Benifits of short runner intake on F/I

[flusted 0]

Thinking about going short runner on my 16vg60 but whats going to be the benifits over the 16v manifold?

 

was guna make 1 like this

[CrazyDave 0]

The main benefit is shorter pipework for turbo applications. Gives a better response when coming back on the throttle. The downside is the loss of the tuned pipe length which is designed to boost torque at some part of the rev range, or several parts if you have a variable manifold design (like a Schrick).

 

You may see a slightly better repsonse when opening the throttle as you'll have less pipework to fill and it may also reduce the pipe runs to / from your cooler, so that would help.

 

But be prepared to loose some bottom end torque, especially if you have the smaller (42mm?) manifold on already.

[mrbeige 0]

Aren't the long runners and a turbo/supercharger counter-productive? The turbo/supercharger should improve the torque figures anyway, therefore reducing the need for the long runners?

[CrazyDave 0]

That's correct, when on boost. But off boost and at low engine speeds the reduction in length of the runners will cause a drop in bottom end torque. The shorty may actually hit another resonant point much higher up the rev range

 

Most people notice the drop in torque between the two types of 16v runners. Most opt for the large diameter runners and the small increase in top end power that this creates. But I've stayed with the small diameter runners to maximise bottom end (I've actually got the large manifold in the garage), cos I'm lazy and don't like thrashing the poor old gal :)

[Kevin Bacon 5]

Back in my 16V days, I did the 42mm manifold plus exhaust cam mods and it made 2lb-ft more than the 50mm manifold. It also didn't rev as cleanly past 6000rpm with the smaller mani.

 

The thing I found with valvers was you got good ones and bad ones, and that was the biggest influence on how they felt on the road. No matter what you did to a bad one, it was never as quick as a good, standard one.

 

The best one I had was a stock 89 F reg MK2, with 66K on it. That thing was ballistic. No other valver I had after that (except the 16V T) came close, despite tonnes of mods.

 

Anyway, short runners..... yep, nearly all turbo engines use them for the reasons already stated. Less volume for the turbo to fill, so quicker response. Most OEs use them with piddly little turbos and high compression though, so bottom end isn't an issue.

 

There are ways to compensate for a lack of bottom end, such as more timing, shorter gearing etc etc.

 

One thing with shorties though is the throttle is placed at one end, rather than in the middle of the runners like NA manifolds, so you can get some slight port balance issues. I get round that by taking 3% fuel off the 2 furthest cylinders from the throttle (that's why I recommend sequential injection) and it smooths the engine out nicely.

 

The only shorties I've seen with centrally mounted throttles are Volvo 16V Turbo and an Audi engine and HGPturbo.de do aftermarket shorties with central throttles.

 

On boost though, that doesn't matter as the air will just force it's way into all the cylinders regardless, but if you want crisp and stable part throttle behaviour, you need to take these minor things into account :wink:

[flusted 0]

Yeah im using a 42mm jobby. I suppose with the g's type of boost control, you dont actually get boost until you floor it so round town pottering of boost will suffer with the shorty?

[Kevin Bacon 5]

You might be OK. AFAIK, the GLader is a positive displacement charger so should be making the same boost at 2000rpm as it does 5000rpm?

 

Not sure if it is tbh.

 

Get a nice roots blower on there, plenty of torque everywhere :-)

[dirtytorque 0]

You might be OK. AFAIK, the GLader is a positive displacement charger so should be making the same boost at 2000rpm as it does 5000rpm?

 

Not sure if it is tbh.

 

Not sure either but unless you are close to WOT alot of that boost gets bled off because of the G's throttle arrangement.

If you have a spare manifold to try it on why not just experiment and see what it feels like?

[boost monkey 0]

I wouldn't recommend you do make your own one unless you've had previous experience, but of you do, get a GOOD engineering book on "pulse dynamics" which will show you the differences between the two manifolds (or at least the science and calculations behind it!).

 

long runners will hurt an F/I engine as you literally want the boost getting into the chambers ASAP and not fannying around in the tracts or the plenum itself.

 

opposite applies for an N/A engine afaik, but that's due to back-pressure and the generation of torque through the "tunnels" of air waiting to enter the chambers.

[ProdigalSon 1]

You might be OK. AFAIK, the GLader is a positive displacement charger so should be making the same boost at 2000rpm as it does 5000rpm?

 

Not sure if it is tbh.

:scratch: I thought that the boost generated by the G-Lader was proportional to rpm, roughly 2psi per 1000rpm (ignoring losses due to leaks etc.) in a stock arrangement, and more with a smaller charger pulley...

 

dirtytorque is right that the great majority of that boost gets recirculated unless you are on the throttle, but it is a progressive changeover from bypass to full boost, so you might just find that the shorty gives sucky low-end torque when you are on

 

Here's a few pics of the bypass valve, and you can see the position of the throttle (albeit the underside) and the bypass valve:

 

climatronic wiring-Golf from May 01.pdf_DSC6150.jpg[/attachment:2hmebyvw]

2.8l 24v Climatronic system.pdf_DSC6151.jpg[/attachment:2hmebyvw]

_DSC6152.jpg[/attachment:2hmebyvw]

Or am I going :cuckoo: ? :lol:

[mrbeige 0]

So how do you take the rest of the pipework into consideration? If you have a front monted intercooler as opposed to an inline charge cooler, does the length of the pipework between charger (super or turbo) and throttle body have any effect? Would it be correct in thinking that you have similar issues with filling that pipework up with pressurised air?

[Dec 1]

You really have the opposite problem with the rest of the pipework. when you come off the throttle, the throttle valve closes, but he turbo is still producing boost as it starts to spin down. The airflow cant flow into the inlet manifold, causing pressure waves that travel backward through the inlet piping to the turbo, causing it to stall. It's the problem that bov's attempt to resolve. They basically release the pressure caused by the closing of the throttle plate, so the turbo can keep spinning freely.

[flusted 0]

Ive adjusted my throttle bypass to shut a tad earlier, can notice a difference. I want as much low down power as poss.

 

Forget all this turbo talk aswell :ignore:

[ProdigalSon 1]

Works both ways - the more total volume of all the pipework and intercooler between the compressor (super- or turbo-charger) and the inlet manifold, the longer it takes for pressure to build in the system and the more pressure to dissipate when it's not wanted. With a supercharger, there's little instant step-change in pressure because it's always spinning, so there is a 'smooth' build up and fall off of pressure.

 

With some turbos, there is a definite spool point where suddenly there's way more pressure than before - this can cause the pressure wave 'bounce' that Dec mentioned, if I understood correctly...

 

In a G60, the Idle Stabilisation Valve acts as a BOV, quickly dumping overpressure from the system during high-rev WOT gear changes, for example. When the pressure is not excessive, the sudden closure of the throttle just causes the charger to have to 'push harder' against the slug of high pressure air ahead, but only very briefly until the now-open bypass valve dumps the excess pressure to the inlet side of the charger, helping it to deal with the sudden increase in backpressure (and minimising the mechanical shock, I would imagine).

[flusted 0]

so what happens when you have no ISV :lol:

[dirtytorque 0]

Works both ways - the more total volume of all the pipework and intercooler between the compressor (super- or turbo-charger) and the inlet manifold, the longer it takes for pressure to build in the system and the more pressure to dissipate when it's not wanted. With a supercharger, there's little instant step-change in pressure because it's always spinning, so there is a 'smooth' build up and fall off of pressure.

 

With some turbos, there is a definite spool point where suddenly there's way more pressure than before - this can cause the pressure wave 'bounce' that Dec mentioned, if I understood correctly...

 

In a G60, the Idle Stabilisation Valve acts as a BOV, quickly dumping overpressure from the system during high-rev WOT gear changes, for example. When the pressure is not excessive, the sudden closure of the throttle just causes the charger to have to 'push harder' against the slug of high pressure air ahead, but only very briefly until the now-open bypass valve dumps the excess pressure to the inlet side of the charger, helping it to deal with the sudden increase in backpressure (and minimising the mechanical shock, I would imagine).

 

 

Apart idle regulation i understood that the isv's only other function was to bleed boost under the control of the ecu in the event of knock...

 

?!?!?

 

:)

[boost monkey 0]

So how do you take the rest of the pipework into consideration? If you have a front monted intercooler as opposed to an inline charge cooler, does the length of the pipework between charger (super or turbo) and throttle body have any effect? Would it be correct in thinking that you have similar issues with filling that pipework up with pressurised air?

 

STU, FMICs (good ones) are generally cross-flow: they have inlet on one side and outlet on the other. This promotes excellent flow rates. Standard G60 ones are a horrible design. Very small, tucked away in a corner of the engine bay and have pretty much 2 x 90deg bends in them (as the inlet and outlet are on the same sides) :eek:

 

The amount of pressure (or head loss) generated when you ask a fluid (in this instance, air) to navigate anything more than a straight line is quite horrid (I want to say that the angle of direction change is exponential but I don't think my recent coursework findings can justify that :scratch: : I will pull out my report and let you know soon :salute: )

 

The fact that you are asking the air-flow to conduct heat into the IC (or the IC to absorb it, potatoes potahtoes) THEN make a 90degree turn and THEN make another one just destoys a good chunk of the useful pressurised airflow.

 

Pipework will always have an effect, and even straight sections of pipes have a headloss across them, although these are generally tiny or at least negligible with respect to the rest of the system.

 

hth,

 

Jon :salute:

[flusted 0]

Air really wouldnt like my set up then, lots of bends

[ProdigalSon 1]

Apart idle regulation i understood that the isv's only other function was to bleed boost under the control of the ecu in the event of knock...

 

?!?!?

 

:)

Er, may have been a bit enthusiastic with that last post! :lol:

 

My personal experience is that the ISV will dump excess boost to the return line at high rpm (making the characteristic 'whoosh' noise, a bit like a whistle on a stove-top kettle). It is meant to do so above about 5500rpm to ease the transition into rev limiting. It also does a more severe job of restricting boost when knock is detected, but fortunately I haven't noticed much of that.

 

Because the throttle and bypass valve are mechanically linked, as soon as you drop the throttle to idle, the pent-up boost can escape down the return pipe to the low pressure side of the charger, which is why you have to work hard to get much of a whoosh out of the ISV. Unless you have a crazy small pulley and regularly have 1+ bar in the inlet!

 

Didn't mean to suggest that the ISV was the equivalent of a BOV on a turbo :wink: It's much more low-key than that.

[flusted 0]

what about short runner with large or small plenum? what difference would it make?

 

The 50mm has small plenum and the 42mm has large plenum

[boost monkey 0]

I can heartily recommend the section on Inlet Manifold Plenum Design on page 30 of A. Graham Bell's book Four-Stroke Tuning.

 

there's too much to type up on here, plus it's not my experience and it's copyrighted. Interesting stuff though which goes against what you may believe is true...certainly got me thinking!

[ProdigalSon 1]

Ditto boost monkey's recommendation - I read it at the weekend, and it was excellent stuff, really interesting to see how the VW engineers have dealt with a lot of that stuff (you can see reason behind what looks like random design decisions when you look at the 8V G60 inlet and think about the engine's rpm/power/torque curves).

[flusted 0]

do you do book hire :lol:

[Kevin Bacon 5]

Oh give over..... "My Dad knows something about your friend's sister but I can't tell you what it is" :roll:

 

You don't have to recite this book word for word.

[ProdigalSon 1]

I would spill the beans, but I can't remember exactly, and like the monkey said, some of it goes against what you'd expect, so it just sounds wrong second-hand... Will have a think and see if I can recall it.