BFI Anyone???

[COFFEE]

Guys,
I have heard of the BFI and read Peters page.
I thought i would do a little stuffing around of my own with some rubbish i had lying around the place.

I removed the air box all together, found an air intake off a 3.8ltr vn commadore ( long striaght with a 90 bend in it ) and used it from the AFM forward.
I made up out of fibre glass an adaptor from the AFM to the commador intake pipe, also heated up the pipe and flattened it a little to pass under the light.
From here i used a 90 degree bend in 80mm plumbing pipe and glued short peices in the bend so to attach the commadore pipe and pod filter.
I clamped the pod filter and the siliconed and pop riveted the commadore intake to the bend.
With the stock bar it lines up at the opening next to the turning lamp ( some think it's a fog light ) cut two triangles into the fins and all done.

Sounds a little crazy but works a lot better than i expected.
The car gets as colder air as naturally possible and ramed straight in the filter.

The down side is that the air intake at full throttle and above 4000rpm is louder than the exhaust and i don't have a staock system.
You can feel the car start working pretty significantly from 3500rpm up, you get a surge like there were a small turbo.
That and the fact that it sounds like a formular one car and edges you to keep pushing it, then there is the attention factor. It's mad

After seeing this work and wanting something a little tidier i am going to get it all made up out of 3inch mandrel bent exhaust.
The only problem then is keeping the heat soak out of the exhuast pipe.

Regards

Stephen

 

[Zuffen]

Stephen,

I think 80mm sewer pipe is a little small.

If you want to deliver the maximum amount of air to the AFM try 100mm. I know it's harder to fit it in but the increase in airflow is enormous, over 50% increase in potential flow.

I have two 90degree bends and the airfilter (stock Crown with the snorkel removed from the front and an enlarged exit) is open at the front with no bodywork in front of it. It gets the most and coolest air available. I plan on opening up the front of the filter housing to see how much more air I can get into it.

 

[COFFEE]

Zuffen,
Whilst 80mm doesn't sound that big and the aim is to get as much air as possible, you can only get as much air in as the smallest section area will allow, this is the AFM.
The AFM is smaller than 80mm.
That and the fact that the intake size has the same effects as a turbo, to small and she luanches of the mark and dies in top end ( starves of air ) to big and she is a pig off the mark and hauls %$ in the top end ( not enough air speed at low rpm due to size )
Whilst the motor makes good power for it capacity, I think 80mm in mandrel bent exhuast pipe would be plenty big for a stock motor.
But thats just my opinion, that and the fact that you can really feel the cam kick in around 3500rpm and up which says it is definately getting plenty of air and when made in mandrel bent pipe there will be a lot less restriction so the air flow will increase again.
Trying to get some long strights is a bonus so the air speed picks up.

Regards

Stephen

 

[Zuffen]

Stephen,

Think of it this way; If you remove the air intake from the air filter to the AFM and run the car the AFM is getting the maximum air it can pass without having to suck it trough a similar sized pipe as the AFM.

All pipes have internal resistance so the bigger the pipe the more air that can flow for a given pressure drop.

The rule of intake speeds relates to ports etc which are the real restrictors. I figure give them the most air you can and you won't do it any harm. If you restrict the amount of air the restriction can access you are limiting how much air the restriction can pass.

 

[SCV8]

I found good gains after getting rid of the panel filter and replacing it with something with about twice the filter area.
Any problems with the lower revs should be tuned out, usually by the ecu after a couple days of driving. The high revs can be tuned with fuel pressure, and or ecu, or piggyback adjustments.

 

[COFFEE]

Zuffen,
Whilst it sounds practicle and logical it doesn't work that way.
What is happening in a manifold is that the port is usually a restirctor, usually.
There has been cases where they have got better performance from filling the port as it is to big for the application, such as the VN Commadore heads.
Becuase the intake path from start to finish is so short and small it is very critical.
Air builds up speed in long straights. It slows down in resticted areas such as bends and section areas that are to large for the amount of flow that there is no restriction, that and large increase or decreases in section areas along with pretruding edges.
The problem with intakes is the dramatic changes in section size and shapes thus cuasing are to slow.
If you get the heads right your half way there, a decent size and length runner to the plenum so the air speed can increase.
A bell mouth in the plenum from the runner would be ideal to assist with the transition and lack of pressure.
Then the second stage would be to get the plenum as pressurised as possible to increase the air speed entry to the runner, thus greater air speed through the runner to the head.
To do this, as long straights as possible with as little bends and not to larger section area but not to small as to restrict.
This way the whole system is as pressurised as possible.

See the factory air box creates a large pressure drop in front of the AFM, that and the short run to the plenum with a bend makes for slower air speed.
What Peter is trying to do is get more pressure in the box plus more air
What i have done is just that, becuase the air is from the front of the bar it's cold and forced into the intake path.

The other factor is the maximum air flow required matching what the cams will let you use.
Another words, there is no point in making the intake system large enought to carry 8000rpms worth of air if the stock cam only makes power till 6000-6500rpm, otherwise it will be like watering the garden through a stormwater pipe.
The best application would be to make a twin throttle set up like the Group A Walkinshaws that used twin runners that joined just before the AFM.
This would allow for max air flow for top end with out comparmissing the low down torque, this is why quad throtle bodies are so effectivebut more so with tuned length trumpets.

Regards

Stephen

 

[Zuffen]

The "Ram" effect of a forward facing intake does not take effect until over 100MPH or 165KMH. If you get to use the Ram effect you may also end up in jail. Particularly in Victoria.

The longer the pipe the greater the frictional loss and hence horsepwer. That's why 4x4's with snorkels put out less power than their brothers without snorkels.

Assuming your theory is right AA Fuel dragsters would run long runners in front of their superchargers.

I agree the ports/valves are the usual restriction but this does not forgive having a restrictive inlet tract.

If you dyno'd an engine with an 80mm and 100mm inlet tract you would find more HP from the 100mm and I wouldn't be surprised at (perhaps) higher torque from the 80mm pipe than the stock system. Air speed is critical to torque so the more air you have available to be drawn thru the restriction (where the air speeds up) the better.

The double throttle body on a Walkinshaw has a restrictor plate in the secondary opening which reduces it's diameter to less than 50mm. I know I have one at home that I took out of my Walkinshaw the day after the Holden Dealer delivered it to me. I did it at the same time I adjusted the idle they couldn't get right.

Sometimes you need to look at extremes to see what minor effect changes make. If the inlet tract was 10mm in diameter the engine wouldn't run. If the tract didn't exist and there was only a bell mouth on the AFM you would get a lot more HP and Torque than stock.

We all go for larger air filters to pass more air.

Have a look at the excellent work done by Pete Scott on Planet Soarer or Julian Edgar in Autospeed on the impact of intake size plus air filter and air box implications.

 

[COFFEE]

Zuffen,
You are right.
The longer the pipe the greater the amount of friction restricting air flow, less speed, hence less air.
Keep in mind the small distance the whole intake path is, frictional loss would be small in that respect.
As for the 50mm restrictor in the Wlkinshaw throts ?
Never owned one, nor would i. I was merely using it as an example.
Whilst i have not put my car on a dyno to see the figures on paper and sometimes they seem better than they are, i am happy to see change and a well felt one at that.
Greater air speeds generate greater acceleration which is due to increase in torque.
Two ways to get power from a motor: revs and torque.
Whilst there is no doubt that these motors will rev and can handel it, the standard cams wont give much.
However these motors are not great in the torque aspect and not down low in the revs.
If you choose to go larger on the intake the friction will be less and also the air speed, thus generating less torque and possibly greater power figures if the air speed is enough in the cams top end of it's rev range.
If the intake is so large that the air speed wouldn't pick up until say 8000rpm and the cams finish at 6-6500rpm you will have a pig of a car.
As for the RAM effect, i don't know at what speed the air would be moving faster than the amount being drawn through the intake creating the RAM effect.
But i do know that the colder air being drawn from the front of the car is colder than that in the engine bay, along with the speed creating a wind chill factor to the air temp is significant enough in it's own merit to make change to the performance.
I would imagine any air blowing at any speed, straight into the air filter whilst in it's direction must have an effect over drawing air from a confind space at atmosphereric rate ?
I most certinely agree that a larger filter should pass more air but if the filter for one, isn't getting enough air it would defeat it's purpose.
Secondly, if the inlet tract was to increase likes ours does rather dramaticly you would get a pressure drop, robbing us of air speed, hence power/ torque.
As for the looking at extremes i certinly agree, sometimes we need to look out side the square !

Eg: 10mm inlet tract compared to the bell mouth.
Why didn't you say block off the inlet tract compared to the bell mouth ?
We can make things work, then we can make them much better, then we can fine tune them to there application.
Your eg i would consider some what back at the beginning of the creation of the combustion engine, little behind the eight ball here.

Stephen

 

[Zuffen]

The air speed is only critical after fuel is injected.

Air speed leading to the ports is inconsequential. It's the air speed passing thru the ports that counts.

How fast is the air moving in front of the inlet to the intake system. Probably about 1/10th of the speed at the ports, but it doesn't affect performance.

The increase in pressure at 100mph is less than 1" of Mercury. The increase in density of intake air from a CAI is the best gain you can get. A good air filter will rob you of a minimum of 2" of mercury and some can rob up to 5".

So if you get rid of your air filter you will save twice the effective ram effect of driving at 100mph.

The ideal system would have no restriction between the ports and the outside world so the ports were getting air at 14lb/sq" rather than having to suck it in at 5 or 6lb/sq".

Remenber a comustion chamber only fills because the air pressure is less (we would call it a vacuum) in the cylinder than outside so the air rushes in the open valve. The less restriction for the air making it to the valve the greater the fill of the cylinder when the valve opens.

 

[MWP]

Just to correct you on one point there Stephen...
Moving air isnt any colder than stationary air.
Wind-chill factor is caused by air moving over a persons skin which speeds up the rate at which heat is removed from the body.
It wont effect an engine.

 

[1youZee]

Air speed leading to the ports is inconsequential. It's the air speed passing thru the ports that counts.

that's kinda true.
this is where the cam selection becomes important. think of the air as it enters the intake runner heading towards an open intake valve while the piston is heading down in a cylinder creating a pressure drop or *vacuum*. air has mass and mass has momentum if it is in motion, when the valve closes all the air in thin intake runner/port slams into the back of the intake valve. now there is an area of increased pressure. The air then heads back up the port towards the now lower pressure intake plenum as it does it collides with the air that was about to come into the runner and the reverse happens again. now the air is again headed towards the valve, and depending on how long the intake runner and port are, and if the valve timing is just right, instead of hitting the back of the valve, the valve opens, just as the air would have hit it. this pulsing of air in the intake is what "tuned length" intake runners are all about. and also why cam selection plays a huge role in how the engine "breaths"

the longer the intake path from the plenum to the valve, the lower th RPM it will be good for. a wide/short path will not show benifits of this pulsing until high rpms.

 

[COFFEE]

MWP,
It's not the speed of the air that makes the difference thus the decrease/ increase in pressure on the surface of the object.

Zuffen,
With what you are saying, i should take my ports out as far as i can go and make the intake tract as big as possible that way there would be as little restriction as possible.
This way the car can flow as much as it can draw without resistance, the maximum power gain available from intake ?
I will agree with you on one thing "Remember a comustion chamber only fills because the air pressure is less (we would call it a vacuum) in the cylinder than outside so the air rushes in the open valve. The less restriction for the air making it to the valve the greater the fill of the cylinder when the valve opens."

After saying this and putting it into practice there is only 1 way to do this !
1- Make the air pressure outside the combustion chamber greater ( forced air ). Because you cant lower the pressure inside the chamber the only other way to make a greater difference between the two areas would be to increase the inlet pressure.

Pressure- "A stress or force acting in any direction against resistance."

You need resistance to have pressure !

Not enough resistance ( to larger section size ) will stop flow and to much resistance ( very small section area ) will stop flow.

Ask a head machinist if machining the ports out to the max along with an increased intake track will give the best result, he will ask whats done to the motor or whats going to be done, cams, FI ?
Stock motor, he will say a small- mild port polish.

It's like sticking a 5000rpm stally behind a stock engine, why ???
By the time it would be in the revs to work it would launch have nothing left.

 

[Zuffen]

Stephen,

We can debate the topic until we're old and grey (I allready am) so I guess we should both follow our own paths and live with our decisions.

I'll stick with my 100mm sewer pipe that's working very nicely right now.

 

[COFFEE]

Zuffen,
By any chance do you have any photos ?
I would be interested in having a look.

Regards

Stephen

 

[Zuffen]

Coffee,

Here you go.

I've painted it black so it looks a little better.

In the second photo you can see the air filte inder the front mudguard.

I used a 100mm floor waste and moulded it to the rear of the housing and ground out the opening to suit. I have 2 90degree bends set at 90degrees to each other to get to the filter. Total length is under 400mm.