Governor spring and high idle screw

[rdodd]

I have a question about the high idle screw and the 3000 rpm gov. spring. If just the high idle screw is set up to allow for more rpm,s does this also increase the defuel point without doing the gov. spring? If so, by how much, and how much more with the gov. spring?Is the 3000 rpm gov. needed if one wants to obtain 3000 rpm,s as a defuel point?

 

[BushWakr - RIP]

The short answer is... . no/yes...

The high idle scew (which is all mark has used) will raise your governed speed upward. Normally the defuel point begins (very roughly) around 300 RPM before governed speed. This will fluctuate with RPM and Load.

So if you raise your governor to, say, 3200 RPM then the defuel will start at roughly 2900 and continue to fall off rapidly prior to 3200 RPM.



The governor spring does one thing primarily,,, it overrides the defuel function of the RPM and Load governing systems. This means that if you set you governed speed at the same 3200 RPM then what I have seen is the engine will pull hard a brass bearings all the way up to the 3200 RPM level.

Under a no load/WOT situation I've seen an RPM flare well over the 3200 due to the heavy fueling continuing right up to or near the 3200. This pushes the engine over 3200 before the RPM/Load system can take control and bring fueling down.

A good valve set is important when you start getting into the 3000 RPM range.

If you are running an auto, then the governor spring makes it's own presence known in a different way.

The auto which is prone to running right up to the max speed before each shift means that defuel is happening before shift happens. You can tweak your shift points on the valve body but normally guys use the throttle valve cable. . not the best choice.

Now since the governor spring holds full fueling all the way up, you atleast get that heavy fuel load right up to the point were the darn auto HAS to shift up... . works good.



bob.

 

[rdodd]

Can the engine handle 3200 rpm,s safely with the stock valve springs? I would like to set my high idle setting to about 3200 to obtain appr. 2900 rpm defuel, but i will probably have to get a more reliable tach before setting this. My isspro tach seems to be temperature sensitive and can vary as much as 200 rpm,s on a hot day as opposed to a cold day.

 

[BushWakr - RIP]

Your tach should not be temp sensitive ... ...

Having said that, set your RPM to 3200 using the temps that result in the lowest readings... .

You can run these truck's up to about 3400 RPM before you really should (in my opinion MUST) consider 60 lb springs..... like I should talk..... 3800 arghhh... ... .



Pastor Bob.

 

[JLEONARD]

Your tach should not be temp sensitive ... ...

I agree, but I also have an Isspro tach that seems to be acting the same way last couple of months... haven't gotten into it yet.

Some boaters I know complain of Teleflex tachs acting the same way... some have removed the back covers in an attempt to keep them cool... . helps a little.

Didn't meant to wander from the subject... .....

Jay

 

[rdodd]

I need to call isspro and ask them about the temp sensitive problems i am having with my tach. Heated conditions, like a hot day or sun shining on tach makes the tach reading slower. When cold,tach says 800 rpm for idle and 2000 rpm at 70 mph. When hot outside idle speed reads under 700 rpm and 2800 rpm at 70 and can vary even more at temp extremes. What i don,t understand is when diesel shop hooks up there snap-on shop tach it reads same as mine even at different temps. Could the computor in the truck be the culprit since the shop tach seems to jive with mine?

 

[rdodd]

Back to increasing the high idle rpm,s , there seems to be different ideas concerning increasing the rpm,s, for instance i was talking to the guy at tst and he said he would,nt recomend setting rpm,s over stock setting. He said he has seen camshafts break from even 3000 rpm,s and that the newer 24 valve trucks have changed design on cam bearings to allow for more rpm,s. He seemed more concerned about the camshaft breaking than problems with valve float. Has anyone else heard this?