Unusual Intake

[Anonymous]

Hi Everyone,

This intake has raised a question in my mind.
http://www.500cid.com/mts/pics/SRgiveaway2.jpg

I know, it's a V8 and a Cadillac. But that's not the point.

This is a tunnel ram with super long runners, about 20 inches. They say it pulls like mad untill 4500 where it quits due to runner length.
If you look at the construction (right side plenum feeds left side head) it looks like another set of shorter runners could be added from the other side of the plenum. If so the shorter set would need a set of butterflys and some form of RPM switch, to switch it to the short runners at 3000 rpm or so.
I know that this has been done many times with EFI, but has it ever been done with carbs :

BTY: That Caddy pulls 690 ft.lb. torque on 87 octane.

John

 

[Thad]

Remember the Taurus SHO 3.0 V-6 by Yamaha?
Two intake valves and two intake runners per cylinder, one long, one short. butterfly in short. Lower RPM used long runner only even with both intakes valves working. At a particular RPM the computer opened the butterfly and both runners flow air to valves, both runners had the same effective length as the short for higher RPM.

The wildest I have seen was a Mazda prototype GT racer. N/A engine with sliding intake runners like a trombone, controlled by computer. Work the throttle and the the intake runners extended or retracted with RPM to stay in ram effect.

 

[Asa]

ok, the real question is who is going to fab one for their car?

 

[rbohm]

8) sorry but i dont think the cad V8 sheemetal intake is going to fit my 170 six cylinder :rolflmao: :rolflmao: :rolflmao:

 

[addo]

That Mazda thing really amuses me. I was wondering if, like the "big bands", it stood up for solo on the trombone intakes.

For that matter, couldn't you alter the pressure in the tubes with little valves on the side, like a sax? Now I'm in the mood... The Tex Beneke motor?

This has given rise to the evil idea of putting a brass wind reed inside an intake, to give a really annoying whistle.

But as to fabbed intakes - I thought space/cost were always the issues in real world installations. Not the physics.

Adam.

 

[Anonymous]

Let's take Thad's engine for example.

If it had a multi length, switchable intake, that could switch from a 18 inch runner with a split plenum to a 8 inch runner with a single plenum at about 3600 rpm then the torque curve would be as follows.
2500...344ftlb increasing to 405ftlb at 5000 with 410 horse power at 5500.

The newer DOHC Ford Ozzie 6 has such a system with the exception of a second set of butterflys that would turn the split plenum into a single plenum.
I was just wondering if it would be worth the trouble to build it for a pushrod engine?
Just a little food for thought

John

 

[addo]

If you were running triple Webers or similar, it ought to work. But it'd almost be like mechanical fuel injection then, wouldn't it?

 

[Anonymous]

*shrugs*

MarkZE has a dual length intake adapted to his crossflow..

 

[StrangeRanger]

The good part is that a 2 position intake valve is a straight RPM related phenomenon. Vacuum strength, throttle position, spark advance, etc are largely irrelevant. All you need to control the flapper is an RPM activated trigger, such as an MSD RMP activated module. The Mazda continuously variable system with the trombone slide takes a computer.

 

[66Monterey]

The newest BMWs use a "trombone" system inside a common airbox. Each intake runner can be individually adjusted. These engines don't even need a throttle body!

Some of the newer Ford pushrod V6s have "split port" intakes, where short and long runners feed the same intake valve, and a valve switches between the two. Maybe pirate the system and hook it up to an RPM switch like the trigger from a shift light? But with the low end torque of an I6, would there be much of a benefit?

 

[Anonymous]

The thing is that the low end torque is not sacraficed in any way. In fact you could build an intake with even better low end torque and still have better top end power with an extended rev range.

It's a win-win situation. But it works best with a good flowing head.
That's why Thad's engine showed off so well. His head flows like the Ohio at flood stage.

John

 

[Anonymous]

What would the optimum intake length and plenum size be for 1500-3500 rpm or has ford done it with the efi manifold?

 

[StrangeRanger]

The stock EFI manifold @ 1.62 ID is optimized right at 3000 RPM and in the good range from 1000-5000 RPM. Basically diameter isn't the problem. Optimum length is given by:

L = T x V / N

Where

L = length in inches
T = time reguired for the pulse to reflect back to the intake horn, expressed in degrees of crank rotation. Experimentally found to be 90°
V = the speed of sound, approx. 1100 FPS
N = RPM

For 1500 RPM: L = 90 x 1100 / 1500 = 66"
For 2500 RPM: L = 40"
For 3500 RPM: L = 28"
For 4500 RPM: L = 22"
For 5500 RPM: L = 18"

This measurement if from the face of the valve to the end of the horn on the carb or T/B. I'm not at all sure how thw hose lenght in front of the t/B affects this.

 

[Anonymous]

Hey SR,

Aren't those numbers for a single runner on a single cylinder :
Won't they change when a plenum is involved :

I seem to remember some thing about a hamonic reflector effect on a 3 cylinder plenum. Maybe it's just the voices in my head again :!:

John

 

[StrangeRanger]

You're right those numbers are for individual runners. Just put 3 dual sidedraft Webers on it and the numbers will work fine.

I'm not sure HOW the plenum affects things, but if I were to guess I'd say the measurement would be either from exit of the plenum to the valve face or from the T/B. Professor Smith didn't deal with pleni in "the book"

 

[Anonymous]

From the plenum, just like exhaust is calculated to the collector. That big open area frightens the little pressure wave and makes it run back the way it came.


-=Whittey=-