Sure...... Mass flow is Pounds of air per hour (or minute or second, whatever time unit you like). Volume flow is cubic feet of air per hour ( or minute or second, whatever time unit you like also.) (We usually use mass flow in pounds per hour and volume flow in CFM, but any unit will due as long as you convert properly.)



The impact the difference has to us when talking about twins (which should not be called twins, they should be called COMPOUNDS, twins imply two turbos in parallel like some gasser cars have, compounds are compressors in SERIES) is that the density (a measure of mass per unit volume) is directly proportional to pressure. Increase the pressure and you increase the density, which means that for every cubic foot of air you move, you move more POUNDS of air. The combustion process requires a certain MASS (pounds) of air for a given MASS (pounds) of fuel.


An example is best to clarify:

Let say you need 3,000 Lbs of air per hour to burn your fuel properly in your cranked up CTD. At atmospheric pressure and 60F, that’s roughly 700 CFM of volume flow (don’t nit pick here, I don’t have my chart with me at this moment, I am pulling that out of my head). So with a single charger, the intake of the compressor section would have to be sized properly to flow about 700 CFM of air without undue velocity and flow restriction.

Now lets say you have twins and want to move the same 3,000 LBS of air per hour. The primary charger (bottom) would see the same 700 CFM, as its sucking from atmospheric pressure. Lets say the primary charger boosts the charge to about 20 Psig. So now the intake of the secondary charger is taking the same 3,000 LBS of air per hour (mass flow is constant so long as nothing is leaking) but since its taking its suction at 20 Psi above atmospheric pressure the density is higher, and so each CFM of air has more mass and so we need less CFM to move that same mass. So at 20 Psi intake the second charger only sees 300 CFM of airflow at its intake. Now in reality its actually a bit higher than that, because the first charger heats the air and this has the effect of lowering the density a bit, so the actual volume flow through the second charger is probably around 400 CFM or so.

So in our example here, you have 700 CFM through the primary compressor and 400 CFM through the secondary compressor and in both cases 3,000 LBS of air per hour. Remember, mass flow is always constant( unless you have a leak), volume flow is not.


KP

 

Thanks KP, good Example...

Cost.. some of it has to do with time.... How long it will take to build a set.. and making sure you have all the parts.. (all the little stuff... fittings, clamps, hoses...) and that everything will work together.. and fit... I can't say I'd buy one.. that's the fun of it.. building it yourself.. but spending 80+ hrs on a set.. and then to find out it won't spool.. scrap it and start over...
Just ask NeeMoPower about twins.. and why his hot pipe is like it is...

 

Alright guys, I am getting ready to start buying some parts for this twin project. What turbo should I run with my stock turbo, if I want to modify my hx35/16 can I buy the kit and do it myself or does it need to be sent off and done, and if I want to go with a stock HT3B can I buy the kit to modify this one also or does it require machining.I would like to have a dependable setup that is good for about 500rwhp that is still street worthy with good spoolup.

 

Its pretty straight forward IMO. I ve been thinking about producing the parts needed to do the hx35/ht3b transformation....I just about at that point. No machining.....or anything. The biggest problem is the ht3b down pipe, pretty much a custom piece that needs to be fabbed from pieces. Its 5 inches...so if you run a exh brake or 4 inch exhuast you ll also need to reduce it. I run a 4 inch us gear decelerator (brake) so its 5 inch back to the decelerator, were it reduces to 4 , then stays 4 the rest of the way.

I can do the oil lines in and drains, the cold pipe, and brackets to mount the ht3b and the spacer for the hx35. An air intake is pretty easy to make, and the down pipe is cut, weld, moddify, fight with it.....try some more, till you get it.

I think it could be done for 1500 to 1800....if the ht3b is still the same price...

 

I am already running 5" under the cab to my stacks off of the 3" downpipe, so the 5" off of the HT3B would not be a problem. What kind of mods need to be done to the HX35 and the HT3B to make them perform well as a pair? I don't mind spending countless hours fitting and fabing to get it right, that's why I do this stuff, because I enjoy it. I just want to get as much info as possible on the best setup so I get it right the first time.

 

quote
600 Megawatts said:
"The impact the difference has to us when talking about twins (which should not be called twins, they should be called COMPOUNDS, twins imply two turbos in parallel like some gasser cars have, compounds are compressors in SERIES)"
----------

I've done some smalltime automotive hobbyist's research in this area. I'd like to bring in new terminology to describe 'twins' as we know them.

Vehicle and turbocharger manufacturers do not call this method of charging as 'compounding'.
Compounding is a totally different ballgame. That means connecting turbocharger mechanically to crankshaft. Please do read more here: http://www.vehicular.isy.liu.se/Publ...3443_OF_MG.pdf

I quote that research:
"2.2 Turbo Compound
A turbo compound is placed after the primary turbine, and consists of a turbine,
a shaft, a hydraulic coupling and gears. The compound turbine works
in the same way as the primary turbine, and is connected to the hydraulic
coupling via the shaft and cog wheel transmission. The hydraulic coupling is
then connected to the crankshaft via cog wheel transmission.
The purpose of turbo compound is to use the energy in the exhaust gases,
which drives the turbine and thereby generates torque. The torque is then
transmitted to the crankshaft via the hydraulic coupling and gears."

---

Let's get back to issue at hand. Two chargers connected in series, feeding off from another is called: Two-Stage Turbocharging.
More here: http://www.google.fi/search?hl=fi&q=...btnG=Hae&meta=

Reputable manufacturers as Caterpillar, Holset, Borg Warner (former: KKK) use this terminology.

Can we all agree on this?

Two-Stage Turbocharging is the way to go.



sincerely - Arto L.

 

You are correct, "turbo compound" means mechanically driving a shaft with the exhaust turbine and this is nothing new and has been done for literally decades on large size two and four stroke marine and stationary power generation diesels.

BUT compressors/turbines arranged in series with each taking a share of the pressure rise/drop are also called compound. Examples: tandem compound steam turbines, cross compound steam turbines, compound compressors, triple compound, quadruple compound centrifugal compressors as are used in very large air compressors and compressed natural gas applications.

And yes we can almost agree, that for boost pressures higher than 30 Psi, MULTI stage compression (ideally with intercooling between stages) is the way to go!! After all, why limit ourselves to just two stages !!!


KP

 

I'm with Swank on this one. Probable just different strokes for different folks......but, there are guys out there that put in the time, spent $2,000 +/- for parts, had their truck down for a month, and still ended up with dysfunctional twins! Talk to us after you try it.
If you have access to the tools, the shop, and enjoy the prospect of the 60-80 hrs required to do the work...go for it.
Everybody that paid hard earned money for their performance shop twins, may not be "blowing $4,000 foolishly".
Like I said...different strokes....but room for all of us....no?
RJ

PS: GREAT classroom on Mass Flow vs Volume Flow! Thanks KP....Read it three times and still have trouble following. Got a grade school CTD example for the challenged?

 

OK, RJ...... The combustion process requires a certain mass of air for a certain mass of fuel right? Well air is compressible, and when you compress the air, the molecules or air get packed together more tightly, and so a given number of molecules (mass) can now fit in a smaller space. And so when moving along through a pipe, lets say, a larger number of molecules can pass through the pipe at a given speed.

How bout some analogies : Kind of like traffic on a highway... If nicely spaced out 3,000 Lb cars are going 60 MPH pass a spot on the highway lets say 30 cars past that spot every minute. So then there are 90,000 Lbs of cars passing the spot per minute. But now lets say the cars are talgaiting and still going 60 MPH, and since they are tailgating and packed closed together 45 cars pass the same point every minute, so now there are 135,000 Lbs of car passing per minute. To get the first case mass flow of 90,000 Lbs of cars passing the point per minute, the taligating group of cars could slow down to 40 MPH and still move 90,000 Lbs of cars past the spot per minute.....

Or this one: A certain process requires 10 Lbs per minute of ping pong ***** to pour into a tank, but the shape of the ping pong ***** is not important only that the ping pong ball plastic (mass) gets into the tank. You would need a pipe about 2 feet in diameter to move the 10 Lbs per minute of ping pong ***** through it and into the tank, or you could compact the ping pong ***** together with press and get the same 10 Lbs per minute to flow into the tank through a say, 3" pipe....

Help any???



KP

 

Good posts, KP-- all of them.

I ran some numbers and 54lb/min looks like what I need at my current fueling to support combustion with EGT under control.

jh

 

At the begining of the post it was hot, was about on 1500*
later it went down to 300*F ready to shut down
makin it with closed eyes, sounds like i could do it with open eyes...

hey i looked through your gallery, nice twins!

 

KP -Thanks. I was trying to make it to complicated.
Did not realize you were explaining the difference between Mass & Volume ... in answer to Bryans question. I do get the compression theory and how it works in twins.... ah ....compound ....ah ... multi stage turbos.

What confused me was "mass flow is always constant". Tried relating that to two different sized single turbos... both putting out the same boost pressure with different masses & volumes.... had my head spinnng a bit!
But this thread is about twins.
Thanks again.

 

TWINS ARE AWESOME!!!

Just installed the BD Twins I had laying here over the weekend, and for this old 360hp 12v they are the shiznit!!! (sorry) The B1 would hold temps below 1300* to about 2700RPM, then it would shoot RIGHT to 1450-1500*. These suckers hold it at 1100* to the same place, but I won't go any farther 'till I get the studs in.

60psi + 312K mile engine can't be asking too much of stock headbolts can it?? I need to figure out how to get the boost below 50psi 'till I get the Studs, External WG, and the HX40/B2 Twins on there

For now, I'm all smiles though.
Chris

BTW, the BD Twins are available if anyone is looking

 

Yes, Hohn, I would say you are very close. I allways figured about 3,000 Lbs/Hr at 50 Psi would cover 500 HP worth of fuel quite nicely. But I am shooting for about 1,300 F at full tilt. I am not onboard with cooling the combustion process with too much excess air ... Thats what alot of guys around here like to do... they take a combo which is about perfect at 1,200 F when maxed out, and then add more air so that its now at 1,000 F... and their happy about it ???? I am not sure they realize that they just dumped tons of excess air and diluted the combustion process so bad it cooled it 200 F and they lost power.....



KP

 

correct me if I'm wrong, but 1250* is the optimum thermal efficiency of our little 5.9 isn't it? That's the number I am always shooting for at full power. Since our huffers are waste energy scavengers and thermal differentials play a major role in turbine operation, I believe at 1250* we are making the energy work the best for us without compromising parts integrity.......