Om605 compound turbo build, my Corolla Ke70 tracktoy

Alcaid

TA 0301

58

06-05-2015, 02:31 AM #304

(06-04-2015, 05:31 PM)Turbo I am a engineer to profession so please get it down in technical terms and we can discuss sizing, perhaps we both will learn something out it so I think it would be of good benefits for both of us and a great deal of fun actually

I am engineer as well Wink

The corrected mass flow from the HX40W is outside of the choke line of the HX30W 44mm compressor map at the higher RPMs, this is why EMP rises quickly.

The difference in turbine choke flow between the two turbos gives an ideal PR for the LP turbo to share the load and give both turbos similar operating conditions (IMP/EMP ratios). The HX40W-18cm turbine is quite a bit bigger than the HX30W-6cm turbine so the LP needs a fairly high PR. Would have worked better if the OM605 needed more total PR, leaving more PR or "work" for the HX30W to do so that it would end higher up in the map where there is more choke margin. but as I mentioned earlier, my model for higher RPM volumetric efficiency was off.

With closer turbine sizes ideal PR on LP stage would be smaller meaning one could run fairly low PR on both stages and share the load more equal. The thing then is that Holset compressors are really not the optimal one for low PR. Could be used off course but there is high trim compressors out there with better efficiency at these low PR levels and better transient response due to less mass to spool up.

I have a compound setup ready for my 1.9TDI 4Motion Golf as well (but not the time to build it yet, want to get rid of the GTB2056VL vnt turbo) sized this way with both turbos only operating at a PR of 1.75. The optimal turbos for this application to get the highest combined compressor efficiency over the widest possible RPM range ended up being a Garrett and a MHI turbo. Holset HE200WG would be close as a HP but not as ideal as the Garrett.

To avoid EMP issues at high RPM due to choking HX30 compressor there really is these options for Stamsaas:
- set a lower RPM limit (boring)
- upgrade the HX30W (I will do this free of charge together with a rebuild just for the sake of doing it. No fabrication needed if there is room for the bigger OD turbine housing scroll)
- changing out the HX30W for an out-of-the-box turbo that will do the job (pain in the ass as that requires fabrication)

This post was last modified: 06-05-2015, 02:36 AM by Alcaid.