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I am a mechanical engineering student here at Oklahoma State University. This year I joined the school formula SAE team to help out with designing and building thier car for this years comptetition

For the car's engine, we are going to use a honda cbr f4i engine out of a bike. the engine Powers 2 wheels and has a good amount of torque. It is a very good fit on our 4-wheeled, 400lb car.

 

Anyways my question is about the engine's air intake. The competition requires that we put a 20mm diameter fitting somewhere along the air intake. This air intake retrictor is meant to level the playing field.

So my questions are this:

How big/what kind of an intake is the engine designed to run with?

and

How can I tune the engine to run right with the 20mm intake restrictor?

Our current air intake design is a small cone ait filter with the 20mm restirctor right behind it and then it runs straight to the throttle bodies.

 

 

 

The openings of the stock intake tubes (there are 2) on the f4i are approximately 4 inches by 1.5 inches, so putting that restrictor on will definitely sap power. As a mechanical engineering drop out (now bio major) id say put the restrictor as far away from the motor as possible. And after the restrictor have an expansion (just like the airbox and the expansions in the ram air tubes) in the air tubing so that their is a reservoir for the engine to pull air from. You said you wanted good torque so the reservoirs will help. But as far as the engine, it makes very little torque to begin with, perhaps use a v twin instead.

to tune, if you are using the stock computer get a power commander (or similar).

also, if you need any parts i have these for sale:
 http://cbrworld.net/forums/thread/293130.aspx

I hear the Austria team was kick a$$ last year.........their car made over 100hp, I believe they had an R6 engine.

It's kind of like this.........The F4i engine will make around 95-98hp avg in the stock form......with the restrictor, it makes around....70-75hp?????....so you have 20-25+ hp to be found in the intake/exhaust systems..........  A lot of teams seem to design the int/ex system around the car.....maybe you should try the other way around......obviously within reason....

Smaller intake ports......600rr valves......don't forget about the airflow before it enters the the restrictor...I've seen a lot of designs where the team will just bolt an air filter before the throttle body, without thinking about trying to make the point of entry as smooth as possible(velosity stack maybe.....hidden inside a larger airfilter..etc)   Get creative....you'll need to find a local shop that has a flowbench to see the different results, otherwise, you're just shooting in the dark....

Have fun

Jeff

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My bike-2002 F4i-With OEM CCT......And no rattle
"Life would be boring if everyone was perfect"

Uncle Jeff:

I hear the Austria team was kick a$$ last year.........their car made over 100hp, I believe they had an R6 engine.

It's kind of like this.........The F4i engine will make around 95-98hp avg in the stock form......with the restrictor, it makes around....70-75hp?????....so you have 20-25+ hp to be found in the intake/exhaust systems..........  A lot of teams seem to design the int/ex system around the car.....maybe you should try the other way around......obviously within reason....

Smaller intake ports......600rr valves......don't forget about the airflow before it enters the the restrictor...I've seen a lot of designs where the team will just bolt an air filter before the throttle body, without thinking about trying to make the point of entry as smooth as possible(velosity stack maybe.....hidden inside a larger airfilter..etc)   Get creative....you'll need to find a local shop that has a flowbench to see the different results, otherwise, you're just shooting in the dark....

Have fun

Jeff

Nice estimate there jeff! Last year's car with an f4i put down about 70hp to the wheels.

We spent a long time discussing intake options yesterday. The intake design that the team went with on last year's car was definetly not optimal, so hopefully this year we will ahve the time to put more effort into that area. 20+ more hp would really make a difference competetively.

What exactly do you mean by "velocity stack"?  You mean an intake design that will that will get the air flowing fast before it hits the air filter?

LOL.........It wasn't actually a guess, since I was helping the University here work on their engine.   

Yes and no as to your question......yes to the velosity stack, but mount it so that the stack is mounted to the restrictor, which is mounted to the throttle body.  Then hide the velosity stack inside an air filter.  Most of the designs that I've seen have a K&N style air filter (off a carbed bike), mounted to the throttle body.  This means that the air has to pass through the filter then the restrictor, tb, intake, then the intake port, past the valve into the cyl.  thats a long way, so why not help the airflow, and speed it up before it enters the restrictor in the first place?..  

Think of it this way....why do you think when people concentrate on the seat/valve angles on a particular head?  because as the valve first starts to open, it's like a mini venturi. .  I'll try to explain  why  a little better.......I hope.

 The air that is traveling down the intake port is moving at a particular speed, it then starts to slow down as it reaches the valve seat .....it then has to pass through the opening (between the valve, and valve seat which is quite small at low valve lifts), then it speeds up again as it goes into the chamber/cyl..  The air flow is  suppost to speed up as it goes between the seat, and valve.  This is why so many  cyl head guru's  spend a lot of time/focus on the low valve lift flow #'s, by trying various seat angles/radius designs.

Put it this way...I got an increase of 40% in airflow at .025" valve lift over stock, with the port design/valve/seat angles..... It avg around 17% increase in airflow at all valve lifts.   I have yet to get my bike dyno'd only because I need a custom map made, and there's only one guy around here with a Eddy Current dyno, who charges an arm/leg for a map.  Hopefully next year I can afford it........LOL.

Now before you ask me what I did to the head........I did alll the work myself....and this is where it will get quite expensive......and I lost track of how many hours/heads I went through.  It has 600rr valves, springs, retainers( can't remember if I used the RR or F4i retainers now that I think about it), it has smaller intake ports, the chambers have to be reworked,  as well as the head gasket( this was the hardest part), and the block( for valve unshrouding)........  and the Stock pistons have to have larger/deeper valve reliefs  for clearance.   you'll also need smaller shims(way smaller, since the 600rr valves are longer, I believe the shims were around .030" thinner than stock). 

Like I said....be creative.

Jeff

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My bike-2002 F4i-With OEM CCT......And no rattle
"Life would be boring if everyone was perfect"

Good explanation, Thanks!

So what basic concept/design of a "velocity stack". I have never really heard that term befoire.

FormulaOSU:

Good explanation, Thanks!

So what basic concept/design of a "velocity stack". I have never really heard that term befoire.

get a hold of a fluid dynamics book and look up Nozzles, preferably converging-diverging nozzles w/ isentropic flow. plenty of info to be had on this topic. the final design will prob come down to how good u r w/ a lathe and how close u place it to the engine like UncleJeff said.

if u really want power out of an I-4 motor w/ an air restrictor, ure going to need a turbo or supercharger. a 30% gain of HP is ez to get, but wat u r really after is the near 100% torque gain. by restricting mass air flow into the motor, u r limiting horsepower no matter wat. the motor will only spin soo fast w/out all that necessary airflow. however, torque will continue to increase w/ modifications so long as u can fill the cylinders. because a supercharger aids in the "filling" dramatically, ull be amazed at how much torque u can produce.

heres some pics for an old car from my university. http://sae.ucsd.edu/images/fsae_images/fsae_images.html theyve got a dyno chart in there, and if ull notice they are running an old FZ6 motor. not nearly as potent as a F4i motor, but they managed 3rd in the acceleration test w/ a very heavy car (450lbs or so) and no traction control. the new car prob woulda been more powerful, punched and stroked 450cc single, and much much lighter... but it never made it to competition for other reasons.

ull def want to spend a lot of time considering head design. smaller intake (and exhaust) is def the way to go. theres no sense in increasing max flow through the head w/ bigger ports and bigger valves since u r going to be dealing with a lot less air due to the restrictor. hell, some race teams have had great results w/ smaller ports and they dont use an air restrictor at all. but ya, aim for/start with sonic flow through the ports and go from there. u should actually be able to treat the entire head as a converging-diverging nozzle, though the outlet obviously changes w/ valve lift... just something to think about.

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Naked 93' F2...... RIP -- 04/12/07
04' 600RR Black - currently stuck between track and street usage
- Brembo Master, Sato's, & Ohlins out back

So Im definetly glad I saved my fluid mechanics bbook from last semester then! And that I remember (most of) it.

 I had figured a velocity stack would involve some kind of nozzle design. I definetly can see how a nozzle on the intake would help get it though the restrictor faster. I would want to place the restrictor BEFORE the ait filter though, right?  

I personally have not ever worked on heads before, so I cant picture EXACTLY what your talking about  in that area,  but the team will be startin on that aspect soon enough and ill learn.

We have not really started the motor's design yet, we are still workin on getting the suspension and frame together.

 Thats cool that you mentioned adding a turbo to the f4i though...because that was the FIRST thing i had suggested to the team leader when we first got the motor delivered. This is my first year on the team so I asked if they had thought about adding a turbo. The team leader said "some teams use turbo but we have never had enouph time or man power to put something like that together." I then suggested that a turbo might fix all of our fuel mapping Woes becuase it would compensate for the reduced air flow cause by the restrictor. He just kinda said "meh" and ignored the thought, probably because Im new and he doesnt think I know what im talking about or somethin : / .

So how hard IS it to design a turbo sysyem for a motor? It seems that we would save a lot of design time if we concentrated on makin a good turbo system instead of having to put all the time into the air intakes design. ( I assume that adding a turbo would make the air intake's design less of a factor).

Idk...hell what do you think?

 

I think a turbo is cheating.......but that's just me.  The Austrian team managed to get over 100hp from their motor....so why can't you?    Your fuel mapping woes aren't going to be fixed by bolting on a turbo.....it just means a whole lot of "other/different" mapping woes....and with a turbo, get the mapping wrong, and you'll have a nice conversation piece for the next years SAE team......ie the paper weight/engine.   If you do decide to go with a turbo design ,are you going to use an intercooler?  The air from the turbo/supercharger is hotter than  a N/A engine....so is this going to cause you even more problems with the fueling?  An intercooler and and piping will add weight.( which might affect the handling/braking of the car)   what about traction as well?  The engine might have too much wheelspin in the lower gears with the turbo, so then you gear it numericaly lower to try and fix this, but this puts more load on the engine, and adds to the fueling woes....Which again turns the engine into a grenade waiting to happen.....  Can you adjust timing with your FI system?  Adding a turbo is not just a bolt on and go system........and find out the pricing on all the components for the turbo system....You've got just as much if not more work with a turbo system than a N/A engine.

 

The restrictor has to be placed after the velosity stack...this is why you have the velosity stack in the first place.....(to speed up the air before it has to pass through the restrictor.)  Think of the velosity stack as a funnel for the air.  Now I believe the taper of the velosity stack has to be around 7 deg ( but don't quote me)....... 

Yeah you're going to have to do your homework, and it's not going to be easy what ever system you decide to do...Teamwork is the key!

Jeff

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My bike-2002 F4i-With OEM CCT......And no rattle
"Life would be boring if everyone was perfect"