I highly doubt that any of the aforementioned relationships are anywhere close to linear in nature.

 

Josh, I really like your enthusiasm for the planning stage on this. Especially the part where you're researching and planning, instead of throwing poo at it and seeing what sticks.

As far as not finding info on an S258, that is probably because you should be looking for an S257. It's a Borg Warner S200 series turbo with a 57mm inducer. The newer sxe line includes a forged milled wheel, lighter, stronger and cheaper than a billet wheel. It is not, however, a vgt. Just a super light fast spooling turbo. Justin at R and D sells it as the mildest upgrade with some fancy ceramic coat.

As far as compounds being simple, I think you're right and wrong. Don't forget about oil feed and drain lines, mounting brackets/ pedistal, and the tough part, making sure the hot side doesn't have pin hole leaks from welding and designing it so that all of the insane temperature changes don't cause it to crack or put a lot of stress on the turbos. Then you have to find space in the engine compartment, up top, for both turbos. Mounting one or both under the truck is no good unless you have them drain into a separate resivior with an electric sump to move the oil back to the pan. Again, if this is the route you want to go. Don't let me discourage you. It's your truck, it's been done, it could be a very fun rig to drive when it's done. And I'll cheer you on the whole way. I just don't want you to short change the complexities of the system and end up working on the truck forever instead of driving it.

vgt controllers: I stopped looking a couple years ago. But at that time I had only seen one on the market that promised good vgt performance, reliability, and the ability to operate one like it should be operated. It had a brain box, a lot of sensors to install, a USB interface to tune it, and it came with a free engineer to get it all dialed in to your rig. It was geared toward fleet fuel efficiency. And cost more per unit than most of our trucks. The others I'd seen used rudimentary step functions to give you 6 or 8 predefined exhaust housing areas. Didn't take into account all of the variables you'd like them to and could offer great driveability in ONE driving style. I hope they're better now. But I gave up.

As far as your cylinder pressure math goes. Your method could work. Or it could work on one number set. Or not at all. I don't know. To do it right when looking for a conversion, you'd have to take into account the non linear nature of compressed non ideal gases, like air. If this was a thermo class that would be a final project type question. I looked through the home office yesterday for my thermodynamics of internal combustion engines book. But it looks like it never got unpacked after I moved. The still packed boxes are totally unaccessible until I finish construction on my basement. Which won't be starting again until I'm off crutches and learn to walk again. In the meantime you could run a search for diesel engine cylinder pressure calculator. If some bored grad student or awesome gear head has built one; you could run Justin's numbers through it at red line and try to reverse the max cylinder pressure to 1000 ripums. Might be a good start.

Any way I'm off to go get fitted for a temporary peg leg. If that works out I'll at least be able to feed myself for the coming months. And I won't starve to death before I see your truck finished!

 

Thank you! I have the technician approach to fixing things and building. While it can be slower, at least I'll know WHY something did or didn't work, instead of having 3-5 variables and guessing. One step at a time in the planning phase, too!

Ah, you got me. I definitely wasn't thinking about the drain lines. Those really are a pain. And the pedestals. And yes space will be an issue... this build will be mocked up outside of the engine bay to get things as tight as possible to the block, if and when it ever gets done. Won't be for a while for sure. Would be a pretty sick winter project though. For the welds and such I did my N/A exhaust which held up for a couple years and is still great but now I have a turbo, which I also welded the exhaust up for. Also holding up great so far. Hopefully that trend can continue for future fun!

VGT controllers: the market seems better now. Of the three that I saw, at least two of them had constant input sampling(I want to say ever 15ms?) and so were nearly infinitely variable. But also if you sent the unit in they could do custom stuff as well, for free from one vendor and not sure about the other. So it seems that they are much better than when you researched it before. They ALSO sell the step-version like it's a good thing...not sure what that's for but not me.

Well that's a little unsettling...actually sounds like fun without all the math.

Well I'm sure they aren't too. But it's a start and maybe someone that knows can chime in and keep me from guessing!

 

Could always do a VGT in a compound setup. I have seen that before and it spools like crazy! Anyhow, what other controllers are you talking about other than the Banshee controller? The Banshee is the more simplified one correct...

 

Yeah the Banshee II is the predominant controller. Seems to be the cat's pajamas for our diesel application. Apparently he does all his biz through facebook/email. Can't find a homepage link anywhere... But his rep seems to be super solid. He even let all users of the Banshee I upgrade to the Banshee II, and only pay HIS COST of manufacture. Wow.
The other two were just ones I found poking around. Didn't keep the links as I didn't care too much and VGT wasn't the purpose of this thread. Although one of the other's seemed pretty solid, if I find it again I'll link it.

Holy cow VGT compounds?! You must be thinking to make the VGT the smaller turbo?

 

Yeah the VGT would be the small turbo. Most are around 61mm. Throw a big turbo on that and it would spool like crazy. I have seen it on both Ford 6.0s and Duramax. It would have to be tuned to keep drive pressure reasonable but with a custom controller it would be easier. I would actually prefer one of the more intricate controllers if I were to do it though.