Tunnel Ram.............intake

[Two Oh]

Remember back in the 1960's when drag racers started using tunnel ram intake manifolds? I can only think of "Ridge Runner" and "Edlebrock" brand names at the moment.

Well, What was the purpose of these tall monsters topped with dual 780 double pumper Holleys carbs??

Would a 5 inch tall hand made intake for a 911 be a good Idea??

Low end, top end, midrange gains?? Any ideas??



-two oh

[Botman]

Tunnel Ram air intake? Sounds very Rat Fink to me. Goofy.

Idea...Not so goofy. What about...

Originally posted by Bill Verburg
Heres another nice way to duct cool air to the intakes, from a friends RSR;

Check out this thread

[cstreit]

THere was a guy in excellence a while back, completey trricked out concourse GT-1 level racecar... Yellow with purple flames and interior trim if I recall that built a custom cold air intake out of plexi on the rear window.. Reminded me of the old 356 (?) GT cars with the scoop on the hood. I've always thought that looked cool.

Most common setup I see is like the one above with the NACA ducts going to the engine comp.

[masraum]

I don't think the tunnel ram was for cold air intake, it refers to long, large, vertical runners for the intake manifolds. It seems to me that short runners are for low end power while long runners are for top end power, but I can't remember for sure.

tunnel ram

not

[BlueSkyJaunte]

My coworker's new *****subishi Eclipse has variable length intake runners. Is this similar to the VarioRam that came out with the 993? (or was it 964?)

They were short at low throttle opening and long at high throttle...I think...

I guess you'd want to tune the length for whatever RPM range you'll be spending the most time at, and just deal with the crappy response elsewhere. Unless you engineer variable length runners...

[A Quiet Boom]

OK here's the long and short of it

Tunnel ram intakes are for top end power and they aren't necessarily longer than short manifolds, they are designed like this to give the air a straight shot at the valve and this is the shortest way to do it. Since the runners are a little longer than what is necessary for topend they compensate with large cross-sectional area. If you take a good look at a dual plane V8 manifold you'll notice that some of the runners are actually longer than a tunnel ram. The other reason for the design is wave tuning, by varying runner length and volume an engine designer can use the negative pressure waves to acheive VE's (volumetric effiencies) higher than 100% in other words by using the negative pressure pulse to "pull" in the positive one the engine naturally supercharges itself over a short rpm band. Shorter and larger raises the range and longer and narrower lowers it. Tunnel rams also benefit from a large plenum under the carburators to insure that no cylinder starves for air, here again plenum volume can be varied to change the rpm band. Finally on Pro Stock drag engines they use a setup that looks like a sheetmetal tunnel ram on the outside but has no plenum on the inside to create an IR (individual runner) system like webers on a 911. Those Holley Dominator carbs are specially designed to operate like 4 individual carbs and are use in tandem to provide a "carb for each cylinder" allowing wicked throttle response, tons of torque and HP, and individual cylinder tuning. The designers of these manifolds go to great lengths to disquise their internal designs from competing teams with even minor changes yielding big HP increases. I'm taking about engines that make in excess of 2 hp per cubic inch WITHOUT nitrous or boost.

The problem with engine building is coming up with a SYSTEM that works. And while gains can be made on street engines in some cases, it is far more important to address the engine as a whole. Cam timing, intake size and design, compression, bore and stroke relationship and exhaust all need to work together to acheive real gains. After that the chassis and gearing need to be optimized to match.

My .02 for the evening

[JohnC]

Two Oh,

I thought the same thing. The 3.2 Carrera intake is similar to the tunnel ram in that the intakes are quite long, about 9" @ the centerline (popular with the turbo guys too). I think the text "Scientific Design of Intake and Exhaust Systems" mentions a certain "sweet length" of 9"... interesting huh?.

I was thnking along the lines of a 3.2 Carrera intake with the plenums on opposite sides of the motor i.e left bank would it's plenum over the right bank etc...

If you read any texts you'll typically hear that the long intake runners create higher torque values at lower RPM's. I think the long runner idea would be great for the street but I've never seen an example. Porsche's are'nt "drag cars"....right?

[Superman]

Botman remembers Rat Fink, which means he is old like me. I am surprized that I have never seen a 911 with a blown big block poking out of the hood in FRONT of the driver. I think that would look cool in a Rat Fink sort of way, and I'm sure someone has done it.

[old_skul]

Oh yes, Super, it's been done. In a most horrific and disturbing way, I might add.

Imagine a 912 with a blown big block poking through the bonnet cover. Painted red (of course) with flames everywhere. Ferry is *still* spinning in his grave over this one.

[Superman]

I imagine it was tubbed, with 30" rear tires, etc. I'd like to see a picture, ugly though it may be.

[pwd72s]

Wave tuned? Straight shot to the intake valve? MFI!

[gregk1]

I still Have a RAT FINK tee shirt, I wore it the other day and some kid about 7 was looking at me and thinking what the heck is that!! I have seen a picture of that 911 I think It had a supercharger on it. Tunnel ram manafold's are a thing of the past no bottom end at all basicly 3500 rpm and above you only see them on Jet boats any more

[masraum]

If someone wanted to put long runners on a 911 engine with carbs my first thought to try to reduce the amount of carving that needs to be done would be for some type of crossram intake like the old chryslers and then maybe some type of side-draft carb. Just thinking outloud...

I only remember Rat Fink from Car-toon magazine, but I'm a little young to know much about Rat Fink

[911pcars]

Many cars today have a variable-length intake system to optimize low and high end torque. They accomplish this with a long intake manifold containing short and long paths to each intake port. The path is controlled by a vacuum or servo-operated valve(s) controlled by the engine ECU.

The famed "high butterfly" injection stacks lengthened the effective intake tract by increasing the distance from the throttle plates to the intake valves. Not optimal for low end torque, but not important for its intended use.

All of this is much easier with fuel injection; as only air moves through the longish passages.

Sherwood Lee
http://members.rennlist.org/911pcars

[HawgRyder]

I think the ultimate long runner setup was on the Chevy 594's that were used in Can-Am.
If you remember them...they had 14 to 16" long tubes that were all different lengths with flared horns on top.
Quite a sight.
Bob

[Bill Verburg]

Here's some nice info on
variram

[A Quiet Boom]

Originally posted by pwd72s
Wave tuned? Straight shot to the intake valve? MFI!

Exactly. But even webers benefit from this as well. Fortunately 911 heads are well designed in the port department.

[cegerer]

[Doug Zielke]

Originally posted by A Quiet Boom
The problem with engine building is coming up with a SYSTEM that works..........Cam timing, intake size and design, compression, bore and stroke relationship and exhaust all need to work together to acheive real gains. After that the chassis and gearing need to be optimized to match.

People who are planning to modify their engines need to read and re-read the above, and use it as their Mantra.
It's apparent A.Q.B. knows of what he speaks.

[pwd72s]

Agreed Doug...Quiet Boom has nailed it. When it comes to Detroit cars, Edelbrock has "systems" figured out...just ask for one of their free catalogs, you'll soon see what I mean. Race or street, for most domestic engines they have a formula, from intake to bottom end, that delivers the power promised. We 911 folks should be so lucky....the 911 world? Well...we may be scratching our donkeys trying to figure out a system...but part of our problem is that the factory pretty much had the "system" figured out to begin with. As evidence, I submit the early 911S engine from '69 to '73. "Tuned" intake stacks going straight to the intake valve, fed by mechanical injection which hotrodders even today will tell you doesn't work on a street car...wild cam, "squirter" dry sump engine, tuned exhaust inside the heat exchangers, exotic alloys used, the list goes on. It's tough to improve on the basic design...but Jack did his thing by going with the stroker McGurk theory that there is no substitute for cubic inches. And there is NOTHING wrong with that either...Purists beware...up to a certain point, a point hard to determine, the 911 is a natural born hot rod. Parts easily interchangable...Gawd, any guy who read HOT ROD in the 50's has to know this...