Twin Turbo Question

[bvanetten]

Is there a reason no one has tried running two identical turbos in parallel? It would require a custom manifold but with the money some of you seem to be spending I wouldn't think that would be much of an obstacle. Would it work well? Two Piers superturbos or something similar with say, 10 cm housings? Would it get you the quick spool-up and the flow needed?



Just a question from the un-educated masses.



Bruce

 

[TomGolden]

Well, this is purely my own speculation, but if you were to run two turbos (of any sizes) in parallel, you would be getting no better spool up than running a single turbo. It has always been my impression that one of the benefits of multiple turbos is the almost instant spool up at low RPM. You get that from the first turbo, usually a smaller (or at least "small") one that is directly attached to the exhaust manifold. It then force feeds air to the second, usually larger turbo at a much sooner and lower RPM time than any single turbo would get by itself. Therefore, the second (larger) turbo spools up much sooner, and therefore you get boost much sooner into the cylinders with the multi turbos.



At least that's how I think it works



Tom

 

[bvanetten]

I think my point is this. With a small turbo you get the benefit of quick spool up but are hurt on the top end with restricted air flow. By running two small turbos in parallel you would still have the quick spool up but by adding the 2nd turbo you would effectively double your flow or volume. Right?



Bruce

 

[Mark_Kendrick]

If you were to have parallel vs compound turbos ...



you would have to run much smaller housings on the two turbos than you would a single. . 2 HX35s vs 1. . to get them to spool at the same rate, but now you have twice the mass to spin up. . a loosing proposition. You would still only be able to make the pressure that a single turbo would.



Gassers generally run twin turbo's to simplify the plumbing and allow them to use 2 smaller, cheaper turbos . They also run less than 20psi(way less) for the most part. Performance diesels usually run 40+psi of boost.



Because diesels use compression vs ignition to fire the fuel charge they are not harmed by the increase in pressure that is possible with compounds... and boost+fuel = power



Turbo boost pressure is not absolute. . not a fixed increase... but is expressed in terms of a factor of input pressure. Therefor if you take a small turbo that would normally be undersized for an apppliction (this means it will spool really fast) and feed it with a larger turbo you can build huge pressures without the need to exceed the map of the smaller turbo.



an HX35 easily attains 35 PSI of boost... ambient + (250% of ambient)



if ambient is changed from 14psi to 25psi you go from 35psi of boost to ~88psi of boost WITHOUT OVERSPEEDING THE TURBO!





I got distracted and you typed this while I was gone... .

I think my point is this. With a small turbo you get the benefit of quick spool up but are hurt on the top end with restricted air flow. By running two small turbos in parallel you would still have the quick spool up but by adding the 2nd turbo you would effectively double your flow or volume. Right?

you will still only make 40 or so psi of boost. . which means you can only stuff the same amount of air in the cylinder given the same temperature. the size of the cylinder is fixed so the power at 40psi is the same across the board... until temperature changes. Larger turbos make cooler boost for the most part so the air is denser an makes better power.



This is sorta hard to explain is so few words yet be accurate. there are some simplifications here.



Later,

Mark

 

[drawson]

Here are som of my thoughts... It isn't just about boost PSI, it's about a cooler charge of air. Here is a personal example...



Before putting on my Piers Super HX-40/16 I was running my stock turbo(HX-35) with a 16 CM2 housing on it. I was getting 45+ psi out of the stock turbo and still had alot of smoke at full throttle. With the HX-40 the smoke was gone with only 38 PSI. IMO the reason why this happens is the air is cooler out of the HX-40 so even at lower boost numbers the fuel is being burnt better. My EGTs where also lower by 200 deg. IMO alot of this has to do wth having a 4" exit instead of a 3".



Now running two turbo in parallel should also allow cooler air to enter to motor and with two outlets reduce EGTS also.



But here are some of the draw backs all of the turbos designed for us have two inlets a new exhasut housing will have to be created. And just as with multiple Carbs of days gone by I think it will be hard to get both turbos to spool up together and each to make the same amount of boost at all times.



It sounds like fun and I know of a couple of Rammer that have talked about making a set up to run two HY-35/9 like this. Hopefully in a short time someone will have a working system.



The other Cool thing would be true dual exhaust

 

[Strick-9]

Drawson,



I like your way of thinking. Using your example of how important cool air is, do you think compound turbos would have higher or lower EGT under moderate to heavy fueling?



-Chris

 

[drawson]

I reaaly think I have twin turbos in my future, I'm leaning towards HVAC set up. I hope to check it out at the Utah Dyno Days as well as in Calagary in July.



Compound boost will lower EGTs because niether turbo is running out side it's map. And I believe keeping the turbos inside there maps keep EGTs down. Ideally it would be best to have some sort of intercooler between both turbos as well as after the last one. But with all this plimbing we'd run out of room for the Cummins. Man it's fun to dream!!!

 

[Mark_Kendrick]

drawson is correct. . heat is the killer. I did not emphasize that enought earlier.



My B1 made more power w/less fuel and boost ... . comp off w/B1 vs 5/5 w/HX35... why? much less heat. I was burning all the fuel I injected instead of sending it out the pipe.







compounds have the same effect. . but compunded.

 

[HVAC]

DRawson is making some very astute points.

 

[RustyJC]

Insofar as quicker spoolup and response is concerned, yes, there are benefits to running two smaller turbos versus one large turbo. Examples - variants of the Porsche 930 competition cars with a small turbo driven by each bank; the Volvo S-80 T6 that uses two small turbos for quicker response. The benefit comes from the reduction in the moments of inertia of the smaller compressor and turbine diameters of the smaller turbos.



Rusty

 

[drawson]

My ideal set up for twin turbos would be a small turbo about the size of the HX-40 on the intake side with a custom exhaust housing with over sized waste gates on both inlets with good flow into the outlet, then a large HX-55/60 w/waste gate as the top turbo. I would start opening the waste gates on the small turbo at 25-30 PSI. In a perfect world the waste gate would flow as much as the turbo itself so that there would be no back pressure even when the boost number where 80 PSI or so.

 

[KWIKKURT]

Just . 02 cents more... ... Two turbos like a hy9cm2 will not spool well because you will be driving them with only three cyl's worth of exhaust gasses/Cfm..... (2. 45 L cummins) So then you would want to use to smaller turbos like a Garret AirResearch T02 or T03... Fine for gassers at 5 to 20 psi..... But on our Diesels we want 40 Psi to 60Psi... . The Small ThrustBearings on the small turbos will not stand up to high boost. Not to mention that smaller turbos heat the air up more so you are negating the whole idea about more Boost... .



BUT it sure would look cool... .

 

[HVAC]

Kurt,



My concept for a quick parrallel twin setup would have all six barrels blowing into the first HY35 up to say 20 psi at which point a large divorced waste gate would open to let any further drive pressure spool a second HY35. This would provide very quick boost response and low drive pressure along with a large volume of cool air.



You might call this a consecutive twin system.

 

[drawson]

Nowel, I like the way you think. Here another Idea...



A triple turbo set up, I just saw a interesting exhaust housing for some gasser honda that had two outlets. So using this line of thinking a custom exhaust house for a HX-40 or B1 with two outlets feeding two HX-35/12s. The plumbing would be a nitemare but we could do just as they did for the P-38 Lighting and stick all the charger in the bed.