What is your all time favorite vw engine? no 8valves haha

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fredobd said:
wouldn't oversixing the exhaust slow down the exhaust thus making the turbo spool at a higher RPM?

The way I see it is this: the amount of ''air'' that comes out of the exhaust is independent from the size of the xhaust. So, smaller exhaust = faster ''air'' speed through to the exhaust = faster/earlier spool... :dunno:

I'm just curious as to know the ''mechanics'' of it..



And to answer the question, Any n/a with high displacement, take a pic! V10TDI probably or W16!! :D
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what you fail to see is that the exhaust gas is expanding once it leaves the turbine, so the more room it has to expand, the quicker it can go across the turbine... this is why a k03 on 3" DP tends to overspool and makes boost control difficult throwing CEL's and whatnot, this is what affects the spool directly, not really the velocity of the exhaust as this is a function of volume AFTER it has crossed the turbine

your theory that the "amount of air" being independant from the exhaust volume is not totally incorrect as this statement implies mass air flow, but the velocity of the air is not an abolute indicator of efficiency, allow me to explain

you want the pressure differential between the manifold and the exhaust to be as great as it can be, this is accomplished by increasing the exhaust system volume, thus the velocity of the exiting air is directly affected by its volume, but you are not looking to increase said velocity thru the tailpipe, but across the turbine wheel...

if the exhaust volume is too small, it will increase the exhaust velocity at the tailpipe but also increase the pressure making it harder to pass from the manifold (under great pressure) to the exhaust (the smaller one having more pressure). this means the turbine wheel does not get all the energy from the gases due to increased temps and pressure in the manifold, rather it is lost in the form of heat thru the manifold piping, making a less efficient system with overall less power, this can also lead to reversion if the exhaust pressure is so great as to impede the passing of the exhaust thru the turbine forcing the gas back into the combustion chamber

it is only desirable to keep the exhaust velocity greater in the exhaust manifold so it will transfer more energy to the turbine wheel, as long as there is not so much heat, pressure, and/or ultimately reversion as to harm performance

i hope this helps you out freddyboy, fabio... danther is abolutely correct

and to answer the Q, G60 and 16v's ftw, the shittiest motors that require the most love are my fav's, heh, maybe this is why i can put up with high-maintenance woman, or not, lol
 
i am straight 3'' with a 3DP and it's not spooling faster then a stock exhaust... but when i was open headers it was spooling way faster!
 
Rocc and Rado said:
what you fail to see is that the exhaust gas is expanding once it leaves the turbine, so the more room it has to expand, the quicker it can go across the turbine... this is why a k03 on 3" DP tends to overspool and makes boost control difficult throwing CEL's and whatnot, this is what affects the spool directly, not really the velocity of the exhaust as this is a function of volume AFTER it has crossed the turbine

your theory that the "amount of air" being independant from the exhaust volume is not totally incorrect as this statement implies mass air flow, but the velocity of the air is not an abolute indicator of efficiency, allow me to explain

you want the pressure differential between the manifold and the exhaust to be as great as it can be, this is accomplished by increasing the exhaust system volume, thus the velocity of the exiting air is directly affected by its volume, but you are not looking to increase said velocity thru the tailpipe, but across the turbine wheel...

if the exhaust volume is too small, it will increase the exhaust velocity at the tailpipe but also increase the pressure making it harder to pass from the manifold (under great pressure) to the exhaust (the smaller one having more pressure). this means the turbine wheel does not get all the energy from the gases due to increased temps and pressure in the manifold, rather it is lost in the form of heat thru the manifold piping, making a less efficient system with overall less power, this can also lead to reversion if the exhaust pressure is so great as to impede the passing of the exhaust thru the turbine forcing the gas back into the combustion chamber

it is only desirable to keep the exhaust velocity greater in the exhaust manifold so it will transfer more energy to the turbine wheel, as long as there is not so much heat, pressure, and/or ultimately reversion as to harm performance

i hope this helps you out freddyboy, fabio... danther is abolutely correct

and to answer the Q, G60 and 16v's ftw, the shittiest motors that require the most love are my fav's, heh, maybe this is why i can put up with high-maintenance woman, or not, lol
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Leo, I concur completely but you omit too many factors in the hopes of furthering your argument... However, I will save it for another sleepless night in Connecticut... hahahahaha.... By your same token of logic, you are using a "debit volume" theory, could we not bump it up a notch and say that 3.5" is even better, heck, why not 4"? Though I agree with bigger being better, I must say that optimal sizing for a K03 is 2.5"

Think about pressure, flow dynamics, flow efficiency and many other factors... But hey this is a forum, not important. Our discussion would be lost on 95% of the masses.... PM me....
 
Nay, hide not this wondrous discussion from trolling eyes!

The 2.5 vs. 3.0 debate is one that's been very interesting to me over the last few months, and I've been reading up on it as much as possible. Take my 2.0T for example. Though it uses a K03s, the very same debate is going on. Companies like AWE, Neuspeed, Supersprint, etc. made their TBE a 2.5, while others like APR, Eurojet etc. made it a 3.0. The blanket statement from AWE is that though a 3.0 should in theory increase up top power, the increase is minimal to the point of not being worth the loss of down-low torque. Eurojet argues back that the car has loads of torque as it it, and needs all the higher end help it can get. I agree with this statement, but if the net result is that I'm losing noticeable torque down low for a tiny amount of top end power I will never notice or feel, it isn't worth it.

There are valid arguments from both sides of the fence, and it's hard to dismiss any of them really. The only way to truly settle this is to have the same car run back to back dynos in as near to identical as possible conditions equipped with a 2.5, 2.75, and then 3.0.

/sigh
 
thanx for the theory Leo! we<re definetly lacking good informative posts like that and have WAAAAYYYY too many <<full force sandro bit ftw>> threads! :bigup:
 
MarvinDaMartian said:
Leo, I concur completely but you omit too many factors in the hopes of furthering your argument... However, I will save it for another sleepless night in Connecticut... hahahahaha.... By your same token of logic, you are using a "debit volume" theory, could we not bump it up a notch and say that 3.5" is even better, heck, why not 4"? Though I agree with bigger being better, I must say that optimal sizing for a K03 is 2.5"

Think about pressure, flow dynamics, flow efficiency and many other factors... But hey this is a forum, not important. Our discussion would be lost on 95% of the masses.... PM me....
Click to expand...

why do i always picture you wearing a tophat and monocle everytime you post, heh?

i could tell you another guy i met on another forum that has a drag rado uses a 4" uppipe through the hood, theoretically less restriction, more volume is always better, of course there are other factors, like he was using a much larger turbo and pushing much more mass flow through the system, but i was just trying to discuss the basic physical thermodynamic properties to fred and anyone who displays a curiosity in the subject because he theorized that a smaller exhaust would expel gases faster decreasing lag or spool threshhold, either way...

other factors such as exit turbulance, noise level, design restrictions such as passing a 3" pipe over the back axle (for the oldschoolers), overspool/boost control, etc, all play a role. This is what engineering is about, maximizing as many conditions possible according to function/goal. there is a point and i agree, where going bigger cannot be justified due to gains becoming exponentially minimal and increasing difficulty of fabrication (ex: 4" pipe k03)

i'll still adorn the "bigger is better" robe on this subject though, within reason at least... practically, in this particular case, a larger exhaust does not really harm anything (so long as you have the boost control in check) and makes for upgrades to a BT much less demanding... why build a 2.5" SS exhaust if you think there might be a possibility of upgrading to a BT that will require at least a 3" in the future?

if engineers built everything to spec without compensating for extra forces this world would crumble... imagine your injectors going static just because you chipped your car, wouldn't that be a biatch? why subject your exhaust to the same woes when performance is the primary objective?
 
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