Compound turbos vs supercharger->turbo

I know a lot of guys go with a compound turbo setup. What would be the advantages/disadvantages of using a supercharger (something like a supercharger from a Pontiac Grand Prix 3.8) instead of a low pressure turbo?
I'd be using the engine is a conversion, so space wouldn't be an issue.

Uh supercharger needs power to make power.

cushioning the belt drive is a big hurdle to long term life
go look up the videos from manta about their blown mercedes, that blower just sounds like it's going to **** its gears out any moment

You don't say what your base engine will be but that supercharger may be 'enough'
on its own. Having ridden in a recent supercharged Audi, I can say they make great
power at any RPM.

Turbochargers and crank driven superchargers go together like peas and carrots... Examples like the Republic P47 and Lockheed P38 come to mind, and then later the R3350 that used exhaust turbines to add to crankshaft power.
cheers,
Douglas

supercharger will need the mechanical drive - i.e. belt. Response will be faster (no lag in spooling) but it will be a little less efficient since it's siphoning some of the crankshaft power. Turbo will be more power efficient but plumbing more complex with two turbos as with heat management.

What's the power goal? If your just looking for around 200 hp with excellent spool, a gtd1752vrk is hard to beat. Would certainly simplify things a lot.

turbobrick240 said:

What's the power goal? If your just looking for around 200 hp with excellent spool, a gtd1752vrk is hard to beat. Would certainly simplify things a lot.

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x2. Dual turbo, super and turbo charging are overkill/unnecessary until pushing out major HP

PakProtector said:

Turbochargers and crank driven superchargers go together like peas and carrots... Examples like the Republic P47 and Lockheed P38 come to mind, and then later the R3350 that used exhaust turbines to add to crankshaft power.
cheers,
Douglas

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ehhh pretty much all of those early turbochargers were for altitude compensation only

and the superchargers' impellers were barely a step above the flat bladed charge-beaters originally made to ensure even fuel distribution across all cylinders of a radial

kind of interesting to look at an old allison's compressor wheel geometry, they look positively ancient, kinda because they are.

They still made north of 35psi manifold on the Thunderbolt. And while the turbo aided in altitude compensation, it also very much contributed to power, especially if you set her to war power.
2 speed centrigufal supercharger being fed by a turbo... awesome for the day, even if the impellars were pretty much air beaters haha

I'd echo going with a 5th gen VNT and calling it good. GTD1752 or 56 would probably be pretty great depending on your needs.

As for the 'needs power' comment, nothing comes free, turbos take power to make power too, just in drive pressure pumping losses.

Typrus said:

As for the 'needs power' comment, nothing comes free, turbos take power to make power too, just in drive pressure pumping losses.

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properly sized, they're working with the delta T across the turbine

you'll see higher intake pressure than exhaust pressure pretty often in something that isn't atrociously undersized like the stock turbos on TDIs

Turbos are more efficient system compared to superchargers. Bound by pulley sizes instead of just controlling what the turbo dumps out at. Maybe I’m wrong or just sold on turbos instead.

They are more efficient if sized right. No argument there at all. That does not mean they are free power though. I've just heard it argued too many times that they are "free power and just use wasted exhaust heat". No, it is not that simple.
In some modes, a properly sized centrifugal supercharger will be more efficient, but it will quickly fall behind outside of those "sweet spot" areas. The turbo will be more efficient overall, hands down.

Alberta 7.3 said:

I know a lot of guys go with a compound turbo setup. What would be the advantages/disadvantages of using a supercharger (something like a supercharger from a Pontiac Grand Prix 3.8) instead of a low pressure turbo?
I'd be using the engine is a conversion, so space wouldn't be an issue.

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A roots style blower from a L67 would be great for low end grunt, something you can easily get from your OEM turbo and a tune. I wouldn't bother.

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turbobrick240 said:

What's the power goal? If your just looking for around 200 hp with excellent spool, a gtd1752vrk is hard to beat. Would certainly simplify things a lot.

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Ultimately I'd like to build a BHW that can do around 230-250hp (just for get up and go, cruising wouldn't need a lot of power.) Just tossing around some ideas looking for knowledgeable opinions and input. I looked at Whitbreads build that uses twin turbos and thought a supercharger may help getting boost building. Swap recipient would be a Ford Ranger. At this point everything is on paper since I only have the Ranger so far and haven't picked up an engine donor. I'm used to working on diesels like the 7.3 PSD

Build an alh to make that power goal. Probably cheaper and parts are more abundant.

True, sizing the turbo is key but super chargers seem to peak their hp gain compared to turbos a lot faster. I guess there is always a right application for everything. A friend of mine has a cts V that he dumped 10k into it to make around 850hp when I think a turbo set up would of been less cash and more HP. But it came supercharged so that’s how he went with it.

06E145601 if you're going to put any kind of supercharger on a TDI.

The primary benefit of a bigger turbo (or compounds) in a diesel is not necessarily "moar boosts" it is lower EMP.

It doesn't get any lower EMP than a Blower. If your ONLY goal is performance, then a blower is the way to go.

Frankly the only reason(s) to use a turbo is emissions (backpressure for EGR) and convenience (car already comes with one, so easy to fit, cost, etc) and because everyone is used to it (herd mentality).

You missed the most important disadvantage of a mechanical compressor and that is the increase in specific fuel consumption due to the not-insignificant amount of crank power needed to drive it.

As for performance being the only goal as a justification, a supercharger delivers a fixed pressure ratio and airflow depending on the engine RPM, VE characteristic and the drive ratio (pulley size); it is as little or as much power as the chosen charger and pulley, a bit like the choice of turbo.

People are pushing TDIs to 400 HP turbo only, and if low-end torque and minimum lag are of primary importance, turbos can be sized to suit that too, or a 2-stage sequential system to have your cake and eat it too.

Putting a blower in a TDI is a novelty and curiosity but doesn't put us into any previously uncharted performance territory not already achieved with turbos, but I'm honestly looking forward to someone stepping up to doing a very well thought-up system using a 3.0 TSFI unit (latest and greatest Eaton TVS series). This could possibly be done relatively straightforwardly in a PD since it doesn't have a separate pump pulley, but using a longer timing belt from an ALH or CR, and designing and fabricating a mounting bracket for the supercharger and any necessary idlers.

Well put tdimeister, thank you.

TDIMeister said:

You missed the most important disadvantage of a mechanical compressor and that is the increase in specific fuel consumption due to the not-insignificant amount of crank power needed to drive it.

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I am well aware that a supercharger needs mechanical input to operate. A turbocharger is not free performance either, energy and efficiency is lost to drive the turbine blades.

The difference being that the turbo is basically driven by waste energy. Turbos add power more fuel efficiently than superchargers, no doubt about it.

on the subject of supercharging diesels it does bring to light one perverse benefit of the negative cam overlap:
you won't be over-scavenging and blowing charge air out the exhaust

Rather small peanuts, but it is a concern on a gasoline engine where there's a tendency to put in a high-revving cam with tons of overlap and then toss a blower at it as an afterthought. You get a lot of wasted energy both in what amounts to a boost leak of sorts and also in the fuel going out the exhaust.
Makes for really neat flames out the zoomies, though.

ETA: speaking of zoomies, always sorta wanted to do a supercharged 1.6IDI with the exhaust poking out the hood. be able to see the firing order in smoke-signals heh
got to the point of getting a mazda millenia IHI blower, never went anywhere further with it

Alberta 7.3 said:

I am well aware that a supercharger needs mechanical input to operate. A turbocharger is not free performance either, energy and efficiency is lost to drive the turbine blades.

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You're right, but a SC "costs" more at most operating points, which is directly quantifiable by the higher BSFC.

Perfect example is when bmw supercharged the Mini Cooper type s then changed the game on the ladder with turbo. Cheaper more power and dependability.

Superchargers will cost more power across a wider range than turbos, even when both are properly sized. In a purely power-making scenario, they both have their strengths and can be configured to play specifically into those strengths. They both have their downfalls, but you can generally work around them.

If you are wanting to play around a bit, look into the 5th-gen VNT turbos from Garrett. GTD series. They are even better at allowing a larger turbo to spool lower down than the stock series. A ceramic ball 5th-gen in a bit larger size may meet your needs.

I’m making 350hp and 600 lb ft with sequential turbos .... in my BMW 335d

My opinion on supercharging is that it is difficult to adequately aftercool the charge air efficiently, although it would certainly be cool to see someone pull off a turbo feeding a supercharger on a TDI

Centrifugal is straightforward to intercool.
Screw it, put an F3R on it, 4000cfm will cover you hahaha

dogdots said:

My opinion on supercharging is that it is difficult to adequately aftercool the charge air efficiently,)

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intake manifold design on a 4cyl means that an intercooler is pretty easy rather than a V-config motor where you can plop the blower in there nice and low with nowhere to easily stuff an intercooler

Have you ever seen v-valley on v6 or v8 tdi [emoji23]