How to assess the mechanical resistance of the engine?

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Dumindu
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How to assess the mechanical resistance of the engine?

Post by Dumindu » Sun Oct 27, 2019 7:56 pm

My car is a 1987 Toyota Tercel DX Wagon RHD 1452cc manual driven car.

Since my car fuel economy is still not come upto the optimum, I want to assess whether engine mechanical resistance is so high or engine works under restriction.

what are the ways to assess it?

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Mattel
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Re: How to assess the mechanical resistance of the engine?

Post by Mattel » Sun Oct 27, 2019 8:43 pm

If you can get onto a dynamometer you could test how much power is getting to the wheels but I think its expensive. There are so many things that could be the issue. Could even be the way you drive it. tyres. I would imagine that your carburettor is probably giving you issues if it hasn't been serviced. kits are available online to service the carb.
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Re: How to assess the mechanical resistance of the engine?

Post by xirdneh » Mon Oct 28, 2019 8:25 am

Try a different carb first. I am assuming you checked the usual stuff - dragging brake, low tire pressure, roof rack etc
Love those Tercell 4x4 wagons but they sure suffer from road noise.

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Re: How to assess the mechanical resistance of the engine?

Post by Petros » Mon Oct 28, 2019 11:11 pm

jack up each wheel, one at a time and see how it spins (trans in neutral, brake off).

if the engine is running good, not under powered, than likely leaky AAP (auxilarly acceleration pump). pull the vac line to it and if it is full of fuel, cap off both ends. if running rich, could also be choke that is not opening all the way, or fuel metering valve in the carb sticking open, both would make it rich.

you can "scientifically" determine car drag/drive train drag, and engine drag, with a stop watch. find a level and straight stets of road without wind (or average your results going each way). time how long the car takes to slow down from say 100 kph, to 80 kph while coasting in neutral. knowing the weight of the car (either get it weighed, or estimate it with an empty car), you can calculate deceleration, and at the average speed of 90 kph, you can determine your power required for steady state speed.

you determine your engine drag by removing the spark plugs and than try and find how much torque it takes to turn the engine (steady state speed). from that you can calculate power required to spin the engine.

as a practical matter, if the car seems to coast down thought the speeds at normal deceleration, and it is fairly easy to turn the engine without the spark plugs, your problem is not excessive drag.
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Dumindu
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Re: How to assess the mechanical resistance of the engine?

Post by Dumindu » Sun Nov 10, 2019 7:41 am

Thank you for your valuable advice.

What is the normal torque need to rotate the engine manually in neutral gear?

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Petros
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Re: How to assess the mechanical resistance of the engine?

Post by Petros » Mon Nov 11, 2019 4:51 pm

with the spark plugs out, I think it would take less than 20 ft-lbs to rotate the engine. if it is all warmed up, likely even less.

that is a guess, I have not measured it. Perhaps I should, that would be an interesting (and useful) value to know.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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Dumindu
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Re: How to assess the mechanical resistance of the engine?

Post by Dumindu » Tue Nov 12, 2019 11:33 am

I tested the torque. If your given values correct, my engine internal drag is in the normal range.

I removed all the spark plugs. Car was in the neutral gear. I did put a 27cm long spanner to the nut of the crank pulley. I connected a spring scale to the other end of the spanner. I pulled the scale in a right angle. It was 10-11kg when pulley starts to spin.

Since 1kg equals 9.8N, 10kg equals 98N.

So the torque was 98N x 0.27m = 26.5Nm

26.5Nm equals 19.5 lbft

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