I would think since you were alternating exhaust pulses the smaller the exhaust housing the better but I'm not sure.

 

Gas guys do it quite frequently with 6 and 8 cylinder motors. IIRC, some Porsche and Toyota Supra had parallel twins from the factory. Most tuners would then replace those with sequential turbos to increase the boost.

 

Gas guys do it quite frequently.

That's where I got the idea from. The new BMW Inline 6 is twin turboed and it puts out 300hp and 300ft/lbs stock. My uncle has one and it is pretty sweet. Most tuner cars that I have seen that were stock twin turboed, usually ended up with just one big single. I am looking into this just as something different. My goals would be to have a very strong engine for towing, with decent everyday driveability. I know compounds would get me where I want to be, but like I said, I'm looking for something different. I agree with Redheadbronco, I'm thinkin the smaller the exhaust housing the better for this type of application. Keep up with the suggestions.

Stephen

 

Bad idea. Not being rude just saying its been tried many many times on differnt diesels and noone has liked it so far. I would imagine you could find a suitable set of turbos to do it but they would be so small and you would have to get the math spot on to make it work right. I have seen several guys try it with the duramax, powerstroke and cummins 5.9L and noone has like it so far. I do know that banks runs parrallel turbos on the drag racing durmax powered s10 but they also use a ton of nitrous and I mean alot to make it all work.

By all means dont let me tell you it wont work, I had lots of people tell me my ideas on my project wouldnt work and its been great so far. I am just saying parrallel turbos have been tested, retested and tested again by many different people on different types of diesels and none of them like the results on any of them that I have come across.

 

The problem with Parallel turbos it for it to work with out nitrous you have to run smaller turbos if you used the HX30s you may increse the CFM but not the density and cooler denser air is what makes power if you ran the HE341's you would get better density but I think they would be very laggy you would be better off running a single HE341's It would give you more air and density then the twin HX30 and should spool faster.

 

Usually the reason for "twin turbos" (in gas engine lingo and applications) is that the engine has two banks of cylinders, boxer or vee engines. An exhaust crossover pipe is a weak point/problem in a single turbo on a two banks-of-cylinders engine. For an in line four, it really makes no sense to use two turbos when one will work better (what I mean is, there are many turbos to choose from for a conventional single turbo, pick one that's optimized for the performance level you want. For parallel twins, you'll need two 'half-sized' turbos that are 'on the map' at one half the mass flow of the optimum single, and you'll be on your own to find those turbos...)

 

The idea for twin chargers on a diesel is to support high HP and have a broader power band. Two chargers in a series work very well because the small charger gives quick spool and bottom end power and the big charger feeds the small one, compounding the boost to create high pressure for top end power. Parallel chargers will not even come close to this in comparison because they have to be so small to get quick spool and the boost pressure required to support high HP will put them way beyond their efficiency range. Gas engines can use parallel chargers with great success, because they do not require high boost pressure to create power, which leaves the turbos in their efficiency range.

 

Well said Lee. Thats where the nitrous comes in for the top end charge.

 

Thanks Lee and Carcrafter, that is the info I'm lookin for. :beer:

 

Draggin up an old thread, Reading an issue of offroad or diesel there was a triple turbo'd cummins in parallel making huge power. Any thoughts

 

Making huge power isn't the problem. You can simply size everything for high rpm.
It's making something that is usable when you aren't on a dyno that is difficult.

 

Very true. The article didnt go into much detail about where the power started in the rpm range but the company is gonna start making kits for the public. The idea of more air at lower boost pressure

 

A lot of people claim they have a magical setup which gives more air at the same or lower boost. Unfortunately for them it's physically impossible.
Your engine is fixed displacement, the only way to get more air through it is to compress that air.

 

Its all about turbo sizing. It can be done with the right combo of compressor and turbine sizes along with the right exhaust housing size and smart use of a wastegate.

I followed a thread on a duramax forum for a guy trying parallel turbos on a dmax. After several different combinations he hit the sweet spot and was able to adjust the gates to where he got the performance he desired. He claimed they spooled like stock but had a much broader power band and much more power.

I'm sure it can be done on a 4bt, but I'd liken it too finding a needle in a haystack to get just the right setup versus finding the haystack itself to get a set of decent performing twins (compounds turbos).

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Not exactly. Boost is a measure of restriction. An intake tract that isn't set up properly can restrict thoe power. If you're trying to make 1000hp on a first gen Dodge intercooler and 2" boost tubing... if that would even be possible... you'd be well above 100psi of boost because you have to compress the air so hard just to move it through the system. Change out that tubing to 3" and a huge high performance intercooler and you will make more power with less boost. Every time.

The cast intake and poor flowing head on a cummins means they need a lot of boost to get airflow. Guys that mill off the stock intake manifold and p&p the head see big power gains without boost increases.

In the duramax world I've seen guys make 7-800hp with 80psi of boost and I've also seen guys make 1000hp with 50-60psi of boost.

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Not exactly. Boost is a measure of restriction.

The restriction is your fixed displacement engine. Those pistons and cylinders. Yes you can make some gains with flow improvements, but the pistons and cylinders remain.

Claimed power figures can be all over the place. But compare torque to air density through boost and all the BS stops.

 

wow I started a war. If i can find the issue ill post the "info". Should be fun.

 

"Its about cfm not boost."

Clearly true, but only up to a point. But, a determinant pipe network (engine) has a finite max CFM @ __psi boost. "It" is really about both. Velocity of non-turbulent flow is the limiting factor in a given network where the other two are fixed, once this threshold is topped, any velocity increase just makes heat.

Ideal Gas Law: PV=nRT
where P is the pressure of the gas, V is the volume of the gas, n is the amount of substance of gas (also known as number of moles), T is the temperature of the gas and R is the ideal, or universal, gas constant, equal to the product of Boltzmann's constant and Avogadro's constant.

This is what Dougal is saying.
Matt

 

Unfortunately you must not have had many physics classes. What you're forgetting is that the reason an engine can make more power with less boost is due to cfms and air density. By density I mean due to the charge temp. Compression heats the air. And the compressor wheel speed has a somewhat exponential correlation to the amount of heat produced. Hence a turbo map... That 40psi from a hx35 will be so hot its practically useless since the compressor is so far out of its map that all its doing is spinnig so darn fast its just making very very hot air. And we all know air expands by large amounts as its heated, meaning its less dense. 40psi from a larger turbo (size and description really don't matter) can be right in the sweet spot of the map meaning its delivering not only more cfms, but cooler air which is much denser, the end result is more o2 in the combustion chamber. Obviously that means more power. It dosesnt get anymore straight forward than that. And if you think I'm wrong then ask yourself why nearly all turbo diesels are intercooled.

50psi of superheated air (400*+) wont make as much power as a cool 40psi (>200*) will. That's just physics and if we're talking theory it doesn't matter what rpm. But a well designed 6bt turbo setup will make boost similar to the stock turbo. I've been around several setups anywhere from 60-66mm that spool awfully close to the same as stock. By 2000rpm they're able to produce as much boost as they want, so your higher rpm theory isn't really true. The difference is that with a larger turbo you have the option to extend your powerband to higher rpms due to the higher cfm flow of a larger turbo. An hx35 will start to choke out much past 3000rpm on a 6bt if you're pouring the fuel to it. Egts skyrocketing and so does drive pressure. You're making lots of boost but power falls off because the cfms aren't there.

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Unfortunately you must not have had many physics classes. What you're forgetting is that the reason an engine can make more power with less boost is due to cfms and air density. By density I mean due to the charge temp. Compression heats the air. And the compressor wheel speed has a somewhat exponential correlation to the amount of heat produced.

Quite the opposite, I have many years of physics and thermodynamics. I have modelled and measured turbocharger and intercooler temperatures. There are no surprises, I know how they work and can predict results pretty well. I have a multitude of calculation sets I use which run through about half the average thermodynamics text.

Virtually every turbo is running at 60-75% adiabatic efficiency. There is no "superheated air", that's a myth and there is no "exponential correlation".
Adiabatic compression is the process and you modify the results of that to fit with the efficiency of your compressor. Ax HX35 is still on the map at 40psi.

It is another myth that larger turbos produce cooler air. Look at the maps some-time, take the measurements. The only part that matters is where on the map you are and how efficient the compressor is at that point. Larger turbo compressors are not more efficient than smaller turbo compressors.

So instead of repeating the bollocks rolled out by guys with no idea, I suggest you find a thermodynamics book, read up on adiabatic compression, the brayton cycle is a good place to start.
Once you have that down, apply the results to turbo compressors and you might see that 40psi is indeed 40psi and further once intercooled any minor differences in compressor outlet temperature are nullified.

Crunch the numbers yourself, even better, take some measurements. There is never 200F difference in charge temperatures at the same boost. Never.

As I said earlier, boost, torque and air density are where the BS stops.

The exhaust side choking at high rpm (and the resulting power loss) is another matter entirely that has nothing to do with the compressor not being big enough.

 

So you're trying to tell me that the compressed air from an hx35 making 40psi is the same temperature as 40psi from a larger turbo... how about an s362 for example. Absolutely not true. According to the map of an hx35, yes you're right its not off the map at 40psi, but they're known to grenade much past 35psi, mostly since its turning like 115k rpms (best case scenerio) at 40psi. Compare that to the s362 and it's about 85k rpms. The faster the wheel spins to make the same boost the more heat there will be... simple as that.

And an intercooler can only dissipate so many BTU/hr or per min or whatever. So it'll cool the charge air but only some. Once it becomes heat soaked its not doing much good. Its not like it cools it to ambient air temp or anything. So saying its a cure all is just flat out not true. I watched post I/C charge air temps on my duramax for two years with a scangauge. Anything over about 15psi of boost and charge air temps shoot through the roof even though intake temps stay the same as ambient temps. They'd regularly be over 200*f even with the huge intercooler on the dmax.

And I'm not talking about the exhaust side choking I'm talking about the compressor. What happeneds when you run an engine to higher rpms and the compressor can't flow enough air? That's choke, but you should know that. Once you get to the far right of the compressor map you hit a wall where further gains really aren't possible due to the wheel speed. Duh, right?

If you can read a turbo map then tell me what happens on that hx35 map when you follow the ~2.7 PR (~40psi) line to the right... once you get past about 50lb/min what happens? Gee the compressor speed goes through the roof to keep up with the airflow needed... that means heat goes through the roof too. But 40psi is 40psi right? At 60lb/min on the s362 your still right in the middle of the map and the wheel speed has barely changed meaning not adding anymore heat. 60lb/min on the hx35 is near where choke starts. On any turbo map if you follow a PR line from left to right the heat of the charge air goes up as you move to the right. Which is why 40psi is NOT just 40 psi. I said it before, 50psi from a smaller charger wont necessarily make more power than 40psi from a larger charger. That 40psi will likely be much cooler meaning more dense air and more power. And its been proven plenty of times in the real world.

You can try and argue about torque... but that's only half the equation. HP is the motor doing work. HP is the felt power of the motor. HP is the haul ass feeling, its what gets the load to the top of the hill. If I'm pulling a 5% grade I'd want that 40psi of cooler denser air rather than 50psi of hot air. That hot air is stealing the cooling air from the radiator and that's just going to help the truck overheat along with higher egts and drive pressure.

So I'll say it again, 40psi is NOT 40psi from different chargers. You said it yourself... air density... not the same from charger to charger... end of story

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Well, I'll chime in since I am actually a physicist. The heat in the charged air does not come from the compressor wheel spinning (ie friction). A small amount would, but not a significant amount. The heat comes from compressing the air. This heat is a product the work done by the compressor wheel on the air. Same way the charge in the cylinder increases temperature as the piston compresses it. Wheel speed would have nothing to do with it.

 

I understand the thinking behind this but I disagree somewhat as I've seen it. I've seen a small turbo setup on my rx7 over boosting the stock turbos (13psi) run as high if not higher temp(before intercooler) than my truck making 40psi. I don't remember the numbers as the gauge i threw on was temporary, i was originally checking my intercooler effectiveness.

 

Well whether is from friction or the compression itself, as you move to the right through a turbo map (increasing engine rpms) the temperature of the compressed air goes up. And its been shown to go up dramatically as you approach the choke point of the compressor due to the inherent inefficiencies that show up when the compressor blade speed approaches the speed of sound.

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Well whether is from friction or the compression itself, as you move to the right through a turbo map (increasing engine rpms) the temperature of the compressed air goes up.

No. Compressor outlet temps have nothing to do with engine rpm. Nor indeed with compressor wheel speeds.

And its been shown to go up dramatically as you approach the choke point of the compressor due to the inherent inefficiencies that show up when the compressor blade speed approaches the speed of sound.

Compressor efficiency drops towards every edge of the map. Running against the choke line isn't much different to running against the surge line for efficiency and outlet temps.

Sorry mate, but you have no idea about boost or compressor outlet temps. Same for torque and hp. You've got a physicist and an engineer both disagreeing with you.