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I read an article about TR3s discussing how, even if the motor is running fine , the Su's can still be too rich at idle and too lean on acceleration. The upshot was that if an 02 sensor was installed it would provide info to dial in the exact type of SU needles that would really wake up the power. Anyone installed an 02 sensor..what type? any advice? I use my 3 for fun driving and maybe autocross. Have a mild cam and header. I realize that doing head work is the best way to increse power but I'm intigued by the notion of the right SU needles maximizing my existing mods. Karl
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TR2/3/3A TR3untapped power from SU needles re Oxygen Sensor
- Thread starter karls59tr
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PeterK
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I think that by using the data from an O2 sensor you could reprofile the needle for the power curve of your engine with the mods you have done. I don't know how you would read the data though.
Somewhere I have the SU needle profile that shows the shape of the needle and how each portion is related to flow. So at (rich) idle, you would leave it thicker to keep it leaner, then thinner to lean it out, etc.
BTW. I drove my TR3A in it's first autocross this weekend. It screams off the line leaving rubber and more rubber as I shift into 2nd. I've chirped it in 3rd before but at an autocross, you rarely get that fast. This is with the stock SUs, no headers but tuned correctly. I won a trophy for Fastest Vintage Car in the vintage class of 2!
Somewhere I have the SU needle profile that shows the shape of the needle and how each portion is related to flow. So at (rich) idle, you would leave it thicker to keep it leaner, then thinner to lean it out, etc.
BTW. I drove my TR3A in it's first autocross this weekend. It screams off the line leaving rubber and more rubber as I shift into 2nd. I've chirped it in 3rd before but at an autocross, you rarely get that fast. This is with the stock SUs, no headers but tuned correctly. I won a trophy for Fastest Vintage Car in the vintage class of 2!
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Re: TR3untapped power from SU needles re Oxygen Se
The O2 sensor only gives part of the needed information. There is no correlation between throttle position & needle height/step. SU needle calibrations/diameters are given in .100" height intervals.
I think the trick/problem is in knowing exactly what step the needle is actually on for a given engine load-throttle setting. The carb pistons move pretty much independently of carb throttle position. ie. - full throttle at 2,000 rpm will give a much different needle height than full throttle at 5,000 rpm.
If you could run on a dyno, you could get a pretty good correlation between piston/needle height, rpm, & load. Or, a linear position transducer on the piston would be one way to determine needle positions under actual driving conditions.
Most folks just determine workable needle profiles by trial & error or some one elses experiences..
D
The O2 sensor only gives part of the needed information. There is no correlation between throttle position & needle height/step. SU needle calibrations/diameters are given in .100" height intervals.
I think the trick/problem is in knowing exactly what step the needle is actually on for a given engine load-throttle setting. The carb pistons move pretty much independently of carb throttle position. ie. - full throttle at 2,000 rpm will give a much different needle height than full throttle at 5,000 rpm.
If you could run on a dyno, you could get a pretty good correlation between piston/needle height, rpm, & load. Or, a linear position transducer on the piston would be one way to determine needle positions under actual driving conditions.
Most folks just determine workable needle profiles by trial & error or some one elses experiences..
D
PeterK
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Re: TR3untapped power from SU needles re Oxygen Se
Try this link. Enter your current needle. eg. TR2's used .090" FV(street) or GC (competition) and is the number stamped on the base.
https://www.mintylamb.co.uk/suneedle/
Also this link https://www.teglerizer.com/sucarbs/index.html
You can use the teglergizer needle profiler to sort by station (the .090" or .100" band of the needle profile). Then select a needle that gives you more of what you need in that station, and then model it in the first link program. and visually see the effect in RPM range.
Try this link. Enter your current needle. eg. TR2's used .090" FV(street) or GC (competition) and is the number stamped on the base.
https://www.mintylamb.co.uk/suneedle/
Also this link https://www.teglerizer.com/sucarbs/index.html
You can use the teglergizer needle profiler to sort by station (the .090" or .100" band of the needle profile). Then select a needle that gives you more of what you need in that station, and then model it in the first link program. and visually see the effect in RPM range.
Re: TR3untapped power from SU needles re Oxygen Se
I really think you need a dyno to tell if you're making any progress. Since the dyno guys will have a wideband O2 sensor they can hook up when you are there, you wouldn't need your own.
If you really want to go down this path without the dyno, you'll need a wideband O2 sensor - the other types won't have enough range to help with what you want. The wideband sensors will be in the $400 range.
Bryan
I really think you need a dyno to tell if you're making any progress. Since the dyno guys will have a wideband O2 sensor they can hook up when you are there, you wouldn't need your own.
If you really want to go down this path without the dyno, you'll need a wideband O2 sensor - the other types won't have enough range to help with what you want. The wideband sensors will be in the $400 range.
Bryan
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Re: TR3untapped power from SU needles re Oxygen Se
An engine that has relatively large carbs for it's displacement will have much less piston lift for a given condition than the same engine with smaller carbs. If the carbs are large for the engine size, they may never get beyond 1/2 or 3/4 open at full rpm/full power. The first half of the needles calibration range may be all that is actually used.
D
As I tried to point out earlier The needle stations/piston lift, do not directly correspond to engine rpm or engine load but to both at the same time ie - air flow only. The needle charts only show a given piston lift. Assuming that 1/2 needle is mid range can result in great errors.PeterK said:
An engine that has relatively large carbs for it's displacement will have much less piston lift for a given condition than the same engine with smaller carbs. If the carbs are large for the engine size, they may never get beyond 1/2 or 3/4 open at full rpm/full power. The first half of the needles calibration range may be all that is actually used.
D
Don Elliott
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Re: TR3untapped power from SU needles re Oxygen Se
The guys you race TRs and who have installed an oxygen sensor put the in a boss that they weld onto the header. One fellow put his 2" down which others said was too close to the engine. They thouught he was reading the flame temperature. Most put them 6" down so they read the exhaust temperature - not the flame temperature. At the end of a long straight, the temperature reads about 1200 deg. F. This temp info is all they use it for.
The guys you race TRs and who have installed an oxygen sensor put the in a boss that they weld onto the header. One fellow put his 2" down which others said was too close to the engine. They thouught he was reading the flame temperature. Most put them 6" down so they read the exhaust temperature - not the flame temperature. At the end of a long straight, the temperature reads about 1200 deg. F. This temp info is all they use it for.
D
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Re: TR3untapped power from SU needles re Oxygen Se
I've often thought about putting two O2 sensers in the lower part of a manifold on the 1 & 4 sections. Thinking this would make setting the mixture a snap to do. Any thoughts?
I've often thought about putting two O2 sensers in the lower part of a manifold on the 1 & 4 sections. Thinking this would make setting the mixture a snap to do. Any thoughts?
PeterK
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Re: TR3untapped power from SU needles re Oxygen Se
I understand this Dave. Have you seen the program that I linked. Here's a screenshot comparing needles and effect on mixture over rpm. Needles in the comparison are listed in the service manual for TR2 .090" street FV vs. competition GC, as an example.
https://www.mintylamb.co.uk/suneedle/graph.php?n1=FV&n2=GC&n3=&n4=&n5=
So what I suggested was to take the needle chart (as a starting point) to select a couple alternate needles and apply it in this modeling program to graph to effects (and go from there). Maybe the program assumes constant engine load? I didn't write it so I don't know.
Dave Russell said:
I understand this Dave. Have you seen the program that I linked. Here's a screenshot comparing needles and effect on mixture over rpm. Needles in the comparison are listed in the service manual for TR2 .090" street FV vs. competition GC, as an example.
https://www.mintylamb.co.uk/suneedle/graph.php?n1=FV&n2=GC&n3=&n4=&n5=
So what I suggested was to take the needle chart (as a starting point) to select a couple alternate needles and apply it in this modeling program to graph to effects (and go from there). Maybe the program assumes constant engine load? I didn't write it so I don't know.
martx-5
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Re: TR3untapped power from SU needles re Oxygen Se
I've been thinking real hard about doing this myself. I made two bungs up at work just in case I go this route. I'd use a double throw switch so I'd only need one AFR gauge. It would be the best setup. I know I will have at least one O2 sensor on this resto. Might as well take advantage of modern technology. All of the traditional methods of getting fuel mixture correct seem rather quaint and mystical yeilding who knows what results. Chances of getting the mixture more correct by reading Air Fuel Ratios is a whole lot better then lifting pistons, looking at plugs and just generally guessing. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
Edit: As far as which O2 sensor to get. I'll dig up the generic Bosch number when I get home, but you want a four wire heated unit. They are more consistent then the one wires, and if you have to locate the O2 sensor far downstream, it will still work. Most O2 sensors have 18mm threads, so that's what size bung you'll need.
Bill said:
I've been thinking real hard about doing this myself. I made two bungs up at work just in case I go this route. I'd use a double throw switch so I'd only need one AFR gauge. It would be the best setup. I know I will have at least one O2 sensor on this resto. Might as well take advantage of modern technology. All of the traditional methods of getting fuel mixture correct seem rather quaint and mystical yeilding who knows what results. Chances of getting the mixture more correct by reading Air Fuel Ratios is a whole lot better then lifting pistons, looking at plugs and just generally guessing. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
Edit: As far as which O2 sensor to get. I'll dig up the generic Bosch number when I get home, but you want a four wire heated unit. They are more consistent then the one wires, and if you have to locate the O2 sensor far downstream, it will still work. Most O2 sensors have 18mm threads, so that's what size bung you'll need.
TR3driver
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Re: TR3untapped power from SU needles re Oxygen Se
For that matter, how does one sort out the temperature signal from the O2 signal, on one wire ?
I give up; why would they install an O2 sensor to read exhaust temp ? A thermocouple is far more rugged, and cheaper to boot.Don Elliott said:
For that matter, how does one sort out the temperature signal from the O2 signal, on one wire ?
Re: TR3untapped power from SU needles re Oxygen Se
Hello all,
with regard to piston height, i seem to recall someone using a fuel gauge sender linked to the piston and coupling it to an instrument to read piston height. Slightly crude but it is better than nothing?
Alec
Hello all,
with regard to piston height, i seem to recall someone using a fuel gauge sender linked to the piston and coupling it to an instrument to read piston height. Slightly crude but it is better than nothing?
Alec
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Re: TR3untapped power from SU needles re Oxygen Se
Sounds kinda elegant to me, Alec! Ohm meter connected to a sending unit would be fairly accurate, dependent on the spacing of the wires wrapped on the vernier of the sender... Interesting!
Though I s'pose one could be as accurate by just setting a finger athwart the space between piston and block at near TDC and feel the piston hit the full height.
I guess I'll keep the dial indicator. /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif
Sounds kinda elegant to me, Alec! Ohm meter connected to a sending unit would be fairly accurate, dependent on the spacing of the wires wrapped on the vernier of the sender... Interesting!
Though I s'pose one could be as accurate by just setting a finger athwart the space between piston and block at near TDC and feel the piston hit the full height.
I guess I'll keep the dial indicator. /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif