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Help with building your Speeduino, installing it, getting it to run etc.
By toddTR6
I've been trying to decide where to put the O2 sensor (Bosch Lsu 4.9) A search of the interwebs is telling me either 2", 20", 24" or 40" from the exaust port. :roll: Seems that the interwebs can't agree with itself :roll: I looked for Bosch data sheet for it, but they are not specific, only that the temp should be in a specific range.

Can any one tell me what a suitable distance is for the sensor to have a decent length of life and still be accurate? Does it make much difference?
By LAV1000
Sensor has its own heater.
2" seems to me to close but 20" and above should be fine.
The further away the more delay in the signal.
But there is a setting in Tuner Studio where you can put in your delay.
User avatar
toddTR6 wrote:
Mon Oct 26, 2020 9:28 pm
I've been trying to decide where to put the O2 sensor (Bosch Lsu 4.9) … Can any one tell me what a suitable distance is for the sensor to have a decent length of life and still be accurate? Does it make much difference?
I've posted the installation spec's below. In a general sense, closer is better, but not so close it overheats (>600°C wrench hex temperature continuous is the critical spec). As-mentioned, it also has a heater allowing you to place it further down the exhaust if you prefer for any reason, such as reading two engine banks for average Lambda/AFR or temporary placement at the tailpipe for dyno use, etc.
Bosch wrote:4.3.1 Design measures:
- Locate sensor as close to the engine as possible, respecting max. allowed temperature range
- The exhaust pipe in front of the sensor must not contain any pockets,
projections, protrusions, edges flex-tubes etc. to avoid accumulation of
condensation water. A downwards slope of the pipe is recommended.
- Make sure, that the front hole of the double protection tube does not
point against exhaust gas stream.
- Attempt to achieve rapid heating-up of the exhaust pipes in the area in
front of the sensor and also of the complete sensor thread boss area, to
avoid developing of condensation water
- The sensor thread boss must be designed as shown in 4.9 to reach a rapid
heat up of the sensor protection tube area. Make sure, that the protection tube is fully reaching into the exhaust gas stream.
Bosch_LSU4.9_boss_specs.jpg (52.86 KiB) Viewed 1461 times
By tylerwerrin
Glad to see you are still working on the TR6 conversion! I too have been going very slowly, as I have been away from my car for the past couple months and finally have a couple weeks to work on it again. I have been trying to gather up all the parts, as well as familiarize myself with the Speeduino & tuning program.

Per your suggestion, I picked up a silverado harness as well as the accompanying coil packs. I'm still waiting on the manifold & plenum to be fabricated, as it is a custom job by a fine gent I met on the Triumph Experience forum. I can give you his information if you are interested - it looks like a very fine polished piece.

Good luck moving forward - will be following your posts eagerly. If I get ahead of you (which i doubt I will), I'll post some pictures.
By toddTR6
Well still hacking away at this project.

I previously had thought that the high pressure pump, filter and swirl pot, and pressure regulator would fit into the engine bay, to be supplied the the existing mechanical pump. But I don't see any way to make them all fit unless I put them at the frame rail, where they will be exposed to the elements. I'm probably going to relocate them into the trunk (or boot since it's a British car). This seems to be the most common place for the pump and filter from looking at pi versions of the car, and electric fuel pump conversions.

Because of this I am toying with the idea of making the fuel rail returnless. However I've read that there can be issues with inconsistent fuel pressure, making tuning more difficult. The supply to the rail will be an-6, the rail will be made from 3/4" square steel tube.

Alternately for a return type fuel rail, there is a fuel line (mixed steel pipe and 5/16 hose) that is used to supply the mechanical pump, that I could use for the return fuel line from the pressure regulator at the rail. I'm not sure if this would have enough capacity though.

My third option is to bite the bullet and use the an-6 for both to and from the rail.

Does any one have any thoughts? I'd like to hear them.
User avatar
You have not stated your fuel system plans, but I have a feeling you may have far over-sized your setup in your mind. Let's assume you have a Pi running about 150hp. It will need about (150*0.5)=75 pounds per-hour of gasoline/petrol at max power. 75 PPH is 75/6 = 12.5 GPH or 12.5*3.7854 = 47 LPH. Yes, 47 LPH. 8-) I like to add a random 20% flow for things like dirty fuel filters, cheap fittings and other restrictions, so 47*1.2 = 56 LPH

Considering a typical 30mm motorcycle pump can do 65 LPH or more at 3 bar, something like a Bosch 044 or Walbro 255 is lots of wasted flow, space and money. Using math, we find your 150hp consumes about 6.7 ounces of fuel at max power in 15 seconds. Typically for street or road racer, the accumulator (surge tank or swirl pot) is sized to feed the engine for 15 seconds at full power without main tank supply. Yes, that means your swirl pot with the pump inside will be about the size of your fist.

I think you can see where I'm going with this, and that all of those parts should easily fit in your engine compartment or virtually anywhere along the line. And, they are all rated for exposure to the elements. Keeping in-mind that large pumps use more power, and can override the regulator with excess flow, knowing that everything over 47 LPH is excess flow. ;) Considering fuel lines the size of a drinking straw can feed 500hp at EFI pressures, likely your stock line is more than adequate. Use care to avoid planning a mismatched fuel system for a monster when isn't needed nor even wanted.

Dead-head fuel rail? Yes it can be done, but you are right, they do carry some drawbacks. In OEM cars there are purge valve controls, temperature sensors, and other stuff to make them work reliably with their quirks. Go for it if that's your thing, but generally with simple EFI a simple return system removes some of the unforeseen headaches. Using reasonably-sized lines should also be relatively inexpensive and easy to handle as-well. Hey, you asked, so there is my 'IMO'. ;)


Just for ideas; the popular Honda TRX/VT fuel module (accumulator/swirl pot) with internal 65 LPH pump, smaller than a beer can. Designed for bikes and off-road things, it can be mounted anywhere and survive:
Keihin-Honda_pump_module_16700-HN8-601_sm.png (118.13 KiB) Viewed 1098 times
By toddTR6
Hi David,

I did ask, and I appreciate your help.

Actually I didn't go for the bosch 044 setup or equivalent. I have an oem external fuel pump for a gm (I forget off hand which vehicle). I was going to fabricate a swirl tank but I haven't done it yet. I was just going to use an small empty propane cylinder, cut it in half and weld it and put some bungs on it. I will take a look at that honda pump.

User avatar
No problem and knowing that you can address the calculated parameters and goals of the fuel system, you have endless viable options to get there. Similar to your propane cylinder idea, my first surge tank was the bottom of a household fire extinguisher body. My easiest are repurposed $20 oil vapor catch cans. My quick-but-looks-engineered is a 10-minute pickup tube extension and fitting mod to a common $20 fuel filter assembly. Take your target parameters and get results whatever way makes you giggle.


By toddTR6
If anyone is curious, the fuel pump I have is a carter CARTER P74028. Used on many ford products like the 89 f150 external pump. One of the reasons I choose it is because it is well known and easy to get.

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