Telescoping intake runners, anyone ever seen them (or make them?)
 

Has anyone ever seen the telescoping intake runners like the 787B had on it? I'd be interested in checking into them and seeing either how much they are (if someone made them) or how hard they'd be to make. I imagine they'd simply be sold individually with a throttle body of their own also, so they could be bolted on to a 13B, 20B, or whatever.

Anyone have any info on them?

Oh, and how much benefit would this have on a turbocharged car? I know it was done on an N/A and made a big difference, would it make a bigger difference on a turbo car with a plenum?

It's a one-off custom system.
You willing to pay $10k+ for a set?
I thought not...


-Ted

well with some clever fabrication skills it could be made for a lot less than $10k. it would help a turbo just as much as an n/a, but when you figure out a way to have continuous variable intake runnersall feed into one surge tank behind the TB let me know. this works on the 787b because each track is completely independent of the others. doesnt work that way on a turbo.

If you were to do this on your own you would have to devise a system to control the throttle body, as that is the point that needs to move for it to work, as it causes the highest resistance. So with that a simple cable would not work. You would also have to do calculations to figure out the optimum length for every given rpm, and either have a computer, or a mechancial system that would position the tb at the desired place to give the desired volume for that specific rpm. So there is a lot more to do than just fab them and make them move

- Steiner

asside from making the mechanism, tuning to where you will realize its power potential would be very difficult because you are adding 1 more variable that has to be determined and maneged somehow. i mean do you know the fluid dynamics involved in determining runner legth.........i dont.

exactly snowman. the cost isnt so much in the part as it is in engineering it to actualy work. but hey, if you are smart, thinking is free:)

,My friend Mikael have fabricate a telescopic set up on our N/A PP motor. It has a variable of 4" from shortest to longest set up. When we tested on a dyno it made 313 hp w/ the short set up at 10100 rpm. Then we add 2.5" to the system and made 306 hp at 8900 rpm, and the torque was up 20Nm. The intake system has an id of 60mm which we think is a little bit of much id. The systen is made of aluminium with a taper of 7' We plan to make a new manifold of 56 id to gain some velocity and torque. Wish i had a faster computer so i could show you some pics! In the future maybe...

Here's a good read about this...
https://www.rx7club.com/showthread.p...hreadid=248556

he why do you think I'm pushin so hard to get a budget for my senior thesis project :D . That and trying to get our SAE team to do a setup similar to this.

- Steiner

I found this one day when thinking the same thing and saved it

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I've got a simple formula that was developed by engineers at Chrysler in the 1950s when they were working on ram induction sonic tuning. Anybody remember those big long ram tubes that cross over from one bank of cylinders to the other? Anyway:

L=72C/N

L=length of intake tract in inches
N= engine speed in rpm where maximum ram effect occurs
C=velocity of wave in ft./sec.

A good number for C is 1100 ft/sec.

However, this formula was developed using 4-stroke passenger V8 engines with relatively mild cam timing. A guess for intake timing is 265 degrees duration. For a 2-stroke, the intake duration is around 165-200 degrees, depending on the particular motor. So I modified the formula to compensate for the shorter intake duration:

L=72C(intake duration)/N(265)

When you work the math for 165 degrees of intake duration and 6500 rpm, the length comes out to 7.59 inches. This length is the total length of the intake tract from the end of the velocity stack to the face of the intake valve (reed, rotary, piston port). Using telescoping tubes and a tach would be an easy way to adjust the optimum for your motor. Just like setting a tuned pipe length - only the other end.

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There's one problem that I see with that equation, it doesn't take into account the diameter of the intake runners.

- Steiner

yeah, dont know what to do with that

I swear you're the eternal freaking naysayer... you sound like the guy down the street who's always got something to say why everything won't work. If it's sunny, he's pissed because it's bright out. If it's cloudy, he's pissed because it's dark out... waa friggin' waa...

Do you get a hard-on just bashing all ideas that come across or what? How about I know it's a custom system, but I didn't know if anyone else ever developed it. How about "yeah, with some aluminum tubing and the proper seals, designs, bearings/runners, linear actuators, and control system, you'd be able to do it. Won't be easy, but it'd be cool to do"

I'm glad to see there's some *other* people on here with sense enough to not bash everything like you do, and offer some constructive advice, and even some who've done it and are curerntly doing it.

I was thinking doing a large plenum kinda like the old Formula car (CART I believe) turbo motors used to be.

I can get access to a dyno that will measure all those variables, and I work with a building full of mechanical engineers who live for this junk, and I'm friends with an equal number of engineers.

And I see bullshit spitting out peoples' asses everyday on this forum.
I can't count the number of times I hear pipe dreams being posted and never completed.

Why don't you prove me wrong and actually do it for once?
Wouldn't you love the satisfaction of getting this done and then throwing it in my face?

I don't think you need my input on HOW to build such a system.
Getting everything to work nicely is a whole nother matter.

Just look at all the 20B posts that have come up.
Getting the engine to SIT in the engine bay of an FC is kids play.
Getting the engine to fire up and drive around is a whole nother ballgame.
How many are actually running?
I think I can count them in my fingers and toes right now.
I can count the number of 20B FC's on both hands.
How many idiots have said they were going to do this?
Nuff said.

Until I see the project completed, I call your bluff and wait to see if you can do it.


-Ted

Once you run any engine with forced induction there is not much to gain from variable length runners. The whole point in variable length is to tune the intake to different rpm bands by establishing a resonance in the system to encourage additional airflow (much like tuning the port on a ported speaker system).

Once you have a turbo or supercharger doing that for you there is not near as much to be gained in doing so and the complexity becomes enormous as andrew lohaus explained. Your talking about building a manifold that is easily adjustable in length on the fly and yet able to withstand boost pressure without leaking. It's tremendously easier on an NA motor to make variable length intakes with individual stacks and individual throttle plates inside them.

Only easy way to do it for a turbo application would be to build a very large plenum with the adjustable stacks inside it and pressurize this entire plenum. That would be a terrible design though. First you have to pressurize the plenum before getting anything into the engine. A small plenum would take less volume to fill but it would severely choke the throttle bodies. A large plenum would not choke the throttle bodies but then it would have enormous lag because you'd have to recharge the whole friggin plenum every time you lift the throttle. No reason to do it unless you have unlimited funds and are not able to make gains anywhere else.

What kind of percentage gains were accomplished by using the variable intake runners on the 787b anyway?

Obviously enough for them to take all the trouble to make a cumbersome elaborate system with a lot of moving parts and pulleys.

Any numbers anyone has either read of the 787 or can theorize based on experience with tuned intake systems on other setups?

It flattens the crap out of the torque curve on that engine if it's continuously varied (not in steps as this graph shows). The graph is a good example of the difference each length makes.

http://www.mymazdarotary.com/mazda_r...s/image012.gif

R26B full SAE paper here...
http://www.thecarricos.com/ACRE/
"4rotor" PDF


-Ted

It's not cumbersome when you have an NA engine; the 787b was not turbocharged.

I knew that, infact it think it was even mentioned in this thread. But you look at that dead simple layout of a rotary in a car like that and add all that mess that had to be hard to make and control properly, so it must have easily been worth the extra effort to add it to the system that they wanted to be somewhat foolproof.

http://www.scuderiaciriani.com/rx7/787B/787_016.jpg

it must of been worth somthing as its one of the things the FIA banned for the next year after the win in 1991.

Have you seen the car graphic videos with the 787b and the spirit R Rx-7 ? it has some video of the inlet bellmouths moving on that.

I would have to agree with Ted, that many projects are dreamed up but never materialize. Ted offers a REAL opinion on subject matter. It's the real world and that's what he takes into account when he says something. Back on to the subject, the power gains made on the 787B with the variable length intake runners may not have been their primary goal, it may have been oriented more to the fact that they could have peak hp at almost any specific rpm, which means that the entire torque curve is flatter, and thus the car will pull better anywhere in the rpm range. This might also relate to response, so that if you shift down low in the rpms, you don't have that bog from not being in the power band.

- Steiner

2 things.

1. the 787b runners collect in a big air box, they do have a giant filter on the thing, but you could just copy them and pressureize the airbox

2. they used either miata or fc headlight motors for the telescoping, controlling them is another matter