Max rpm?

[Flinty]

My '92 will pull pretty hard to about 2000 rpm, anything after that and all I'm doing is adding revs. I'm pretty sure the pump has been monkeyed with due to the copious amounts of black smoke under hard acceleration. My '97 will rev to 2700 lickety split. So... why won't my first gen? I see 19 to 22mpg, Good power loaded or empty, idles like a top. I've owned the truck like this for a few years now and figured I shouldn't look a gift horse in the mouth due to the good service it's delivered. The extra rpm with some power would be nice from time to time, though. Any advice would be much appreciated.



Thanks,

Jon

 

[Bob Beauchaine]

Factory original Cummins should start to defuel somewhere around 2450 rpms. If you want to increase the defuel point you will need to change the governor spring to the 3200 GSK spring. You will find that it will pull hard up to about 3000 to 3250 rpms. As far as mileage goes you can look at my sig for mods and I see 18. 5 city and 22+ at 65mph highway.



Bob

 

[cerberusiam]

First check the high idle stop on the side of the pump and check your linkage throw. You may just not be getting full throttle on it. Back the high idle screw out and adjust the linkage bar so you are just getting into the throttle shaft break over spring and that will get you all you can there.



The gov spring gets weak over time and the pump itself gets weak but you should be able to get it to pull to around 2600 without too much issue and to 3000 by holding WOT without going into the pump.

 

[mysteryman]

2500 rpm ismax by the book. Anything over 2000 rpm is a waste of fuel on a stock motor. 18-22 NMPG IS WHAT THEY ALL GET WITH A STOCK ENGINE AND AN AUTO TRANS.

5 speeds get as high as 27 on the road but most get about 23/24 mpg on the highway.



the mpg figures I mentioned are for stock engines in mild climates on basically flat terrain with trucks empty to lightly loaded. . Extream heat , high mountains , a trailer or heavy loads will bring the mpg way down. .

 

[Tippin Spotted Cow]

Mine would do 2700 before the "366" governor spring. Anything above 2200-2300 was like watching grass grow trying to accelerate. That was with bigger injectors and basically all the "free" pump mods turned to their max. Now with the 366 spring and advanced timing it'll pull hard right up to 3000-3100 and still not too bad to get it up to3200-3300 from there.

 

[MMeier]

Cow, what does the extra RPM's do for boost ? Just installed the 366 spring last night while replacing a leaky throttle shaft seal. Unfortunately, during the LAST step of snapping on the rod ends for the linkage, one of the effers snapped in two on me !!!! #@$%! :{#@$%! It will be probably next Monday before the replacement part(s) arrive !:{ Anyone have any extras laying around ?

 

[JLEONARD]

Mine would pull up to about 2450, then start to defuel

 

[glhs]

Back the high idle screw all the way.

Check the linkage rod from pump lever to pivot point mounted on side of the engine.

I also ground the "stop" of the pivot point where the pedal cable linkage meets the injection pump rod.

This allowed my engine to rev to 3400-3500 rpm before the use of a 366 spring. Even though the pump should/did defuel at 2500 it was much stronger and easier to rev.

After the addition of the 366 spring, it would rev to 4000. Additional timing will will also help it rev higher/easier. I have had mine to about 4200-4300 rpm.



Sixty pound valve springs are needed for regular reving over 3500.

 

[CToney]

My second '93 would not rev properly, it had the fuel supply line bent in such a manner as to not get full throttle. I bent it out of the way and it would then rev to 2500rpm with load and 2700 rpm no load. My '97 would pull hard to 2700 and after the 3kgsk it wouldn't quit. It would be nicer if they would rev higher especially in the city or when towing heavy. Advancing timing moves the power band higher too. With the VE pump finger the narrow way between the AFC and intake is advanced wide way stock.

 

[RSchwarzli]

Whats the diff between the 366 and 3200 spring? Why so many with the 366?



I ask as I am also looking to do this. With the 5 speed now installed with the 3. 07 gears, there is a nice gap between 3-4. Hoping with a spring kit I can rev a bit higher to even that out a bit.



Thanks!

 

[JLEONARD]

Whats the diff between the 366 and 3200 spring? Why so many with the 366?

I believe they are the same. I have one in my hand and it's inkmarked 366.

I think the 366 is a portion of the Bosch part number?

 

[cerberusiam]

Whats the diff between the 366 and 3200 spring? Why so many with the 366?



I ask as I am also looking to do this. With the 5 speed now installed with the 3. 07 gears, there is a nice gap between 3-4. Hoping with a spring kit I can rev a bit higher to even that out a bit.



Thanks!

The 366 spring is the Bosch +3200 rpm governor spring. On is the spring number last 3 digits, the other is the rpm description as noted by Bosch.

 

[RSchwarzli]

Wonderful! Thanks guys!



Edit: Is this a internal or external spring?



Also, why is this spring not installed from factory if it is an actual Bosch spring?

 

[cerberusiam]

The gov spring is under the top of the pump. You have to pop it off to install it.



Because the CPL for the CTD specced 2600 rpm for max governered speed

 

[JLEONARD]

 Is this a internal or external spring?

It's an extension spring with attachment loops on the ends.

And internal to the pump as Cerber said.



There are several springs that Bosch uses in their VE pumps. For example the old VW used a 5200 rpm spring, Volvo uses a 4200 rpm spring in one of their marine 6 cyl diesels, etc.