up to 30ft/lbs tq improvement from a better induction and exhaust setup. It is even more inspiring to see how much better ITB's will perform in the near future.

post #39 says: Still OEM manifold - RBC, played with various intake lengths/diameters and velocity stack. Custom race header and 3" exhaust.

so as you can see the people down at IPS that have posted up in that forum say to use 3inch....anyways

 
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so in reality its just not one person...i myself have heard the same thing from many other local people that work on k20's.. so based on what i have read and what i have heard from the people at IPS, Crower, Hasport.. etc.... yes a 3inch exhaust setup is better.. IF.. and only IF you do some head work to your car such as better cams and better induction system... meaning something that sucks air in with no restriction or some ITB's

 
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The displacement is still the same. K20 is quite a different creature than most Honda motors, especially a D series motor.

Is this all taking into account tuning of the ECU with some form of EMU?

If so, then those gains can be made just form tuning with a decent flowing exhaust system. The only true way to see if this is the case, is by dynoing a bone stock K20A2, adding all of your mods, then adding a 2.5" exhaust (dyno tuning) then a 3" exhaust (dyno tuning). No other variables can be different.

With one particular set-up such as PNP, ITB's, headers, a particular cam...That 3" theory may hold some truth because of a port match to a microphone collector on a header, however to mearly state it is true accross the board with a statment such as "because K20's need to breathe" is absurd. Modifications have to work in conjunction with one another to work in harmony. Ultimately, a tuning device will have to be utilized to bring this harmony together.

Based upon math, which once I go ahead and get all the specs, I will post just for mere FYI and information to the masses.....

Given info on the K20:
121.9 CID (86mm bore & stroke)
HP level acheived: 200 WHP

Given info on exhaust gas thermal dynamics
Drag point of exhaust is near .4 Mach (the speed of sound)

The drag point is when exhaust gas travels so fast that it eventually begins to swirl backwards and create back pressure on it's own regardless of any other restrictions such as a cat, a cazy bend in the piping, muffler, resonator....You want to get as close to the .4 Mach as possible without exceeding it.

Edit: Sorry for the delay....

1)Approx air flow for the exhaust system is 1.5 times the base HP of 200.

1.5*200= 300 FT/SEC

2)Velocity of air = airflow/ area

= 300 ft/sec 1 min/60 sec
_____________ x ___________

PI *(2.5 in piping/2) ^2 1/144

= 146.75 ft/sec @ 2.5" exhaust

or

Now substituting 3 in for 2.5 in the equation.....

=101.91 ft/sec @ 3" exhaust

Speed of sound is ~ 1100 ft/sec

146.75/1100= 0.13
101.91/1100= 0.092

.13 is closer to drag point without exceeding it.......therefore 2.5" is more ideal for the displacement.

This is why I stated what I had earlier.

 
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awsome!

 
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Sorry for highly math oriented stuff.......some people I know are not that good with numbers.


What did all that mean as far as exhaust gases?

Answer: The 3" exhaust is actually providing slower air flow in comparison to a 2.5" exhaust.

Mid you, this does not take into account bends, resonators, muffler baffles....these all hinder gas flow as well.

 
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sorry, I'm not following the math.

what is 1/144? ... I'm trying to do the math and I can't seem to come up with the same answer.

what is the exact formula you used?

hm, as far as I know, slower airflow doesn't mean that it will create less power. If you take a 2" exhaust, the flow rate is gonna be much faster than that of a 2.5" exhaust...

 
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Correct. If for example, hp does not permit larger exhaust, there is no need for it. Hence why an exhaust on a stock vehicle, unless it is REALLY restrictive, won't have much power increase if any.

The formula is far too hard to type out. If I could show you it or write it, it would look much easier.

Use excel. Do the top part of equation, save the number. Do the bottom part of the equation (REMEMBER TO USE THE MATH ORDER OF OPERATIONS), the divide out the answers from each.

The 1/144 is a constant in the equation.

 
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300*(1/60) = .0166666666

^^ This is the top half

_____________________________

3.14*(2.5/2)<--SQAURE VALUE IN "()" = 3.14*(1.5625) = 4.9062

NOW take the 4.9062*(1/144) = .034071

Now take 4.9062 * .034071 = .16715




NOW take .0166666666/.16715 = ~.09 (there was boat loads of rounding and double rounding typing it out this way....)

 
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ok, from what I understand, I could stick a 1" exhaust on the k20 and it will have a crazy flow rate.

I don't think the exhaust velocity equation has anything to do with how much power it will gain

 
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*missing the boat*

It has to do with the motor's exhaust pulses and power output. DRAG plays a huge role in power.

1" would be incredibily more drag than the system could handle.

 
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WHAT exactly has to do with the motor's exhaust pulses and output?

the drag of what plays a role in power? ... the "drag point of an exhaust" ? ... I don't know why the hell you would want to get as close to .4 mach. If you stick a 1" exhaust on the car, it still won't be .4 mach ... so you're telling me that smaller piping will net better results?

if I'm "missing the boat" ... explain to me what I'm missing. because from the way you're talking to me, I don't know what I'm talking about ... and I may not ... so explain plz

edit:

ok, I see that the 3" exhaust creates less drag, according to your edited quote.

 
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I learned something today

 
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sorry if I'm not understanding this ... but 300*(1/60) = 5 ... not 0.0166666

1/60 = 0.0166666

where was the 300 in the top portion?


edit: also, I just did the calculations according to your formula ... without the 300 part.

it seems a 1.75" exhaust would BARELY exceed .4 mach. and I know for sure that a 2.5" (for EXAMPLE) would create more power than a 1.75" exhaust.

 
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.4 is the point of DRAG. You want to be close to, but not exceeding the drag point. .4 is too close. Stay within the range of .20-.35 (these are generally where I try to stay in) when calculating.

Why do you think most of these stock systems have 1.5" diameter piping?

I did not edit ANY of my calculations BTW. FYI

A 1" exhaust will be WAAYY more drag than .4......what does that mean? Super drag.....huge lack of power because of choke.

When you stay under the .4 mark, power is created. The closer you get without exceeding it, means more power is made at that given HP plugged into the top part of the equation. I don't know how else to explain this to you.

 
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Your right, but try typing all this crap out and explaining to someone of your nature all while juggling 14 phone calls in the meantime. LOL

Not easy. The equation still works. Trust me.

I can't continue to argue over this, do your math and explain to you thermal dynamics. I am sorry I do not have the time.

However, these are proven principals, not developed by myself but engineers who have studiesd this and use these forumals to make 8 sec 1/4 mile cars. Who am I to undermine them.

I appologize for being short, but business calls. I would love to have this discussion in person over coffee and some food. I will go with you for hours, but over the net with formulas and such is not easy at all.

 
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hm ok. I wasn't using 300 in any of my formulas. there are far too many errors and variables to assume that that formula is correct in every aspect.

3" > 2.5" in my book.

so ... who wants to swap a K20 with a 1.75" exhaust?

 
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Not the case....

I will repost all of my calcs and show you later, when I have time.

Yes true 3" exhaust is larger diameter than 2.5". That is a correct assumption.

 
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3" exhaust:

300*(1/60) = 5

^^top half is always going to remain the same in this case.


3.14*(3/2)^2 = 7.065

7.065*(1/144) = .049063

Hence: 5 / .049063 = 101.91

Convert to mach = 101.91/1100 = .0926 Mach

__________________________

2.5" exhaust

300*(1/60) = 5


3.14*(2.5/2)^2 = 4.90625

4.90625*(1/144) = .034071

Hence: 5 / .0434071 = 146.75

Convert to mach = 146.75/1100 = ..1334 Mach

___________________________

2.25" exhaust

300*(1/60) = 5


3.14*(2.25/2)^2 = 3.973984

3.973984*(1/144) = .027597

Hence: 5 / .027597 = 181.1784

Convert to mach = 181.1784/1100 = ..1647 Mach

______________________________

2" exhaust

300*(1/60) = 5


3.14*(2/2)^2 = 3.14

3.14*(1/144) = .021806

Hence: 5 / .021806 = 229.2994

Convert to mach = 229.2994/1100 = ..208454 Mach

_________________________________

Your 1" accusation

300*(1/60) = 5


3.14*(1/2)^2 = .785

.785*(1/144) = .005451

Hence: 5 / .005451 = 917.1975

Convert to mach = 917.1975/1100 = .833816 Mach


These calculations were done throughly by myself (Paul) in excel using a four figure rounding tactic to eliminate any rounding errors.

I had it all originally all figured out right when I did it here, but goofed up typing the little steps on the previous post. I appologize.

I will attempt to explain this a little better than I did before. To put it simply, with a 200 BHP, the proper exhaust size to keep the gases moving at a rapid pace in their exit is the one by the diamter of 1.5", which I believe is the stock set-up. Honda would not have engineered this, this way, if it were not the case.

However, all the bends, resonators, restricitive mufflers are not taken into account with this equation. This equation is under the assumption of a piece of straight pipe with no bends, restrictions or hinderences in flow. (This means no mufflers, resonators, cats, cush bends or mandrel bends...)

After all this dust settles...The drag point being .4 MACH means the exhaust gases actaully start to back pressure themselves and revert backwards to an extent causing a loss in flow, which creates huge loss in power.

Your 1" exhaust flows over twice the drag limit of that HP with that size diameter exhaust.

In conclusion, I am not stating that a 1.5" stock exhaust is better than a 2.5" or 3" exhaust. Taking some smooth mandrel bends (if necessary, trying to stay as straight as possible), maybe a resonator and a straight through muffler with no restricition; using the knowledge dispelled above, if a larger, more free flowing exhaust is mandated with the use of some other mods (more aggressive cam profile), a 2.5" would yeild more ideal for power and exiting the exhaust gases at a faster rate than that of a 3" with the case of a 200 HP figure.





it's Friday....I feel REAL brain dead now....

 
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I think 2.5 is enought for na.... And 2.5 is loud enough.... When straigh pipe...

If he was to get k pro and get rid of that crappppy ecu, 3 inch exhaust, and get a cai he would get a min of 220+ hp to the wheels with his mods

 
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I already figured out the calculations for an ideal .4 mach

ok, you can run 1.75" exhaust ... I'll run my 3"

 
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this is why I got confused by your formulas.

 
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I created a new thread for the exhaust talk.


Like I said in the other one, respect and don't waste another member's thread.

 
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Sorry Havok. Just wanted to provide some truth to the conversation because there are far too many speculations, internet racers that pollute lots of young minds with half truths and just plain out right lies.

These people need to be educated about the whole truth in the matter. That's what we do....Provide truth, technical data & customer guidence. An educated consumer is the best kind.

 
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Actually, 1.5" would be even better, which is .3705 Mach.