Gain 100HP with an intake manifold change?? - Cross post from Ferrari Chat
04-13-2016, 10:52 AM
#649
Rennlist Member
Join Date: Feb 2011
Location: Mostly in my workshop located in Sweden.
Posts: 2,230
Received 463 Likes
on
248 Posts
Tuned intake manifold
First introduced by Mercedes 300SL in 1954, tuned intake manifold is not exactly a new technology. It is discussed here just because its principle is useful to our further study of variable intake manifold.
Before 1950s, engineers believed short intake manifolds were the best to engine breathing. Then they discovered that under some conditions long intake manifolds could actually improve output, thanks to a so-called "supercharging effect". How is that done ? Let's see the following illustration:
When fresh air is sucked into combustion chamber, it gathers speed and momentum in the intake manifold. As soon as the inlet valve is closed, the fast-moving air hits the valve and compresses, generating high pressure. With no where to go, this high pressure bounces back, travels along the intake manifold, hits the plenum at the other side and bounces back again. In this way, the high pressure bounces back and forth along the intake manifold until the inlet valve opens again, creating pressure waves.
Now the interesting thing is: if the inlet valve opens again exactly when the pressure wave comes back, the pressure wave will help charging the combustion chamber due to its high pressure. This is not unlike charging the combustion chamber with a light supercharger, thus we call this supercharging effect.
In order to match the timing of valve opening, the frequency of pressure wave shall synchronize with engine rev, obviously. This frequency is dependent on the length of the intake manifold (L in the figure). The longer the length, the longer the time pressure wave takes to bounce back thus the lower frequency of pressure wave is attained. As a result, a longer intake manifold leads to supercharging effect at lower engine rev. A shorter manifold leads to supercharging effect at higher rev. By selecting a suitable manifold length, we can obtain the desired power characteristic.
Calculations found in order to achieve useful supercharging effect, the intake manifold shall be unusually long. If it is too short, the pressure wave will bounce back and forth too many times in the manifold before the valve opens again, by then the high pressure is largely diminished. Therefore a tuned intake manifold shall be long.
Unfortunately, tuned intake manifold works only across a narrow rev band. If the engine revs beyond that band, the pressure wave will arrive too late in the intake stroke, contributing little to charging. If the engine runs below that rev band, the pressure wave will arrive the inlet valve before it opens. In both cases, the low pressure area of pressure wave may even work against cylinder charging, hampering torque output.
A sports car engine may employ a shorter tuned intake manifold to optimize its output at high rev (in the expense of low to medium rev output). On the contrary, a heavy sedan or commercial van engine may choose a longer manifold to favour low-rpm output at the price of high-rev output. As you can see, the selection of manifold length is always a compromise. That's why many modern engines turn to variable intake manifold...
First introduced by Mercedes 300SL in 1954, tuned intake manifold is not exactly a new technology. It is discussed here just because its principle is useful to our further study of variable intake manifold.
Before 1950s, engineers believed short intake manifolds were the best to engine breathing. Then they discovered that under some conditions long intake manifolds could actually improve output, thanks to a so-called "supercharging effect". How is that done ? Let's see the following illustration:
When fresh air is sucked into combustion chamber, it gathers speed and momentum in the intake manifold. As soon as the inlet valve is closed, the fast-moving air hits the valve and compresses, generating high pressure. With no where to go, this high pressure bounces back, travels along the intake manifold, hits the plenum at the other side and bounces back again. In this way, the high pressure bounces back and forth along the intake manifold until the inlet valve opens again, creating pressure waves.
Now the interesting thing is: if the inlet valve opens again exactly when the pressure wave comes back, the pressure wave will help charging the combustion chamber due to its high pressure. This is not unlike charging the combustion chamber with a light supercharger, thus we call this supercharging effect.
In order to match the timing of valve opening, the frequency of pressure wave shall synchronize with engine rev, obviously. This frequency is dependent on the length of the intake manifold (L in the figure). The longer the length, the longer the time pressure wave takes to bounce back thus the lower frequency of pressure wave is attained. As a result, a longer intake manifold leads to supercharging effect at lower engine rev. A shorter manifold leads to supercharging effect at higher rev. By selecting a suitable manifold length, we can obtain the desired power characteristic.
Calculations found in order to achieve useful supercharging effect, the intake manifold shall be unusually long. If it is too short, the pressure wave will bounce back and forth too many times in the manifold before the valve opens again, by then the high pressure is largely diminished. Therefore a tuned intake manifold shall be long.
Unfortunately, tuned intake manifold works only across a narrow rev band. If the engine revs beyond that band, the pressure wave will arrive too late in the intake stroke, contributing little to charging. If the engine runs below that rev band, the pressure wave will arrive the inlet valve before it opens. In both cases, the low pressure area of pressure wave may even work against cylinder charging, hampering torque output.
A sports car engine may employ a shorter tuned intake manifold to optimize its output at high rev (in the expense of low to medium rev output). On the contrary, a heavy sedan or commercial van engine may choose a longer manifold to favour low-rpm output at the price of high-rev output. As you can see, the selection of manifold length is always a compromise. That's why many modern engines turn to variable intake manifold...
04-13-2016, 10:53 AM
#650
Nordschleife Master
Join Date: Dec 2004
Location: Guelph, Ontario, Canada
Posts: 6,164
Likes: 0
Received 5 Likes
on
5 Posts
im thinking of buying it.. found another newer one for cheaper too.
why do you say the 16valve is a no go? due to the shape? the shape looks like the S4 runners, no? i wonder how close in size.
the challenge is cutting them off and whats left, either connecting to the short manifold of what carl has made , or something else , maybe 968 manifold?
then, seeing if you can spread them out by about 1/2" each and spread the side to side spacing by about 1-1.5 " as well.
why do you say the 16valve is a no go? due to the shape? the shape looks like the S4 runners, no? i wonder how close in size.
the challenge is cutting them off and whats left, either connecting to the short manifold of what carl has made , or something else , maybe 968 manifold?
then, seeing if you can spread them out by about 1/2" each and spread the side to side spacing by about 1-1.5 " as well.
Doooooo iiiiit!!!!
04-13-2016, 11:55 AM
#652
Former Sponsor
Actually, those AM ports look huge, too....although it is tough to tell from a picture.
04-13-2016, 12:12 PM
#654
Administrator - "Tyson"
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
04-13-2016, 12:15 PM
#655
Archive Gatekeeper
Rennlist Member
Rennlist Member
_That's_ where BMW got that idea? Wow.
04-13-2016, 12:30 PM
#656
Nordschleife Master
...Unfortunately, tuned intake manifold works only across a narrow rev band. If the engine revs beyond that band, the pressure wave will arrive too late in the intake stroke, contributing little to charging. If the engine runs below that rev band, the pressure wave will arrive the inlet valve before it opens. In both cases, the low pressure area of pressure wave may even work against cylinder charging, hampering torque output...
Insane power across a very narrow rev band.
I know snowmobile racers who do some amazing stuff. They get the engine/pipe combo dialed in, and then work over the clutch/CVT combo so that the engine is revving "just right" no matter what the speed the machine is going.
These are mostly "Ice Drag Racers".
They are really fast.
04-13-2016, 01:21 PM
#658
Rennlist Member
04-13-2016, 01:23 PM
#659
Rennlist Member
2-stroke engines use a tuned exhaust that accomplishes essentially the same thing.
Insane power across a very narrow rev band.
I know snowmobile racers who do some amazing stuff. They get the engine/pipe combo dialed in, and then work over the clutch/CVT combo so that the engine is revving "just right" no matter what the speed the machine is going.
These are mostly "Ice Drag Racers".
They are really fast.
Insane power across a very narrow rev band.
I know snowmobile racers who do some amazing stuff. They get the engine/pipe combo dialed in, and then work over the clutch/CVT combo so that the engine is revving "just right" no matter what the speed the machine is going.
These are mostly "Ice Drag Racers".
They are really fast.
04-13-2016, 01:24 PM
#660
Rennlist Member
