RPM question

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pinzinator
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RPM question

Post by pinzinator » Fri Sep 20, 2019 8:34 pm

Those of you who have good tachometers, what RPM do you show at 83 KPH, which is about 50 MPH, in top gear? I think my cheap tach is lying to me, it says around 2250. Or else the dip switches are set wrong.
It seems to be correct at idle, around 600-700 RPM. PinzSSI gives a pulse every 720 crank degrees, or 1 pulse per cam revolution. It can be programmed to give 2 pulses instead of 1.

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David Dunn
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Re: RPM question

Post by David Dunn » Fri Sep 20, 2019 9:42 pm

It's a pointless question without a tire diameter. It would be easier to use an online speed calculator and input the trans ratio, the combine portal/dif ratio and tire size/diameter
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rmel
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Re: RPM question

Post by rmel » Sat Sep 21, 2019 7:59 am

Ballpark, assuming 32" tires @ 50mph pretty close to 3,000 rpm with the stock Tranie and Xcase.
So for sure if your clocking in at about 2,200 it's about 0.75 of true.

For a more accurate calculation, I'd use the tires advertised rev's/mile than the diameter.
The rev's/mile must be validated on a track, the diameter often is less precise.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

pinzinator
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Re: RPM question

Post by pinzinator » Sat Sep 21, 2019 9:51 pm

The tires measure 32.5 inches in diameter. 3,000 RPM sounds a lot more accurate. So much for cheap tachometers!

Texas710
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Re: RPM question

Post by Texas710 » Mon Sep 23, 2019 8:45 am

I thought the proper idle speed was a lot closer to 1k RPM?

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rmel
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Re: RPM question

Post by rmel » Mon Sep 23, 2019 6:32 pm

Between 750 to 900 or at the point where the brake Vacuum boost is operational.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

one2many
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Re: RPM question

Post by one2many » Tue Oct 15, 2019 1:02 am

As we know 710's have higher gearing (T-case) than 712's. Which model do the above figures relate too?
1985 pinzgauer 712K factory 2.7lt civilian (RHD, 4 door K)
1979 Volvo tgb 1314a (under construction to om606 diesel/722.6 trans. Dual cab/tray)

pinzinator
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Re: RPM question

Post by pinzinator » Tue Oct 15, 2019 6:31 am

My Pinz is a 710M. I think I'm going to mess with the tach dip switches this weekend to see if I get get it close, may be good enough.

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rmel
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Re: RPM question

Post by rmel » Tue Oct 15, 2019 11:22 am

one2many, Ya, I forgot to include the model type as Pinzinator's 710 is well know on the forum.
Stock 710 RPM@50MPH ~ 3,000
Stock 712 RPM@50MPH ~ 3,400
These are in the ballpark numbers, assuming 32" tires. Though as mentioned before, the most
accurate tire metric to calculate your RPM more precisely is to use the specified revolutions/mile.
The tire companies are actually suppose to measure that on a track at a specific speed and it has
to repeat after two trial runs.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

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