XR4Ti Archived Tech Articles

    Intake Porting? - A collection of posts and off-list emails about the act of porting and the theory behind porting the upper and lower intakes on the 2.3 turbo engine.

Post Date:    Thu, 21 Mar 2002
Subject:      Re: Pictures of a split intake
List:         imon@lists.merkurowners.org

I have posted images of a cut-open upper intake and the porting, knife-
edging and blending work I did to the upper portion of the webbing 
inside the intake manifold.  [Go to the Picture Page portion of the
MerkurTech.com web page]

For those curious on how I cut it open, I carefully measured the location of 
the webbing in reference to the upper opening, so I knew how far down to cut. 
Then I took a very large hose clamp and tightened it around the intake 
manifold to provide a guide for the blade in the proper place.  Then I began 
hacksawing away.  I used a 18 tooth per inch hack saw blade.  I would have 
probably used the 14 tooth per inch blade, but I didn't have one handy.

the position of the cutting guide (hose clamp)

Position of the cutting guide (hose clamp)

It took me about an hour to cut the intake in two.  This was being very 
careful to make the cut as straight as possible.  It wasn't too difficult of 
a task.

hacksaw midway through the cut

Hacksaw midway through the cut


Post Date:    Thu, 21 Mar 2002
Subject:      Re: Pictures of a split intake
List:         imon@lists.merkurowners.org

> You're going about it differently than most, Chris.
> Most people completely remove the division 
> in the upper intake and then knife edge the 
> lower to distribute the air. 

Yes, there's not doubt that most gut the upper and knife edge the lower.  
I remember Rick Byrnes preaching about the importance of runner length for 
low end torque in turbo applications.  Godfrey reminded me of this.

Here's a possible theory on why gutting the upper and knife edging the 
lower is more popular than the way I've tried it.  You don't have to cut 
anything open to knife edge the lower.  I don't what method people are 
using to gut the upper, but I think it could be done fairly easily without 
cutting the intake open like I had to do, or chose to do, depending on your 
perspective.  Opening it allowed me to make the knife edging easier to do 
properly and cleanly.

Here's what is elegant about Don's method (or whomever did it first - 
Slocum?  Schlitz?).  It's a good compromise between maintaining runner 
length and gutting the upper.  I also like the way the knife edging looks 
on Don's lower.  It looks much neater in comparison to how knife edging of 
four runners in a square looks.  Of course the air doesn't care about looks.

Don just had to connect two tangent lines between the circles.  I had to 
make the runners more square at the top so I could get the edge between 
them.  This is somewhat apparent in the Phase 2 pictures.


Post Date:    Fri, 22 Mar 2002
Subject:      Re: Pictures of a split intake
List:         imon@lists.merkurowners.org

>  The benefit to gutting the upper has been postulated as the creation of
>  a plenum approximating one cylinder's swept volume, within the upper
>  intake, not any benefit to airflow by reducing restrictions.

I'm aware of that theory.  Not really all that up on it, as I haven't read 
much about it, if anything, other than lists.  It's a good theory, 
certainly, just not the one I was focused on.

>  But your design can not take
>  advantage of this effect, if in fact, it does exist.

Very true, but that wasn't the goal.

>  The knife edged lower is theoretically not the best solution, but it is
>  so obvious that most people just do it anyway to remove the square edges
>  of the stock lower intake. A better shape for airflow would be a rounded
>  cross section.

The intake is still open out in the garage.  What's the recommended ideal 
radius for the rounded cross section?  If I have enough material left I 
should be able to round it off, at least a little.

Intuitively I didn't like the knife edging as I was doing it.  I had 
absolutely nothing to base my dislike on as I was doing it, so I went with 
what other people had done and it had worked (the knife edging itself, not 
the location of the knife edging).

As I looked over the stock runners and their webbing, I knew the factory, 
who made a big nasty mess of the casting right around the openings of 2 and 
3, probably rounded off the webbing for some reason.  That was the basis for 
my intuition.

>  If your objective is more low end torque, then simple comparison with
>  some of the best torque intakes, 5.0 EFI HO, the low speed portion of
>  the SHO engine, etc. will quickly lead you to determine that a low rpm
>  torque benefitting manifold cannot be created out of the stock 2.3 T EFI
>  intake casting, due to it's smallish size.

>  So just what are you trying to accomplish here?

I wasn't trying to create more low end torque certainly.  I was trying to 
prevent the (theoretical) loss of low end torque.  What would reduce low 
end torque?  My understanding is that gutting the intake will reduce low 
end torque.  That's what my general understanding of torque vs hp (re: dual 
SHO runners), and discussions on the various lists have led me to believe.

Accomplish?  Well, the Phase 1 image doesn't show it all that well, but the 
openings  all the runners, particularly 2 and 3 were a mess.  The top 
runners had big flanges of casting flash, or what ever it's called, right 
at the lip around 110 of the opening.  I wanted to get rid of all the mess 
in the area, which is exactly what I did.  And while I was in there I 
decided to do the other work.  It's not shown in the pictures, since this 
was all about the webbing, but I also cut off the nubs (back halves of the 
throttle cable mounting bosses)  in the top half of the upper.  I did one 
of them while intake was closed, but opening it made the second, much 
larger nub easier to remove.

> And once boost is present,
> then any resonant tuning is irrelevant.

My understanding is that runner length is important while under boost as 
well.  At least this is what I've gleaned from Byrnes' post on the subject.  
Perhaps my understanding is not accurate, but I had to pick some 
theory/premise to do my work under the guidelines of.


Post Date:    Sun, 24 Mar 2002
Subject:      2.3 intake manifolds
List:         imon@lists.merkurowners.org

A definitive post on the subject by David Godfrey

The thread on porting 2.3 intakes has been of interest since I have done 
so many. Please allow me to share some thoughts on this topic.

What is really going on here is an attempt to optimize various principles 
of Bernoulli's law, Helmholtz effect or inertia supercharging, and the 
whiz-bang natures of turbos within the design constraints dealt us by Ford 
when they made the manifolds. Since engineering is really the art of 
compromise one needs to consider what the end result really needs to be. 
Both the upper and lower manifolds have some short comings when viewed 
from a performance perspective. Some of these short comings can be easily 
dealt with, others are more trouble.

When designing the intake manifolds Ford used an approach of necking down 
the upstream port to make sure that regardless of core shift or 
manufacturing tolerances there was not an edge protruding into the air 
stream when mated with the next part of the motor. To accomplish this they 
necked down the runners at the base of the upper and lower intake a couple
of inches before the gasket surface. Other areas of compromise are the 
runner junction in the upper manifold and relief for injectors on runners 
2 & 3 of the lower manifold as well as the 'dog leg" bends in these same 
runners. Note that if the only mod one is doing is porting the intake 
manifold the whole effort is really a waste of time. However, a ported 
intake as part of a system is very beneficial.

fitting the template to the lower intake manifold

Fitting the template to the lower intake manifold

the template from the lower intake juxtaposed over the outlet of the upper intake

The template from the lower intake juxtaposed over the outlet of the 
upper intake - template off center to show size difference.

What to do with the upper intake has been the point of much debate lately. 
There is a nasty golf ball size knob in the upper intake where the runners 
merge. This is what Ford did to provide an adequate transition from the 
plenum to the runners that, after the manifold was cast, did not require 
further manufacturing operations. This transition has to occur somewhere. 
If you gut the upper manifold and turn it into an open plenum the runner 
junction moves to the lower intake.  

Runner length can effect what the torque curve looks like. The current 
motor philosophy of 4 valve heads and  variable runner length simply are 
not an option on the 2.3. The die was cast back in the early 70's when the 
motor was designed as to how much can be done with the intake. Even the 
dual plug head 2.3's have to deal with engineering choices made back then. 
Custom manifolds could provide a different torque curve when off boost, but 
why bother? For more info on this look up inertia supercharging. You will 
see that there is a fairly narrow RPM range where the benefits of optimized 
runner length work for you. Outside of this range other characteristics are 
compromised. Spend you time and effort getting the motor on the turbo 
quickly and forget arguments over runner length. The period of time where 
runner length might play a role in motor performance is so short efforts to 
maximize torque during this brief duration do not provide very much bang for 
the buck.

My view on the length of the runners is, whether you gut the upper intake or 
not, that it does not matter. Until the motors get on boost you are driving 
around a SOHC 2.3 4 cylinder designed in the early 70's Whoopie. 3-4  more 
inches of runner length is not going to dramatically change the performance 
of the motor. Real power is made when the turbo comes in. Those who want 
torque down on the bottom need to get a turbo sized to come in quickly and 
not worry so much about runner length. 

My preference for a motor that will use the upper intake casting is to cut 
the manifold apart, knife edge the junction, and weld it back together. I 
cut the manifold apart so a proper job of knife edging can be done. On a 
motor with a rotated or custom upper intake I knife edge the lower manifold.

There has also been debate wheather to knife edge the junction or radius the 
edges in an attempt to make this area some type of venturi. A venturi is a 
restriction designed to create a pressure drop. The common application of a 
venturi is that of a carburetor barrel where the venturi is used to create a 
pressure drop so that fuel can be siphoned from the booster ventuires or, in 
the case of an annular discharge carb, from the narrow portion of the venturi 
itself. Now I might have read the post incorrectly, but it was implied that 
by rounding the runner junction vs. knife edging a venturi effect could be 
created that would assist in air flow. This is simply not the case. Air 
velocity through a venturi is increased only during the region of the venturi. 
Other wise the velocity remains constant. The goal of porting is to reduce 
restrictions an since by definition a venturi is a restriction it has no 
place in the middle of an intake manifold unless the pressure drop is needed 
to introduce something into the intake. 

In the case of actually porting a manifold it is much more difficult to put a 
radius on an edge than it is to knife edge. Maintaining a consistent radius 
is tough and requires templates to get it right.  I have done both and prefer 
to do the knife edge. If it were advantageous to put a radius on I would use, 
but it is not.

My preference, for a motor that will use the stock upper intake, is to cut the 
manifold apart at the runner junction, knife edge the junction, and weld the 
manifold back together. It takes me 4-6 hours to rework the runner junction. 
It would take the same amount of time to rework the junction at the lower 
intake if the upper intake is gutted. Again, my preference is to not gut the 
upper intake since this is more work to do properly and  when manifold pressure 
gets above 2 bar runner length is not as important as minimizing restrictions.

On motors with a rotated or custom upper manifold I knife edge the junction at 
the lower manifold. Cliff Walton has a motor with a custom upper manifold. The 
upper is an open plenum with the lower runners knife edged. There is no problem 
with lack of torque on this motor. If it were possible to measure the difference 
in off boost torque  on this motor vs. one with a stock upper I doubt if there 
would be any difference. If there were it would be more than offset by how 
quickly the motor comes on boost. I have also been driving my car with the air 
to liquid intercooled upper manifold. There is no problem with off boost torque 
on this motor either. 
On the lower intake I weld up the injector relief pocket on the outside of 
runners 2 & 3. I then make a template of the intake ports at the cylinder head 
and transfer this layout to the lower intake. Do not use the intake gasket for a 
template as the ports in it are grossly oversize. With the head port layout on 
the lower intake you can see how much the runners were necked down. Remove 
material from the ports using an aluminum carbide cutter and finish smoothing 
the ports with cartridge sanding rolls. The bumps into runners 2 and 3 can be 
just about completely removed. Due to the shape of the manifold at this point the 
limiting factor is the placement of the injector. You will probably break into 
the injector o-ring bore. This is OK if you are careful and don't break through 
to much and limit this break through to the engine side of the injector o-ring. 
Using a large diameter cartridge roll clean up the runners where the upper intake 
mates. You don't need to make the ports bigger, just try to make them rounder so 
it is easier to match to the upper intake. Make a template of the lower manifold 
and transfer the pattern to the upper.


Post Date:    Fri, 22 Mar 2002
List:         off-list conversation

From David M. Johnson:

The ideal radius for flow entering a tube from a plenum would be 1 diameter or
greater.  That is, the diameter of the tube.  Obviously, that's not possible
inside the Merkur upper and lower intake manifolds.  If you look at some of the
log designs, they use a horn which achieves this level of radiusing.

You're trading off several factors when you modify your intake.  Opening the
runners increases flow area while the sharper edges increase the inlet
restriction for the tube.  Air velocities in the intake runners are typically
tuned to interact with the pulsing which results from the piston and intake
valve action.  When optimally configured, a ram effect occurs which forces extra
air into the cylinder.  Conversely, it's possible to configure the ram effect
such that flow is impeded rather than helped.  Changes to the runner volume,
friction (roughness), and inlet restrictions will change the intake tuning. 
Changes in engine speed and throttle opening change the rate of pulsing, the air
mass, and the velocity of the flow.

I'm sure that someone on the list is capable of doing the detailed transient CFD
analyses that would be required to analytically determine the answers here. 
Without that, (and perhaps even WITH that) it really comes down to the Edison
approach... build it and bust it.  Changes to the runner configuration will
result in changes in the overall behavior of the engine with peaks and flat
spots moving around.  If everything moves up, then it would be hard to argue
that a mistake has been made.

I'm a little supprised that no one, who commented publicly, mentioned that Don's 
over/under approach manages a nice flow splitting before the turn and
thus prevents the aerodynamically induced preferencing toward the top two
runners (1 and 4?) that I think occurs with the gutted upper and knife-edged
lower.  I'd guess that this approach is the best of all with the possible
exception of extrude honing.  I look forward to all of the dyno results.


Finally, I'll add my comments here about the method I've chosen to use.

I will not be radiusing the tops of the runners.
I will not be removing the webbing in the upper intake.

The ultimate goal is getting the engine on the turbo as fast as possible.
That's where the power in our engine is made.

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Published by Chris Anglin.