MG Midget Forum

Aw, man, no fair. I've been staring at my M45, wanting to rebuild it...

If you've got a 1500, then you have those nifty openings in the lower valance. I'm going to have to cut one like Larry's. I also need to anticipate eventually being able to mount my air dam, so have to think about a shape and height that will end up in the flat portion of the damn dam. Haven't yet figured out whether the Audi inercooler will reside below, or if I'll move the oil cooler down there.

P.S. The compact 1999 Audi A4 1.8L intercooler I listed above is only $75.00 on Amazon, brand spanking new and free shipping. That is half what Autozone is charging.

Joel



Edited 1 time(s). Last edit at 2017-01-10 06:55 PM by Yankeedriver.

I felt well enough today to take a pad and pencil into the shop and do some design work.

I put the little blower in place (one-handed, very carefully) and designed the inlet-outlet plate. It took three tries, but what I settled on did some things I want in a DIY supercharger setup.

First, it's totally reversible.

Second, it will permit retention of the OEM heater inlet duct and crankcase breather--though I'm thinking an oil separator might be a good idea to prevent oil condensation in the intercooler, if people mount one.

Third, there will be unfettered access to the dipstick, spark plugs and wires, and the OEM temp gauge tube (on my car, it's screwed into the head, not the radiator).

Fourth, the blower's outlet angle and position will allow users to mount an intercooler initially, add one later on, or just forgo it altogether.

As for the latter option, there's one nice thing about remote-mounting a roots-style blower. Even though compression takes place in the intake manifold and not the lobe chamber, if a roots-style blower is mounted directly to a fairly short intake manifold, heat transfer through the housing and via the ends of the lobes exposed to the hot air can heat up the chamber, increasing the chances of detonation. Even without an intercooler, that won't happen here, especially given silicone snorkel elbows to insulate the unit from conduction.

Back to fitment.

Fifth, the Model 207018 M45 is mounted as Mercedes does: inlet-outlet side up, so the oil can be changed without removing the blower or even loosening the belt. You just unscrew the star-drive plug up front (photo attached) suck out the dirty oil with a syringe, then refill up to the hole. Idiotic, in my view, to follow Mercedes 'run it 100,000 miles, then change the oil and bearings' recommendation. A bottle of supercharger oil is $9.00 and the operation on a Spridget will take 15 minutes. On the Mercedes, it's an absolute bear, due to the subterranean mounting position.

The M45 207018 is compact (the body is a little over 10.5" long, and just 6.5" wide x 5" high). With the late model Spridget alternator lowered all the way, there is ample clearance for the supercharger with 2.75" inlet and 2.5 outlet under the bonnet. I may oval the outlet to use 2.5" silicone elbows, as they easily flex to fit onto an oval barb shape, to allow a little extra clearance for people who've gone with a Saturn/GM alternator, which I think is a little bigger diameter than the late model Spridget... anybody know the diameter of the Saturn alternator?

The K&N-style air cleaner will mount where my DIY EFI setup puts it (attached photo). Cool air wafts up under the fender/wing from in front of the wheel in that location, so I figure it's at least as good as the OEM location. A 2.75" snorkel from the air cleaner to the supercharger inlet will clear the bonnet atop the rear of the valve cover. The snorkel to the carb or throttle body mounted to the Minispares / Minisport manifold will come around the front of the engine just above or below the top radiator hose, no problem. Also, that means only one additional part for carb folks: a little flange to attach a snorkel to the HIF44. There are scads of throttle bodies with integral injectors and throttle positions sensors that accommodate a snorkel. I like the Hitachi pictured, but designs abound.

So, the intake tract will be: air cleaner > snorkel > inlet barb on supercharger > outlet barb > snorkel > [intercooler if wanted] > throttle body/carburetor.

Oh - and I figured out the belt run, which is dead simple. In fact, I may initially try what the guy Trevor linked to above did--running a V-belt. Though a much shorter run than his, scarcely longer than stock, in fact. V-belt's have a deceptively wide contact area, and the supercharger doesn't take much effort to turn. So, it's at least possible it will work. I'll just turn on the heater motor, halogens on hi-beam, wipers and see if it's charging at idle, then rev it a few times and see if she slips.

If I can run a V-belt, this conversion might be doable for under $1,000, and one wouldn't have to lift the engine to R&R the crank pulley. Just swap out the stock Mercedes serpentine pulley for a V-belt version, the enormous variety of which would make it easy to get the correct gearing, too. Or I could have one CNC-machined to achieve precisely the boost I'm aiming for. A simple pulley like that would be extremely cheap to produce.

I won't be able to design the mounting brackets until I have two good arms, but they're also going to be simple, as the blower will be solid-mounted. The alternator gets flipped, essentially, so its adjustment is down/out rather than up/out, to maximize clearance for the blower. No tensioner or idler pulley needed!

Joel



Edited 4 time(s). Last edit at 2017-01-14 11:47 PM by Yankeedriver.

I had a breakthrough this morning on one of the thorniest aspects of the conversion--the belt drive to the blower. Sometimes, the most elegantly simple solution is staring you right in the face.

So, I was thinking about the cost of either pointing people to the Moss $200 serpentine pulley--which is the cost of a used supercharger, for crying out loud--or coming up with a dual V-belt option. Well, it suddenly occurred to me that the fastest, easiest way to drive the supercharger with a serpentine belt without having to touch either the OEM Spridget belt drive or the pulley that comes on the Mercedes M45 blower, is to simply bolt a shallow H2O pulley like this later model Mini Cooper job (see photo) on top of the existing Spridget pulley. It would replace the steel spacer/reinforcing disc that sits on my pulley now, given that I've gone to an electric fan. (see 2nd photo of my bare pulley)

This is really cool, because all I have to do is compare the ratios/revolutions between the crank and the add-on H2O pulley, and between the latter and the blower's OEM pulley. Either I can find one with the right diameter to bolt onto the face of the OEM Spridget pulley to produce the boost I want for stock 1275s, or I'll make one up as part of the DIY kit. That also means the kit would consist of fewer parts than I'd anticipated originally and would cost less, too:

1) CNC machined supercharger inlet/outlet adapter plate;

2) CNC machined mounting brackets with threaded hole to mount some vehicle's OEM tensioner pulley for the short serpentine belt (loads of cheap Toyota, et al. options to choose from);

3) [only for carb folks] snorkel to HIF44 adapter flange.

As with the DIY rear disc brake principle--using low cost, mass-produced parts wherever available--I'd point users to an existing 'add-on' H2O pulley, or include one in the kit if the right diameter isn't available. But that seems unlikely with the proliferation of ribbed pulleys out there.

Joel



Edited 1 time(s). Last edit at 2017-01-15 02:38 PM by Yankeedriver.

How are you going to make it concentric?

Hi, Trevor.

Good question.

I don't yet know if I'll get lucky enough that the above pulley, or whatever I settle on due to diameter, will have a central bore the same as or smaller than the raised central portion of the Spridget water pump. If smaller, it could be enlarged via dremel/drill and be 'self-centering' just like the rotors on the DIY rear disc brake conversion. Then the bolt holes either line up or need to be drilled out using the spacer ring or OEM pulley as a template. Easy-peasy.

More likely would be the central bore is too large, and I'd make a drilling template and toss it in the box as part of the kit. That is, it'd have holes corresponding to those in whatever pulley I settle on, and users would just bolt it onto the pulley, then drill through holes whose position would match those on the Spridget pump/pulley.

Of course, if I can't find one that's the right size, I'd just machine a pulley with bolt holes in the right places from the git-go.

One thing that vexes me is figuring the right diameter. This same concept used to hurt my head when I'd watch my grandfather, a watchmaker, messing about with all of those teensy, shared-drive gears. They'd have very small drive gears attached to the back of a larger gear that engaged something else--which of course could be smaller or larger than the gear driving it.

So: on one hand, it seems like all I'd have to do is find (or make) one whose diameter is slightly smaller than the Moss crank pulley (because we know we want to reduce that a tad because my blower pulley is smaller than the Moss stock blower pulley).

But for some reason my brain says, 'no that's not right,' because if the water pump pulley is turning faster than the crank pulley due to its smaller diameter, then wouldn't it be whirling a pulley the same size as the crank pulley faster than the crank pulley? If so, then the right size 'add-on' serpentine water pump pulley would actually be much closer to the size of the Mercedes blower pulley. I think that's right--which is to say, I think the right sized 'add-on' water pump pulley is actually going to be very close to the Mercedes blower pulley, or even a little smaller.

Any help on this front would be greatly appreciated!

Joel



Edited 1 time(s). Last edit at 2017-01-15 04:56 PM by Yankeedriver.

Help: think about your 10 speed bicycle. To go fast the front gear is large and the rear gears are smaller, this makes it so you turn your front gear (feet) a few times for your rear wheel (small gear) to turn many times.

To go up a hill, when you want a really low gear, the rear gear is changed to the one that is the same size as the front. Then your feet the same number of times around as your wheel does, and it is easy to push.

So, if you want to gear down your drive so the SC turns more slowly you want to increase the diameter of its pulley compared to the driving one.

And vice versa.

To figure out how much, simply measure the diameter of each pulley and the ratio between them is the "gear".

N

Joel,
I know you are trying to think outside the box and come up with an affordable solution, but my gut is telling me that you may be oversimplifying things.
I understand that you are not trying to tune for peak power or efficiency, but there are a bunch of variable to consider.
I think that by trial and error you can get a working system, but the reliability may be highly questionable.
For example, regarding the pulley: You will be loading the water pump bearings to tension two belts (yes I know it was also done to drive an air pump). I suspect you will either have significant belt slippage or very short bearing life. Additionally, I wonder you you can get a flat belt to properly track with a pulley tacked onto the existing water pump v-belt pulley.

I'm not trying to be a Debbie Downer but I really think a single belt system is a much better option to pursue despite the cost.

Norm -

Thanks, that makes sense. And now that I've made a couple of sketches with some representative numbers, I realize that the dual-sized, middle wheel in question--the H2O pump pulley--is kind of an illusion. That is, the small (existing) pulley is going to complete 1 revolution just like the 'add-on' regardless of the size difference.

Joel

Trevor,

I don't take constructive criticism that way. But thanks for being sensitive.

As for bearing load, you note that the late model 1275's dual-groove H2O pulley drove an air pump--and in roughly the same position as where the blower will go, I believe. I think that alleviates bearing load concerns, unless people are aware of higher incidence of H2O pump failure in air pump-equipped cars.

I'm not too worried about belt tracking. We'd be talking two, rigidly mounted units and precisely aligned, 6-rib pulleys.

I don't think belt slippage H2O pulley-to-blower will crop up. Again, we're talking two pulleys with a short run and minimum 50% of each pulley contacting a 6-rib belt. The spring-loaded tensioners on A/C compressors, power steering pumps, and other units that generate a healthy amount of drag are likely to be sufficient to prevent slippage. Or I could use a screw-driven tensioner, like on my Subaru, my Dad's Camry, et al. You can dial in just the amount of tension you need to stop the squealin'.

Slippage crank to alternator should also not be a problem because the routing and drag-to-surface area calculations wouldn't change from OEM with an air pump.

So, the question to my mind is how much less the frictional requirement of the H2O and air pumps is than that of the H2O pump and blower. Haynes says the air pump is supposed to turn out 1.5 lb. sq. in. (1.035 bar) at 850 rpm, but their test says nothing about the extent of increased pressure as engine rpm increases. The Eaton roots-style blower's power consumption is non-linear and situation specific. It uses near zero energy at idle and steady state cruising due to the bypass feature, and I'll be dumping excess pressure at 5 psi, assuming a bit higher output for users at sea level. So, we're talking a fairly modest added load from 1 to 5 psi, the high end only during spirited acceleration. Also, if the H2O pulley slips under higher-end blower load, I think I'd be able to see any failure to achieve the bypass point on the boost gauge during beta testing, wouldn't I?

However, all that said, two things may recommend a serpentine drive over the 'add-on' pulley solution--or a custom V-belt + 6-rib H2O pulley: bonnet clearance and simplified mounts. Fixed mounts for the alternator and blower are easier to design and mean more clearance under the bonnet for the supercharger's inlet and outets, because I don't have to leave room to lift the alternator and tension the OEM V-belt.

Also, if the DIY conversion saves folks in the range of $2,500 as I expect it will, I think you're right that it's a bit silly to worry about a couple of hundred bucks in custom pulleys. I just like pushing things as far as possible when engineering a solution because the exercise tends to force innovation. At any rate, I'm meeting with the machine shop foreman tomorrow to discuss the cost of making a billet crank pulley of just the right diameter to achieve the desired drive ratio (maybe with integral steel crank trigger wheel), so I'll talk to him about adding a billet 4" ribbed H2O pulley, too.

Speaking of that, did you get a chance to measure your boosted pulley diameter? I'm wondering about that ratio.

Joel



Edited 2 time(s). Last edit at 2017-01-16 11:41 PM by Yankeedriver.

I should get a chance to measure it today. I intended to do it this weekend but some unforeseen obligations popped up.

I mentioned the oversimplification because Arnold Hermann had a similar attitude, but kept running into unanticipated problems. One of those problems was belt slippage.

Joel,

I think the concern for bearing life will come from trying to over tighten the v belt to get enough grip to drive the blower successfully all of the way up the RPM band.

Although the blower is going in the same area as the air pump, that air pump required less force to turn (it was a centrifugal, vane type blower, pushing less than 2 psi into the exhaust tracts). The blower is positive displacement and will require more force to turn at high rpm, and will be called on to output at a higher pressure.

I think this is why they use those wide, flat belts, to get way more surface area. "V" belts are also called "1/4 hp belts" in the industry because that is what they are typically used for.

I googled on "how much hp to drive rootes blower" and read about numbers in the 20 ~ 120hp range (depending on size, of course, and output pressure), at high rpm.



Norm

Joel
I've installed a few super chargers system ( designed for their application) they simply used a longer serpentine belt that still drove the water pump . The belt route was the same as OEM but of coarse went around the supercharger pulley . The only issue I had was with the harmonic balancer but it wasn't due to the supercharger. These were LS3 engines 1 running 6lbs of boost the other 13lbs

Trevor, Norm, and Steve -

I think you're right: a single serpentine is the right way to go. Thanks for the input--and for saving me the time and trouble of designing brackets twice!

As I've said, rigid mounting the alternator and blower will allow me to mount the supercharger lower, which means I don't have to oval the outlet. It will either be 2" or 2.5". The inlet doesn't have the same height restriction, as it sits back far enough that the slope of the hood/bonnet affords plenty of room.

*Note: I read some more of Eaton's literature, and they insist that an intercooler is not necessary--but of course acknowledge that using one can produce more power. The nice thing about confirming this, however, is that the DIY conversion sans intercooler can be 100% reversible, something I really wanted. It'll also be ~ $300 cheaper without the extra silicone tubing, elbows, clamps and cooler. I intend to install and beta test w/o an intercooler, then add one later on.

Trevor - I'll be meeting with the production manager this afternoon and will get bids on both crank and H2O pulleys. Whenever you measure your hi-boost blower pulley, please measure the H2O pulley. I'm curious as to whether it's standard 4" or slightly larger (to avoid cavitation, or perhaps because it's just what they sourced).

A.G. -

Cool e-blower! But my designs revolve around a core CNC part (if necessary) that allows use of OEM production car parts so people can do cool performance upgrades on a budget. Those e-blowers are crazy expensive--cool, but ouch!

I am keenly interested in an engine swap, and have been corresponding with several people, amassing info for a Zetec to Tremec T5 swap that looks very doable. However, I will get a bugeye for that project due to all that glorious space under the tilting bonnet. The '67 Midget gets a blower for reasons discussed earlier in this string, I think.

Joel



Edited 1 time(s). Last edit at 2017-01-17 09:16 AM by Yankeedriver.

Diameter of Moss small sc pulley. again crest to crest 2.745 inches.
Water pump ... and this is approximate because it is hard to reach ... is 3,93 inches