Engine/Transmission (1994 - 1998) how to fix the flat spot?

[SEmerson]

my 97 starts to flatten out at 2500 and at 2900 to stops. What do I have to change to get it to flaten at 3500 or later and stop at 4000?

 

[Reddog1]

Assuming your signature on the '97 is complete, I am impressed that you are making 2900 RPM. Mine stopped closer to 2500 RPM.



Have you considered a Governor Spring Kit (GSK)? It is my understanding the 4K GSK with exhaust valve springs would do what you are asking. There are those that would argue that the 3K GSK would be sufficient.





Wayne

 

[SEmerson]

I was thinking of setting the transmission to shift at 3500. So I figure if I can go to 4k the I will get no tapper in power at my shift point. Where is a good place to get a gsk and ex v springs?



And yes sig is right



Bombs awayOo. Oo. Oo.

 

[Cooker]

Yep a GSK is what you need. Call Piers and he will get you taken care of. www.piersdiesel.com

 

[Strick-9]

What are you trying to accomplish by setting the shift points at 3500, if you don't mind me asking?



Getting a governor spring kit will allow you to fuel to a higher rpm, but the power will still fall off at that rpm. The airflow in the engine is poor at that rpm because the engine wasn't designed to turn that fast. A camshaft change, different turbo(s), and a ported head help, but the engine will never put more power down at 3500 rpm than it does at 2600.



-Chris

 

[JohnE]

Piers Diesel Research (PDR) is a great place for many Cummins parts including governor spring kits (GSK).



You will need both intake and exhaust valve springs to sustain rpms in the 3k range.



Your hp peak will also depend on your injection timing.



My trany shifts around 2,800 rpm which is good for me, i see no reason to go furher.



diesel on

-John

 

[SEmerson]

I guesse I am trying to match my 24 v power band. That is where I got those figures. Still new to the 12 v world but this thing is such a dog compared to my 24.

 

[Deezul1]

I have the 4k GS in mine and so far have not seen the need to upgrade the valve springs. I have turned it to 3500 but not often. If the valve springs are letting the valves float I cant feel it and I sure could feel it on gassers.

 

[Jim Fulmer]

Chris is right about the RPM band, I can manually shift mine at say 3400-3500 but it's falling on it face there, right now it shifts at 2800 ish and pulls like heck and never stops, there is a difference in the 3k's and 4k's on my truck. I did two runs back to back on my 2 lane test road one with 3K's one with 4K's and you can visually see the smoke difference at the gear change as well as a change in the seat of the pants. Think of it like this, what would you change on your gasser if you wanted it to work better at 6-7K RPM's cause a stock head, cam, and air won't do it.



Jim

 

[JohnE]

SEmerson;

I'll ask JJW-ND to reply on this thread. We put GSK in his 96 and he drives (heavy towing) 24 valves at work. He's very happy with the performance of his 96.



Jim;

You noticed <em>that</em> much difference in the fueling by adding the 4k spring?

What is your timing at?



Everyone;

What rpm do you get your peak hp after installing governor springs?.



For me, with just the governor springs (stock plate, no injectors) my peak hp was around 2,800 rpm with 12&deg; timing. The timing was reset to 20&deg; and peak hp is 3,100 rpm. I added the #4 plate and haven't been back to the dyno, but the power still peaks about the same 3,100 rpm per my but-o-meter.

I'm going to drop timing to 16&degrees; for the better driveability. I'll be heading back to the dyno later this fall and remap things.



-John

 

[Reddog1]

I haven't any experience with timing our cummins. From what I have read, I am begaining to think 15. 6 to 16 degrees should be one of the first mods we make. Someone care to elaborate?



SEmerson - Do not underestimate that "Dog". With a little tuning, you may find you have a "Junk Yard Dog". I am very ignorant to the 24V, but know enough to use care in direct comparrisons.



JohnE - Was it a typo, or do you really reccommend upgrading the valve springs for the 3K GSK? It was my understanding that the springs were needed for the 4K GSK.



Deezul 1 - I don't know from experience, but it is my onderstanding the cummins cannot float the valves, unless they are hitting the pistons. If my understanding is correct, please don't float your valves in the presence of Phords.



Floating valves - piston damage, someone with experience please educate us.







Wayne

 

[Deezul1]

Reddog1

Anytime the valves start to float there will be a power loss when the valves are no longer closing completly and that will be the first sign of float. This will happen before valve/piston contact so by being aware of when this occurs will set the RPM that you stay away from.

 

[JJW_ND]

Not sure what to say!

On a stock truck, especially 12Vs the GSK kits really help when pulling. I shift my work truck (2001 HO 6sp) when pulling hard at or over 3000 every shift. This gets you up to where it doesn't have to work so hard in the next gear and lower RPMs. I also downshift in the big hills (MT, WY) at 2200. The higher RPMS would really help downshift and Ebraking at higher RPMs.



The other thing that greatly enhances pulling is MORE POWER! Since running with the #11 plate I honestly don't need to run over 2500 rpms. Maybe 2800 between 3nd and 4th if grossing over 20K. It is nice to have the extra RPMs if needed. But not a necessity with the extra power.



On the down side with the fuel turned up, the higher RPMs really bring out any minor EGT problems on 12V.



JJW

ND