Series 2 vac port for dissy. Where?

[RobThomas]

I'm after the exact location in the intake tract for the take-off of vac for the dissy. Some cars use the vac measured after the throttle and some are measured at the lip of the throttle plate. Makes a difference. I have a knackered 1952 Sidevalve dissy (on the '52 sidevalve) and have replaced it with a Cooper S 23D4 dissy as a temporary measure but am wondering if modern (hey, 1954 technology was modern back in 1954) vac advance might be a good fuel saving measure. The difference in the advance curves is going to be noticeable but relatively minor compared to the weird advance curve that was on the car with one broken spring.
I have a B.N.I.B. '54 dissy on the shelf.

[bmcecosse]

Well - proper original Mini Cooper S dizzy had NO vacuum advance ! On A series engines it doesn't really matter where it is taken - as long as it's on the inlet manifold a little way from the carb is the norm. Yes -some strange models used a connection that was on the throttle plate - I think it was a misguided adventure in emissions control! Just take a tapping from the inlet manifold.

[RobThomas]

Cheers. Cast boss on the SV manifold gave a hint!
I know that the HIF44 has the 'weird throttle plate' take-off and that the 1330 Midget engine has had the take-off moved towards the engine as part of the tuning process on the rolling road. He did explain why but it was a bit over my head at the time.
I had assumed that it was going to be a more basic take-off in the manifold itself since it would be a bit less technologically advanced.
Max dissy advance on the 23D4 (40819, IIRC) is 18 degrees, same as the sidevalve dissy (40033 or is it 40215? Summat like that).
Shame it is near impossible to see the timing marks now that the waterpump is on. Back to drive/guestimate/twist/drive/curse/twist.

[bmcecosse]

I would drill/tap that boss and use it. You can adjust any dizzy to give whatever mechanical advance you want - simply open it up and read off the figures on the bob weights - then double them ! If say it says 7 which equals 14, then you simply cut a small amount off the stop leg which meets up with the stop pin. How much to cut I hear you ask - well - you measure the original amount of free travel and if it is say 7mm for 14 degrees, then to get 18 degrees you would cut a further 2mm off the leg, and so on. Obviously i've used easy figures for the maths - it won't be quite as easy as that - but it is a proprtional amount you need to cut off.

[RobThomas]

Yup. Thanks for the reminder. I've done it before when the aeroplane ran a Bosch 009 distributor but I've converted it to run 2 fully electronic variable timing systems using Ford Mondeo trigger and coil packs.
I run 3 ATDC below 600 rpm to prevent nasty kick-back during hand-propping the engine in order to keep my few remaining fingers working (One hand rather knackered in a car crash) but it advances to 28 BTDC by 3000 rpm and stays to 3300 max.
Pic shows a Honda CBR600 alternator grafted onto the back of the crank with 2 magnetic hall-effect trigger mechanisms.

I'll "T" it to give me a vac gauge port to help with the tuning. There is a Crypton 322 in my garage but not much use if you can't see the timing marks.<br><br>

[bmcecosse]

Good grief - looks complicated!

[RobThomas]

Basically just an overbored 1300 VW taken to 1835cc and then the heads are redrilled to take an extra sparkplug. The prop is added on the timing pulley end and the flywheel removed. I tried the dual Lucas SR4 magneto option and the Bosch dissy option before going full electronic with the Hnda alt in place of a flywheel. The electrics for running this are complicated by the need to top up 2 batteries from one alt without any chance of one dead system making the other one fail. The exhaust system is a mixture of bits but has a fancy Lambda sensor in it to aid tuning. You can't put it on a rolling road for tuning!! It has a Stromberg CD150 carb on it (Spitfire/Landrover/Stag etc) since they are capable of having 45 degrees of tilt (bank) before they flood. Handy if you get a bit aerobatic by accident.
The exhaust system is believed to add about 3 bhp since the addition of it adds a hundred plus rpm at full throttle, thus suggesting that the scavenging effect helps with efficiency. Similar effect shown by adding a decent quality LCB manifold to an A-series engine (or sidevalve). I've elongated the holes between camshaft and pulley to bring the peak in the torque curve closer to optimum for a 3300 rpm max engine. I cheated and copied somebody elses' design.
If you think mine was hard work, check out the Webster Whirlwind. Seven VW barrels, seven DAF variomatic heads plus a home-made crank and crankcase. Designed and built the whole thing himself.<br><br>

[RobThomas]

I forgot to mention. It has seven cylinders and a lucas 45d4 distributor. Guess how he got it to fire 7 cylinders?

[bmcecosse]

I'm amazed - and this lot takes you (him) into the sky !!!
7 cylinders - no idea - if it was 8 I would say just fire 2 each time as on 2CV Citroen - for 7 cylinders I guess it needs to have 7 terminals in the cap equally spaced around - so a very special cap ?

[RobThomas]

Being an old-fashioned reeeeeal engineer (what the Welsh call Potchers) he took a 45d4 cap, drilled 7 holes in it, pulled 7 brass rivets through and shortened the rotor arm. Hey presto! 7 cylinder cap! I have no idea how he gets 7 pulses at the points. Maybe geared 4:7 off the crank?
Twin sparks = twin distributors!<br><br>

[RobThomas]

http://www.youtube.com/watch?v=drw7kFC_teU
Me in the background.

[bmcecosse]

Yes - further thought on this and he would obviously need a 7 lobe cam inside the dizzy to match the 7 terminal cap. But considering the other mods - that would be a 5 minute job I imagine !!
Still find it hard to believe this kind of 'bodgery' is allowed to fly up in the sky!! Please don't fly over ME !!