Snorkel, Hiclone and Restrictor.

The issue with harmonics is a little more complex. Certain harmonics that can occur in air intake systems set up harmonic waves that actually impede air flow and can cause less air to reach the engine while they happen. So you may notice an improvement at high revs but may develope a flat spot elsewhere in the rev range (ie at 3-3500 rpm in the middle of the torque band!).

Only a dyno could tell for sure, and I don't think they would put these in only on certain vehicles if they didn't have some benefit.

Peter

pjchris if that is the case, how can they tell if it will make an improvment in my car vs a 2.8L 3L Hilux which is a totally different engine, air intake etc etc etc. How can they tell if the vehicle is turbo'd or naturally aspirated. Sounds like hogwash to me as this same snorkel kit is fitted to many differnt engine models and configurations all with different air inakt pathways, air boxs and filters...

My bet is they use the same basic snorkel set up, install their first one, take it for a drive and if it seems to have a flat spot or a harmonic then they fit a restricter plate (and I'm sure they don't call them that) or alter tubing sizes/shape etc and try again. It seems to be a bit hit and miss as some vehicles have them and some don't.

If they had the equipment they would set the vehicle up on the dyno and graph air flow and pressure across the rev range and compare power and torque figures before and after snorkel fitment. Analysing the after figures would show up harmonic problems as rate of air flow would not increase in line with engine rpm or air pressure at the air filter would drop and a 'flat' spot would be apparent on the power or torque graph.

Then you would alter the volume/size/shape of the tubing that comprises the snorkel to tune it differently to eliminate the problem.
Remember every tubular system has a resonant frequency be it intake, exhaust, manifolds etc. Any engine tuner will tell you that if the resonant frequency of the exhaust or inlet manifold is wrong the resultant standing wave (or harmonic) can spike the backpressure on the exhaust side or increase resistance on the inlet side resulting in a momentary loss of power that can vary from almost un-noticeable to a very noticeable flat spot.

That's what all those computer modelling programs are for. Comparatively, Snorkel design is fairly crude. fit it to the car and see how it goes. Of course they all follow certain rules relating to size of piping, sharpness of bends and inlet area, but without access to the engine design data they are a bit behind the eight ball so to speak.

In many, if not most cases, the fitting of a snorkel does not cause a harmonic or noise issue. But sometimes it would. Given the sheer number of vehicle variations, as you alluded to, Turbo, non, engine size and different air intake systems when the same engine is fitted to different vehicles it would prove to be very expensive to undertake a full computerised design process, followed by rigourous real world testing given the relatively small number of snorkels they sell.

Safari, who also design and manufacture the dtronic, have obviously done just this with the dtronic which partly explains the high price. Given the developmen costs, it took 6-12 months to design and test the unit for the DiD Pajero, the research cost per unit sold would be significant. And they have to recoup that.
Naturally they will sell more snorkels for a particular model than Dtronic's but people are not going to want to spend $1000 for a few pieces of plastic tube and a ram, which could well be the all up cost for a computer designed/modelled and tested unit.

Peter

As I said above the snorkel shape may actually hinder airflow with the resricter removed.

However...
To install such a device which WILL restrict airflow at higher revs witout telling the client to help solve a potential flat spot issue is just plain stupid.

there are far better ways to solve harmonic/noise issues than restricters. Witness those plastic boxes that go nowhere that hang of the side of the intake (between air filter and inlet manifold) on many vehicles. By changing the volume of the intake tube here they change the harmonics of the system as a whole. This is a far better way to do it. I suspect most Snorkel manufacturers don't have the equipment to design this solution thogh, so they build one, drive it, see they've got a problem and fit a restricter. Problem solved as far as they're concerned.

Lazy, just plain lazy. And cheap too. A bit like certain car makers that fit restricters to exhausts to improve Cat warm up time on ULP vehicles, or to avoid exhaust manifold resonance. Again the cheap, quick way out.

Peter