Hi Ryan,

Something else has just occurred to me,
you will probably have to slip some insulation
over the T/C sheathing,
to prevent it from grounding anywhere along its length.

Unless you can just grommet where it passes through,
see what you think anyway.

John

 

Still nothing. If I reverse the inputs from the TC then the gauge reads negative, actually the needle wraps around backwards since there's no stops. Bridging the ground to either lead still give faulty readings. Rigging the PS is looking more and more like the only viable solution, am I right? --Ryan

 

Hi Ryan,

Oh yes, you're right, reversing the thermocouple connections
would reverse the output to the gauge.

I'm a bit curious about what you mean by 'bridging the
ground to either lead' for this, it doesn't want any other
ground applied. Doing so would provide another ground loop
and possibly give false readings.

I've drawn the sheathing and the amp (black) terminal joined
and to be treated as one wire, try it on the yellow and the
black, without crossing over the thermocouple wires. By
Using the sheath as ground at the thermocouple end, the fault
becomes irrelevant, so long as it is the only ground applied
to this unit and amp.

You would have to check (visually) that the sheathing doesn't
touch ground anywhere along its length, insulate if necessary,
maybe grommets would do, see what you think.

I have a friend here who is fairly familiar with this air cooled
volkswagen engine, he says its a 'boxer' engine (flat four) and
he would like me to mention some points that you may already
know. He says to change the head bolts for studs, as the bolts
can stretch with the extra load, also to mention that the heat
shield also helps to duct the air, some people remove it, they
think that will help the cooling, but actually it can make it
worse. Looking at the engine from the rear, he says that the
head on the left is the one that generally overheats, and to
pay extra attention to this one. Also that the standard fan
arrangement is not very good, and to consider changing it for
the porsche type fan arrangement, this may involve other mods.
Also he says that a 'Fast-road-cam' is about the maximum lift
reasonably, and that nossing is not an option on those heads,
it would just damage them.

please excuse the writing, i've just re-written this, i had a
TYPICAL 98se crash, just as i was posting, and i lost the well
written version of this. I am still fuming over it. I think
this PC needs more ram, i only have 64mb in there. I hope this
is written well enough to follow, just ask if its not clear!


If this cannot cure your mis-reading problems, then yes, you
will probably have to fit one of those little isolated supplies
that you spoke about before. I'm not very familiar with them.

Best of luck with it, John

Attached Images

Sheathing.jpg (38.0 KB, 339 views)

 

Yes that was what I had tried. By bridging I meant hopping the ground from the sheath rather than chassis ground. I've tried both that and a ground wire from the washer at the TC junction itself, still didn't make a difference.
Your friend has a few misconceptions about the engine. First off, all ACVW engines came with head studs, none ever had bolts. Since the case (block) is a soft AL/Mg composite, using bolts would rip the threads out of the case after a few R&Rs. The studs are actually supposed to stretch. When the engine comes to operating temp it will expand from heat, if the studs didn't stretch you'd pound the seating/sealing surfaces for the cylinders at the heads and case. After a few cycles, they would lose their torque and be loose. This is why it's not recommended to go with chromoly studs untill you start boosting (turbo) beyond about 23-25 lbs. Stock studs will hold up to that point, they'll also hold to beyond 12:1 compression.
The tin part is considered common knowledge nowadays, though it wasn't always. I have every piece of tin in place as does anyone who has to worry about engine temps from larger engines.
The 3/4 head (left facing engine) will always run a little hotter due to the air flow vane configuration of the fanshroud, but not much, maybe 20F, #3 cylinder in particular. This is where the TC is located, always measure the hottest part.
As for the fan, it's much better than most believe, provided all oringal tin is in place, thermostat and air flow control flaps are present and working. A Porsche style fanshroud is nice, but leaves few good options for carb linkage, eliminates the stock oil cooler (no problem I run a thermostatically controlled 'extra' cooler), and few are made that fit correctly due differences in engine width from stroking, longer rods, flycut heads, etc. Oh and the biggest problem is they tend to overcool most streetable engines, high CR engines would be an exception. And worst of all they don't accomodate any sort of thermostat for airflow controll. It's always 'on' so to speak.
Funny that he says the heads can't handle nitrous, NOS by the way is a brand name. There are a number of VW engines I know of running large amounts of nitrous with no problems, mind you it's not a cheap setup. All the horror stories about people running nitrous are from people who didn't know what they were doing or skimped on the setup. Here's a tidbit for you. Last year, a flat four VW style engine, Al heads and all, set the world record for quickest and fastest 4 cylinder powered dragster and was the first 4 cylinder engine into the 6's on the 1/4 mile. Before the imports, before Lingenfelter, before them all. All Al engine, well except for the cylinders, crank, rods, and such, but case, pistons, heads. This was pushing at least 65 lbs of boost, exact number is a secret.
This should make your friend laugh and call me crazy. Here's the specs on the cam I run. 260 degrees @ .050" lift, valve lift - .550", did I mention I commute 70 miles/day? If you know what you're doing, anything is possible. I never said it was cheap though, my engine is worth 6x as much as the car itself.

Allright way off topic there. Thanks for all the help John. I did just go ahead and order the dc/dc converter a few minutes ago from Digikey, ran me about $12. I'll have to find some nice way to package it up and setup a voltage regulator for the input, but I think it'll work. However I am still open to ideas because I have some friends who'd like to try this gauge but don't want it to be so involved. The most common gauge to run is a VDO gauge where the TC drives the gauge directly. It's a totally isolated circuit. I just don't like it. Anyways, thanks again. --Ryan

 

One last thing, take a look at the videos at these links and show them to your friend if you want.

http://quicksitebuilder.cnet.com/vin...ance/id13.html

The one in the middle. This one is dated about a year. There are two street legal VWs in the 9s now that I know of, brothers actually. Not only that, but they are the guys that built the two dragsters on the next two links, the Lauffer Family of VW Paradise.

http://www.oceanstreetvideo.com/download5.html

The one on top, Kris Lauffer breaking into the 6's.

http://www.geocities.com/crgrapevine/videos.html

Check out Sacramento BOR (Bug-O-Rama) 8-30-03. This is the newest dragster by the Lauffers that shattered the record again just last month. I've seen these guys run. It sounds like a friggin' jet engine going down the track.

Even for those not into the VW scene, these are impressive simply because they are infact VWs. --Ryan

 

Cheers Ryan,

Some great pics !

John

 

Woo hoo, I got it working. Well at least it's working on my breadboard, but I did hook it up in the car with the car running and all looked well. And to think I was pissed that after spending all that money on my breadboard I only used it a few times in classe. Guess this made it worth while as it took a few trial and error steps to get it going. I used ended up with a dc/dc unregulated isolating converter at the heart. Finally got a current reading off the amp (helps to set it to dc and not ac, doh!!), 67mA. So my 167mA limit (converter max) is just fine. I did have a little issue when I first hooked it up, I finally got a reading, but the needle was all over the place. Tracked it to two things, both were possible issues mentioned in the spec sheet for the IC. First the output ripple was causing some problems, throw a 1uF cap on the output and that went away. But now I was only getting 6vdc out, when I should be getting a pretty solid 12. There was some mention of having to use a 2.2uF cap on the input as well when for some reason I already forgot. Did that and I have a perfect garbage in, garbage out (1:1) ratio. Gonna have to pick a regulator for the input though cause it's spec'd for 10.8-13.2 input, and I'll be kicking up to 14.4. Luckily I'm still under the "absolute" max input of 15V so I should be good for the mean time. I'll take care of it this weekend. Thanks for all the help guys (John). --Ryan

 

Hey Ryan,

Good going man !!
glad you're geting some positive results after all the
messing about !

Hope it transfers from the breadboard to the car with
no problems.

Best of luck with it, John

 

Just did it and it works great. I almost laughed when I thought I finally used something I learned (am learning) in school, but in a field that actually interests me. I just packaged it up on a PC board and project box I got from radioshack. --Ryan

 

I expect you're pretty pleased about that !
Could you give me the make and model number
of the 12v to 12v isolating unit that you used,
just in case i ever need one!

John

 

Sorry for the delay, was out of town this weekend. It's a TI chip, part number DCP021212P. There are lots of other listings too, this is just the one I felt would work best for me. Search on 'dc converter' at digikey.com, then select dc/dc converters. From there it gives you a host of options to refine the search based on power ratings, input, output, etc.
Did have to end up using a regulator to step down the input voltage. It worked for the short trials I did while mocking it up, and then to verify the final product. But after 5 minutes on the road it turned off. There's a 'watchdog' feature on the chip to prevent damage from operating outside the parametes, so it just kept tripping the circuit. I picked up a cheapo 12vdc regulator from Radioshack for about $1.50 and wired that into the circuit, works great now, even for extended periods. --Ryan

 

Cheers Ryan,
Thanks for the info,
John

 

is this of use?

http://homepages.picknowl.com.au/pkl/turbotimer/picproject1.html

mm linking doesnt work. ohh well, you can cut and paste

__________________
Transformers are work
Electronics is a hobby

 

I wouldn't worry about this thread, it's three years old!

__________________
I also post at the following sites:
http://www.stop-microsoft.org http://www.heated-debates.com
Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.

 

lol yes. ahh well, the link may still be useful

__________________
Transformers are work
Electronics is a hobby