Competition how much boost out of twins?

[BPonci]

You can make 560 with a hx35/12 and a bht3b/26. All using a internal w/g. Its all in how you set it up.

 

[Jim Fulmer]

You can make 440hp on a hx35/16.



And make 496 with a 35/18. 5... ... ... ... @1500 degrees.



And 670 with a 35-18. 5/HT3B/26.



When I first did my Twins I was at 450hp.



Jim

 

[Mark_Kendrick]

You can make 440hp on a hx35/16.



And make 496 with a 35/18. 5... ... ... ... @1500 degrees.



And 670 with a 35-18. 5/HT3B/26.



When I first did my Twins I was at 450hp.



Jim

I have a buddy witha '96 12v, 370 inj, custom plate, and a 35/16 that makes 440 hp on the dyno and is still able to tow reliably.



He's putting on twins to get to 500. He's also using an external gate on the twins.

 

[mjoppie]

so it should be pretty easy to get right around 500 hp with my fuel and the twins setup properly? but my question still is at how do you control the boost output of the big turbo by wg the 35? your still driving the big turbo even though it is bypassing the 35, right? guess i dont know as much as i thought about twins probably be a lot of trial and eror in the coming months i can see.

 

[cjohnson]

I'm no twin expert, but the idea of wastegating the 35 in to the bigger turbo and maintaining boost levels is that the ex. housing on the bigger turbo is so big( a 26 or so) that even dumping the 35 off to it won't drive it hard enough to produce too much boost. Controlling the boost on the high pressure turbo (the 35) should give you all the control you need.



Craig

 

[mjoppie]

ok so basicly the gasses coming out of the exhaust tube are pressurized higher than that of the wastegate gas passing into the big turbo. so the more air you wg past the little turbo the less boost you would have out of the big turbo right? kinda like the exhaust wheel acts like a compressor to drive the big turbo and the wg just kinda dumps excess into the operation. am i understanding this right or am i making it harder than it is?

 

[Mark_Kendrick]

ok so basicly the gasses coming out of the exhaust tube are pressurized higher than that of the wastegate gas passing into the big turbo. so the more air you wg past the little turbo the less boost you would have out of the big turbo right? kinda like the exhaust wheel acts like a compressor to drive the big turbo and the wg just kinda dumps excess into the operation. am i understanding this right or am i making it harder than it is?

I'll give you little class in compound turbo charging...



It takes heat and pressure to drive a turbo. The heat expands the gasses to increase the pressure. The pressure drop across the turbine (inlet pressure is higher than outlet) is the energy that's harnessed to drive the compressor. The exhaust gasses are allowed to expand throough a turbine wheel that causes it to spin. The other end of the shat is attached to the compressor. If you flow too much air through the turbine it will spin too fast and cavitate the compressor. At that point it isn't putting more mass through the compressor the compressor is heating the gas more and causing it to try to expand. The energy contianed in the compressed charge is measured in terms of heat and pressure. You want higher pressure and less heat. Less heat means more mass.



Larger compressors compress gasses at cooler temperatures given the same mass (turbos are actually rated in Kg/s not cfm or hp. The mass limits the hp). All turbos are effectivly limited by the pressure difference between the inlet in outlet of the compressor (expressed as a pressure ratio, PR, ex. . 1:1 ,3:1 etc) Turbos being centrifugal compressors are very efficient, as a rule of thumb, below a 1:3 pressure ratio. This is commonly called staying 'on the map'. the map is graph that shows flow in KG/s or Lb/min, efficiency and pressure ratio.



here's one for a T66 garrett. .

#ad




The problem on a diesel is we need a lot of air (mass) in a small space (359 in^3) which means to make lots of hp we need lots of pressure but it also needs to be at a low temperature. 40psi of boost(3:1) is where a single turbo starts to generate a lot of heat.



To keep the turbos on the map and make 50-60psi of boost (4-5:1) you need two stages of compression, Compoud turbo chargers commonly referred to with the misnomer, Twins.



Now comes the hard part picking the twochargers and their exhaust housings. the smaller turbo is the sendary charger (second stage compressor). It needs to spool well at lower rpm and HP levels while still fowing enough (on the exhaust side) to drive a primary charger that must be about 2. 2 times the size of itself. The only way to do that efficiently is with a large wastegate. The waste gate must run from before the secondary to before the primary. It's purpose is to increase exhaust flow into the larger charger. see pic:



#ad




more pics... http://www.texasdieselworks.com/twinspics/





I gotta run for now...



FWIW,

Mark

 

[Snow man]

mjoppie,if you had acess to a machine shop, you could make thei nternal gate bigger. The problem with the 35/12 housing is the gate is already right up against the sides of the housing,there isnt much room to make it bigger. If you used a 14housing you may be able to get away with the internal gate a little better since that housing flows more air reducing the amount you need to wastegate. Im sure taht this woukld work to at least 450-500 hp,after that you might need a custome gate. With the hx40/16 there is more room to mess with the internal gate. I like using the internal gate only because there is less things to go wrong,and less chances of leaks,and clutter is reduced. It also tidys up the engine compartment a lot,you dont need that top chaarger hanging way off the engine,with the spacer,it stays tighter to the head,and looks better internally gated. I do think the tunablity of an external gate is better though,and the amount of exhaust that can be diverted around the exhaust housing is greater with an external gate. I know that you can over gate the secondary and literally stall it,ive seen it,and it kills overall boost.

 

[BPonci]

You can use a 12cm housing that is heavily modified. I have one under the bench. Flows good and is controlable. Its all in how you present it into the large charger.

 

[mjoppie]

just how much bigger would it need to be? i do have acess to a machine shop and am pretty decent with them,(one of my 4 year things in school) i see the hole could be bored much bigger but the limiting factors are (in my opinion) the size of the flapper and the front intake to the wg could be opened up to flow a little better. what do you mean by overgating the seconday? bypass to much around the little turbo, or not enough? or do you mean wg the big turbo? i think im going to try and machine the 12, just for sompthing to do. its free and gives me sompthing to do and the worst i can do is end up throwing it away. what is the little flapper made out of copper, or steel? i tried to make sompthing of the "turbo 101" class but dont quite understand it all, does the air ratio mean 1:1 one pound in the exhaust = one pound boost in the intake? or is that the volume it takes to drive the turbo to get one pound of boost?

 

[Jim Fulmer]

Matt, build the dang things and don't read in to it, all the info to do this is in the TDR achives, I've posted tons of info about my first setup and it's just like the one's your building. I didn't have trouble controlling boost till I put a real pump on my truck, when I first got it going I actually had to hold the wastegate closed(driving the 35 harder) to make the boost (55-60psi) I wanted, the biggest pain was getting all the parts together to do the setup.



Jim

 

[mjoppie]

sounds like a good plan, i planned on just building them, but i love to learn about these trucks and the different systems used to make them perform at different levels. just trying to gather as much info as i can so i can make informed decisions about what to do. i made one set and it wasnt quite right so im just looking to improve on what i have done in the past and trying to learn from my mistakes. i like to see what worked for others and what didnt. you have my dream setup right now and would like to build towards that goal but want to take the right steps in doing it. 804hp in a daily driver almost brings tears to my eyes in envy :-laf thanks for the blunt imput its kinda what i needed so i would stop doubting myself as i always do. thanks again for laying it down for a simple man to understand Oo.



matt

 

[HoleshotHolset]

I like Jim's advice - less talk... more action!



I'm with Matt, though to a certain extent - I research the heck out of things before I embark on such a project.



I've still got a brandy new HT3B (36cm²) in the box... maybe it'll end up on the blue truck over the winter... OR - the green one.



Matt

 

[mjoppie]

or you could donate it to matts turbo project LOL :-laf i really needed the extra oomph to get this project started and you guys are a huge help, i think ill show jim up at some event this year maybe after i hold him captive and make him trade me motors Oo. but as the turbo project goes its in the process, i will try and post some pics of my truck for you to see what im playing with. thanks again guys, probably be stock without ya!!!

 

[Jim Fulmer]

804hp in a daily driver almost brings tears to my eyes in envy



Envy is not a good thing, if it were me I'd stay at 550 hp or so, it's allot of fun and the Maintenance level is allot less.



Jim

 

[mjoppie]

yes 550 hp would be fun but wheres the challenge in that :-laf my truck will probably stay right around there for quite a while. theres a lot of other things i need to do to the truck and heck, if i do like it maybe i might just keep it there. oh who am i tryin to fool it will probably be a never ending battle until its either burnt to the ground or runs me into collections hehe :-laf

 

[Idaho CTD]

Gypsyman,



A 4LHR isn't near as nice of a turbo as a HT3B. Their housing sizes tend to be large and are slower to spool.

 

[Gypsyman]

One last question. After reading over a hundred threads in the last three days I now understand the basis for the HT3B. My question is why is the 26cm the most common? Will a 22cm be to hard to control for overall boost? It seems to me that a 22cm on a mild 3rd gen (TST + pressure box) would be easier to light. Is this incorrect? Most of the kits and the home jobs I've seen use the HX-40 and the HT3B/26 but it seems to me that for mild bombs and especially on the 3rd gens (which only fuel when they see boost) for towing that an HX-35/14 and a HT3B/22 would be a better combo for achieving off idle boost.



Any thoughts?



Richard

 

[mjoppie]

if im not mistaken i think that the piers towing twins use that housing, thats what he told me anyways, as far as boost control youd have to talk to someone a little more informed.

 

[Gypsyman]

I'm going to keep trying to get thru to Piers. I know how busy he is. What makes me ask is that for the 3rd gens he only lists the 40 and the HT3B/26. I can't find anyone running this setup locally to see what rpm they start to light at and I'm curious as to why that combo is all that's listed for the newer trucks while there are options for the 2nd gens.