I was thinking about a very streetable twin turbo setup that would be geared more toward crazy spoolup and an effecient and reliable low temperature supply of roughly 45 lbs of boost.

I am pondering a compound setup with the existing HX35W as the primary and a cute little HX30 as the secondary. Arranging the compressors in series as normal, BUT feeding the turbines in parallel as opposed to series. The HX30 only flows .35 Kg/s as a single, but with it recieving air at 22 Psi it might match up well with the total airflow requirement. Drive pressures with both in parallel might me a tad low, but the HX30 does have a real small exhaust housing. I will work up the numbers and see, but I would think it would spool wicked fast, might be a real neat setup for about 400 HP and should be GREAT for towing, as both turbos would be confortably in their map, so discharge temps should be quite low..... REAL CHEAP TOO !!


Whadyathink???



Zino

 

Zino;
That sounds like a resonable idea. I'm definently no expert on turbos but Iam interesred in the same thing. 400 hp w/ quick spool up keep us informed.

ramguy

 

i keep thinking a hy9 with a hx 55 would make a killer tow set up, limit the boost to 45 or 50#s and it would spool like no other.

 

Hey Gunracer, that twin setup sounds like one I may be interesed in except substitute that 55 for my B1(not starting a war, the B1 is just what I have on hand).
BTW: how are them Alcoas comming?
Scott

 

tires are some high dollar sob's. the best price i have got for 6 is 1450 bucks. so i need to save some more.
i have the hx 55 so that was my pick on the bigger one. it has a 19cm housing so it should spool quick. i think it would be a killer tow set up.

 

Zino, I am not sure if I understand how you want to feed the turbine housings. In the setup I think you are talking about, I think you would need a split exhaust manifold, two downpipes and would need even sized exh. housings for balanced cylinders. Would be alot of fabricating. I know where you can buy ht3b/23 turbos new for $375. It would be easier and cheaper to build a standard set of compond turbos. PM me if you need part #s or vendors. Tim

 

Zino, I don't think that's the route you want to go.

I think I understand what you are thinking. You intend to set it up like regular twins on the exhaust side (turbines), but setup the compressors in parallel instead of series (primary feeding secondary). You intend to have both the primary and the secondary compressors plumbed to the intake...

Here's the problem: This would only work if you had identical turbos. Also, you would have very little compounding effect.

Why? Well, if you have one turbo putting out 30psi, and another putting out 15, what does the engine see? NOT 45psi!! It sees 30! Moreover, the 30psi of the big turbo would PUSH the air back into the compressor of the little turbo. Doubt it?

Take two air tanks. One has 30psi in it, the other has 15 psi. Connect them to each other only. Soon the pressure equalizes, and you have between 15 and 30psi in BOTH tanks.

So you can see why you can't use two non-identical turbos setup this way.

What if you use two identical turbos? Well, since the turbo closer to the exhaust manifold gets more enthalpy, it will spin faster than the next one down the line, given identical turbos. So again, you will have a mismatch because one turbo will make a little more boost, than the other, and cause all kinds of problems.

My big question about compound setups is why the big turbo is where it is. Why not use a big secondary and a small primary? The thinking here is that the big turbo needs more heat to spool, so mount it closer.

Of course, you don't need to have instant spool from the big turbo since you are relying upon the small turbo to boost you until you get the big one to spool.

I suspect the real reason is that it's hard to feed a compressor capable of 700cfm with a small one that moves 400cfm, so you have to mount the big and little where they are to get the compounding effect. Did I answer my own question? Tim?

I personally thing a GREAT small twins setup would be a Nasty Nine (HY35) on top with a standard housing B1 on the bottom. That should give you a REALLY quick spooling 50psi easy.


Justin

 

Oops! I had it backwards on the turbines vs compressors.

Anyway, it WOULD be a LOT of fabbing to divorce the turbines. Plus you would lose a lot of heat.

What it boils down to is that someone somewhere probably tried about every other turbo arrangement. There's a REASON that almost all twins setups follow the same basic plan.

Justin

 

Well my thinking is as follows.... First for clarification there are differing naming conventions used on this and other forums about which turbo is the primary and which is the secondary. In all other industrial applications, the primary compressor is the first compressor taking in atmospheric air, and subsequent compressors are secondary, tertiary etc.. So this is the convention I follow... i.e. by primary, I mean the turbo that sucks in atmospheric air. And of course it needs to be the larger compressor. In reality the way twins are done on our trucks, the primary compressor is driven from the secondary turbine, and this is probably where the confusion started.... None the less, calling the primary turbocharger the first stage large turbo, lets continue from there. Say the primary is operating at a PR of 2.5:1 than the secondary compressor should be roughly 2.5 times smaller due to the increase in density. So in reality even an HX35/12 used as a secondary is still too big for anything under 500 HP. So I got to thinking, that the ideal sized secondary compressor for about 400 to 450 HP would be an HX30, but if arranged in true compound turbine fashion (series turbines) the small exhaust housing would be so restrictive that it would create very high backpressure and to correct this one would need to install an external waste gate of fairly large size, dumping into the turbine of the primary turbo. (I still am thinking about going this route actually). So then I thought why not arrange the turbines in parallel and the compressors in series. Granted, if would not be as thermally efficient, as you are not lowering the exhaust gas enthalpy any lower than with a single, but you still would be benefiting by running two compressors squarely in the center of their map and still have 45-50 Psi of cool boost.
Fabrication is not an issue, as I have a full shop, and I intended on making a thin walled stainless steel header/manifold from scratch no matter which route of twins I go. In this parallel turbine /series compressor case, I would make the manifold plenum a fairly large volume and have two exhaust flanges front and back for the turbos, one turned up a bit and one down. The primary turbo would be waste gated to 23 Psig, and for the second turbo I planned on fabricating a custom differential pressure wastegate, so it would wastegate with about 23 Psig. ACCROSS it.
As for balance, think about this... The primary turbine exhaust housing being larger than the secondary and with both being fed with identical pressure from the exhaust manifold plenum, the ratio of exhaust gas flow through the turbos would be the ratio of the areas. So in this case the primary turbo would pass about 65% of the gas, and the secondary turbine would see 35% of the gas. With the above stated wastegate pressures, the primary compressor would be running a PR of 2.5:1 and the secondary about 1.6:1 which would balance quite well actually with those exhaust flows.

So now the engine 'sees' a total effective exhaust ‘housing’ of better than 20 cm^2 but you have two small turbos with compounded compressors smack in the middle of their maps delivering 45 Psi of boost to the engine.

The only downside I see is that this setup would not remove as energy from the exhaust as a true compound and so it would not be as efficient. I still am thinking long and hard though about arranging a HX35w/14 and HX30 in a typical compounded fashion with a large (like 44mm) wastegate dumping around the 30 into the 35. I would think this would be CRAZY quick spool up as well...

Zino

 

Justin the reason compounded setups have the large turbo as the primary compressor/secondary turbine and the small turbo as the secondary compressor/primary turbine is two-fold and makes perfect sense.... Obiously due to the density increase of compressing the air, the primary compressor needs to be the larger one... So the naturally the primary turbo is the BIG turbo and as such has the larger exhaust housing. And so with its larger exhaust housing area is better suited to recieve the cooler, more dense gasses that are leaving the secondary turbocharger (which has the primary turbine). Sounds a little like who's on first.. I know I know, but read it slow, its right.... I had to think about it a few times myself as I am typing...

Kind of like our discussion regarding the gradually tapered exhaust system to have more area available as the gasses cool....



Zino

 

Thanks, Z.

I see where you're coming from, now.

Why don't you try it and tell us what the results are?

Justin

 

I just might try it both ways actually, and compare. I am thinking that I will put a HX40 compressor wheel in the HX35 when I use it as a primary so it would be an HX35-40/14 hybrid primary and an HX30 secondary. What the heck, if it doesnt work, then I can put the HX30 on my compact diesel tractor and turn it into a mini-smoker


Zino

 

If you are talking about installing a "Y" in the exhaust and running the exhaust to two different turbo's, in effect wouldn't it act just like one HUGE turbo????

Lots of Lag.... this isn't scientific but wouldn't you have the effect of a HY35 on a 3 cyl diesel... Large turbo for a 3 cyl???


Curious
James

 

Well, not exactly a 'Y' but in effect the same thing. Yes the 'effective' exhaust area that the engine 'sees' will be just like one big turbo, but instead of one big turbo's big compressor, there are two compressors, one of which is small and the other really small. The thought is that at first the secondary turbo, the little HX30, would spool quick covering the 'hole' while waiting for the primary to spool. Dont get me wrong, I am not sure if this will work well at all, just trying to come up with a way that an HX30 sized compressor as the secondary can work.



Zino

 

How would drive pressures work out? I think that being the turbine were parrallel that the pressures would be equal?