Probably shouldn't have thread crapped so hard. Apologies.
Probably shouldn't have thread crapped so hard. Apologies.
There is a lot of good information in this thread and I hope people keep feeding more in. A constructive debate is a good thing.
dean1484 wrote: There is a lot of good information in this thread and I hope people keep feeding more in. A constructive debate is a good thing.
I don't know if its that good though. We've been over this before. I distinctly remember a rear mount turbo thread from years ago that went into the details of turbine sizing/matching. That was proper. This thread is kinda fluff
Then by all means, make it more useful. Contribute.
In reply to Fueled by Caffeine:
I've gotten sanity checking on my impression of lag in my WRX, notions of the drawbacks to attempting to intercool a supercharger (I'd been leaning towards an SC and it had never crossed my mind that you couldn't just throttle downstream; a combination of not thinking it through and assuming that the Eaton types did a fairly automatic/internal closed-cycle when the throttle shut), covered difficulties with SC idle (and got some indication that it's tameable)... Sure, I'd love to see more specifics on how to really get turbo sizing right, but some of what we've covered I've never gotten answered before. Also, while I've certainly heard of air/water (water/air?) intercooling, for some reason I've always thought of it as a weird niche thing. I don't know why... And while I should probably be more scared of it than I am, if it gets me what I want I'm inclined to build my own intake manifold for the purpose of getting the SC where I want it (if that's how I go) and minimizing downsides.
As far as how completely turbo lag can be banished, I'm heartened by what I've heard but bummed to realize that until I get to actually drive something that is as lag-free as I want it, I'll just be guessing whether I've made the right call when I start assembling the 2002, whichever way I end up going. (Or I may freak out and just build the largest-displacement N/A M42 I can manage).
Is this the rear-mount/sizing discussion you were referring to?
Fueled by Caffeine wrote:dean1484 wrote: There is a lot of good information in this thread and I hope people keep feeding more in. A constructive debate is a good thing.I don't know if its that good though. We've been over this before. I distinctly remember a rear mount turbo thread from years ago that went into the details of turbine sizing/matching. That was proper. This thread is kinda fluff
So instead of providing useful information or at least pointing us to the other thread you post this? Just dont read the thread anymore if it bores you. Or help us that are a bit less informed and post up some information that we can use so we dont bore you with "fluf"
Normally i try not to talk about things i havent done yet because i pride myself on more walk than talk when it comes to my OWN projects, but....
Since yall mentioned compound turbocharging, i figured id bring up my plans for my Dodge Caravan! (zing!)
RIght now it's a 2.5L 4cyl with a tiny td04h turbo with a 39mm inducer. I threw it together with spare parts, not because i was trying to actively select a properly sized turbocharger. The powerband is predictable.. What some have called evidence of 'proper' turbo selection. 
Anyway, i've long planned and collected parts to swap the van to a mitsu 6g72 3.0L V6 with an m90 roots blower on it. Lately, ive begun to consider the feasibility of compound charging with the M90 AND a turbo. There has been some misinformation about how turbos in general and compound turbocharging work in this thread, but instead of specifically addressing that with lots of typing im just going to talk about this theoretical setup which will already take long enough.
The roots m90 on the 3.0L will give significant 'instant' torque, and could conceivably (depending on how far you wanted to push the m90 displacement with coatings and case mods, etc vs using a larger blower) support 400+hp. But, the setup/tuning issues of a maxed-out roots setup have almost no appeal to me due to the heat issues and the driveability problems mentioned in this thread already.
But, if you kept the PR across the m90 fairly low, it wouldnt be horribly inefficient heat-wise. You could then use a larger turbo in a compound setup to effectively enlarge or multiply the PR of the roots blower (and its 'power potential') by feeding it air at a higher pressure, and get more HP through the blower with nearly the same heat contribution from the blower. The turbo could be sized to be as efficient at its low target PR as possible. Even if that ended up being huge, it would be a non-issue for an already-boosted 3.0 to spool it, and it wouldnt even matter when it spooled because a 3.0 that's already on 6 or 7psi from the roots blower is making ~300 tq already.
If you wanted to do an intercooler between the turbo and the blower, that volume would not be throttled and result in no real driveability change. If you were able to take most of the heat from the low-PR large turbo back out before it went into the m90, you'd basically have your total HP for only a little more heat than the low-PR m90 was adding by itself. You'd have ~300tq off idle, and depending on your intercooling you'd have massive HP potential from the large turbo. Something like 6-900hp depending on on how the compressor sizing ended up, but there'd be no point using any smaller than a 600hp turbo on a roots-blown 3.0L for a compound setup. It could probably spool a 1000hp turbo before 4000 rpm.
If there are any holes in this goofy idea feel free to point them out.
Keith Tanner wrote: Hal, looking at pictures of the engine bay, the basic SC/manifold package would fit. You'd have to take care of things from the supercharger out - the Miata has the throttle body on the other side so the intake plenum wouldn't fit. Still, the hard part is done - assuming there's enough room in front of the engine. What do you think, possible?
Unfortunately, based on the pic, I don't think there will be enough room in front of the engine for that setup.
The one I have on the Zetec in the Focus has the SC turned 90 degrees from the pictured package with the A2W plate above and then the intake manifold.
Other than the space in front of the engine problem I think it would work. The intake is in the right place to hook up the Throttle Body and it is drive-by-wire on the TC
In reply to Hal:
The powerworks was essentially setup the same way as the s/c ecotecs wasn't it? S/C, w2a, then intake plenum?
Probably similar packaging, aside from the zetecs having everything on the opposite side of the engine
... This thread is kinda fluff
So start defluffing...
Vigo, I can see what you're thinking. It's hurting my brain. There has to be something wrong with it, but I haven't come up with what yet 
Vigo wrote: Normally i try not to talk about things i havent done yet because i pride myself on more walk than talk when it comes to my OWN projects, but.... Since yall mentioned compound turbocharging, i figured id bring up my plans for my Dodge Caravan! (zing!) RIght now it's a 2.5L 4cyl with a tiny td04h turbo with a 39mm inducer. I threw it together with spare parts, not because i was trying to actively select a properly sized turbocharger. The powerband is predictable.. What some have called evidence of 'proper' turbo selection.
Exhaust Throttle or turn valve (directing flow between a compounded setup) would probably be a little simpler. I built a few, but have never been able to get an exhaust throttle to live for long.
Just noticed this thread.
I'm a fan of both, although I prefer supercharging for larger displacement engines.
Turbos got a bad rep in the early days when the lag was so bad that the BMW racers had to put the accelerator to the floor before they hit the apex of some corners, so that the power would kick in when they were leaving the corner.
Modern turbos, sized properly, offer damned good service. Ecotecs give essentially flat torque curves from around 4500 through 5000. They don't affect mileage - the supercharger is costing you fuel whenever you are running. Having said all that, go with whichever gives you the most fun project - and only you can decide that.
Swank Force One wrote: The correct answer is variable-geometry turbo setup.
Fixed that for you
I am surprised that the VGT hasn't come into this discussion more than it has. I guess no one is up to figuring out/adapting a control system for them (yes that is a challenge 
)? That is another surprise if that is the case because this is GRM. Holset's brand of VGT from the Cummins motors are dirt cheap and would do wonders on lower displacement motors. There should be some electrical engineer here that can figure it out right?!
In reply to jere:
It's certainly wobbled through my head, though I've had so much to learn that I haven't begun to ponder how to do something like that... Seems like once you figure out how to physically drive the thing, a relatively simple map could do better than fixed geometry without introducing a bunch of weirdness...
jere wrote:Swank Force One wrote: The correct answer is variable-geometry turbo setup.Fixed that for you
There's already solutions to control them.
My problem with them is that they're obscenely huge and heavy, and it's one more moving part (electronically controlled) to go wrong. A proper compound setup is largely pneumatic. (Though probably no lighter)
Porsche uses VNT technology in their new cars i believe.
In reply to Swank Force One:
Yeah porsche is the only manufacturer to still use them in a petrol powered car but get ready to sell your house and car to buy that overpriced turbo from them.
I think as far as packaging they wouldn't be that bad, you don't need a crazy twin scroll manifold and dual wastgates or even a wastegate at all. I think on FWD/AWD cars there would be plenty of space over the transmission, that would help with the weight distribution too. Also that would leave plenty of room for a full size radiator. One large turbo would be a lot easier to place than a big one and a small one plus extra pipe W/G.
Aerocharger used pneumatics to control their VGTs, if you didn't want the extra electronic control/headache that might be a thought.
I am curious as to what you control systems you are talking about. I have seen some less than ideal options around and some that haven't gone any where. Care to share a link?
jere wrote: In reply to Swank Force One: Yeah porsche is the only manufacturer to still use them in a petrol powered car but get ready to sell your house and car to buy that overpriced turbo from them. I think as far as packaging they wouldn't be that bad, you don't need a crazy twin scroll manifold and dual wastgates or even a wastegate at all. I think on FWD/AWD cars there would be plenty of space over the transmission, that would help with the weight distribution too. Also that would leave plenty of room for a full size radiator. One large turbo would be a lot easier to place than a big one and a small one plus extra pipe W/G. Aerocharger used pneumatics to control their VGTs, if you didn't want the extra electronic control/headache that might be a thought. I am curious as to what you control systems you are talking about. I have seen some less than ideal options around and some that haven't gone any where. Care to share a link?
Just going off my current FWD turbo car, i couldn't really put it above the transmission, as my intercooler piping and distributor is there. Would make for some annoying FMIC piping as well.
One of these monsters HAS been fitted to an MX6 GT or two...
Anyways as for controlling them, Megasquirt can do it.
And here's one of the other options. This company makes/made a standalone controller, and i believe this is it. Works/controls based on MAP, TPS, and speed.
http://www.xtremediesel.com/fleeceholsetvgtcontroller.aspx
Vgt. Is one answer but not the answer. I worked on a project with a compound setup with a vgt and a small conventional. We untilised a valve to change gas flow from one turbo to another. The reason for the compound was that we had a small engine with big eff and a big power needs. Nutty project, too bad it never went to production.
Let me get to a computer and ill type more.
I have two VGT 'projects' that have not gone past the parts collection stage. Both are t-25 based turbines. One has a tiny 200hp compressor side for my 1.0L Insight, and the other is one is getting a 400hp compressor side and a wastegate for my new yorker limo thing. The insight thing i know will work other than not knowing exactly when it will spool.
The other one i am trying because i want to find out if the vanes can make the small turbine able to use a large compressor, and whether the wastegate+turbine will allow similar performance to a larger turbine and smaller wastegate with more area under the curve.
In reply to Swank Force One:
Oh wow I had no idea MS was an option, this thread is going to get me in trouble.
In reply to Vigo:
I am guessing you are using the old Shelby style VNT? That should make a for interesting match with a 1L motor.
I have a conventional T-25 on my 2L NX2000, it has instant power as soon as you put your foot down (roast 1st and 2nd gear at stock gated 7psi) but it stops making power in the upper rev range.
The Shelby VNTs seemed like they would have been way too small for the motors they came on. I don't know much about them though.
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