marco, intake manifold question

[Audi_CQ]

Originally posted by The Spanish
Great car Mate.

I am very interested on your rear brakes setup.
How did you get the RS2 hubs to fit to the rear?
I have been thinking a lot about it.

I also have RS2 wheels front and back, but only RS2 hubs front.
My temporary solution for the rear is using H&R adaptors from AUDI to PORSCHE wheels.
Info here: http://www.s2forum.com/forum/showthr...&threadid=1871

Can you give me info on this please?

Rafael

Hi Rafael,

Here are a couple of photos of the modified hub. It's machined out to accept an RS2 wheelbearing, and have been added with a ring of metal so outside diameter is same as RS2 hub. It's also been machined to make a flat surface to attach the RS2 "backplate" to. Here you must measure the distance from bearing to surface on the RS2 hub and make the same distance from bearing to machined surface on the S2 hub. (Did that make sence to anybody but me ) A bit difficult to explain, but hope the pictures gives an idea of what have to be done.
NB! The calippers have to be in the S2 position and not as on the RS2. Because of this you have to move the bleeding to the other end of the calippers.

Cheers,
Roger

[Pisobiker]

Originally posted by Mark Halligan
Tom,
yeah does look a bit weird doesnt it, I finally found the post I saw it on in Kruemmer, message # 887. Just want to know if I have got it right in my head and if it would work to any advantage?
Tempted to build something different .

Cheers,

Mark.

Uhmmm, strange layout Mark.
I've never seen something like that (which actually doesn't mean it doesn't exist and doesn't work.... ).
Anyway my first thought is it will create some significant pressure drop because of highly increased turbulances and flow restrictions. My guess here is the internal pipe with all those holes will disrupt flow thus "killing" the kinetic factor and allowing an even distribution of pressures in the outer pipe.
This might be fine if running a cold side capable of very high pressure ratios, significantly exceeding the ones actually usable by the engine at any rpm, so that the eventual increase in pressure drop is compensated by cold side performances.

Apart form this, from the little I can remeber of my generical "Dinamic of fluids" lessons, I think the most important rule to bear in mind when playing with pipe dimensions is:

apart from drag dissipation through ducting walls we can simplify the law saying

TOTAL ENERGY OF FLOW THROUGH EACH DUCTING SECTION REMAINS CONSTANT

Total energy is the sum of:

"KINETIC" (related to speed of flow)
"PRESSURE"
"POTENTIAL" (don't know if this latter is correct in english, but anyway it relates to eventual "height" changes of flow mass through the ducting).

The latter we can actually don't care about and assume constant, being height changes and charge specific weight and density very small.


All this leads to saying:

1) IF YOU INCREASE DUCT DIAMETER THUS DECREASING FLOW SPEED, THEN PRESSURE INCREASES, and VICE-VERSA.

2) IF DRAG DISSIPATES FLOW ENERGY, THEREFORE ACTING LIKE A DIMINISHING OF PIPE SECTION, TO COMPENSATE FOR THIS DISSIPATION PIPE SHOULD PROGRESSIVELY INCREASE IT'S DIAMETER IN ORDER TO KEEP FLOW PRESSURE CONSTANT.


On next post I'll try to give my interpretation of this phenomenon applyed on our IMs.



Marco

[Pisobiker]

Looking at the drawing attached lets say:


RESULTS:

1) Each time plenum intercepts a runner actual total flowing cross sectional area
is increased of the runner area;

2) pressure from "A" to "B" increases while velocity of flow decreases;

3) pressure in "2" is higher than in "1"

4) if max boost before knock occurs is say 1.8 bar you than will have to decrease overall boost accordingly to have at "5" 1.8 bar, therefore very likely having only about 1.6 bar at "1"

5) Your average boost limit will therefore be ~1.7 instead of 1.8 which leads to about 3.6% less flow...... (on a 500 hp engine this is 18 Hp)

6) while running same injector duty cycles among the runners, if average A/F ratio at WOT is say 12.5 and given this is a good average A/F ratio, only "3" will actually work at this AFR while "2" and "1" will work progressively richer and "4" and "5" leaner (with all the temperatures, fuel consumption and power output related issues).

[Pisobiker]

So, modding IM in a similar way as the attached drowing shows we have:


RESULTS:

1) Each time plenum intercepts a runner its section decreases accordingly to have constant flowing cross sectional area;

2) pressure from "A" to "B" remains constant;

3) pressure in "2" = pressure in "1"

4) if max boost before knock occurs is say 1.8 bar you can have each runner work at 1.8 bar;

5) Your power output is optimized;

6) Your A/F ratio among the cylinders is optimized.

[Pisobiker]

BUT


This is an IDEAL case where dissipating forces on the walls and turbulances along the plenum are not taken into account.

In REAL world those dissipating forces, and for example turbulances on runner entryes, will restrict flow, messing things up.

[Pisobiker]

So, to avoid some of those turbulances and to compensate for flow reduction of the ones not avoidable, it is then necessary to both act on the runners entry layout, and plenum tapering (decreasing taper)

[Pisobiker]

All this is of course anything but easy to obtain having many factors influencing not only pressures among the runners but also flow among them:

1) Pressures:

Layout and dimensioning of plenum (volume, lenght and taper) will be influenced by flow speed (drag increases with the square of velocity) and also it's density (a denser charge will cause more drag dissipation).
This means if you optimize plenum for lets say 16500 liters/min (which corresponds to 2 bar boost @ 5000 rpm on a 2.2L engine with 100% VE), if you change any parameter (boost, rpm, engine displacement, VE) your optimezed IM layout will change.


2) Flow:

Flow, therefore VE of each cylinder depends on "porting"of both intake and exhaust and also EM runners layout.
If any of the above mentioned parameters are uniqual among the cylinders, theyr specific VE will be different.

So, even if you have designed a IM capable of allowing perfectly balanced pressures inside each intake runner, actual flow (thus amount of charge) entering cylinders will not be the same thus needing at least separateand optimized fuel delivery for each of the cylinders accordingly to have the correct AFR (therefore all the consequent EGT and knock issues optimized as well).



Hope all this does not discourage any of our great DIY tuners here in the forum. Just wanted to point out, if what I know of the subject is correct, all the parameters and phenomenon involved.
Making an excellent IM isn't impossible, but of course needs some extensive testing.



Marco

[S2 Ant]

Marco do you actually have a job during the daytime?!!?!?

All very interesting stuff tho!!

[Pisobiker]

yeah, I do. But having mostly managerial and supervising functions I still can handle some thecnical talking....


Marco

[Doug_RS2]

Nice explanation Marco

Now - what are the internals of the standard IMs like - ABY, ADU, 3B???

[Mark Halligan]

Marco,

thanks, great answer .

Mark.

[timucin]

hmmmmm

may be i should get one from mtm

[Doug_RS2]

Originally posted by timucin
may be i should get one from mtm

It might be better to see if the MTM is designed with a tapered main body - and takes into account Marcos theories on design - anyone know?

[Audi_CQ]

Marco : Nice
The bigger the plenum the less % difference, right? (open runners = infinite plenum = no difference )

Big plenum with a small taper (~50cm2 -> ~35-40cm2) = OK? (Hope so, because thats what mine's like )

Roger

[Stick Insect]

Originally posted by Pisobiker


yeah, I do. But having mostly managerial and supervising functions I still can handle some thecnical talking....


Marco

Marco, What is your occupation?

David