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Thread: Changing cam lift and duration.

  1. #1
    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?
    Sriganesh
    Random Bitch '06
    ECU and DAQ '07 '08 '09
    Engine '09 '10
    Ashwa Racing, RVCE
    Bangalore, India

  2. #2
    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?
    Sriganesh
    Random Bitch '06
    ECU and DAQ '07 '08 '09
    Engine '09 '10
    Ashwa Racing, RVCE
    Bangalore, India

  3. #3
    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:

    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.

    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

  4. #4
    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.
    "The highest happiness of man is to have probed what is knowable, and to quietly revere what is unknowable."
    -Johann Wolfgang von Geothe

  5. #5
    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.
    Branden Wittenauer
    2008-current
    Engine team Leader
    The Ohio State University

  6. #6
    @ 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
    Sriganesh
    Random Bitch '06
    ECU and DAQ '07 '08 '09
    Engine '09 '10
    Ashwa Racing, RVCE
    Bangalore, India

  7. #7
    GT-Power is available for 100$ for FSAE teams. I think this is affordable even if you are on a tight budget.

    Regards,

    Tobias
    Regards,

    Tobias

    Formula Student Germany
    FSE Rules & Organisation
    http://twitter.com/TobiasMic
    http://TobiasMic.Blogspot.com

    Not many people know the difference between resolution and accuracy.

  8. #8
    @ 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?
    Sriganesh
    Random Bitch '06
    ECU and DAQ '07 '08 '09
    Engine '09 '10
    Ashwa Racing, RVCE
    Bangalore, India

  9. #9
    @ Sriganesh,

    Ricardo WAVE is free for FSAE teams.

    Contact CAEPRO.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.
    -- Apurva Agarwal
    Powertrain team , 2010
    Formula Manipal
    Manipal University

  10. #10
    <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.
    Wesley
    OU Sooner Racing Team Alum '09

    connecting-rods.blogspot.com

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