So I have short intakes and 44IDF's with 38mm vents
How long of an intake should I go to with these carbs or should I go to 40 IDF's with 32 vents or 28 vents.
I have some longer runner intakes and the other carbs so it's just a matter of experimenting I guess.
2.0L Bus piston Web 86B portmatch intake and exhaust ports. 13lb flywheel Bursch SSI Car weighs 1965 lbs 205/50-15 Kumho V700 R tires.
Thought of playing with spacers under the carbs to get more length and maybe spacer under the common length velocity stack. Looking for more torque down lower to pull harder exiting the apex of tight AX turns.
Whose got the experience of really been there done that? great gains or don't bother.
Full Version: Intake length vs torque
Please correct me if i'm wrong anyone.....
Generally speaking most torque engines use a low rise intake. More low end and quicker response. The closer to the head the better the response. At low RPM's the air velocity is slower unless the intake runners are more narrow. If I was you i'd go more narrow tubes. Shorter intake. The trade off. Smaller intake runners = less top end.
Top end motors use high rise intakes and velocity stacks to optimize air pulses stacking one on top of another.
My intake is a high rise and runners are very open all the way to the ported heads. I am trying to avoid lots of low end torque in my setup. The oposite of what you want.
Generally speaking most torque engines use a low rise intake. More low end and quicker response. The closer to the head the better the response. At low RPM's the air velocity is slower unless the intake runners are more narrow. If I was you i'd go more narrow tubes. Shorter intake. The trade off. Smaller intake runners = less top end.
Top end motors use high rise intakes and velocity stacks to optimize air pulses stacking one on top of another.
My intake is a high rise and runners are very open all the way to the ported heads. I am trying to avoid lots of low end torque in my setup. The oposite of what you want.
| QUOTE (rogergrubb @ May 18 2005, 02:25 PM) |
| Generally speaking most torque engines use a low rise intake. More low end and quicker response. |
actually, it's exactly the opposite ...
longer intake runners will promote more low end torque/hp, shorter runners will promote more high end torque/hp ...
what size is your engine? 38mm vents sounds awefully big for a smaller engine, you'll have *no* air-speed to speak of.
i use 32mm vents in my 44s (on a 2056 with a hot cam) and that really helped with the low end grunt and the top end HP and the transition between idle jets and main jets.
with the old 36mm vents, it would fall flat on it's nose at around 4k rpm ...
now i have power all they way up to 7k rpm ...
Andy
| QUOTE (SirAndy @ May 18 2005, 02:03 PM) | ||
actually, it's exactly the opposite ... longer intake runners will promote more low end torque/hp, shorter runners will promote more high end torque/hp ... |
Nope, the other way. Short = torque; Long = HP.
tom...
pull a move like mazda racing did-
varying intake length on the fly!
varying intake length on the fly!
| QUOTE (Tom73 @ May 18 2005, 03:18 PM) |
| Nope, the other way. Short = torque; Long = HP |
are we sure about this?
because that's not what i have learned and that's also not what the factory had to say when i was researching the numbers on the various air-cooled porsche intake designs ...
everything i dug up said that longer intake runners will promote low end torque.
but i was only looking at porsche factory FI setups, maybe carbs operate differently?
but then again, what do i know?
Andy
Andy's right. Long = low-end weighted power curve, short = top-end weighted power curve. In both cases, with all else equal, the area under the torque curve is the same, you're just moving the peak up and down the rev band.
Picture a typical dyno chart, with RPM rising left to right, and HP and torque rising bottom to top. Move the torque peak to the right (higher revs), and you move the HP peak UP as well as farther to the right. Make the intake tract longer (no other changes), and the torque peak moves left (better low-rev torque, but less HP at peak). Make it shorter, and the torque peak moves right (less torque at low-revs, but more HP at peak).
Same thing happens with exhaust header lengths.
Picture a typical dyno chart, with RPM rising left to right, and HP and torque rising bottom to top. Move the torque peak to the right (higher revs), and you move the HP peak UP as well as farther to the right. Make the intake tract longer (no other changes), and the torque peak moves left (better low-rev torque, but less HP at peak). Make it shorter, and the torque peak moves right (less torque at low-revs, but more HP at peak).
Same thing happens with exhaust header lengths.
Well actually it's got way more than just intake length and size.
Skinny intake=higher velocity.
Larger intake = slower velocity buy higher max volumnes of air.
Longer runners allow air to be "stacked". Stacking meaning.... As the column of air is drawn into the cylinder the intake shuts.
At this point pressure ouside the intake is building up for a milli second. Depending on the velocity of the air and the runner size it can maintain a positive pressure for either a shorter or longer time. You might want a shorter time for low end engines and a faster time for high revving engines.
Ideally I want the pressure waiting outside the intake valve to still be there when the valve opens again. Kinda' like a blower but not.
If I take a straw and fill it up with water. Then remove my finger from the end and then stick my finger back on the end I feel a vacuum for a quick second. The water is acting kinda like the air column in the intake runner. Air has mass and inertia. Having air going in a straight line and making these pressure surges at the right times of intake and exhaust is the key to REAL tuning of the intake and exhaust systems.
the same canbe done with the exhaust system. Using the air rushing out the exhaust valve, a negative pressure can be exerted in the exhaust stroke more effectively ridding the cyl of exhaust gasses. Kinda like on my 500cc 2 stroke dirt bike. =-)
Skinny intake=higher velocity.
Larger intake = slower velocity buy higher max volumnes of air.
Longer runners allow air to be "stacked". Stacking meaning.... As the column of air is drawn into the cylinder the intake shuts.
At this point pressure ouside the intake is building up for a milli second. Depending on the velocity of the air and the runner size it can maintain a positive pressure for either a shorter or longer time. You might want a shorter time for low end engines and a faster time for high revving engines.
Ideally I want the pressure waiting outside the intake valve to still be there when the valve opens again. Kinda' like a blower but not.
If I take a straw and fill it up with water. Then remove my finger from the end and then stick my finger back on the end I feel a vacuum for a quick second. The water is acting kinda like the air column in the intake runner. Air has mass and inertia. Having air going in a straight line and making these pressure surges at the right times of intake and exhaust is the key to REAL tuning of the intake and exhaust systems.
the same canbe done with the exhaust system. Using the air rushing out the exhaust valve, a negative pressure can be exerted in the exhaust stroke more effectively ridding the cyl of exhaust gasses. Kinda like on my 500cc 2 stroke dirt bike. =-)
Nice theory. Wrong, but nice-sounding.
You can the below (which is very imperfect, and diagrams are really called for), or you can just look at any motorcycle made in the past 20 years. Bikes make power (lots of it: 150-160hp per liter is common) at high revs, and very little power at low revs. They also have very short intake tracts. The typicla car engine makes power much lower (like half the revs or less, and most don't break 100hp/liter, many are below 80hp/liter), and have long intake runners. Short = high revs, long = low revs.
Now, the treatise:
Intake length is tied to valve timing and engine speed, and only really makes a big difference with cams that produce lots of overlap.
You open the exhaust valve as the piston is about 80% of the way to BDC on the compression stroke, as you've extracted all of the useful energy from the pressure rise after combustion. This sets up a positive pressure wave out the exhaust and down the pipe. This wave keeps going until it hits a major change in section (like in the collector), where it reflects back up the pipe to the valve as a negative pressure wave. This helps to suck the burnt charge out through the open valve. The wave reflects again, and keeps travelling back and forth, diminishing in strength, until the next time the valve opens. A similar thing happens on the intake side, except the "sign" is reversed. A negative pressure wave travels up the tract until it hits open air (or the airbox), when it gets reflected back as a positive pressure wave.
In an engine with lots of valve overlap, the wave coming back in through the exhaust can travel across the cylinder and try to push the new charge (and some residual exhaust gases) back through the open intake valve. With ideal timing, the reflected intake wave will arrive at the valve just in time to prevent the exhaust wave from pushing any charge out the intake valve. With bad timing, the charge will be blown all the way back up the tract, only to be reflected back. With really bad timing, the intake valve will close before it can re-enter.
If you look at the torque curve on an engine with lots of overlap, you'll see a series of hills and valleys. The hills are where the timing works out, the valleys are where it doesn't. Typically, each hill is higher as the revs rise, and each valley is deeper, until the torque peak is reached, which generally happens about when the speed of sound is reached by the charge attempting to flow through the intake valve.
Less overlap smooths out the hills and valleys, but at the mean between the peaks and troughs, not at the tops of the hills. Changing the length of the intake and/or exhaust tracts also shifts the height and position of the hills and valleys. With variable length intake tracts, variable valve timing, and variable exhausts, you could conceivably smooth out the bumps with the torque peak up near the peaks, rather than at the mean. This is the sort of thing current F1 engines are using, which is how they're managing to get any kind of drivability with 20K rpm 3.0 engines. Most motorcycles do not have these kinds of toys, but they have the severe cam timing, so you end up with peaky engines that make very little power below (say) 5K rpm, and huge power above 9K rpm. Motorcycles make lots of power at high revs, and have very short intake tracts. Short = high revs. Long = low revs.
You can the below (which is very imperfect, and diagrams are really called for), or you can just look at any motorcycle made in the past 20 years. Bikes make power (lots of it: 150-160hp per liter is common) at high revs, and very little power at low revs. They also have very short intake tracts. The typicla car engine makes power much lower (like half the revs or less, and most don't break 100hp/liter, many are below 80hp/liter), and have long intake runners. Short = high revs, long = low revs.
Now, the treatise:
Intake length is tied to valve timing and engine speed, and only really makes a big difference with cams that produce lots of overlap.
You open the exhaust valve as the piston is about 80% of the way to BDC on the compression stroke, as you've extracted all of the useful energy from the pressure rise after combustion. This sets up a positive pressure wave out the exhaust and down the pipe. This wave keeps going until it hits a major change in section (like in the collector), where it reflects back up the pipe to the valve as a negative pressure wave. This helps to suck the burnt charge out through the open valve. The wave reflects again, and keeps travelling back and forth, diminishing in strength, until the next time the valve opens. A similar thing happens on the intake side, except the "sign" is reversed. A negative pressure wave travels up the tract until it hits open air (or the airbox), when it gets reflected back as a positive pressure wave.
In an engine with lots of valve overlap, the wave coming back in through the exhaust can travel across the cylinder and try to push the new charge (and some residual exhaust gases) back through the open intake valve. With ideal timing, the reflected intake wave will arrive at the valve just in time to prevent the exhaust wave from pushing any charge out the intake valve. With bad timing, the charge will be blown all the way back up the tract, only to be reflected back. With really bad timing, the intake valve will close before it can re-enter.
If you look at the torque curve on an engine with lots of overlap, you'll see a series of hills and valleys. The hills are where the timing works out, the valleys are where it doesn't. Typically, each hill is higher as the revs rise, and each valley is deeper, until the torque peak is reached, which generally happens about when the speed of sound is reached by the charge attempting to flow through the intake valve.
Less overlap smooths out the hills and valleys, but at the mean between the peaks and troughs, not at the tops of the hills. Changing the length of the intake and/or exhaust tracts also shifts the height and position of the hills and valleys. With variable length intake tracts, variable valve timing, and variable exhausts, you could conceivably smooth out the bumps with the torque peak up near the peaks, rather than at the mean. This is the sort of thing current F1 engines are using, which is how they're managing to get any kind of drivability with 20K rpm 3.0 engines. Most motorcycles do not have these kinds of toys, but they have the severe cam timing, so you end up with peaky engines that make very little power below (say) 5K rpm, and huge power above 9K rpm. Motorcycles make lots of power at high revs, and have very short intake tracts. Short = high revs. Long = low revs.
Yea, Andy is correct--
A good view of this in work is any 80's-early 90's chevy small block FI---you can see how chev wanted as much TQ as possible by incorporating those really long runners from the plenum--they are about 14 inches long from plenum side to the vavle head--made a real stomper of a motor--but lacked any real serious high end power. 205 HP but over 300 TQ
The antethesis of this is look at any modern crotch rocket--absolutley no intake runner length at all from throttle plates to the valve head--this makes unreal screaming power on top, and a real deficit of TQ just about everywhere. 165 HP but only about 70 TQ
i.e.--the shorter the length the more top end power ( cammed properly )and less TQ
the longer the length the more TQ generally across a stock rev range--but,
really hurts breathing abilities up top where most of the HP is made
A good view of this in work is any 80's-early 90's chevy small block FI---you can see how chev wanted as much TQ as possible by incorporating those really long runners from the plenum--they are about 14 inches long from plenum side to the vavle head--made a real stomper of a motor--but lacked any real serious high end power. 205 HP but over 300 TQ
The antethesis of this is look at any modern crotch rocket--absolutley no intake runner length at all from throttle plates to the valve head--this makes unreal screaming power on top, and a real deficit of TQ just about everywhere. 165 HP but only about 70 TQ
i.e.--the shorter the length the more top end power ( cammed properly )and less TQ
the longer the length the more TQ generally across a stock rev range--but,
really hurts breathing abilities up top where most of the HP is made
So why to make HP on a V8 do you use a "high rise" intake manifold? That increases the runner length and that is done to build HP. Right?
That's right... 
Quote from CarCraft Magazine...
Smaller carburetors are commonly suggested for building torque, because their smaller venturis keep air velocity high to promote good fuel atomization. If you want to broaden the power band to retain good torque at the low end and extend power at the top end, you can make a case for a larger carburetor if it is teamed with the appropriate mix of components. The primary reason for keeping venturi size small is to maintain air speed through the boosters. This is especially critical with single-plane manifolds and larger cams, which generate weak booster signals at low rpm and the resulting loss of atomization quality and metering accuracy. This results in reduced torque output and poor driveability, but correcting it with smaller high-speed venturis may limit power at the high end.
Bottom line. there are trade-offs. U need to decide what's best for you.
Quote from CarCraft Magazine...
Smaller carburetors are commonly suggested for building torque, because their smaller venturis keep air velocity high to promote good fuel atomization. If you want to broaden the power band to retain good torque at the low end and extend power at the top end, you can make a case for a larger carburetor if it is teamed with the appropriate mix of components. The primary reason for keeping venturi size small is to maintain air speed through the boosters. This is especially critical with single-plane manifolds and larger cams, which generate weak booster signals at low rpm and the resulting loss of atomization quality and metering accuracy. This results in reduced torque output and poor driveability, but correcting it with smaller high-speed venturis may limit power at the high end.
Bottom line. there are trade-offs. U need to decide what's best for you.
OHHH CRAP! Why-oh-why will my hood not fit right??? It did when it came off the car!! SHEEEEEEZE!!!
And a little tip...
Before removing any lid's, make an outline with a pencil around where the hinge bolts to the lid.
I learned that in Mr Batterman's auto shop class. 1979.
Well I knew all that. But what I want is the recipe for the engine I have. I am going to try the 40 IDF long intake with 46mm opening at the top vs 50mm short intakes.
I may make up some spacer shims to lengthen the intake even more. Also try to lengthen the velocity stack. can't go to much as I have short filters.
I'll let you know how it goes.
By the way this motor does rock above 4500 RPM doesn't fall on it's nose ever I have seen 7200 RPM in 3rd. Co- driver thought I was going to scatter it all over the track.
That was 10,000 miles ago. I put a rev limiting rotor in it now. Shift light @ 5500 makes my shift About 6000.
I may make up some spacer shims to lengthen the intake even more. Also try to lengthen the velocity stack. can't go to much as I have short filters.
I'll let you know how it goes.
By the way this motor does rock above 4500 RPM doesn't fall on it's nose ever I have seen 7200 RPM in 3rd. Co- driver thought I was going to scatter it all over the track.
That was 10,000 miles ago. I put a rev limiting rotor in it now. Shift light @ 5500 makes my shift About 6000.
| QUOTE (Tom73 @ May 18 2005, 05:26 PM) |
| So why to make HP on a V8 do you use a "high rise" intake manifold? That increases the runner length and that is done to build HP. Right? |
You nailed it right on the nose. High rise itakes straighten out the air flow increasing velocity.
Personal experience:
really really short intake = never get below 3400 rpm or there is no torque. Motor just flys from 4000 to 6000
really long intake = plenty of pulling as low as 2000 rpm, not as quite as quick getting to redline.
For street and AX, I'd use long ones. For runoffs or high speed tracks, use shorties. I would also use the 40 idf carbs for higher flow speed to get quicker on/ off throttle response..
Put those phenolic heat resistant spacer 'tween head & manifold, too. I left 'em out when I switched and under the right (wrong) conditions ( 200 miles, then stop, then restart 3 minutes later) I had some burbling and gurgling from the vapor mix in the hot manifolds, Seems to have been eliminated by heat spacers.
really really short intake = never get below 3400 rpm or there is no torque. Motor just flys from 4000 to 6000
really long intake = plenty of pulling as low as 2000 rpm, not as quite as quick getting to redline.
For street and AX, I'd use long ones. For runoffs or high speed tracks, use shorties. I would also use the 40 idf carbs for higher flow speed to get quicker on/ off throttle response..
Put those phenolic heat resistant spacer 'tween head & manifold, too. I left 'em out when I switched and under the right (wrong) conditions ( 200 miles, then stop, then restart 3 minutes later) I had some burbling and gurgling from the vapor mix in the hot manifolds, Seems to have been eliminated by heat spacers.
What I don't understand is why runner length would affect anything at full throttle. With the butterfly all the way open, shouldn't it all be runner? Couldn't you get the best of both worlds by putting "runners" on the intake side of the throttle valve?
Hmm, I just realized... that's exactly what velocity stacks are for. Talk about reinventing the wheel!
Hmm, I just realized... that's exactly what velocity stacks are for. Talk about reinventing the wheel!
i did get a ride in joe's car, with the exception of starting i dont think he was ever below 2500 rpm, he was amazed at the pull my engine had in 4 th gear at 1500 rpm.
joe the only thing i would try with your car is MS with a stock fi runner and throttle body, you want torque and the stock system made gobs of it. heck even subaru made the same basic intake setup and you saw what that is like
joe the only thing i would try with your car is MS with a stock fi runner and throttle body, you want torque and the stock system made gobs of it. heck even subaru made the same basic intake setup and you saw what that is like
Yea Scott, Your motor in my car and it would be pretty damn scary fast. HOWZ it going with the Transaxle? Figure out 3rd gear yet? I'll bet you are hitting the plastic bushing before getting full rod motion.
nope i have done almost nothing... got a new battery... pulled the alt
i just charge the battery and go driving, sometimes with 3rd some times with out i can go an hour with no alt with out worring. i just need to rebuild money before i look at it too much
i just charge the battery and go driving, sometimes with 3rd some times with out i can go an hour with no alt with out worring. i just need to rebuild money before i look at it too much
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.
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.
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
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
What was the thinking behind this type of setup...lots of Can-am cars seemed to have tall and short VS's
| 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.
Looks like organ pipes- each one tuned to a different frequency.
Thats so the driver can play tunes with the engine
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.
Ken
Thats so the driver can play tunes with the engine
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.
Ken
Didn't Jake do a test of different length Webber intakes on his dyno?
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.
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.
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.
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.
So how DO you measure throttle response? That's important! 
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
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
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.
Also higher velocities help. Meaning smaller air passages.
And in conclusion.....
Lighten your flywheel. Much snappyness is to be had there.
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. 
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!
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....
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
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!
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!
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....
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
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!
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.
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.
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.
Note the short stacks are pretty tall.....that is probably a fuel reversion issue...my best guess.
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.
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.
| 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... |
Don't quite understand who you were ranting about as you confirmed what's already known
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.
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.
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