Inliners International Forums General Discussion Hi Performance supercharger feeding a turbo

i was reading some stuff on how some engines, large turbo deisels mainly, use dual turbos with the large turbo feeding into the smaller one to spool it faster. now the question i have is why not use a small roots blower to help spool up a large turbo? with the blower creating boost quick off idle it seems as though it would work great and worth more power than just a turbo. has anyone ever heard of this being done? another idea i have is a turbo blowing through a draw through roots blower setup. im not sure how that would work though...ideas anyone?

In the last days of the 2 stroke Detroit Diesels they used a turbo to feed the blower. If you run across a Detroit 6V92T or 8V92T then you've found one to look at. The blowers were a necessity on the Detroits to scavenge and recharge the cylinders and the turbos were added to boost power, unlike why we use a blower on a 4 cycle engine. GM began phasing out the 2 strokes in the early 90's and introducing 4 cycle Diesels that were more emissions and electronically compliant than the 53, 71, and 92 series engines.

BTW one of my all time favorite inlines is a 6N71 Detroit. You gotta love the scream!

Mike

I could be wrong, but I thought that on some of the late 2 strokes the air to the blower was shut down after the turbo spooled up and the turbo supplied all the air to the engine. The blower continued to spin, but because it wasn't compressing anything, most of the parasitic drag
was removed so that there was more net power.

I've only ever heard of a turbo feeding into a blower. It got to be a pretty complex system but apparently pretty impressive. My book on Engine Management Systems has a "compound Forced Induction" chapter in it. They took a toyota MR2 engine and put a turbo feeding into a blower. Amazing beast apparentely. Soon as you put your foot down she went from a gas sipping v6 (3.0L i think) into a torque beast. The blower carried the engine into the 3500 RPM range at which point the turbo made enough boost that the super belt was putting power BACK into the crankshaft. Fast!

On the Detroits there is no way to isolate the blower from the engine. The air box from the turbo goes directly to the inlet of the blower and the blower is gear driven off the front accessory drive. If the blower was somehow dropped out of the picture then the vanes ended up becoming a big restriction for the turbo to overcome. Whatever the reason GM decided to add a turbo to feed the blower it obviously worked but on the surface it seems like the induction system was more complicated than it needed to be.

Mike

if the turbo feeds into a blower at what point would the blower stop and the turbo take over? wouldnt the blower become a restriction? if this were a blow thru turbo/draw thru supercharger how would that effect the fuel air mixture?

Diesel turbos only blow air, direct injection handles fuel. Reread Greg's post on the MR2 for gasoline engine application.

The air/fuel ratio is generally not going to change no matter what you're doing with the intake. Forced induction engines typically use richer mixtures because they have serious intake temperature problems. The extra fuel promotes more cooling of the intake charge from the vaporizing of the fuel. Beyond this though there's not a whole lot of difference. You've got to have reasonable mixture for the conditions by the time the mix gets to the cylinders - or you're in trouble. I'm not sure I'd try to do a turbo-blower setup with a carb.

Quote: "dual turbos with the large turbo feeding into the smaller one to spool it faster"

I'm not sure what this means........I've heard of increasing responsiveness with two turbos but it doesn't really work like that. The idea is that a single turbo can't do everything - if it has huge high end flow it's probably going to take a while to get up to speed, if it has good responsiveness at low speed it's probably traded off further up. They're kinda like engines that way - you can't usually have massive lowend torque and a high end screamer.

So what you do is add a few valves so that you can control where the exhaust is going. When you punch it all the exhaust is diverted to the small, quick acting turbo. As the power climbs you quickly run of capacity in the small turbo, but at this point exhaust is going to the big turbo as well and it's coming into it's own.

You can also just use two smaller turbos. Usually ends with more responsiveness but still a lack of high end.

It's been done on a hotrod here in OZ(Queensland)he has a ford inline 250 and a small jap blower blowing into a TO4 turbo.looking at the photo's on his web site(forgotton what it is at the moment)it seems to go really well!(put blown six into the search engine-it might find it)

Compound supercharging was used on GM Allison V-12 aircraft engines during WW2.Either 2 mechanical blowers or in combination with an exhaust driven supercharger.This was used to give the 1710 cubic inch engines sea level power at 30,000 feet,no so much to add extra power.Other aircraft engines used multispeed superchargers with 2 and 3 spd gearboxes.The Germans used a variable speed hydraulic motor to drive the blower on it's V-12 engines.
The 4300 cubic inch radial air cooled engines by Wright or P&W used an exhaust driven turbine geared to the prop to add wasted power from the exhaust directly to the engine output.
Other tricks used to boost piston aircraft engine's power or reduce detonation was alcohol injection into the intake,nitrous oxide and sodium cooled ehxaust valves.
Late in the war,Allison engines were using supercharger boosting in the range of 45 psi at 4400 rpm,with a 5-1/2 stroke.Oh yeah,V type aircraft engines are called Inlines

Question, I've thought about supercharging beacause turbos are just to complicated for my taste; the problem is that superchargers are too expensive, turbos are far cheaper by comparison.

Would it be possible to remove the compressor from a turbo and drive it from the crankshaft through some gearbox?

It is possible, and it has been done. It's called superfugial (sp) supercharging and that's how the vortech and prochargers work. I don't think you could do it yourself for anything near cheap as the gears and machining would be rough. Those supers are designed for low RPM's too, you'd be talking turbo speeds which are easily in the 90,000 to 100,000 RPM range. Difficult to say the least I think.

Just my 2 cents. Greg

just another note on the gm deisel,these things use a LOT of air thus the reason for two turbos feeding one blower as the 892 v8 did.first of all it is a two stroke so it fires and produces power on every downward stroke and exhausts on every upward stroke,so you can see the need for lots of air,there are four vaves per cyl and they are all exhaust vaves,air enters thru ports in the cylinder walls thru the crankcase.the intake charge is pulled in to the cyl underneath the exhaust gases so extra air pressure is needed to make the eng more efficient as it is the intake charge that pushes out the exhaust gasses.there would be no need to have both on a four sroke eng as one or the other would be enough.the 2 strokes had no bottom end power at all,were made to be run at high rpm under load,incredible power at high rpm but not fuel efficient,they were putting out five and six hundred horsepower back when cat and cummins were still struggling to get four hundred out of their motors. :p

Cheapest method is buy an Eaton M90 on eBay for $200. and rig up your own belt drive.