Need a refresher on turbos

[Devildog]

1, Housing sizes such as HY-HX-35, HX-40, 12cm, 14cm, 16cm, etc... is that the intake side or the exhaust side?



2, When increasing size on one side do you increase the other side proportionally or just increase the one side?



3, At what point does boost become inefficient with the HX-35 and HX-40 with say DD's Super Mental injectors?



4, With a twin turbo set up, would the smaller turbo overshoot it's efficiency range enough to cause problems with the larger turbo?



Thanks.

 

[Big_Daddy_T]

I can answer one of those. The hx 35 loses efficiency above 35 psi. I think the 40 is around 42(not sure).

The little turbo on a twin setup is wastegated. You set it to build like 20#s then let the big one do all the rest. That way you dont sacrifice the bottom end and your top end creates a more than ample oxygen supply.

 

[illflem]

Joe D''s article starting on page 15 of the recent TDR mag will answer may of your questions.

 

[Diesel Freak]

Originally posted by Devildog

1, Housing sizes such as HY-HX-35, HX-40, 12cm, 14cm, 16cm, etc... is that the intake side or the exhaust side?



Exhaust housing size is designated by the 14cm, 16cm, etc...



2, When increasing size on one side do you increase the other side proportionally or just increase the one side?



it is easy to swap exhaust housings, but the HX and HY housings are not compatable. The Center Rotating Housing Assembly is different. you can increase the size of the exhaust housing to try and lower EGT, but this does not affect peak combustion temps. To increase the air side of the turbo, you must install a larger compressor wheel, and machine the compressor housing accordingly. At most you can gain 10 to 15% more air flow by doing this



3, At what point does boost become inefficient with the HX-35 and HX-40 with say DD's Super Mental injectors?



The HX40 can flow . 3KG/sec of ait at a pressure ratio of 4. 2:1 which correlates close to 39 PSI at the manifold... . not the turbo discharge.



The HX35 can flow . 3KG/sec of air at a pressure ratio of 3. 9:1 which correlates close to 36 psi at the manifold... not the turbo discharge.



Here is the kicker. The HX40 can still push . 5KG/sec of air at a pressure ratio of 3:1 where the HX35 gets way inefficient at anything over . 37KG/sec at a pressure ratio of 3:1



Injectors have nothing to do with turbo efficiency, but they will require more air to keep things cool, and even the HX40 will have a hard time keeping EGT down when using SM's to their full potential.



4, With a twin turbo set up, would the smaller turbo overshoot it's efficiency range enough to cause problems with the larger turbo?



I think I will explain what the Pressure ratio of a turbo means.



the Absolute Pressure ratio of a turbo is the ratio of inlet pressure to outlet pressure in atmospheres.



a PR of 4:1 means that at STP the turbo will produce 58. 8 PSIA of boost at the specified flow rate... . or 44. 1 PSIG



If you have a small turbo running at a pressure ratio of 3:1, and feed it compressed air from the larger turbo at a pressure of 12 PSIG and a flow rate of . 3KG/sec your final boost pressure will be 65 PSIG in the twin set up, but if it were trying to produce 65 PSI with a single turbo (in this example I used a HX35 as the small turbo) it would be practicly impossible. The small turbo is still in its efficiency map with the twin set up even though its discharge pressure is much higher than it would be if it were by itself.



but to answer your question... yes it is possible to build a miss matched turbo system.



Thanks.

You're Welcome

 

[csevers]

man did you copy that out of a book?

you know your sheet!

 

[Diesel Freak]

just my notebook on BOMBing

 

[Devildog]

Thanks again, great answer

I wonder what the air pressure inside the cylinder is during the intake cycle with the stock head vs. a ported head with the HX-40 pushing 40psi? I doubt it will be 40psi because of the air passages and the brief opening of the valves.

 

[Devildog]

UP

Any educated theories?

 

[Diesel Freak]

Not a clue on how to calculate that one... but I would hope at least for 20 psi at BDC