You are correct of course, those hp numbers are indeed based on roughly 11 hp per lb/min, petrol numbers.
OK, deep breath, Mad Scientist Hat on….
As discussed at length in the thread about YD25 power,
viewtopic.php?f=9&t=7539&start=0&hilit=power+yd25
it seems fairly difficult to find a single, non VNT turbo that will cover this engine’s demand lines in a completely satisfactory way.
So I basically settled on:
-The smallest turbo that will max out the stock injectors and fuelling, around 290 hp, and accept whatever minimized loss of lower end response that comes with this choice.
OK, so now on to the choices for a 500cfm/37lb/min turbo, required for such power levels on a diesel.
As I was unable to find sufficient info on commercially available BorgWarners of this range, this narrowed the choices to Holset (HX25, HX30), Garrett (GT25-28) and Mitsubishi (TD04-TD05).
Holset first. Generally, Holsets seem to give a nice wide comp map (most, if not all of these, are unofficial maps, btw), especially when compared to other makes, at higher PR’s (3+), in the midrange turbine sizes. Obviously the Holsets would seem to be a good place to start. The practical problem: the HX25 just doesn’t flow quite enough, and the HX30 is just slightly too big. There is a HX27 mentioned here and there but I was unable to obtain more info.
Which, after some more sifting through compressor maps, lead to the Garrett GT2860R and the Mitsubishi TD05H-16G.
Notice how the GT reaches higher PR’s , but with a quite narrow upper end map, when compared to the Holsets as mentioned.
Notice also that the GT2860R map goes to much higher PR’s than the official GT2860RS map, with a turbine wheel of 53.8mm (RS) instead of 53mm (R) being pretty much the only difference. At the time the RS was released, it was mapped to similar shaft rpms of the R above, but some reason (reliability?) it was trimmed to about 145000rpm on later maps:
Earlier hi PR map:
Current official map:
Up to 145000rpm/2.7 PR, the two maps seem nearly identical. Now look back at the nearly identical GT2860R which allows for 3+PR’s and 165000rpms. I picked the brains of a few turbo experts on this and they advised that on our diesel application one might as well experiment with 28-30psi (but then again, such an answer might be expected…) on the RS. As advised, rpm limits are mostly compressor(-diameter/mass) driven, no difference there between the R and the RS, and the .8mm larger turbine should help reducing egt and backpressure. So I took the plunge.
So now on to demandlines. I previously dabbled with calculated VAC’s, using the formulas posted here:
http://www.stealth316.com/2-air-fuel-flow.htm and
http://www.stealth316.com/2-3s-compflowmaps.htm
This came out reasonably similar to Kiwibacon’s demandlines in the other thread mentioned. Because of this, I shamelessly and lazily copied his lines in maps below!
If one accepts the earlier high-rpm/PR RS map, then the demand lines look something like this, along with a crude boost/rpm prediction, based on a self imposed 28psi boost limit:
Which doesn’t look too terrible for a single turbo upgrade, I think…The turbo will wake up just before 2000rpm. Those who run an rpm adjustable fuel chip (DTE, DMS and Racechip Pro) have noticed that you can easily take the YD25 to 5000rpm, btw, so one regains a few rpm in the powerband back up on the top, so to speak.
I also plotted just the 2000rpm and 4750rpm demand lines in a quick side by side comparison of the TD05H-16G and the RS, which shows the Mitsu Turbo being a decent choice as well, IMO, slightly better at the low end.
![Image]()
Finally (phew!), empirical evidence shows quite a good track record for both the RS and the TD05 as a popular upgrade on the Navara, the 2.5/3.2 Triton, 2.5 Hilux and the 3.0 Isuzu in Thailand and Malaysia. I’ve been in contact with a handful of owners of these tuned trucks over the past two years, most, if not all, running 28-30psi on both the RS and the TD, making up to 280hp at the rear wheels with supporting mods. Recall also our own ex-forummember Sirnixalot, who ran a RS for a limited time, and he was quite impressed, even with low end response, after adding some extra low end fuelling. In the end, it was a near toss up between the TD and RS for me, with the slightly better expected transient response because of the dual ballbearings, tipping it in favour of the RS....
Again, it would have been nice to obtain a 500+cfm/37lb/min turbo with a compressor map that covers the demand lines from 1500rpm to 5000rpm, but I was unable to spot such an animal so far.
A single, non VNT, turbo upgrade will remain a compromise, that much seems clear…
Edited to add: Correction: Difference between GT2860R and RS is on the compressor trim (and therefore the inducer size) and compressor housing, with the RS being the bigger of the two. The turbine wheel is identical on the R and RS, 53.8mm. The 60mm compressor and 53mm turbine combo is found on the GT2560R.
11/22: Edited to add demandline colors, for clarity:
--:2000rpm
--:2500rpm
--:3000rpm
--:3500rpm
--:4000rpm
--:4500rpm
--:4750rpm
Bw!2k~$(KGrHqV,!hcEyrsF6JN3BM0ppsiQvw~~_12.JPG)
