Intake Runner Length

[galahs]

After fitting my K&N Lunchbox, I thought to myself... I wonder how this affects the bikes intake runner length.

Can't say it shortens it that much more than the distance to the airbox, so it wouldn't affect the tune too much in the regard.

Short Intake Runners = Higher top end Horse Power (And you can't get any shorter than a Lunch box whacked on the carbs)

Longer Intake runners = More low down torque

so I was thinking, has anyone tried playing with the runner length on a GS? It would be interesting to see if a longer runner length made any low down performance gains. 

[galahs]

This sight could be helpfull:

http://www.rbracing-rsr.com/runnertorquecalc.html


Does anyone know the RPM's at which the GS produces its peak torque?

[ducati_nolan]

In my understanding, the intake runner is the portion after the carbs, but I know what you're talking about. You loose those rubber pieces that smooth the airflow into the carb, which would reduce power at all RPMs. In reality, you get enough extra flow through the filter that it dosen't matter, but I bet if you could open up the hole in the stock airbox to allow it to take a filter with a larger opening, you could probally get more power than the clamp on k%N without those pieces.

[galahs]

I was thinking if a new bellmouthed runner was added onto the carbs you could get better airflow than a K&N.

If it was the right length runner, + bellmouth/trumpet end you could end up with a much bigger HP increase (after proper jetting of course) than just a lunch box/pods alone.


Hmmm. 

[Turd Ferguson]

Intake runner lenght generally relates to the runner after the throttle plate.  When at WOT, longer runners before the throttle plate can help port velocity too, though.  Think velocity stacks...

Considering that the stock air box has no true "runners" in it, you have likely not changed the port velocity for your motor.  It would be hard to predict the change anyways because of the strange set up of the stock air box.

-Turd.

[Turd Ferguson]

I was thinking if a new bellmouthed runner was added onto the carbs you could get better airflow than a K&N.

If it was the right length runner, + bellmouth/trumpet end you could end up with a much bigger HP increase (after proper jetting of course) than just a lunch box/pods alone.


Hmmm. 

Adding runner length and a bell mouth would likely increase port velocity at lower RPM's.  The effects of longer runners diminish as RPM increases in nearly all applications though.  This is why you will see race engines with single plane intake manifolds and with uber short runners.  Many street motors (think of the old 5.0L H.O. engines in Mustangs and Thunderbirds) have longer intake runners to aid in low-end grunt; something that is very important for a street car.

-Turd.

[galahs]

I guess your saying the GS500 operates best in the higher rpm ranges so increased runner lengths wouldn't be a benefit.

[Turd Ferguson]

Well I suppose that all depends on when the benefits of having a long runner begin to taper off.  If you can see the benefits up to 8,000 RPM, then yeah, I suppose it would help out a bit.  It also isn't realistic to believe that you'll see a difference on the street.  At part throttle, I honestly don't think a longer runner upstream of the throttle plate is going to do a single thing for you.  Unless you run WOT all of the time, nah, I don't think it'll help out.

-Turd.

[makenzie71]

"length" is a pointless worry before the bellmouth.  You should worry about volume.  Intake runner length and volume are after the butterflies, vortex between the butterflies and bellmouth, and air supply before the bellmouth.

[galahs]

"length" is a pointless worry before the bellmouth.  You should worry about volume.  Intake runner length and volume are after the butterflies, vortex between the butterflies and bellmouth, and air supply before the bellmouth.

No true.


Cars have had big power differences with different intake lengths prior to the throtte butterfly, but you are correct that most of the performance gains are from differeing te length after the butterfly.

[makenzie71]

What car has "big power differences" with altered lengths prior to the butterflies?

[CirclesCenter]

I don't know that length would have anything to do with it.... (before the butterflies)

And you guys I think are talking about a tuned manifold. (After the butterflies)

A tuned manifold basically lines up pressure pulses so that at a certain flow rate and rpms and a bunch of other crap the pressure wave helps cram more air into the cylinder.

It's obviously a complicated thing.

[galahs]

The change in the Ford Falcon's intake pipe that feeds air into the throttle body was changed from the ED to the EF to improve performance by 4% (6 kW's).

Also the length of intake trumpets on race cars change their power out put, and they too are located prior to the throttle body butterfly.
Ford Pinto motors are know to have lower RPM power increases of upto 30% with different trupet lengths.
Same goes for trumpets fitted to the V8 Supercars intake systems.

[makenzie71]

The change in the Ford Falcon's intake pipe that feeds air into the throttle body was changed from the ED to the EF to improve performance by 4% (6 kW's).

I would like to see back to back dynos of the Falcon with the only change being the "pipe that feeds air to the throttle body"...because I'm sure that the different intake manifold, crankshaft, electric fans, and engine control didn't have anything to do with the power increase ED and EF bodies.

Also the length of intake trumpets on race cars change their power out put, and they too are located prior to the throttle body butterfly
Ford Pinto motors are know to have lower RPM power increases of upto 30% with different trupet lengths.
Same goes for trumpets fitted to the V8 Supercars intake systems.

First, they're called "velocity stacks"...we've already discussed how the bellmouth does stuff.  Velocity stacks have an effect similar to their name sake; their length alters the flow rate of the air from the air supply.  It's the air supply we're discussing. Pay attention.

[galahs]

And how does that differ to what I'm talking about!


The test on the Falcon was done first with NO other Change to the engine. JUST the air intake pipe. They did prototypes first with mandrel bent pieces of pipe before tooling up a plastic moulded piece. People can get the same gain by replacing the pipe on their ED by adding the EF pipe.


And are you trying to say a velocity stack/intake runners length prior to the throttle butterfly has no effect?
If so, are you saying the research I have sitting infornt of me is wrong,
If not, then we agree? Whats the problem?
I'm confused. 

[galahs]

Are you saying its just the bellmout and strightness of the intake tube that produces the increase in airflow.

If so I would like to argue you are incorrect, and that length of the intake runner prior to the throttle butterfly does pay an important part in the type of power delivered and I have dyno figures of the Ford Escort to back up my case.

[makenzie71]

The test on the Falcon was done first with NO other Change to the engine. JUST the air intake pipe. They did prototypes first with mandrel bent pieces of pipe before tooling up a plastic moulded piece. People can get the same gain by replacing the pipe on their ED by adding the EF pipe.

Like I sad...back to back dynos.

And are you trying to say a velocity stack/intake runners length prior to the throttle butterfly has no effect?
If so, are you saying the research I have sitting infornt of me is wrong,
If not, then we agree? Whats the problem?
I'm confused.

You need to pay attention to what you write:

Can't say it shortens it that much more than the distance to the airbox, so it wouldn't affect the tune too much in the regard.

You made no alterations to the bellmouth.  The only thing you changed is supply.

[galahs]

I'm still confused as to the point your making?


Do you think changing the legth of the intake runners prior to the gs's butterfly will or will not make a difference? and why


The dyno graph I have infront of me is of an Escort run back to back with three different length trumpets before the butterfly flap. They are all the same diameter, with the same bellmouth.

Trumpets 12 inches long produced a power peak of 98kw's with a dip or power at mid-high rpm range

Trumpets 13.5 inches long produced 100kw's with no dip in power along the power curve

Trumpets 14.5 inches long produced only 88kw's. Much lower than the other trumpets results.

so the difference of 2.5 inches of runner length before the carbs could make a huge difference.

[galahs]

Here's me thinking out loud again....

currently a lunch box filter or twin seperate pods are the least restrictive intake availalble for the GS500.

What if one developed a y pipe intake.


If you imagine, it would be smilar to this picture. The two out let ends attatched to the carbs and the large single opening would have a large pod filter clamped to it.

This could benefit the air intake by using the momentum of air sucked into the single opening created by the opposite cylinder.

The momentum would continue after one cylinder intake valve shuts, but this air would then change path down into the other cylinder.

this process works in car engines so I see why it couldn't provide a small gain to the ol GS500.

[makenzie71]

I'm still confused as to the point your making?

Go back and read your first post, since quoted text eludes you.  You said alteration to the bellmouth was minimal.  You made NO alteration to the bellmouth.  You didn't alter intake runner length or anything remotely similar.

And a y-pipe isn't the best idea as then you'll have two cylinders charing a common supply.