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The prospect of something like that was what made me tap the easy button for the Racepak in my racecar - a programmable fuel gauge: drain the tank, press button. Fill the tank, press button. Job done.
The prospect of something like that was what made me tap the easy button for the Racepak in my racecar - a programmable fuel gauge: drain the tank, press button. Fill the tank, press button. Job done.
Have a cat for saving me the time and effort of doing this myself. It was literally on my checklist of things to do before my next event. My fuel level readings have been all over the map and swing wildly. I still need to figure that part out, but the info in your post is invaluable.
For anyone else reading, I calculated the sensor resistance at the various gallon markers, for your convenience. Go forth and be nerdy!
Last edited by thebeerbaron; 07-19-2023 at 05:54 PM.
@curly & @thebeerbaron I hope I made it clear, I realize I set this up wrong. It is "working" for now, but I realize at this little of a voltage any corrosion etc. will make it no longer work properly. I still don't understand how to set it up correctly.
AIM has the following diagram in some instructions I found online from them:
This makes it look like if I take one of the 5ref signals from the PDM and attach that to the wire coming from the sender in the tank (add the pull up, which using the AIM formula should be ~2400 ohm, and I'll admit, I would probably just use the 2K pull up the PDM provides) and all will be correct signal wise? (obviously I will need to "redo" the readings) I don't understand how adding 5volts to the wire works (since it's the same wire we are trying to get the reading from, I don't see how it meets any of the resistance to change from 5 volts....I would think the 5 volts would go directly to the Analog input.)
How do you all set this up / set this up for the 5volt ref? I would prefer to have it set up correctly.
You have it set up correctly right now, it's just that the pull-up resistor you're using causes the output voltage to be in a very small range of 0.014-0.263 volts, when your analog input is designed for 0-5v.
What we're using here is a voltage divider circuit, where the second resistor is the fuel level sender. I've taken the following image from ohmslawcalculator.com which is a handy resource.
Your dash is providing the 5v source voltage. It's reading Vout, using the analog input and the sensor ground. (ie, the input pin is connected at the point between the two resistors).
The math is easy and they provide a lovely calculator. You're currently using a 2k ohm pull-up as R1 and the sender is providing resistance of anywhere from 5.6-111 ohms, if you look at my spreadsheet above. If you play with the numbers a bit, you can see that a smaller value for R1 will give you a larger range of Vout.
Here's how the numbers work out with a 2000 ohm pull-up. You minimum step size of 0.005 volts per gallon is 1/1000 of the range of the 0-5v analog input. That's tiny!
If you use Curly's suggested pull-up value of 220 ohms, this is what you get. Now your input is using a range of 0.12-1.68 volts. That's much better! Now your minimum step size is 4x larger; it's still small, but most of your steps are around 0.1v per gallon, 1/50th of your input range.
I have a metric buttload of resistors just lying around, so for my fuel level circuit, I grabbed a 68 ohm resistor. Here's how that works out. (Yes, for the real EEs out there, I understand I'm consuming more current than I need to, but it's literally the only sensor using this voltage source)
After that lecture, maybe I should address the more direct end if the question.
You need to connect one end of a pull-up resistor to the 5v sensor voltage source, as shown in the voltage divider circuit at the top of my post. The other end of this resistor goes onto the fuel level sensor wire that's going into your AIM. The ground leg of your fuel level sender should/must be connected to the sensor ground of the AIM and nowhere else.
To extend the explanation above, after re-re-re-reading your post...
You need the pull-up to 5v because the analog input can't measure the sensor resistance directly. Instead, it reads a voltage. So you need to provide some amount of voltage to the analog input. Hence connecting it to 5v. Now, if you were to disconnect the fuel level sender from the circuit, your analog input would be "pulled up" to 5v. Once you re-connect the sender, you have a voltage divider circuit and the resistance of the fuel sender can be determined by looking at the voltage at the analog input.
Couple of gotchas - you need to be using the 5v source from whatever black box contains the analog input. You also need to be using the sensor ground from that black box. Otherwise your voltage divider circuit ... isn't.
Thanks Beer for the super quick & informative responses. I've read what you wrote a bunch of times and I'm not trying to be thick, but I'm more confused now then when I started
That said, you mention ground wires. All my ground wires are attached to the body of the car. I don't have one going from the fuel sender back to the PDM32.
Here is (very bad) diagram I drew up really quick of how I have everything wired. Sorry, this is my "Good" handwriting too.
Some additional questions I have.
Is Channel 1 sending out voltage to the fuel sender? (This has confused me since the start & maybe why I'm so confused...Where is the electricity coming from?) If so, is it sending 12 volts or 5 volts or ??? and how do I know what is being sent from the PDM? I was under the impression the inputs should be receiving an electrical signal. Not sending any electricity out.
If Channel 1 is sending out power, then I'm guessing the PDM can then read the current changes based upon the resistance from the fuel sender (and pull up) and that's how I'm getting my readings?
I keep looking at this picture you sent. I guess I don't understand what Voltage Out (Vout) is if it's also not going to ground. (This is where I probably need to do a lot more reading on electrical circuits). My understanding from what you wrote is that Vout is my Input channel. If so, I'm missing the + at the beginning.
Sorry, for all the ignorant questions. If you have somewhere you recommend I go and read to understand all of this, please let me know. I have been searching and reading on my own, but I'm getting different pieces and haven't put it all together yet. Thanks for the patience & info.
Stop reading at the "Calculating Sensor Voltage" section, they needlessly complicate things there.
Originally Posted by rdb138
That said, you mention ground wires. All my ground wires are attached to the body of the car. I don't have one going from the fuel sender back to the PDM32.
I don't like that design, but it would probably be confusing for me to try to explain it here in the midst of everything else. Maybe I'll try later.
I re-ordered your questions a bit...
I keep looking at this picture you sent. I guess I don't understand what Voltage Out (Vout) is if it's also not going to ground. (This is where I probably need to do a lot more reading on electrical circuits). My understanding from what you wrote is that Vout is my Input channel. If so, I'm missing the + at the beginning.
Remember that voltage is always measured/defined between two points. If you have a volt meter and touch the + probe to the positive post on your battery, you don't get any sort of reading until you connect the - probe to something. If you touch the - probe to the negative terminal, you'll see battery voltage.
Same thing here. Vout is measured between two points - in this case Ground and Channel 1.
Is Channel 1 sending out voltage to the fuel sender? (This has confused me since the start & maybe why I'm so confused...Where is the electricity coming from?) If so, is it sending 12 volts or 5 volts or ??? and how do I know what is being sent from the PDM? I was under the impression the inputs should be receiving an electrical signal. Not sending any electricity out.
I'll simplify here - your sensor supply voltage is 5 volts.
Your pull-up resistor, whether it's internal to the PDM or external, is applying the sensory supply voltage to the Channel 1 input. If the input is not connected to anything, it'll read as 5v. If you connect Channel 1 to ground, it'll read ground. If you connect Channel 1 to ground through a resistor (like your fuel level sender), the voltage will be related to the resistance of the pull-up resistor and the sensor. This voltage is Vout of the voltage-divider circuit I showed earlier.
If Channel 1 is sending out power, then I'm guessing the PDM can then read the current changes based upon the resistance from the fuel sender (and pull up) and that's how I'm getting my readings?
The PDM is reading the voltage difference between between Channel 1 and Ground.
With @thebeerbaron help (Thank you) and a lot of reading / watching some videos (I normally prefer reading, but HPAcadamy also has a video on pull up resistors and discusses a temp sensor which works the same as the fuel sender sensor and was very helpful (seeing him program it into the link ecu helped too.)
I didn't realize the PDM was sending the 5volts and that you could measure the total resistance from the two resistors (fuel sender & pull up) anywhere in the circuit. I thought you needed to read at the resistor itself. Like it was a large funnel of electricity waiting to enter the resistor so you couldn't measure just anywhere in the circuit. Now I realize it's more like a single line queue and you can measure it anywhere in the circuit.
I'll get a proper sized resistor to use instead of the internal pull up. (& super happy to realize that I can do a little spreadsheet math vs re-pouring gallon by gallon too!)
As seems to always be the case, I'm behind on this build thread again. I continue to work on the car, but haven't had the time to keep the thread up to date as I should. I just thought about where the car was last year at this time and where it is today. Its come a long way! Especially while also driving her at events this year.
The Car Last Year in October: I was working on getting the cage finished & the drivers seat (not mounted you can see the tunnel is even cut in this picture with exhaust pipe showing) fitting straight.
Car today: Some spoilers in these photos :-)
This is the final work I did to the car before going to Barber in June.
Main Door Windows:
I haven’t graduated up to the big boy enclosed trailer yet. So weather (more specifically rain) is an issue when you don’t have windows, which I can't re-install with the door bars. I’ve been rolling the dice ever since the cage install and decided I need to resolve this issue before I went to Barber (back in early June) where the car would be outside for 3 - 4 days & guaranteed rain if I didn’t have windows!
With gutted doors and the door bars extending into the door shells, you can’t just reinstall the windows. After looking at my options, I decided to take a page out of the spec miata’s handbook and hang the windows in the door using hooks. This supposedly holds the windows in place well enough to tow the car and keep water out, I’ll admit I had my doubts, but Spoiler alert. It holds the windows in place surprisingly well and I would say seals better than expected.
I pulled the windows out of storage, and then removed all of the pieces attached to it.
After a good cleaning I reused some of the parts I took off to attach the “hook” I purchased. (You can get hooks that install inside the door or onto the window. I went with the window version…You can obviously make these yourself, but I purchased the for the same price I would have paid to just buy the metal)
With the window all ready, it was time to work on the car. First step was modifying the metal window channel that is vertical and goes between the Triangle window / main window. Lucky for me, Mazda bolted it in at both the bottom of the door, just below the window sill (where I still had metal / attachment there) and the very top. So a quick pass in the band saw and I now had a piece that would work attaching at the very top and just below the window sill
Already cut and re-installed in this picture, originally the bar went to the bottom of the door.
The cage builder cut out the inside door sill right after the Triangle window. I needed that piece back to hold the glass in place with the “hook” method. So I took a piece of 3/4" wide X 1/8” thick steel and welded it across the door, making a new inner window sill. I needed a little extension downward on the door latch side since there really wasn't any metal to weld it straight across. The metal ends right where the push pin for the rubber seal is.
Here it is, welded in and with a quick coat of primer / paint. (easier to see how the metal at the latch doesn't go up high enough in this picture)
When I test fit my window, it wasn’t sitting level. It was too low up towards the front of the car. (I guess the original door sill isn't exactly level across, or these hooks had the holes drilled in the wrong places.) So I grabbed one of the plastic window stoppers and used it as a shim. (It needed to be sanded down a little to get the right height & then boom…I have a window properly in the door again.
Picture before sanding down the stopper & installing it to level out the window. (I could have also modified the metal attached to the window, but this seemed easier at the time.)
With spacer sanded down to the right hight and installed:
Window installed & sitting just a little tall at front, before the shim was sanded down, but you can see the end result in this picture.
Triangle Windows
I also needed to reinstall the triangle windows, since I removed those for the cage too. I had seen these plexiglass tri-windows with little NACA ducts that help keep you cool. (Which is a win in my department!) So out came the credit card. The triangle come with the naca area cut out, & holes drilled but you need to drill the holes in the naca duct itself to install.
Here you can see one built and the parts to build the other.
The hardest part of this install is getting the window back into the door. The plastic isn’t as sturdy as the glass so you can’t just manhandle it back into place. A little lube on the rubber gasket (especially at the bottom) and they slide back into place. These worked great at pushing a cool breeze into the car. If you live somewhere it’s hot, I highly recommend them. More than one person was a fan of the breeze these add when they rode in the car at Barber.
FYI...I stick a tennis ball in the naca duct to seal it up so rain doesn’t blow in when traveling or on cold days. This works well for me.
Hood Louvers:
It was getting hot in the Atlanta area and I’m sure it would be in Birmingham too. Last year the car was running on the hot side in August at Road Atlanta, so I wanted to get the Hood Louvers installed. First step was just cleaning the hood and then getting the patterns placed on the hood correctly that Singular supplies. (Yes, these are the NC louvers, but they work on the NB and I like the look.) I found it easiest to mark a couple pieced of tape on the hood and then use that to mark the correct place and then tape the template down so I could attach the template in the correct place. Otherwise I would try and move something and of course it would move the other side and I was off again.
With the template in place I removed the hood and placed on saw horses so it was easier to work. I also put some additional tape around the template to keep from scratching up the metal. I know singular recommends using a cutoff wheel, but I found a jigsaw made a cleaner cut. (Thus the pilot hole in the picture below)
If you use a jig saw, make certain you install the plastic shoe (or put tape over your metal one) so you don’t mess up the paint.
Louver holes cut out
After that I flipped over the hood and slid the unbent vent in place under the hood support ribs that were still left. At first I was going to install this way, but realized it wouldn't work with the louvers bent up.
I marked where I needed to cut and pulled out the dremel so I could cut them without cutting the hood.
Test fitted one more time after I cut the ribs back
Then I bent the vents up to 45 degrees. I used an angle finder vs just eyeballing it. (This was a bit harder to bend then you would first think.)
Once more, some test fitting.
I drilled one rivet hole on each side at first.
This looked good with the vents again test fitted so I drilled the second from the template (against my better judgement). I wish I had not done it this way, cause the hole didn’t line up without trimming another 1/16" - 1/8" off the side so I could shift everything that little bit. I spent an hour trimming the sides that little extra bit to get things to line up just right. Verses if I have just lined up the louver from the first hole and drilled out the rest that way.
After getting things trimmed correctly so I could use both holes from the template, I installed the rubber trim piece. This corner didn't want to lay flat.
From there it was rivet time. I used some black painted rivets since I thought that would look better. Riveted in the two holes I had already drilled out and then used the louver as the pattern for the other 4 holes.
And the finished result:
If I was to do this again, I think I would separate the template into two halves and straighten out the louvers to the car a little bit. They might even work better with the air going across them straight (or straighter) vs the angle they are installed at using the Singular template. Then again, that might look like **** and not work any better. I did feel a bunch of heat being pushed out on the one side I have the radiator fan when it was running, so in the paddock these seem to be helping.
Passenger Seat:
This in many ways was just a rinse and repeat of what I did on the drivers side. I pulled out the front & rear humps to get the seat lower, and I also hammered in the tunnel a little bit to get the seat moved over some. You can see all of that "handywork" in this picture. Along with the holes I drilled for the mounts and the eye hooks for the submarine belt. This all looks like crap, glad the seat is covering it.
Here is the seat & belts installed (still had the padding to install)
I think this seat sits too high, and definitely my cage builder should have given me that extra inch of room with the door bars. The bottom is touching the floor and I have it laid back a good bit. I may revisit this at a later time to see if I can get it any lower, but this will have to work for now. <- Have I mentioned how much I hate installing seats in a Miata! This holds true for the passenger seat as well.
I'll be interested to see how much the hood louvers reduce engine temps, I'm sure it helps a ton with getting more air through the radiator.
Unfortunately, I don't have any real numbers to compare and even if I semi did, I keep modifying the car so much between each time I drive it (and temps / track the same) that they wouldn't be a good reference. I can say that I felt the heat blowing out (pretty strong, like a heater vent in your house) from the radiator fan in the padock. So they definitely help there. The car also ran (hottest) at 224F at Barber (Alabama) in June. I don't remember the exact outside temp, but it was probably mid to high 80's maybe even low 90's with the track being much hotter I'm sure. (FYI...224F sounds hot, but Chevy built these engines to run hotter for efficiency / emissions from what I've read. The low fan doesn't kick on till 220F and I believe high speed is 230F (I only have one fan and wired it into the low speed so it kicked on sooner.) I do plan to do better ducting in front of the radiator to give it a little more head room, and I'm also considering an oil cooler, but for 20-30 minute sessions she is running cool enough.
Originally Posted by crxguy52
This build thread is basically "how to LFX swap a Miata", it's been super helpful so far! Thanks for documenting the process so well.
Thanks! I'm glad it's been helpful! There was only 2 other well documented builds at the time I started and they had pieces missing (as I'm sure I do too.) I was semi sold that this was a "kit" build when it's more some parts you can buy from V8Roadsters that will help you put together a build. It's been a real learning process, but I'm glad I did it.
Wow, great updates, hell of a build. Pretty much a dream track car, beautiful cage work, nice aero, and the LFX!
Thanks! Car is a lot of fun to drive. I enjoy her a bunch!
Originally Posted by Fireindc
How is the shift feel on the trans, and in general, how is the trans holding up? I've always heard that was somewhat of a weak point on these.
So (knock on wood) I haven't really had any issues with the drivetrain at all. The trans has been holding up well for 10 track days and ~1000 street miles so far. That said, I used the overly heavy 50 pound (that even hurts to write) OEM Luk Flywheel and Clutch since others had a lot of issues with aftermarket flywheels / clutches. I also drive with some mechanical sympathy for the car. IE. I don't flat shift, manhandle the shifter, shift so fast you over-shift etc.. I'm fairly positive I would have issues pretty quick if I did any of that.
As far as shift feel...It's not JDM, but it's no where close to the 3 speed non-synchromesh 1st gear tranny in my 66 Stang back in college either. It's pretty much par for the course for what you would expect in a modern Camaro.
Here is video of a track day at Atlanta Motorsports Park back in October. You can get an idea of how she shifts (and how much fun the car is!)
Great build, looks like a blast. I just finished up an LFX RX8 swap and my first track test day is in a couple weeks. What oil are you running on track?
Great build, looks like a blast. I just finished up an LFX RX8 swap and my first track test day is in a couple weeks. What oil are you running on track?
Thank you! Car is a blast. I need to update this build thread, I'm a bit behind.
Congrats on getting your RX8 build finished up! I know a lot of work is involved in it. I've seen an RX8 LFX on track once before. It was a great car.
To answer your question: I've been running Valvoline racing synthetic VR1 10w-30. (I don't have any emissions, so high zinc isn't an issue.) Oil pressure has been really good, no issues even under braking. I do not have an oil cooler. I need to install a proper oil temp gauge (the temp you get from the ECU is from an algorithm, there is no actual oil temp sensor in our cars stock.) It reads hot, but supposedly the algorithm isn't very good and will say its a lot hotter than it is. This makes me want to go to a higher oil viscosity, but I choose to stay with the stock(ish) oil viscosity since the engine tolerances are very tight. I know the ShakyDog guys had engine failures on the track with their enduro LFX Miatas due to low oil pressure issues under braking. They were running 20w-50 if memory serves and a big oil cooler (oil coolers generally lower oil pressure a bit incase you didn't know.)
Thanks. I just dyne'ed it and it put down a perfect 300whp and the torque curve is crazy flat and smooth. Good little motor.
Interesting point on the oil cooler. I currently have the big center/front mounted oil cooler that comes with the Keisler kit, plus a thermostat. I don't love how the front ducting is working out so I think im going to switch to using one OEM RX8 oil cooler in the factory spot. Then I can use the factory bumper inlet as intended, etc and it'll free up the front intake for the radiator. I do wonder how about much pressure drop the factory cooler will create. The way the thermostat works in it seems a little restrictive. I could go with an aftermarket cooler in the same location, but fitting the external thermostat is sort of a pain.
I also need to get an oil temp sensor hooked up. I wish i tapped the oil pan before I installed it.
07-18-2023, 02:30 AM
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