Fun with turbos :D
25-09-2005, 03:57 PM
#41
DEYTUKURJERBS
How are you sorting the charge temps? w.i. too i guess? as staged turbos equals big charge temps dont they?
where you spraying it? normal sorta place or direct into mouth of the compressor?
where you spraying it? normal sorta place or direct into mouth of the compressor?
25-09-2005, 04:56 PM
#44
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wouldnt know - this is one setup being run well within its limits - not the mega boost deisel stuff - dont know - would guess any mega boost silly setup would be v hot - mine is fingers x'd pretty well matched 
so not an issue.
so not an issue.
25-09-2005, 06:19 PM
#45
Norris Motorsport
It'smeagain or Steve for those who don't know your name, LOL,
The high temperatures you are talking about are due to compound charging when using two similar turbos, to achieve high boost levels. (i.e. both turbos contribute significantly to high boost level)
However the best way to compound turbocharge is when using one small and one large turbo as in Martins setup. In this setup the small turbo is first to spool up giving a relatively good response associated with small turbos. In the very fact that the small turbo has now increased engine power and hence exhaust energy, once the boost level has risen to the actuator level of the first small turbo, the wastgate opens allowing residual exhaust gas to then feed the 2nd turbo. (This is because you use an internally gated primary turbo, with its exit feeding the larger turbine.
The large turbo now begins to make siginificant boost, and as boost levels rise beyond the rating of the primary turbo the primary turbo wastegate continues to open further allowing more and more exhaust gas to feed the 2nd larger turbo. (Remember that the primary smaller turbo's wastegate will continue to open further as the boost rises as the actuator continues to extend, opening the wastegate further.
At this point you can now see that the wastegate on the primary turbo is now far more open than would allow it to produce any usefull turbo work, and hence in effect mainly assists the larger turbo which breathes through the smaller turbo (i.e. outlet of large compressor feeds intake of smaller which then goes to engine).
Hence the overall boost you see can be as dependant on the large turbo as much as you like depending on how you rate the primary turbo and at what pressure the primary turbo wastegate is set.
In this manner the large turbo produces very low ACT's anyway and as the small turbo contributes very little to any additional power (Except for low boost applications below the primary turbo wastegate rating) its actual work effect is minimal and hence does not increase charge temps.
As mentioned earlier if you chose to make both turbos work hard then you will get higher ACT's and the traditional compound turbo route is indeed to use two large turbos and compress one turbos charge by the next raising both boost to potential 60psi + bbut also extremely high ACT's too!!
Horses for courses so to speak!!! Hope that helps.
The high temperatures you are talking about are due to compound charging when using two similar turbos, to achieve high boost levels. (i.e. both turbos contribute significantly to high boost level)
However the best way to compound turbocharge is when using one small and one large turbo as in Martins setup. In this setup the small turbo is first to spool up giving a relatively good response associated with small turbos. In the very fact that the small turbo has now increased engine power and hence exhaust energy, once the boost level has risen to the actuator level of the first small turbo, the wastgate opens allowing residual exhaust gas to then feed the 2nd turbo. (This is because you use an internally gated primary turbo, with its exit feeding the larger turbine.
The large turbo now begins to make siginificant boost, and as boost levels rise beyond the rating of the primary turbo the primary turbo wastegate continues to open further allowing more and more exhaust gas to feed the 2nd larger turbo. (Remember that the primary smaller turbo's wastegate will continue to open further as the boost rises as the actuator continues to extend, opening the wastegate further.
At this point you can now see that the wastegate on the primary turbo is now far more open than would allow it to produce any usefull turbo work, and hence in effect mainly assists the larger turbo which breathes through the smaller turbo (i.e. outlet of large compressor feeds intake of smaller which then goes to engine).
Hence the overall boost you see can be as dependant on the large turbo as much as you like depending on how you rate the primary turbo and at what pressure the primary turbo wastegate is set.
In this manner the large turbo produces very low ACT's anyway and as the small turbo contributes very little to any additional power (Except for low boost applications below the primary turbo wastegate rating) its actual work effect is minimal and hence does not increase charge temps.
As mentioned earlier if you chose to make both turbos work hard then you will get higher ACT's and the traditional compound turbo route is indeed to use two large turbos and compress one turbos charge by the next raising both boost to potential 60psi + bbut also extremely high ACT's too!!
Horses for courses so to speak!!! Hope that helps.
25-09-2005, 06:23 PM
#46
Steve,
Martin's ENTIRE front end has been removed (you can see how much work this has required in photos elsewhere) and is filled with an intercooler that is twice the width of your Skyline one and just as deep and tall
, hence why he has no charge temp problems. I have the graph here of it back to back against my Sapphire: It made more horsepower than mine EVERYWHERE (apart from at 7000 to 7500 rpm, as they daren't rev it any higher than 6500 
, so my car made 395bhp at the wheels more than his did at this rpm 
).
I still can't get my head round the fact that the T3/4 SHOULD be restricting it, but it doesn't
, even Martin can't clarify, as he had Alan explain it to him and undertsood it at the time, but can't adequately put it into words again (or refuses to ).
Martin's ENTIRE front end has been removed (you can see how much work this has required in photos elsewhere) and is filled with an intercooler that is twice the width of your Skyline one and just as deep and tall
, hence why he has no charge temp problems. I have the graph here of it back to back against my Sapphire: It made more horsepower than mine EVERYWHERE (apart from at 7000 to 7500 rpm, as they daren't rev it any higher than 6500 , so my car made 395bhp at the wheels more than his did at this rpm ).I still can't get my head round the fact that the T3/4 SHOULD be restricting it, but it doesn't
, even Martin can't clarify, as he had Alan explain it to him and undertsood it at the time, but can't adequately put it into words again (or refuses to ).
25-09-2005, 06:37 PM
#48
15K+ Super Poster!!
All the exhasut gas on small turbo, well most, is going to go straight through the wastegate when big turbo is on boost - i imagine the wastegate needs to be able to flow well. The small turbo compressor isn't actually then doing any significantt work on the inlet air, and hence not adding any temperature to it. The 'flow' limitations of turbos are usually thought of on the exhasut side - the compressor just becomes increasingly inefficent/oversped - but here it's not acually trying to do anything.
25-09-2005, 06:45 PM
#49
Karl,
Fantastic explanation
, but that does not clarify the restriction issue (can you shed some light on that? ). I just can't get my head round why the exhaust housing on the smaller turbo doesn't restrict the amount of exhaust gases available to spin up the huge one. Surely when you are combining the amount of air that both turbos are providing the engine with, the smaller exhaust housing "should" bottle neck and cause extreme cylinder pressures / high EGTs?
I suppose this is why it is so critical that the turbos are perfectly matched.
Fantastic explanation
, but that does not clarify the restriction issue (can you shed some light on that? ). I just can't get my head round why the exhaust housing on the smaller turbo doesn't restrict the amount of exhaust gases available to spin up the huge one. Surely when you are combining the amount of air that both turbos are providing the engine with, the smaller exhaust housing "should" bottle neck and cause extreme cylinder pressures / high EGTs?I suppose this is why it is so critical that the turbos are perfectly matched
.
25-09-2005, 07:14 PM
#52
Norris Motorsport
Hi Mike,
High EGT's are caused by back pressure. The primary turbo is there solely to increase the engine power so that there is sufficient exhaust energy to allow the large turbo to spool at all!!!
The back pressure does initially rise in the manifold pre small turbo during the initial boost phase where the engine boost is largely dependant upon the small turbo. During this time the major exhaust restriction is the small turbine housing.
However this is purely a means to an end in order to increase exhaust energy, necessary to produce boost early from the larger turbo. Once the boost has passed the initial primary turbo wastegate rating the primary turbo wastgate will continue to open.(Boost provided by large turbo) As engine mass air flow rises as a result of the large turbo, due to the fact the large turbo blows through the primary compressor (i.e. the primary compressor is now processing the work done by the large turbo) the work done by the small turbo reduces which in turn reduces the work done by the small turbine.(i.e. energy extracted form exhaust gas) This in conjunction with the fact the small turbine wastegate is well open by this time means that very little back pressure is now produced by the small turbo, meaning the large turbo is free to do its work.
What not to get confused into thinking is that the small turbine housing size and wastgate together are restrictive. They are only restrictive when used to create usefull boost. After the large turbo is producing good boost the small turbine housing and wastagate offer a restriction similar to having no exhaust wheel in there at all. As such this allows the small turbine housing/wastgate to process the large quantities of exhaust gas that feed the large turbo.
High EGT's are caused by back pressure. The primary turbo is there solely to increase the engine power so that there is sufficient exhaust energy to allow the large turbo to spool at all!!!
The back pressure does initially rise in the manifold pre small turbo during the initial boost phase where the engine boost is largely dependant upon the small turbo. During this time the major exhaust restriction is the small turbine housing.
However this is purely a means to an end in order to increase exhaust energy, necessary to produce boost early from the larger turbo. Once the boost has passed the initial primary turbo wastegate rating the primary turbo wastgate will continue to open.(Boost provided by large turbo) As engine mass air flow rises as a result of the large turbo, due to the fact the large turbo blows through the primary compressor (i.e. the primary compressor is now processing the work done by the large turbo) the work done by the small turbo reduces which in turn reduces the work done by the small turbine.(i.e. energy extracted form exhaust gas) This in conjunction with the fact the small turbine wastegate is well open by this time means that very little back pressure is now produced by the small turbo, meaning the large turbo is free to do its work.
What not to get confused into thinking is that the small turbine housing size and wastgate together are restrictive. They are only restrictive when used to create usefull boost. After the large turbo is producing good boost the small turbine housing and wastagate offer a restriction similar to having no exhaust wheel in there at all. As such this allows the small turbine housing/wastgate to process the large quantities of exhaust gas that feed the large turbo.
25-09-2005, 07:17 PM
#54
15K+ Super Poster!!
iits not like ive built a twin compound thingy - but the flow restriction of a turbo is on the exhasut side. U need to flow a certain amount of gas to produce compressor air flow. But here, ur not actually producing any boost - so the gas doent need to go through the compressor - it can go straight out of the wastegate
25-09-2005, 07:25 PM
#58
Rick,
I COMPLETELY understand that, but on a T4 fitted with the smaller waste-gate penny, when it is FULLY open, the turbo can still produce 2 bar of boost at 7000rpm, due to the size of the compressor compared to the wastegate hole. Obviously the small turbo that is fitted to Martin's car has an exhaust housing that can only have an even smaller penny in it (due to the physical dimensions). Obviously a T88 can give more airflow into the engine than a T4 (which it is definitely doing, as it is making more power than my T4 car did), so what goes in, must come out. So why is it not as restrictive as it "should" be?
Maybe THIS is why they didn't go above 6500 rpm, as the turbo matching isn't "quite" there yet.......? However, trying to get info out of Martin is like trying to get money out of any of his fellow countrymen .
I COMPLETELY understand that, but on a T4 fitted with the smaller waste-gate penny, when it is FULLY open, the turbo can still produce 2 bar of boost at 7000rpm, due to the size of the compressor compared to the wastegate hole
. Obviously the small turbo that is fitted to Martin's car has an exhaust housing that can only have an even smaller penny in it (due to the physical dimensions). Obviously a T88 can give more airflow into the engine than a T4 (which it is definitely doing, as it is making more power than my T4 car did), so what goes in, must come out. So why is it not as restrictive as it "should" be?Maybe THIS is why they didn't go above 6500 rpm, as the turbo matching isn't "quite" there yet.......? However, trying to get info out of Martin is like trying to get money out of any of his fellow countrymen
.
25-09-2005, 07:35 PM
#60
Originally Posted by Karl
What not to get confused into thinking is that the small turbine housing size and wastgate together are restrictive. They are only restrictive when used to create usefull boost. After the large turbo is producing good boost the small turbine housing and wastagate offer a restriction similar to having no exhaust wheel in there at all. As such this allows the small turbine housing/wastgate to process the large quantities of exhaust gas that feed the large turbo.
.
25-09-2005, 07:42 PM
#61
15K+ Super Poster!!
Rick what do you mean by that?
1. Little turbo produces boost.
2. Engine power then increses.
3. Exhaust gas energy therefore increases.
4. Big turbo starts to spin.
5. Small turbo wastegate is fully open, and it's no longer producing boost - just flowing air.
6. It's not doing work, it's just acting as a pipe which air flows through. This is NOT the same a restirction when it IS doing work. There is no significan pressure difference across the exhasut wheel.
Karl - ur explanation is v easy to follow - Mike ur just slow
25-09-2005, 07:46 PM
#62
15K+ Super Poster!!
Mike - what does a turbo do? It extracts work out of the exhaust gas, to put work into the intake gas. THAT is why it eventually restricts NOT because its a small hole, and the air cant fit through. If u suddenly stop asking the turbo to do work - it can quite happily flow air.
Think of this. If u put the exhause housing of a t34 in the echasut system of an 8litre NA 800hp engine - would it suddenly only produce 400hp?
Think of this. If u put the exhause housing of a t34 in the echasut system of an 8litre NA 800hp engine - would it suddenly only produce 400hp?
25-09-2005, 07:53 PM
#64
15K+ Super Poster!!
Steve - u have a logical mind 
Not gonna happen is it. U'll defo lose some power - not 400brake. Turbo's cannot be thought of as just different sized tubes u blow down.
Not gonna happen is it. U'll defo lose some power - not 400brake. Turbo's cannot be thought of as just different sized tubes u blow down.
25-09-2005, 08:00 PM
#66
DEYTUKURJERBS
rick- thats cause T34s are restricted by the compressor rather than the turbine.
im suprised a T4 or whatever dont restrict more than it seems to in dumpeds car tho.
but like i said, am i right in saying if the smallest turbo had a big enough wastegate(s) then you cant lose really...
im suprised a T4 or whatever dont restrict more than it seems to in dumpeds car tho.
but like i said, am i right in saying if the smallest turbo had a big enough wastegate(s) then you cant lose really...
25-09-2005, 08:06 PM
#68
15K+ Super Poster!!
thats cause T34s are restricted by the compressor rather than the turbine.
am i right in saying if the smallest turbo had a big enough wastegate(s) then you cant lose really...
25-09-2005, 08:08 PM
#69
Norris Motorsport
Guys, you've completely missed what I wrote!!!
Mike, the large turbo compressor breathes THROUGH the small turbo, meaning the compressor stage of the small turbo is actually driven by the large turbo at high boost levels. This in addition with the small turbine wastgate being held open wider by the high boost from the large turbo means the small turbine is just processing exhaust gas, not extracting energy from it!!
Rick seems to have grasped it, its all about harnessing heat energy from the exhaust gas. If you are'nt extracting energy from the gas then you are not creating work and hence no additional back pressure! The physical size of the T34 0.63 turbine and wastegate together can easily handle the 1000bhp + exhaust energy potential of a large turbo!! (i.e. they are large enough to process the exhaust gas)
Mike picture this....................
On a T4 engine say you wish to run 2 bar at 7K. This will require X amount of energy to drive the compressor stage. This energy is extracted from the otherwise wasted exhaust gas energy. However the price for doing this is increased back pressure as the turbine wheel offers significant restriction as it is having to convert heat energy into rotational energy which is by no means an efficient process. (laymans terms lol). This rise in back pressure is what limits the exhaust flow potential.
Remove the energy harnessing factor by driving the primary compressor as in Martins setup, and the turbine no longer has to do work, and hence only has to process the exhaust gas which causes minimal back pressure!
Mike, the large turbo compressor breathes THROUGH the small turbo, meaning the compressor stage of the small turbo is actually driven by the large turbo at high boost levels. This in addition with the small turbine wastgate being held open wider by the high boost from the large turbo means the small turbine is just processing exhaust gas, not extracting energy from it!!
Rick seems to have grasped it, its all about harnessing heat energy from the exhaust gas. If you are'nt extracting energy from the gas then you are not creating work and hence no additional back pressure! The physical size of the T34 0.63 turbine and wastegate together can easily handle the 1000bhp + exhaust energy potential of a large turbo!! (i.e. they are large enough to process the exhaust gas)
Mike picture this....................
On a T4 engine say you wish to run 2 bar at 7K. This will require X amount of energy to drive the compressor stage. This energy is extracted from the otherwise wasted exhaust gas energy. However the price for doing this is increased back pressure as the turbine wheel offers significant restriction as it is having to convert heat energy into rotational energy which is by no means an efficient process. (laymans terms lol). This rise in back pressure is what limits the exhaust flow potential.
Remove the energy harnessing factor by driving the primary compressor as in Martins setup, and the turbine no longer has to do work, and hence only has to process the exhaust gas which causes minimal back pressure!
25-09-2005, 08:10 PM
#70
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I'm loving this thread. I've worked with compound turbo charging on fast ferrys, and it can be a nightmare...... Especially on 25 year old jobs, that the company has just bought from Poland
But it trebles the output of ship engines anyways, but thats with a small boost increase They normally run 0.8 Bar for 12000 horsepower, but these ran, on exactly the same engines, 3.2 Bar for 32000 horsepower.
Mind you, they did break down on a weekly basis.
But it trebles the output of ship engines anyways, but thats with a small boost increase
They normally run 0.8 Bar for 12000 horsepower, but these ran, on exactly the same engines, 3.2 Bar for 32000 horsepower. Mind you, they did break down on a weekly basis.
25-09-2005, 08:22 PM
#75
15K+ Super Poster!!
It is simple Mike It's just people are used to thinking in terms of just mass air flow, and not what the airflow is actually doing - or having done to it
I totally agree that the theory is simple - but getting it to work nicely in practice commands much respect
It's just people are used to thinking in terms of just mass air flow, and not what the airflow is actually doing - or having done to it I totally agree that the theory is simple - but getting it to work nicely in practice commands much respect
25-09-2005, 08:30 PM
#79
Norris Motorsport
Rick what do you want to know about current engine?
ETA is early months next year mike. Initially will be single GT30 and single GT42R but will see how temps go and then decide on relative rating of each turbo. (i.e. these are initial turbos.)
ETA is early months next year mike. Initially will be single GT30 and single GT42R but will see how temps go and then decide on relative rating of each turbo. (i.e. these are initial turbos.)