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ajg193's 1983 KP61 Sprint


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I did some fuel consumption calculations today.


The MicroSquirt/TunerStudioMS seems to over estimate fuel consumption by about 10% - My belief is that this is due to my injector dead times being larger than estimated in the software. Then again, this could also be due to my data being collected from an ill-conditioned system as I only based these results off of about 35 km of driving.


For the fuel consumption tests, I had the headlights on and held the car at a steady(ish) speed on a flat road to take the readings. For the fuel figures obtained for anything other than 5th gear, there was a fair bit of noise in the consumption signal as I had difficulty writing down the numbers while driving (a passenger would be useful next time). Also the samples were taken over a very short time period, with slight undulations in the road etc.


For the 35 km trip, the computer estimated a fuel consumption of 2.26 L. The actual fuel consumption was 2.04 L. This gives a fuel consumption of about 5.9 L/100 km, which is very good considering I wasn't being nice to the car during this time. It's actually on par with the best result I ever had with the carburetor driving like a granny.fuelconsumption.png.48701707d3b131a558ed710243c76210.png


Fuel consumption at 80 km/h in 5th gear is about 4.2 L/100 km. I think the 4th gear value is unreasonably high and I will have to take the reading again at some point. The same goes for the 100 km/h 4th gear result as earlier indications today suggested it was about 10% worse than in 5th gear.


The values in the graph have been corrected by 10% to allow for computer error.


Judging by these numbers, if I drive 70 km/h constantly (at sea level, without wind, in the dry) I should be able to make it to Auckland on a single tank of fuel.




Car is great on fuel now, more testing is needed.



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  • 2 months later...
  • 2 weeks later...

Anyone know where I can track down some brand new rear springs for the Starlet?

One side is sitting about 20 mm lower than the other, I think it may be a result of hauling reasonably heavy loads in the car for long distances a couple of times.


Looking for factory height and preferably factory stiffness or slightly stiffer.



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  • 2 weeks later...

Thanks guys for the suggestions. Tried oldscool but they reckoned they'd come from Chch anyway so I just bought a pair from Chamberlains down here. New springs are in. Look at that lush height!





New springs (bit of a bugger they don't come in black though):


Old springs:

Next to eachother:

Now sitting nice and level again:


The car seems more flat around the corners now, but I have only driven it like 1 km since I put the springs in.

It was an easier job than I expected it to be, just undo the top nut on the shocks, jack the car up and pull the old springs out and put the new ones in. I marked the old ones left/right and top/bottom so I can get them back into their original spots if I ever need to.

I can now crawl under my car without having to jack it up so that's a bonus.

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I changed some settings in the tune, I found that at 4 squirts per cycle I was hitting areas where the pulsewidth was just too low to accurately deliver fuel (like 2500 rpm with no load on the engine). I changed it to 2 squirts per cycle so that the pulsewidth is now essentially doubled. I think that this has helped with that problem, and doubling the PW at idle is probably also reasonable as well as at 1.5 ms before I reckon it wouldn't have been far from the nonlinear region.

I took the car on a good thrash through the hills to retune the VE map and whatnot. Shown in Figure 1 from the datalogs.VEMAP.png.eb5fba90a2fe2d3d57e963f546a1eda9.png
Figure 1, VE map

Don't worry about it being greater than 100 (colourbar is the VE value), these numbers are essentially a nondimensional scaling factor, that coupled with the fact that I am running lower fuel pressure than the injectors are rated at (I'm running 3 bar above manifold pressure).

You can see above 5000 rpm it really starts to drop off significantly, but it peaks around 3500 rpm (I'd as that this is around the max torque point)

I also used the Duty cycle values from the injectors to calculate approximate engine power, assuming a 100% duty cycle flow rate of 210 cc per injector, an energy density of 34.2 MJ/litre of fuel and a thermal efficiency of 25% across the board (which is a huge assumption, but I'd say is fairly typical for a petrol engine).

The results of this calculation are shown in Figure 2

Figure 2, power curve

The colourbar is manifold pressure (in % of barometer).

This would give a peak power of around about 58 kW (79 ps/hp), and the curve pretty much perfectly overlaps the one given in the JDM Starlet brochure for the 4K-E. I'd say that the power is probably over estimated by about 5-10% but isn't too far off.

I've also found that the car can now get up Hackthorne Road in 4th gear quite happily where I would have needed to stay in 3rd gear with the carb setup.

Figure 3 shows a map of the pulsewidth vs RPM. The colourbar is the manifold pressure value. The line of points along the RPM axis/0 PW is where fuel cuts were active on deceleration.


Figure 3, Pulse width map

Figure 4 shows the observed AFR of the engine, mapped to manifold pressure and RPM. I'm generally holding around the 13.0 mark at full throttle and cruising at around 16.5. My idle AFR is currently a little high at around 14.5, I'll probably drop this down to around 13 as that seems to minimize any effects of heat soak if the engine has been sitting for 10 minutes or so. I probably also need to adjust the VE values on the trace route back down to idle as occasionally it will miss the idle and stall after a hot start since I changed from 4 squirts to 2 squirts (used to be good with my old map).

I'm currently not running any EGO correction, I may enable it at some point in the future once I am convinced that the O2 controller starts reliably (I've been having issues recently where it sometimes doesn't output anything to the ECU, but I seem to have gotten it to work reliably again).
Figure 4, Observed AFR

What is interesting to see from the VE map/PW map is the general operating range of the engine, where it's pretty much all used below 3000 rpm but above that I am generally either fully on the gas or fully off the gas. Then there are some areas which are never hit, such as low RPM/low manifold pressure, or just about anything below 1000 rpm in general.


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  • 4 months later...

I've finally gotten around to making a return fuel port for the tank, I'll put it on the car either tomorrow or Saturday. I should probably zinc plate it first, or do you guys have any paint recommendations?



It has 3/8 feed and using the original 1/4 feed as return

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Car was making a bit of a belty noise the other day so I pulled off the alternator belt. Pulley on the alternator had a little slop in it so I stripped it down. The front bearing seemed to have a bit more play than I'd like so I threw a new one in and vapour blasted the front half of the alternator (illegally borrowing @ProZac's blaster).

I went to put it back together but my OCD couldn't cope



So I pulled off the back half and cleaned it too



Anywho, it looks a lot better now and doesn't seem to have any unreasonable play. I also put a new belt on, last one was about 6 years old. Nice and quiet now.

$22 fix

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