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Discussion Starter #1
My first X758 didn't have the digital dashboard, just two analog gauges (temp and fuel) and an hour meter (it was a 2015). This one has the fancy digital panel, and there's a tachometer of sorts there. I was wondering if anyone had worked out exactly what each mark is analogous to. So, for example, say three tick marks is 1200RPM, five is 1800, and so on.

So...anyone work this out yet? Perhaps someone with an add-on tachometer can make the correlation?
 

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My understanding is the tach display is not that accurate. The tick marks only give a generalization of the engine RPM. In other words, if 10 tick marks are displayed the engine is running faster than if 5 tick marks are displayed. Then again, your ear will usually tell you the same thing.

You guessed it... it's pretty much just a gimmick. :)
 

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Discussion Starter #3
I don't know...if the readout is repeatable based on throttle position (meaning, it always reads say 5 ticks when the throttle is exactly in the middle), then a correlation can be established.
 

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The x738 has the digital tach like you I have no idea. For the gas version I was told run wide open all the time , no matter what you are doing or where you may be going.

:dunno::dunno:
Just know , to engage mower at wide open throttle on x 738 and at idle when operating my 1025r.


Like others I've noticed the x tach doesn't seem to be accurate. :dunno:
 

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The x738 has the digital tach like you I have no idea. For the gas version I was told run wide open all the time , no matter what you are doing or where you may be going.

Just know , to engage mower at wide open throttle on x 738 and at idle when operating my 1025r.
I can see needing to use a lot of throttle with a belt driven mower deck and electric clutch but it just makes no sense at all with a shaft-drive deck.
 

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I can see needing to use a lot of throttle with a belt driven mower deck and electric clutch but it just makes no sense at all with a shaft-drive deck.
Its all about the Torque curve of the engine. The V-twin gasser needs high RPM to develop the torque needed to get the mower blades moving from a standstill. Less than 3/4 throttle and you risk stalling the engine when you engage the mower deck.

My machine runs 3/4 to WOT for any work being done. The generally equates to the right below or in the little highlighted grass cutting RPM range marked on the top of the digital tach gauge.

As for what that digital gauge is telling you, I would say the bars are roughly equal to throttle position. The digital gauge is measuring engine RPM directly though, what each bar means in terms of rpm is anybody's guess.
 

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I can see needing to use a lot of throttle with a belt driven mower deck and electric clutch but it just makes no sense at all with a shaft-drive deck.
Torque transmission has virtually no difference in how much torque is produced. The only real difference would be how much made it through. Between belt and shaft it would be very close in efficiency. Within a few percent at least. The gearbox would eat up most of the losses in either system.
 

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My first X758 didn't have the digital dashboard, just two analog gauges (temp and fuel) and an hour meter (it was a 2015). This one has the fancy digital panel, and there's a tachometer of sorts there. I was wondering if anyone had worked out exactly what each mark is analogous to. So, for example, say three tick marks is 1200RPM, five is 1800, and so on.

So...anyone work this out yet? Perhaps someone with an add-on tachometer can make the correlation?
Bring a Garmin or equivalent GPS based street navigation . . . many tell you the speed you are traveling . . . at least mine does
 

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Its all about the Torque curve of the engine. The V-twin gasser needs high RPM to develop the torque needed to get the mower blades moving from a standstill. Less than 3/4 throttle and you risk stalling the engine when you engage the mower deck.
Actually, even on my X500 the faster engine speed seems to only be required when the mower deck is cold. Once the deck has run for a bit you can easily engage it at less than half throttle and it will not stall the engine and there is almost no belt screeching.

My point is... the manuals for the various tractor models don't always give sensible information. And they don't always distinguish between engine types. Example... the X700-series manuals for both gas and diesel models all contain the same information telling you to engage the mid-PTO at wide-open throttle. Which of course makes no sense. Whereas the 1-series manuals advise to engage the mid-PTO at less than 1500 RPM and then increase engine speed to operational speed.
 

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Torque transmission has virtually no difference in how much torque is produced. The only real difference would be how much made it through. Between belt and shaft it would be very close in efficiency. Within a few percent at least. The gearbox would eat up most of the losses in either system.
I agree. The difference seems to be the deck itself. On my X500 when the deck is cold (hasn't been run for a while) you need to have the engine at WOT or else it will stall when the PTO is engaged. This usually results in a lot of belt screeching. However, after the deck has run for a while and is "warmed up" you can easily engage the PTO at an engine speed around 1/3 throttle with almost no belt screeching.

Almost all lawn and garden tractor manuals always instruct to engage the mower at WOT. Which seems to be a CYA move so you don't have Johnny Homeowner calling the dealer and complaining because the engine always stalls when he tries to engage the mower. All SCUT/CUT manuals always instruct to engage the mower at a low engine speed (less than 1500 RPM).
 

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Discussion Starter #11
If my old X590 could handle engaging the PTO at less than 1/3rd throttle, then so can your X738!

Wuss. :)

:hide:
 

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Discussion Starter #12
As for the tach...I guess the answer is "no."

So I will do it. I just ordered one of these:

https://www.amazon.com/Neiko-20713A-Digital-Tachometer-Contact/dp/B000I5LDVC/

I'll let you guys know what I come up with. I'll also test for consistency/accuracy of the digital "tach" though that may take a while to get reliable results (different temps, elevations, etc.). Fortunately I have access to a range of elevations on my property.
 

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If my old X590 could handle engaging the PTO at less than 1/3rd throttle, then so can your X738!

Wuss. :)

:hide:
:nunu:

I mean I guess it "can" handle dropping in the PTO at lower throttle but it really doesn't seem to like it all that much.
 

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As for the tach...I guess the answer is "no."

So I will do it. I just ordered one of these:

https://www.amazon.com/Neiko-20713A-Digital-Tachometer-Contact/dp/B000I5LDVC/

I'll let you guys know what I come up with. I'll also test for consistency/accuracy of the digital "tach" though that may take a while to get reliable results (different temps, elevations, etc.). Fortunately I have access to a range of elevations on my property.
Mike01: Have you asked your dealer about the tach? Your dealership group is one of the best in the northeast. On the remote chance that they don't have an answer, I would bet that they will get it real quick.
 

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Discussion Starter #15 (Edited)
Mike01: Have you asked your dealer about the tach? Your dealership group is one of the best in the northeast. On the remote chance that they don't have an answer, I would bet that they will get it real quick.
That is a fantastic idea! I will do it right now.

EDIT: Called, they don't know, but will look into it.
 

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Discussion Starter #16
Got the tach today. It's easy to use, just stick some reflective tape on the flywheel, run the engine, point and click.

So as promised, here is the preliminary data. These numbers are averages of several readings.

Idle (2 tick marks) - 1350

3 tick marks - 1600

4 tick marks - 1800

5 tick marks - 1900

6 tick marks - 2050

7 tick marks - 2200

8 tick marks - 2300

9 tick marks - 2450 this is about 50% throttle

10 tick marks - 2550

11 tick marks - 2650

12 tick marks - 2750

13 tick marks - 2850

14 tick marks - 3000

15 tick marks - 3100

16 tick marks - 3300

17 tick marks - 3450

18 tick marks - 3600

This tachometer is not an idiot light as some people have suggested. These numbers are repeatable and consistent (plus or minus about 30 rpm). The tach display drops momentarily (shows fewer ticks) when you engage the PTO, and when you apply a load, so it's clearly reading engine RPMs and not throttle stick position (which is what would have made it a useless idiot light).

Conclusion: this is a real tachometer. These diesel X75x tractors idle at about 1350 RPM and WOT is 3600. This is probably why Deere does not want to make this data available...high revving diesels make some people nervous.

These numbers make sense, because unlike a 1025R which has the same hp, this engine does not like to engage the PTO at idle. It won't stall, but it will come close. So the 1025R's 25HP engine is actually a more powerful, higher torque engine than this one, and the reason they produce the same HP is that this one is tuned to produce torque under load at a higher RPM (which is what HP actually is).
 
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