Compound Procharging!

[Procharmo]

What are your views on the results that would be encountered when the outlet of one Procharger was fed into the inlet of another Procharger the same size driven by the same crank shaft at identical speeds.

I would like your opinions on possible gear drive torque issues, inter/pre and post stage meth/water injection cooling, and any other phenomena that would be encountered.

Here's some info to get you going....

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AIR are Procharger's Industrial sister company using unit similar in size to the F2 they are used in the commercial aircraft industry. Here twin F2 sized blowers can be configured parallel or series giving 15psi or 40 psi at 2500cfm or 5000cfm.
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http://www.yellowbullet.com/forum/showthread.php?t=216811

Below is my set up, will I damage it if I compound them or is excess air flow cfm compressed inthe manifold resulting in additional boost over and above the pressure created in the volutes.

That is to say if then engine at a particular rpm consumes 700cfm at 25psi but the blowers produced 1400cfm at 25psi what psi would I see? I suspect surge and stall still apply but to a lesser degree than with turbines due to the engine rpm/impeller rpm relationship.
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[Scott Parkhurst]

There are SO many factors to take into consideration here.

What's the application? What benefit are you hoping to acheive by doing this?

How do you intend to combat the inherent heat issues that multiple stages of compression bring with them?

Here's my point- If you're looking to make power with boost, and budget is not a primary concern, what are you looking to do that cannot be done with existing superchargers and/or turbochargers? Is this 'simply' an experiment to see what will happen? Or, is the application experiencing issues you feel multiple stages of compression will solve?

I feel there's benefit in spinning a smaller turbo compressor into a larger one to get it to spool up faster, as Porsche did. But with belt-driven compressors, you're limited by the physical size of the housing. That becomes your air restriction, and since it's belt-driven, designing the supercharger system to optimize the need for airflow with pulley ratios, compressor housing sizes, etc. based on the engine's displacement and target rpm/boost levels is well-researched. There's really no need or benefit to a belt-driven blower feeding into another belt-driven blower, especially if they're the same size. Once you max out the airflow, no more is to be gained. If you need more airflow, get a larger compressor. If you need more boost sooner, get a smaller pulley.

JR Granatelli published an entire book of boost maps based on compressor displacement, pulleys of varying diameters, and a wide range of rpm. Maybe you should take a peek at that before stacking belt-driven compressors?

The 'gearbox' being discussed could be used for a very particular drag race application, which is the only place I can think of where any possible benefit could be found from doing this. Even then, it'd be for very few individuals with very specific needs, and for a very limited period of time (in a quarter-mile pass, which only lasts a few seconds). It builds the boost at a controllable rate to keep up with the tire as the car goes down the track.

It seems to be designed for an aircraft application, where thin air needs a slew of compression, and engines are run at relatively low, steady rpm levels for long periods.

[Procharmo]

Hi Scott,
the question was posed to see if the boost curve of a twin staged centrifugal set up could equal or better that of twin screw blowers.

Inter stage cooling will be via meth/water injection to aid engine bay packaging.

Smaller pulleys/gears will only result in maxing out blower rpm before engine rpm. I was hoping that the second blower would further compress the pre compressed air resulting in twice the psi for a given engine rpm...

The gear driven supercharger applications are used in drag racing as you mentioned, but they are and have been used in street cars as well.

In fact the first most successful road race cars were boosted via a crank/gear driven roots blower!!!!

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My goal was to merely ask what the pro's and con's were. I will build this for my street strip application as originally intended in parallel not staged. I was just being inquisitive as it would only take fabricating a second set of charge pipes, meth/water injection nozzles and lines.

As far as getting a larger compressor goes the Procharger F4 is the larger alternative.
Let me know when you have found an example of a car with an F4.

https://static1.pt-content.com/images/pt/2010/05/IMG_14461JPG-1.jpg

LOL!!! Only kidding.

Thanks for your comprehensive answer.

[exwestracer]

Compounding typically involves a large compressor section feeding into a smaller compressor for increased boost. Looking at your setup, you would have an un-avoidable pressure drop as the outlet from the first "stage" fed into the much larger volume of the second stage.

The result of this could be a huge loss in efficiency as both stages are spinning at the same speed (assumption), so the volume of air they are expecting to see is the same...?

Look into Pro-stock Diesel pulling tractors, as they routinely use 4 (!) compounded turbochargers to blow those John Deere engines apart...

[Procharmo]

Thanks. I'll get surfing straight away.. It still dosn't explain why Procharger are selling this.....or how in efficient it is!!!!!

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[exwestracer]

Thanks. I'll get surfing straight away.. It still dosn't explain why Procharger are selling this.....or how in efficient it is!!!!!

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I looked up the AIR website, and while there is no further information there, I have to believe that the staged units use 2 different compressor sizes...

[Procharmo]

Just found out that whilst the fastest procharged car over 1/4 is at 6.92 with twin parallel F2 blowers. A pro mod car has just hit 4.008 for the 1/8 mile with compound Prochargers... They look to be dual F2's.....They are looking to get in the 3's any time soon!! They got in the threes. And it's F3 into an F2!!

New Procharger Record (http://www.yellowbullet.com/forum/showthread.php?t=277623&page=3)

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[Procharmo]

He (Flex of Flex Racing) has jnow ust gone 3.92 @ 183 mph 1/8th. Twin F2's compounded can provide enough airflow and boost for a BAE engine to run against other PSI screw blower equipped BAE engined cars.

Granted one is reverse drive so he must be spinning one slower but they are twin F2's. And he is the fastest Procharged car out there....The rules for turbo's and centrifugals can't be the same, similar but not the same when it comes to compounding....

Anyone have industrial or commercial experience of compound centrifugals?

[Gtrpunk23]

Isn't the point of force feeding to help spool up in a turbo application. I may be way off but I was under the impression that a smaller turbo is used to spool up quickly intern help the larger turbo spool up and get to peak boost/power. I am CERTAINLY no expert at all, I am very interested in this thread.

[overZealous1]

i have only seen turbo's feeding a supercharger before. was going to do this on another project and did quite abit of research but never got around to doing it.
plan was twin turbo into a 6/71 huffer. it had been done years ago by rick dobberton. i contacted him directly to see his findings. with the turbo's feeding the blower, whatever your turbo boost is set at, will be multiplied by the blower boost in theory.
i would assume the same to be true for a compound supercharger set up, but would imagine effiecientcy losses to make it a loose theory.
i would try to contact racers who are doing it and get more info. if they wont give up their secrets, procharger will to sell ya the parts!! haha

[Procharmo]

Isn't the point of force feeding to help spool up in a turbo application. I may be way off but I was under the impression that a smaller turbo is used to spool up quickly intern help the larger turbo spool up and get to peak boost/power. I am CERTAINLY no expert at all, I am very interested in this thread.

Yes your correct. But turbo's have different sized hot pipes and turbines to fine tune the percentage of exhaust gases that turn either turbine.

Then each impeller and volute is sized so that the interstage pressure and volume dose not cause surge in the secondary turbo.

Finally the pressure ratio of the first is multiplied buy the second along with a drop in density caused by heat. So it can get pretty complicated to work all of this out in theory or very expensive in practice....

[Procharmo]

i have only seen turbo's feeding a supercharger before. was going to do this on another project and did quite abit of research but never got around to doing it.
plan was twin turbo into a 6/71 huffer. it had been done years ago by rick dobberton. i contacted him directly to see his findings. with the turbo's feeding the blower, whatever your turbo boost is set at, will be multiplied by the blower boost in theory.
i would assume the same to be true for a compound supercharger set up, but would imagine effiecientcy losses to make it a loose theory.
i would try to contact racers who are doing it and get more info. if they wont give up their secrets, procharger will to sell ya the parts!! haha

Regarding asking the racer himself. I did just that and he stated that it cost them a lot of "blood, sweat and tears" to develop the system..

Unfortunately Procharger are not as progressive in the racing scene as they are with the "bread and butter" street scene. They only developed a gear drive many years after the Supercharger Store launched theirs. Also Procharger do have a gear drive now but only for the F3's on BBC's.

My thoughts were as to wether a smaller gear set on one side of the twin gear drive hence spinning one slower with meth/water injection in the pipe between them and in the intake of the first blower. Then finish with boost control on the charge pipe. It should have twin screw performance at the bottom end with ultra high boost on the top end!!!!

This would be using all the components of my existing twin parallel set-up with just a change in pipe work and gear sets.

When studying the Promod car it appears they have one standard rotation F2 and one reverse rotation F2. this indicates a fourth gear set in the twin gear drive meaning the step up ratio was quite drastic. But then they are identical blowers...
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Obviously they didn't go with an F3 and and F2 due to flow issues or they didn't want to go staggered due to the Pro mod packaging issues...
https://static1.pt-content.com/images/pt/2010/07/389176110-1.jpg
Yet twin F2's didn't allow enough difference in speed without and additional gear.

Just to clarify a single input (from the crank) gear turns two other output gears (to the blowers) either side of it. If you add a fourth to either side you reverse the rotation!!!!

[T/Aaron]

Wouldn't you need 2 compressors to feed into 1 compressor to make this idea viable? If you have 2 compressors, you're airflow is limited by how much air flows through the first compressor. Pressure should not matter if the volume of flow is not increased. P1V1=P2V2. Not sure how compounding is going to change this fundamental equation.

[Procharmo]

Wouldn't you need 2 compressors to feed into 1 compressor to make this idea viable? If you have 2 compressors, you're airflow is limited by how much air flows through the first compressor. Pressure should not matter if the volume of flow is not increased. P1V1=P2V2. Not sure how compounding is going to change this fundamental equation.

Well it depends on how, much pressure and volume you can use. What Flex has done is to take a pair of off the shelf F2 Prochargers and have performance equal to the much more expensive Pro Mod PSI twin screw blower. If he were to do as you suggest and run an larger F3 into and F2 or two F2's into one F2 then the resulting pressure and heat would be much more than his engine could utilise.

If we look at the inner workings of jet engines the multi-stage compression can be achieved with either a larger slower spinning impeller or faster smaller impeller.
I think due to packaging and compressor efficiency reasons the twin same size blowers at different speeds worked out to be adequate...

The idea has been proved viable due to his record breaking run. It just hadn't been done when I first had the idea... I'm now just looking to see if it can be used out of the 3500hp arena and in our lowly 1000hp and below arena............

[Wicked]

For supercharging, you are limited by how fast you can turn the impeller...i.e. You can only fit so many gears in a given package and it still fit in the car.

Think about a turbo, it may spin up to 120,000 rpm depending on the size. Smaller one's approach 200,000 rpm I believe. So a much smaller compressor can be used to make big power.

Its much harder to make a blower spin that fast, i.e. a 6000rpm engine would require a 20:1 step up(including pulley ratio) ratio to get the same rpm as the turbo. If you could achieve the 20:1 you could use a smaller impeller. However, its then much less efficient due to all the gear losses and the fact that its always spinning 20 times faster than the engine.
To put it in perspective. My Procharger P1SC has an internal ratio of 4.1:1 and with my belt ratio was turning about at the limit 62000rpm.

The compound supercharging allows you to run two compressors in series. Here's an example of two identical centrifugal superchargers in series. These are vortech since that's the first compressor map i came to. One blower, for example, spins at 40000rpm, pumps 30lbs/min of air at a pressure ratio of 1.8:1. So the first blower would create 1.8*14.7psi-14.7=11.76 psi gage.
No the air coming into the second blower is higher. But the second blower is still pumping at the same rpm, will yield 60lb/min and 1.8:1 pressure ratio. So the final boost should be about 33psi at 60lb/min.

The good thing about this is the blower doesn't have to spin right at its limit to make a lot of boost. Because its two larger compressor(as opposed to a turbo), less heat is being added to the air. However, this should be quite inefficient compared to a turbo setup and possibly just as heavy.

This is the first time I've ever done the compound supercharging calculations, so I may have made an error.

In my opinion, twin turbos are better and definitely my qeapon of choice. And I have owned both. You can have the car setup for 500hp one day, and 800ho the next with the same turbos. No belts to change. Better efficiency. Etc.

[Procharmo]

For supercharging, you are limited by how fast you can turn the impeller...i.e. You can only fit so many gears in a given package and it still fit in the car.

Think about a turbo, it may spin up to 120,000 rpm depending on the size. Smaller one's approach 200,000 rpm I believe. So a much smaller compressor can be used to make big power.

Its much harder to make a blower spin that fast, i.e. a 6000rpm engine would require a 20:1 step up(including pulley ratio) ratio to get the same rpm as the turbo. If you could achieve the 20:1 you could use a smaller impeller. However, its then much less efficient due to all the gear losses and the fact that its always spinning 20 times faster than the engine.
To put it in perspective. My Procharger P1SC has an internal ratio of 4.1:1 and with my belt ratio was turning about at the limit 62000rpm.

The compound supercharging allows you to run two compressors in series. Here's an example of two identical centrifugal superchargers in series. These are vortech since that's the first compressor map i came to. One blower, for example, spins at 40000rpm, pumps 30lbs/min of air at a pressure ratio of 1.8:1. So the first blower would create 1.8*14.7psi-14.7=11.76 psi gage.
No the air coming into the second blower is higher. But the second blower is still pumping at the same rpm, will yield 60lb/min and 1.8:1 pressure ratio. So the final boost should be about 33psi at 60lb/min.

The good thing about this is the blower doesn't have to spin right at its limit to make a lot of boost. Because its two larger compressor(as opposed to a turbo), less heat is being added to the air. However, this should be quite inefficient compared to a turbo setup and possibly just as heavy.

This is the first time I've ever done the compound supercharging calculations, so I may have made an error.

In my opinion, twin turbos are better and definitely my qeapon of choice. And I have owned both. You can have the car setup for 500hp one day, and 800ho the next with the same turbos. No belts to change. Better efficiency. Etc.

Thanks, great breakdown. I'm not saying Centris are better than Turbos. Just saying that compound Centris can equal PSI twin screws or get close. Then again there are twin turbo Pro mod's as well as nitrous ones. At that power level I believe the engines are somewhat similar but the cost of a pair of F2's is less than the the other power adders when above 3000hp.....

Here's a test video of a twin compound F2 set up.....


http://www.youtube.com/watch?v=MLWwv6siRaM&list=ULBbLyMQAWeWA&playnext=2

[Wicked]

Notice how the bypass and reversion blows the air filter off.

[Procharmo]

That's not the air filter. This is a compound pair of Twin F2's that later went on to be the current fastest Procharged Vehicle......It's the Flex Racing Pro Mod mentioned earlier on a conventional BBC as opposed to the BAE Hemi.

43829

What you saw blow out was the bung they had in the discharge tube whilst testing pressure....The output of the second blower was connected to that bung.

There was no air filter on the primary blowers intake.

[DeltaT]

It might be worthwhile to consider an intercooler after the first head unit to keep the temps down heading to the second.

Looking good.

Jim

[zombiekiller]

If you're seriously interested, maybe try to track down Hennessy.

They did a twin turbo + supercharged + nitrous setup on a friend of mine's ford gt.

I believe he's just under 1300hp without the juice. While it may sound like low ponies for that kind of setup, he's in it for top speed. He has a hard on for Texas mile type events.

[Procharmo]

Funnily enough I've just been watching Hennessy's video on the Venom. He buids quality set ups that last. And won't squeez out extra hp if it scrafices too much reliability. It seems like a great tunning shop.