Intake pipe length?

rushy

Evening guys. Quick one. Does the length of pipework from filter/Maf to TB have to be a certain length? I know the length of runners on manifolds is specificity calculated but is it the same with the intake pipe? notsure.gif Cheers steve.

edbutler

No mate, you can just stick a filter directly on top of the throttlebody if you wish (like on many ITB setups). Make it as straight and direct as possible though, the longer the pipe the more restriction.

Jase_MK

I think you'll find that the length of that intake pipe is specifically calculated, yes. Air doesn't flow in continuously, but in a series of pulses (depending on the engine rpm). For each rpm, there will be a particular tube length that maximises air flow for a given air mass and velocity, such that air isn't bouncing back on itself etc. So, altering the pipe length should shift your torque around a little, to different rpm ranges.

Whether this has a noticeable effect on a detuned z22se is questionable, I guess.

Pretyy sure I've heard of some performance cars with variable length intakes that change according to the rpm. Porsche Turbo, perhaps?

Bit like a wind instrument. As you change the length of the piping by pressing buttons, you maximise air flow at different frequencies.

vocky

when I had a single tb I used a really long tb intake pipe, maybe this helped with the engines performance, who knows dunno..

alanoo

This was smart vocky, especially with the 2.4 manifold and the big 2.0 SC TB

The intake pipe is effectively calculated for a specific length even if it is less important than runner lengths

rushy

Interesting reading, thanks for the comments guys. So in affect I should keep the pipe from MAF to TB the same length? If the pipe had a larger bore though which would increase its volume could you shorten the pipe and keep the same characteristics? Also would it be the same from air scoop to filter, the GSi has a very short initial intake to filter, but the 2.2's on the Vec C is an extra foot or more longer?

The reason I ask is, if I could shorten the intake from filter/MAF to tb I could then I move the filter nearer the tb which would enable me to open the bends out in the initial intake. So instead of the intake passing right in front of the engine and rad twice whilst going through the airbox then a small bend then a 90 into the TB, what im potentially after would be one 90 bend after the scoop, through sealed filter (vipor type of thing) then 90 into TB?

As usual your comments welcome.

vocky

do what I would do, try it and see 🙂

rushy

vocky said:
do what I would do, try it and see 🙂

Think thats the plan. thumbup

drpau

Interesting this should come up as I was about to do this myself (went to get a 90deg elbow today), Vocky where did you get your pipe? B&Q? what.. and what length is your pipe (if I can ask a man such a question :lol: ). I remember Oakmere had mentioned the differences in torque he had experienced with a few pipes in his airbox, so all these slight tweaks can make a difference, maybe this could be the thing Im looking for to claw back a bit of my midrange torque whilst not sacrificing the top end power, and if it doesnt work then not much £ spent anyway.

drool.gif

Cheers

Paul

vocky

I bought some 75mm alloy tubing off ebay for £20, I simply made it long enough for the filter to sit next to the air intake

but plastic drainpipe would work just as well

rushy

Does the MAF need to be near the filter or can it be mounted nearer the TB but before Cam breather?

edbutler

Mine is exactly the same as Vockys design wise, however mine is a standard TB... Therefore i use a 70mm 90Deg Elbow and... Wait for it... A 68mm B&Q Drainpipe (£2.52!!). Ive not bothered with PCV return pipe, or the FPR (open to atmosphere) and just drilled a hole for the MAF. 10 minute job 😃

Cant say i noticed a performance difference, but induction noise and TB 'squeak' is a fair bit louder!

edbutler

rushy said:
Does the MAF need to be near the filter or can it be mounted nearer the TB but before Cam breather?

You want the MAF BEFORE the PCV (Positive crankcase ventilation) return pipe from the top of the engine. MAF's are placed near the airbox so that they have the least chance of getting oily from that and the EGR on some cars.

On a side note, how come only the late Vectra's have MAF's?!

drpau

I thought MAF's were for diesels dunno..

edbutler

MAF's were/are usually just used on Forced Induction cars, as it lets the ECU know more accurately how much air is going into the cylinders. The engine can get a better idea about Air's oxygen content from both air pressure (MAP) and non-compressed air density (MAF).

Most Z22SE's just use an Intake Temp Sensor however which is just a cruder version of a MAF 🙂

MAF's usually use very sensitive electronics though (often a gold leaf). They pass a constant electrical current through this component which heats it up. As the air goes past, the wire cools (Cooler, Denser air will obviously cool it much more than hotter, thinner air). When the wire cools its resistance decreases. Voltage = Current x Resistance... Therefore as the resistance decreases the voltage decreases, which is read by the ECU. So basically a lower MAF voltage means that cooler denser air is going into the cylinders.

(Edited as i got higher and lower mixed up!!) :lol:

drpau

edbutler said:
Therefore i use a 70mm 90Deg Elbow and... Wait for it... A 68mm B&Q Drainpipe (£2.52!!).

Prices have gone up in the drain pipe world my friend, nearly £6 for 2 metres now.No discount for that clay brown colour pipe either, it would have set the VX engine bay off no end. Robbing barrstards.
Couldnt fit it in the VX anyway (it was raining so couldnt have taken roof off - not that the rain would bother you mind rofl.. ). I will have to wait to commendere her indoors' vehicle or use Shanks' pony to get the pipe later. showo..
Tried sourcing an elbow (rubber, silicone, whatever) locally but couldnt, ended up resorting to internet and paid about £19.
When Ive connected it up I will report back and tell all of the massive increase in horsepower and turbo esque torque levels walkthedog.. .

rushy

Cheers ed. I have no idea why we have a MAF and it doesn't make any difference when trying to get the 2.4 TB to work, still go limp. Our FPR is also by the tank rather than up front so fitting the 2.4 manifold becomes a little easier. 🙂

drpau

Well, I said I would report back so here I am, my set up is pretty much identical to Vocky's, tube length, 90 degree elbow etc, linked straight to my K&N. Induction roar puts a smile on the face, strange though is the change in power, <u>seems</u> that now it gives less power/pull in the mid range (3-4k rpm) but more pull still (seems like it) up the top. So it seems like as mentioned further up in the thread, intake length is crucial to power at certain rev range, so playing around with drain pipe :lol: length (shortening), may bring back some of the mid range power, but then possibly at the expense of the top range power given by the 2.4 inlet mani which could make it a useless addition. Seems its a tricky balance. Ive still got another 1metre plus of B&Qs finest drainpipe so I will experiment with the effect of shortening the pipe length ( if I can get that air sensor back out of my current pipe :roll: was a tight fit going in so should be well hard to remove).

OAKMERE

I am not 100% sure that the intake length has everything to do with it. I had a silicone 90 degree and 70mm pipe going to the original box and it gave the same results i.e felt better top end but not as good mid range. I think the original intake pipe helps increase air velocity and therefore torque mid range. Though without a dyno testing it is difficult to know.

Perhaps a smaller diameter unrestricted pipe may be better dunno..

Cheers Oakmere

alanoo

Intake pipe length helps getting equal air distribution in the plenum
It is not directly (well it is, but much less than runners) impacting the power curve like runners length but if done correctly it will help