Compound Turbo 6.5L

[6.5L]

Well it seems that there is some argument going on about twins, so let's just get this out the way here and not so much hijack another thread. I can honestly say I have sure contemplated it, but I simply do not have enough practical use for it. I am just going to throw out my concept of compound turbos. Yes, it may be wrong, it may not be factual at all, but it is the impression I get. Keep in mind I am young and stupid So here it goes. Compound turbos to me increase the efficiency of the entire turbocharging system. Hypothetically, It would be like trying to run a GM-3 at 30psi. It is hard on the motor, hard on the turbo, and the GM is already well out of it's efficiency range. Now, if you were to run compounds, each turbo would only have to work half as hard to create boost, so say you compound with an ATT or something. Now each turbo would only be supplying 15psi, and the amount of air substantially increased, and also it brings the GM-3 a bit closer into it's efficiency range. Now, I am by no means saying that is an ideal setup, because it is not. Let's face it, the GM-3 kind of blows. But take the same concept with something a little more realistic and that runs less back pressure to begin with, like an HX-40 or something (I am not sure how efficient those are, but you get the idea) and it would be a pretty golden system. I believe the twins would also spool a lot faster/earlier than say a large single turbo. The downfall is not many of us are running enough fuel to make a set of compounds practical. Yeah, maybe a GM-4 with a GM-8 would be fun, but you would only be able to practically run about 20 psi out of the whole system, and back pressure from the GM's is not all that good. The practical use of twins to me is if you are running enough fuel for about 40psi+ of boost from the system, something I really wouldn't trust on a 6.5L to begin with unless it had enough supporting mods to handle it. Below 40psi+, it just seems like it having a set of medium-sized twins would be pretty impractical, and you wouldn't be using the turbo's to their true potential. I think for most of us, a medium-sized single at the most would be just fine. If you are going for all out performance on the strip or just making big numbers with a modded pump where you need extra air volume, I can see a set of twins being practical. Will I one day have a compound turbo 6.5L? you bet ya! Will it be practical? Not a chance. But I enjoy being different. BY THE WAY!!! if you post, refrain from rude remarks. We are not here to argue back and forth like children, but to piece together the puzzle and increase the knowledge of the system for all.

 

[great white]

Well it seems that there is some argument going on about twins, so let's just get this out the way here and not so much hijack another thread. I can honestly say I have sure contemplated it, but I simply do not have enough practical use for it. I am just going to throw out my concept of compound turbos. Yes, it may be wrong, it may not be factual at all, but it is the impression I get. Keep in mind I am young and stupid So here it goes. Compound turbos to me increase the efficiency of the entire turbocharging system. Hypothetically, It would be like trying to run a GM-3 at 30psi. It is hard on the motor, hard on the turbo, and the GM is already well out of it's efficiency range. Now, if you were to run compounds, each turbo would only have to work half as hard to create boost, so say you compound with an ATT or something. Now each turbo would only be supplying 15psi, and the amount of air substantially increased, and also it brings the GM-3 a bit closer into it's efficiency range. Now, I am by no means saying that is an ideal setup, because it is not. Let's face it, the GM-3 kind of blows. But take the same concept with something a little more realistic and that runs less back pressure to begin with, like an HX-40 or something (I am not sure how efficient those are, but you get the idea) and it would be a pretty golden system. I believe the twins would also spool a lot faster/earlier than say a large single turbo. The downfall is not many of us are running enough fuel to make a set of compounds practical. Yeah, maybe a GM-4 with a GM-8 would be fun, but you would only be able to practically run about 20 psi out of the whole system, and back pressure from the GM's is not all that good. The practical use of twins to me is if you are running enough fuel for about 40psi+ of boost from the system, something I really wouldn't trust on a 6.5L to begin with unless it had enough supporting mods to handle it. Below 40psi+, it just seems like it having a set of medium-sized twins would be pretty impractical, and you wouldn't be using the turbo's to their true potential. I think for most of us, a medium-sized single at the most would be just fine. If you are going for all out performance on the strip or just making big numbers with a modded pump where you need extra air volume, I can see a set of twins being practical. Will I one day have a compound turbo 6.5L? you bet ya! Will it be practical? Not a chance. But I enjoy being different. BY THE WAY!!! if you post, refrain from rude remarks. We are not here to argue back and forth like children, but to piece together the puzzle and increase the knowledge of the system for all.

Ya kinda loose me there at the end. It sounds like you're using "twins" and "compounds" interchangeably (it's also kind of hard to read one really loooong paragraph).

This is not the case.

a compound uses a larger "atmospheric turbo as the primary and a smaller one as a secondary. The primary feeds it's output to the secondaries input. One of the advantage sof this system is the primary can produce more boost at a lower IAT, but since it's big, it's slow to get on speed. The smaller turbo gets on speed sooner and covers the "dead zone" while the larger spins up. There's a bit more going on than that, but in a nutshell....

Twins are two identical turbochargers feeding into a common plenum. Pressure does not add in this case. If they are both putting out 10 psi, the manifold sees 10 psi but the air mass can be doubled if sized right. The turbine is less of a restriction as now only one side of the engine (in a V configuration) because it only has to pass 1/2 the exhaust that a single did. Other side of that is now the turbo only has half the energy to extra to run the compressor.....

As always, there's much more going on in each system but that's a start on it......

 

[6.5L]

when i said twins, i was refering to the compounds. I think two turbos as twins. I dont believe that twins refers to the type of configuration, just the number of turbos

 

[great white]

when i said twins, i was refering to the compounds. I think two turbos as twins. I dont believe that twins refers to the type of configuration, just the number of turbos

Generally, if you say twins to someone it means two separate turbos. If you say compound twins it's one feeding the other.

But, there are no hard and fast rules. It just a kind of generally thing...


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[6.2 turbo]

Very low compression,like 11-1 and 80-100 psi boost would be my idea of compounds. I also think a DB2 with 4 plungers could fuel it. A DS4 with a DB2 cam ring would possibly be enough fuel also.

 

[buddy]

But that is just one way to utilize compounds. It can be used in different ways. Those are the only people that are doing it now, seeking that high boost, high performance.

Compounds are more efficient, its well supported in calculation and documented. Some day soon you will see it used instead of Variable Geometry turbos from the factory, with truck wars between brands and Government efficiency laws. And I am sure within the next year there will be a couple 6.5s running them. And Europe will probably beat us to the punch in BMWs or other such cars.

I do think twin should be reserved for running two identical turbos independently, then there is sequential, and then compound a different variation. But lack of recognition in the industry has made the term twin synonomous with any of the type of dual turbos.

 

[red]

for power efficiency compound turbo's is my favorite setup, with both high power applications and for towing. The key is to find a pair of turbos that work the best with each other in the rpm range your aiming for, with the fuel to back it up.

For towing you want maximum torque, so aiming to have the larger turbo operating at maximum efficiency or at least well into its powerband around 3500-3000rpm's would be well suited. The high power setups will probably want a larger turbo that is peaked out at much higher rpm's.

great white I've also seen the turbo's setup where the smaller turbo was the first, feeding the larger, only seen that on a few towrig setups though. Don't know if that would be a benefit or not if they were setup in that way.

A option for the towrig setups with the small turbo would be a gm4 or hx35. Building boost from just above idle then being well into their efficiency around 2000 rpm's makes them a viable option for the smaller. Then something along the lines of the ATT, hx40, or hx40II for the larger turbo to provide the boost from 2000rpm's on up.

hmm, might be diving into this after the truck is rebuilt this summer since I have a working gm4 and will be ordering a ATT here pretty soon.

 

[Twisted Steel Performance]

Not to hijack this at all, and I will be following this close.

Why doesn't someone with the shop, tools, and know how come up with a different manifold / header for our motors ???? Even if for a specific model year/frame set up/ it wouldn't need to be a one size fits all.

I have the know how, but no longer have the shop to do the R&R for this.

Other than some custom race builds that some have done, drag/pulling and such as that I have yet to find anything on the web about this. I think before I would try and work up a idea for 2 turbos, I would think that it would need to be looked at from the head out, meaning header/ manifold would need to be a LOT better than what we have to work with now.

If someone does know anything about a source for a different manifold then please let me know, I would be very interested to find some info, I think---- NO, I know that a lot of our trouble with back pressure & flow is in the exhaust system we are using.

Again, I don't mean to hijack or derail this, just adding that this area needs to be addressed at the same time I think.

Chris

 

[sshewins]

OK, do the two turbos in a compound set-up neccessarily have to be physically different in size? Before you laugh, the compounds on my C-13 are very close in physical size. Does or would that make one or the other work too hard or not hard enough? I know its not a 6.5 engine, but its still a compound set up.

 

[great white]

OK, do the two turbos in a compound set-up neccessarily have to be physically different in size? Before you laugh, the compounds on my C-13 are very close in physical size. Does or would that make one or the other work too hard or not hard enough? I know its not a 6.5 engine, but its still a compound set up.

Depends. Same turbos in series is a sequential setup. First used on recip aircraft to deal with thin air at altitude.

Keep in mind, just because two units are similar in size externally doesn't mean they are the same internally....


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[buddy]

Using a larger turbo is part of the efficiency factor. If you can run a non-gated turbo as the secondary large atomspheric turbo then exhaust flow out the tailpipe could be less turbulent and maintain better velocity. Compared to gating a smaller turbo and having the sources merge.

The HX40 would not be good choice as the large secondary, unless you get the 18cm^2 turbine housing w/ big 10-blade 85mm turbine and high trim compressor and still have it gated. I wouldnt use the GM8 as the primary small turbo, but not a bad choice because of how it spools and people have them available to try. I just dont know if the internal wastegate is large enough, as in its still a restriction just to have to go through it. An HX35 would be a better choice for spool and better flow, and the internal wastegate is convenient for testing it out. Some people might even consider the HX40WII as a small primary.

It really depends how much boost you are looking to get, and what fueling you plan to have. I personally would not run a 6.5 over 30psi of sustained boost, and from from limitations in block design, IPs and injection pressures compared to cylinder pressures I really would max one out at 40psi with 18:1 CR and 2700psi pop injectors. Not saying you can't make it work with more, but just not something I'd recommend for a daily driver or a reliable tow vehicle.

As for manifolds, more than one person has customized setups, for center mount, twin turbo or even the single in a Camaro in front of the engine. A user extrude honed his stock manifolds, which in and of itself helped a lot. Obviously going to have to customize some stuff for a compound setup too. A center mount primary to a side mount secondary would be pretty sweet. Of course that side mount would not be connected to the manifolds but to the exhaust output of the center mount primary.

 

[uniquediesel]

Going to try a T4 S366 (66/71/90) over T3 S357G (57/65/14), but building the setup where a T4 S472 (72/74/1.00) would bolt in place of the T4 S366 if I found it necessary.

 

[Twisted Steel Performance]

As for manifolds, more than one person has customized setups, for center mount, twin turbo or even the single in a Camaro in front of the engine. A user extrude honed his stock manifolds, which in and of itself helped a lot. Obviously going to have to customize some stuff for a compound setup too. A center mount primary to a side mount secondary would be pretty sweet. Of course that side mount would not be connected to the manifolds but to the exhaust output of the center mount primary.[/QUOTE]

I did check into extrude honing the exhaust manifolds, 800$$, not worth it for the stock ones, still looking for a shop that has built real headers for a 6.5 turbo, might never find a shop that could or would do it, but still looking. The extrude honing would help, but I think it would be a long time before I got my money back out of cost from it.

Chris

 

[buddy]

The problem is space in any 1500-3500 truck engine bay, hard to get any kind of other setup in there. And the amount of time and pieces to custom weld all of it together would probably end up being over $1000 anyway. I know extrude hone prices are ridiculous, thought they would have come down in last couple years.

The center mount turbo with a cowl hood seems like a decent compromise since they at least dont combine in the crappy passenger turbo maniofld with equal length to the turbo. That setup may be especially appealing if then trying to fit a compound turbo in there.

 

[red]

out of curiosity with the headers is there any other motor out there that has a similar flange to what the 6.2/6.5 use? (like a 454 for example)

 

[vdb11]

Check your 454. I had the same thought myself and IIRC, the bolts on a 454 manifold are across from each other in a straight line, whereas the 6.5 has staggered bolt locations. Although the 454 has four equally spaced exhaust ports (right?) so thats a step in the right direction. Maybe like 454 ratrod headers that combined in the center with a custom head flange and a turbo flange on the other end. Like buddy said, space is the issue. Are the 454 ports spaced about the same as the 6.5?

 

[Mike K3500]

I've got several sets of big block heads here as well as my old 6.5 heads, I could measure sometime today.

Mike

 

[Twisted Steel Performance]

The problem is space in any 1500-3500 truck engine bay, hard to get any kind of other setup in there. And the amount of time and pieces to custom weld all of it together would probably end up being over $1000 anyway. I know extrude hone prices are ridiculous, thought they would have come down in last couple years.

The center mount turbo with a cowl hood seems like a decent compromise since they at least dont combine in the crappy passenger turbo maniofld with equal length to the turbo. That setup may be especially appealing if then trying to fit a compound turbo in there.

Well, 1000$ wouldn't be so bad for a real good flowing set of pipes, I would even remove the inside of my finder wells for room, just isn't any where around here that has a shop that can custom build them that I know of, and my 91 has a little more room than a later model does....

 

[6.2 turbo]

A right side military header fits my Tahoe on the left side ,with the outlet front. Didn't check the other side yet.

 

[red]

Check your 454.

the big block is still in the truck, wont be out till this summer most likely.