Wideband Oxygen Sensor Mounting

In reply to bentwrench :

To deal with the risk of water drops, just wait 20 seconds before you turn it on.  By then, the exhaust will be well beyond the dew point.

Besides, I've run WB's for a long, long time in development, and even turning them on to record -20F starts, I never managed to break one.  UEGO's seem far more robust than normal HEGOs.   I'm wagering that most don't put the heater on full blast when warming them up- and recent research told us that it's the heater reaction that actually was breaking things.

In reply to alfadriver :

We had one of these AEM widebands many years ago in our first LeMons Amazon; I'd gone in with 2 other guys to buy it at the time; it got passed around and used in a variety of cars.  As I recall one of the guys eventually bought out the other two's shares in it.  The wiring harness got burned up once in an engine fire, but to my knowledge the sensor and the gauge never had an issue.  

Regarding SU tuning, my understanding is the dashpot is a basic spring-damper type of arrangement, in principle like a simple automotive suspension.  The spring rate and the mass of the piston regulate how high the piston goes under a given manifold vacuum.  The damper (little piston in the center of the SU piston + dashpot oil) controls the rate of rise and fall, but not the ultimate position at any given vacuum signal.  

My understanding of the fundamental operation of this is that when the throttle plate is opened (starting from a steady state condition), the increased airflow across the jet causes more fuel to be sucked into the engine- this is what serves as an "accelerator pump" - the squirt of gas to enrich the engine to support the increased engine speed.  The piston rise is slowed by the damper/oil, but as the throttle stays in the new position, the piston gradually (but typically in less than a second or so) rises to bring the mixture up to its new position, as determined by the needle taper.  So, the needle taper provides (mostly) the steady-state mixture at a given engine vacuum signal, and the dashpot/oil determines how much temporary enrichment occurs and how fast the needle rises - but the spring and the weight of the piston determines the ultimate height of the piston - and the corresponding position of the needle relative to the jet.  

Lowering the jet- either via the choke, or via the mixture nut - enriches the engine across all piston/needle positions.  

I'm wondering if watching the carburetor piston position at various RPM, with the engine unloaded, and simultaneously monitoring the wideband, would provide any useful tuning data for setting needle profile for actual operating conditions under varying load?  My understanding is that under a heavy load/ low RPM, the throttle plates would be wide open and the engine speed would be low, so the SU piston would be in a lower position, with a less rich needle/jet orientation, than the same throttle position but the engine "caught up" and running at a higher RPM & higher vacuum signal.  

In reply to volvoclearinghouse :

You understand correctly but running under no load  won't get  you tuning information. 

    A chassis Dyno is really worth the $100 it costs to tie down.   Because you can stand right there and using an exacto knife to mark the needle.  Then do the emery paper thing to reduce the diameter st that spot.  
 Does LeMons count tune up costs? 
    You do the dead drop to confirm the pistons  are in the right dash pot don't you?  

In reply to frenchyd :

I disassemble carbs one at a time, and keep the parts together.  I know that the pistons and pots are NOT interchangeable.  When I assemble pistons and pots I clean them both so clean I would put either in my Manhattan and drink it.  Then when assembled I check the full motion of the piston in the pot and make sure it's smooth and perfect.  And the piston-pot mating surfaces are cleaned only with carb cleaner- not an abrasive.  Tolerances there are in the ten-thousandths of an inch.  

LeMons does not count tuning costs, but I don't have a chassis dyno anywhere nearby.  And they charge way more than $100 around here.  My "dyno" are back country roads and hills.  

There's also nowhere within 30 miles of my house that sells E85.  Yes, I've checked online.  I have political issues with ethanol as well, but this being GRM, that's immaterial to the current discussion.  So simply consider that discussion closed.  

Fair enough.  
  I used to tune on hill but I went through a lot of needles until things were right. 
  Adding a sensor will help. Because you you won't need to pull the plugs and read them like I used to do.  
  Try removing the air cleaner and tape your phone on video  to help you figure out where to richen things. 
    Did I ever show you how to measure the needle?   
  Remind me which engine you have and any mods I'll look up the measurements on your needles when I get home tonight. 
   Do you have spare needles?  

volvoclearinghouse said:

In reply to alfadriver :

We had one of these AEM widebands many years ago in our first LeMons Amazon; I'd gone in with 2 other guys to buy it at the time; it got passed around and used in a variety of cars.  As I recall one of the guys eventually bought out the other two's shares in it.  The wiring harness got burned up once in an engine fire, but to my knowledge the sensor and the gauge never had an issue.  

Regarding SU tuning, my understanding is the dashpot is a basic spring-damper type of arrangement, in principle like a simple automotive suspension.  The spring rate and the mass of the piston regulate how high the piston goes under a given manifold vacuum.  The damper (little piston in the center of the SU piston + dashpot oil) controls the rate of rise and fall, but not the ultimate position at any given vacuum signal.  

My understanding of the fundamental operation of this is that when the throttle plate is opened (starting from a steady state condition), the increased airflow across the jet causes more fuel to be sucked into the engine- this is what serves as an "accelerator pump" - the squirt of gas to enrich the engine to support the increased engine speed.  The piston rise is slowed by the damper/oil, but as the throttle stays in the new position, the piston gradually (but typically in less than a second or so) rises to bring the mixture up to its new position, as determined by the needle taper.  So, the needle taper provides (mostly) the steady-state mixture at a given engine vacuum signal, and the dashpot/oil determines how much temporary enrichment occurs and how fast the needle rises - but the spring and the weight of the piston determines the ultimate height of the piston - and the corresponding position of the needle relative to the jet.  

Lowering the jet- either via the choke, or via the mixture nut - enriches the engine across all piston/needle positions.  

I'm wondering if watching the carburetor piston position at various RPM, with the engine unloaded, and simultaneously monitoring the wideband, would provide any useful tuning data for setting needle profile for actual operating conditions under varying load?  My understanding is that under a heavy load/ low RPM, the throttle plates would be wide open and the engine speed would be low, so the SU piston would be in a lower position, with a less rich needle/jet orientation, than the same throttle position but the engine "caught up" and running at a higher RPM & higher vacuum signal.  

It's in the lowest right hand drawer of the big box waiting for Pete to finish his engine. I used it last year to tune the idle of the truck in the driveway.

In reply to frenchyd :

The three needles most commonly used in the B18 and B20 Volvo engines with the SU HS6 carburettors:

https://www.glenngoodspeed.com/volvo/NEEDLES.HTM

A reprint of something I've seen before, believe this was official info from Volvo:

http://www.networksvolvoniacs.org/images/4/47/Needle_Types.pdf

General SU tuning/ rebuilding info:

https://tecb.eu/onewebmedia/Tuning_SU_Carbs.pdf

I have several SU HS6's and a bunch of used needles, most of which are the SM profile.  I beleive that was what Volvo fitted to most of them stock.  

I have a small USB camera I can plug into a laptop, fitting that in the engine compartment should allow me to watch the carburettor piston movement in real time, with a laptop in the cockpit.  

In reply to volvoclearinghouse :

I am envisioning an alternate universe where some manufacturer was stubborn enough to make SU carbs OBD-II compliant, with position sensors on the air door/needle...

Sensor in a collector works just peachy.  I had to put it there on one of my cars because there was no other place to put it.

The other car I have with a wideband has the collector over the rear axle (it's a rotary thing) so I am just reading only one of the pipes, figuring the two can't be TOO far off.

In reply to volvoclearinghouse :

That's a great solution and should help you figure out where on the needle you are.   But if the engine is stock. You're done. The factory did it for you. 
 

 You can mill the head to increase compression.    A lot of cam grinders will regrind your cam for you.  And the two go together because a reground camshaft lowers the base circle. And will keep the  rocker arm geometry close. 
   Between the two of those peak power should go up around 15-20%  at some cost to bottom  end power. ( you won't really notice it) 
   Crower and ISKY are my go to people.  
     Don't get too aggressive. You can always take more off but you can never put it back on. 

In reply to frenchyd :

That's the thing...it's not a stock B20.  Plus, the SUs I have came from a B18 (not many B20's made it to America with carburetors, and they were usually HFs or something else).  It's a fuel injected 'F' head, which has bigger valves.  I had the head milled, calculated static compression is 10:1, and some port work was done on the exhaust side to improve flow.  I'm also running the 'D' grind Volvo cam, more aggressive cam than the stock grind.  And the exhaust is freer flowing, dual exhaust with an X-pipe.  I don't have the specs for the D grind cam in front of me but they're published.  

I've seen those charts of SU needles, but they don't tell you how far down the needle each of those points is.  Also, some of the non - 'SM' needles I have in my collection are longer than others, which adds to the confusion.  

Pete. (l33t FS) said:

In reply to volvoclearinghouse :

I am envisioning an alternate universe where some manufacturer was stubborn enough to make SU carbs OBD-II compliant, with position sensors on the air door/needle...

The thought has crossed my mind to have a little actuator on the jet of the carb, tied in with the O2 sensor, to adjust the mixture on the fly.  

In reply to volvoclearinghouse :

Sorry I misunderstood.  Yes you will need to adjust.  I take it you're using racing gas?  Not pump?   Pump stuff is a bit scary.  Variation happens. 
  The hardest part when I start mixing and matching parts is figuring out timing first.   Otherwise you can be like a dog chasing its tail. 
   Get it slightly over rich   May be easier to pull up the needle or ream out the jets .   Then  using one of those cheap Digital   infrared thermometers  adjust timing back and forth until you're about 1250.  Degrees F on the exhaust manifold.     That's not all the way home. But I'm a bit conservative. Hate to burn things up.  I'll trade a horsepower or two for longevity. 

Here's a tip I learned while messing with an SU setup on a Datsun 1200:

The car had a mid-range hesitation under acceleration. The SU setup had a choke/cold start setup, where a pull knob lowered the SU metering jet, richening the mixture. I found by pulling the choke knob slightly, the car would accelerate smoothly through the previous hesitation with more power. Since I knew how far out the choke had been pulled, it told me the offset, and therefore, the needed needle diameter in that load range. I know this is separate from the O2 sensor issue but figured it could be helpful.

That should work.   Start out on the rich side with the choke out. Once warmed up push the choke in until it leans out under acceleration. ( pops through the carb) 

In reply to kb58 :

Good trick. I think I read that in one of those SU links I posted, too. 

Between that,the video scope, and the air fuel ratio gauge, we'll be tossing all sorts of high tech at these 50 year old carburetors to get them to work right!

The story continues here...