Increasing Plenum Runner length and Volume in Turbo

[wilbo666]

I'm looking for a help to point me to some information regarding the effect of increasing (/changing) the runner length (and hence volume) off the plenum in a turbo setup. I know the general vague "longer runners = lower max torque" for NA but I'm looking for something a little more scientific than that (ed like).

I haven't been able to find much on the topic myself!

Cheers
Wilbo

[joecoolmk2]

look up does size matter?, started by 1jz747. it has a bit in there, as well as links i think.

i don't think there is much tuning in turbo setups, as the air is forced in, instead of sucked in. there wouldn't be much difference if the runners were longer, except to give you a bit more response before boost maybe?

[Earlyrolla]

The purpose of intake tuning is to increase cylinder filling which in turn means more fuel and air to combust and thus more torque.

Intake tuning is based around the Helmholtz resonance system, look it up in Google!!!

The basic gist is a pulse wave is created in the intake runner due the piston and intake valve motion, this wave travels up the runner to the open end (the plenum) and is reflected back down the runner. If the timing of the reflected pulse is correct it should reach the intake valve when it is opening thus forcing more air and fuel into the cylinder. (Remember the pulse is effectively a compression of particles, maybe look at some basic sound wave stuff first).

The intake system can generally only be effective through this tuning around a narrow RPM band unless you start going into variable length runners and switching in different plenum volumes.

The following is from a car magazine based on suggestions by David Vizard (well known engineer in the US):

Remember you should be tuning for peak torque.

Start with a runner length of 7 inches at 10 000 RPM and add 1.7 inches for every 1000 RPM less.

E.g. for 4000RPM peak torque this would be 17.2 inches or 17.2 * 2.54 = 43.7cm

Runner diameter can be calculated in inches as square root((volume(L) * volumetric efficiency * RPM @ peak torque) / 3330)

E.g. 2 litre engine, with a VE of 80% (0.8) with peak torque at 4000RPM, sqrt((2 * 0.8 * 4000) / 3330) = 1.39 inches or 1.39 * 2.54 = 3.52cm

These are good 'rules of thumb'. Technically there are other factors that also influence the speed at which the pressure waves travel in the intake runner.

As for plenum volume, the suggestion is for around 80% of the volume that the runners are attached to.

E.g. a 2 litre would need around 0.8 * 2 = 1.6 litre plenum volume

There are still benefits to be had from intake runner tuning in a boosted car but they are not as substantial as in an NA car. Even if there is a positive pressure in the manifold the pressure waves will still occur in the runner and there is still the potential to aid cylinder filling through making use of the reflected pulse. This is important in turbo cars when not on boost.

[ed]

may i suggest a read here:
http://www.v-eight.com/tech_forum/viewtopic.php?t=22

and:

http://www.v-eight.com/tech_forum/viewtopic.php?t=34

and finally:

http://www.performanceforums.com/for...php?t=67181367

[ed]

ps - those numbers above, along with this graph, are *rough as guts* but i guess its a place to start...



if i were you though id just download the damn engine simulator posted above and have a free play for 30days

[wilbo666]

Thanks guys, I know about Helmholtz resonance tuning, what I was interested was in confirming the effect of boost on what appears to be a very largely NA only field...

I haven't had a chance to follow up the links yet (but I will, and then will then repost from a perhaps more enlightened viewpoint)...

Ed, does that simulator let you play with boost? In my searching I found a matlab plugin (not free) that suggested that it could take into accounts boost...but in general not much talk about turbo / SC inlet design...

I'll offer some more details at this stage I'm not looking at making an inlet manifold from scratch, I've seen heaps of people push more power than I'm after through the stock 1JZ-GTE manifold so I don't believe it to be a large restriction...what I am thinking about doing is adding a spacer (of ~ 60mm) between the existing injector manifold and the inlet plenum manifold (1jz has a two part inlet).

I'm trying to determine what the effect should be! (and hope that it is not detrimental...). I don't think it will be a particularly large effect but I do/would like to know

Thanks again for the help so far!!

Cheers
Wilbo

[Ben Wilson]

Zoom did a back to back test comparing a RB26 6 throttle body short runner setup to a RB25 (I think) convential long runner setup. It's been a while since I read it, but i think the conclusion was that once boost was involved, the important thing was to have as little restriction as possible.

Bear in mind that with an good pulse tuning setup, you might get 120% VE over a narrow rev range. While that's the same as 3lbs of free boost, when you've got a decent amount of artificial boost, it's a much smaller percentage. And every inch of runner length is more surface area for friction to act on as well....