SC Intake setup

Rich Thomson

Registered User
As I have been rebuilding the SC motor out of my 94 I have some thoughts I wanted to throw out there about the intake and supercharger IC setup.

First I wanted to talk about air flow. Air flow through a 2.5" pipe is pretty much constant. Just like our favorite topic of exhaust flow through a mandrel bent vs. compression bent pipe. Air flow is reduced through a compressed pipe.
exhaust_pic2.jpg


If we believe static air flow is reduced when it is compressed by a smaller diameter then we must believe total air flow is also reduced. I use the formula 1mm=8cfm so for a 2.4" pipe the flow is 488cfm.

Now my point here is the SC intake and intercooler system is subject to the same rules. From the MAF to the intake matching air flow is the key to increased HP. Any one point along the air flow tract that restricts the flow of air reduces the overall air flow to the engine. A fact is the M90 Supercharger is capable of moving around 550cfm MAX. 500cfm inlet and 500cfm outlet flow see chart.
m90_1b.gif


Verifying air flow through each part of the intake system is key. On the intake side of the supercharger the Air filter, MAF, throttle body & inlet plenum are all components we need to match. We only need to match components that are capable of flowing 550cfm each. More is OK but less is not. Matching a Pro-M 75mm MAF with a BBK 75mm throttle body is one example of flow matching components. Using a Stock 70mm MAF with a 75mm TB is a mismatch. This will restrict the air flow to the smallest component which is the 70mm MAF with stock center post reduces air flow even more. The only time this mismatch does not affect performance is when there is a greater restriction in the system or your SC air flow is at or below the components air flow capabilities.

Now onto the Intercooler side. I will begin with some numbers. The opening in the outlet side of the SC has about a 3 sq inch area opening. More on MP and S-Model SC setups. The stock SC top has about 1.5" opening for air flow. The raised top offers 2" (see pic) of opening for air flow. Modifying the top to allow increased air flow is possible (see pic). Removing the area from the front side of the neck will allow for about .25" increase. Not ideal since the ID of the nect is only 2.30" So porting the neck can get you upto 2.4" with a 1/8" margin of safety. So the best you could expect from modifying the current MP top is 2.4" of area for air flow.

sctop_silencer.JPG

top_opening.JPG


Using the stock IC tubes and expecting anything close to 2.4" is not going to happen. The average ID is anywhere from 2-2.25". Extrude hone IC tubes I have seen but for the $$ you are better off spending it on a custom setup. More on the custom IC later.

The next point I want to discuss is the intake pluenum (outlet plenum) which bolts to the intake and delivers air to the intake. The stock part is the least restrictive part in the IC system. The flange where the IC tubes bolts to is about 2.3" ID and the opening to the intake is equilvant to a 2.75" opening. Mild porting and you have a good flowing part. The last part I wanted on comment on is the intake itself. Intake gasket matching and porting of the outlet plenum area is a big key to better air flow. The intake has a center triangle which can be removed to increase plenum volume by 4sq inches and increase air volicity when pressurizing the intake under boost. Also porting the opening to unshroud the air flow to the #3 cylinder is another important point when increasing air flow.
intake-bottom.JPG

intake-pic5.JPG


Rich
 
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Rich:

You may be ovesimplifying the situation. There are other things to consider. For example, although the minimum radius is an issue for flow, how the plumbing transitions to and/or from that minimum can be more important. The pictures that you show of the compressed bend I'll admit would most-likely cause a flow restriction. But that depends on the CFM you're looking to push through it. This sounds like it's going to be a fun discussion.

John
 
We only need to match components that are capable of flowing 550cfm each

Rich,

I'm guessing that the 550 CFMs you mention assumes that you don't exceed the M90 speed rating. I'm overdriving mine about 23% and reving the engine to around 6200 rpms before shifting. I don't remember the rpms, but I think it's turning over 21,000. How many CFMs would mine be moving ?

David
 
jpetillo said:
Rich:

You may be ovesimplifying the situation. There are other things to consider. For example, although the minimum radius is an issue for flow, how the plumbing transitions to and/or from that minimum can be more important. The pictures that you show of the compressed bend I'll admit would most-likely cause a flow restriction. But that depends on the CFM you're looking to push through it. This sounds like it's going to be a fun discussion.

John

Flow through transitions does affect total flow ability. Choices should be kept to smooth transitions and avoid hoses or pipes that have ridges inside that upset the laminar flow of the air.
 
silly

This may be a silly question, but would the air flow benefit from like "rifiling" the inside of the intercooler tubes, like the barrell of a gun so it actually helps control the turbulence. Or would that be a waste of time and effort? :confused:
 
David Neibert said:
Rich,

I'm guessing that the 550 CFMs you mention assumes that you don't exceed the M90 speed rating. I'm overdriving mine about 23% and reving the engine to around 6200 rpms before shifting. I don't remember the rpms, but I think it's turning over 21,000. How many CFMs would mine be moving ?

David

According to the chart which your speed takes it way off of I calculated 940cfm of air being pushed. In theory. Actual flow will be affected by the inlet and outlet air temps of the SC. Not to mention bearing failure. :cool:

Higher SC rpm is really bad. With 15psi of boost the outlet air temp jumps to around 240 degrees at 4,000 rpms then at 16,000 rpms the air temp takes off to 280 degrees then at 20,000 rpm its well over 325 degrees.
m90_1c.gif


The HP it takes to spin the SC at 20,000rpm can be 100hp.
m90_1d.gif


Running 14,000 rpm which is within the limits of save SC operation you can expect 600 cfm of air being moved.
 
M90TAURUS: Rifiling on the inside off the IC tubes would create turbulence
and I beleive hinder air flow.But the a blower with screw rotors are more
efficient than straight rotors.This is for a blower or turbo set up.A motor
with a carburator has differrent rules,your rifiling may apply here.

And in some cases straight ridges or air vains can be use to make air
flow more laminar .When you have obstacles in the air flow path such
as a valve guide or valve stem.

When you have a straight tube.You may flow more CFM.But this is not
what you allways want for max perfomance.Some time you need to
reduce the diameter of a tube or port to bring up velocity of air
for max performance.

I guess the point that I am trying to say is .When porting or trying to
improve air flow. Sometimes known air flow rules are not set in concrete.
To do a write up on air flow characteristics.And cover all of the variables.
Would eat up all of Georges MB on his server.

RANDY
 
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Randy N Connie said:
When you have a straight tube.You may flow more CFM.But this is not
what you allways want for max perfomance.Some time you need to
reduce the diameter of a tube or port to bring up velocity of air
for max performance.
RANDY

My flow figures show a 2.5" exhaust pipe at 600 cfm flows 300 FPS while a 2.75" flows at 247 FPS while a 3" flows 195 FPS. Which is better depends on the amount of air the engine uses each cycle. My intercooler system is being made out of thick walled 2.5" ID aluminum tubing with a 3" OD. My optimum choice was 2.75" ID for that amount of air volume. With 14.7 PSI of pressure the 2.5" pipe will restrict the air flow. Not enough to for me to change it now. Since my IC will have 2.38" ID openings it should match up nicely.
18inchic-sameside.jpg
 
Rich: Your right on with the 2.750,And I beleive this is a starting point even with
a stock cam & valves with all the boltons.The 2.5OD is just to small.I would really like to buy
this popular FMIC that is being sold.But I just see it still to restrictive.
With the 2.5 OD tube .Then with the even smaller ID nipple that hooks
to the plenum.About the max that the stock lower IC tube and plenum
can be ported is 2.650 at the largest points.And be safe to not crack in
two.

The biggest benefit I see with the other FMIC with 2.5" OD outlet is that the
charge is cooler. Not so much as an increase in flow.The stock tube and
plenums that I have measured are from 2.395 to 2.400 ID .This is not much
of an increase over stock when useing a 2.5 OD.I do not know the wall
thickness of the tubes used on the MP FMIC.But counting the wall thickness
of the tubes it can't be much more than stock if any.

Now I like the looks of you intercooler and the MP FMIC.But I beleive
that the routing of the MP FMIC tubing has a lot to be desired.I
think that if the blower hat was raised and turn to 220 degrees. And
run the blower IC tube a straighter shot to the IC on the passenger side.
And the intake manifold plenum IC tube ran as straight as possible to
the plenum would be a great help in reducing pressure drop.This is
kind of nitpicking number wise, but a help.Unless you don't want to
say,how are you planning to route your IC tubes.

Since we are talking supercharger application ,we should not leave out
the plenum effect,of stored air charge when sizing IDs.But I don't want
jump to far ahead in this discussion,But when crunching numbers for
the best flow.You need to match port flow,valve size,cam size,bore
length.bore diameter, plenum size.This is all to much for my little brain,
So in the past 15+ years I have allways relied on a computer program.
To match up the bore,stroke,CFMs To get a proper cam size.

RANDY
 
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By changing a few parts and checking dimentions the location is revealed.
Below is a picture of where the upper and lower IC tubes will run. The pipes shown are 3" OD. My final setup will be 2.5" ID with 3" OD. So the 3" exhaust tubing works great for mock up. The Upper IC support will have to be cut but no problem using a cut-off disc. I have the stock lower tube in the picture to show where the origional runs vs the new route. The key is to replace the power steering dip stick with a NA dipstick. Low Profile. Allow for the needed space to run both IC tubes on top of each other. Tubing and silicon hose bends are all that is needed. I will have better pictures after the parts arrive next week.
IC-routing.JPG
 
Rich Thomson said:
Flow through transitions does affect total flow ability. Choices should be kept to smooth transitions and avoid hoses or pipes that have ridges inside that upset the laminar flow of the air.


Rich:

On the issue of laminar flow and roughened or rifled surfaces, laminar flow isn't necessarily the best thing, not it ot goes al the way to the walls. With laminar flow comes a boundary layer up against the walls of the tube. The velocity near the surface is slow and goes to zero at the wall. With the right surface texturing, you can create turbulence just at the outer edge and break the boundary layer, and improve flow overall. The flow is still pretty much laminar in the middle of the tube, which is what you want, but not drawn back by the wall.

Randy mentioned that air flow rules are not cast in concrete. Well, the rules are cast in concrete, but how to get the system to do what it needs to to take advantage of those rules is not. Then getting the system to do what you want across a wide range of operating parameters is also not easily done.

I need to come back when I have time and read and think about the comments in this thread. It's a good one.

John
 
jpetillo:I said, the KNOWN rule are not set in concrete.Meaning there
is more that can be learned.

Rich have you given any thought of using ,Spintech oval tubing.

Randy
 
Randy N Connie said:
I said, the KNOWN rule are not set in concrete.Meaning there is more that can be learned.

Randy, agreed, there's always more that can be learned, and the rules will always change.

If we're talking about just flowing air through pipes and plumbing, that's pretty much known, and is an easy one for computers - sometimes hard for our heads. But when you need to also get that air into an engine and flowing just right, then even our computer codes have a hard time predicting that.

Either way you slice it, I agree with your statement.

John
 
Rich,

Why are you going with 1/4" wall tubing ? That sounds extremly heavy and the greater mass will also absorb more heat. Most IC tubes I've seen are only .065 wall.

David
 
Engine Air Flow Requirements

For a SC running a single-plane manifold, you only need an induction system 110% to 130% larger. SC's engine's with higher lift cams, and/or supercharger, require tighter control of the fuel air mixture, and higher velocity to keep the extra fuel it needs fully atomized.

So the question is how much air a supercharged 231 ci engine draws at 6000 RPM? Well, one cubic foot is equal to 1728 cubic inches. We need to factor in an item called Volumetric Efficiency (VE). VE is how much air the engine can actually pull in, compared to its displacement. Most SC engines running 500 lift or higher roller camshafts and single plane intake manifolds have a VE of about 110%-120%. With some race engines capable of 150%-170% VE.
For a 231, it takes two revolutions of the crankshaft to pull 231 cubic inches of air at 100% VE. A four-stroke engine pulls half its total air needs for each time it turns over.

(231 cubic inches (ci)) / (2 revolutions) = 115.5 ci of air per revolution
(115.5 ci per rev) x (6000 revolutions per minute) = 693,000 ci per minute
(693,000 cim) / (1728 ci per cubic foot) = 401 cfm


Multiply the cfm of 401 by the appropiate VE.

401 cfm x 1.20 VE = 481 cfm

With the SC single-plane intake manifold multiply this by 110% and 120% to come up with a cfm range.

1.10 x 401 cfm = 441 cfm
1.20 x 401 cfm = 481 cfm


So, a SC 231 engine running at 6000 RPM red line, needs between 441 cfm to 481 cfm. A typical race engine has 150%-170% VE which uses 601 cfm to 682 cfm.
 
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David Neibert said:
Rich,

Why are you going with 1/4" wall tubing ? That sounds extremly heavy and the greater mass will also absorb more heat. Most IC tubes I've seen are only .065 wall.

David

Aluminum tubing I purchased from Online Metals. They only offered the .25" wall tubing. I would have liked to get 2.5" ID and 2.75" OD but it was not available. The aluminum does not hold heat like steel so it should work. Plus aluminum with a 1/16" wall would deform with clamps.
 
jpetillo said:
Rich:

On the issue of laminar flow and roughened or rifled surfaces, laminar flow isn't necessarily the best thing, not it ot goes al the way to the walls. With laminar flow comes a boundary layer up against the walls of the tube. The velocity near the surface is slow and goes to zero at the wall. With the right surface texturing, you can create turbulence just at the outer edge and break the boundary layer, and improve flow overall. The flow is still pretty much laminar in the middle of the tube, which is what you want, but not drawn back by the wall.

Randy mentioned that air flow rules are not cast in concrete. Well, the rules are cast in concrete, but how to get the system to do what it needs to to take advantage of those rules is not. Then getting the system to do what you want across a wide range of operating parameters is also not easily done.

I need to come back when I have time and read and think about the comments in this thread. It's a good one.

John

Laminar flow is not a concern on the IC side. Just keeping the pipe open enough to allow the needed air to be forced through. Laminar flow is more important on the Inlet Plenum Side. One thing I did do to my 75mm throttle body to help the laminar flow was to port the back side of the casting to allow better laminar flow to the inlet plenum.
tb-porting.JPG
 
JPETILLO (quote)
But when you need to also get that air into an engine and flowing just right, then even our computer codes have a hard time predicting that.

Yes a computer can predict this.This is why you need to flow test each part or each port.
& then combination of parts together.to test for pressure drops. And then enter the numbers to be to be added up.

mathematic formulas are in concrete,but flow testing is a guessing game.
About the only way to get close to real world flow numbers.Is to put a
engine block on a flow bench with all the intake parts assembled.AND
NO part in side of the engine,AND with the oil pan off ,or even better
cut the bottom of the block off to the bottom of the cylinders.With no
pistons,etc.Then bolt to the bench.The motor that I used to do you cannot
do this,they have no oil pan.But I have cylnders that would set in a
fixture on the bench to do this type mock up to flow test with most
intake parts together.To mimic an assembled motor
This is about the only way that I would know to get close to a
accurate flow numbers.

RANDY
 
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Randy N Connie said:
Rich: Have you made any head way on your project?

Thanks RANDY

Waiting on the Spearco intercooler parts. Engine still on the stand.

I am working on the exhaust setup now. The Kooks downtubes do not fit the headers. The pipe bends are way off.

kooks-downpipes-pic2.JPG
 
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