Intake Plenums, does size matter

[1JZ.747]

Hi boys and girls


i am at the stage of starting to accumulate bits and pieces for my 1.5jz project.

i have motor and 1j head etc.

i am about to order pistons and rods.

i am going to cnc port the head so each port is of similar size

i plan to get 264 272 cams down the track and valve springs.

but my question is around plenums

what is the benefit of increasing from the factory plenum size?

why would a person change it over?


i understand bellmouthing runners etc and increasing the throttle body size etc, also how does one work out the best volume for a plenum?


are different material used better for heat soak prevention?
ie cast steel or folded sheet metal?

any advice or evidence would be greatly appreciated.

Shane.

[takai]

Yes, plenum size does matter. How much is up to each invididual car, and without extensive flow or dyno testing one will never really know for their individual application. It will probably matter more for an NA engine, rather than your FI, but every little bit helps in the end.
This thread (http://www.performanceforums.com/for...ghlight=plenum) on PF contains most of my queries about the NA plenum concept. And one of the big things seems to be that overall volume is always useful, but the clearances from the inlet runners seems to be more critical.

Also, while protruding bellmouths seem to flow better for NA applications (keep intake air speed high while not maxing out the airflow) flush bellmouths seem to be the go for FI where the plenum is infact a restriction of sorts.

Hope that helps, ill see if i can post more later in the day when i dig up all my old bookmarks.
For now, have some inspiration

[1JZ.747]

when you look at a 1jzgte plenum they are about the same size as a 4g63 mitsubishi intake plenum which makes me think the plenum on th 1jz is either too small or the mitsubishi is to big. probably not a real good comparison but just a thought floating around in my head.

I look a the power Pauls OWGOOR is making with a custom plenum compared to similar cars and its impressive. yet i have seen 1.5jz's reportibly making 150 rwhp more than me running the same MPH in a lighter car with a more drag purpose built drive line.

[Fattony]

i remember reading in 21st century performance once that plenum volume is ment to be atleast 1.5 times that of the motor so 2.5 litre motor should be 3.75litre plenum, but as takai said it depends on motor, but its a rough guide if that helps.

[1jzracing]

The shape and design is far MORE important than the size

as for 1j plenims they are not very good at the best of times, the flow path has a bad direction change at the top of runner no 1

with no other changes i picked up 20rwkw by changing my intake to a side entry by welding the top half of a 7m intake to the bottom half of the std 1j intake

the result is only slightly more volume but much better flow and more even distribution hence the gain and i had to retune the fuel map because the volumetric eficiency increased (ecu is MAP sensored)

[ReQuieM]

^ Yep and more. According to my turbo book (second hand knowledge i guess) the plenum is a surge protection 'device' recommends 1.5 - 2 the displacement. From my basic understanding its there as a buffer of air/pressure, runner length and the correct flow paths are gonna make more difference. For mine, I'm angling the 'In' pipe/flow so that it has direct line of sight (flow) to each of the runner mouths. I'm gonna use half tubes for the walls, making no corners, just rounds and under ~30deg angles. I can send you some scetches of my plans, might be of some use. < copyrighted of course!

[ReQuieM]

PS 1jzracing, got any pics to share?

[Disturbed1]

as most of u know i bought a plenum for my 7m from states... i have no evidence of flow properties so i phone up of the best guys in WA regaurding flow testing and he told me...

do not waste your money... a plenum behaves totally different when mated to a running engine having air sucked.

runner length is what mainly effects the consistency of flow rate between cylinders

without going into to design depth cause i know i cant change anything - he said the best thing to do in any circumstance is test each EGT from each manifold runner - that way u get spot on AFR providing your computer allows u to tune each injector independantly

[PlacentaJuan]

what about the aftermarket plenums?

do the aftermarket ones have anything different other than their volume?

[AndyTTR]

I know final year aerospace engineering students that are doing their thesis on intake plenum design... from what i gather its all about flow velocities, volumes and accoustics.

On our F-SAE team there's a group of 2 or 3 people who work specifically on the intake plenum, they've probly got some good reference material if anyone's interested in the science behind it - I can find out more if you'd like?

[mrshin]

Always interested in this stuff... Anyone who's got anything GOOD I love to hear from.

I sure won't call myself any kind of expert on the topic, but it does seem that a lot of manifolds people fit to their engines appear to have absolutely no design whatsoever in them, are merely bigger so as to have a larger area to polish...

[ReQuieM]

More would be nice. I read a paper on it by a guy doing his masters. Gotta admit most of it went over my head. Sumed up it comes down to tuning the length of the runners to time the harmonic puls from the invlet valve closing and creating a build up of pressure. Basicaly Air that was flowing can't and it pounds up against the back of the vavle. air particles bash and against air particles and then bounce back up the runner. They hit the back of the runner/plennum and pendulm back down the runner. The idea is to 'tune the length of the runners as to time the pulse to get to the inlet vavle at the time of opening. obviously this timing changes as as the RPM does so this is way its 'tuned' to an RPM.

The Flow side is pretty obvious not too big not to smal yadda yadda.

From what i've read (as above) plenum = surge protection. So you dont starve the engine on quick acceration changes. ect ect.

Andy get what you can about design principles of the plenum. More info the better.

PS forgot to mention I've included a tapered design to provoke aire flow to rears so i dont starve the rear cyclnders.

[ReQuieM]

HAHA shin too true! And always with SHORT runners! whar RPM is that foo 20,000RPM???

[ed]

they've probly got some good reference material if anyone's interested in the science behind it - I can find out more if you'd like?

links and references please!!

[1jzracing]

PS 1jzracing, got any pics to share?

only my intake