twincharging question/argument

Purely academic... but i have to ask it here because asking on a place like vortex will net 10 pages of flames and no answers.

This all came from a video of a twin charged diesel benz on a drift course using an eaton M90 and a GT45? (i think). so we were hanging out in the shop and arguing how it would work, and nobody really won the argument... lol

If one were to twin charge a diesel, using a roots or twin screw, can it be done without any bypasses? not including the turbo's wastegate. Ive seen the TSI diagrams on how they use bypasses to make it a sequential setup... but thats not really what we were talking about.

which order would they be placed in order to not have a restriction?

If you go airbox --> turbo --> super --> intake manifold would either a roots or twin screw become a restriction or would it just compound the pressure made in between the turbo and super?

if you go airbox --> super --> turbo --> Intake manifold would the super become a restriction because the turbo (once spooled) wants to suck in more air than the supercharger is sending through it?

either way should be able to use a bypass to send air past the supercharger instead of through it once a certain pressure is met... but i was leaning toward the first one as the "right way"... or maybe both scenarios are true, and it NEEDS a bypass someplace. I dunno, thats why i seek the wisdom of TDIclub.

Not exactly related to what youre asking but I've never seen anyone use a bypass on the intake side on a compound or sequential tdi build. I think for a low revving small displacement diesel you're not pushing enough air volume that it would start to hurt performance noticeably. There may be some power to gain from it but probably not worth the effort/complexity it would add.

I remember their thread on STD, sounds like it's about to sling the blower to pieces at all times, haha

Fixed ratio supercharger does become a restriction when paired with a larger sized turbocharger, and running a blower inline with a tiny turbo doesn't make any sense for a myriad of reasons.

Old 2-stroke detroit diesels, when they started asking more and more from them in the 'silver series' of engines they started to run blower bypass valves. These are two strokes that need the blower for normal aspiration, but when they get up on the turbo the blower indeed does become a restriction.

Look at the blower like a fixed displacement vane pump, they can be used as pumps, motors, or metering devices.

Most factory applications of blowers in cars tend to have a vacuum activated bypass valve, solely for fuel efficiency, it will unload the blower just like you would unload a semi-truck brake compressor rather than letting it blow off out the overpressure valve. It is conceivable to use this preexisting bypass valve with different plumbing or springs to achieve the same performance related bypass.

Volvo penta has been doing this for years on their boat diesels. google it

If you don't bypass, you'll have a lot of parasitic losses (low mechanical efficiency) at part load.

The plumbing should be: atmosphere > supercharger > turbocharger > manifold. One charge cooler after the turbo is a minimum, but even better would be to put an interstage cooler between the SC and TC; this will reduce compressor work in the TC, reduce thermal stress in the compressor wheel and just generally make everything more efficient (read better IMP:EMP ratio).
The SC must be sized for the maximum target power output of the engine.


Can you do it the other way around: ATMO > TC > SC > IM? Yes, but the SC would be sucking through the TC while waiting for it to spool up. Here, the TC must be sized for the maximum target HP, and it is vitally important to put an interstage cooler between the TC and SC, because extra compressor work from the hot air at the SC inlet translates directly to more power that is taken from the engine crankshaft to drive the SC. Hot air can also damage the SC rotor lobes. Precisely because you cannot turn off the SC, it is best to plumb using the first method above, since this represents the lowest parasitic loss to compress air from ambient conditions.

Either way, a bypass valve is strongly recommended, unless it is a purpose-built race car. Otherwise, you will get unneeded boost pressure at idle, part-load, coasting/overrun, thus wasting fuel, and you can also build dangerous boost pressure because of the compounding effect of compressors in series and you can't just "turn-off" the SC without an electromagnetic clutch.

Edit: Recommended reading, already posted somewhere else, but although it's mostly about 2-stage turbocharging, there is some content on twincharging with an SC/TC together as well starting from p. 27. http://bit.ly/2I6Kuyb

this topic has come up many times, and while I agree with MOST of the reasoning to put the positive displacement blower up front, I still like the roots or screw at the end of the line - with bypass. You can't easily "turn it off", but if you reduce its pressure differential, you reduce the drive load accordingly. Bonus is that mech blower will spin up turbo when at lower speeds, both from induction airflow and increased exhaust energy.

Being a positive displacement device, unless you have a PID-controlled bypass around it, you don't have any control its pressure differential/ratio. It is what it is based on the compressor's displacement per revolution, drive ratio, RPM and the aspiration curve of the engine to which it is connected.



Edit: As you can also see in the above map, compressor efficiency of a Lysholm (screw-type), which tops out at 65%, is crap compared to turbocompressors, which peak in the mid-to-high 70s percent. Old roots blowers are usually even worse for efficiency, except Eaton's new TVS series ($$$$$):

I know a number of Cummins guys that’ve done it. The primary reason for blower first for them is sc rotor flex when the turbo achieves a higher pr. The sc does become a restriction to the turbo inlet, and that’s where a 1 way valve with a 2nd air filter is used. None of the trucks I’m aware of use any kind of unloader on the sc though.

Brad ponci built a pretty cool dragster with an f4 (I think) procharger, and I want to say a 91mm single turbo that would do 2:1 boost:drive pressure at well over 1000hp.

been a bit busy to reply but i have been looking at the things posted here. i appreciate the input and responses. i didnt realize there were that many ways to skin this particular cat.

i looked at the penta and i think it was johnson tower? boat engines. looks like the penta used a clutch and the johnson used a bypass in order to make it all work together.

i looked at a few cummins builds with twin charging as well. and also stumbled on an audi here: https://www.s2forum.com/forum/member-s-area/projects/50702-urs4-2-2t-avant-project/page94

i havent finished reading but it all but it makes for an interesting read with good pics. he started with just an hx40, but i died so he decided to replace it and mount a blower too... page 99 has a simplified diagram of the setup.

he used a second air filter and a 1 way valve to get around the supercharger becoming a barrier (due to fixed displacement) to how much air the turbo really wanted to suck in.

Yes, quite ingenious what the guy did on his UrS4 (BTW, I have owned 2 - a NA V8 Avant in Germany and a 2.2T sedan on this side of the pond, both `1994s, so I have a natural affinity for these cars ). The one-way valve is smart, there is actually an OEM part for this if, like me, you prefer aspects of OEM engineering: 059145901B.

If you can find a cheap TVS charger (good luck, so have I!), it will be great to connect it to get rid of turbo lag. And unlike what I said earlier, like what was done on the S4, it can be sized smaller with a big turbo doing most of the work at the top end; the charger only getting rid of turbo lag down low. That the turbo will start to overwhelm the SC and create a vacuum between stages, the one-way valve will then draw air in through a separate inlet. Just understand that your part-load FE will not be what it used to be because of the additional power used to drive the SC.

Edit: The VW 1.4 TSI Twincharger SC's PN is 03C145601B. eBay has a number of them and they're quite reasonably priced. I was always looking for something bigger like from the Audi 3.0 V6 TFSI, but I digress...
https://www.ebay.co.uk/itm/2007-VW-...GER-03C145601B-EATON-327215-EZ4-/272820012774

this was all just a thought exercise... im sure the naysayers would come out of the woodwork if i actually said i was doing this to a TDI... lol

i saw that one way valve in another thread about compounds or sequential turbos... which thread escapes me now...

"IF" i were to do this with a TDI, i would think a twin screw from a mazda millenia would be the choice, and put it where the AC is... Because those can be had for under $200 whereas a TVS is big bucks. Or BBMs twin screw G-lader replacement - also big bucks though.

for that kind of money i could just get the latest and greatest VNT... but i prefer to source my parts from the scrap heap. As for fuel efficency, if it gets better than an ALH/01M car, i dont feel bad about it...

That TSI charger looks small, eaton M45 size? M62?

The VW 1.4 uses an Eaton TVS (what model number or displacement I don't know), so of I were put an SC into a TDI, this is exactly what I would use. That it is relatively small is not a handicap, because I want to minimize parasitic losses and want the SC only to help with turbo lag down low and have a big TC automatically take over the job up high.

ahhh i didnt realize that it was using the TVS type of technology, I had just assumed it was a typical roots blower.

until that one, i hadn't seen any small (in physical package size) TVS superchargers.

My bad, the 1.4 TSI's SC is not a TVS, but one generation back (5th gen). This link gives a concise listing of all TVS applications.
https://www.wardsauto.com/news-analysis/five-tvs-programs-boosting-eaton-s-supercharger-prospects

Awesome resource:
http://www.roadkill.com/supercharge-everything-cheap-blower-shopping-local-u-wrench/

that roadkill article is exactly why i thought of the mazda millenia supercharger. the toyota previa one is a smaller package but i never see those... and the eaton, though plentiful and fairly cheap, is bigger.

ketchupshirt88 said:

"IF" i were to do this with a TDI, i would think a twin screw from a mazda millenia would be the choice, and put it where the AC is.

Click to expand...

Hey, I've got one of those on the shelf, want it? haha

[486] said:

Hey, I've got one of those on the shelf, want it? haha

Click to expand...

What are you looking to get for it?

Did you also have a half baked twincharge idea? hahaha
I hesitate to say "great minds think alike" because your signature threads show you are in a whole new league up from me...

If i didnt have work, school (CAD drafting) and 3 kids i might spend enough time in my dad's shop to catch up... but i doubt i'd ever get there. lol

my only concern with that unit is how i would do the oil... i wonder if i can just fill and seal it instead of running engine oil through it?

ketchupshirt88 said:

this was all just a thought exercise... im sure the naysayers would come out of the woodwork if i actually said i was doing this to a TDI... lol?

Click to expand...

I guess I could be considered as one of the naysayers, going back at least 12 years...
http://forums.tdiclub.com/showthread.php?p=1429088#post1429088

Nothing's changed, really. Parasitic losses are still there, but with a few more grey hairs I'm able to understand that people have different motivations for what they do.

With the benefit of technology I now think that it would be far more interesting to integrate an electric compressor with a conventional exhaust gas turbocharger to deal with lag à la what Audi has done, or an MGU as is done in F1 to recover some of the exhaust enthalpy.

But I truly am excited for someone who is committed to step up and do the first twincharged TDI here and I'm happy to lend any expertise.

Thread-jack here, but has anyone just plopped a scuba tank in the trunk, regulated it down to 30 psig, and blown the air right into the turbo compressor's annulus? If we're concerned with slow spool, just farkin throw a ton of air at it (in the direction of the vane rotation) which helps the turbo spin up, relieves parasitic back-pressure, and pretty much near-instantaneous boost. Set it up so that a solenoid just opens fully whenever requested boost is above actual. Shut it otherwise (by then the turbo is spooled or no longer needed).

Let the compressor act like the check valve. A common scuba tank will hold 80 SCF air (atmospheric) or 40 CF @ 30 psig/ 2 bar. Enough for a few sprints if the valve is only open for 2 seconds or so at a time, I'd hope.

Plenty have. Though nitrous oxide is the preferred compressible.

DMan1198 said:

Plenty have. Though nitrous oxide is the preferred compressible.

Click to expand...

No one's tried it the way I've described--I'd love to be wrong.. Volvo is using something on the exhaust side to spool there, but that's not alike. I see tons of posts about spooling the exhaust side, no one mentioned my way before.

Nitrous isn't used to generate boost, just used to increase the boom factor. I'm talking about using already compressed air instead of compressing it with SC or TC.

You'd need a fast acting solenoid that can support airmass flows for engine at the rpms' when lag is greatest (1500-2500 range)--I think that's why it's not been tried.

Back to the fun SC stuff. Sorry.

nicklockard said:

No one's tried it the way I've described--I'd love to be wrong.. Volvo is using something on the exhaust side to spool there, but that's not alike. I see tons of posts about spooling the exhaust side, no one mentioned my way before.

Click to expand...

Yes it has been proposed - at least twice:
https://patents.google.com/patent/US8434305
https://patents.google.com/patent/US20110083646

Edit: Volvo's approach doesn't make any sense to me. Why would I waste that pre-filtered air and inject it into the turbine, when I can do it to the compressor wheel, as you, Nick, and Honeywell in the above patent propose? Injecting air into the exhaust completely messes up the downstream aftertreatment, because you mess with the fine stoichiometry for them to work. Plus, when you expand that pressurized air to essentially ambient, it gets very COLD, again, killing your aftertreatment effectiveness.

Now, that stored pure, compressed air can have a much more direct, shorter-path benefit being injected into the cold side, where the cold expanded air also helps with knocking (in spark-ignition engines), and no deleterious impact on exhaust aftertreatment.

Nitrous isn't used to generate boost, just used to increase the boom factor. I'm talking about using already compressed air instead of compressing it with SC or TC.
You'd need a fast acting solenoid that can support airmass flows for engine at the rpms' when lag is greatest (1500-2500 range)--I think that's why it's not been tried.
Back to the fun SC stuff. Sorry.

Click to expand...

80 SCFM would be emptied in about 3 seconds when an engine aspirates the order of 5 sm³/min (177 scfm/min) at low RPM rising roughly proportionately the higher the RPM and multiplied further by the requested boost density ratio.

Part of the value of nitrous oxide is that it is stored as a liquid, so the equivalent volume at STP is much, much higher. In addition, more heat is withdrawn from the injected N2O by the latent heat of vaporization (374.286 kJ/kg) when it goes from liquid to gas, then when N2O decomposes to O2 and N2 above 850K in the combustion chamber, it is exothermic (gives off heat), so in effect it is acting like a fuel.

ketchupshirt88 said:

What are you looking to get for it?

Did you also have a half baked twincharge idea? hahaha
I hesitate to say "great minds think alike" because your signature threads show you are in a whole new league up from me...

If i didnt have work, school (CAD drafting) and 3 kids i might spend enough time in my dad's shop to catch up... but i doubt i'd ever get there. lol

my only concern with that unit is how i would do the oil... i wonder if i can just fill and seal it instead of running engine oil through it?

Click to expand...

I think I paid 50 bucks for it with the little dinky intercoolers and throttle body. Yours for that plus shipping, unless you can find someone passing through from the cities, then just $50.

I was going to use it on a datsun 320, draw through carbureted. Didn't get around to it before I got into EFI and turbos. I remember hearing the rotors are solid teflon, without gears between them just relying on them to act as their own gears, so that probably means the oil feed is for plain bearings. Meaning they would definitely need the pressure oiling.

Sounds like you're busy winning at life. More important than winning at building stupid timesinks of cars.

'Compressed air supercharging' has been done, in drag cars as a "look at me" sort of deal. Search it on youtube, you'll get a few videos. Gasoline or diesel doesn't really matter, it's all the same.

Interesting reading. Among other things, a supercharger driven by a CVT (not an altogether new idea, but one of the first to be studied in such detail to be part of a PhD dissertation) .
https://core.ac.uk/download/pdf/83960328.pdf