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914World.com _ 914World Garage _ Guagues
Posted by: GTeener Jul 1 2004, 11:51 AM
I already have the /6 dash guagues but not the center console guages (voltmeter & oil temp).
I am not totally sure my oil pressure guague works properly, but I digress...
What I want to know is, would it be be advantageous to have all these guagues (and working of course)?
What are the most important secondary guagues (not Spedo & Tach) for these cars?
Posted by: lapuwali Jul 1 2004, 12:24 PM
Discussed recently, and there are a lot of opinions. IMHO, more info is always better, as you can (with experience) diagnose a budding problem by checking gauges against each other.
At a minimum, some temp gauge (oil or CHT) and some indication of oil pressure (light or gauge). A voltmeter is a nice to have, but the alt light will get you 90% of the way there, with some failed system usually telling you there's an electrical problem w/o requiring a voltmeter.
I would go with a CHT over an oil temp gauge, if the choice comes down to that. I'd have a temp gauge over a pressure gauge, between those two (but I'd at least have a light for pressure).
Why do you feel your oil pressure gauge isn't working? What readings are you getting?
Posted by: SirAndy Jul 1 2004, 12:33 PM
oil idiot light
oil pressure
oil temp
oil level
CHT (dunno which one on a /6)
volt meter
Posted by: lapuwali Jul 1 2004, 12:46 PM
The 911 oil level gauge is pretty useless. Really, checking the oil level at all in any way on a dry sump engine is trickier than most people give credit for. The level in the tank will change very significantly depending on whether or not the engine is running, how hot it is, and how long it was sitting since it was last started.
As for CHT, the same VDO spark plug ring usable on the four or the Bug can be used, and I'd venture that the driver's side rearmost cylinder is the one to check, as it's nearest the oil cooler.
Posted by: J P Stein Jul 1 2004, 02:08 PM
Oil pressure, oil temp.....the rest is window dressing....including the tach & speedo.
Even tho I try to remember to do it, I've never looked at any gauge during an AX pass....maybe next week 
Posted by: GTeener Jul 1 2004, 02:41 PM
Because I don't think I've ever seen it move very far to the right, not even half way I don't think
Posted by: GTeener Jul 1 2004, 03:01 PM
I would go with a CHT over an oil temp gauge, if the choice comes down to that. I'd have a temp gauge over a pressure gauge, between those two (but I'd at least have a light for pressure).
What's a CHT
I'm a visual person, anyone have pix of the various compatible guagues?
Posted by: Andyrew Jul 1 2004, 03:04 PM
CHT= Cylander Head Temp..
Critical guage..
Posted by: GTeener Jul 1 2004, 03:22 PM
Critical guage..
Thanks. What's it look like?
Posted by: tat2dphreak Jul 1 2004, 03:32 PM
CHT,oil temp, oil press. (light ok)
Posted by: Jeroen Jul 1 2004, 04:49 PM
The fact that people don't know how to read it doesn't mean the 911 oil level gauge doesn't work
A dry sump engine will only give a good reading (either gauge or dipstick) when the oil is up to operating temps, the engine is idling and the car is sitting on a level surface.
The gauge may not give you an exact measurement, but it gives a very close indication on your oil level
cheers,
Jeroen
Posted by: lapuwali Jul 1 2004, 05:22 PM
I think my point is, if you have to be sitting stopped on a level surface, why even have a gauge? The dipstick is adequate, the level gauge superfluous.
You can see a photo of the CHT gauge on aircooled.net (electrical/gauges). The aftermarket VDO is the item in question. Reads in degrees F. Fast responding and very useful to tell you you're about to drop a valve seat...
Posted by: GTeener Jul 1 2004, 05:38 PM
Is this a good price? Can they be found used and function reliably?
Attached image(s)
Posted by: mistro Jul 1 2004, 05:39 PM
... CHT gauge ... Fast responding and very useful to tell you you're about to drop a valve seat...
How does it warn you? Sudden increase in temperature?
Rgds, Michael
Posted by: SirAndy Jul 1 2004, 05:45 PM
while this all reads fine i think someone should make a nicer one that automatically takes ambient temperature into consideration. can't be too difficult.
maybe even a nice LCD display with 4 rows, one for each cylinder ...
Andy
Posted by: GTeener Jul 1 2004, 05:46 PM
oil pressure
oil temp
oil level
CHT (dunno which one on a /6)
volt meter
In thi$ order of importance (on a budget)
Posted by: lapuwali Jul 1 2004, 05:53 PM
Not necessarily a sudden increase. Bad things happen if the heads get above 450dF. Normally, they should be no higher than 350dF. The temperature varies widely based on load. It can be as low as 250dF on a fully-warmed up engine while idling, up to 400dF when pulling up a steep hill at low revs.
$100 is about average in price. All of the expense is in the gauge. You'll see they also sell just the sender for only $15.
Andy, I agree on the nice display with temperature compensation. I'm working on it. Not four numbers, as I think just monitoring the hottest cylinder is adequate (and I want to keep it small, perhaps three 7-segment digits on the tach face). Just can't seem to find the necessary circular tuit.
Posted by: SirAndy Jul 1 2004, 07:15 PM
what about this layout?
(can you tell i have way too much time on my hands?
)
Attached image(s)
Posted by: TimT Jul 1 2004, 07:28 PM
I look at one maybe two gauges....
oil pressure, and oil temp
I shift when I bounce on the rev limiter...
I have a wide band O2 gauge that isnt a permanent mount..
few gauges just whats important
Andy you can get a similar gauge to what you posted from Aircraft Spruce...
individual CHT or EGT or A/F...
Posted by: SirAndy Jul 1 2004, 07:59 PM
damm, just when i tought about getting into gauge design ...
Posted by: SirAndy Jul 1 2004, 08:04 PM
well, if you have a spare $1489.00 in your wallet
http://www.aircraftspruce.com/catalog/inpages/gem610.php
Posted by: TimT Jul 1 2004, 08:09 PM
you wanna play you got to pay...
Posted by: SirAndy Jul 1 2004, 08:27 PM
ok, i haven't done any hands-on electronics in a while, but i just looked up some IC for LED bargraphs.
all one would need is a linear IC, which can be had for $1.50 ...
$1.50 x 4 plus the LEDs and other materials. let's say $20 total, a old empty vdo-gauge and you're good to go.
i just saved you $1469.00 bucks!
AndyPosted by: TimT Jul 1 2004, 08:37 PM
Heck I wouldnt pay $1500 for that instrument either......
Id hope that the mixtures in each cylinder were "close" same jettiing, injector duration etc..
http://www.westach.com makes some cool custom gauges
Posted by: mistro Jul 1 2004, 08:39 PM
I'll give you $60 for the first one! Rgds, Michael
Posted by: TimT Jul 1 2004, 08:41 PM
Still just two gauges are important to me
oil pressure, and oil temp
Posted by: lapuwali Jul 1 2004, 08:45 PM
The LM3914 is also found in nearly every narrow-band A/F meter on the market. There are schematics for a several such meters available online. You'd need an op-amp to boost the weak thermocouple signal from 10s of mV to at least 1v, but that's also pretty cheap.
The thing I have in mind is a low-end microcontroller driving an LCD display. An 8x2 character display will fit on the lower third of the tach face, and this would give enough room for four CHTs, or two CHTs and two EGTs, or several other things. Still under $50 in parts costs.
Posted by: mistro Jul 1 2004, 08:49 PM
Whats an EGT?
Posted by: J P Stein Jul 1 2004, 08:52 PM
Hay, Tim, CHT gauges would be impotant to us if we had (perish the thought) t-4 poopers
I usually try to shift via earball just before the limiter kicks in.....even get it right once in a while
Posted by: Lawrence Jul 2 2004, 02:45 AM
Am I the only one that thinks this is a bit hokey? I don't want to have to recaclulate CHT temps in my head, based on what I think the weatherman said this morning. 
-Rusty 
Posted by: tat2dphreak Jul 2 2004, 10:12 AM
westach.com has some nice ones and cheaper, but they won't look as stock as a VDO unit... the westach's are supposed to be more accurate, I've heard...
oil idiot light
oil pressure
oil temp
oil level
CHT (dunno which one on a /6)
volt meter
In thi$ order of importance (on a budget) icon14.gif
I say this order:
oil idiot light (adequate for pressure on a budget)
oil temp,
CHT
oil pressure
oil level
voltmeter
I may be off, but that's my opinion...
Posted by: Scott Schroeder Jul 2 2004, 10:22 AM
After reading Jakes posts, I think I would do 4 CHT's an oil pressure and a gas guage!
Posted by: lapuwali Jul 2 2004, 10:25 AM
Rusty, it is a bit hokey, but that's how thermocouples work, and I can only imagine how much more the gauge would cost if they built in temp compensation. EGT gauges have the same problem, but with temps commly in the 1500dF range, the 40-50dF potential error isn't really significant. 
Of course, here in the wonderful San Francisco Bay Area, the weather is always the same, and so the gauge always reads consistently.
Dakota Digital also sells a CHT gauge with temp compensation, for something like $250.
mistro, EGT is exhaust gas temperature. EGTs will change with mixture and ignition timing, just as CHTs will. The curves for EGT v. mixture and CHT v. mixture don't exactly match, so you can determine rich/lean from how the EGT and CHT change with respect to each other.
Posted by: Aaron Cox Jul 2 2004, 06:15 PM
Andy, i talked to my dad about your gauge design. he's an electrical engineer. i suggested LED's cuz they are cheaper than digital bars. he said it would require a simple circuit. alll in all less than $100.00 he could do it for in parts.
youd have to say that 'x' volts means 'y' temp. and when temp reaches 'y + 1' degrees, the next led would light up. so 450 could be the red LED and 350 could be the last green LED.
i may take on this project..... anyone want to donate a gauge to my cause? (old console gauge i could use for my experiment?)
Posted by: Aaron Cox Jul 2 2004, 06:16 PM
doh!
Attached image(s)
Posted by: TimT Jul 2 2004, 06:21 PM
Aaron, I have a bunch of old VDO gauges that you could have..
I dont have any console gauges, how about a non functioning 911 clock?
Posted by: Aaron Cox Jul 2 2004, 06:25 PM
wow, that was like what, 3 minutes after my post?
thanks tim, if you could spare a clock / gauge that'd be great!
Posted by: SirAndy Jul 2 2004, 06:27 PM
cool!
the only reason why i tought bars is that you get a better resolution on the reading, with just 6 LED's per cylinder and a range of 500F you get a whooping 83.33 degress per LED!
that might not be that helpful.
Andy
Posted by: Aaron Cox Jul 2 2004, 06:29 PM
Could always use more smaller led's andy. that was just to get you the idea.....
ok... 12 LED's per cyl?
Posted by: SirAndy Jul 2 2004, 06:31 PM
the moah the better, in this case
if you can squueeezzzee them in. the 911 clock gauge is bigger than a normal VDO console gauge.
BUT, i so happens that this is the only gauge in my 911 cluster that is not working properly.
if you can make it work with that gauge, i'll buy one from you!
Andy
Posted by: Aaron Cox Jul 2 2004, 06:36 PM
the moah the better, in this case
if you can squueeezzzee them in. the 911 clock gauge is bigger than a normal VDO console gauge.
BUT, i so happens that this is the only gauge in my 911 cluster that is not working properly.
if you can make it work with that gauge, i'll buy one from you!
Andy
heh, then only you and the people with getty dashes could use them!
i want to try and do it with a console gauge or a vdo gauge so that everyone could use it.
Posted by: Aaron Cox Jul 2 2004, 06:36 PM
oh and they make led's the size of pin heads and smaller!
Posted by: TimT Jul 2 2004, 06:42 PM
Aaron, send me your address, Ill send an old gauge out after the holiday
Posted by: Aaron Cox Jul 2 2004, 06:43 PM
i pm'd it to you.
thanks again dude,
Aaron
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