steel
01-03-2011, 11:44 PM
Hi people,
Given that forged internals are out and about it got me thinking about higher boost levels and turbos.
I have scratched around on the web and found a few compressor maps.
On these I have used the bog standard formula to calculate air flow requirements for an engine of a given displacement and given volumetric efficiency - 1468cc x a default of 85% VE in our case with other bits of jiggery pokery thrown in.
The sheared trapezoidal shapes I have overlaid represent the air flow requirements of the 4G15T from 2000rpm to a theoretical 8000rpm for whatever boost level you care to examine. On all but one of these graphs I have overlaid lines representing 4000rpm and 6000rpm as well.
These maps plot turbo efficiency as a function of pressure and flow.
The larger your displacement and/or your max RPM, the more sheared to the right this shape should appear. How high you can go on the graph is a function of your engine internals and cooling system.
From what I have understood from reading up about compressor maps, the one that seems best suited to the Colt's engine is the TD04-13T, which I believe is the variant of the TD04 that daed and jemjem are running.
If I understand the graph correctly, if the internals could take it, you could boost up to 1.8 bars (2.8 pressure ratio) from 4krpm to 6krpm without overspeeding the turbo, after which you would need to follow the curve of max usable turbo speed down to about 1.25 bars by the time you hit 8000rpm. Looks like it would give big torque around 5krpm.
Looking at the TD04-19H, it looks more suited for top end power as with rpm increasing you are working up towards the sweet spot of efficiency, rather than overrunning it. I think that this would give you less peak torque but hold what torque you do have further and longer up the rev range, and perhaps result in a cooler charge? This one looks like it can boost up to 1.8 bars to its heart's content.
For those who know more about these kinds of things, is it a waste of turbo capacity to have your redline near the peak efficiency island - does that indicate that the turbo is oversized for your engine?
The GT28 variants seem even more so this way, with the 4G15T below the surge line before 4krpm at all boost levels, and the GT3031R totally wack.
I have been given advice that running 25 to 30psi of boost is inefficient as it will generate too much heat - if I need to run that much boost, I ought to be running a bigger turbo at a lower boost level.
From doing this though, I have understood that the air flow requirements of an engine at any given boost level are a function of displacement and VE, and I would have thought you can only improve upon the VE so much before you hit a wall. Can MIVEC work wonders in this regard?
Do these Garretts look oversized for the RColt?
Given that forged internals are out and about it got me thinking about higher boost levels and turbos.
I have scratched around on the web and found a few compressor maps.
On these I have used the bog standard formula to calculate air flow requirements for an engine of a given displacement and given volumetric efficiency - 1468cc x a default of 85% VE in our case with other bits of jiggery pokery thrown in.
The sheared trapezoidal shapes I have overlaid represent the air flow requirements of the 4G15T from 2000rpm to a theoretical 8000rpm for whatever boost level you care to examine. On all but one of these graphs I have overlaid lines representing 4000rpm and 6000rpm as well.
These maps plot turbo efficiency as a function of pressure and flow.
The larger your displacement and/or your max RPM, the more sheared to the right this shape should appear. How high you can go on the graph is a function of your engine internals and cooling system.
From what I have understood from reading up about compressor maps, the one that seems best suited to the Colt's engine is the TD04-13T, which I believe is the variant of the TD04 that daed and jemjem are running.
If I understand the graph correctly, if the internals could take it, you could boost up to 1.8 bars (2.8 pressure ratio) from 4krpm to 6krpm without overspeeding the turbo, after which you would need to follow the curve of max usable turbo speed down to about 1.25 bars by the time you hit 8000rpm. Looks like it would give big torque around 5krpm.
Looking at the TD04-19H, it looks more suited for top end power as with rpm increasing you are working up towards the sweet spot of efficiency, rather than overrunning it. I think that this would give you less peak torque but hold what torque you do have further and longer up the rev range, and perhaps result in a cooler charge? This one looks like it can boost up to 1.8 bars to its heart's content.
For those who know more about these kinds of things, is it a waste of turbo capacity to have your redline near the peak efficiency island - does that indicate that the turbo is oversized for your engine?
The GT28 variants seem even more so this way, with the 4G15T below the surge line before 4krpm at all boost levels, and the GT3031R totally wack.
I have been given advice that running 25 to 30psi of boost is inefficient as it will generate too much heat - if I need to run that much boost, I ought to be running a bigger turbo at a lower boost level.
From doing this though, I have understood that the air flow requirements of an engine at any given boost level are a function of displacement and VE, and I would have thought you can only improve upon the VE so much before you hit a wall. Can MIVEC work wonders in this regard?
Do these Garretts look oversized for the RColt?