Variable intake manifold

[kenmorton]

Does anyone here know if the variable length intake manifolds make a lot of difference to the torque curve of an engine ?
I have seen a graph of a Mazda v6 torque curve but there wern't any figures on it apart from the rpm when various flaps opened or closed.
To my cynical mind it looked like rather exagerated bullshit but I could be convinced - particulaly if anyone knows of any links to dyno printouts of Honda v6 engines with the variable lengths enabled/disabled.

[cptsideways]

A big difference, especially low rpms.

I've seen some info somewhere on this subject, I'll dig it sometime tomorrow.

[danhay]

My Vauxhaull V6 has a variable intake, and there's a noticable switchover at 4,000 rpm. They definately do make an important difference.

[Marquis_Rex]

I've been involved in the design and development of several "variable intake manifolds"-both V8 and V6. Am also quite familiar with the Mazda engine which I believe is variable resonace.
The V6 or straight six by its very nature lends itself better to variable intake manifolds.

But first we should seperate the types of "variable" concepts: there is variable runner length and variable resonance intake manifold:
Variable Runner length simply changes the the tuning frequency of the intake runner to suit different engine speeds while variable resonance is a little more complicated and uses flap valves that switch the the intake plenum from twin to single back to twin again to change the natural frequency of the plenum(s) until it matches that of pressure pulses in the intake runners until resoance is used.
Both concepts work better with Varaible Cam phasing, ESPECIALLY the latter.

With Variable resonance charging done properly and good wide range (47 degrees) VCP you can expect 6% to 10% gains in torque from 2500 rpm until even up to peak power giving a good wide torque curve range.
The system must be optimised properly, ideally using computer software and the resonance valves must seal well and operate quickly to give good transient perormance.

The Vauxhall 195 Bhp 2.5 litre engine also uses variable resonance I believe.

[Mtv Dave]

Bump...

I've ben thinking about this recently and wondering if there's some more info available. This was the best thread I found here, but it has no links... can anybody point me to some.

I was thinking if what sounds like variable runners on intake for a twin cam V6 as a cheap upgrade, then possibly doing something on the exhaust side, which will obviously cost more, so I want to know if it will make any difference on the intake side first.

From what I thought I knew the systems running in cars today have two sets of intake chambers and some sort of butterfly valve to open them or close them to have up to 4 options. I was thinking of something more like a trumbone giving more controlled variance for volume and length of the system... but I have no real idea about it.

I have a little benched single cylinder engine that I was going to try it on first, but sounds like I won't be able to see much difference with this compared to a 6 cylinder.

[Pigeon]

Honda's V6 system was something like a trumpet, with valves that opened and closed to give three discrete lengths of inlet tract according to rpm. I know this because I was working at a place that handled patent applications when Honda patented it, and I used to grep the application files for interesting stuff I didn't keep copies, but patents are searchable, this was a European patent and the date would be 1989 or 1990 ish.

A single cylinder engine would be a very good test engine as it reduces things to the simplest case. It means you can't play clever tricks using the pressure pulses from one cylinder to help charge other cylinders, but I'd rate that as "stage two" to be tried once you're familiar with the basic effects as displayed by the single-cylinder case.

[arseofbox]

Rex...From what Ive read / researched on the subject, the Vaux. 'Dual Ram' intake uses a solenoid valve that opens at a specific volume to notably increase the plemum chamber volume.

Would this case the resonant frequency to increase, due to the volume increase.

Its something Ive been pondering to have a go at using one of the few spare throttle bodies I have lying around

[aldi]

Toyota did two types, TVIS had 8 complete intake runners (on 4 cylinders/16v) with four being closed off at low RPM. ACIS had an extra chamber halfway allong the runners which was opened up or closed off depending on RPM. I think later types even had 3-stage ACIS.

[jitsukadave]

They all sounds like they have a discrete choice to make, and not a continuous system, which seems odd to me. But as Honda appear to have looked into this 15 years ago, I'm sure somebody would have tried the trumbone style system but found it lacking.

Still, It'll be fun to have a play with.

Oh, also the single cylinder is running a carb... think will that help or not?

[JonRB]

The 2.9L VR6, as destined for the Corrado, was originally designed to benefit from a dual tract variable-length inlet manifold called the VSR (German: "Variables SaugrohR" ) and made by Pieronberg for VW Motorsport. This gave extra low-down torque but was deleted before production on cost grounds and was instead offered as an aftermarket option. The design was later sold to Schrick who redesigned it and offered it as the Schrick VGI ( "Variable Geometry Intake" ).

(Before anyone points out that this is basically cut-&-paste from the Wikipedia page for the VR6, I contributed it to the Wiki page in the first place )

Edited by JonRB on Monday 5th June 13:24

[Pigeon]

jitsukadave said:

Oh, also the single cylinder is running a carb... think will that help or not?

It means you have to watch out for triple fuelling - when you get flow reversal through the carb so the same bit of air is fuelled once when it goes in, then again when it bounces out, and a third time when it goes in again. FI is of course immune to this.