Hi,



i'm wondering, what purpose a plenum has and how it effects performance.

the FC manifold does have a plenum, the FD one doesn't.

there are larger plenums, smaller ones...

but why?



could anyone give basic hints about plenums in generall or point me to some useful sources?



thanks



Chris

You need this.....





http://www.amazon.com/exec/obidos/tg/detai...=glance&s=books





A plenum can be tuned to use the pressure pulses created by the intake ports. With the right size plenum and intake runner length, the pressure rises in the intake as the intake ports open to help push more air into the combustion chamber. (this is one super simplified take on it)

Yeah, tyson hit it. The air in the runner hits the plenum, and turns around and fires back at the port. You try to time it so that the returning pulse hits the port at opening.

judging by the reviews it must be a really nice book.

thanks for the hint, guys!



edit: it's pretty old though https://www.nopistons.com/forums/pub...DIR#>/wink.png but i guess it's nice to know the basics

[quote name='Old Splatterhand' date='Apr 29 2005, 09:25 AM']judging by the reviews it must be a really nice book.

thanks for the hint, guys!



edit: it's pretty old though https://www.nopistons.com/forums/pub...DIR#>/wink.png but i guess it's nice to know the basics


[/quote]





THat book is heavy reading for most people. Expect to read and reread if you not familiar with the basics.

the fd manifold does have a plenum, its just not very big.

[quote name='Old Splatterhand' date='Apr 29 2005, 07:14 AM']

i'm wondering, what purpose a plenum has and how it effects performance.

the FC manifold does have a plenum, the FD one doesn't.




[/quote]

Im guessing it has an effect on torque or low end power, cause the cosmo RE has a large one.

[quote name='kahren' date='Apr 29 2005, 12:42 PM']the fd manifold does have a plenum, its just not very big.


[/quote]



In the actual intake manifold there is basically no plentium.





[quote name='RONIN FC' date='Apr 30 2005, 08:39 AM']Im guessing it has an effect on torque or low end power, cause the cosmo RE has a large one.


[/quote]



I dont think big plentiums help so much in the torque department. Long skinny runners are the big helpers there.



im still learning so...

plenum is a plenum, small or large its there

[quote name='TYSON' date='Apr 29 2005, 08:40 AM']You need this.....

http://www.amazon.com/exec/obidos/tg/detai...=glance&s=books

A plenum can be tuned to use the pressure pulses created by the intake ports. With the right size plenum and intake runner length, the pressure rises in the intake as the intake ports open to help push more air into the combustion chamber. (this is one super simplified take on it)


[/quote]





Bah, that book had one picture of a plenum intake as something new and futuristic. Overall was not impressed.

My understanding is the plenum is there as an air reservoir which provides non-turbulent air, not to bounce the air back down the runners. Most of the plenums I have seen are all different shapes and certainly not at an angle that would support this idea as far as I can see - that's not to say it doesn't work, but plenum chambers are there first and foremost to reduce turbulence.



Turbo cars generally have smaller plenum chambers, I haven't read this anywhere but I'd imagine it has something to do with the fact that the air is denser so a smaller chamber will hold the same amount. General rule of thumb is that the plenum chamber should hold twice the engine's capacity (or more).



Mark

[quote name='TYSON' date='Apr 29 2005, 08:40 AM']You need this.....

http://www.amazon.com/exec/obidos/tg/detai...=glance&s=books

A plenum can be tuned to use the pressure pulses created by the intake ports. With the right size plenum and intake runner length, the pressure rises in the intake as the intake ports open to help push more air into the combustion chamber. (this is one super simplified take on it)


[/quote]





Im about halfway through that book, and I think its a good read so far. Its old, but the principles that book goes through are the basis for modern intake and exhaust tuning.



And the MPI used to graph the pressure waves is an ingenious device.

Whats a book similar to this that will give some basics of engineering and building??

[quote name='MrScary' date='Jun 5 2005, 09:49 PM']Whats a book similar to this that will give some basics of engineering and building??


[/quote]





http://www.grapeaperacing.com/GrapeApeRaci...tionsystems.pdf



Theres a little bit of info there. Youre probably best off copying a design thats proven to work, and then experiment with the volume some to suit your needs. A larger plenum will make for more top end hp at the expense of some throttle response. A smaller plenum will make the engine more responsive, but wont make quite as much peak hp.

[quote name='mazdaspeed7' date='Jun 5 2005, 09:06 PM']http://www.grapeaperacing.com/GrapeApeRaci...tionsystems.pdf



Theres a little bit of info there. Youre probably best off copying a design thats proven to work, and then experiment with the volume some to suit your needs. A larger plenum will make for more top end hp at the expense of some throttle response. A smaller plenum will make the engine more responsive, but wont make quite as much peak hp.


[/quote]





What I meant was like an somewhat basic intro to engine building or engineering. Not sure if there is anything that'll give a broad view of it. I'm only in high school and would like to jump into a little engineering. https://www.nopistons.com/forums/pub...#>/BURNOUT.gif

[quote name='MrScary' date='Jun 7 2005, 04:59 PM']What I meant was like an somewhat basic intro to engine building or engineering. Not sure if there is anything that'll give a broad view of it. I'm only in high school and would like to jump into a little engineering. https://www.nopistons.com/forums/pub...#>/BURNOUT.gif


[/quote]





https://www.nopistons.com/forums/ind...howtopic=50748

Hi there in my "opinion" the best all around intake systems are the variable runner length intake systems(used on like a 787b(normally aspirated)) but as far as something turbo, longer and thinner for low end torpue(limits high end hp) or short thick runners will do good high hp #s with sacrificing low end torque.

ohh and as far as how big the plenum is just a combination of varibles like; boost psi, and even fuel type. It can all be better adjusted by the pressure pulses of the intake and exhaust.