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Home made supercharger?
bi22le - 11/7/11 at 08:42 PM

Hi all,

I was day dreaming the other day again about supercharging my car and had a look for Rotrex superchargers, they cost soooo much!

You can get a MINI Eaton supercharger for a fifth of the price but it wont fit in a 7 as far as I know. I dont think there is room in my Striker anyway!!

So, after looking at a Rotrex and speaking to my mad mate (bending and building a bonkers V8 MG Midget from scratch) it was thought as possible.

Could I not get a small ish turbo, split it and pulley the shaft?

A machined plate may need to be made up so the oil cooled bearings dont melt and internals are weighted, supported correctly?

10 to 1 ratio pulley.

. . . . . . . I dont know, I was just dreaming.


Thoughts, experience?

Happy driving all,

Biz

tomgregory2000 - 11/7/11 at 08:46 PM

I dont think you will be able to spin it fast enough, simple as that

clairetoo - 11/7/11 at 08:48 PM

In a word - no .
The Rotrex has an epicyclic gearbox , which increases the revs so the pulley can turn at a reasonable speed - even multi V pulleys cant run at 60000 rpm...............

[Edited on 11/7/11 by clairetoo]

daviep - 11/7/11 at 08:55 PM

I think the pulley ratios would be prohibitive, I think you'd need at least 20:1 you're looking for turbine speeds of about 100,000rpm, which mean having a crank pulley bigger than 2 foot diameter.

Davie

bi22le - 11/7/11 at 08:58 PM

Ah nuts.

any alturnatives to rotrex or a method of skrinking an eaton?!?

bi22le - 11/7/11 at 08:58 PM

Ah nuts.

any alturnatives to rotrex or a method of skrinking an eaton?!?

tomgregory2000 - 11/7/11 at 09:03 PM

Just use the turbo as it was intended!!!!!!

You know you want to

MikeRJ - 11/7/11 at 09:03 PM

quote:
Originally posted by bi22le
Could I not get a small ish turbo, split it and pulley the shaft?


Certainly, but you'd need the budget to develop a suitable gearbox and solve all the lubrication issues. I doubt that it would be cheaper than buying a Rotrex...

balidey - 11/7/11 at 09:24 PM

Why can't you do it? I looked into this a while ago for my cinquecento, very small engine, very small engine bay.
A Rotrex is just a turbo housing on the side of a bespoke made gearbox.
As for speeds, I seem to remember from AG Bell's book on charging, a smaller turbo needs to run at faster speeds than a larger turbo, so if you can't achieve the same speeds as a Rotrex unit just use a larger turbo running slower to achieve the same effect (OK, simplified it, but thats basically the gist of it)
Ultimately you may not get it spinning at the same RPM, but you will still be achieving a positive pressure, so you will still have supercharged your engine for a few hundred as opposed to a few thousand pounds. All you need to do is source or make the right gearbox. And as Rotrex have made one that tells me there must be similar ones out there that you can adapt to do a similar job.

zilspeed - 11/7/11 at 10:11 PM

12V winches have planetary gears.
Not sure of the ratios though.

Badger_McLetcher - 11/7/11 at 10:27 PM

To get up to those kind of speeds a suitable gearbox is needed. Get one and then yes, you could make yourself a a supercharger. Not entirely sure where you could source such a beast though. It may be possible to make one yourself, dependent on your facilities.

Doctor Derek Doctors - 11/7/11 at 10:37 PM

Instead of gearing it up you could just use a much larger compressor. Something like an IHI 85mm truck turbo compressor would need to be spun less quickly to to give the same flow than a tiny car turbo needing to pin at 80,000+ rpm.

But then again I think even with that size compressor you would need at least 30,000 rpm to get 10psi of boost. So you have a Turbo thats nearly a foot accoss with a 1:5 (ish) pulley ratio to make a fairly low amount of boost.

You might as well just use a turbocharger, superchargers are a dieing technology, the manufacturers are selling them at a loss to the car makers and they are less efficient, more complicated and make less boost. Turbos on the other hand are are getting, cheaper, smaller and more efficient.

MikeRJ - 12/7/11 at 06:59 AM

quote:
Originally posted by balidey
And as Rotrex have made one that tells me there must be similar ones out there that you can adapt to do a similar job.


The compressor is the trivial part of the Rotrex. The clever bit is the friction driven epicyclic gearbox which gives the massive gear ratio required to spin the compressor at the required speeds, whilst taking the large peak torque during engine speed changes.

Simply fitting a pulley to an old turbo and hoping to be able to drive it fast enough is a total non-starter.

MikeRJ - 12/7/11 at 07:02 AM

quote:
Originally posted by Doctor Derek Doctors
You might as well just use a turbocharger, superchargers are a dieing technology, the manufacturers are selling them at a loss to the car makers and they are less efficient, more complicated and make less boost. Turbos on the other hand are are getting, cheaper, smaller and more efficient.


But still suffer from the same problems they always have, i.e. non-linear boost characteristics when they are working, and relatively high RPM required to get them working in the first place unless you have the complexity of staged turbos etc.

bi22le - 12/7/11 at 09:29 AM

Would it need to get to high RPM?

I only want a little boost, like 10psi or so. a big diesel compressor may do this.

a few have mensioned a massive pulley. is this to achieve tge possible required ratio needed and not due to torque required to spin the turbo?

I can get my hands pn a good condition massive boat engine turbo, garrett aswell i think.

bi22le - 12/7/11 at 09:35 AM

quote:
Originally posted by MikeRJ
quote:
Originally posted by Doctor Derek Doctors
You might as well just use a turbocharger, superchargers are a dieing technology, the manufacturers are selling them at a loss to the car makers and they are less efficient, more complicated and make less boost. Turbos on the other hand are are getting, cheaper, smaller and more efficient.


But still suffer from the same problems they always have, i.e. non-linear boost characteristics when they are working, and relatively high RPM required to get them working in the first place unless you have the complexity of staged turbos etc.


there are acouple of reasons why i want to avoid a turbo and this is one. power figers is appealing to me but i want good usable power in a light car. a supercharger is better for this i feel.

the other reason is just to be different. although i would rather have a faster car and 4 figures of change than nothing!!

nick205 - 12/7/11 at 09:54 AM

Didn't flak monkey use an Eaton charger on his GTS Duratec?

Might be worth looking at the install to see how he fitted it and whether a bit of imagination would see it in the Striker. There's nowt wrong (IMHO) with having a charger poking out of the bonnet in a hot rod stylee

daviep - 12/7/11 at 10:10 AM

quote:
Originally posted by bi22le
Would it need to get to high RPM?

I only want a little boost, like 10psi or so. a big diesel compressor may do this.

a few have mensioned a massive pulley. is this to achieve tge possible required ratio needed and not due to torque required to spin the turbo?

I can get my hands pn a good condition massive boat engine turbo, garrett aswell i think.


You would need a huge pulley for two reasons:-

  1. The ratio, you need to be gearing up by a factor of around 10 or 20:1
  2. The pulley on the turbine has a minimum size depending on the belt used, it's not only the torque requirement but the minimum bending radius of the belt.

I don't think a turbo turbine will have a linear output like a supercharger, I think you'll need to reach the correct operating speed.

Bolting on a huge turbo would seem counter productive to me, they aint going to be well packaged under the bonnet and it aint going to be light.

Davie

Doctor Derek Doctors - 12/7/11 at 12:33 PM

quote:
Originally posted by MikeRJ
quote:
Originally posted by Doctor Derek Doctors
You might as well just use a turbocharger, superchargers are a dieing technology, the manufacturers are selling them at a loss to the car makers and they are less efficient, more complicated and make less boost. Turbos on the other hand are are getting, cheaper, smaller and more efficient.


But still suffer from the same problems they always have, i.e. non-linear boost characteristics when they are working, and relatively high RPM required to get them working in the first place unless you have the complexity of staged turbos etc.


At the end of the day though they're still a better solution, thats why more and more cars are turbocharged and less and less are supercharged. Even the most somplex turbo's ar still simpler than a supercharger as well. Thats why the new forced induction F1 engines are all using Turbos and not superchargers

Toniq-r - 12/7/11 at 01:01 PM

Well Im very happy with my SC fair it was not cheap but no complaints

flak monkey - 12/7/11 at 04:23 PM

quote:
Originally posted by nick205
Didn't flak monkey use an Eaton charger on his GTS Duratec?

Might be worth looking at the install to see how he fitted it and whether a bit of imagination would see it in the Striker. There's nowt wrong (IMHO) with having a charger poking out of the bonnet in a hot rod stylee


No I used a Rotrex.

A big compressor doesn't solve the problem, they just become very inefficient.

Either stick with a Rootes type charger, which are pretty simple to fit and set up, or shell out for a proper centrifugal one like the Rotrex.

The americans do produce some centrifugal superchargers with 20:1 step up belt drives, but none will produce very much boost and are very inefficient....

Liam - 12/7/11 at 05:25 PM

You can't just fit a truck turbo and run it slowly! It'll be so far away from anywhere on its compressor map it is actually intended to operate it'll be next to useless.

ianjenn - 12/7/11 at 08:14 PM

I have supercharged my kitcar with an Eaton M62, full details here with rolling road results and link to pictures supercharging through bike carbs

[Edited on 12/7/11 by ianjenn]

madflow - 20/1/12 at 12:02 AM

since im always interested in the unusual and homemade, this idea has me dreaming , have you seen the GATOR web site --they seem to make the idea of belt driving the turbo possible, that is until you go futher into it --its an engineering exercise in bolt together components from your local bearing supplier. more for show purposes than actual use , as i cant see those bearings taking the rpm and lack of oil feed for the turbo floating bearing system.Still it does seem to have been done in the past and been made to work if only for limited period on short run time engines---not weekend use even , let alone a daily driver .My next let down was calculation of cost , toting up the prices and its couple of hundred just in materials and bearings , then add on machine costs so unless you can do machine/ lathe work your- self and get the bits for free or next to nothing , the eaton 45 or 62 unit is going to work out cheaper ( providing it not knackered) and at least give an almost guarenteed result of sorts. But this still hasn t put me off the idea totally --bugger for self inflicted / time wasting/ money pit projects. cheers

spiderman - 20/1/12 at 01:29 AM

I seem to remember that PPC magazine were doing a x/flow supercharged Westfield which was looking quite promising but as usual the articles stopped before it was finished. Yet another unfinished project from the boys at PPC, I don't think I have seen a completed project of theirs yet, perhaps they should have called it "Projects Permanently Ceased".

coyoteboy - 20/1/12 at 02:51 AM

If you want relatively low boost and a linear power band from low revs get yourself a SMALL compressor turbo with a relatively large turbine housing and a BIG intercooler. IT'll spool quickly, probably just off idle with something suitably small, and it'll be right out of its efficient envelope at high revs, probably choking the engine a bit, but through the IC you should be able to keep the heat bearable.

gazza285 - 20/1/12 at 05:45 AM

Use an electric supercharger

coyoteboy - 20/1/12 at 11:32 AM

You might laugh, there is actually someone developing one that effectively uses a fairly large compressor housing and a powerful brushless DC motor in the kW size range which does actually work a treat, I'll see if I can find it.

MikeRJ - 20/1/12 at 01:00 PM

quote:
Originally posted by coyoteboy
You might laugh, there is actually someone developing one that effectively uses a fairly large compressor housing and a powerful brushless DC motor in the kW size range which does actually work a treat, I'll see if I can find it.


Only for very brief, intermittent operation though.

coyoteboy - 20/1/12 at 01:41 PM

quote:

Only for very brief, intermittent operation though.


Limited by battery capacity and alt charge rate I suppose! But when you look at a normal road-use car, the turbo use is only intermittent high intensity or long duration low intensity.

Quick calcs: Power required (hp) to run the supercharger to boost an engine from shaft power:

hp=(0.0043*boost psi*cfm)/compressor efficiency.

i.e. you could boost a small bike engine to 1bar at 14Krpm for about 6kW, requiring 500A from your battery. Clearly this might take a bit of re-charging

[Edited on 20/1/12 by coyoteboy]

hypersonic - 20/1/12 at 07:17 PM

My mate fitted an eaton from a mini to an mi16 engine in his 205. Did it all himself and it made an impressive 252bhp at the wheels.

madflow - 25/1/12 at 04:18 PM

on the ppc supercharged xflow , did it ever get going--i stopped getting the mag , and it always puzzled me to see the dummy /mock build which showed the twin side draft manifold with throttle bodies on it--how was that going to work out ?

NeilP - 25/1/12 at 05:54 PM

quote:
Originally posted by coyoteboy
Quick calcs: Power required (hp) to run the supercharger to boost an engine from shaft power:

hp=(0.0043*boost psi*cfm)/compressor efficiency.

i.e. you could boost a small bike engine to 1bar at 14Krpm for about 6kW, requiring 500A from your battery. Clearly this might take a bit of re-charging


Separate high voltage battery system - weight penalty and a fairly sophisticated ECU / alternator setup...

Had too much sugar today

coyoteboy - 25/1/12 at 06:33 PM

Personally I'd just make space for a supercharger

AntonUK - 25/1/12 at 07:37 PM

I cant see the problem with finding a properly spec'ed turbo for your engine... got to be cheaper and less hassle?

That's what i'm planning to do eventually.

bi22le - 5/11/13 at 07:24 PM

And the dream rumbles on. . . . . . .

Even more so now as its time I dont have, well and money. I am full of ideas though.

I have acquired the turbo and dismantled it. Its a big Holset so I am currently on the hunt to find the effeceincy map for it.

I am thinking I can gain about 2 or 3:1 at least via the pulley set up. I am also thinking that I can gain approx 4:1 from a home made gearbox. Thats nocking on the door of 80,000 RPM. Well within the expected efficency range of a large turbo.

Gears will be sourced from somewhere. I can get metal gears from work which look quite strong but if not ill see whats available from gear companies or scrap gearboxes.

Shafts I can turn up or get turn up or get turned up at work.

Bearings ill source from a bearing company, they will be oil cooled.

Casing will be made from CAD cut plates, possibly water laser but probablt not due to numbers req. Design will include internal bearing carriers. These layers can be nice and intricate and then welded together. This allows for cheapish manufacture, idealistic design and and oil ins and out, or I might seal it. so it just has a front piece.

The more I think about it the more I think I can do it.

Thoughts?

I know people have resivations on large turbo compressors being used but the high volume and cool compression from low RPM is appealing.

I also know that people ask "why bother?".

This forum is called locostBUILDERS not low costBUYERS. The fun is in the thinker and tinker not the deliver and believer.

[Edited on 5/11/13 by bi22le]

sky12042 - 5/11/13 at 08:24 PM

To get the required rotational speed for the turbo why not use a coupe of pulleys so if you need a 20:1 ratio use two 10:1 pulleys
That way it will keep the size down and allow you to mount it in a suitable position. I think it could be possible with some good bearings and strong belts.

Agree that a turbo used as intended might be easier. But worth playing about with just so you can say that it's been done.

Andy.

bi22le - 5/11/13 at 08:40 PM

quote:
Originally posted by sky12042
To get the required rotational speed for the turbo why not use a coupe of pulleys so if you need a 20:1 ratio use two 10:1 pulleys
That way it will keep the size down and allow you to mount it in a suitable position. I think it could be possible with some good bearings and strong belts.

Agree that a turbo used as intended might be easier. But worth playing about with just so you can say that it's been done.
Andy.




Thoughts on this peeps?!?!



[Edited on 5/11/13 by bi22le]

scimjim - 5/11/13 at 09:17 PM

quote:
I am thinking I can gain about 2 or 3:1 at least via the pulley set up. I am also thinking that I can gain approx 4:1 from a home made gearbox. Thats nocking on the door of 80,000 RPM. Thoughts?


The efficiency map is based on an rpm that's controlled by the shape of the turbine blades (hence variable vane are so much more efficient).

your belt driven design with large pulley and gearbox may be nearly as effective as a conventional turbo between 7 and 9,000 rpm (engine) - but just extra weight and restriction to the airflow in every other part of the rev range?

from an engineering point of view you're losing all of the advantages of a turbo (weight, cost, simplicity) but from a "built it in my shed" view you could be up for massive man points as long as it sticks out of the bonnet and has a loud dump valve

owelly - 5/11/13 at 09:17 PM

Take a drive off the flywheel. Big gearwheel driving a starter motor gearwheel and then step that up to whatever you need.

scudderfish - 5/11/13 at 09:53 PM

quote:
Originally posted by sky12042
To get the required rotational speed for the turbo why not use a coupe of pulleys so if you need a 20:1 ratio use two 10:1 pulleys


That'll give you 100:1! Two 4.5:1 will give 20.25:1

sky12042 - 5/11/13 at 10:29 PM

Scudderfish your right didn't quite think it through correctly, but you get what I mean two smaller belts will give you a more compact belt driven install.

Andy.

mark chandler - 5/11/13 at 11:34 PM

You need to consider the power involved in spinning it up, my db7 has a 10 rib wide belt on a 3" pulley, it must be able to absorb maybe 40bhp without overheating.

Getting the speed in theory is fine, actually translating this into reality is another thing, at the speeds mentioned you really need a mechanical solution on the final drive.

Cog off the flywheel sounds good, I bet the gears will howl when running!

scudderfish - 6/11/13 at 07:18 AM

What is the effective ratio between the flywheel and the starter motor?

mcerd1 - 6/11/13 at 09:41 AM

quote:
Originally posted by scudderfish
What is the effective ratio between the flywheel and the starter motor?

count the teeth on each.....

I don't think most starters will have less than 13 teeth, but I've no idea what the average ring gear has...

[Edited on 6/11/2013 by mcerd1]

mcerd1 - 6/11/13 at 09:52 AM

quote:
Originally posted by bi22leI also know that people ask "why bother?"

I'd guess your going to have more than a few issues with the ratio's, cooling, lubrication and the strength of any gears/gearbox etc...

but it sounds like a good project to keep yourself amused with and it'll be really satisfying when it works



and if you ever change your mind there are ways to make an eaton fit
(thats on an RV8, so no space at all in the engine bay )

MikeRJ - 6/11/13 at 10:57 AM

quote:
Originally posted by scudderfish
What is the effective ratio between the flywheel and the starter motor?


A Ford Crossflow, for example, has 135 teeth on the ring gear, and 9 on the starter, so a 15:1 ratio. It wouldn't be useable to power anything continuously though since the teeth aren't lubricated, so would wear away to nothing in short order.

I suspect some kind of geared final drive would be needed though, probably an epicyclic gearbox which would minimise any radial forces on the compressor shaft bearings.

[Edited on 6/11/13 by MikeRJ]

sky12042 - 19/11/13 at 11:22 PM

Found this on the net. Thought it might help with any ideas or problems you might come across, Andy

http://www.cachassisworks.com/Attachments/DataSheets/CDS_DS_WEB.pdf

flak monkey - 24/11/13 at 08:03 PM

quote:
Originally posted by bi22le

Thoughts on this peeps?!?!



Dont bother

High shaft speeds needed for the turbine need very precise manufacturing tolerances for alignments and bearing housings.

Belt drives have belt speed limits be sure to check them too as a lot of belts aren't capable of running anywhere near the speeds you are thinking about. Also remember they will be carrying huge loads at those speeds to make 10psi of boost.

There's good reason people don't do this sort of thing. Procharger do make gear driven chargers, there's some tech on their site. Even they only run an internal ratio of 4.1:1 You are into specialist gears at those speeds too.

http://www.procharger.com/supercharger-cutaway.shtml

They do higher ratio ones for big boost (20-50psi).

Post up a video the first time you run it up....

stevio73 - 24/11/13 at 10:13 PM

Seems like a whole bunch of hassle that will effect reliability IF it works. Don't get me wrong, I love a challenge. If your going to all the trouble of machining mounts, bearing housings and stuff like that, why not scratch build a rootes type blower?

Ultimatly what size are we talking? Sounds like you need someone who can cast aluminium. (Nudge, nudge)