New look at a old manifold

Internal view:

Pretty slick, but the upper plenum lacks the butterfly's ...I can see out through the flange where the intake bolts to the head. Won't this be a problem with excessive air going through?

On top of the spacer shown in the first pic fits the fuel injection throttle body, that contains the butterflys for the whole manifold (both upper and lower) they control the overall air flow into the engine.

The manifold butterflys only control the amount of air going to the lower half of the manifold thus controling the airspeed through the ports but not the overall volume.

It works like this: below 3000rpm manifold butterflys are shut, air only flows through the upper manifold controlled by the throttle body and so only 1/2 the port area is used causing the air to flow very quickly through the ports.

Above 3000rpm that would be too restrictive so then the manifold butterflys open and allow the full area of the ports to function, (that's both the upper and lower parts of the manifold), slowing the port flow but increasing it's volume up to the limit set by the throttle body.

This is completely different to the way Offenhauser intended the manifold to function but they had designed it for a carburettor, with the primaries feeding the lower section and the secondaries feeding the upper section of the manifold.

That just doesn't work out with multi point fuel injection and also the downleg they cast into the plenum to take the primaries down through the upper part of the manifold to feed the lower section was appallingly restrictive to the secondary flow to the 4 front cylinders therefore causing a ton of distribution problems.

The mods i made removed the restriction to the 4 front cylinders and allow separate control of airflow to the upper/lower sections.

Looking at it you could probably still use a carb on a Offy Dual port modified in this way, but with MPFI there is no doubt about any fuel distribution issues.

Gotcha, your work looks nice. Clever idea, you may have the best of both worlds or a tuning nightmare. Keep us informed of how this plays out. Do you plan to pop the lower butterflies open, or probably open progressively? Thanks for posting. Bill 1362

Type of throttle body that fits on top of the spacer in the fist pic:

Gotcha, your work looks nice. Clever idea, you may have the best of both worlds or a tuning nightmare. Keep us informed of how this plays out. Do you plan to pop the lower butterflies open, or probably open progressively? Thanks for posting. Bill 1362

quote:

Originally posted by lastpushbutton:
you may have the best of both worlds or a tuning nightmare

Lol, yes i know what you mean. I have quite a bit of work to go yet but i'll post some results when i have them.

The arrangement i'm working on at the moment moves the butterflys from closed to full open in about 3 seconds, it may need to be faster than that, i'll have to try it and see.

Thankyou for your interest.

Thats a pretty clever idea to incorporate into an old manifold. It should give you very nice driveability and economy. We tune a bunch of cars with secondary runner systems. Its really not all that difficult. Typically they switch just by an rpm setpoint. Usually on the dyno you see a minimal bump in air fuel ratios. Typically the switchpoint is right at the power transition so if set up properly is unnoticeable.

quote:

Originally posted by PanteraTurbo:
Thats a pretty clever idea to incorporate into an old manifold. It should give you very nice driveability and economy. We tune a bunch of cars with secondary runner systems. Its really not all that difficult. Typically they switch just by an rpm setpoint. Usually on the dyno you see a minimal bump in air fuel ratios. Typically the switchpoint is right at the power transition so if set up properly is unnoticeable.

On the cars you have worked with how fast do the blades in the secondary runners go from closed to full open ?

Do they open slowly or really fast ?

quote:

Originally posted by Aus Ford:
Type of throttle body that fits on top of the spacer in the fist pic:

This is what I thought you would do. I like it.

I have two cars that are FI that have secondary controls.

One is a Taurus SHO which the secondaries work off of a vacuum controller like a Holley with secondary vacuum diaphram. The other is a Contour SVT that the secondaries are mechanical and computer controlled.

I think you will need an aftermarket CPU that has secondary control and has a ramping feature by which you can control the rate.

I wouldn't know which one but I think you will need to match the rate of opening to the engine load, or engine vacuum vs. rpm?

The Contour has the ability to change the rate on the secondaries, but my son is the programmer and would know the rpm and the rate of opening.

I can ask if you want to know, but I may get an answer back in a language that is unknown to me at present. There is always hope in the future though?

quote:

I can ask if you want to know, but I may get an answer back in a language that is unknown to me at present. There is always hope in the future though?

Haha lol... yes that would be great ! I don't mind a bit of technospeak, i'm keen on learning other laguages

Well I only speak English and Martian. My Martian is a little rusty, but I still have the accent.

Good news. I asked and he answered in English.

The Contour opens at 3800 rpm and it opes to WOT.

It is computer controlled, and he has not changed the programing on it.

How this helps you I don't know, but this helps father and son relationships. Now we both realize we are Martians.

The other one thought we were Wookies when he was young.

Wookies from Mars are ok, it's the wookies from Uranus that you have to watch out for...

I have a rpm activated switch that i can set the opening/closing point anywhere between 600 and 6000 rpm. I was thinking i might just have too use that to start with to get the setup going and then fine tune it later by varying the opening speed according to load with a pwm control on the motor of the linear actuator.

There is a few different ways of doing it, i've heard that most of the late model cars just utilize a rpm switch but no engine load input.

I even considered just having a simple switch so the driver can just flick it from half manifold to full manifold at will.

I might be getting ahead of myself, i think i will have to test things and see.

Not even so much people from Uranus. I have a lot of...controversy...with the Venusians.

They have a strange way of speaking. They start in the middle and talk in opposite directions at the same time. Very frustrating.

A veiw of the actuating mechanism.

Sorry I missed the reply. Yes the valves do open fully and go from full closed to full open over about a 200 RPM span. Adding a manifold pressure modifier could allow you to open at different rpms where the power transition may vary from WOT. As far as opening speed I would not worry too much about it. Where the torque graphs cross from a run with the valves open and one with it shut will tell you where to switch. Opening as fast as possible will give you a seamless transition.

quote:

Originally posted by PanteraTurbo:
Adding a manifold pressure modifier could allow you to open at different rpms where the power transition may vary from WOT. As far as opening speed I would not worry too much about it. Where the torque graphs cross from a run with the valves open and one with it shut will tell you where to switch. Opening as fast as possible will give you a seamless transition.

Thanks for that info, it is much appreciated.

What does a manifold pressure modifier consist of and how does it work ?

Is it a electronic device that modifies the output of a MAP sensor ?

I just meant that some way of modifying the opening signal via manifold pressure as well instead of just rpm. Im not sure what the best way to do that would be. Depending on what ECU you run for the EFI it may have a general purpose output that could be used for such a thing. We tend to use a lot of Haltech units as well as Vi-Pec. Both are made on your side of the pond.

Some more photos with the fuel rails and injectors fitted.

The drab blue and rust colored paint work is to make this alloy manifold look like it is 40 year old cast iron.

The setup has to look at a glance like it is stock.

A stock Ford 351c air cleaner fits on top of this and covers most of it.

Well i finally got this gizmo on the engine and tuned it to a reasonable standard.

At first i had a few issues with hunting and surging at idle, which i feel is something to do with harmonics within the manifold due to it's peculiar configuration, but i found firing the injectors in a different order and bleeding some air into the lower manifold seemed to cure that.

How does it perform ? I can only say it is spectacular !

Taking off from idle it kicks you in the back and accelerates hard using the upper part of the manifold, response is very crisp with no hesitation or flat spots and my car weighs nearly 4000 lbs and the throttle body is 1000 cfm.

Then as the motor starts reving up past 3000 rpm the lower part of the manifold opens and the car just keeps accelerating hard untill you run out of road.

It was a bit of a gamble using the old Offenhauser Dual Port in this way but I must say i'm very pleased with the result and i would highly recommend the use of multi point injection with any Cleveland. You can use a throttle body with a much larger CFM rating than carburettors for stunning top end performance and still have fantastic low end response with no off idle bog down or flat spots.

The injectors i used are Bosch 33.9 lbs per hour, they are the ones used in stock LS2 motors.

The fuel injection computer i used was a very simple one and can be picked up on Ebay for a couple of hundred bucks with the throttle body, it is the old (very old) Holley tbi computer.

It is a analogue computer (not digital) works on the Alpha-n system (only throttle position sensor and tach input required) and needs no laptop, ajustments are done using trimpots on the dashboard (like the volume control on your transistor radio). More complex engine management systems could be used but i like to go by the old engineering adage Keep It Simple and also utilize components i already had.

I'm also pleased it all fit under a stock air cleaner for a stock look.

WOW...
This was my first read of this thread!
Not being interested in the automotive world for a few decades, I feel more ignorant every day as I listen in.

The controlled dual plane was one of those ideals I dreamed about. what did you finally use to control opening the lower (just the 3000 rpm switch). and how are you controlling if you are doing a normal acceleration where the shift is above, but it drops below with the next gear

quote:

Originally posted by JFB #05177:
WOW...

The controlled dual plane was one of those ideals I dreamed about. what did you finally use to control opening the lower (just the 3000 rpm switch). and how are you controlling if you are doing a normal acceleration where the shift is above, but it drops below with the next gear

Yes i'm controlling the opening with the RPM switch and it is ajustable by a control on the dash to whatever RPM i want and it can also be ajusted so it is open all the time or closed all the time.

If it is set to say 3000 RPM it will open as you rev up in 1st and if the rpm drops below 3000 as you shift into 2nd it will close breifly as the revs build up and open again as it again hits 3000 rpm.

This seems to work just fine but as i say the RPM limit is ajustable anyway so you can tune it in to your own driving style.

Hi Aus Ford,
Cool idea...for sure. I'm confused on one point though. The injectors are spraying into the primary (low volume) ports. But when you open your butterflies to the secondary ports (large volume) there won't be fuel injected into that air stream.... Or did you do some creative work at the ports also..?

quote:

Originally posted by Rob Borruso:
Hi Aus Ford,
Cool idea...for sure. I'm confused on one point though. The injectors are spraying into the primary (low volume) ports. But when you open your butterflies to the secondary ports (large volume) there won't be fuel injected into that air stream.... Or did you do some creative work at the ports also..?

Hi Rob,

Actually this set up reverses the way Offenhauser set the manifold up to work. The upper ports are the larger ports which on this are used all the time But when Offenhauser designed it for a carb the upper ports were connected to the carb secondaries.

The injectors fire straight in at the inlet valve, a small amount of the divider was cut away just below the injector so it sprays fuel through both air streams.

Although it is a bit academic really as this is a batch fire system,firing the injectors in four pairs of two. That means some of the injectors are firing at a closed inlet valve anyway.

This is a common way many cars fire their injectors.

You can have sequential firing if you have a very fancy computer and setup but that is a bit academic too as the injectors will only fire at a open valve when the engine is going slow, when it speeds up the valve is open for a shorter and shorter time and the injector will be open for a longer and longer time.

So even with sequential injector firing at some stage the injectors fire at a closed valve.


When the lower butterflies open in the set up i have it does not allow more air to enter the engine but rather it changes the dynamics of flow within the manifold utilising the same amount of air so no change in fuel flow is required when the lower butterflies open.

Your flow path sort of illustrates one of the advantages I hyphotisized in that the opening exhaust pulse into the intake will swept into the lower "mixing chamber" at low rpms, hopefully giving a cleaner charge from the upper runner at idle and reduce cam lopping.

Have you considered measuring the upper and lower manifold vacuums. thinking that the primary flow will draw a vacuum (ventura effect)on the secondary runners

quote:

Originally posted by JFB #05177:
Your flow path sort of illustrates one of the advantages I hyphotisized in that the opening exhaust pulse into the intake will swept into the lower "mixing chamber" at low rpms, hopefully giving a cleaner charge from the upper runner at idle and reduce cam lopping.

Have you considered measuring the upper and lower manifold vacuums. thinking that the primary flow will draw a vacuum (ventura effect)on the secondary runners

I haven't compared upper and lower manifold vacuums yet, but i would expect they are very similar due to the "short circuiting" taking place in the runners and ports of the valves that are shut.

It must be remembered that the lower butterflies don't really initiate a difference in pressure between upper and lower plenums but rather a change in the manifolds internal flow path.

With the butterflies open the "short circuiting" ceases and the manifold acts pretty much as any other single plane.