only for the 3rd gens
at 600 on a 12 valve, the bd's get HOT!

 

So Guy's what would you run for a primary under a 62/71/13ss??

 

Well, I'm considering that very turbo, and for a primary, I'm looking at either a K31 (housing is 1.24 A/R, if I remember, plenty large) or a Garrett 4202 or 4508.

The 4202 Garrett would flow enough, but I think it might be a little constrictive for the flow. The 4508 is what I'm favoring even though it's technically a little too big.

Bigger turbos are generally more efficient for a given requirement. A larger compressor spinning a little slower will be more efficient than a smaller one spinning faster.

The penalty of course is spoolup. But it's the age old compromise-- you can have fast response or good efficiency, but not both. All you can do it try to come up with the best combination of compromises for your particular application.

jh

 

Thanks for the info.

 

Justin,
Lots of misconceptions out there about twins and what works best! I did not realize how many till I got these BD's (the only engineer designed twins available to us, AFAIK). For example I realized the top turbo is best left set up for max boost (near top of MAP). This creates lower EGT's and lowest drive pressures. My secondary wastegate came from BD set at 40 psi!
Also, both turbos do not necessarily spool up together. The top turbo handles initial spool up and the bottom comes in as exhaust is by-passed to it.
And, a hugh balancing problem with twins is controlling the temps of the compressed air coming from the primary..... often well over 350*.
This is where matching turbos comes into play.

Unfortunately, BD's engineer has stopped sharing on public forums. I got to speak with him once (luck of the draw). He told me he got sick of people arguing with his statements instead of listening and trying to understand what he had to say. i sure wish more expert info was available.

RJ

 

Good info Rowland.

They must have done something right because they have handled everything I've thrown at them and grown with me since I was at about 400 hp. I don't know whether they'll keep a 12v cool or not, but they keep my 24v comfortably cool while towing heavy even with big injectors.

Thanks for sharing, Matt

 

Now to find the cheapest vendor for the B-D twins?????

 

Yep !

 

I ran them at 400hp with my 12v, and they ran cooler, spooled faster, and towed nicer than my HX40/B2 setup...but I really doubt I could have made their advertised HP with them...temps would have been too hot for me.

With the HX40/B2 setup, the temps actually got cooler when I bumped the fuel up over 450hp...then I took them off and sold them!

Chris

 

Am I missing something obvious? I can't see how I misconceived because I agree with everything you said. I don't see any disagreement between what you posted and the excerpt of mine that was quoted. It wouldn't be the first time I've missed something obvious though After all, I'm the guy who will spend 5 minutes looking for his keys only to find them in his pocket

I don't think twins should spool at the same time. I don't think it's something you CAN achieve, even if a person was misguided enough to think it's a good idea. How can you spool a larger turbo with less drive energy at the same time as a small one with more drive energy? It seems to defy reason to me.

My conception of twins is that you'd ideally have the maps overlapped in such a way where one compressor is entering the sweet spot of its map as the other is leaving it, therby balancing efficiencies thoughout the operating range.

For example, let's look at the map for a GT4088 (just as a hypothetical):


If I want to operate this top turbo at a PR of 2.75, then I can see that's it's nearing the "sweet spot" of its map at around 50lb/min. Past that point, it's beginning to lower in efficiency. The GT4508 appears to be a good match because it's increase in efficiency at this mass flow


We could also select as a large charger a bigger unit. A bigger turbo in this case will have a larger operating range, but less efficiency at any given point in the operating range. In other words, we can either optimize for efficiency within a somewhat narrow operating range OR we can give up a little efficiency and go for a broader range.

Compare the GT4718 map below:


With this big turbo, the compressor is just coming out of surge at 50lb/min range. Garrett's "recommended" twins set it actually the 4718 big turbo with a 4088 on top. This is the latter scenario where you have a huge bottom charger just coming out of surge when the top charger is leaving it's center efficiency range.

I think the Garrett method has some validity (i.e.-- bigger than "normal" bottom turbo) because you have to keep in mind that the top charger has efficiency losses. For example, say your top turbo is operating on the map where it's making 50lb/min with 70% efficiency. That's means that only 70% of what goes into the turbo comes out at 50lb/min (the rest shows up as more heat). Thus, we have to supply that top turbo with about 71lb/min at the inlet to get 50lb/min out. So we go back and look at the at the big charger's map at the 71lb/min range to find out where it is operating, and we seee that the 4718 is just about to enter the center efficiency range at this massflow.

So that's how you size the massflows. But the PRs matter, too. This determines how much pressure you'll need to get the massflow to the top charger. The higher the PR, the hotter the discharge temps will be and the more PR you'll have to run to compensate.

Needless to say, it gets pretty complicated, and I'm glad that someone like BD has bothered to put together such a well-engineered kit for our trucks.

Justin

 

Not missing anything! I was agreeing with you (trying to anyway)... about lots of counterintuitive misconceptions about twins!
I was just adding to what you said....for anyone interested!

RJ

 

So is a S400 with a 23cm housing a good match for a S300 based 62/14. What about a 26 housing.

 

OK, I think I need to cross-check my reasoning.

I posted above that compressor inefficiency shows up as heat and thus we need more mass flow into the compressor than out. I postulated that 50lb/min output of the small turbo might require 72 lb/min in to produce.

Well, I was wrong. The reason is simple: the maps are "corrected" already. That means they account for the inefficiency of higher compressor discharge temps.

Because the maps are corrected, we can assume that 50lb/min IN= 50lb/min OUT.

This really simplifies turbo matching. Now, turbo matching just becomes a question of how much compounding you want and where. Think in terms of compressor maps.

The question then becomes: how much do we want the compressor maps to overlap? As I proposed earlier, Id say that you'd want the compressor maps to overlap such that you have an operating range with the centermost efficiency island on either side of your operating range. Referring to the maps above for the 4088 and 4718, we'd have an operating range of 45-90 lb/min. As we increase mass flow from 45lb/min, we "fall off" the map of the small turbo and "climb up" the map of the big one. This gives us an operating range of 375-750hp roughly with high efficiency.

If you don't need such a broad HP range to be covered, you can narrow the "operating range" such that the two centermost efficiency islands begin to touch and you end up with one big island in the middle. This is what you'd gain by choosing the smaller 4508 primary instead of the 4718 to hang underneath the 4088. Now our "operating range" still starts at 45lb/min, but only goes up to 80-85lb/min range. In return for this narrow range, we've gained a little spoolup and efficiency at the cost of HP support-- this setup will only support a "paper HP" level of about 625.

Now we've got a well-matched setup, but they're too big to be truly useful. The small charger's center island shouldn't start all the way out at 35lb/min. We could gain a little response by going to a smaller turbo like the GT3782:




This turbo would do well with even the 4508, but it would be better with 4202R. This would give better spoolup and support over 500hp on the centermost efficiency island.


As always, this is just thinking out loud-- I could be totally wrong, but this is how I learn, so I apologize now for all the effort you just wasted in reading this....

If you have corrections/counteproints, please offer them.

Justin

 

The question is are you driving the truck to work aka daily driver or a tow rig. If you determine to go for more power down the road put a S400 on the bottom of your existing turbo. If you want BD twins for fast spooling towing twins, decent 575 rwhp max power. Go BD. If you want to rule the diesel streets and tow go bigger on the turbo's. My twins are old school. They spool ok and man you can run big sticks and tow all day long. The spool-up on a s300 and s400 turbo like your thinking isn't that bad. Sorry I like big turbos, they hit harder above 2k rpm's. It makes you forget about the boss for 2 seconds.

 

My truck is a DD and I tow about 4 times a year. Looking to go to about 500 hp.