Twin Turbo Configuration Question

[BMancin]

All of the twin turbo configurations I have seen so far all utilize a primary and secondary turbo in series progressive configuration. Is there some inherent problem with configuring 2 separate turbos, 1 for each 3 cylinders in parallel? Seems a non-series setup would have lower egt, quicker spool up since you could use smaller units, and a true dual exhaust! I realize this set-up would require a different exhaust manifold, but is that the only obstacle? I see parallel turbo set-up on gassers all this time, on v8 diesels, but not sixes. I am really curious as to why?



Thanks,

 

[HoleshotHolset]

I know someone who ran what you are describing with twin Holset HY-35/9's on a 24-valve.



It was a lag PIG... . I never saw anything as laggy as that setup. It literally would NOT spool unless you whacked it with NOS.



Once it was spooled - HOLD ON... . it pulled REALLY hard.



This setup works well on high RPM gassers, but not too many people run it on diesels... . The tried and true compound turbo setup works extremely well on the diesels..... great spool and tremendous boost/flow potential.



Matt

 

[Idaho CTD]

The problem with parallel turbos is most people dont match the turbo size correctly. As in Matt's example most people try to use a turbo that is small as a single but too big as a parallel setup. When you run it off three cylinders it becomes too big. Also the rotating mass isn't lower because you have to turn two sets of wheels. Basically running two HY35-9's would be about like putting a HT3B on as a single.

 

[Forrest Nearing]

the benefit of twins is that you reduce the pressure ratio each turbo is operating under... this keeps the charge temps (and resulting EGT's MUCH cooler)



as you compress air, it gets hot, the more it's pressurized, the hotter it gets...



when you ask a turbo to operate outside of its efficiency range, it starts heating up the air a lot...



if you have a single turbo (or even twins in parallel) making 60psi, you're asking it to pressurize the atmospheric air FOUR TIMES over atmospheric



now, if you ask a pair of twins in series (one blowing into another) to make 60psi, if they're sized right, you don't need them to pressurize as much... say your big turbo pressurizes the air to 20-30psi, and then the small turbo takes that pressurized air and pressurizes it to 50-60... each turbo is only has to pressurize a couple times over atmospheric, so it doesn't heat up the air nearly as much.



anyhow, twins in parallel are good for a gasser that makes high power at low pressure ratios if you can't afford one turbo that's big enough to move the necessary CFM... there's a BIG difference between making 800hp at 25psi and making 800hp at 100psi!!! the first will require one HUGE turbo or a pair that can support 400 each...



you also run into problems with making sure the compressor maps are right... I'm pretty good with maps on gassers, but I don't have enough experience (nor can I find detailed holset maps!) with the diesels to know how they react to different compressor maps... taking two stock turbos and running them in parallel is usually a recipie for disaster... the turbos aren't any more effective at high boost, they just tend to surge off boost and take forever to spool up. you'd generally go with two slightly smaller turbos that are more effective at higher pressures, BUT in this day and age, unless you're talking about rediculous HP numbers like 2,000+ a properly sized single is the way to go (on a gasser of course!!!) with the pressure ratios required to make these diesels really get, compound setups are THE way to go!!!



Forrest