Changing cam lift and duration.

[Gaanja]

I had thought about changing the cam lift and duration.

I was thinking that reducing the duration and lift a little wrt the stock would benefit the VE and response at the low and mid range rpm due to the following reasons.

1) As the engine is restricted, it would behave, on the stock camshafts, like a normal engine fitted with performance camshafts with higher lift and duration.

2) When the engine is restricted the velocity of charge entering the cylinder at lower rpm is lower than when unrestricted and does not fill the cylinder efficiently. Hence reduced duration and lift would increase VE here.

3) We have always had lumpy idling. This seems like the problems that would be faced when a stock engine (unrestricted)
is fitted with camshafts of higher lift and duration to increase performance at high RPM. Considering we run a restricted engine and design for a lower resonant RPM and lower red line, a camshaft with a lower lift and duration should help.

It'd be great to hear opinions on this. Also what problem could be face because of the modifications?

[Gaanja]

I had thought about changing the cam lift and duration.

I was thinking that reducing the duration and lift a little wrt the stock would benefit the VE and response at the low and mid range rpm due to the following reasons.

1) As the engine is restricted, it would behave, on the stock camshafts, like a normal engine fitted with performance camshafts with higher lift and duration.

2) When the engine is restricted the velocity of charge entering the cylinder at lower rpm is lower than when unrestricted and does not fill the cylinder efficiently. Hence reduced duration and lift would increase VE here.

3) We have always had lumpy idling. This seems like the problems that would be faced when a stock engine (unrestricted)
is fitted with camshafts of higher lift and duration to increase performance at high RPM. Considering we run a restricted engine and design for a lower resonant RPM and lower red line, a camshaft with a lower lift and duration should help.

It'd be great to hear opinions on this. Also what problem could be face because of the modifications?

[Martin Matuschek]

Hi Gaanja,

this year i'm working with 1-D engine simulation on improving cam timings at the FH Wiesbaden Team.

In my opinion, you are on the right track, what to do to get improvements in the lower and mid-rpm range.
If you want that, you have to find the solution not to loose high-rpm power output.
You need to invest some money in 1-D Flow software like GT-Power(gtisoft.com: spcial deal for FSAE) or Ricardo Wave...
It's the cheapest way to get your theories proven.

In my work, i wanted same as you better midrange torque.
Since the stock cams are designed for after 12k rpm high power it was necessary to tune them.
Especially the intake valve open time ist much to long for good midranges.
I see the inlet cam closing time as the most effective parameter, for what you want.
If you close the inlet faster, in lower rpm, the gases would not be pushed back in the intake, otherwise you loose dynamic load in the highest rpm.
I shortened the valve lift too, because i did not want to gain the valve acceleration in respect to the stock setup.

What you see in a simulation might look like that:
http://www.fhw-racing.de/martin/flow.jpg
Hereout i see where there is backflow or a flowrate irritation over the lift of the valve.

If you find a suitable setup, it maybe shows a difference like that:
The blue torque is last year(stock cams), the other two ones are options for this year.
http://www.fhw-racing.de/martin/results.jpg
If you ask why there is "more" in low and high rpm:
Cam timings are optimized for low rpm torque, but we also change intake runner length to get some more power at 9500rpm.

For the valve lift i can say, you need to be aware of the pressure drop of a to small opening gap. There is a point in lift/flow curve where more lift doesn't bring you more flow and the other way round.


Good luck with your resaerchs
and get simulation, if you don't already have it's worth the money

[Ockham]

My understanding of cam timing events is incomplete, but my impressions are these.

1] "Loping" or lumpy idling can be reduced by decreasing the overlap, which is the amount of time the exhaust and intake valves are open simultaneously. On OHV engines, this is a function of intake/exhaust cam phasing, but it's built into pushrod camshafts (probably not something any FSAE team has to worry about). My impression is that the lumpy idle is a result of excessive intake vacuum, which can be reduced by decreasing plenum volume or decreasing cam overlap.

2] Engines are more sensitive to duration changes than lift changes. I don't think that "too much" lift really hurts anything, aside from increasing the energy needed to actuate the valvetrain relative to a lower lift.

Plenty of teams have run custom camshaft grinds in the past. Comp Cams, Mahle, and probably a bunch of others can make them at surprisingly low rates, but they're still plenty expensive. If I were to try this project, I'd try to assemble enough funds for two or three custom grinds, all modified relative to stock, but with only lift or only duration changes. Throw the lot on a dyno (after checking for piston/valve interference), and see what happens.

Odds are that some cam changes won't show up as altered torque, but as different engine manners. If you're going to decrease lift, I don't think you'd run into any mechanical issues with the engine. Your biggest problem would be quantifying the cam swap's changes in any way beyond "it feels better."

Bear in mind, I still have a lot to learn. I wouldn't try any of this unless some of my learned colleagues confirm my opinions.

[BuckeyeEngines]

get your self an engine simulation program such as virtual four stroke. There is alot of power to be gained by rephasing/changing lift and duration, even the rate at which you are accelerating the valve. Keep in mind you are going to pay a few hundred bucks for the software, and a custom grind will cost around 1000.

[Gaanja]

@ Ockham, Martin and Branden,

Thanks a lot. I dont have any software that i can use to do the engine simulation. I just spoke to our faculty advisor over the weekend about getting an engine simulation software. The problem is we do not have too much money at our disposal to buy any high end software. Could you please suggest software packages apart form GTI-Suite, Virtual four stroke and ricardo that we could get at a reasonable price? I need to do a compare the different software packages and submit a study to the department and justify why i need to get a particular one.

Thanks in advance

cheers

[TMichaels]

GT-Power is available for 100$ for FSAE teams. I think this is affordable even if you are on a tight budget.

Regards,

Tobias

[Gaanja]

@ Tobias.

I tried contacting the people for GT power in India. they are quoting 2800 USD. Do i contact the USA office for the FSAE special price? Could i please get a name of a person at gtisoft who can help me out with it?

[Apurva]

@ Sriganesh,

Ricardo WAVE is free for FSAE teams.

Contact CAEPRO (http://www.caepro.com).They take care of the distribution of Ricardo software products in India.
You may have to provide a few documents establishing your team's identity as a FSAE team, which you must be having. You will need a desktop computer at your college on which you shall be carrying out all your simulations. This computer has to be a desktop.
We use one the computers at the CAD lab of our college.

I think it shouldn't take too much time to get your program started.

good luck.

[Wesley]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ockham:
My understanding of cam timing events is incomplete, but my impressions are these.

1)My impression is that the lumpy idle is a result of excessive intake vacuum, which can be reduced by decreasing plenum volume or decreasing cam overlap.
</div></BLOCKQUOTE>

Actually it trends the other way. Lopey idle manifests with LOW plenum vacuum, because when the intake valve closes later you're shoving some of the mix back into the plenum when the piston comes up - there's not enough flow momentum to overcome it at low speeds. Overlap compounds this by hanging the exhaust valve open and allowing reversion from exhaust to shove more intake charge back into the plenum. Reducing overlap reduces part of the problem, where closing the intake valve sooner addresses the other part. You also can have all kinds of crazy acoustical effects.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">
2] Engines are more sensitive to duration changes than lift changes. I don't think that "too much" lift really hurts anything, aside from increasing the energy needed to actuate the valvetrain relative to a lower lift. </div></BLOCKQUOTE>

Yes. Especially with these engines. Look at the lift vs. flow profile of the engines and it's pretty apparent that any more lift isn't likely to change flow rates by much, and in fact the decreased entry speed (and subsequent higher pressure) of the air/fuel can reduce mixing and vaporization effectiveness, especially in batch-fire cars that have fuel just waiting on the backside of the valve. If anything, a reduction in valve lift will benefit low speeds due to the already-slower inlet speeds simply because of improved atomization. At the same time, going much lower can kill top end, so like everything, it's a balance.

Ockham's right in that cam changes can significantly alter the "feel" of an engine, even if it doesn't make it much faster or slower. I think the biggest thing people forget about when worrying about cam timing is that an engine relies of fuel delivery as much as airflow - when they treat the engine simply as an air pump they forget that the subtle pressure and velocity changes have an amplified effect because of their effect on the fueling.

If you slam your valves all the way open and wait super long to shut them, you can potentially cram a bunch of air in - but only if the rest of your geometry can take it and your flow momentum is sufficient. Otherwise your flow speeds are lazy and your fuel all condenses, resulting in poor mixing and poor power.

With all this said, the extent of our cam modification research has been Ricardo WAVE and a few spreadsheets - and, for us at least, we felt that spending the extra 500-1000 dollars on cams wasn't worth it when we could spend that money on lightness instead.

[Martin Matuschek]

@gaanja:

follow this link:
http://gtisoft.com/contact/con...act_by_Territory.php (http://gtisoft.com/contact/con_Contact_by_Territory.php)

and call or write to the worldwide headquarters in westmond, IL

The contact person we had for our fsae-license was "tara petrusha"
Don't forget to tell you are FSAE.

Sure it is 100$/per license and year -&gt; good deal

regards

[Tinke]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Wesley:
With all this said, the extent of our cam modification research has been Ricardo WAVE and a few spreadsheets - and, for us at least, we felt that spending the extra 500-1000 dollars on cams wasn't worth it when we could spend that money on lightness instead. </div></BLOCKQUOTE>
I just have to comment on this because I think the 500-1000 dollars spent on cams are exactly the place to spend it. The weight savings you gain with that sum of money is nothing compared to the 15-20hp you can get with right cams from a 600cc 4cyl. Getting the intake and exhaust right puts you in to the +90hp zone and after that begins the real work http://fsae.com/groupee_common/emoticons/icon_wink.gif
Playing with the stock cams wont get you anywhere.

[Gaanja]

Thanks a lot guys for all your help.... We will be getting GT- Suite in about 2 weeks time and ricardo around the same time too...

@Tinke: I was contemplating on whether it was wise decision to go in for cam mods. Now that you said it would give about 15 to 20 hp change i am definitely doing this http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Ockham]

A cam change can give a 15-20HP gain. Bear in mind that Tinke is at Helsinki Polytech, which has one of the best FSAE teams in the world. They're a high standard, but you can meet it with plenty of elbow grease.

[Wesley]

I wouldn't say nowhere. But yeah, that's what I like about the competition, is that everyone has a different idea of how to go fast under the budget constraints, and what should see the attention first - and if it's well done, it works!

Gaanja - Not that I think you figure you'll 'bolt on' 20 hp, but just note that it is a significant time investment to develop or choose a new cam profile.

That was another factor when I looked into it back in '08. We didn't have the manpower or design time for it either. It's something you should ideally look at in conjunction with your intake and exhaust, but in the event of an engine failure you have to make sure you have the time to swap the cams or another engine prepped and ready to go with the modifications in case of failure - wherein the real cost lies, because if you've designed your intake and exhaust to take advantage of changed geometry and then you have to slap another engine in there, you've just lost a lot of time and effort.

As with all things, be sure to look at it in context with your budget and team priorities.

[Hector]

As far as custom cams and cost go, don't forget that you can always grind your stock cam to a custom profile. If you find the right company that's maybe willing to sponsor your team, you can have this done for $100 or less. Ours is free this year =)

Since the most beneficial change to these cams (IMO) is to lower duration and overlap, you already have more than enough material on the stock cam to work with. Don't ever let budget stop you! Usually, with enough phone calls and pestering the right people, you can get stuff done for free, or at highly reduced rates.

[Gaanja]

@ Ockaham and Wesley: Yes i do know that Tinke is from Helsinki Polytech and i do know that they are one of the best teams in the world. Its just that if they have achieved a 15 to 20 hp increase by cam mods it just gives me the assurance that it is actually possible to gain something significant by modifying cams. We may not be able to 'bolt on' 20 hp . But we could get there sooner or later. It also is not about whether we get that increase in power. Its the experience and knowledge we gain by doing the exercise.

With respect to man power, we have about 50 members in the team including freshmen and sophomores and 8 guys working on the engine and a separate 4 working on the ECU and tuning.

For the last five years we have just been looking at optimizing the intake and exhaust designs to increase performance. Last year we had a system that was doing much better than any other year.Also we are sticking to a similar design this year and just optimizing the manufacturing part of it. So before i leave the college i am looking at setting up a base where the other guys who have time left in the team can take the next step forward.

Thanks a lot again

cheers

[Ockham]

Oookay, you should have more than enough manpower. You have more workers for your engine than we have for our whole team (lucky bugger). Great attitude, sir, and best of luck!

[Martin Matuschek]

just to clarify,
if you just want high power output 90+ hp, you don't have to change cams.
we had 94Hp just with slight shifting of the timings last year.
For me it seems impossible to get another 15-20hp.
we do it to get more max. torque in middle rpm-ranges and engine behaviour ind lower rpms.
be sure what you want and what you need to do for that.

[vandit]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Gaanja:
With respect to man power, we have about 50 members in the team including freshmen and sophomores and 8 guys working on the engine and a separate 4 working on the ECU and tuning.

</div></BLOCKQUOTE>

50 !!.... Holy crap! We have so much now ??. Who is attending college then ? I suggest you keep the head count of first year "yo dudes" every month. Let see how many can we save at the end of 1 year.

[Gaanja]

@ Ockham: Thanks a ton... will be pestering you guys a lot more before i get the things setup back at the workshop.

@ Vandy: How do you change timings without changing the cams?

If you count all including the first years you do have 5o people. At any given point there are at least 15 people working from each year.

[vandit]

I change timings by making GT-Power available to you. http://fsae.com/groupee_common/emoticons/icon_smile.gif

My knowledge on Engines is similar to my knowledge of kannada (may be kannada is better), so excuse me. I used up little space in this thread because i was surprised by the number 50.

[RenM]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Gaanja:
@ Vandy: How do you change timings without changing the cams?
</div></BLOCKQUOTE>

try elongated holes in your camshaft sprocket...

[Gaanja]

@ Ren M: could you please be a little more specific and explain the how....

cheers...

[Mikey Antonakakis]

There are bolts that hold the cam to the sprocket, and holes in the sprocket for the purpose. Make those holes into slots and you have an adjustable cam gear. Of course, you could always just buy one...

[Martin Matuschek]

@gaanja:
see this link to know how yoshimura sell that adjustable cams:

http://www.yoshimura-rd.com/t-...le_cam_sprocket.aspx (http://www.yoshimura-rd.com/t-kit_adjustable_cam_sprocket.aspx)

of course, the benefit is not that big, as new cams.
how it's working:
you can shift the start point of your cam by +-5degrees(earlier or later) but not the duration.

maybe there's a chance to slightly decrease the duration by increasing the valve lash a bit:-) but as always, be sure what you do and what for

[rajeevdevaragudi]

Hey guys just finished going through this thread. A lot of useful information shared but I still have a query regarding this topic. An optimum number for valve lift and duration can be found out using softwares like Ricardo Wave and GT power but how exactly should one go forward with the manufacturing of such a cam profile. I spoke with one of the manufacturers of custom cams and they can grind the cams to a custom design if I provide them with a designed profile in lift per degree figures. Now I know the lift and duration not the lift per degree. Can anyone help me to find a way to figure out how to calculate this?

[Jay Lawrence]

You (most likely) have a flat-faced follower running against the cam surface. This tells you how much the follower moves linearly for a certain angular movement of the camshaft. The other thing to worry about is the acceleration of the follower, which is determined by the ramp angles of the cam profile (obviously a steeper profile creates higher acceleration). The aim is to have the valve 'fully' open for as long as possible (thus increasing pumping efficiency) within a given desired opening phase. This has to be balanced with accelerating the valve too hard, which can cause valve bounce (though given our engines' tendency to choke there's not much point revving them high enough for valve bounce to occur, and if it does you can run harder springs anyway).

So: you have found your desired lift and duration via some software. This means that you have a starting lift at a starting angle, a maximum lift at half your duration, and a finishing lift (same as starting lift) at a finishing angle. Your job now is to determine the 2 profiles that join these 3 known points, via consideration of maximising fully open duration whilst avoiding valve bounce. Personally, I would start by measuring the lift/degree of a standard cam (attach a replica flat-faced follower to the end of a dial indicator and rotate the camshaft) and go from there. Have fun

I haven't read through the whole thread before responding, so apologies if I've repeated stuff.

[rajeevdevaragudi]

Thanks Jay.
But I have some queries. First of all what you told about opening the valve for more time at max lift increases the performance but not for our engines. We run them under restricted air supply and the velocity of air entering the cylinder is less than the stock air supply. So opening the valve for more time at max lift can cause back flow of air in a restricted engine. The previous posts in the thread also agree with this. So the duration required is less than that of the stock ones.

Secondly after finding the lift per degree of the stock cams how do you want me to determine the lift per degree of the required cams. I may be able to estimate the approximate lift per degree but that won't work for me.

[tromoly]

So opening the valve for more time at max lift can cause back flow of air in a restricted engine. The previous posts in the thread also agree with this. So the duration required is less than that of the stock ones.

I don't think Jay is saying to have longer duration than stock, rather that you want to have the longest opening time possible for the operating conditions. As you said, you'll probably want to have a shorter open time, however you still want to maximize the amount of time the valve is open.


Secondly after finding the lift per degree of the stock cams how do you want me to determine the lift per degree of the required cams. I may be able to estimate the approximate lift per degree but that won't work for me.

Wouldn't you analyze the stock profile and analytically make changes, eventually arriving at a satisfactory cam profile? My knowledge of cam profiles is limited, to me it sounds like it's an iterative process to find a profile that meets the desired characteristics.

[Jay Lawrence]

Correct, I was not saying to keep your valves open as long as possible, I was saying maximise the fully open time for a given phase requirement (i.e. you want to open and close the valves to fully open/closed as quickly as possible and hold them there for as much of your open duration as you can). An ideal valve (as far as minimising pumping losses goes) would fully open instantaneously, hold open, and then close instantaneously (I think this is what F1 were trying to achieve with their pneumatic systems). I think this is true of any engine (a valve on its way up or down is simply adding friction (mechanical and aerodynamic) to the equation). However, with our restricted engines, a higher maximum lift cam won't necessarily work (as you have said), which is why some teams regrind for smaller lift (increasing the aerodynamic friction to create swirl, thus improving combustion efficiency even if the pumping efficiency side is reduced).

Anyway, to work out the safe mm/degree of your theoretical cam, you need to follow the advice I gave above regarding valve bounce. Essentially you need to work out the mass of the valve assembly, how fast it is going to move due to a given cam profile at a given maximum RPM, how much the spring is going to resist, and whether or not the momentum caused in the valve assembly in this system is enough to overcome the force that the spring applies to keep the valve/follower in contact with the cam lobe. Given that you appear to be interested in reducing lift you probably won't have to worry about valve bounce. So I would take tromoly's advice and analyse the stock profile (using the experimental method I outlined above), which will produce a pretty picture. You can then essentially scale down that picture to create your cam profile. Just make sure you don't go crazy with ramp angles (i.e. KISS).

[rajeevdevaragudi]

Thanks tromoly. Jay thanks for the info. Sorry I could not get it in the previous posts itself. I think you are rite about not worrying about valve bounce as I'm decreasing the duration. I will try to get the stock cams profile and than scale it down. Thanks guys.

[RenM]

I would advise you to change cam timings first, because this can be done easily and has a big effect.
Changing the duration of the cams without any calculations of the influence it has on your gas exchange is pretty much useless.

If you know what cam duration you want to have (simulated for example with a 1D engine Simulation like GT-Power or Ricardo Wave) , then you can follow Jays way to estimated the Forces in the Valvetrain.
Besides the Valve, Retainer, and Lashdisk mass you will also have to calculate with the active spring mass which is typically around 1/3 to 1/2 of the springs weight.
Another thing to factor is the natural frequency of the spring which is quite low and causes the spring to swing thus reducing the actual "usable" force of the spring (a big reason for F1 teams to go for pneumatic springs, because their natural frequency is much higher). So you should have at least a 30% gap between the spring force and the mass forces of your valve train to be on the save side.

[rajeevdevaragudi]

I am not getting it. How changing the cam timings without changing the duration can help. If I am not changing duration and only change the time at which intake and exhaust valve closes, how will it help in increasing the performance. Coming to the forces on the spring, if I am just decreasing the duration, the amount of forces acting on the springsis less than the stock valve trains forces. So why do I have to consider the forces acting on the valves. Please correct me if I am wrong.

[apalrd]

I am not getting it. How changing the cam timings without changing the duration can help. If I am not changing duration and only change the time at which intake and exhaust valve closes, how will it help in increasing the performance. Coming to the forces on the spring, if I am just decreasing the duration, the amount of forces acting on the springsis less than the stock valve trains forces. So why do I have to consider the forces acting on the valves. Please correct me if I am wrong.

The IVC angle is extremely critical to a lot of things (both performance and efficiency, which usually prefer different IVC angles). So, just changing the cam centerline timing, changes the IVC timing, which can change performance and efficiency quite a bit.

Specifically, the IVC angle tells you what the effective compression ratio is (IVC at BDC produces highest CR), due to either LIVC or EIVC (late IVC or early IVC). Some engines use this to their advantage, drastically reducing CR with early or late IVC, allowing a higher mechanical CR for a higher ER (higher thermal efficiency) while reducing peak cylinder pressures and displacement (as a means of load control).

IVO angle sets the overlap, which changes primarily the residual (internal EGR).

For the exhaust valves, the EVO angle sets the blowdown volume. Less blowdown (later EVO) keeps mechanical expansion ratio (ER) high for thermal efficiency, but more blowdown helps use the in cylinder pressure to reduce exhaust pumping work, so it's always a balance. Turbocharger load can also change the optimal EVO angle.

EVC angle again sets the overlap, which changes the residual like IVO angle.

So the duration is relevant to the IVC and IVO angle, if you set IVC and IVO (or Overlap) targets then you can set your duration.

In general, the only time I have specified more duration is for Late IVC cam phasing, with very long duration intake cams (to keep a bit of overlap).

tl;dr, the IVC angle is what you really want to target

[rajeevdevaragudi]

Totally agree with you. But by changing the closing and opening timings of the IV I am effectively changing the duration itself. My main aim is to Chang the valve opening and closing times and also change the overlap as well. To decide these timings I am using Ricardo and I have still not decided the suitable timing. My main concern till day is how am I supposed to grind the cams to the required profile. If you have any ideas regarding this please feel free to post!!

[apalrd]

I would start by looking at the available aftermarket cams that fit your engine. For example, we run a WR450F engine, but can use cams from the YFZ450 quad engine as well, and have investigated most available aftermarket and stock cams from the WR and YFZ engines (we currently have a Hot Cams intake cam and stock quad exhaust cam).

As long as the duration and lift are to the spec you want, you can phase the cam to get the IVO and IVC angles you want.

What engine do you use?

On a very unrelated note, I once had the pleasure of working on an engine that could vary the valve angles (through Multiair), and playing with the valve IVO and IVC angles in 'real time' and driving it around is probably the coolest thing I have done with an engine.

[rajeevdevaragudi]

I guess you have not read the previous posts of this thread. Aftermarket cams are not an option as they are more aggressive cams than the stock ones but the required cams for FSAE as we run our engines under restriction. Aftermarket cams are not preferable for engines under restriction. I have not actually searched for cams of other engines suitable for CBR 600RR ( the engine which we use BTW ). I don't really know how feasible that can be and it is really difficult to find such type of cams. Most of the camshaft mamfacturers whom I have spoke with have advised me to grind the stock cams to the required profile. So I need to grind the cams to a custom profile rather than going for aftermarket cams.

[RenM]

Okay i am trying to clear things up a bit.

As apalrd said the IVC (intake valve closing) is the most important part of the cam timings and is very influential for cylinder filling for a naturally aspirated engine.
A correct timing of the IVC allows you to use the inertia of the fresh gas to increase the cylinder filling:
During the intake phase the gas in the intake runners is accelerated. Now when the Cylinder is moving up again the kinetic energy of the fresh gas can be converted into a charge effect which increases the pressure and density of the gas charge in the cylinder. With increased density and air mass your power is increased.
In order to fully use this effect the IVC timing has to be appropriate. If the IVC is too early the charging effect is reduced because the pressure wave hits the valve while its closed. If the IVC is too late the piston moving up will press fresh air back into the intake runners, reducing the cylinder charge. For lower revs you will need an earlier IVC then for higher revs because the kinetic energy of the fresh gas is lower.

Finding the right IVC (which will probably be earlier then for stock configuration because of the reduced revs in FSAE application) will yield the biggest gains that can be found with changed cam timings and durations.
Determining the cam timings always starts at IVC.

apalrd has already explained the exhaust valve timings very good so i will only add a bit to the valve overlap.
As apalrd has said changing the valve overlap will have an effect on the residual gas mas in the cylinder. A higher overlap will generally reduce the residual gas mas in the cylinder but also increase the pumping losses. (with a proper set up of intake and exhaust runner lengths, the intake pressure during valve overlap is higher then the exhaust pressure, helping to flush the residual gas out of the cylinder) Another thing to keep in mind is, that with a high overlap you might loose fresh air charge going through the exhaust valve which is something that should be prevented especially for an engine with an air restrictor.

I can only repeat myself: If you dont understand the effects of the basics its not useful to think of new cam durations. Try out different cam timings on the dyno, look at the data and try to understand whats happening. AFTERWARDS you can think of new valve lift profiles.
Ricardo Wave can help you to understand the effects of the gas exchange. Look at the pressure at the valves and the mass flow through the valves during your gas exchange.


Regarding the spring forces:
Reducing the duration while maintaining the same valvelift will increase the accelerations (less time, same valve movement -> higher acceleration) and thus the forces. Looking at cam timings and valvetrain dynamics its always useful to look at the accelerations of a valve lift curve. Its actually the way they are designed. You are designing the acceleration curve and from there on you integrate to the actual valve lift curve. Its important to do it this way round, because you will want to have a smooth acceleration curve.

[Jan_Dressler]

I agree with RenM that cam timing and valve overlap are probably the most important things to get right.

But on the other hand (and if you get the timing right), the CBR 600RR WILL in fact benefit from an intake cam with shorter duration.
Now before you think aftermarket, you might take a closer look at your engine, and realize that there are two (2) camshafts in that engine. When you do some measurements (or spend about 5 minutes of searching the www), you will find out that one of these two camshafts has shorter duration and less lift than the other.
Maybe you try to purchase another one of these instead of some aftermarket stuff...?

[Jay Lawrence]

I second what Jan says^
Also, some places have different emissions requirements for the CBR600RR than others. I'd look into that too.

RenM has explained (as have I) how to get your desired geometry. Further, if I recall correctly, Ricardo allows you to input either standard assumed profiles (as you have done) or fully mapped custom profiles (as you could do).