Intake pipe theory

[Mike Schmid]

Why is that when you look at many people's setups that they have the turbo outlet to a J pipe of say 2" diameter, the LICP of say 2.5" diameter and then an UICP of 3" diameter?  What I'm getting at here is steadily increasing diameters of pipe size as you progress through the intake tract.

Shouldn't it be the other way around?  Like you have the turbo outlet to a really large diameter J pipe because the air is hot and expanded (even though it is compressed) then you stay large into the LICP because the air is the same, then in the IC you cool the air and it should compress slightly with loss of heat so you exhaust the IC into slightly smaller diameter pipe to keep velocity up?  

In my understanding raising intake velocity raises volumetric efficiency which raises power so shouldn't we be steadily deceasing pipe size in order to steadily increase intake velocity?  

Now granted going from a regular turbo outlet to a 3.5" J pipe would be a bad idea because a step change like that is worse than a smooth but smaller than ideal diameter pipe.  Also, yeah, it's a little hard to fit huge LICP in the car but ideally should diameter not decrease?

[Jovan Ceklaj]

I hate to bring up memories from the past, but it's time to get why-vez on your ass Mike .  Recall that the equation for loss in an (assumed straight for simplicity) pipe is described as follows...

                   H = Fs * (L/D) * (Vs^2)/(2*g)  

where H is the head loss, Fs is friction factor, L is length of pipe, D is diameter, Vs is velocity of fluid and g is the gravitation constant.  Larger D makes losses go down and increased velocity makes the losses go up exponentially.  In contrast, as you said, the volumetric efficiency goes up as it gets faster, so it's a trade off there.

Since a turbo increases volumetric efficiency above 100%, the trade off towards less head loss seems more desireable to me.

Of course, this is all I could come up with off the top of my head, I'm sure someone much more qualified like Kimyee can correct me, or make me look like a fool for leaving that mental dump on your doorstep :wink:

Jovan

[Graeme Shaw]

Head loss?  No wonder you're so annoyed at the spammers!!!  You're not getting any!!


hahaha :laugh:  :laugh:

[Mike Schmid]

AAAHHH WHY-VEZ!!  EEK!

lol  :laugh:  where would we be without him...

But why change the size?  I should really dig out my old textbooks...

That formula still doesn't account for why you'd adjust the size as you go through the intake tract... unless of course more plebian concerns are all that are really at work here, like "well, I had the smaller pipe when I thought 13s would be fast enough, but now I want 11's so this other pipe is larger"  Or something lame like fitment problems.   :roll:

[Mike Schmid]

And on another similar topic... why is IC pipe always round?  Just because pipe stock is round and it's easy to work with?  

I'm thinking with a rectangular or square shape (with rounded corners) you could fit a larger cross section pipe in the engine bay and thus flow more air with less losses.  

If you think it's dumb take a look at the intake manifold, the runners in it are rectangular, same with the exhaust.

[Jovan Ceklaj]

more likely than not, it's more of a fitment issue or possibly just some guy originally put bigger pipes on and said "hey, Dyno says I got more power doing this. Hey everyone! I got more power! do it MY way!!!".  I've never seen any technical papers on DSM intake theory.  Gotta love trial and error.  Where would NASA be without it :wink: .  Keep in mind, there are TONS of factors, so it's impossible to say without writing a paper.

And Graeme, remember that if you increase the length between you and a certain girl and she is traveling at a higher velocity than you, there will definetly be a head loss....er, did I say girl? I meant air flow :roll:

Jovan

[Marty van den Bosch]

round is better than square - turbulence and flow path equidistance and efficiency

Small to large
Turbo outlet is smaller, engine intake is bigger
The idea is to go from matched size to matched size as smoothly as possible without causing excess backpressure but not to be so big as to be inefficient.

The lower your turbo flows, the less air volume you want since you dont want to waste flow filling and maintaining the pipe path with excess volume that could be pushed into the engine.
The higher the flow of turbo installed, the larger  air volume you want since you can fill and choke a smaller path fast and lose boost to backpressure.

The larger you pipe you use, the more air volume. Due to the turbo outlet size and engine intake size, it makes flow-sense to widen from the widest end first and move back to the smaller end

The theory relates to efficeincy.

Just like huge intrecoolers are not always a good thing - it is the right sized onee that counts (loss of heat vs loss of psi)

[Mike Meron]

dont forget the pressure vs flow differences which marty started to touch on.. 15lbs of boost generated by a 14b, feels quick 15 psi by an evo16g feels freakin fast 15psi by a t3/t4 feels like a frieghtrain pulling.
BUT they are all pushing 15 psi... on that trusty autometer

[Mike Schmid]

Which is why I tried to make a distinction between ideal system considerations and practical actual system considerations.  Like I realize the throttle body is larger diameter than the turbo outlet and you don't want big step size changes.  But if I'm talking about ideal systems, and in that system wouldn't you want the intake tract to be ideally be a huge velocity stack, instead of being a backwards velocity stack?

[Mike Schmid]

I guess practically though it's the concern of going from the small turbo outlet to a larger than the UICP transition that keeps us from doing it then?  Thus creating the reverse velocity stack design...

[Marty van den Bosch]

Now if your turbo outlet was bigger than your intake... :shock:

Good times......and yes.....then large to small

Of course a massive intake will require a massive exhaust

[Travis Merrick]

its all if you wanna have lag or not, you could run a a flared 3" jpipe, but when that turbo (im guessing we are all talking about a 14b here)

Well if we are talking about a 14b, you could run a 3" jpipe but then you start getting into lag, cause before any boost starts to get recorded on that little gauge of yours that whole UICP, sidemount and LICP need to get filled with positive air, so its gonna take a little while for that to fill up.  But you also dont wanna run to small of a pipe cause you will lose to much pressure, run into the turbo over working itslef, in a stock sidemount it loses "x" amount of pressure, so if it boosts 15psi really the turbo may be boosting 17psi, but you lose that amount on the way into the head.  If you ran a slower transition pipe like from a 2" to a 2 1/2 to a 3" along the way then you have a quicker fill up time and it doesnt have any harsh changes in size.

Take a piece of paper and make it into a funnel, get another one and make it into a perfect circular tube, now dump water down the whole as if it was perfectly on the nozzle and plugged on one end, the funnel one still has the same size going at the end where the head (tap end being turbo and plugged end being the head) is, but because the funnel is tapered it took alot less time for it to fill up in water or pressurized air.

Now slap a turbo on that has a large turbo outlet, such a t3/t4 and you can fill that non tapered tube quicker.

Hope that meant sense, what I think we forget to start off with Mike-o is what turbo is this being talked about  :wink:

[Mike Schmid]

I think y'all are kinda missing the point though.  Lag is going to be greater with larger piping yes, the 14b has a small outlet yes, but I'm talking ideal system here.  WOT is all I'm talking about so lag is a non issue.  I'm just saying ideally wouldn't you rather have a slightly larger LICP than a slightly larger UICP?  Being that the LICP is full of hot compressed air which should take up more volume than the cool compressed air in the UICP...

[Travis Merrick]

if you have the ideal system yes, but unless you have money to do the turbo, ic and what not then awesome.  But alot of people dont drive these cars at WOT everywhere, so they dont do what your saying or it would be un-driveable.  If your car was WOT all the time than awesome, but back to reality  

[Marty van den Bosch]

Ideally, the pipe matches the intlets/outlets and gradually gets to an apropriate size for the turbo's flow capacity.

Ideally the air should hit the intercooler at a specific velocity and momentum - both too slow and too fast are bad. It wi8ll depend on your flow and pressure as well as IC design to know what is ideal.

I understand your theaory of cold air is smaller than hot air, but there are many other factors involved in this situation.

To put it very simple - yes large to small would compensate for air volume reduction due to cooling, but it also affects other factors like overall back-pressure, friction, sharpness of bends etc.
The LICP is also less length than the UICP - this affects resistance pre-and post IC

Note: This IC is too big for a 14b  :shock:

But may be really sweet for a large turbo (3.5" thick)