850 Sport Coupe series 2 track car.

I did something similar with a vintage motorcycle. However in that case it was a matter of swapping one mechanical device for another one. But there was one issue with it....

Does using the original Fiat tach gauge face have the correct read out to match the new tach guts? I mean in terms of the numbering and spacing being the same as the new tach's sweep and values? Or to put it in other words, is it accurate now?
The original tacho was 0 to 8000 rpm the same as most of these cheap Chinese tachos. There are no stops on the tacho face, it's a mechanical stop inside. The needle is just a push fit so it's just a matter of holding the bit inside on the stop with a finger and putting the needle on zero. The signal goes to the tacho from the ECU. The ECU gets it's signal from the 36-1 wheel on the crankshaft so there are no mechanical errors like the distributor gets from the gears. It's about as accurate as you can get!
In this video the problem with the car's original tacho is obvious. On top of the dash in the middle is a similar 52mm tacho that I have now removed. I also removed the change light. On the tablet I have re-arranged the dials so the tacho is now on the top right and I have made the dial about 120mm diameter. I set the parameters so that as the engine passes 7500 the dial will go red. This will work like the change light and should be visible out of the corner of my eye.

 
I might not have stated my question correctly. I wasn't asking about the accuracy of the tach signal.

If I understand correctly you re-used the original Fiat tach face (the round visible dial display part of the old tach) with a new electronic drive unit behind it. When mixing two gauges (the old Fiat face with the new drive unit) the scale (numbers printed on the display) of the old face may not correspond to the sweep of the needle from the new drive unit. Not only the actual RPM numbers, but how they are spaced across the gauge...how far the needle needs to move to go from one extreme to the other end of the scale. If the face from the new tach is different than the old face (on the Fiat tach), then when the needle moves it won't correspond to the correct reading on the display.

Not sure if that was worded any better. But basically you can compare the two tachs; the round gauge on the dash with the tablet display. If they indicate the same then the combination of old and new parts worked correctly. ;)

Either way, really nice job with the conversion. :)
 
Yes, I rotated the interior mechanism from the minimal stop to the maximum and the needle went from 0 to 8000. the spacings of the numbers are the same, just a different-sized dial. I have run the engine to check the operation at lower revs and the needle movement is nice and smooth up and down.
 
That Spridget sure slows down for the corners.

Looks good and sounds better.

Thanks!
 
Thanks for posting. Looks like a fun track!
It looks like you're using RaceChrono for your lap timer. Don't you just love the big Green highlight when you improve your fastest time!
 
That iPad screen near the shifter looks like it's showing an eBay ad for an 850 spider. That does look like a fun track.
 
That iPad screen near the shifter looks like it's showing an eBay ad for an 850 spider. That does look like a fun track.
No ad there. That's just the fuel map being tuned as I drive. The different colours are just showing how many times each cell was visited and how trustworthy they are.
 
Last Sunday I competed in the local hillclimb. I only had 3 runs and they were below my usual times. Driving to the start line for the fourth climb and the alternator quit. I'm fairly certain the diodes were failing on the earlier runs and causing poor engine performance. Voltages are critical with EFI and there is a possibility the O2 sensor was giving the ECU a bum steer! Apparently, the failing diodes can allow AC current back in the system. The alternator is being rebuilt now.
Huntley feb23b.jpg
 
Last Sunday I competed in the local hillclimb. I only had 3 runs and they were below my usual times. Driving to the start line for the fourth climb and the alternator quit. I'm fairly certain the diodes were failing on the earlier runs and causing poor engine performance. Voltages are critical with EFI and there is a possibility the O2 sensor was giving the ECU a bum steer! Apparently, the failing diodes can allow AC current back in the system. The alternator is being rebuilt now.View attachment 70876
That's interesting if the diodes were actually causing it to run differently.
 
I ran data logs for each run and each one showed very lean mixtures as I accelerated through the esses. The photographer stationed nearby reckoned the engine sounded flat! Looking at the videos of each run the AFR's were OK at high revs. Just around 4000 was the problem. Interestingly the new tacho is very accurate mid-range but at the top reads low. Changing up from 2nd to third I used 7000 on the tacho and the data log says this was actually 8500 for a brief moment!
 
I had no joy with the alternator rebuild. I have bought another identical unit, a Denso 40 amp alternator that is normally installed on Diahatsu Charades etc. This time I will be fitting at least a 70mm multi rib pulley. The blown up one has a 50mm pulley driven from a 150mm pulley. Checking the data logs from the last two events I exceeded 8,500rpm on a few occasions. The alternator was spinning at 25,500! They are not meant to exceed 18,000.
 
Sounds like a good move. I use the same alternator on my track X, 60mm pulley from a 120mm pulley, so 16,000rpm at 8,000rpm engine speed. I had never considered an alternator rev limit. 8,500 revs on your push rod engine is pretty impressive.
 
Sounds like a good move. I use the same alternator on my track X, 60mm pulley from a 120mm pulley, so 16,000rpm at 8,000rpm engine speed. I had never considered an alternator rev limit. 8,500 revs on your push rod engine is pretty impressive.
It was not intentional. I was using 7,500 on my tacho but the new unit is out by about a 1000rpm! I will have to allow for that in future. I will look for a larger pulley for the alternator than 70mm in the wrecking yard. On my new engine I'm going to drive the alternator off the back of the OHC camshaft so it will be half the speed. Did you get the details for the Fiat Nationals at Bendigo?
 
It was not intentional. I was using 7,500 on my tacho but the new unit is out by about a 1000rpm! I will have to allow for that in future. I will look for a larger pulley for the alternator than 70mm in the wrecking yard. On my new engine I'm going to drive the alternator off the back of the OHC camshaft so it will be half the speed. Did you get the details for the Fiat Nationals at Bendigo?
Yeah, I saw the Nationals post, unfortunately I won't be able to make it, I have another commitment that clashes with those dates. It looks like an interesting track though.
 
It was not intentional. I was using 7,500 on my tacho but the new unit is out by about a 1000rpm! I will have to allow for that in future. I will look for a larger pulley for the alternator than 70mm in the wrecking yard. On my new engine I'm going to drive the alternator off the back of the OHC camshaft so it will be half the speed. Did you get the details for the Fiat Nationals at Bendigo?
Stupid question, are you not using a rev limiting feature in your injection system? If not, why?

(I can imagine a few reasons such as not wanting to destabilize the car when hitting it in a corner for example)
 
I could use fuel cut to limit the rpm or even ignition but there is the danger of being lean at just the wrong time. E85 is very tolerant but I think the answer is to not over-rev. On a circuit, it's not really a problem as you tend to change gears at the same place after a few laps. On a hillclimb there is a tendency to maximise the acceleration just off the line and in my case it's second into third where I went past 8500. The runs I did complete at the last hillclimb were slower than my usual where I change normally at 7500. I think the hp was falling away at 8500.
 
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