Intake length vs torque, Just anthoer carb question No boobs Options

[messix]

quick and dirty

big and short= high rpm power

small and long= low rpm power

this goes for the valves, head port and intake runner and carb or thottle body

here is your power balacing act .

intake, head ports, cam and exhust have to be matched to get max preformance.

[Joe Ricard]

OK Well I'm going to do it and then write down the recipe including results.
So base line has already been described. Above 4000 RPM it rocks Short intakes 50mm opening, 44IDF, Velocity stacks short air filter. SSI Bursch, 86B cam 2.0L heads port matched. Bus pistons all the compression I can get.
Hauls ass to 120 MPH

[JmuRiz]

What was the thinking behind this type of setup...lots of Can-am cars seemed to have tall and short VS's(IMG:http://www.photoessayist.com/canam/images/laguna-seca-c-60.JPG)

[URY914]

QUOTE (JmuRiz @ May 20 2005, 06:32 AM)

What was the thinking behind this type of setup...lots of Can-am cars seemed to have tall and short VS's

The best of both worlds.

[Katmanken]

Looks like organ pipes- each one tuned to a different frequency.

Thats so the driver can play tunes with the engine (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

In that picture, we only see half of the answer. I bet the exhaust pipe lengths are matched in some way to each intake length. (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif)

Ken

[don9146]

Didn't Jake do a test of different length Webber intakes on his dyno?

[Dr. Roger]

Excellent info.

Quote:
But there's also a performance benefit because the airbox is a Helmholtz resonator. That is, a resonance effect occurs when you connect an enclosed volume of a suitable size and shape to an engine's intake stacks causing the air inside to resonate at a frequency that results in pressure peaks coincident with the cylinders' intake stroke frequency (at a particular RPM.) This can theoretically increase power by 10-15% within a particular RPM range by boosting airflow into the engine. Air boxes need to be well sealed and stiff in construction to maintain these resonance characteristics. A simple way to illustrate this is to blow across the mouth of an empty bottle. The sound you hear is the natural frequency of a Helmholtz resonator.

If you change the shape and free volume of the airbox, you change its resonance frequencies, and the engine RPM at which it responds to enhance filling the engine with air. For example, a larger Corse airbox is tuned for optimum filling a at higher RPM where race bikes normally operate, but street bikes usually do not.

An airbox also functions as a plenum, a space where the air velocity is reduced so as to eliminate turbulent air flow prior to being smoothed and accelerated down the velocity stacks. In fact, if you just place your finger anywhere near the edge of the top of the velocity stack you'll see dyno power drop off due to the disturbed air flow pattern.

The air in the plenum is also considered "free air." That is, its already passed through the air runners and filters so it can be supplied to the engine without any flow restriction. If you use the auto industry's standard calculation of air required for "nil" vacuum restriction within the air intake system, you should have at least 130% of engine capacity in available air volume between the throttle butterflies and the air filter element.

All of this tells us why Ducati places the Superbike air filters in the air runners. This location avoids lowering the frequency of the airbox (by not filling up a large portion of the airbox volume with a bulky foam filter) and prevents disturbing the airflow near the velocity stacks as well as improving throttle response by maintaining a large free air volume between the filter location and the velocity stacks.

This is also why Ducati didn't use over-the-velocity stack bellmouth style filter. This location doesn't meet that 1,300 cc. plenum volume needed to avoid degrading throttle response (which a dyno doesn't measure BTW.) Dyno tests say you get somewhat less peak horsepower with these filter types but on a stock bike they don't seem to make a lot of difference.

Another point to consider is that unless you have customized a FIM chip on a dyno in an attempt to match the flow and resonance characteristics of an over-the-bellmouth filter you'll have to use a chip that was developed using the stock filters.

The computerized engine management system uses a fixed fuel injection metering scheme controlled by the EPROM chip that was developed in combination with the stock intake/exhaust configuration. Unless you install a programmable FIM chip and sort out any changes on a dyno with a knowledgeable operator/programmer you won't get optimum (low-end?, midrange?, high-end?, power?, throttle response?) performance.

[Dr. Roger]

Oh, on the Can Am thing...

Those stacks were another way to squeak out some broader power band on a very peaky engine. Half of the stacks are for high and half for mid RPM band.

[bondo]

So how DO you measure throttle response? That's important! (IMG:http://www.914world.com/bbs2/html/emoticons/driving.gif)

[JmuRiz]

Great info on the ducati airbox design! The best of both worlds description for peaky motors is good to know also. I'm working on modifying the airbox on my bandit, and was planning on doing a long and a short intake runner, to replace the single long runner (really bottlenecks the intake side) to better suite my aftermarket stuff. Seems like this might be a good choice.

I think the only way to measure throttle response is by feel. You can tweek the jetting of the carbs etc tom compensate for that though.

BTW here's the thread of Jake's dyno tests with different VS heights:
Velocity Stack thread by Jake

[Dr. Roger]

Hmmm, in my limited experiences with a few small block chevys, several motorcycles and one '63 ghia convert w/1.6 litre, i can say keeping the jetting a hair lean gives it a little better "snappyness".
Also higher velocities help. Meaning smaller air passages.

And in conclusion.....

Lighten your flywheel. Much snappyness is to be had there. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[Jake Raby]

Due to the intake and exhaust port designs the TIV is a different puppy than any other engine I have ever read about or worked with. (IMG:http://www.914world.com/bbs2/html/emoticons/pissoff.gif)

My data has been specifically done with the TIV so I really don't give a damn about theory with other engines because it just doesn't impact the TIV! (IMG:http://www.914world.com/bbs2/html/emoticons/monkeydance.gif)

Now with that out of the way I can tell you that runner length, especially with carbs is a huge thing to the engine's combination and is even impacted by something so far from the combo as the exhaust system.

Generally long runners and tall stacks boost down low power but they kill top end- I have seen this SO MANY TIMES when the opposite is conventional wisdom. Read those posts and what I wrote on them, its a repeatable thing that my dyno shows me over and over again.... (IMG:http://www.914world.com/bbs2/html/emoticons/aktion035.gif)

Now with that being said the 3 liter uses my Billet heads with a TI style exhaust port and one healthy D shaped intake port - It does NOT follow this trait! This absolutely indicates that the difference is the standard TIV heads. I plan on testing this on the 3 liter when I test my Billet heads Vs the super worked 2 liter 914 heads to show the power differences... That will tell the tale on the same engine with the same CR and etc, just different heads.

Comparing the TIV with another engine is the first and biggest mistake made by newbies or even TI tuners.

BTW- I have played with variable length stacks and found some small benefits on high speed engines, according to the exhaust design but generally its too small to matter.. My belief is that the can am guys did it to keep the stacks from robbing air from each other which can be a big issue with a healthy engine at that RPM.

Direct back to back dyno testing of the stacks ad intakes is easy and fun and its always part of designing a new combo- to find out what it really wants for later...

FYI_ as stacks and runner lengths change so does the jetting in the carbs... Air speed greatly effects the atomization of the fuel and the runner length effects the mixture motion of the charge so don't be suprised if a jet change and timing change makes more power or less power for you as you experiment. In some tests the engine wanted as much as 4 degrees less ignition timing, indicative of efficiency changes and in this case it was a positive change!

To date the best stack I have found with engines built my way with our heads and camshafts is the 1-7/8 stack (stock on 44 webers) and the CB style manifolds shortened 1 full inch.... On our FP engines we run the manifold length as short as the rules allow with short stacks with one hell of a tulip on them but very litttle height to them, basically they are flared all the way down to the carb entrance- Thats just one key to digging up 186 HP from an 1832cc engine (IMG:http://www.914world.com/bbs2/html/emoticons/boldblue.gif)

Its ALL in the combo fellas- forget that Chevy, 911 and TI knoowledge and start letting this engine teach you how to manipulate it- don't question it just listen, try and try again and learn!

[lapuwali]

Jake, I don't know where this "conventional wisdom" is that you reference is coming from. However, what I said, and Andy said, and a couple of others here have said, and virtually every academic book on intake tuning will tell you, exactly matches what you say above. And it works on ALL engines, not just the Type IV.

I know you don't like "theory", but I think sometimes that if you sat down with a good book on the theory and actually read it, you'd find a lot of the hard-won knowledge you've picked up over the years right there on the page. And a lot of this research is pretty old. Much of it was known as early as 1920, and I doubt there's been a whole lot of new knowledge added to the pile on intake and exhaust tuning since 1950.

[J P Stein]

From what I have read on the long stacks/short stacks Can Am deal, it was to tune out a two peak torque curve with a mid range dip....basicly treating the engine like 2 seperate 4 cylinder engines to smooth things out.
Note the short stacks are pretty tall.....that is probably a fuel reversion issue...my best guess.

[Joe Ricard]

Well the butt dyno tells me I have more torque lower in the RPM range. Intake difference is 1" longer and smaller opening at the 44 IDF carb. from 50mm short intake to 46mm long intake.
Throttle response is Much quicker. Enough to make me say DAMN!!!! that's cool. Pulls much harder on my favorite on ramp hit the freeway at 90 something MPH 4th gear. Never did that before.

Real test will be this weekend next A/X event should see the top of 3rd gear now.

[Air_Cooled_Nut]

QUOTE (lapuwali @ May 20 2005, 06:38 PM)

Jake,  I don't know where this "conventional wisdom" is that you reference is coming from.  However, what I said, and Andy said, and a couple of others here have said, and virtually every academic book on intake tuning will tell you, exactly matches what you say above.  And it works on ALL engines, not just the Type IV...

(IMG:http://www.914world.com/bbs2/html/emoticons/agree.gif)
Don't quite understand who you were ranting about as you confirmed what's already known (IMG:http://www.914world.com/bbs2/html/emoticons/blink.gif)

[messix]

the stacks jake is using are doing nothing but smothing the air flow into the carb-t/b.

the can-am cars with the multi level stacks was a botch up job of tuning out flat spots in the power curve of the motors. and those exposed stacks had bad problems at speed due to unstable and turbulent air entry. take a look at all forms of racing now , do you see any thing like this now? modern tech has shown how important smooth and calm air entry and port tuning of the intake runners to produce the best power.

it is not a magical art or some big mistery.

jake has done the hard work of trial and error, where engineers have modeled all this with modern hydrodynamics models aided greatly now by computers.

all this is alot of math for us garage builders so trust the cams grinders and intake designers to what they tell you about what the rpm range and torque band will be for your combo will be.