ALFAGTV6.COM

Has anybody played with different length intake runners? Please don't inundate me with the equations for calculating the lengths, Helmholtz, etc. It seems that if you used a 164 style intake, and sent it left, you would have some room for varying the length. And yes, I was thinking about some kind of cumbersome, clunky, Rube Goldberg throttle linked continuously variable arrangement-hee hee!
-Al

Just a brief FACT: a certain 2liter 105 on the dyno made 143hp/6200 and when the 100mm trumpets were removed, went to 156/6500.
Don't ask, just believe. No more on this as its an ongoing project.
Jim K.

Yes, that is very interesting-
If I remember correctly, I would expect short runners to help on the top end, and lengthening them to improve the low end torque.
For me, improving low end torque would really be advantageous in a road course situation.
The problem seems to be that in order to be effective, the runners need to vary over a somewhat wide range, which brings on space concern. I have seen the very nice dual fixed length runners that many newer cars have, it would be interesting to see if any of them would be applicable to our application.
-Al

Removed? As in removed and left the square edges instead of full radius?

Damn thats weird. I'd guess that a 100mm trumpets would come pretty close to the side of the engine bay though.

Don't be too impatient Mats, I'll pm you with more on this in about 2 weeks when we hit the dyno again. Right now I've got an issue with deepening piston pockets for correct cam timing. Funny thing is the cams are 310*,12,5mm. What I want to do, is experiment with various length horns: Destroy one set of horns by cutting the base and the first 1/2" or so and leave that piece bolted on the carbs, use a rubber hose with clamps and fix the rest of the horn on the other end of the hose. What you now have is a horn you can shorten at will, until the dyno says "Bingo!". Start with say,100mm and keep cutting the hose down by 10mm with every measurement. Damn, you're bound to find the correct length for the application and then go buy the proper horns. It sure beats paying for umpteen different horns and its a helluva lot quicker than undoing and redoing 8 locknuts at a time!!All you have to do is slit the hose with a knife and retighten the clamps. Whaddya think?? We'll beat that mf Yugo, one of these days!!
Jim K.

Sounds like a plan, unless the edges creates some weird flow separation effect that make the tract narrower flow-wise, then the lenght would be a bit off (if I understand the Heimholtz resonator furmula right).

I was thinking about welding up some intermediate "risers" that could be switched but that would mean 16 (!) nuts to undo/redo between pulls. Maybe the engine need the cooling down period anyway..?

Does the intake length affect fuel and timing? I'm guessing carbs would be less affected but with EFI surely you need at least a couple of pulls with each length?

Couldn't you work with a several interchangeble tubes between engine and intake plenum. Only interfacing has to be the same.
And plenium has to be repositioned according tube length.
Is it so that you could tune between torque and power.
(Theory was longer intake: more torque at lower rpm or do you just move your powerband?)

Yes, switching between two sets of runners is what many newer car manufacturers seem to be doing-I think the newer Audis might even have retractable "fins" in the intake path that purposely generate turbulance (!) in certain regimes.
What I envisioned is exactly what Jim is getting at, but with a twist:
Determine optimum runner length for high RPM (using equations and empirical data), and for lower RPM torque. If you could build telescoping runners, then you could do this-clearance issues in the engine bay notwithstanding. Depending on your findings, the length change might take place WITHIN a plenum. Or, you could discard the plenum entirely, and do this with an IR setup. All of this, of course, has been done before. Also, you would need to consider how to actuate the length variation--coupled to RPM or throttle settings or some kind of hybrid? Perhaps a code modification to Megasquirt???
-Al

Sounds cool, but complicated...

How do you shorten the tract without introducing sharp edges or irregularitys?

I got a cut-through of the Ferrari F1 solution somewhere... Lemme se if I can find it.

Guys, there are a number of cars (several) on the market, using the variable intake length system, like Ford, Audi, Porsche, Opel, you name it. Many use plastic intakes (mostly DuPont stuff) and switch from long serpentine tracts to shorter direct ones, all ECU controlled of course. These systems have been around for 10 years now I think,if memory serves.
Jim K.

Maybe longer than 10 years....Lotus Carlton-era Opel Omega 3.0 had a 'dual ram' intake. When was that - '91?

Head must have been Lotus-work, like the big brother Carlton.

Under full throttle, the intake route changed at some RPM point and it felt like someone turned on the afterburners.

I thought we talked about infinite variating length runners, not crude switching between two lengths.

How about double VVT with infinite settings too while you're at it.

Oh, wait, this is going onto a Nord is it? haha..

Yes, a sliding/telescoping arrangement was what I was considering. If the interface is smooth, I don't think that flow disturbance would be much of an issue.
You know, the 164 runners are longer than GTV6/Milano ones. Anyone have any nifty facts on whether or not their length was "tuned?"
Going to the track today, test tomorrow, races on Sat. and Sunday!

-Al

Ferrari F1 -98

Found a long time ago this simple program for calculating optimum length http://www.bgsoflex.com/intakeln.html
Don't know if the numbers are any good, but looks straight forward.