DaveAVT

Yes, its a Gordini headed 5, standard head, Piper 300 cam, tubular manifold, custom plenum, 22psi and 260bhp.

Monster VNT anybody?

http://cgi.ebay.com/ebaymotors/Garre...spagenameZWDVW

Only if you have big enough balls.

DaveAVT

This is a video of the car in action on the strip. One of his 11.6 runs, with no effort..

http://www.rtoc.org/library/fileroot...SZHWVIJNGC.wmv

Porkie

iTrader: (1)

Mr Whippy

I..........want.............one..............

Anonymous

What does a GT turbo have to do with it? There is nothing variable about a GT turbo


The problem with the VNT turbo is that you get different VE from the engine at the same RPM and same boost depending on what the vanes are doing at the time, hence different airflow.
So its like you are trying to map a car and not know if its going to be a T34 one minute and a T4 the next

L8 etc wont cope with that, you need either an AFM, or you need to know where the vanes are at the time via some other method.

Then if they do start to stick, and arent where you think they are, you get fuelling issues accordingly.


Im not saying its an insurmountable problem, merely thats its more involved than just bolt it on and remap it.

Stavros

Because you said (or seemed to say) youd need an AFM based managment to work it right.

But the GTT mentioned runs Autronic and a MAP sensor, and seems to do quite well...

And the other run carbs!

DaveAVT

Look at my VNT actuator



It has a sensor with a plunger type system that constantly touches the diagphragm in the actuator. The sensor is a 3 pin 5v in, earth and return like a map sensor, so you can use this as a signal to tell you where the VNT mech is, so use it for enrichment, or on a dual map ecu, simply switching maps.

Anonymous

Carbs is fine, thats effectively IS an AFM.

The GTT will have an additional sensor (like the one dave pictured there) to allow it to keep track of the vanes location.

Apologies if i worded it slightly wrong, i should have put a "basic YB type MAP sensor system" is innapropriate.

What i'm getting at is you need SOME way of knowing what the hell the turbo is doing if you are going to fuel for it, beyond just knowing the boost level, AFM is just one way of doing that.

DaveAVT

The GTT isnt running a sensor, but its mapped as a WOT car mainly. His fueling may be wrong at some points on spool, but when you have to consider a VNT can get from zero to full boost in a matter of around 500rpm, its a very small issue..

Mapping to be a nice road car in all conditions is far harder, but not insurmountable with the sensor shown.

foreigneRS

bloody interesting thread. hope we see more of these in the ford world soon

especially interesting is the VNT actuator sensor which would need to fed to the ecu as well as MAP and TPS.

Jay,

iTrader: (4)

seems very hit or miss to me surge probs fuelin ect like you sat chip your just noy goin to know where the turbo at , ive also heard there unreliable siezing solid coming apart under to much egt

in my mind there guna have to go along way to beat a proper speccced turbo , head and antilag or nos used as antilag for reliability

Anonymous

The thing is though, most of the people commenting on this thread about how great they think VNT turbos would be are talking about SPECIFICALLY for a road car that they want lovely and driveable all through the rev range, so having 500rpm holes in it would be a nightmare for them.

To do it properly you ideally need an AFM, so you can see whats REALLY happening, or you need a sensor like the one you posted so you can see whats supposed to be happening at least.

Rab

Great thread! Dave@AVT you sure seem to know your onions!

I'm really looking forward to the future!

frog

I WANT the future... I have a 4x4 cos which I am happy to use a guinea pig
Any takers (PS: My budget is low... )

DaveAVT

Trust me, in practice, it really doesnt happen like that. Even on standard management, it copes with the fast spool up, even though the boost level is high at low revs so you would think it runs lean on standard management, because the engine VE is artificially low due to the turbine restriction, it evens it out some what..

I think the main problem, and one that will upset alot of people, it you can't really do a high power engine with VNT because of the surge problems..

When I say fast spool, its not like having a T4 that spools like a T3 - with a VNT the boost can rise with as quick as you push the throttle, almost instantaneous, even in 4th, you can go from zero to full boost in a second..

The more power you want from your engine ( and could be a longer duration cammed lump) and the bigger turbo compressor side you need to supply it, the more surge you are going to encounter, as the engine isnt designed to consume the large air flow at low revs..

This is why VNT 'suits' diesels which have max air flow at low revs, and even the 21 J7R engine I am using, naturally make peak torque very low down, and I wont be increasing cam or breathing spec, I just want a broad torque band from 1500-5000 which should pull at least 240-260lb/ft through all of the rev range.

Seeing as this GTA will be around 900kgs max, it will make a very streetable car.

VNT would be a good option for a standard YB and somebody wanting 300bhp max.

Anonymous

Dave, with all due respect you just said yourself it does happen like that :S

Have you ever actually mapped a car with one of these turbos on, cause while on one hand you clearly know a reasonable amount about them there are some definate holes in what you are saying, especially in terms of applying it to standard cossie management, have you ever mapped a car on cossie management or anything similar (ie BASIC stuff)

DaveAVT

[quote="chip-3door"]

Ok, think of this way. If you took your standard map that you currently have for say a T3, or T34, and then took that turbo off and stuck on a tiny T2, whats the worse that would happen...?

Anonymous

Thanks mate, that PERFECTLY demonstrates what i meant

At least you can see what im talking about, even if you dont grasp the significance of it!

The worst that could happen?


High EGT's at some point in the range that would kill the turbo potentially

Lean spots that might melt a piston or do in a headgasket

Rich points that would lose power and waste fuel



ALL of the issues that you get with ANY petrol car thats not mapped properly basically!



Like i said, the standard cossie setup isnt really suitable for this sort of turbo IMHO, and anyone who tunes cossies will see you statement above and agree with me i suspect


Im NOT trying to start a row with you here, i just dont think you really understand this as well as people are thinking you do!

You didnt answer my question if you have ever mapped either a VNT turbo car or a cossie though?

DaveAVT

Yes, but what would happen?

And remember, the turbo will only be T2 sized for a second at most...

Anonymous

Apologies, was updating the thread with more detail when you replied.

Please see above.

Im NOT saying you cant make it "work ok" im just saying to get it mapped PROPERLY takes more inputs.

DaveAVT

So basically, you map the car with the VNT mech fully open, so you will never see high boost at low revs..

Then go back, remap the points of no boost on the previous map (probably <2500rpm) with the VNT mech closed, so you have covered most of the rev range across the two main differences of VE caused by the VNT system...

The only problem is, in high gears, motorway cruising, with the VNT closed and running boost...but it still is a brief period. At most, it will run rich at these points...

To get round this, you need standalone, with a fueling trim against the sensor on the actuator..

Anonymous

Indeed, or an AFM on the setup, now why didnt i think of that?

Anonymous

PS

Dont forget its the timing too, not just the fuelling



Basically if you do it on cossie style management you would need to map for the worst case permenantly, so the most amount of fuel and the least amount of timing, and that in itself will kill many of the benefits of it!

Rick

Very intersting reading. I've been thinking, and don't think the mapping issue is such a big one. At low rpm, torque is high, but power and airflow low. So, the small turbine housing isn't really restricting anything, and airflow stays pretty constant. You may go slightly rich, but would be for a very short period.

As for surge, again surely that can be worked around. As an example, on my 1600 a 0.63 housing is quite laggy. The same front end can be used (and is used) with a .36 turbine. Now i would be more than happy to have the low down punch of the 36 with the 7k+ power of the 63.

If u went to a bigger turbo still - say Gt35 on a 1600, surely all u have to do is limit boost until a certain rpm - easily done these days.

Rick.

Fiecos Dan

intresting stuff.

frog

That's not so bad surely, most cossies are stg3 for reliability and make really good punchy cars, but have the drawback of either being good in mid-range and hopeless nearer the red line, or, vice-versa.

I am sure that a stg 3 with neither of the above drawbacks would please many people here

zippyobrien

iTrader: (2)

whats the diffence between vnt and vvt???

James

It's interesting to know the internals are actually the same between petrol and diesel turbos asside from the actual VNT vanes and housing.

I have been told previously when i've mentioned it that fitting a vnt from a diesel to a petrol wouldn't work due to the egt's being to high on a petrol and literally melting the turbo.

But it seems as i suspected thats bollocks.

Yes they do sieze up however i've only seen siezed ones on cars that are driven by grannys that only go to tesco. Mr bloogs the sales rep who drives to bristol on a weekly basis doesn't have a problem and the turbo vanes are always moving thus don't sieze.

If you took a 911 and never drove over 3krpm i'd bet that would sieze up aswell, but porsche have taken the gamble that the people spending Ł90k on a sports car will be using it as intended.

James

vvt= varible valve timing [honda vetec] vnt= varible nozzle turbo [most turbo diesels on the market today]

zippyobrien

iTrader: (2)

thanks, i thought vvt was going to mean variable vain turbo in this case

frog

Or, that the car will be out of warranty before it reaches a mileage that's high enough for anyone (or should that be Porsche) to worry about it (now, that's cynical )

James

yup it could well do.

vvt in that sense and vnt is the same thing just different names.

in granny driving mode i have seen them sieze up in under 30k miles!

DaveAVT

The other point ref. mapping issues...

You don't have the VNT mech holding 20psi restricted, and then switch to fully open mode...

Normally, you only have the VNT mech restricting up to say 3-5psi, and then fully open above this point, so the issue that Chip brought up is only on a low boost level, not the extremes of full boost on both scenarios..

End of the day, if you map for full open VNT, then when it is closed it will only run rich, so EGTs should be still stable, leaning etc..

I have only played with VNTs with the actuator sensor and standalone management, but have been in a couple of VNT efi GT Turbos which run a single map and found no dead spots in performance, just shed loads of wheelspin..

DaveAVT

I will bring up this point again, it is possible on a GT turbo, with the VNT mech fully closed to get nearly 10psi at IDLE (NO LOAD) by just revving it hard...

Ive got a video somewhere by two 'geezers' but they show whats going on...

DaveAVT

Boost at idle.

http://www.rtoc.org/library/fileroot...LQVZNGYEPJ.wmv


Skaky camera action on the road..

http://www.rtoc.org/library/fileroot...JFURKJPOTJ.wmv

Stavros

How is revving it hard at a standstill "boost at idle"? Thats boost without moving.
Boost at idle is surely boost at idle.

I could get 23psi+ by revving my Cossie at a standstill (nothing to do with ALS, honest

DaveAVT

lol, yes it means boost with no load.

Anonymous

revving in neutral watching the boost gauge?

FUCKING CHAV

DaveAVT

you know it...