Engine RPM basics

["Mad Max"]

I have another general question for the masses, and this one is in the differences in 'comfortable' engine rpm's between the generations.



The goal: Solid fuel/power up to 3000 rpm. I want to mod my IP to give me useable power/fuel up to 3000 rpm without pressing the pedal through the floor. How do I do it, what parts, and how do they interrelate?



Case in point - my buddy's '99 2500 4x4 will very happily spin 2600 rpm and like it all day long. It'll cruise at 2400 rpm no sweat, which is good because he has 4. 10's and likes to go highway speed.



Now, with an unmodified 1st gen, 2000 rpm is the 'happy' rpm - don't need a whole lot of pedal to stay at 75 mph (if equipped with 3. 55's), and will do 2400 rpm if you really toe the pedal to the floor. Obviously, it's at it's (unmodified) fuel limit and won't spin any more rpm. The pedal is pretty far down - not much more, so what mods increase the fuel flow across the rpm range?



My question is, what are the basic differences between the two generations as far as why the 2nd gen engines have much more useable rpm than the 1st gens?



And more to the point, what is the series of events/upgrades required to enable the little VE to provide the fuel above 2500 rpm as happily as the 2nd gens, without mashing the go pedal?



What are the pump tweaks to get the fuel - not necessarily power though I know that will be there too - to allow the IP to flow happily above 2500 rpm? And, please explain to me, in simple terms, what the combination of parts does and how they work to enable the rpm increases - in other words, what is the effect of rotating the diaphram with the 3400 rpm spring with the injectors with the pin with the starwheel with the ??? I still have a lot to learn, and I'm still reading the threads, and I have no problem stating that I have a lot more to learn.



I know there's the fuel flow at a particular rpm, which gives good power through 2000 rpm, but what about above 2000 rpm - what is the voodoo required for that? Does the 3400 spring do it all, or does the spring only 'allow' that rpm if combined with additional parts/mods? Which ones and how?



Let's say my goal is 3400 real, useable rpm, with fuel and power across the board without defueling. 3400 rpm wide open, third gear, full throttle, lots of Fords to pass, on ramp... you get the idea . 3400 rpm. How do I do it, and which parts make it so? I don't need big smoke, just plenty of useable rpm and lots of power. Am I talking head/cam upgrades?



My last rig had PODs, HX-35/16, and some pump mods - nothing too extreme. It ran awesome, but still ran out of rpm at ~ 2400 rpm. Great power up to that point, but I want way more rpm. I'm also presuming increased fuel pressure - how? What is the best way to get a reliable increase in fuel pressure? FASS system? Bigger pump?



What have y'all done, and what works, what do I want to avoid? The fuel management is one of the aspects of the business that I need to become smarter on, so this thread is my start.



- M2

 

[dpuckett]

First, make sure you have good supply in terms of fuel volume and pressure.



Second, back that high idle screw all the way out. I have seen Greenleaf throw them in the trash . I could pull hard to 3000-3100rpm in my old 91 with a stock governor spring. Natrually, put a couple zip ties on the accelerator pedal cable under the dash (the actual thin cable part, not the rubber/ plastic coating), to effectively give you more pedal and throttle. Adjust the linkages under the hood as necessary.



Third, put in a 366 governor spring. I had that done to my pump, (along with literally double stock fuel flow), and I run out of nerve (sans tach for the time) before I run out of RPM. 52mph in 3rd gear with half throttle.



This should take you into the area of valve float, or the need for stronger valve springs.



Daniel

 

[sdstriper]

I like everything Daniel said. The 3200 rpm gov spring or "366" spring is under $20 and heavier valve springs are cheap compared to the costs involved if you drop a valve.



You'll want to verify this number I had in my notes, 60lb. valve spring p/n 3916691 . Just under $7. 00 each.

 

[cerberusiam]

My truck will quite happily run 2400 all day long and have plenty of throttle left for some more go. Take it easy on the throttle at low boost and smoke is not an issue. The hearing, well, thats another story.



With a 3400 rpm target valve springs are definitely at the top of list. Next would be a cam and turbo that will enhance and allow the flow at that level. There is quite a bit of throw in the stock throttle setup that can be used to get things rolling also.



The last ingredient, which is the toughest and most expensive, is the pump mods to get there and stay alive for more than a 3 month period. The cheap and easy way is put a door spring in place of the typical gov spring. It simply overides the governor trying to pull the fuel back and drags the rpm's into the higher levels.



The key here being "drags" the rpm's up instead controling it. I don't think we are doing our pumps a big favor by overiding the set defuel points this way. I feel it is introducing a lot of wear and tension on the governor assembly trying to make it go where it is not set up to go.



A much better way would be set the fueling curve, both for delivery thru the range and a defuel point that is where you want it rather than forcing the issue. The pump is quite capable of making the rpm, supplying the fuel to do it, and live a relatively long life if set up this way.



This is where the "expensive" part comes in. Building a pump this way takes some effort and R&D to provide the performance and longevity that is acceptable. A flow bench doesn't hurt either. If your lucky you can find a pump guy that will know how to do this AND be willing to do it.



Cheers.

 

[rlyons]

The last ingredient, which is the toughest and most expensive, is the pump mods to get there and stay alive for more than a 3 month period. The cheap and easy way is put a door spring in place of the typical gov spring. It simply overides the governor trying to pull the fuel back and drags the rpm's into the higher levels.



The key here being "drags" the rpm's up instead controling it. I don't think we are doing our pumps a big favor by overiding the set defuel points this way. I feel it is introducing a lot of wear and tension on the governor assembly trying to make it go where it is not set up to go.

I don't think we are hurting our pumps at all with the 366 spring only when you turn the full load screw all the way and put more pressure on the pump without the proper bigger injectors. I would still never recommend turning up the pump all the way as it was not designed to operate at those pressures. There are a lot of industrial cummins engines just like ours that run at 3,000 RPM day in and day out without any damage so the engine and pump are designed to do it but at a lower fuel pressure and constant load and speed, not racing from one light to the next. So put in the 366 spring, turn the pump up a turn or two, tun in the high speed stop screw and run it all you want. I would highly reccomend the exhaust valve springs if you are going to run 3,000 RPM steady but not necessary at 2400 to 2800 RPM.

 

[1stgen4evr]

Since I have never had a VE apart, I don't know the answer to the question I have. Maybe someone would know. Greenleaf? What if you took some mass from the flyweights so that the rpm would go higher without using a stronger spring?



If you have an automatic transmission, some of the pedal resistance comes from that apparatus.



I can also say for sure that if you are going to take the rpms much higher than stock, the engine would benefit from a carefull balancing by a good speed shop.



James

 

["Mad Max"]

Fantastic advice fellas. My benchmark of 300 0rpm is solely for 'passing gear'. I plan to run a 35" tire (285-70/19. 5) on a 19. 5 rim, and with a 3. 73 gear she'll run right at 2100 rpm cruising 75-80 mph. But, when I want to gun 'er to get around lapped traffic, well, that's when I'll dip the clutch, drop to third, and hammer down, and that's the only time I'll see the 3000 rpm range. And for sure, even though it won't live there, I will install the 60 lb springs on the exhaust side, mainly though for the exhaust brake function.



My own limitation for bombing the engine is actual engine internal mods. If, however, I go with twins later on, I'll have the cam, head, exhaust upgraded, but that's a long way away. In the end I will have a PDR HX-35/16, PODs, and Snow's water/meth kit, and with that I think I can reach 350 hp easily without opening up the engine, and if I can get that I will be completely happy.



- M2

 

[JLEONARD]

I think if you are at 2100 and just mash the go pedal you will have all the power you need without dropping down a gear. I know when I'm at 70/75 mph and 2000/2100 rpm I get instant max boost and plenty of passing power right up to 90 when the fuel drops out.

 

[bgilbert]

You'll be happy with a piston lift pump and a 3200rpm (366) governor spring. Can't beat the mechanical piston lift pump in reliability. The 366 spring will allow you to max fuel to 3000, then start to fall off slowly to 3200-3300. Here is a dyno sheet of when I had the same mods as you are wanting to get. PDR35-16, gov spring, piston pump: https://www.turbodieselregister.com/user_gallery/displayimage.php?&photoid=20157&width=0. As you see, from 1800rpm to 3200rpm I had at least 500ftlb's to the ground, and over 300hp to the ground from 2100rpm to 3200rpm. Even the new trucks aren't doing that at the crank oem.

 

[dpuckett]

Yeah, I'd tend to only drop a gear if you are below about 17-1800rpm. Above that, and I have ALWAYS had great throttle response. My truck pulls hard from a hair above idle to whenever I decide I need another gear. Aint bought that tach hook up kit yet. You aint building no high RPM gasser, here



DP

 

[cerberusiam]

As you see, from 1800rpm to 3200rpm I had at least 500ftlb's to the ground. Even the new trucks aren't doing that at the crank oem.

Ooohhhh, I think there are a few misconceptions in there. :-laf



#ad




And that is bone stock fueling.

 

[cerberusiam]

I would still never recommend turning up the pump all the way as it was not designed to operate at those pressures.

Another whole discussion topic that could take days to explore.



There are other ways than dragging rpm's up there and considerations for such tactics. All depends on how one wants to go about making the power.

 

[glhs]

1. Back out high idle screw all the way.

2. Install the 366 spring.

3. Check for full pedal travel. Adjust where necessary.

4. Done.

If you want to play it safe, I would install 60# springs on ALL the valves.

Set up like this mine will spin to 4000+ and defuels at ????? I've only dynoed it to 3600 rpm and it was still holding.

 

[rlyons]

Another whole discussion topic that could take days to explore.

Yep I know, that's why I only express my opinions and not try to be matter of fact on anything here because these trucks have amazed us all at times by the things that work to bomb. :-laf

 

["Mad Max"]

Alrighty... I appreciate everyone's input for increasing rpm and how the engine responds.



Now, my other question is, what happens to a modified engine, as we're discussing above, in the lower rpm range?

For example, right now my engine hums along really nicely between 1700-1900 rpm - really likes that 'sweet spot'. Even with 3. 55's I am often wishing I had another gear on top of the od - the engine just 'feels' good there. Will that sweet spot shift up on the rpm curve after power mods are done, or, does the power come on as before and simply remain there longer on through the rpm band?



My main question is this - Will 1700-1800 rpm be too low for cruising along at 80 mph, or, would y'all think that'd be juuuust right?



Yeah, I am planning to cruise at 1800 rpm, mainly because I'll have a GV overdrive behind my NV4500/205 combo, and with a 35" tire and 4:10's the rig will hum along at 1800 rpm cruising at 80 mph .



Okay, lemme hear it!

- M2

 

[1stgen4evr]

Will that sweet spot shift up on the rpm curve



I don't know the answer but:



One of the reason I mentioned the BENEFIT of a balance job by a competent shop.



The sweet spot is a combination of tangable and mental inputs. For me, high rpms just don't 'feel' right. But I can't seem to feel the rpms on a nicely balanced engine, so to a point, the tighter it gets, the sweeter it sounds (to me).



James

 

[dpuckett]

In my experience, changing governor settings by one means or another only resulted on fuelling staying on longer before falling off, NOT shifting the power curve to the right. I. E. power came on at 1700RPM, and stayed well beyond 3000.



My current set up (3200rpm spring, backed out high idle, enhanced overall fuelling), lets me pull as long as my foot stays in it. If I only push the pedal 1/4 of the way, it defuels similar to stock- 45mph in 3rd. If I put it to the floor, I have no idea where it would stop- probably when parts came out through the hood and/or fenders. I need a tach... ...



DP

 

[cerberusiam]

Will that sweet spot shift up on the rpm curve after power mods are done, or, does the power come on as before and simply remain there longer on through the rpm band?

Once again, it all depends on the fuel curve set up in the pump AND what you have for air flow with the turbo.



Given you just use a spring to pull past the governed speed and use a turbo that spools well the curve just extends out and flattens a little slower. Add a big turbo that is laggy and you loose the bottom end plus kill a lot skeeters (not a bad thing but it draws unwanted attention) and the top end gets stonger and higher before it falls off.



Fuel is important but ya gotta have the air to burn it, top and bottom of the curve.

 

[Don Tanklage]

how high will a ve pump with stock gov spring let the engine rev to in neutral?



anyone know?



thanks, don

 

[glhs]

If you back the high idle stop out... ... ..... about 3600.