second alternator position plumbed into a sealed air box..........will it work? what <!--StartFragment --> will it do to our turbos map?..........



<!--StartFragment --> Thanks to this new technology, the industry leading power and durability of gear-driven centrifugal superchargers is now available without tapping into the engine oil system. In addition to the P-1SC and
D-1SC models, F-1 through F-4 models are available for racing applications in the 800–2,300 hp range. These F-1 through F-4 models are also self-contained, but contain higher step-up ratios for the higher boost (20–45 psi) and airflow levels required for competition usage.

I thought about that for awhile. It would certainly increase boost, be easy to install, and fairly cheap. No reprogramming should be necessary. Might throw overboost codes, but that could be fixed by moving the MAP into the post-turbo, pre-super tubing. A blower that was designed to generate 5PSI, would actually increase boost 33% instead. So if you were 30PSI, you'd step up to 40PSI.

got some leafblower parts left over):h

I am putting one of these on my drag car right now and i must say they are amazing. The cfm they will flow is unbelievable. I will be flowing about 1300 cfm with around 1000 hp out of a 468 ci chevy. Boost would be around 12-16 psi.

I have talked to ati procharger about doing this to my 03 duramax and they say that they can do it but haven't yet on an already turbo'd diesel. I would think it could be done for 3- 4k but you would have to take your truck there so they could custom make one for ya.

Sdaver - ol' Fingers was musing about this a while back and I think he's got some ideas....send him a PM....

Just my thinking, but wouldn't you want the turbo to feed the blower?

easier to plumb the other way

Or lose or gut the turbo. It may be more of a hinderance.

It would be a wash. You'd intercept the CAC feed from the turbo which is right near the 2nd alternator bracket.

One thing I wonder... Without a throttle, how will it affect your mileage. With a gas engine, the blower has less resistance when the throttle plate is closed, but with the diesel, it will always be making it's boost. Even at idle, you will have some boost.

I thought the reason that diesels didn't have superchargers is because the pulleys robbed a bit of power.

Some diesels do have superchargers. Detriot Diesel bus engines for example.

IIRC, most 2 stroke diesels do. But I'm not sure what it actually does. Something about keeping the flow going in the right direction?

Super needs to feed the Turbo. Super should be about twice the capacity of the turbo. Feeding the stock turbo with precharged air will unload the turbo a huge amount. Boost sensor should stay in the same place but keeping it from coding might be a challenge depending on pre-boost. 5-10 psi of pre-boost will reduce the turbo load by at least 1/2 for a given boost and allow much higher max boost. (30-60%)

I personally don't have the extra $3000 to play with right now to buy the super, but if I did.....

Unload the turbo? If you do that it takes work. Why not unload the turbo literally? I think if you supercharge with a vengeance, the turbo becomes a restriction.

steve caps the boost signal with his programing.....off and on with a ac clutch(dreaming)................guess I could whore for one like the twin turboed intercooled nonphotgraphed GJ............****et Id rather spend the money

I think there is something to be said for feeding the super with the turbo:

MAP issue resolved. Power comes from tuning.

When cruising or idling, the turbo will act like a throttle, and reduces the load the super puts on the engine.

The super does not have to be huge. It will only be seeing compressed air when making power. It DOES have to exceed the peak output flow of the turbo, so it releaves load on the turbo.

limiting factor is the CFM of the turbo.

are not the cfm ratings based on o psi at the inlet

Actually they are mapped on the differential between inlet/outlet. You have to be very careful about the units being used.

so who knows how to figure this out?

Hmm...

[wildass guess] If going post turbo, it will see the same CFM as a naturally aspirated 396ci V8 at 3200 RPM. Or a 198ci engine at 6400. So I'd ask for one that would feed about a 302 Ford 5-10 PSI of boost. This size is also popular and cheap. [/wildass guess]

I would think the s/c would take the lag out of an inefficent turbo, nothing else. Nox is much better for this if needed. 2 stroke motors had no bottom end, therefore no exhaust flow at startup and the s/c helped out . Am I wrong?

While compounding the supercharger is not necessarily the best way to go, it should be just as effective as adding a compounded turbo to our existing turbo.

But we don't have enough data to verify that it would work yet! :D It's SECRET.

The beauty would be it could be installed in a few hrs, and not affect the engine bay layout. It would also work on all years, and with minor changes, Ford's and Dodges also.

steve caps the boost signal with his programing.....off and on with a ac clutch(dreaming)................guess I could whore for one like the twin turboed intercooled nonphotgraphed GJ............****et Id rather spend the money
Mel Gibson already figured this out for you.

Mad Max style. :D

The Stock turbo on the LLY draws about 1600 - 1800 CFM outputting about 600 CFM @30PSI. (my best guess since I can't find the specs off hand) The F-2 ingests about 2700 CFM and should be able to keep the turbo fed with 10-15 PSI of boosted air.

Really need to sit down with the map for the turbo to match it to the output map of the supercharger.

Mel Gibson already figured this out for you.

Mad Max style. :D
Did we forget Lone Wolf McQuade? Stuck underground, crack open a warm beer, start the engine, turn on s/c, watch the red lights flash, kick butt big time. :bow: Was that cool or what? :ro) :ro) I'm just a kid, so what? :D

steve caps the boost signal with his programing.....off and on with a ac clutch(dreaming)................guess I could whore for one like the twin turboed intercooled nonphotgraphed GJ............****et Id rather spend the money):h

Oh, Forgot to add... SP33D has another 'Unique' truck like mine.

Bug him for pics.... he's feeling lonely and left out.:grd:

HES NOT THE ONE PRODUCING ALL OF THE USELESS HYPE(peanut trufont)......trippin the on and off s/c has always been a dream since I saw ole mel do it

mcrat wrote"The beauty would be it could be installed in a few hrs, and not affect the engine bay layout. It would also work on all years, and with minor changes, Ford's and Dodges also."

MY THOUGHTS EXACTLY

I put lots of miles on a truck quickly...my 04 bought in october now has 26K.....if I thought I could easilly move the s/c from one truck to another it just makes it more desireable

Here is an interesting bit of information that is VERY timely for this post.

The company I am with is the Utah Dealer for Squires Turbo Systems. www.ststurbo.com (http://www.ststurbo.com/)
(STS headquarters is about 20 Minn from our location)
I had my truck over at the offices last week, and had a VERY interesting conversation with the head of R&D.
He told me that they are interested developing a, "Remote mounted Second Stage Turbo for the Duramax".

I don't know much more than that at this point. However I have no doubt if it ends up being produced it will be very well done. The systems they currently produce for the Gasoline engines are amazing!
My guess is if they have enough interest from the Duramax community I believe they will invest the R&D dollars into the project.

If anyone is interested in seeing this developed, Send me an E-Mail and I will get it into the right hands...
ZRATED@COMCAST.NET

i'm likin the supercharger idea. But the remote turbo idea has never settled with me well. Having a 14 foot oil line run under the truck. Thats a worry i don't wanna have fun but still have to worry about sumthin coming up off the road and breaking that oil line and cuzing very big problems. But everyone has there own there own .02 cents.

The whole idea of running a supercharger is to make the plumbing simple and reduce EGT's. Some of the centrifugal blowers are sealed oil systems.

But if you were to run a STS, you wouldn't put it that far back. You would want it right after the downpipe.

Move the alternater to the other side. Install a F2 or equiv in the old alt position. Easy plumb from the stock air cleaner to the Super chrager then to the turbo.

Brackets and such for he alt reloacate are already available.

Will need to fab the brackets for the Super.

Whole thing could be undone without much fuss and moved to the next truck.

I like.

ME TOO.

You could relocate the driver's side battery to the passenger side where the air cleaner used to be. Then use the space from the old battery location to put your air filter. An AFE for a dodge would probably work perfectly in relation to where the SC would sit, and where the battery was. :) We're on to something..

Two camps. Pre and post turbo. I'm in the Pre turbo camp. Anyone with me?

It would be simpler to blow through the turbo..

Just got off the phone with ATI, set up my dealership with them, and I should get the package by the end of the week.

They say that it's going to be hard to overdrive the charger enough to make it flow at such low RPM's that diesels run.

I don't think that it will be much of an issue.

It would be simpler to blow through the turbo..

Just got off the phone with ATI, set up my dealership with them, and I should get the package by the end of the week.

They say that it's going to be hard to overdrive the charger enough to make it flow at such low RPM's that diesels run.

I don't think that it will be much of an issue.
You can't do it with just a smaller pulley. Too much load on to small an area. Need some help from the SC's gearbox. Need to max the blower at about 4000 engine RPM. Remember, the Dmaxes will grade-brake the engine up to about 4000 RPM and you have to protect the blower.

JMO

So, is project "fingercharger" going into development soon? :)

I vote run it pre turbo. Run it into the old air box if neccasary.

The problem ATI mentioned is a real problem. Heres why.

There are 2 different types of super chargers. Roots and Centrifigual.

Roots blowers make boost linear. Meaning the boost amount is similar at idle all the way to 6000 RPM. That is why roots equiped vehicles have gobs down low.

Centrifigual blowers build boost proportional to RPM. If you ever watch a boost gauge on a cent. car there is not much boost below 3500 RPM. IT is way up there by 6500 RPM.

So to overpower our air hungry turbo and do it all by 3200 RPM the centrifigual blower you choose will probally have to be fronted with a gear box or the absolute biggest charger they make. Anything to get it to produce boost down low.

With all of this time and money, would it not just be easyer to get COMPETITION CAMS off there lazy ass and make a bigger camshaft?

http://www.compcams.com/ :ro)

The mulitplication ratio of the charger's drive system is available in 5.73:1 or 10:1

The 10:1 unit would have to be fine for us since most cars redline much higher than 4000-4500.

There are no alternative compressor wheels available for the procharger. So there goes that avenue.

Anybody talk to vortech? Powerdyne? Paxton?

So, now that you are a dealer, want to send me some map data on the F2?

But is it boost pressure we need or flow.

On another note, The compressor wheels, housings are made in house. The shaft to compressor wheel bond is a hot/cold interference fit. If you could get one without the compressor wheel on it, you then could put a larger (more aggressive) wheel on it, depending on the space restrictions.

Yeah as soon as the dealer package gets here, they said later this week.

It has to develop boost. Even if it is just .5 psi.

The drive wheel they choose is sized accordingly to the inards of that particualar charger. Some of the big chargers do not allow pulley swaps because the charger is already maxed. Faster input speed will not always equal more output boost.

Which ATI charger you are looking at?

F2

Two other problems I can see with the Centrifugal super charger method.

1: Belt slippage on a pulley which is overdriven to that extent so as to make full boost by 3200 rpm. Belt slippage on a non Cog system will be severe.

2: If one was to use a cog system the reliability issues. Even Procharger doesn't recommend a cog system for a street driven vehicle

So to digress a bit, what would be the disadvantage of using a roots type blower and turbo combination? The little 2-71 or similar (magnacharger/eaton) would be capable of adding 10psi or so from idle to redline. The only drawback would be the compressor surge problem of having the positvie displacement blower right on top of the intake.

In order of airflow : flilter --> turbo --> CAC --> Blower --> Intake Manifold

IF they had a 7:1 ration drive, we would be golden. Pully diam would still be big enough to give a good enough bite. Still need to look at the map to see when we start making efficient boost so we can stay under the curve. Might have to dbl pully the bugger to get the speed we need.

So to digress a bit, what would be the disadvantage of using a roots type blower and turbo combination? The little 2-71 or similar (magnacharger/eaton) would be capable of adding 10psi or so from idle to redline. The only drawback would be the compressor surge problem of having the positvie displacement blower right on top of the intake.

In order of airflow : flilter --> turbo --> CAC --> Blower --> Intake Manifold
Roots blowers consume significant power to run. However, they are nearly linear in their output throughout the range. Big package too. Huge grunt and amazing low end. But for arguments sake the roots will multiply anything you push into it. (absolute pressure)

What would happen durring a grade braking deal? foot off the trottle, up to 4k it goes(the SC would really be blowing then) Nothing? Blow out the flame and the truck dies?

You can't use a "positive displacement" roots-style blower upstream of the turbo. You might as well remove the turbo. They do not flow more than their displacement. You'd have to go downstream. The roots blower will not restrict the turbo output if downstream. It doesn't care how much the air is pressurized before it gets it, it pushes volume, not pressure.

This is another reason I think downstream makes more sense. You won't need to flow as much CFM, hence gearing won't be as big of an issue.

What would happen durring a grade braking deal? foot off the trottle, up to 4k it goes(the SC would really be blowing then) Nothing? Blow out the flame and the truck dies?

I don't think you are spraying fuel on decel at high RPM. If you are, it's not very much. While grade braking, my pyro reads ~150-175 deg.

Preturbo- you'd actually spin the turbo. The super would still pressurize the intake tract, and the turbo would develop RPM instead of slowing down.

Postturbo- Hmm... it would still spin the turbo, but to a lessor degree. The turbo would act somewhat like a throttle, and reduce the load on the belt. For the LLY's, the turbo would act like more of a throttle.

I think you'd have more grade braking with the preturbo.

I think you'll see results from turbo + S/C to be similar to using K&N filter. In fact, if it can't flow fast enough for the turbo, it may be a hinderance. This would be a bigger issue for a positive displacement SC.

I wouldnt be worried about the grade breaking being effective, I would worry about it pissing things off if you were squirting little fuel and huffing lotsa air.

....what would EGT's be like with a super and a turbo

We use V16 Detroit Diesels that have four turbos feeding two roots super chargers to power generators, so it does work....

....what would EGT's be like with a super and a turbo

Better than compound turbos. Less back pressure. And significant EGT drops might be had in the 1500-1800 range where the turbo isn't making much boost yet, the super would be making about 1/2 it's boost already, and getting a more complete burn with big tunes. Less smoke from "low RPM fueling" and more TQ.

Thanks McRat now you get me wondering of the trannys would hold up

So if the stock turbo feeds the super, we could probably get by with one of the factory prochargers, no?

If you could gut all the EGR stuff out of the valley on our motor, you might be able to squeeze a roots type down in there.

The detroit 8V92 has one charger feeding one super in the valley which is driven off a gear drive in the back of the motor.

So now which camp is everyone in?

And another question, which one centrifugal or roots?

1850 cfm at 4000rpm...................sealed oil system less than $4k............anybody know the size of the crank pully ?..............got a supplier willing to try..........pretubo

as our turbo passes 33 psi the back pressure becomes excessive and turbo bark or the tendency for the back pressure to drive the turbo in the opposite direction...........repeated use causes a busted shaft...........keep a positive inlet pressure via a pre supercharger and it would reduce the tendency for turbo bark and increase our turbos ablity to flow at higher boost levels......the way I see it..........SO WTF...........is this way off base?

I may have switched camps, but I think the way to go would be for the turbo to blow through the supercharger.

I'm leaning toward the positive displacement variety now since it would deliver much better low end torque. Who knows.. I'm the gotta try it first type.

1850 cfm at 4000rpm...................sealed oil system less than $4k............anybody know the size of the crank pully ?..............got a supplier willing to try..........pretubo
1850 is too small. That is about what the stock LLY turbo is ingesting at full bore. To maintain 5-10 psi inlet pressure you will need to go with something more on the line of 2700 CFM.

the detroit diesel's normally use a bypass valve for the roots blower stewart&stevens first did these(16V92tbi-turbo bypass intercooled), dont think belt slip or drive hp is factor, think blower feeding turbo would be best, any air above atmosphere is plus, maybe modify hood for air filter box(cool air) it seems like when grade braking engine is not firing sc would be fedding full but turbo would be low due to low exhaust gas generation, but may induce thermal stress by dropping piston crown,cyl head temp and then return to power would be like starting engine and floor it with good load(munch-munch) might need deverter valve to operate of grade braking, and maybe water-air intercooler while we dream with radiators placed along seam on hood since we raised hood for intake duct. running boost thru pos disp(roots) would increase alot more heat to remove. jmho

1850 is too small. That is about what the stock LLY turbo is ingesting at full bore. To maintain 5-10 psi inlet pressure you will need to go with something more on the line of 2700 CFM.Not sure why you feel the size or the output of the supercharger has any correlation in what it needs to produce to maintain positive pressure. The gearing in the unit itself will/can be set to ramp up faster to keep from creating a negative effect on the turbo...not to mention you can also adjust pulley sizes. As far as CFM....I doubt there is enough fuel to support 1800cfm at this time.....our turbo is sized a hair above an HX-40 from what I've seen and that is a far cry from the 1800 the Procharger will produce......I think we are still at a little less than half that with the IHI in the 800-900cfm area.

Remember, we use half the scale a these were originally designed for....I would say max boost should be set in the 4200-4400rpm, range just to keep from over running the supercharger. That gives plenty of adjustability on the lower RPM scale.....again it goes back to the gearing of the Procharger itself.

If you go post turbo, you don't have to get the expensive "race sized" one.

There are oil-less centrifugals as cheap as 1000 on Ebay with warranty. These feed 302CI at 6500 rpm up to 9 PSI. Or 604ci at 3250 at 9, or perhaps 396ci at 10PSI.

Big CFM ones are going to require a cogged wide belt. Smaller one will run off of normal 6 rib accessory drive belt.

I guess it all depends on what you consider expensive.....any single or twin set-up is gonna be in the 4k range....the Procharger Sdaver and I are talking about is used in a kit for a late model production car utilizing a standard serpetine belt and is relatively easy to get ahold of........but it is a bit more than the 1k Ebay blower.

Edit: I believe pre turbo is the best route as well......although if you stop and look at the way these are going to react, the turbo will be nothing more than a paper weight.....

For clarification, post turbo meaning blowing through the turbo? Or the turbo feeding the supercharger?

Post Turbo: Turbo blowing through the Supercharger

Pre Turbo: Supercharger blowing through the turbo.

So which one has the higher pressure ratio? Seems as if the higher pressure ratio should be the last stage, correct?

I have played with centrifugals and they react like turbos, they have lag. What's the point in using one in conjunction with a turbo? There is not enough fuel to support any of this yet. The Duramax allready has more tq off the line than needed and can be controlled with various torque converters.

Are you kidding me? Have you driven an LLY? Even with fuel enhancement they've got "pull out in traffic and get killed" lag.

The 500hp+ guys are having problems with fueling and low rail pressure, but for the rest of us under that mark.

We've got EGT problems. Big time. My stock LLY with exhaust runs 1250 unloaded. Running just the edge on 5x5 on the dyno creeps towards 1500 degrees.

These are all pre turbo in the pass side manifold.

If the centrifugal blower is sized large enough it can be providing pressurized air to the charger at idle or vise versa. This will help reduce the lag, since you are already producing boost, which will in turn let the computer fuel harder off the bottom since it references boost among other things and provide even more torque down low.

Then maybe you can get a convertor to harness this new found low rpm torque.

IMO, the goal isn't to double the airflow and hit 1000rwhp. For that? Yeah, a 14-71 custom blower with no turbo should probably do it.

Those $4000 "kits" include a lot of stuff you don't need. The full retail on these centrifiguls is $2100-$3000. The rest of the stuff you don't need.

I would imagine the goal to be to run 500rwhp at 1350 degrees using the existing fuel system, or 600rwhp at 1500 degrees with fuel system improvements. You won't need more than 1/3 more boost to do that. You only need a 10 PSI gain. And the manifold CFM of a Duramax at 3200 is not that great. No worse than a V6 Buick at 6500.

Lag? Sure there will be some lag, but it will be greatly diminished. You will be in essence running 2 small'ish compressors, and they will actually assist each other in making pressure.

I agree with this.. Just like what I said above, if the supercharger can be overdriven enough to come on early or be producing boost near idle then lag will be all but gone.

Another point about lag.

The lag you see from a centrifugal on a Duramax will be about the same (or less) than you see on a Mustang at 3200 rpm. At that RPM it's instant response.

Why?

The RPM range on the Stang is 750-6500. The range on the Duramax is 750-3200. At 1/2 peak RPM, the Dmax is spinning 1600, and most the time you are driving, you are 1500 RPM or higher. You will be gearing the centifugal at twice the rate it would spin in the Stang.

IMO, the goal isn't to double the airflow and hit 1000rwhp. For that? Yeah, a 14-71 custom blower with no turbo should probably do it.

Those $4000 "kits" include a lot of stuff you don't need. The full retail on these centrifiguls is $2100-$3000. The rest of the stuff you don't need.

I would imagine the goal to be to run 500rwhp at 1350 degrees using the existing fuel system, or 600rwhp at 1500 degrees with fuel system improvements. You won't need more than 1/3 more boost to do that. You only need a 10 PSI gain. And the manifold CFM of a Duramax at 3200 is not that great. No worse than a V6 Buick at 6500.Mypoint was, the kit is available with the head we are looking at for about or less than what an aftermarket turbo is going for. We only need the head as everything else is going to be custom.....probably not to expensive for piping and a solid mount.

As for the Tow/Haul set back.....how about an electronic blow off valve between the super and the turbo that was excited by the loss of APP signal....I'm sure one of you electric gurus could handle that......:grd: .

The whole idea behind this is to keep it simple as possible and the ease of extraction.....not to build a 1000hp beast....although I can't see 600 being far off with a little more adjustments. The gearing in certain Prochargers allow them to ramp up quick enough to eliminate a significant amount of the lag we have in our stock turbo.

To be honest....I was hoping someone else would do it....I would rather throw a few extra dollars in the direction of R&D.......

The rough calcs

200 CuIn/Rev Engine
1728 CuIn/CuFt
0.12 CuFt/Rev Engine

3200 Max Rev
370.37 CuFt/Min Engine
740.74 CuFt/Min Turbo inlet @15 PSI Engine Inlet
1481.48 CuFt/Min Turbo inlet @30 PSI Engine Inlet

2469.14 CuFt/Min Super inlet @10 PSI Turbo Inlet

question on the lly? how will the vanes be affected with a positive inlet pressure............or I guess this is a mute point because at low rpm the vanes would be open trying to build boost.........I see the application easier on the lb7 because there are no adjustable vanes..............$3500 is roughly the head unit alone.........anybody know the size of our crank pulley? and how many ribs on our serpt belt?

Won't matter there guy.. The vanes are on the exhaust side.

Also, the vanes close to make boost and open to reduce backpressure and boost. The Turbo also seems to have a "fully closed" position to just generate backpressure for the EGR. That is the hisss you hear at idle. Vanes full closed.

think pulley in front of acc serpentine pulley just to drive compressor in case of slip or breakage. could change easy to experiment with different setups.

when ecm reads overboost do they open........................or close?

Should open to reduce boost.

how many pounds of boost cant you place in the duramax befor gaskets and seals start going out?

Someone correct me if I'm wrong but hasn't juice seen over 50psi with the twins and not blown the heads off his motor yet?

He limits to under 50. I also wouldnt use 1 truck as a test case. I would also look more at tomac or heartbeat since they are fueling much harder and making more power.

I think an important issue with the Dmaxes for typical owners is that you cannot run over 325RWHP towing without risking engine damage from excessive EGT's. We have the fuel to make 450rwhp, but can only use it for short bursts.

We need about 1/3 more air or about 10PSI at low intake temps.

I think an important issue with the Dmaxes for typical owners is that you cannot run over 325RWHP towing without risking engine damage from excessive EGT's. We have the fuel to make 450rwhp, but can only use it for short bursts.

We need about 1/3 more air or about 10PSI at low intake temps.
If you look at the backpressure driving the turbo, you will see it diverges a huge amount when we start making big power. 35 PSI or more to make about 22 boost and only 15 to make 15. Taking the load off the turbo to reduce the backpressure will go a long way to reduce the EGTs.

I am working on getting a head to force feed the turbo. I like the F2, cause it can maintain the 10 PSI, but am considering lesser S/Cs that might do the job. Less than 1800 CFM will not cut it for sure.

This has potential

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7971845976

I've got a few friends running big centrifugals on small block engines. Roughly the same displacement as us, but running gasoline, 7,000rpm, and 25PSI. To drive these sized units, you will have drive issues. Big cogged belts, and poor reliability.

And the vortech is an external oil supply unit IIRC. At that point, just putting on a big single charger would probably be easier.

In my "bench race" opinion, that sized centrifugal will cause more grief, not less.

I agree, the drive is going to be a problem. One of the reasons I am willing to consider a smaller unit.

Right, Vortech is oil plumbed. That is one of the nice things about the Prochargers, Self contained units.

Dropping in a bigger tubo on the LLY would be the ideal solution. We just don't have one available right now. What S/C would you think is right Pat? Pre or post?

What I'm not sure of is how compressed air compares to atmospheric air. Say the turbo puts out air at 3 bar (45PSI absolute), how does this compare to air at 1 bar (15 PSI absolute)?

I still have shifting, bursting, and 1093's to worry about at power levels over 440rwhp. They are #1 on my "list of things to do". I'm also trying to "improve" the existing intercooler we have.

When I get those problems fixed, I'm going to put a centrifugal on my truck. I'm going to go post turbo, with a blower that will supply 6-9 PSI ( ~ 1.5 BAR) to a 302ci motor at 6500. Our crank pulley is big, and does not drive the water pump. I believe I can drive it with the existing serpentine belt, and if it does fail, it won't leave me stranded.

I'm only aiming at LB7 power with an LLY, so I don't need 50PSI. 40PSI at 1600rpm+ is my goal. And I want to retain as much fuel economy as I can. This is why I will try a small centrifugal and do it post turbo.

1 bar absolute is equal to sea level atmosphere, it comes in figuring differential for upper atmosphere usage,
why would you put a restriction in your intake - by putting blower after turbo, turbo becomes a restrictor, compound supercharging builds on funnel(larger feeding smaller vic smaller working harder to fill larger).
why complicate air/exhaust plumbing, extra work.
would make harder to remove or modify unit due to plumbing.
pulling thru turbo may cause peeking on turbo and should also add more heat due to pulling thru restriction of turbo along with increase if it did raise boost.
detroit diesel reduced inlet temp by about 200+ deg when they went to the turbo bypass(turbo air went around roots blower eliminating air stalling at blower and temp increase from blower).
look at diesel tractor puller setup.
jmo

1 bar absolute is equal to sea level atmosphere, it comes in figuring differential for upper atmosphere usage,
why would you put a restriction in your intake - by putting blower after turbo, turbo becomes a restrictor, compound supercharging builds on funnel(larger feeding smaller vic smaller working harder to fill larger).
why complicate air/exhaust plumbing, extra work.
would make harder to remove or modify unit due to plumbing.
pulling thru turbo may cause peeking on turbo and should also add more heat due to pulling thru restriction of turbo along with increase if it did raise boost.
detroit diesel reduced inlet temp by about 200+ deg when they went to the turbo bypass(turbo air went around roots blower eliminating air stalling at blower and temp increase from blower).
look at diesel tractor puller setup.
jmo

The turbo is a restriction indeed. That is why post turbo makes sense.
With pre-turbo, you need a larger super, and it always has access to full airflow. At all engine speeds and throttle positions you will have full drag of a large blower on the crank. Your mileage will probably take a hit. Post turbo has you running a smaller super, that is being restricted by the turbo a little, which reduces load on the super at cruise. Should have better mileage.

It is a good point that Detroit went turbo+super, then went to a bypass. I guess there is a third option of running "dual". Run a second aircleaner, or Y and parallel systems. But remember that the 4-6-8/71-92 Roots blowers they use are 100% positive displacement, and the centrifugals aren't. They are a minor restriction and you can lock one up and the engine still runs. The air will not stall in front of a centrifugal, it goes right though it. Think of it as a second turbo without the exhaust plumbing.

Either way will work, and there may be no difference, or a difference with these two setups. Nobody knows.

how about the good ole electric leaf blower?I seen a 5.0 stang w/ one...he said he was making 10psi of boost w/ it.....Had an extesion cord run tot he cig lighter were his inverter was....lmao....Thats some Blue Collar stuff right there..i tell you what!

rat, thought you were going larger super not smaller, does that mean changing turbo to different size! would stay away from roots maybe lyscholm(kenne-bell) style less heat generation by design, prefer paxton style.
pro400exe search for electric supercharger, from what i've read the toyo, and such use them at stoplight turn it on loads up turbo to cut down on turbo lag street racing, after launch seems use pressure switch to cut-out, turbo takes over.

I had a summer job at Paxton Superchargers about 9 years ago and those guys used to have a setup like you all are talking about on their Kodiac tow vehicle. It was one of those turbo Caterpillars that they'd put a Novi 2000 on top of (pre-turbo). I don't know how much it helped . . . some of those guys had a tendancy to do stuff just for the sake of doing it.

I'd have to cast my vote for pre-turbo simply for the ease of install and packaging . . . but it all comes down to what's going to actually work better.

so what is the verdict?

ill donate my truck as the "test mule" if anyone is interested.........im searching ebay now, what kind of superchargers should i look for?

OPEL has compound turbo setup on 1.9ltr, but bypass valve like spearco units, primary unit sized to reduce turbo lag, secondary unit builds up higher rpm's and opens bypass valves on intake and exhaust reducing thermal load. didn't know if any have seen this, wish wallet could afford dreams, would have fun playing. just my 2c

Post turbo seems to be the way to go for making good low rpm boost without blasting away your MPG.

I didn't read this whole topic so please excuse me if someone already posted this. Back in 67 while in the Navy we borrowed a new launch from the boat pool to ferry guys back and forth across SF bay. It had the usual 6-71 Detroit Gray Marine engine except for the addition of a turbo. It was the fastest boat we had at the time.Later! Frank

Frank - Care to explain how you guys had that setup?

Can you be more specific WAskier? Later! Frank

Detroit's had the turbo blowing into the supercharger. It was probably a two stroke, so it needed the blower just to be able to run.