turbos....how to pick one.... any1 know anything about VNT?
27-02-2006, 10:28 PM
#1
PassionFord Post Whore!!
Thread Starter
turbos....how to pick one.... any1 know anything about VNT?
i know that a lot of reno 5 people run a VNT in T28 size and love em,
but i know a lot of tuners who dont like em and say they are no good, but the people making them say they are great.
how do you know who to believe?
how do you pick your turbo?
i like the idea of a vnt and believe that it will be the next generation of turbo especially as porsche now use them as std but are the current garrett ones good enough? or will the GT series be better?
but theres sooo many different trims, wheels, housings... how do you pick the best one.
i know some1 who builds turbos whos says that the GT series arent much better than a standard T series and VNT are the ones to get,
i just dont wanna go and spend loads of money on a turbo only to find out i could have got one better suited to me
i know most will say to use what the person building the engine wants to use, but if they havent tried a vnt or a certain type of turbo they wont know how it performs.
but i know a lot of tuners who dont like em and say they are no good, but the people making them say they are great.
how do you know who to believe?
how do you pick your turbo?
i like the idea of a vnt and believe that it will be the next generation of turbo especially as porsche now use them as std but are the current garrett ones good enough? or will the GT series be better?
but theres sooo many different trims, wheels, housings... how do you pick the best one.
i know some1 who builds turbos whos says that the GT series arent much better than a standard T series and VNT are the ones to get,
i just dont wanna go and spend loads of money on a turbo only to find out i could have got one better suited to me
i know most will say to use what the person building the engine wants to use, but if they havent tried a vnt or a certain type of turbo they wont know how it performs.
27-02-2006, 10:48 PM
#5
DEYTUKURJERBS
The problem with VNTs are two fold.
High exhaust gas temp seems to fuck them up too quickly.
Setting up the VNT mechanism to work ideally for your car (if it not the standard car the turbo came off) can be a pain in the arse.
Lots of types of VNT turbos, from teeny T2 sized ones to mahooooosive VNT GT40s which look the tits.
Companys like Holset etc also make VNT turbos.
GT turbos are more modern than Garrett T-series ones, but they seem to use thinner shafts in many cases, which makes them slightly weaker.
Most people who has done back to back testing has said to stick with the normal journal bearings too, as the BB cores seem to be weaker, more expensive, and dont seem to noticably help perormance.
And seeing as you dont HAVE to have a BB core on a GT turbo, well...
Many aftermarket turbo companys use a mixture of components, GT, T, and their own designs, to make their ones, so something being called a T or GT summat if its not made by Garrett dont nececerily mean loads.
Working out sizing of turbos is down to wheel and housing sizes compared to engine spec (mainly capacity and working rev range).
But far too long winded to talk about here, when can read about it all over internet.
Give a detailed spec of what car its for and what you want from it, and might be able to help.
High exhaust gas temp seems to fuck them up too quickly.
Setting up the VNT mechanism to work ideally for your car (if it not the standard car the turbo came off) can be a pain in the arse.
Lots of types of VNT turbos, from teeny T2 sized ones to mahooooosive VNT GT40s which look the tits.
Companys like Holset etc also make VNT turbos.
GT turbos are more modern than Garrett T-series ones, but they seem to use thinner shafts in many cases, which makes them slightly weaker.
Most people who has done back to back testing has said to stick with the normal journal bearings too, as the BB cores seem to be weaker, more expensive, and dont seem to noticably help perormance.
And seeing as you dont HAVE to have a BB core on a GT turbo, well...
Many aftermarket turbo companys use a mixture of components, GT, T, and their own designs, to make their ones, so something being called a T or GT summat if its not made by Garrett dont nececerily mean loads.
Working out sizing of turbos is down to wheel and housing sizes compared to engine spec (mainly capacity and working rev range).
But far too long winded to talk about here, when can read about it all over internet.
Give a detailed spec of what car its for and what you want from it, and might be able to help.
27-02-2006, 11:07 PM
#6
PassionFord Post Whore!!
Thread Starter
well at the mo im only thinking about them.
just trying to get some info on them
the problem is im not sure on the power of the engine.
ideally i want a 500/550bhp cossie engine (dont we all) if money allows but at the mo i have what is supposed to be a 400 bhp engine (not ben run yet so dont know but was told it was built for 400bhp.)
its going to be used for 1/4m, track days and sometimes on the road
i know i should wait till i have the engine i am going to settle with but its just something ive been thinking about.
i know turbo technics are building a T38 sized unit at the mo, they say it will be finished around june time and when its ready it will have a 2 year garentee.
a 2 year garentee is good enough for me really.
and it would have an external wastegate and ecu controlled boost
do you know of any sites i can read up on them? whenever i type vnt into a search engine it comes up with useless crap. lol
just trying to get some info on them
the problem is im not sure on the power of the engine.
ideally i want a 500/550bhp cossie engine (dont we all) if money allows but at the mo i have what is supposed to be a 400 bhp engine (not ben run yet so dont know but was told it was built for 400bhp.)
its going to be used for 1/4m, track days and sometimes on the road
i know i should wait till i have the engine i am going to settle with but its just something ive been thinking about.
i know turbo technics are building a T38 sized unit at the mo, they say it will be finished around june time and when its ready it will have a 2 year garentee.
a 2 year garentee is good enough for me really.
and it would have an external wastegate and ecu controlled boost
do you know of any sites i can read up on them? whenever i type vnt into a search engine it comes up with useless crap. lol
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27-02-2006, 11:39 PM
#8
DEYTUKURJERBS
VNT's are not widely available commercially, mainly due to them not waning to take the risk of tons of warrenty cases caused by mis-use.
Ebay is the place to be, esp Ebay america, been a fair few VNT GT40s on there recently, never mind smaller ones.
IMO unless your an expert (dont seem like you are) and got money to burn experermenting (dont seem like you have) id stick with conventional turbos.
What spec is your current engine? Built for 400bhp dont mean much.
Ebay is the place to be, esp Ebay america, been a fair few VNT GT40s on there recently, never mind smaller ones.
IMO unless your an expert (dont seem like you are) and got money to burn experermenting (dont seem like you have) id stick with conventional turbos.
What spec is your current engine? Built for 400bhp dont mean much.
28-02-2006, 07:30 AM
#11
Personally i wouldnt ever want to run a VNT turbo on a petrol car that doesnt have an airflow meter of some sort.
The way the pumping losses of the engine change means the ignition and fueling requirements change too, on something like L8 you would have to make some assumptions about how the VNT side of things was operating and that to my mind is dangerous.
The way the pumping losses of the engine change means the ignition and fueling requirements change too, on something like L8 you would have to make some assumptions about how the VNT side of things was operating and that to my mind is dangerous.
28-02-2006, 07:35 AM
#12
PassionFord Post Whore!!
Thread Starter
i dont know the spec of my current engine. but i will try and find out
im no expert as you can tell and i definately dont have money to burn.
i will have to think about it.
unless one comes up really cheap i wont bother then.
theres loads of names for VNT, VVT, VGT, but basically mean the same thing,
Variable, Neutrane/Vane/Geometry, Turbo/Turbine,
basically they mean that you can run a larger exhaust housing and run less spool up times due to the vanes.... they will change the size of the rear housing
it starts off small to spool up quickly then the vanes move and the housing gets larger.
im no expert as you can tell and i definately dont have money to burn.
i will have to think about it.
unless one comes up really cheap i wont bother then.
theres loads of names for VNT, VVT, VGT, but basically mean the same thing,
Variable, Neutrane/Vane/Geometry, Turbo/Turbine,
basically they mean that you can run a larger exhaust housing and run less spool up times due to the vanes.... they will change the size of the rear housing
it starts off small to spool up quickly then the vanes move and the housing gets larger.
28-02-2006, 07:41 AM
#15
On your new management, how will the ECU know the vanes have moved?
Who is going to map it for you?
In the world of cossies you are unlikely to find anything cheap or easy to do that yields gains that others arent already doing as there are so many people out there developing these engines still.
Stop and ask yourself why no one else is using one on a cossie, is it cause none of the cossie tuners have heard of a VNT turbo? or is it cause they know how much cost is involved in developing one to work properly versus how little gain is involved?
Who is going to map it for you?
In the world of cossies you are unlikely to find anything cheap or easy to do that yields gains that others arent already doing as there are so many people out there developing these engines still.
Stop and ask yourself why no one else is using one on a cossie, is it cause none of the cossie tuners have heard of a VNT turbo? or is it cause they know how much cost is involved in developing one to work properly versus how little gain is involved?
28-02-2006, 07:45 AM
#16
PassionFord Post Whore!!
Thread Starter
thats why i asked on here
cos i havent heard of any1 using one.
but i know R5 people who do. i know its different but worth asking about.
depends what management i buy as to who maps it.
so i could be the person to try it and find out its the best thing you could do to the car,
or the exact opposite. lol
cos i havent heard of any1 using one.
but i know R5 people who do. i know its different but worth asking about.
depends what management i buy as to who maps it.
so i could be the person to try it and find out its the best thing you could do to the car,
or the exact opposite. lol
28-02-2006, 07:59 AM
#19
You seriously need to think about how the ECU is going to know whats going on with the vanes.
Daft as it sounds, the R5 essentially is an airflow based system, cossie is only normally map and TPS
I dont see how map and TPS can really work with a VNT turbo in a high state of tune.
Daft as it sounds, the R5 essentially is an airflow based system, cossie is only normally map and TPS
I dont see how map and TPS can really work with a VNT turbo in a high state of tune.
28-02-2006, 09:40 AM
#21
Part of the Furniture
Originally Posted by chip-3door
You seriously need to think about how the ECU is going to know whats going on with the vanes.
Daft as it sounds, the R5 essentially is an airflow based system, cossie is only normally map and TPS
I dont see how map and TPS can really work with a VNT turbo in a high state of tune.
Daft as it sounds, the R5 essentially is an airflow based system, cossie is only normally map and TPS
I dont see how map and TPS can really work with a VNT turbo in a high state of tune.
That is a good point.
The way I understand it, the variable vane position within the Exh housing will be governed by the Exh gas back pressure, agree? If so, then wouldnt that mean that the pressure within the intake manifold would govern the Exh gas back pressure dependant on engine rpm?
I would have thought that it would be correct to say that by mapping the engine using a map sensor (rather than an airflow meter) would be more accurate considering the above?
In my opinion the most accurate method would be using TPS/MAP/Exh back pressure mode. The Autronic ecu range do offer this option in there software.
Im interested in opinions as this is a discussion that I have yet to see/read on the net
28-02-2006, 09:46 AM
#22
The problem is that the VE of the engine is not fixed at a given RPM/Boost level anymore because it will also depend on the vanes, thats my objection.
Now obviously in theory the vanes should always do the same thing at any given rpm/boost level, but in reality i suspect that the different time to go up through the gears will result in a slightly different response at any given load site from the vanes, especially as they are not instantaneous to react.
However, If you measure exhaust back pressure then thats cool, you just need some sort of feedback in terms of what the vanes are doing so you can use that to alter the fuelling, then you dont need an airflow meter signal, that was just one suggestion on how to react to the vanes.
Now obviously in theory the vanes should always do the same thing at any given rpm/boost level, but in reality i suspect that the different time to go up through the gears will result in a slightly different response at any given load site from the vanes, especially as they are not instantaneous to react.
However, If you measure exhaust back pressure then thats cool, you just need some sort of feedback in terms of what the vanes are doing so you can use that to alter the fuelling, then you dont need an airflow meter signal, that was just one suggestion on how to react to the vanes.
28-02-2006, 10:02 AM
#23
Part of the Furniture
Originally Posted by chip-3door
The problem is that the VE of the engine is not fixed at a given RPM/Boost level anymore because it will also depend on the vanes, thats my objection.
Now obviously in theory the vanes should always do the same thing at any given rpm/boost level, but in reality i suspect that the different time to go up through the gears will result in a slightly different response at any given load site from the vanes, especially as they are not instantaneous to react.
However, If you measure exhaust back pressure then thats cool, you just need some sort of feedback in terms of what the vanes are doing so you can use that to alter the fuelling, then you dont need an airflow meter signal, that was just one suggestion on how to react to the vanes.
Now obviously in theory the vanes should always do the same thing at any given rpm/boost level, but in reality i suspect that the different time to go up through the gears will result in a slightly different response at any given load site from the vanes, especially as they are not instantaneous to react.
However, If you measure exhaust back pressure then thats cool, you just need some sort of feedback in terms of what the vanes are doing so you can use that to alter the fuelling, then you dont need an airflow meter signal, that was just one suggestion on how to react to the vanes.
Yes totally agree. The vanes would react much slower that what the electronics in the ecu/engine dynamics would. If there is a Exh gas back pressure input to the ecu, I would have thought regardless of vane position that the ecu would compare Intake manifold pressure VS Exh gas back pressure to give an indication of vane position (to a degree).
By knowing the approx vane position (hence Exh back pressure) VS engine rpm/manifold pressure I have no doubt that it is possible to tune. The amount of time taken though would be immense considering every possible scenario
Personally Id prefer to stick to my conventional style of turbo too
28-02-2006, 10:05 AM
#24
Yes i agree, you can do it on exhaust back pressure without a problem.
And im not even sure it needs to take very long as you could probably keep it safe just by doing it as an adjustment that worked on a % basis of whatever load site you are in, assuming you had an ECU that allows you to do so.
The problem of course though, like you say is that it would be quite involved to map it to REALLY take advantage of the variable vanes by keeping the fuelling and timing spot on to make sure the engine performed to its optimum, which is obviously very different to just keeping it safe like i mention.
I guess this is why they only tend to appear on diesels normally!
And im not even sure it needs to take very long as you could probably keep it safe just by doing it as an adjustment that worked on a % basis of whatever load site you are in, assuming you had an ECU that allows you to do so.
The problem of course though, like you say is that it would be quite involved to map it to REALLY take advantage of the variable vanes by keeping the fuelling and timing spot on to make sure the engine performed to its optimum, which is obviously very different to just keeping it safe like i mention.
I guess this is why they only tend to appear on diesels normally!
28-02-2006, 10:21 AM
#26
Part of the Furniture
Yes, as you mentioned above the problem would be whilst in a steady state of load/rpm whilst the vanes havent yet stabilised as this would cause variations in fuel/ignition delivery. Admittedly depending on load/rpm the difference could be negligible to some what concerning.
As mentioned, if the ecu is also using Intake manifold pressure vs Exh gas back pressure to add/subtract Ign/fuel to the base fuel/Ign tables then it would be well sorted
As mentioned, if the ecu is also using Intake manifold pressure vs Exh gas back pressure to add/subtract Ign/fuel to the base fuel/Ign tables then it would be well sorted
28-02-2006, 10:22 AM
#27
DEYTUKURJERBS
Oh, BTW, even though people think the new Porsche is the first, here was the first proper production PETROL car that used a VNT (IIRC) 
http://cgi.ebay.com/ebaymotors/Dodge...spagenameZWDVW
http://cgi.ebay.com/ebaymotors/Dodge...spagenameZWDVW
28-02-2006, 11:29 AM
#31
10K+ Poster!!
Originally Posted by chip-3door
I guess this is why they only tend to appear on diesels normally!
A fair bit less than a petrol running lambda 1
Alex
28-02-2006, 02:23 PM
#37
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VNT is used on jet engines across many different applications, so I can't see the temps of a turbo causing too many problems if its built correctly 
Whilst I don't know a lot about the applcation of VNT on turbochargers etc, I can't see the general principles of the systems operations being massivly different, and on aircraft engines the VIGV and VNT (on the compressor and turbine respectivly) are used mainly at lower engine speeds, to try and smooth out the power delivery and stop surging due to bad airflow through the engine as it accelerates.
As far as I can see, the VNT on a car turbo would be used for the lower RPM range, to give extra responsiveness on a larger turbo, so top end performance mapping shouldn't be a problem as the VNT on a turbo should be in its fully open position as soon as the turbo is on full boost, and the lower end operation is controlled by the ratio of manifold pressure to the exhaust pressure, so to control the fuel map etc a decent closed loop lambda system should control it quite happily.
Whilst I don't know a lot about the applcation of VNT on turbochargers etc, I can't see the general principles of the systems operations being massivly different, and on aircraft engines the VIGV and VNT (on the compressor and turbine respectivly) are used mainly at lower engine speeds, to try and smooth out the power delivery and stop surging due to bad airflow through the engine as it accelerates.
As far as I can see, the VNT on a car turbo would be used for the lower RPM range, to give extra responsiveness on a larger turbo, so top end performance mapping shouldn't be a problem as the VNT on a turbo should be in its fully open position as soon as the turbo is on full boost, and the lower end operation is controlled by the ratio of manifold pressure to the exhaust pressure, so to control the fuel map etc a decent closed loop lambda system should control it quite happily.
28-02-2006, 03:21 PM
#38
PassionFord Post Whore!!
Thread Starter
as far as im aware the reason for them sticking is that they were taken straight off a diesel engine and not designed directly for a petrol engine, therefore not prepared for the petrol heat,
also the soot produce in a diesel engine wont help.
jay i would give more details if i had them but i mafraid i dont, and no i havent sold the 21 or any other car. lol
as RWD says the vnt only really does its thing lower down the rev range, to help with spool up.
once on boost surely it wouldnt change the backpressure??????
if it can be asfely controlled during lower boost levels (while spooling up) with lamba, backpressure sensor, exhaust temp sensors....
then it has to be worth a try, how else will any1 find out?
also the soot produce in a diesel engine wont help.
jay i would give more details if i had them but i mafraid i dont, and no i havent sold the 21 or any other car. lol
as RWD says the vnt only really does its thing lower down the rev range, to help with spool up.
once on boost surely it wouldnt change the backpressure??????
if it can be asfely controlled during lower boost levels (while spooling up) with lamba, backpressure sensor, exhaust temp sensors....
then it has to be worth a try, how else will any1 find out?
28-02-2006, 03:26 PM
#39
If they are always fully open before you go out of closed loop, then yes i should think its a pretty straightforward thing to implement, and if the whole of the section of the map you are going to be open loop on is mapped for them open then it would only run rich if they closed anyway i should think, so sounds a nice safe way round, my worry is having a point on boost thats mapped for them shut and then they open.
28-02-2006, 03:32 PM
#40
PassionFord Post Whore!!
Thread Starter
well i guess i need to speak to some mappers and turbo suppliers a bit more before going ahead.
if an external wastegate was fitted then wouldnt that limit the boost it would produce so not much fear of it spiking
also a pop off valve could be fitted at 1 or 2 psi above the desired boost level for safety,
plus if it was mapped for vanes closed but they opened then surely the egts would go down and the ecu could react??? same vise versa to
if an external wastegate was fitted then wouldnt that limit the boost it would produce so not much fear of it spiking
also a pop off valve could be fitted at 1 or 2 psi above the desired boost level for safety,
plus if it was mapped for vanes closed but they opened then surely the egts would go down and the ecu could react??? same vise versa to