Twin questions

[Piers]

"some" 97 blocks have the twin oil drains, never seen any older than that have them though.

Not to rain on your parade, but whoever told you you would see 1-1 drive verse boost at 70psi with a 12/35 and 3b/26 housing needs new glasses or a better gauge. The HX40/16, 3B/26 gives 1-1 at 60lbs

I personally would recomend setting your 35/3B combo to 50psi for best results, that will still give you good bottom end, great midrange & decent top end

 

[Cooker]

Piers thanks for stepping in and letting me know I wasn't losing my mind

 

[Pmaloney]

Not raining on my parade at all, I've just been doing so much reading I obviously remembered wrong, which is fine 40-50 psi is where I want to be since I dont know if I will be oringing anytime soon, just studs. I want to do the oringing now but dont know if I want the truck down for weeks.

 

[**ICEMAN**]

As I said originally I was thinking the truck was a 1996 and I thought at that time my info applied. Now I guess I don't know jack

out of curiousity i had to check a few trucks to find out for sure. no intentions on trying to prove you wrong or anything. just letting you know what i found.



our turbo god stepped in and gave us facts :-laf

 

[Pmaloney]

Piers, I just read through your post again and noticed you said a 12/35, I am using my HTB2 which is a 62/12 what pressure can that bring me to without excessive drive pressure? Thanks.

 

[RBratby]

35/12 is an hx35 with a 12cm2 housing. your htb2 still has a 12 housing with a 62mm compressor wheel. if you want to lower your backpressure go to a bigger exhaust housing.

 

[Pmaloney]

I understand that the 35/12 is a hx-35 but what I was wondering was that the fact that you are feeding air into a larger compressor housing so wouldnt that create higher boost with less drive pressure or would it just be more volume? I understand that compressor wheel design probably affects that also. Not positive on all of this as I am still learning the compound turbos.

 

[RBratby]

i am still learning myself. i would think that the back pressure would still be the same because the exhaust housing is the same. if you went to a bigger housing then the back pressure would go down.

 

[swankmetal]

just a note. i could be way off here, but my observances have been that compressor efficiency is what effects back pressure. i have been running a back pressure gauge while fooling with my single turbo. ran three different compressor wheels, all with the same 12 cm exhaust housing. 54mm (stock) at 40psi boost= 75psi of back pressure, 58mm (out of an old hx40) at 40psi boost= ~60psi of bp, and with a new 6 blade, 60mm wheel at 40psi of boost= ~48 psi of bp. my brain hasn't gotten a firm hold on this yet, but from what i've seen from these different readings, i'm thinking that the map of the compressor has a lot more to do with it than the exhaust housing. i don't know if this holds true for twins though. oh yeah, all those readings were right around 3000 rpm.



dave

 

[Mark_Kendrick]

I understand that the 35/12 is a hx-35 but what I was wondering was that the fact that you are feeding air into a larger compressor housing so wouldnt that create higher boost with less drive pressure or would it just be more volume? I understand that compressor wheel design probably affects that also. Not positive on all of this as I am still learning the compound turbos.

The larger wheels help but most any single above 45psi is going to have issues. That is the reason Compounds work so well. 45psi is a 3. 5 or so pressure ratio. right where most turbos drastically fall off on efficiency. With compounds the big turbo precompresses the air to keep both turbos at or below 3:1 (output:input pressure) making 9:1 (3:1 and 3:1 again) easily possible which explains Maddog's 138psi of boost. at 45-50psi a set of well designed twins will be running 2:1 +/- on both stages of compression usually giving a crosover point (where drive pressure exceeds boost pressure) between 60 and 70 psi.



Larger compressors do allow higher pressures(slightly) but they actually move more mass which allows you to supply more flow(mass os air) at the same pressure.



When using the larger compressor on the secondary stage (the small turbo) you must increase the size of the primary compression stage. An HX35 is a . 46 kg/s turbo (recently updated specs they were . 34 kg/s). Turbonetics supplied me with a BHT3B map showing . 76kg/s. Given the . 34kg and 20% for inefficiency . 34*2. 2=. 748 making the BHt3B almost perfectly matched.



with the upadated numbers . 46 (hx35) and . 53(hx40) puts the hx40 solidly outside the map for a BHT3B and the HX35 on the ragged edge of it(below the 70% efficiency mark). I am assuming that your 62mm wheel is bigger than the HX40 (using a holset hx40 wheel would easier and cheaper since they have the same core. I don't know the size of the HX40). What this boils down to is you need to step up to a little larger charger to compound that turbo properly. The next step up is a B2 from Turbo Auto Diesel (or their distributors ).

 

[Gypsyman]

So what would you use for a primary with an HX-40.

 

[Mark_Kendrick]

So what would you use for a primary with an HX-40.

I normally wouldn't . I would use a 40 compressor on a 35. a B2 would work well. the B2 is shorter in length, flows better, rotates opposite the 3b and spools better. It makes the fit easier. With a B2 you get to keep the heat exchanger for autos (94-02), have more clearance at the oil filter and more room for a downpipe than a 3B.



I'm not a fan of HX40's at high hp. . a blown hose buys a turbo. I would rather use a Schwitzer hybrid.



FWIW,

Mark

 

[NPloysa]

Mark, when we twin-turboing Clint's Segway?

 

[Mark_Kendrick]

Mark, when we twin-turboing Clint's Segway?

:-laf. .



I priced those online and :--) :--) wow are they expensive. Way though

 

[Jim Fulmer]

Poor Guys

Half Truth, half BS on this thread!



Jim

 

[swankmetal]

???? which half is which, jim?

 

[Mark_Kendrick]

Half Truth, half BS on this thread!



Jim

WHICH HALF WOULD YOU BE?



I forgot, Jim has put togeter a couple of compound sets on ONE p-pumped automatic truck that has not been under 500 hp. So he knows all about all turbos in all applications and power levels. Has tons of experience tuning them for all kinds of applications he's never tried.



I really get tired of you following in every thread with little smart *****$$ comments. here's the last thread he chimed in on. .



https://www.turbodieselregister.com/forums/showthread.php?t=123023



No worthwhile content there either.



Try contributing to the discussion for a change.



The next post should be the one where he tells every event and how much hosepower he made in the 2wd automatic truck he drives UNLOADED all over the country. Oh, and I'm supposed to take credit for all of his accomplishments since he's never gotten help from anyone on anything. Try taking 36' goosneck with you next time.



Sorry for the distraction folks. I felt the need to stop the discussion before it started AGAIN!!



Back to the topic...

 

[Pmaloney]

When setting up twins have people found it best to wrap the hot pipe from the two turbos to help keep the heat in the pipes? Also how about the cold piping? I thought I remember reading somewhere that exhaust wrap can help a turbos efficiency. Could be smoking crack to though :-laf

 

[CATCRACKER]

might want to wrap it so when the 40 turbine comes apart it will help in keeping it out of your lap... :-laf :-{}



just joking about the 40 but i have seen it wrapped and have heard that it make very little/ no d/f. it might help keep some heat away from your firewall computer and wireharness etc. some twin setups i have seen the down pipe out of the top turbo gets pretty close to all that stuff. just a thought.

 

[Mark_Kendrick]

When setting up twins have people found it best to wrap the hot pipe from the two turbos to help keep the heat in the pipes? Also how about the cold piping? I thought I remember reading somewhere that exhaust wrap can help a turbos efficiency. Could be smoking crack to though :-laf

You'd be better off wrapping the crack pipe than the charge air tubes :-laf:-laf



Seriously, retaining heat in the exhaust tubes helps spoolup and efficiency because you get less energy loss from the exhaust stream... more is available to drive the turbine. You also get lower underhood temps which never hurts.



you want the heat to leave the charge air tubes so the air going into the motor is as cool as possible. Wrapping them would be counterproductive at worst and ineffective at best.



I prefer to ceramicoat instead of wrap. Some wraps can hold condensation against the exhaust pipes and cause rust/decay. I don't wrap mine because its a PITA and they're usually not on my truck for more than 6mos. I'm always selling the demo models .



FWIW,

Mark