Benefits of a PICT 34-3 with 37mm throttle body?

[ccowx]

I just dropped an original Solex 34-3 off at the machine shop to have the bore opened up to 37mm this morning! It sounds like I have to look for another way to get vacuum for light throttle cruising from somewhere else? Or, if it is not proprietory information, what mods would be done?

For the compression ratio, I don't mind raising it a bit, in fact it makes my head work easier, but I will probably be stuck with 87 octane in some places in North America. What is a reasonable compression to use?

I can probably tweak the thermostat for the air cleaner a bit. I had planned to use a meat thermometer in one of the holes in the air cleaner housing to check it's temperature. I am thinking that the more heat, within reason, that the pre-heat adds here the less of a load there is on the manifold heat crossover.

Thanks!

Chris

PS: It just occured to me that if I hooked it up to manifold vacuum and left it at the full 23-25 degrees mechanical advance, it might work. If I timed it to 5 BTDC and then had the vacuum advance limited to around 6 degrees, it would idle at 11 BTDC or so, wouldn't it? It would also advance at a steady cruise but fall away during hard acceleration.

[busdaddy]

Too much hot air will decrease mileage and power, most factory systems maintain it ~85-90f, any hotter than that and you might boil the carb on a warm day. The later 72-73 Ghia and Euro bus aircleaner uses a vacuum operated hot air valve with a bimetal thermostat valve, it has the bonus feature of leaning the idle slightly on a hot day as well as shutting off the hot air under heavy loads (vacuum drops).

Since this is more brainstorming than must do stuff I wonder if you could solder a lump on the edge of the throttle butterfly to block the advance drilling at idle on the modified throttle bore? Or does the hole just get so big from the bore enlargement it's nowhere near the edge of the plate now?
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[Alstrup]

[ccowx]

Maybe I should quickly call my machine shop and stop them from boring out my 34-3! I could get one of the aftermarket 37mm carbs and then use the venturi that they are boring out for me in that.

The manifold vacuum idea might work, I could always limit the vac advance to 8 or 10 or whatever. That would give 5 + 10= 15 BTDC at idle, 28 at WOT and 38 at cruise. I could put lighter springs in the advance so it would come in at 2800-3000 instead of 3500 or so.

As for the off idle flat spot, I thought that went away to some extent as the engine displacement goes up?

Thanks!

Chris

[Floating VW]

[Alstrup]

A rough texture does the same. Dimpling becomes interesing if you have a fully polished racing intake side and realize that you have condensation issues. Then carefull dimpling can improve flow everso slightly along with a little improved atomization. The dimpling thing comes up once every 15 years or so. BMW has worked with it since the 2002 Ti back in the 70´s. (I believe they were some of the first, but I may be wrong on that) Lately some Honda tuners have picked it up again with crazy flow claims. They are full of it, because every single test I have seen are not back to back tests. Something else have always also been changed and then the test is not worth the paper it is written on. The advantage is that when you have a high rpm engine N/A or boosted that requires A LOT of fuel, you get a better atomization as Floating have noticed. The flow improvement is minor.

Crox, if you are not affraid of the 123 dizzy I would continue with what you are doing.
You can always begin with the SVDA. Then if you can´t make it work right you can upgrade to a programmable.
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[ccowx]

I am not sure what a 123 Dissy is, but for the moment I would prefer to avoid a complete electronic or crank triggered system. I am game to tackle the Bosch unit, it is not my first time modifying a distributor and I even have access to a machine to test it if need be.

Thanks!

Chris

[oprn]

I do not think any electronic ignition system could match good old points for extreme cold weather starts. The down fall of the electronics are that they have a magnetic sensor to trigger a spark and that takes a minimum velocity to make a signal to trigger a spark. Good old points are not speed dependant and will make a spark even when you are rotating the engine by hand to set the valve lash. Ask me how I know!

At -30 and lower the challenge is to get the starter to rotate the engine AT ALL never mind fast enough to trigger a magnetic pickup coil. Nope! Stay away from any ignition system that does not use points for this cold weather application.

[Alstrup]

You may have a point there. On the other hand, if it is that much of a problem to turn the engine (I have never started an engine at lower than -32 degrees C.) why not install a more powerfull starter then (?) I mean, if I have to replace a starter today, especially on an engine larger than say 1900 cc. I go "modern" and use slightly modified starters from VW/Skoda diesel engines. They are typical 1,6 KW and turn the engines approx 600 rpm/m. They´ll start any ACVW gasoline engine, also at -45F. Just make sure that you have at least a gauge 00 from the battery to the starter.
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[modok]

[ccowx]

Points can work quite well, BUT they MUST be maintained in top condition. They do have the advantage of being able to fire at any voltage and rpms. Yes, you can run more power through an electronic set up, which does help starting. The problem that I ran into was that the quality of the commercially available electronic sets has nose dived in recent times and I have that 110% reliability requirement. Add in the fact that many don't trigger at low rpms or low voltage and you can see the problems in my circumstances. The only thing that filled the billl, and probably quite well, is the Winterburn CDI set up that I will be using.

Chris

PS: Interesting on the starter, Alstrup, I may look into that.

[modok]

Yes I think the materials and textures and maybe different shapes could improve the performance, tho.... I've given up being interested in changing the relative sizes .... to the point that I think I will take the advice of those who came before me and.... just LEAVE it be.
It is an evolutionary dead end and leave it alone.

But what IS it?
Some people have the idea that the single port is the dead end, only suitable for basic utility....... and the dual port as being the MORE powerful engine with greater potential.......
actually it may be the Opposite IF restricted to a single carb.

The development of the SP intake manifold NOT dead ended, and IMo a lot of people who for whatever reason NEED to use a one barrel carburetor on a flat four vw.... would be BETTER off to put that on the single port engine.

[modok]

[modok]

But far as the distributor vac port.....if it need to be re-located then you can re-locate it. There is no reason it would work different.
If you make all the parts of the system some % bigger, it will work virtually the same except bigger.

The venturi size should be 75-86% of the carb bore, to work best.
So with 34mm carb bore then a 29mm venturi would be on the upper limit. That is the "short answer" to your actual question.

[spencerfvee]

[modok]

Glow plugs are made to glow...... that's hot, probably too hot.
Maybe run two or three in series maybe they could work as a heater and not glow.

Glow plugs are not really the right thing for the job, but they ARE potentially cheap and easy to fit, it might be better than trying to make the correct part.
When I was rebuilding detroits I threw them away by the hundreds, shame about that. Most of them probably still worked.

[oprn]

[oprn]

[modok]

Some are just better than others.
My starter came OUT of a rabbit, probably a 90's rabbit tho, it was a red convertible I don't remember the year. And it's quite a bit better than what came on a 1970vw for sure. Survives being kicked backward, while from what I've heard some of the gear reduction starters don't like that.
one of the DOWNsides of a powerful ignition system that works down to 0 rpm..... is it will try to start backwards now and then, if the timing is advanced much beyond 10 degrees.

[oprn]

My comments on electronic ignition not starting as well is purely from personal experiance. My '66 Beetle with it's 6 volt system was very temperature sensitive as far as the starter being able to turn the engine over. BUT! If it would make it over one or two compressions it would start every time! Stock ignition in good shape is the key! '69 Bus with the typical wiring/ignition switch deterioration would not always make contact to spin the starter so - I get out, wife puts it in gear and I lean on it, 3 feet travelled, one or two compressions and it was running every time! Stock ignition in good condition.

I now have a type 4 engine in a Buggy with crank trigger. If the battery is low - still cranking fine but noticeably slower than normal it WILL NOT START!! Period!
I have cranked it for several minutes at a time and several times but if it does not see a minimum cranking speed it will not fire! I am not used to that with air cooled VWs.

On to another hobby of mine, model airplanes, for a number of years the gasoline 2 strokes we used were magneto ignition with points and these engines hand started like a dream. In fact when working around and on them you must remove the plug wire from the spark plug because they could and did at times fire with an accidental prop bump. Enter the weight saving electronic ignition. These engines no longer can be dependably hand started. I have tried on numerous occasions and watch others try sometimes for 1/2 an hour at a time to get them to prop start and they very seldom will but a touch of a starter and they are off every time. It takes speed to get a hall effects system to work.