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Ram Effect...

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    Default Ram Effect...

    It's like gettin' boosted with out the huffer. Ram effect in simple terms is the air and fuel that continues to enter the cylinder even after the piston has reached BDC and is on its way up. All along while the intake valve is closing. This stuffing of the cylinder is caused by velocity of the air fuel column. The more velocity we have the more mass this column has which allows it to over come both items that are trying to pervent it....intake closing and piston coming straight at it.

    All engines have this some what but 2 things will always inhance this: Piston speed and restricted inlets. Both of which increase the velocity of the column coming into the cylinder.

    RAM happens in different rpm ranges depending on piston speeds at given rpm. The % of increase that RAM will affect the engine is also enhanced by the amount of compression. Effectively engines in the 9 to 10.5 compression range with a piston velocity of 3500 to 4000 FPM will gain power over an enigne that is 10.5 to 12 to 1 with the same piston velocity. Reason is this type of mechanical compression neturalizes the column much quicker.

    So with low compression boat engines that are strokers, a 4.25" stroke BBC takes advantage of this around 5000 rpm, RAM can play a big part in making extra FREE power in the mill. Simple valve event adjustments on cam timing can play a big part in gaining 5% or more in power.
    Chris Straub
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    here are two formulas for finding the ram tube length, Shopes is 80,300/ N = L you can also use the Chrylsers formula which is 84,000/N = L, both will yield slightly different results, N=rpm
    The result of 84,000/5,500=15.27", the ideal distance for the intake tract as measured from the opening of the ram tube to the valve head.
    the results of the Shopes formula for 5500 rpm is 80,300/5500 = 14.6"
    a difference of about 5/8 of an inch
    might be interested to know that no where in the formula does it mention compression ratios.
    Last edited by Iron Mike; 01-07-2010 at 10:58 AM.

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    Tuning lengths are calculated to optimize the pulse. These lengths are for both intake and exhaust and depending on application can be tuned for either HP or torque. In an all out deal tuning both for HP works the best in drag racing. For an application that is on and off the throttle a mix of tuning for HP in the intake track and tuning for torque in the exhaust track works the best.


    I bring up compression as I posted this as an application of what RAM can do to a NA engine. Stroker engines on pump gas are a favorite of this community and know that there are ways to get advantages from these setups will help the performance boater.
    Chris Straub
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    It's possible to exceed 100 % VE with a properly designed NA induction system?
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    Quote Originally Posted by Infomaniac View Post
    It's possible to exceed 100 % VE with a properly designed NA induction system?
    Yes Ron and even with pump gas engines and RAM effect plays a part.

    I'm sure Warps "engines" exceed 100 by quite a bit.
    Chris Straub
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    Quote Originally Posted by cstraub View Post
    I'm sure Warps "engines" exceed 100 by quite a bit.

    Oh ya!!!

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    Chris,

    Have you seen this effect more on lower RPM motors (5K to 7K) than higher RPM motors (8K to 9K)?
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    again, i may be quite stupid, but along with the length doesnt there have to be an area associated with it? (or did i, as usual, miss something)

    I must have been wrong all along about this. I thought the intake ram effect was frequency derived, like a whistle. I cant seem to find the formulae i referenced (i am looking hard), but it as i remember i used the 4th harmonic which roughly calculated to around 5500 rpm. There was a CID input. I suppose this was to account for volumns of air that were being "dragged" by the piston.

    From what i understand, as the intake valve rapidly closed against the inrush of fluid from the intake manifold, there was a sonic(compression) pulse that went backward thru the runner. Where the runner terminated there was induced a natural forward pulse that could be timed for the valve opening by the runner columb....a calculation that included length and area.

    I seem to remember from the "boys first book of intake manifolds" in the early 60's that Chrysler calculated the best runner length was 36" at the rpm they were running. Worked once they got it started but starting it was a bitch, and there were problems with rapidly changing throttle positions....they settled on the 2/3 pulse at 24" (as i remember) as a poor compromise

    Boiled down (as i understand it)

    If the runner is too small, there will be a massflow restriction
    If the runner is too big (total volume) there will be a massacceleration restriction
    The runner has the ability to be sized to maximize a certain RPM mass thruput, using dimentions of length and area

    In a Jetdrive application, all things are targeted for WOT, and the RPM where that will fall, once the system is put together. This has always been important to me...and the calculations were horsepower based...not a thought about torque, except for headbolts and driveshaft.


    I got to have this figured out pretty soon...Them Torque Fags (Supersoaker, Sunkist, Fakethis and WetDream), if they keep at it, are going to kick mouse ass this summer.

    I have to apply this and many, many other things to a 427 sbc...i dont think my cheep 377 gonna take much more nitrous. I may be asking for some help from thems that know.

    Quote Originally Posted by cstraub View Post
    Tuning lengths are calculated to optimize the pulse. These lengths are for both intake and exhaust and depending on application can be tuned for either HP or torque. In an all out deal tuning both for HP works the best in drag racing. For an application that is on and off the throttle a mix of tuning for HP in the intake track and tuning for torque in the exhaust track works the best.


    I bring up compression as I posted this as an application of what RAM can do to a NA engine. Stroker engines on pump gas are a favorite of this community and know that there are ways to get advantages from these setups will help the performance boater.
    guess i missed the "pulse" thing, although i am somewhat confused about the HP/Torque...unless you mean at what rpm the thing is tuned to.
    Last edited by miketeast; 01-07-2010 at 02:41 PM.
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    Quote Originally Posted by Infomaniac View Post
    It's possible to exceed 100 % VE with a properly designed NA induction system?

    I believe Drag car classes like NHRA Pro Stock prove 100% VE can be exceeded.

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    I thought I heard that the pro stock guys are catching the 3rd pulse. That after the pulse hits the closed intake valve, it heads back up the runner, then starts back down. The more pulses you can catch the more power. But if you get it wrong power goes down.A very fine line to catch the extra pulses.I don't pretend to fully understand this, when it was being explained to me , I kind of went all Homer Simpson, mmmmBeer.

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    Quote Originally Posted by Burnt Sticks View Post
    I thought I heard that the pro stock guys are catching the 3rd pulse. That after the pulse hits the closed intake valve, it heads back up the runner, then starts back down. The more pulses you can catch the more power. But if you get it wrong power goes down.A very fine line to catch the extra pulses.I don't pretend to fully understand this, when it was being explained to me , I kind of went all Homer Simpson, mmmmBeer.
    Pulse also referred to harmonic, and intake manifold tuning to specific harmonics. Usually the runner length (from opening to the seat) will be somewhat dictated by manifold design, so you pick the harmonic closest to your best lenght. If tuning to the fourth harmonic requires a tract length of 18", well, that may or may not be possible given design limitations. Single plane, single four intakes certainly can't have equal length runners, so the outers are tuned to one harmonic, the inners to another. Most design programs that I know of base their calcs on the second harmonic, and most intakes I know of ues the second or third, or some big single planes use the third and fourth.
    Or so I was told.
    Last edited by scott foxwell; 01-07-2010 at 10:57 PM.
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    Quote Originally Posted by Iron Mike View Post
    here are two formulas for finding the ram tube length, Shopes is 80,300/ N = L you can also use the Chrylsers formula which is 84,000/N = L, both will yield slightly different results, N=rpm
    The result of 84,000/5,500=15.27", the ideal distance for the intake tract as measured from the opening of the ram tube to the valve head.
    the results of the Shopes formula for 5500 rpm is 80,300/5500 = 14.6"
    a difference of about 5/8 of an inch
    might be interested to know that no where in the formula does it mention compression ratios.
    You can also use Engelman’s Electrical Analogy / Helmholtz formula or a program called Pipemax.
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    Quote Originally Posted by Iron Mike View Post
    I believe Drag car classes like NHRA Pro Stock prove 100% VE can be exceeded.
    upwards of 115% VE.
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    Burnt Sticks, what harmonic do you think the 18,000 rpm ferrari's are working with ? 8th? 10th?

    anyone familiar with Exspansion Chambers ? Hat was, and he knew how to make a YZ 250 yamaha Fly with the best of them.

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