HOHN

Soul, is there no 4.5" pipe available?

Back to wg theory:

Mike Holmen is right, I think. When you open the top gate, you are "unloading" the secondary (I like that description). But you're not completely eliminating the pressure-- you're just limiting it.

IMO, the ideal setup would regulate secondary TIP by adjusting bypass flow from zero to some set amount with such precision that TIP was constant across a certain range of RPM at hwy speeds/loads. This is not easily done in the real world, short of a PWM valve controlling the pressure to the wg.

Just as we have different pressures on the cold side (primary discharge vs secondary discharge), we will have different pressures on the hot side as well (exhaust manifold vs hot pipe pressure).

The ∆P across the secondary turbine is relative to primary TIP. If we're running that primary at 30psi (~ PR of 3), then our TIP at the primary will also be about 30psi. Thus, secondary ∆P will be somewhere around 20-25psi, assuming we're running 50-55psi total boost.

Now we come to real-world problems, like the difference between "opening pressure" and "regulated" pressure for the WG. If we want to limit total secondary TIP to 25psi higher than primary TIP, then we need to have a gate that "regulates" to 25psi.

Unfortunately, that means that gate will crack open as early as 18psi or so and start bleeding off pressure that we want to keep in the secondary.

So that leads us to a "gate" of some kind that reduces or eliminates the progressive action of the gate-- so that the gate doesn't "see" any pressure until we want to it have pressure to open up. This can be done with a Hobbs-switched solenoid valve. Or a gated ball-and-spring controller valve.

Being able to open the gate at one pressure and close it at another could possibly be of some advantage. I'm not sure how one might do this, though. Is there a pneumatic equivalent of a diode?

Anyway, I have to cut this short--anyone else care to finish my post or elaborate for me?

jh

Tate

You mean a check valve?

Philabuster

I remember reading in Hugh MacInnes book Turbocharging, about redesigning the wastegage actuator to eliminate gate 'creep'. I will have to dig out my book again and read it a bit more to elaborate.

paulb

Okay, a little actual information to supplement the theory. On a twin setup when you open the wastegate on the top turbo (secondary), the drive pressure (TIP) actually goes up to maintain the same total boost. You can actually see this happen on a drive pressure gauge. I am guessing that is one reason that soulezoo's twin setup came with the wastegate set so tight on the secondary turbo.

The theory used to be that you just want the top turbo to produce boost until the bottom one "lights" and then just get the top out of the way by opening the wastegate. Most people have gone away from that theory. By measuring a combination of TIP, boost and IAT, having the secondary working at the "high end of the map", and using the primary to keep the secondary in the map, works better. Not only for total hp, but driveability. Sizing the turbo's properly is the key to this.

Soulezoo, with Nathan at MPI designing your setup, you can rest assured it will work correctly.

Paul

Mike Holmen

Did Tim put down a 900rwhp on fuel or on drugs? Theres a difference. If Tim ran 900rwhp on fuel, thats some big power. If use you NOS you really don't need twins to make big power. We have a couple trucks in our chapter that run those numbers on a single, of course with tons of NOS.
I find if you run too big of wastegate the power kinda stalls and takes longer to build-up the air required to make power. Of course my truck is a long ways away from 900rwhp, but just running the 3B and fully opening the wastegate on either the Hx-40/3782r turbo, the truck would smoke more and build more egt's. The best setting for my truck is to run the wastegate at 24-26psi to start cracking the wastegate open. The gate should be fully open around 40psi. Of course mine truck is a street daily driver, dyno trucks or racing truck might be set-up different. My next twins are the 3782R/K-31 set-up. Latter this year, I'll try the biggest S400 and see for myself. Physically looking at all three turbos side by side the BTH-3B, the two S400's, and the K-31, there isn't a lot of different between them and all will make a great primary that will support 700 rwhp. Turbine housing sizing is really the biggest difference between them.

Mike Holmen

Honn, I found some pnuematic pressure 3 way/4way valve manifolds/switches cheap that could be triggered by an electronic hoobs pressure switchs. The biggest thing is finding a way to regulate how much pressure you can send to the wastegate actuvator once the valve opens. They are about $10. Buy two of the switchs and some pressure sensors, a two sided wastegate actuvator (one that you can pressure both sides), you can do some fine tuning and do what ever you can dream off. Of course the old fashion single sided actuvator works well too, just not as fancy.

soulezoo

Well the turbos are in. I can't post pics or give too much info due to some contractual concerns I was not aware of... I said too much already. Sorry. After Sept... I can divulge all.

The bottom turbo definitely spools twice as fast as the bht3b. No question. In fact, it spools as fast as my old hx35/12 with a lot of fuel thrown at it. 0-15 or 20 psi is just right now. No lag... none. I have not had it over 27 psi yet and guessing about 650-700hp. No dyno yet either. The top turbo is as fast or faster to spool than the old he341 with its 9 cm EH. Very, very nice turbos. The only performance issue I have ran into so far is a tendency to surge with the top turbo.. 2 or 3 gulps.. when at low/no boost condition at higher (over 2100) rpms. No bark at all. I have only gotten them to 60 psi so far, but it is a much, much cooler 60 psi than my old 35/3b set up. This is simply subjective by feeling intercooler surface temps by hand after flogging, but the difference is far too dramatic to dismiss with other theory. Egts in similar power settings in WOT are 200* lower at least; probably more. Cruising egts are 150* lower in most circumstances. With the old set up I could expect 4-5 psi boost in cruise on flat land, now it is 3-4 in identical circumstances. The bottom turbo is always giving me 2psi in that (when 3-4 is showing) and the old 3b would be dead or barely showing .5 psi. All I can say at this point is WOW!!

Mike Holmen

My twins can pull 60 psi in four seconds, with the BTH-3B. Its pretty amazing and I'll bet that it will spool with HX-35. Your twins would at least 0.5 to 1 second faster than mine. The primary really doesn't do anything until the wastegate opens, so its more related to how the secondary is set-up. The primary really starts to work after 20 psi of boost, once the wastegate is open. I can feel the 3b waking up and the boost comes on smooth after the wastegate opens. I still think that a ball bearing primary is over kill in my mind but if you want the best twins period and you got the $$$, it will improve the spool-up. As for air flow, more HP, I doubt it. The engine will regulate how much air it requires assuming your drive pressures are still 1:1, of course I still haven't tried a primary BB, but I have three years using of using twins daily.

soulezoo

I agree about the 3b starting to come on after about 20psi...and would rise pretty fast after that, was my experience as well. I also agree that the engine and the fueling ultimately regulates the total boost. That can be seen simply by manipulating the electronics and watching results. However, the two largest and irrefutable facts I have noticed on the "before and after" comparing the old 35/3b vs the new BB twins are: first, the primary starts to come on from the very start long before 20psi and before the wastegate opens and spools insanely fast. The second is although I may have identical overall boost levels (given same electrics settings and environmental conditions) but the air supplied is significantly cooler and therefore is supplying more lbs/min. And it is that lbs/min that ultimately supports the HP, not boost numbers (or even cfm) which tends to be more an indication of restriction of flow. The mechanic that fabbed the exhaust for me has his own 600 hp CTD (06) truck using BD towing twins and 100hp stix... he thinks these are by far the fastest spooling twins he's seen.

soulezoo

I have not timed spool to 60 psi... this is just relative SOTP feeling from the 35/3b setup. I'll have to get someone in the cab to time this.

As far as airflow... you have a point. 112-113 lbs/min is just that regardless of the name you assign the turbo or whether or not it is journal or ball bearing. How it gets there is the difference.

On edit: I left out the fact that on the same electrics settings and same 60psi with the old set vs new set, egts dropped by 200*... that is another indication of the "quality" of the air and one of the reasons why we go to twins from a single to begin with.

soulezoo

OK, it was bugging me all night about this spool time issue thingie... so I drove the truck to work to see what I could see. First let me qualify a few things: this is info only relative to just me and my experiences. I am trying to be as objective as possible and provide this as simply real world stuff we have wondered about but only speculated on so now I can provide some real input. What I offer, I do so as accurately as possible; I feel no need to exaggerate or play the "I'm better than you" game. I have what I have, it is what it is, and I'm just trying to help put some knowledge out there to answer a lot of the questions posed in the past about these ball bearing turbos and specifically their performance in a compound application.

RonA

Also need to keep in mind that the original poster has a 2nd gen and comparisons between 2nd and 3rd gens are not accurate. My old 62/.8 over K31 made about 80hp less than an identical setup on a 3rd gen when you compare egt to egt. Spool up cannot be compared either. A 3rd gen can make more power with a given size charger and spool it quicker.

soulezoo

First, allow me to set up some of the parameters for reference. Boost gauges: The main boost gauge is a 0-100 Autometer mechanical connected at the intake horn. The Boost gauge for the primary turbo is also autometer 0-30 electronic hooked up on the compressor housing where the boost elbow would be directing air to the wastegate. The TST also reads boost drectly from the MAP sensor.

I am running smarty tnt/r sw3 and TST on 2/0 for the purpose of this test.
For reference, at idle in drive with foot on brake at a stop, the TST (reading the MAP sensor, no boost fooler installed) shows 2psi boost. (It actually fluctuates between 1 and 2 psi on the readout, but spends most of the time reading 2).

So going down the freeway at 60mph with rpms about 1700-1750, boost level at cruise fluctuating between 3-4 as shwon on TST readout. The primary turbo is reading a steady 2psi at this time.

Not having a stopwatch and the difficulty of using one while driving aside, I am simply using the old scientific standard "one-thousand-one, one-thousand-two" to time. Yes I understand my "one-thousand-one" can be slower than some and faster than others and the actual accuracy of this dubious at best; however, I did the best I could here, please bear with me.

soulezoo

Point well taken....
And Ron, you must not have done a good job convincing Piers to send you my turbos...I got them anyway!! LOL

soulezoo

Anyway... cruising at 60 mph, blah, blah... nail it...

Primary (bottom) turbo goes from 2 psi to 28 psi in one second. Give or take .1 or so. Yes, "One-thousand-one" barely gotten out and primary is at 28psi from 2psi.

Slow down to 60 and do this again watching the main gauge for overall boost. nail it and...

From 3-4psi to 60psi in 2secs. maybe slightly less, say 1.8 sec. -- of course all is dependent on the accuracy of my counting.

I repeated this several times to check for consistency and accuracy. It was about the same everytime, the only real difference was the total boost the Primary was giving... it fluctuated between 27psi to 30 psi... spool times remained consistent.