Yet another VW question!

Rob Swain · Post by **Rob Swain** » Fri Jul 08, 2011 3:09 pm

Thanks for that Dave. I did wonder if it was something like this, as I speculated.
I was looking forward to building a 1915cc for my friend's Sonerai, too. Then again, the Sonerai has a proper pressure cowling so the engine ought to be better cooled than a lump buried deep in the bowels at the back of a beetle or type 2 van. Hmmmm!

It does appear that I didn't make myself totally clear in the original post: the case (and head) machining is the same size for both 92mm and 94mm barrels, so case and stud situation is the same for 1834cc and 1915cc engines.

Nigel Ramsay · Post by **Nigel Ramsay** » Fri Jul 08, 2011 7:56 pm

Rob, 1915 barrel walls would be even thinner than 1834 but the extra power would be marginal

cardiffrob · Post by **cardiffrob** » Sat Jul 09, 2011 3:31 pm

the case (and head) machining is the same size for both 92mm and 94mm barrels, so case and stud situation is the same for 1834cc and 1915cc engines.

Are you 100% sure? I recall someone asking me what size I wanted the block machined to. Maybe (probably) I got the wrong end of the story.

Nigel Ramsay · Post by **Nigel Ramsay** » Sat Jul 09, 2011 5:15 pm

Seems this may not be the case.... here is what Bob Hoover (VW Bob not the famous display Bob)

Hector Mora, builder of a superbly built Teenie Two,
writes from
Spain:
>
> I wish to know if it´s
> possible to make biggers holes(for 1915cc) at the
case
> with case savers for 10mm studs.

-------------------------------------------------------

Dear Hector (and the Group),

While this CAN be done it usually is not, unless the
engine is for
drag racing, expected to last only one or two runs.

The spigot-bore diameter (ie, the big holes in
crankcase) for 94mm
cylinders is about 98.3mm, which will cut into the
threads of a case-
saver for 10mm studs.

Indeed, 92mm cylinders, having a spigot-bore diameter
of about 96.3mm
leave very little metal for the threads of a 10mm
case-saver.

Using 92mm cylinders will give you an engine having a
displacement of
1834cc. Used with the stock VW cam an 1834cc engine
will produce
more than enough thrust for your T2. Using 94mm
cylinders (for a
displacement of 1915cc) increases the displacement by
only 4.3% but
INCREASES the difficulty of sealing between the
cylinder and the
head, since the area of contact becomes much smaller.
In practical
terms, increasing your displacment by less than 5%
will have no
effect on the airplane's performance.

If you feel that an engine larger than 1834cc is a
necessity here are
some options.

The wiser course would be to begin with a new
crankcase from Brazil.
It will come from the factory with case savers for 8mm
cylinder-head
stays. (It will also have larger oil passageways than
a crankcase
using 10mm cylinder-head studs.)

G.Dawes · Post by **G.Dawes** » Sat Jul 09, 2011 6:43 pm

The only time I looked down one the bigbore barrels I remember seeing the ripple marks where the fine were on the outside and during the bore the thin bit swelled out. I thought that was a bit too thin.

jangiolini · Post by **jangiolini** » Mon Jul 11, 2011 6:46 am

We are all looking at capacity increase to increase power but there is another route which is easier and about a similar cost! Twin carburettors on either a pair of single port or double port heads! The latter being much more preferable. Stromberg zenith 125 or 150s being the obvious choice. Also use the camshaft from the van engine which is apparently ground and timed for low down torque!
Just a passing thought!
John.

cardiffrob · Post by **cardiffrob** » Tue Jul 12, 2011 8:13 am

FWIW, HS4 carbs weigh less than CD125s but Strombergs will work at most anges of bank/yaw/roll whilst SUs will suffer from float problems. Does anyone know what the story with HIF carbs is? Do they suffer from 'bank angle flooding'? An HIF44, on paper, looks like a good performance carb with an inbuilt temperature compensator.

As for the boring of holes, I may be wrong here but I'm getting the idea that the hole is stepped so that the biggest bored hole is for the OD of the barrels (same on 1835 and 1915) but the 1915 needs a larger stepped inner bored hole to clear the piston skirt, hence a slightly larger hole. If you merely slice right through at the biggest bored hole size then you can go 1835 or 1915 but you've lost some potential strength. The impression I get from reading up is that a good engine shop will step the 2 boring jobs to keep as much crankcase as possible.

GPASC sell cams tuned (retimed?) for the relevant barrel size, just as Jangliolini mentioned.

johnlear · Post by **johnlear** » Sat Jul 16, 2011 5:07 am

I seem to have entered a VW guru location so I wonder if you can help me too?
I have a Turbulent with a 1600 VW and the above carb. It has always had an annoying flat spot rising through 1500rpm and would stop at the least provocation if mishandled
Yesterday I lined up to take off and it just stopped dead! I got out and swung it again and it ran for about 5 seconds and stopped again. Next time I was a bit quicker running round to pump the carb and managed to taxi back to the hangar, all the way it was spitting, banging and misfiring and would not get above 2000 rpm. I stripped the carb, got a compressor to blow out every orifice I could see, put it together again and fired it up.
At least it now ticks over like a sewing machine but when I go thro 1500 it just wants to stop. If I force it thro with pumpings it will get to around 2400 but it feels like its misfiring and running very rough.
It has a slow running adjustment which sets how much the throttle will close and one mixture screw that controls both slow and fast running. I started it at 1.5 turns out on it and standing behind the running engine I spent hours turning it richer and weaker in 1/8 turn increments to get it to run above smooth above 1500....BUT NOTHING WORKS TO MAKE IT RUN SMOOTH EVEN ABOVE 1000 RPM!!! I thank God it stopped on the runway when it did, another few minutes and I'd have been in the air looking for somewhere to crash safely!! Any ideas to help keep my sanity would be welcome

cardiffrob · Post by **cardiffrob** » Sat Jul 16, 2011 9:14 am

A good bet is to beg/borrow/steal a "Wideband Lambda Sensor" kit. I have one for analysing the fueling of modified cars and it is the most fantastic tool and highly accurate. It either fits into a boss drilled into an exhaust or sits in a pipe that you stuff up an exhaust. It gives an instataneous reading of air-fuel ratio and allows you to work out exactly where the lean spots are so you can work out what needle you need. So good that mine can tell me when the float needle valve opens and starts a short increase in fuel height.
"Innovate" sell a kit. Worth a quick Google? Might be worth asking for help at a local race-track/tuning place/Halfords for the name of someone who is into this stuff.

I'm in Cardiff, if it helps.

johnlear · Post by **johnlear** » Sat Jul 16, 2011 7:09 pm

Thanks Foggy, I am now confused...I didn't know that ypu could get different needles! My gut feeling is that mine is running too lean at present....however I have had the a/c for 23 years and it has only just developed this problem, so maybe its some sh*t in a jet somewhere??

John

johnlear · Post by **johnlear** » Sat Jul 16, 2011 7:11 pm

Thanks Foggy, I am now confused...I didn't know that ypu could get different needles! My gut feeling is that mine is running too lean at present....however I have had the a/c for 23 years and it has only just developed this problem, so maybe its some sh*t in a jet somewhere??

PS..its a good job your ma didn't call you JOHN thomas!!!
John

Nigel Ramsay · Post by **Nigel Ramsay** » Sat Jul 16, 2011 9:20 pm

John, reading your symptoms.... firstly I don't think you have a needle in there, it's a fixed jet job I think. The slow running mixture screw is just that, it only covers the mixture up to 1000 -1500 rpm. It sounds like fuel starvation caused by either a blockage or poor fuel delivery OR an air leak on the inlet side.

I suggest you just start methodically by checking fuel delivery; check flow rates from the tank. Make sure you have sufficient flow from there, then move on to the carb (do you have a pump?).

johnlear · Post by **johnlear** » Sun Jul 17, 2011 8:36 am

Thanks for that Nigel...

How this carb works has always been a mystery to me! It has a screw adjustment that physically limits how far the throttle can close and so controls the tickover rpm, and a screw with a point on that I assmume is the jet which controls mixture.

I have always assumed that as this is the only mixture control, it is always going to be a compromise between the slow and fast running mixture...now that you have said that it ONLY controls the slow running mixture (I can see that as I made it stop on tickover by leaning out the mixture screw too much) it means that the only other places to look are a) a strip down to see what goes on where the mixture is delivered just up stream of the butterfly AND b) the inlet manifolds for air leaks where they fit onto the cylinder heads.

I'm going to remove the carb this afternoon and see what sh*t might be stuck in it!!

Thanks, John

mikehallam · Post by **mikehallam** » Sun Jul 17, 2011 11:41 am

John,

With respect, if you really know so little about carb's, your solo investigation may end up with the destruction of your 'plane, even the P1.

Please get an engineer or a clued up buddy to show/teach you the rudiments.
Apart from the obvious, amateur fiddling may bend parts or lose them & you may not know what condition is acceptable or not.
Re-torquing and sealing on re-assembly is vital.
Disturbing the throttle/choke controls can mean the need to reset/adjust to the 'book'. I guess you even lack that accoutrement ??

Carb's are not just an assembly of parts but a clever device for metering fuel over the whole range and normally have four overlapping stages to ensure the fuel/air mixture at all engine speeds and throttle openings (not the same thing) is correct and dispersed.

Sorry to be so blunt, but learning off forum pundits is not the prime method of acquiring the skills you apparently lack !

mike hallam

Bill McCarthy · Post by **Bill McCarthy** » Sun Jul 17, 2011 12:06 pm

See what I mean - yet another candidate for a one day course set by the LAA.

Light Aircraft Association

Yet another VW question!

VW SOLEX 32 PHN - T CARB.

VW SOLEX 32 PHN - T CARB PROBLEMS