Rpm

[NeedMoPower]

I was wondering if some of you guys with tachs can tell me what your max RPM is in your 1st gen. After racing my friend's 97, I noticed I have less RPM than him. I think if i had 200-300 more RPM I could run dead even with him and all of the mods he has done to his truck(tst#11, afc spring kit, big hinking air filter, 370 injectors). What do you think deezul1... . think I could hang?? Since i don't have a tach I'd like to hear what most of the 1st gen guys are pushing compared to the second gens.

thanks,

cody

 

[RDusch]

Stock mine would only do 2500 rpm and stop pulling at about 2300, i have since turned mine up to 2800 and it pulls strong up to 25 or 2600 ... ... ...



Rick D.

 

[AlK]

I recently had Piers set the timing on my truck to 1. 4 and increased the RPM up to 2900. It sure made a lot of difference .

 

[NeedMoPower]

AlK, Does the truck pull all the way to 2900 or does the truck defuel before it hits 2900??

cody

 

[Cummins Cowboy]

i have heard there is a set screw that just has to be adjusted on the outside of the pump to change this. I was wondering if this will change the point at which the pump will defuel. I was just going to ask about this very same topic but cody beat me. I noticed most of the second gen guys are running gov spring kits that make their trucks rev to as much as 4000rpm i do realize the engine looses alot of effieciency above 3000rpm but if i could get my truck to pull hard to about 2900rpm that would really help me on my second to third shift. as the reves go up so fast and it takes a second or so to row the shifter up to third. for you guys with out tachs if you are running stock tires and 3. 54 gears with a 5 speed 70mph=2000 85=2500 and my max at 92mph is about 2750 but truck is really defueling at this point

 

[Lil' Dog]

My 89 will go right up to 2800 in any gear. This was after I had the pump timing adjusted and they set the top RPM.



The 93 currently only goes to about 2600, that will soon be remedied after its first checkup.



The first gens are limited to 2900 tops, the early 89-90's were only supposed to be set for 2800 due to the heavier components.



J-eh

 

[Deezul1]

Hey Cody

If you can get more RPM out of that truck I will need a governor spring kit to stay out front, that 1st gen truck runs real strong. Quit messin with that pump, I cant afford a new clutch that I will need if I have to put in some more HP to beat you.

 

[NeedMoPower]

time for a new clutch!!

Hey John,

Hate to say it, but you might need that new clutch after all. I got bored this evening and started playing with my pump. After adjusting some "stuff" I have more pull in each gear. Not a whole lot, but a little more.

I know our little 1st gens can't flow the fuel like the second gens, but if you play with the pump long enough you can give most of them a run for their money! I would love to get my truck on a dyno some day or find out how much hp deezul1 is making with his mods.

 

[AlK]

NeedMoPower, my truck pulls right up to 2900 RPM in every gear, prior to the change the max RPM was about 2450. I just did a little road test - Max speed: 2nd gear is 46 KM, 3rd gear is 80 KM, 4th gear is 120 KM, 5th gear I was up to 145 KM but ran out of road but she was still moving up very fast - I think 160 KM is possible. If I step hard on the pedal the truck feels like it has a different gear box .

---

Al

 

[NeedMoPower]

Can someone convert those numbers over to MPH?

 

[EOliver]

Mine pulls hard up to about 2500-2600 rpm. Max rpm is right at 2900 (no load). On the flats my truck tops out at 95 mph @ 2800 rpm. I tweaked the power screw on the pump a little the other day and noticed quite a difference off the line. (+ lots more smoke )



Eric O.

 

[AlK]

NeedMoPower

1 Kilometer = approximately . 625 Miles



46 Km = 29 miles

80 Km = 50 miles

120 Km = 75 miles

 

[Dieselman359]

Hmmmmm, got me thinkin'

So how does one go about doing this? Is it the timing change or is there a certain adjustment that raises the RPM. I'm not too sure but I believe that mine only runs up to about 2500rpm or so. The extra few rpm would be helpful between that 2-3, 3-4 shifts. Maybe one of these days I'll get the timing adjusted. So did we ever figure out what optimum timing is? 1. 4, 1. 7 ???

 

[BushWakr - RIP]

Alk was pretty well right on. .



46 KMH = 28. 58 MPH

80 = 49. 71

120 = 74. 56

145 = 90. 10

152 = 94. 45

So far I've hit 152 KMH and chickened out,,, it was still pulling at 22psi and 580*F ( + 10*F per 1 lb. boost =800*F) and 2500 RPM in OD



Regards, Bob

 

[CRWilliams]

I talked to a guy the other day and he said that all you needed to do to raise the top RPM was back off the max throttle screw. It is opposite the idle adjustment screw. I was wondering about that but didn't think it could possibly be that easy. I am going to try it today, I'll let you know how it goes.

 

[Piers]

That's correct, just take off the tin cover off, loosen the two 10mm jam nuts & back the high idle screw out a couple turns. Make sure the throttle linkage is adjusted to obtain full throttle.

 

[Phil May]

If the timing is not set correctly no amount of fuel will make the thing rev up. My trucks pull hard up to 2900 with near stock setups. I think some of this crap is bull. My trucks eat powerpukes without spending mega $ on them. As far as timing a good rule is if your engine dont rattle at idle the timing is not advanced enough. when the timing is correct the engine is quiet while it under load. If the timing is retarded its loud under load because the under utilized fuel burns in the exhaust instead of the cylender where its supposed to burn.

 

[CRWilliams]

Boy, that was easy . I picked up about 150 rpm just backing out the screw a turn and a half. The boost begins to drop off just about 2600 now and it will rev to 2650 or so. I am going to try and adjust the throttle linkage later this week but first I'm going to try and set the pump timing. I was thinking about 1. 5 MM, anyone have any thoughts? I heard someone say 1. 7MM? I really don't want to go too far and hurt something.

 

[BushWakr - RIP]

Pump timing can be a bit tricky, I'd really like to know a

blow by blow on tools, and every step you do to see how it turns out. Piers said (I THINK!) the first Gens do well at around 1. 40mm (no idea what that is in degrees)

Mine is set about 1. 37mm and did make an improvement in idle, less smoke, some power improvement as well. If you use the timing pin on the engine it can apparently vary quite a bit meaning your only going to "come close" with your pump setting

Keep us posted on your results.



Bush'

 

[CRWilliams]

I spent a couple of hours reading a Cummins manual that I borrowed from a friend over the weekend. I have the dial indicator and am pretty good at making things work for my intended purpose. I am a little worried about not having the special wrench to reach the back bolt but I'll look and see if I have something that will work. If not I guess I'll be seeing the Snap-on man tomorrow. The Cummins book I was reading said that checking the tdc pin was easy. It kind of scares me but the manual says to crank the no. 1 exhaust valve down several turns, this actually acts as the stop pin for the piston. Then just use a pointer on the damper and make your two marks, of course half-way between is true tdc. I am going to try this and double-check the tdc pin before I start. It does say, in bold letters as I recall, to make sure you reset the valve lash before turning the engine over or starting it. I'll let you all know what tools I needed and how things went.