This is about something I doubt many people have heard of, DPV, Dispositif Pre*rotation Variable, a form of anti-lag fitted to 205T16 and R5 Turbo GrpB rally cars, and Renault Formula1 Turbo cars.

Ive known about its existance for years, but never had a clue how it works, though I just found an "explanation" of how it is supposed to work...

The explanation is as follows...

And it's when the Maxi's engine is boosting that the major benefits of race and rally engineering collaboration can be seen. As reported in CCC (June 1984), on January 1st 1984 Renault's Formula One engine wizard, Jean Pierre Boudy, was 'poached' by PTS for its works rally team. This was the reason why the 205T16's architect, Bernard Perron, was confident in stating that Peugeot "don't know what turbo lag is". Neither does Renault with its Formula One V6 engines, because before he left Boudy had developed some aviation engine turbocharging technology for the V6.

This was first used at the Monaco GP in 1982, and developments of the same system are still used in Formula One. But because Boudy defected to Peugeot with his ideas, the 205T16 was the first turbocharged rally car to use his system (The T16 being out before the final evolution R5 Turbo – The Maxi 5 Turbo). Which Renault calls DPV, or Dispositif Pre*rotation Variable (Variable Pre-rotation Device).

"At the very beginning we had made the decision to use it on the Group B R5 Turbo. It's not really necessary for road cars and a little expensive for them, but it's not so complicated". It may not be "so complicated" but the DPV system is an 'extremely effective way of ensuring near-instantaneous throttle response from a competition turbocharged engine’. The system provides for variable air areas and direction angles at the intake to the compressor wheel in advance of the rotation period during which the compressor turbine will require those conditions.

It's not a by-pass system, it's essentially a multi-variable nozzle arrangement which is mechanically linked to the throttle and which changes the direction and area of air which hits the compressor wheel according to throttle position. The rate of change of air flow area and direction is not exactly linear, but it's progressive and always increasing toward full flow at maximum compressor wheel speed.

This irregular mid-compressor-speed flow, which constantly changes the way the air hits the compressor vanes in the mid-range, improves the compressor's efficiency under part-load, because it is arranged so that the turbine will idle at a higher speed than it would given a fixed intake air direction and area. And of course, the higher the compressor idle speed, the shorter the time it will take to reach its important operating RPM. Result: less lag.

The DPV is inoperative at each end of the turbine's speed range. Under pedal-to-the metal full boost conditions it has no effect because there's regular full flow to the compressor, and with the throttle closed the DPV is shut down as well. But it is not just retained inertia and completely eradicated turbocharger lag which form the real benefit of the DPV system, because there's another major advantage in that as a result of there being no by-pass or blow-off to atmosphere, and because it's an internal function to the turbocharging system, there is no pressure wastage in the all*important part-load condition (ie. The blades don't stall during gear changes, or on/off throttle movements).

The pic that went with the explanation is this...



Which is just like how a lot of VNT turbos work, but they obv work as part of the turbine housing, this from what I understand is mounted PRE-THROTTLE, demonstrated by this pic, where its labelled "I"



Im not convinced the pic or the explanation is correct, but its about all ive ever heard with regard to how it allegedly works.

Clever peoples opinions please.

 

weird

as you say, the pic seems to show a VNT setup for the turbine side

are they saying that there is a variable size hole in the intake of the compressor so that it closes up under part load to make a faster gas speed? if the turbine i snot spinning fast enough to make boost, are they suing the incoming air being sucked into the engine to drive the compressor wheel by making it go through a small hole at high speed and hitting the compressor wheel?

 

Yeah, im confused too.

Another, smaller, explanation id seen seems to say its like a secondary pre-turbo throttle that opens slower than the "main" throttle, which massivley helps spoolup.
Very little further explanation tho.

 

they mixed up the words compressor and turbine

 

so you saying its just a VNT turbo? thats not what the 2 seperate explanations ive seen seem to say? both seem to imply its a pre-compressor add-on?

 

Steve,
That picture is not the right picture as far as I am concerned.

I was always led to believe that the T16 turbo had a "tongue" arrangement controlled by a seperate actuator that actually did what they describe in the text. This "tongue" arrangement was able to vary the gas speed to the turbine. At low rpm, the tongue was "closed" helping speed up the gas by creating a smaller channel for it to hit the very ends of the blades with. As engine rpm increased - the "tongue" moved lower, exposing more area of the turbine for the gas to "hit".

 

Now I think about it, ive seen a pic that did look like a tongue/throttle thing attatched to the compressor inlet, so again, not turbine...

 

whys has the Rally car got a Bass tube?

 

im sure its just a VNT turbo, i remember reading years ago about how it was unreliable because the moving parts kept sticking!

mike ive seen the tongue idea before, but i dont think it was on t16's

 

well IF
this thing is located between the exhaust manifold and the turbo, i would see it working by reducing entrance volume into the turbo, therefore increasing airspeed onto the turbo (therefore spooling it up faster due to faster air through the turbine?)
then opening up when full throttle is on and the turbo would be running at full boost on full opening while the engine speeds are high enough to maintain full velocity of the air under full entrance volume??

acting as a type of anti-lag maybe?

 

Likewise, thats the version ive heard.

But I have never actually seen it first hand.

 

When I get home ill draw (ive not got a scanner ) the pic that lead me (along with the words that accompany it) to believe it was a pre-compressor thing.

Shame if it is just a VNT thing (the tongue thing is deffo just another form of the VNT thing from what ive seen), but it makes the most sense to be that i guess!

 

There MUST be a picture SOMEHWERE on the net (but I'm fucked if I can find it) .

 

Its ok mike, my PC paintbrush skills are badical and will come in to full effect later as i try to re-create a black and white picture from a book for you

 

right, im SURE we getting confused here now, and this DPV is a compressor inlet thing totally seperate to VNT stuff.

just been looking at the pic I was on about, and it clearly shows what looks like a conventional throttle on the turbo compresser inlet.
it probably isnt conventional, but sure looks like one.
its the early version too.

ive seen a later renault f1 turbo engine, and if any of them was gonna have VNT id think it was a later one, and that deffo hasnt, can clearly see there is no form of adjustment on the turbine side, though it dont look like its got what i presume is the DPV like on the early engine either, but its on a stand not complete, so no suprise.

the T16 was mentioned, well from what i understand that had the DPV but did NOT have a VNT turbo.
the 2litre T16 engines from 405 T16s from the early 90s had what is similar to VNT turbos, but were called VAT turbos and used a single moving tongue, like Mike was on about.
they gave better response, but not as effecient as a normal turbo overall.

mitsubishi have a version of that with twin smaller tongues thats meant to be even better, not sure what cars they fitted to tho.

the DPV writeup in the books says its "basically a fancy name for a variable nozzle in the compressor inlet"

"mechanically linked to the throttle, it changed the compressor inlet area and direction it hit the compressor wheel according to throttle position"

"when the driver lifted the throttle the DPV closed faster than the throttle, ensuring the turbo kept spinning fast in vacum-like conditions"

so yeah, none the wiser really, but im thinking the pic above is DEFFO wrong, and the writing maybe is too.

 

what book you reading steve?

 

I always understood that T-16's ran a variant VNT turbo - can speak to my mate about it in the morning - he'll know

 

Gareth, the same book you got, that Forced Induction Performance Tuning book.
All the bits i just mentioned are on various different pages/sections tho, need to search!

Will- VAT25 it says, which is rather similar to VNT25 of course, but works different, got diagrams and shit too, if only i could draw

 

turbos are complicated bastards

we were messing around with the ported shorud on mine while on the rolling road and it works the complete opposite way from what i thought

 

i havent read it for years, forgot it all now

 

what did you observe? and what did you think would happen?

 

what do you think happens in a ported shroud Gareth?

 

slows turbine down at high rpm

 

Dont think so mate

 

oh well then lol

 

flow rate drops off the smaller the inlet, but of cause this will lower the amount of torque required to spin the turbo compressor

 

we werent measuring speeds of the the turbo mate so I dont know one way or another to be honest.

Slowing the turbine down at high speed is very bad news for power tho I can tel you that

 

what happens if you put your hand over (or knob in) the end of your vacuum cleaner

 

thats how i thought the ported shroud works but infact its the opposite

 

i dont believe you

 

what dont you believe?

 

Im confused about what happened and what people thought happened.
Anyone wanna explain?

I thought (correct me if im wrong) ported shrouds reduced compressor surge by leaking some air out after the inducer, slightly lowering wheel efficiency all round (so everything, spool and max power) but decreasing surge by a much more useable amount.

So unless you have a comp wheel that will suirge without one, it wont do you any good.

Sounds nicer tho

 

I thought air would pass the part of the compressor to reduce effciency but in fact the compressor wheel pushes air back of of the holes and back into the inlet pipe.

very strange to feel air being blown out of the compressor

 

surpised you can feel it coming back out, it does do that, but thought the inducer sucking it in would totally negate anything you could feel.

now i think, im guessing the bit escaping out the ports, though lower in capacity, is at a much higher speed, so that makes sense you can feel it i guess.

 

We tried some funny stuff with my new turbo Stav and got some funny results

We have it working pretty well now and I believe there is more to come with the spec changes Alan has recommended

 

its a restrictor and does as i said earlyer, "flow rate drops off the smaller the inlet, but of cause this will lower the amount of torque required to spin the turbo compressor"

 

I have come across this technology in my new job.

Its an optimised adaption of variable vane turbo charging.

Mapped vane angle control along with mapped throttle angle is available
on a few production cars now IIRC (porsche ???) aswell on the engines I
now design ecu's and software for.

This combination allows optimised air speed into the turbo by controlling
the pressure differential across the compressor for all loads/rpm variables.

I am no expert on the dynamics of the physics but the software control
is very complex and something that takes ages to get right on a dyno.

 

eh? im on about ported shroud inlets in that post, as is euan, you talking about the original DPV thing?

 

steve you have described how it works in your first post

 

that means nothing to me

explain what it does, and how it does it, in a simple way for thickos like me please

it worked purely mechanically in early versions, so that might be the best to explain to me