VNT: has anybody...

[vulcan bomber]

Let me have one more go ....

Would a boost controlled VNT, incurring the MPG reduction as described, still compare favourably (consumption wise) to a standard turbo on the same engine ?

That would all depend on the turbo's in question, you would get MOST of the performance gains with a boost controlled VNT over a standard turbo. Remember that a Turbo alone wont alter your consumption, the fueling for the turbo will.

[Turbocharger]

Still no photos because I'm away for Christmas, but mine gave 26.7mpg today over 130 GPS miles at 60-70mph, measured brim to brim. I could probably improve that by opening out the steady-state position, but that would be at the expense of the transient response.

Spec is a 300Tdi Ninety, Mitsu L200 turbo on my own manifold, RR ZF 4HP22 box with a V8 t/c, 1.2 tbox and 285/55R16 BFG muds. It's a ragtop with a cage too, which probably doesn't help things. With the gearing as it is, the T/C locks up at 50mph and it'd probably give 30mpg at 50mph but life's too short. It's not my daily drive now so 26mpg is fine.

[TheRecklessEngineer]

Let me have one more go ....

Would a boost controlled VNT, incurring the MPG reduction as described, still compare favourably (consumption wise) to a standard turbo on the same engine ?

I think the difference (if any) will be negligible.

[TSD]

I don't think the difference is negligible. My TGV makes 15psi of boost all the time, even in light cruise. My 200tdi makes almost no boost in the same situation. As already mentioned, the TGV has a simple mechanical boost controlled VNT. It's adequate, but it will never be more than that. It suffers some boost spikes and surging, but nothing you can't live with.

Back of fag packet sum says a 2.8 engine at 2000rpm consumes 280 cfm of air,

A quick google suggests 0.05hp/cfm to compress it to 1 atm, so a total of 14hp consumed.

There are some huge assumptions and error margins here, but that's much more than 10% extra power (probably more like 20%) required to maintain cruise. Cruise doesn't usually make up a huge amount of total fuel consumption, certainly not as much as we'd all like, but enough to not be negligible.

I think my TGV was around 10-15% worse on fuel consumption than the 300tdi it replaced, on the same 100mile/day commuter run, which seems to fit nicely with the numbers above - or did I get my sums wrong?

[dirtydiesel]

I plan on using a thottle pedal switch to interupt the switched earth for the vacuum solenoid for the vgt actuator, to allow for low boost cruising.

I am converting my patrol to a garrett 2359v at the moment so i'll post some pics and reasonings for my control method when i'm up and running.

[simonr]

Would a 'mechanical computater' (ok, I made that up!) work?

What I was thinking is the VNT needs to be controlled by two (or more) factors. Say boost pressure and throttle position (or any other combination).

If you were to attach the VNT to the middle of a toggle and the ends of the toggle to a boost diaphragm and throttle for example, the VNT position would be the average of the two. Moving the VNT attachment off centre will bias its action to one or the other input.

If more control is required, you could make two cams which overlap one another and a roller which sits in the V between the two cams. Then by changing the shape of the cams, the VNT can be 'programmed' to respond to the two inputs. You could even make the cams out of 6mm steel bar, which you can bend by hand - then you could 'program' it in the field!

Effectively, this gives you the same degree of control as a microcontroller - if in a slightly more Analogue manor - more in keeping with a Land Rover!

Si

[Nigelw]

Would a 'mechanical computater' (ok, I made that up!) work?

What I was thinking is the VNT needs to be controlled by two (or more) factors. Say boost pressure and throttle position (or any other combination).

If you were to attach the VNT to the middle of a toggle and the ends of the toggle to a boost diaphragm and throttle for example, the VNT position would be the average of the two. Moving the VNT attachment off centre will bias its action to one or the other input.

If more control is required, you could make two cams which overlap one another and a roller which sits in the V between the two cams. Then by changing the shape of the cams, the VNT can be 'programmed' to respond to the two inputs. You could even make the cams out of 6mm steel bar, which you can bend by hand - then you could 'program' it in the field!

Effectively, this gives you the same degree of control as a microcontroller - if in a slightly more Analogue manor - more in keeping with a Land Rover!

Si

Like that idea Si, gives a throttle response as opposed to a vacuum response which would be more in keeping with the electronics of modern ones.

Will see how complicated the flashmantv black box is.

[TheRecklessEngineer]

I don't think the difference is negligible. My TGV makes 15psi of boost all the time, even in light cruise. My 200tdi makes almost no boost in the same situation. As already mentioned, the TGV has a simple mechanical boost controlled VNT. It's adequate, but it will never be more than that. It suffers some boost spikes and surging, but nothing you can't live with.

Back of fag packet sum says a 2.8 engine at 2000rpm consumes 280 cfm of air,

A quick google suggests 0.05hp/cfm to compress it to 1 atm, so a total of 14hp consumed.

There are some huge assumptions and error margins here, but that's much more than 10% extra power (probably more like 20%) required to maintain cruise. Cruise doesn't usually make up a huge amount of total fuel consumption, certainly not as much as we'd all like, but enough to not be negligible.

I think my TGV was around 10-15% worse on fuel consumption than the 300tdi it replaced, on the same 100mile/day commuter run, which seems to fit nicely with the numbers above - or did I get my sums wrong?

Yes, you are right. I hadn't quite thought through the above when I posted it.

If anyone would like to furnish me with a VNT, I'll quite happily develop a microcontroller system for boost control.

[Nigelw]

I don't think the difference is negligible. My TGV makes 15psi of boost all the time, even in light cruise. My 200tdi makes almost no boost in the same situation. As already mentioned, the TGV has a simple mechanical boost controlled VNT. It's adequate, but it will never be more than that. It suffers some boost spikes and surging, but nothing you can't live with.

Back of fag packet sum says a 2.8 engine at 2000rpm consumes 280 cfm of air,

A quick google suggests 0.05hp/cfm to compress it to 1 atm, so a total of 14hp consumed.

There are some huge assumptions and error margins here, but that's much more than 10% extra power (probably more like 20%) required to maintain cruise. Cruise doesn't usually make up a huge amount of total fuel consumption, certainly not as much as we'd all like, but enough to not be negligible.

I think my TGV was around 10-15% worse on fuel consumption than the 300tdi it replaced, on the same 100mile/day commuter run, which seems to fit nicely with the numbers above - or did I get my sums wrong?

Assuming your sums are correct, how would a manually controlled VNT stack up against a super charger for that type of power consumption? It seems pointless to spend on creating power with inherent down falls with power spikes and such when you can do it all the same with a super charger?

[Anderzander]

A manually controlled vnt can be a budget option - I can't imagine a supercharger install being anything other than expensive ?

[Nigelw]

A manually controlled vnt can be a budget option - I can't imagine a supercharger install being anything other than expensive ?

Not sure I entirely agree with that as some of the S/H VNT turbos over here are getting on for 75% the cost of a reconditioned unit circa €350~450 and I have seen easy install superchargers trading around €650.

It just seems almost as easy (in my mind only!!) that if a VNT draws HP and costs fuel then for the same result supercharging may be a different avenue worth exploring?

I do get the whole "on a budget" thing but can long term higher running costs negate any advantages over wastegate turbos?

[simonr]

Superchargers, Turbochargers and VNT's all deliver different power / torque curves which may be more useful in different applications.

A supercharger gives a 'lift' over most of the rev band apart from low RPM where they are (sometimes) inefficient. Also, the boost is proportional to RPM, not to load.

A regular turbo does little below a certain RPM and then delivers boost proportional to both RPM & Load - which can yield more torque when you need it than an equivalent Supercharger.

A VNT can give you the best of both worlds with a lower RPM where it starts producing boost as well as continued boost to higher RPM and can be 'programmed' to change the shape of the power and torque curves of the engine to suit a particular application.

No one is better, each suits different applications. Having said that, a 'mad max' style 'go faster' / engage supercharger button on the gear stick is very appealing!

Si

[Anderzander]

X-max button soon then ?

[RustyNissanPrairie]

will the low (er) down torque available from fitting a VNG/VGT affect the bottom end/crank bearings with the increased levels of torque during a time when oil pressure isn't particularly high?

[TheRecklessEngineer]

will the low (er) down torque available from fitting a VNG/VGT affect the bottom end/crank bearings with the increased levels of torque during a time when oil pressure isn't particularly high?

It's the rotation of the shaft inside the bearings that drives a wedge of oil between the shaft and bearing, not oil pressure.

As long as the shaft has sufficient speed and there is oil present, it'll be fine.

http://www.stle.org/resources/lubelearn/lubrication/#hydro

[Turbocharger]

As requested, here's some pics of my VGT. It's probably got 15,000 miles on it now, and since setting it up the only problems have been rewelding the manifold after several cracks formed, probably from heat cycling.