Intake runner length and turbo spool

[Dialcaliper]

I've been pondering designing an intake recently, and I'm wondering about intake runner length in relation to turbocharger spool. It seems like from a low rpm start that long runners that would produce higher intake velocities and resonance for more low end torque would also cause the turbo to spool faster?

But what happens to your throttle response when you shift and the engine stays above the usual spoolup RPM? Which design would allow the turbo to restore boost pressure faster, or does only the plenum size matter? I'm thinking of this also in the context of a dual runner intake (like the cyclone).

Could anyone who's using a cyclone manifold comment on whether the actuator works off pressure, vacuum or both? I guess the question being, when you shift and the BOV actuates, do the butterflies snap shut even above the threshold rpm until boost is restored?

I guess the real main question is, could you design a dual runner intake that is actuated solely off boost pressure, that wouldn't hurt throttle response after shifting? I'm thinking that you could design smaller short runners that are tuned right around the bottom of your turbo's spool rpm range, and once the manifold reaches near full boost, a wastegate actuator to open butterfly valves (I'd probably get 4 small throttle bodies to use, maybe from a motorcycle engine, and design an actuator that uses something like bicycle brake cables to open all four at the same time)

The problem in this case is that until manifold pressure is restored, you'd only have the short runners functioning.

Your short runners in this case would be sized pretty short for top end power, and the combined frequency would be somewhere in the mid-high range. I'm also thinking that the long runners could join the short runners closer to the butterflies instead of at the head to minimize the extra volume you have to backfill, and also allow slightly larger short runners.

Anyway, and opinions? One of the references I was looking at is this Penn state FormulaSAE design that's kind of interesting.

Penn

 

[Hksvr4]

The JDM engine's come with a cyclone intake. It has dual runner for each cylinder.

 

[Dialcaliper]

Yeah, I'm familiar with it, but I was hoping that someone who uses one could comment on how it behaves - I know it has an electronic control set to around 4000 RPM or so, and that it has a vacuum or pressure actuator, but I don't know how the butterfly valves behave when the engine is pulling vacuum or pushing boost.

The idea I'm toying with is to build something similar, but with a much simpler mechanical only actuator and tuned for a modified engine with higher power rather than for a factory 195hp street car. (It'd have to perform better than a stock 1G to be worth it, otherwise I'd just go with a sheetmetal design or extrude honing the stock intake).

 

[GreenGSX]

The last three years I've run a cyclone manifold. I fabbed up a modifed 14b wastegate actuator to open and close the butterfly valves. No matter what turbo I ran at 11psi it would start to open the valves and by 14psi they fully open to use both sets of runners. The idea was that I was only concerned with increasing spool and low end power. So, I figured that at 14psi the car was making pleanty of power so there was no more need for the short only runners. It was only when I was road racing did the manifold show its limitations. Basically the car would fall flat above 7k and was totally flat at my 8.5k shift points.

Here is what I made to replace it. I used the longest runners I could fit in the engine bay (6"). To me the car felt like it had more power all throughout the rpm range. My limited, and not scientific, data shows it made more power and torque everwhere. Here is how I made it.

click

 

[CutlassJim]

The cyclone works like so

There are two set of runners, one long one short, that you know, well the second shorter set has butterflies mid length that close off the runners so that your only using the smaller longer runners under a certain RPM. The runners are run off an actuator (think waste gate)The runners are OPEN when the actuator sees atmosphere. A signal line from the manifold runs to a vacuum canister with a one way valve, the canister will only see vacuum and never boost, then to a solenoid, then to the actuator.

When you start your car the vacuum CLOSES the valves so that your only using the long runners. No matter what rpm you floor it at you are going to lose all vacuum, even if you don't build boost, so if you have a line going straight to the actuator then it OPENS the valves and you have a regular intake manifold. With the one way valve in the canister the actuator still see's vacuum and the valves stay CLOSED. When you reach a certain RPM (4100 on Keydiver chips or 44-4700 on JDM ECU's) the ECU signals the solenoid to open to atmosphere, the actuator see's atmosphere and the valve's OPEN, causing you to use half the shorter runners for more top end and half the long runners to keep up with mass air flow. Mind you the line coming from the vacuum canister get's closed off so there is still vacuum in it, this way if you shift under the activation point but are still on the throttle the solenoid will close to the vacuum canister and it will CLOSE the valves again shutting off the short runners.

People that hook it up straight to the manifold or have it open via a boost reference (I.E. 5 lbs) are incorectly using the manifold. The need for the short runners is rpm and airflow based not boost based. A lot of people think that when your turbo spools to say 20lbs at 3500 rpm and stays there until 8000rpm they have the same airflow, WRONG! Even if your running 20 lbs under the activation point there is not enough mass air flowing through the motor to necessitate the added volume of the short runners. You hit 20 lbs but are flowing less mass air because the motor is injesting less air making it easier for the turbo to force enough air into the intake tract to make 20psi. Intake pressure is there because of resistance/restriction, the motor can't take in all the mass air the turbo is putting out. That's why on smaller turbo's at higher RPM or on larger motors at high boost it will "taper off" to a lower pressure. The turbo can't put out enough air to keep the pressure at 20psi. That's how you know you need a bigger turbo because you are maxing out your current one, not by asking on a web forum. I feel confident in my lengthy answer because I am in the middle of running a cyclone intake manifold myself and have read EVERYTHING I can find on the subject.

So yeah that's how a Cyclone intake manifold works. /ubbthreads/images//graemlins/grin.gif

 

[Dialcaliper]

Hmm, I think it makes sense now. I hadn't thought of the cyclone being a "normally open" system that was kept closed by vacuum, and popped back open on electronic signal.

I guess in a positive pressure based system that *opens* under boost, having the butterflies closed on shifting would kill the throttle response simply due to airflow restriction, and nothing to do with resonance (it's easy to get tied up on that thinking about dual runner intakes).

I guess in a dual runner setup, because of airflow vs resonance and tube sizing, you can make a good comprimise, but never produce more power or torque than a properly designed traditional intake. Now if you could have one long and two short runners...hmmm that's a lot of butterfly valves.

My goal with the intake was not actually to increase low end torque, but rather to cause boost to come on quicker. I wonder if what I'm after is not actually a dual runner intake at all, but a dual *plenum* intake - one that charges up while the manifold is in positive pressure, closes when the throttle plate snaps shut, and then opens again like a reserve air tank to repressurize the manifold partially.

It wouldn't help spoolup on acceleration, but it would hold reserve manifold pressure between shifts.

I guess the other solution is just to run no blow off valve, or use a burst-nitrous system

 

[Dialcaliper]

...Or anti-lag /ubbthreads/images//graemlins/banghead.gif


Come to think of it, that reserve plenum idea is awful - it would mess up the tuning (go lean for a minute when you step on the throttle, and a bit rich when you hit full boost).

I just realized on my way home that with a cyclone or other dual runner intake, if you happen to have DSMLink, you could use the nitrous control settings, and use the boost control solenoid - you just need a generic vacuum actuator, and a check valve and you're in business. Goes for a standalone as well of course.

 

[curtis]

The problem with a dual plenum is size restrants and when it opens the 21 psi or whatever that is stored will escape quickly. After all its just an accumlulator. You could mount it in the trunk if you wanted to and have a large solenoid or throttle body on the plenum to open but it would have to recharge and would effect airflow during charge up time.

Now for the statements above the butterflys don't do half but whole when its open its open and when its closed its closed. I've tried every boost point from 1 to 21 pounds on mine and the buttometer says 3 to 4 pounds hits the hardest. As for failing up top they do. Cyclones plenum is way to small. Thats why I was planning on the larger plenum on mine. But the whole mass air thing I believe is for the smaller turbos. the Garrett cycled the tires and pulled hard and didn't fall off between shifts . I really never got the schwitzer tuned on the car for fixing other problems but downshifts from 3rd to 2nd caused uncontrolable tire spin and put the car into the other lane above 24 pounds.

Mine is installed with a boost referance using 2 switches one normally closed and one normally open and the one way check valve/vaccum canister. I always planned on an electronic timer for mine but just never got round to it . They way it would work it would trick the open solenoid to stay open and the closed to stay closed for 5 seconds or so....so they butterflies would stay open between shifts. Just never got around to it. you can do a search on boost controlled systems with my name or Ken Inn we both built ours about the same time a few years before Jeff broke the code on the cyclone activation.

 

[CutlassJim]

Quote:
Now for the statements above the butterflys don't do half but whole when its open its open and when its closed its closed. I've tried every boost point from 1 to 21 pounds on mine and the buttometer says 3 to 4 pounds hits the hardest. As for failing up top they do. Cyclones plenum is way to small. Thats why I was planning on the larger plenum on mine. But the whole mass air thing I believe is for the smaller turbos. the Garrett cycled the tires and pulled hard and didn't fall off between shifts . I really never got the schwitzer tuned on the car for fixing other problems but downshifts from 3rd to 2nd caused uncontrolable tire spin and put the car into the other lane above 24 pounds.

Mine is installed with a boost referance using 2 switches one normally closed and one normally open and the one way check valve/vaccum canister. I always planned on an electronic timer for mine but just never got round to it . They way it would work it would trick the open solenoid to stay open and the closed to stay closed for 5 seconds or so....so they butterflies would stay open between shifts. Just never got around to it. you can do a search on boost controlled systems with my name or Ken Inn we both built ours about the same time a few years before Jeff broke the code on the cyclone activation.



Your sentences are a little hard to understand but by saying it's using half the short runners and half the long runners means that the long runners don't get shut off when the valves open, so youre using both the short AND long runners.

And you wouldn't have that problem with your manifold if it was hooked up properly. As long as your shifts kept you above the actuation RPM them the butterflys would never close and you wouldn't have to over engineer something to make it work like it's supposed too.