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Author Topic: Supercharging a Bagheera  (Read 66142 times)
andyowl
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« Reply #60 on: December 07, 2009, 09:54:20 am »

We have a Supercharged Bagheera!

We made it to the MECUK meeting yesterday by 1350 (it started at 1200) admittedly on a trailer because I solved the bad running problems only that morning. Some members were given rides but time did not allow for everyone, so apologies to those who did not get to ride yesterday.

I got the engine started on Wednesday afternoon but there was severe vibration of the blower drive shaft. It was clear that the shaft needed support near the blower and a simple "pillow block" bearing was ordered from RS which arrived next morning together with a harder "spider" for the Lovejoy coupling. These were fitted on Thursday and the engine run again. There was a great improvement in vibration although the engine could not be made to run at less than 2500 rpm. At this speed the vacuum was about 50% but the brake servo was not very effective.

I spent some time on the internet on Friday looking at SU carburettor web sites and learned that vacuum leaks can be a big problem. (This is news to a Bagheera owner?!) Overnight I realised that while vacuum leaks are hard to find, pressure leaks are much easier! If I put some compressed air in the inlet system the application of soapy water to the outside of all the joints will show bubbles if there are leaks! And so it did but it was not until Sunday morning that I had time to try the theory.

I blanked off the carb outlet with Duck Tape and put the air into the vacuum connection. It was obvious very quickly that the inlet box was leaking from every joint! I had purchased new screws to hold it down and had assembled it quickly without checking the thread length nor applying Hylomar gasket sealant. The screws were just too long by about 3mm and they were not compressing even the red fibre washers under their heads.
 I cut about 5mm off the screws and applied Hylomar to the joints and the top elbow. An air re-test showed that all the leals had gone!

The engine this time could be adjusted down to 1200 rpm, which is still too fast, but there was at least enough vacuum to work the brakes! I drove down the road to the first turning point and back again. We had a running car! It was now 1200 and the decision was made to go the the meeting which was about 50 minutes drive from home. But that was only after getting out the trailer and coupling it to our tow vehicle. That and loading the Bagheera took another hour so we arrived at 1350!

Drving across the crowded car park was the longest journey with the blower, but we had kept the promise to have a Blown Baggy Joe at the December meeting. (Why do I make these rash promises??)

There is more work to be done including making or finding a pressure relief valve for the inlet box. Twice it backfired while trying to start the engine and each time the inlet pipe was blown off the elbow (you will see from the photos below that there is no hose clip on the last pipe intentionally to allow explosion pressures to escape). I found out during the air pressure test that it will come off at 0.2bar (3 psi) which is "safe" but very limiting as I hope to get up to 1.0bar supercharging pressure.

My apologies to the many people at the meeting with whom I did not spend enough time particularly "Suffolk Pete" who has contributed many times to this and my other threads. Great to put a face to the words!

Thanks to you all for your support and advice. Very much appreciated.

Andy Owler
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Spyros
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« Reply #61 on: December 07, 2009, 07:00:10 pm »

Wonderfull.
Do you feel some effect already ?
What is this gold coloured bolt above the clutch housing, on the second picture ?
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Anders Dinsen
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« Reply #62 on: December 07, 2009, 07:59:50 pm »

Wow, well done! Congratulations, Andy!  Cool

/Anders
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andyowl
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New exhaust "straight through" - good sound!


« Reply #63 on: December 07, 2009, 08:44:58 pm »

The gold coloured "bolt" above the clutch housing is a brass "female" pipe fitting into which I have screwed the "Low Oil Pressure Alarm" switch which has a 1/4R male pipe thread. The blue circle is the collet through which the nylon pipe passes when it is in place. I have not yet connected this to the oil supply nor to the large alarm lamp in the car. The Shorrock Supercharger consumes engine oil at a slow rate for its own lubrication and I worry that I will run out of oil and not notice in time. One of the corners at the Mallory Park circuit ("Gerrards" is a 180 degree, large radius, very fast turn) is famous for causing "oil surge" and cars which are low in oil level often lose all oil pressure. I am even thinking of fitting an alarm Klaxon just in case I do not notice the alarm light!

On top of the banjo fitting which connects the oil pressure gauge transmitter to the oil supply was what looked like an oil pressure switch but I have never seen a Bagheera with an oil pressure warning light. Is it just that the righthand drive Bagheeras do not have such a light or do your lefthand drive Bagheeras also not have them?

Glad you are pleased with the result! All the support I have received has played a big part in getting the job finished! Well nearly finished anyway!

Yes, I can certainly notice a difference even with only +0.2bar boost pressure.

I need now to check for anything starting to go wrong after the short runs we have had so far and then start to "finish" this part of the project. A dry road would be nice, a pressure relief valve essential and a hose clip to allow the boost pressure to go over +0.2bar. A trip to the rolling road and fine tuning of the SU carb is pretty important too.

An article on SU tuning suggested that an on-board Oxygen ("Lambda") sensor and display would allow continuous monitoring of whether the mixture is "Lean", "Rich" or just right. Does anyone have experience of these devices? Demon Tweeks sell the Lumenition "Air-Fuel Ratio" system where coloured LEDs tell you whether the mixture is OK or not. Changing the needle in the SU carb will allow the mixture to be altered easily and progressively.

I also dribble over the Lumenition "Knock Sensor" which should warn of potential damage due to pre-ignition, always a worry with a supercharged engine. After that a water injection system should allow higher boost pressures and even more power!

So you see why I talk of "phase one" of this project!

Andy Owler
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suffolkpete
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« Reply #64 on: December 07, 2009, 08:57:39 pm »

Quote
Great to put a face to the words!
  It can't be a very memorable face because you saw it last year when you gave me a ride in the Djet Smiley
Seriously, keep up the good work, I'm amazed by what you've achieved in such a short time and I'm finding your progress very interesting and educational.  Maybe I'll get a ride when it's fully sorted.
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andyowl
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New exhaust "straight through" - good sound!


« Reply #65 on: December 07, 2009, 09:11:52 pm »

Oh dear! Sincere apologies! I have (had once upon a time) a reasonable memory for faces in the past but connecting the face with a name is always a nightmare for me! Advancing years has not improved matters and I have become a strong advocate for having name badges at meetings and exhibitions.

I was a sales engineer for many years and gave lectures on my pet speciality (preventing explosions in flammable gas atmospheres such as oil rigs and refineries). People often came up to me and greated me like an old mate. I hadn't a clue what their names were. Very embarrassing!

I hereby apologise in advance to all whose name (and face) I cannot now remember.

Andy
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andyowl
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New exhaust "straight through" - good sound!


« Reply #66 on: December 15, 2009, 09:56:51 am »

Having had a chance to use Baggy Joe several times on the road since the Matra meeting on December 6th the initial impressions are very good!

Damp or wet roads have limited the opportunities to apply full boost but the main limiting factor has been the absence of an explosion pressure relief valve. If a backfire occurs in the inlet manifold the resulting explosion pressure can get up to 7.5 to 8 bar (118psi). Although the pipework and the manifold itself can probably take that pressure, for a few milliseconds at least, the effect on the blades in the supercharger could be very damaging. 

To minimise the risk of explosion damage I have not fitted the last hose clip on the inlet system with the expectation that the pipe will blow off if the pressure gets too high. This happens at around 0.2bar (3psi) And it does, frequently! On Sunday in a drive of only 2-3 km the pipe came off three times! My passenger got tired of jumping out and pushing it back on again. We took a risk and fitted the last hose clip and then allowed the boost to get up to 0.5bar (7.5psi) and the car flew down the road!

The risk of a backfire is very real! While unloading the car from the trailer on Sunday evening after the meeting, in the dark and wet, I had two backfires while trying to start the engine. The first was unexpected and the subsequent noise while cranking was quite different. With a torch I could see that the inlet pipe had blown off as intended. I pushed the pipe back on, got back in and tried again to start it. This time I watched the engine through the mirror and saw a large blue/yellow flash as the backfire escaped through the open pipe, once again blown off!

So the focus is now on finding or making a relief valve. The conventional pneumatic pressure relief valve as fitted to superchargers is only 6mm bore (Norgren 1/4" type). All my instincts say this is too small to relieve the explosion pressure fast enough. The water industry has valves much larger than this and the RS catalogue (www.rswww.com) lists several 3/4" valves at less than 25% of the price of the 1/4" Norgen pneumatic version. Worth a try perhaps?

But my real wish is to make a 30 or 40mm relief valve like the one we patented in 1976 for our company's use. It was designed to act as an automatic outlet valve for a control cabinet that had to be purged with clean air before the electricity was turned on. The walls of the cabinet might be 2m high x 900mm wide and deep so there was a very large surface area for the pressure to act upon. Our valve was 50mm bore, fitted on the outside and the valve disc was suspended on a stainless steel leaf spring. It was held closed by a permanent magnet inside the cabinet with the air gap adjusted to give the right opening pressure typically about 10mbar (0.15psi). When the purging started the cabinet pressure rose to 10mbar and the valve popped open! We detected the opening action with a reed switch and that was calibrated to give us a purge air flow rate. The patent ran out some years ago so we could use the same principle again on the blower! More thought needed.

Maybe there is a new market here!

My other concern it that the blower installation is noisy! Very noisy by most commentators' opinion and I wonder if it will pass the noise tests imposed by the FIA and MSA at race meetings. I am arranging for one of the official scrutineers to check the noise level as 110 dBA is the maximum permitted for our class in Sprints and Hill Climbs. This should happen during the next 2 weeks hopefully. At the last meeting, pre-blower, the exhaust noise was measured at 91 dBA, well below the level allowed.

Happy Christmas to all members and sincere thanks for your continuing support in this project.

Andy Owler

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Stig
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« Reply #67 on: December 15, 2009, 05:14:02 pm »

Hi Andy,

I have been watching this thread with great interest. Faboulus job!!
Great idea with the permanent magnet controlling the opening pressure and giving the "pop" effect.
Only drawback as I see it in this application could be vibrations but maybe the force required to pop the valve is much greater than can be created by vibrations.
An alternative to the permanent magnet could be a solenoid.
Assume that you have a valve body looking very much like an intake or exhaust valve.
Connect the stem to the plunger of a solenoid in such a way that the solenoid keeps the valve closed.
You have to make sure that the plunger is not fully seated in the solenoid since it will be extremely strong at the fully seated position.
By simply regulating the current through the solenoid you should be able to adjust the release pressure.
The solenoids built in nonlinearirity should give you the pop effect.
You may even have a microswitch which cuts the current when the valve pops.
There has to be a weak spring which returns it to closed position and thereby closing the switch and give the solenoid its current back.
In my opinion this could be done very simple. I am visualizing a valve looking something like a thermostat where the wax bulb is replaced with a solenoid.
Just an idea.

Best regards,

Stig
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andyowl
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New exhaust "straight through" - good sound!


« Reply #68 on: December 15, 2009, 11:07:19 pm »

I like the idea of a modified thermostat housing. It is about the right diameter and the solenoid or magnet could replace the wax bulb. As an assembly it could be calibrated for opening pressure before fitting to the car.

I would like to try an opening pressure of 1.5bar, i.e. 50% higher than the maximum operating pressure of the blower.

How well do thermostat valves seal tight? Not something I have thought about before! It needs to be tight under vacuum or we will have an inward air leak.

With the rectangular inlet box we have space for relief valves on each side of the central inlet elbow. Maybe the "clunky" design of the bax has some merit after all. The books recommend that the relief valve(s) are located in direct line of the explosion pressure wave. Having two can only help that.

More thought needed.

Andy
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Stig
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« Reply #69 on: December 16, 2009, 04:22:03 pm »

A standard themostat may not seal good enough. I used it mainly as an example of what I was thinking about.
From what you have said sofar it seems as if the valve has to be designed for frequent useage.

Do you have any idea of the maximum working temperature the valve and its seal has to withstand?

What about the escaping gas. Do you have to have some sort of catch tank to prevent any risk of fire?

Regards,

Stig
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Stig
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« Reply #70 on: December 16, 2009, 11:28:05 pm »

Another valve idea just popped up.
The drain valve in a standard wash basin. It is aproximately the right size, seals well and the fixed part has exterior threads.
Only drawback is that the valve stem points in the wrong direction but that should be easy to fix.

Stig
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Spyros
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« Reply #71 on: December 18, 2009, 09:27:20 am »

Just a question.
On the period compressor adaptation I've seen on the web, I didn't see any relief valve.
- Did I miss it ?
- Do they do it differently ?
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andyowl
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New exhaust "straight through" - good sound!


« Reply #72 on: December 18, 2009, 11:07:07 am »

Did they have a relief valve? Good question!

I think Shorrock and other "rotary vane" superchargers are particularly vulnerable to sudden and severe pressure waves coming from the wrong direction. The vanes themselves are quite thin (I don't remember how thin, but just a few mm) and I could visualise them being bent by the explosion pressure. If they bend, even momentarily, they will jam in their guide slots and destroy the rotor. No second chance.

Other designs such as the Roots/Wade multi-lobe, Sprintex rotary screw and centrifugal blowers do not have this risk and probably don't need relief valves.

Maybe I am being paranoid and worrying too much but I note that the original Shorrock literature I have shows that a pressure relief valve was always provided as part of the installation kit. Manufacturers do not supply something in a kit that is not necessary, it increases their costs and raises the price on a product that was already considered as expensive.

Interestingly, in looking through my old blower literature, I found the receipt for the blower I have just fitted. I paid £475 for the Shorrock type C142 blower in July 1993 after seeing a "for sale" advertisment in "Car and Car Conversions".  In the same year I paid £200 for the car that was to become Baggy Joe, complete with an MoT test certificate, and drove him home. It only took me 16 years to put the two items together! That's a lot of planning time!

Weather permitting I am meeting the MSA scrutineer with the noise tester on Sunday to find out just how noisy we are. I will need some sort of relief valve for that drive and I received yesterday a magnet with which to make a Mk1 magnetically closed valve. Watch this space!

Andy
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Spyros
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« Reply #73 on: December 20, 2009, 10:20:07 am »

Understood,

I must have been confused by the type of superchargers
Like the one described on this page ?
http://www.spridgetmania.com/web/DisplayID/1710/SCatagory/ENGINE/DisplayType/Technical%20Information/ArticleV.cfm

and also by the size of the usual valve
On this picture

Is this the valve that is hidding itself under the rubber pipe, close to the SU ?

http://www.mg-tabc.org/supercharger/Shorrock_ABC.pdf

Could it be that further tuning of the ignition and cooler spark plugs might reduce the backfire tendency of your engine ?
On standard engines, bad ignition timing can induce this.
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andyowl
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New exhaust "straight through" - good sound!


« Reply #74 on: December 20, 2009, 10:06:43 pm »

Yes, the you can just see the Shorrock relief valve below the rocker box oil vent  pipe near the SU Carb. There seems to be a black stain around one of the valve outlet holes perhaps suggesting that there is frequent use of the valve! How nice the installation looks with its bright red paint and everything neat and tidy. Not a drop of rust in sight! Sets us a good example!

The Mini Cooper web site is interesting too. Shame that the supercharger kit is no longer available. I wonder what it cost? The installation is very neat (and small!).

The other Shorrock site is very interesting too. I have visited it before and tried to contact the owner. I learned that he died last year and that a friend is keeping it going in his memory. What a waste death is! I said I would be interested in contributing to it if his widow chose to continue with it for the benefit of other Shorrock enthusiasts. No answer yet though.

We met the MSA Scrutineer today for noise testing despite the snow and bitter cold. I confess that I took the car on the trailer rather than drove it there.  I had not had time to make any sort of relief valve and we reverted to having a loose inlet pipe as our safety device. Just as well we did too as the engine backfired again during starting while hot. I saw the flash from 20m away!

The allowable noise level, he said, for "Sprints" is 105dBA. Baggy Joe without the Shorrock was measured at 91dBA at "Sprint Royale" in October. Today we measured 96dBA on the right side and 97dBA on the left side (where the blower is located). Well below what is allowed. Good news! Even so I want to do something about reducing the external noise level as it does make the car a little conspicuous going down the High Street. Not that a bright yellow, wide wheeled and lowered, competition car is inconspicuous in the first place! At high revs the noise inside makes my ears hurt so putting back a bit of sound deadening might be a good idea there anyway.

A number of FDMC Club members joined in the discussion as to how and why we have installed the blower the way we did. Lots of suggestions were offered (some better than others of course) but lots of interest was shown! I think we are raising the profile of the Matra Bagheera quite nicely. One chap thought we had a V8 in there! There's a thought!

One strange phenomenon is that, at nominal "tickover" 1,800RPM, the engine speed cycles automatically from 900 to 2500RPM, like "hunting" on a big diesel engine. The elbow on the inlet pipe is partially collapsing under the vacuum and this seems to restrict the air getting into the engine. The engine slows down, the vacuum decreases and the pipe expands again and the engine speeds up! Bizarre! I think I can fix that by putting some internal support tubes into the elbow. We might be able to lower the "tickover" speed then.

So we can now proceed with the next stages such as finding an expert in tuning SU carbs on a rolling road. And so many other things too.

Andy
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