Cummins Big Cam HP Questions

Hello to all.

I have several questions about turning up a Big Cam 400. I have searched the internet and have not found the specific answers that I am looking for.

First, let me say that the truck that I am talking about is a work truck. I am an extremely gentle driver (I will be the only driver of this truck), and I feel that if I up the horsepower I can get better mileage (being light on the pedal, driving by gauges). The engine is going into a Freightliner FLD.

Can anyone answer what is a safe horsepower for a stock engine? The dual line feed is supposed to give about 25 hp. So that's about 425. The truck that the engine is going into has a charge air cooler that will replace the aftercooler (using the intake from a n 14). This combined with a hp air filter system I am guessing will make another 25 hp. Does that sound accurate?

If so, that puts the engine at 450 without yet touching the fuel pump.

Now I have read that some guys say to just screw out the throttle shaft screw. Others say to change the button and not touch the shaft screw, others say to do both, others say to do neither and get new injectors and have the pump recalibrated.

Does the throttle shaft screw and the button do the same thing except the button is the big jump in fuel pressure? Is the shaft screw just for fine tuning?

In raising the fuel pressure, does it raise at idle also, or is it higher only through acceleration?

Is raising the fuel pressure hard on the camshaft? Again, some say yes, some say no. I have read that PP engines run at (full throttle) 450 to 600 pressure. If this is true, how is that not hard on the camshaft?

My common sense tells me that if I turn the engine up, and it makes no noise, doesn't carry on with smoking, starts easily and idles correctly, and I can pull hills loaded without the pyro cooking, then the stock engine and timing can handle this amount of fuel. When it starts smoking and getting hot, that means it is time to back off and turn the pump down. Is this correct?

Also, what do you guys think about the high volume oil pump?

Whatever I do, I do NOT want my truck to blow up or have a greatly reduced service life (meaning that I turn it up and only get one or two years out of my engine). How much hp can a stock crankshaft take without problems?

Sorry for such a long post, and thank you in advance.

You need to contact an older mechanic who knows Cummins. I would answer but the most I know is only about heads and cam follower differences.

Well if you look a few post down you'll read a whole lot about the NTC 855. Although mine is a small cam, the fuel system is exactly the same.

I bought mine with a bad cam. I had to replace it so it ran correctly. Cylinder #3 lobe was so bad the push rod wouldn't stay under the rocker arm. Cylinder #4 was hardly even firing. I think the hype about bad cams is from the problems with the small cam.

As far as making more power in m opinion you'll want to tune the shaft screw and put a different button in the pump. I'm running my throttle shaft acre almost all the way out and a zero button in the pump with a stock charger, which is pre-HT3B. I don't have a pyro but there is zero smoke when I pull, only a little haze.

I'm not sure about the power gains you listed. Although the charge so cooler should improve things. I'd love to get rid if the intercooler on mine and run air to air.

I'm sure other will chime in here. SmokinCAT knows a lot about making power with a Big Cam first hand.

Thanks for the replies. Rockinram, That's amazing that you can run a zero button with no smoke. That engine must really pull!

you are fortunate that it was only a cam that you needed. My engine needed a cam, crank, block, and an inframe kit.

There was no cpl tag on the engine, so when I traced the block numbers, it was originally a 290 that they rebuilt to a 400. Turbo and injectors matched for a 400.

So the shop I deal with traced the piston numbers to figure my kit. I've known the guys at that shop for quite a few years, and they use fp diesel. I know that the genuine kit is recommended but like I said, I know those guys and I trust them. If I don't like the rebuild interval, I will get genuine parts next trip.

I tried to see what cummins would charge for a short block, but they would not quote me a price without a cpl. I finally got a hold of someone else at cummins, and he told me that there are no more big cam short blocks available.

Anyway brother, good luck with your engine and your truck!

Thanks for the replies. Rockinram, That's amazing that you can run a zero button with no smoke. That engine must really pull!

you are fortunate that it was only a cam that you needed. My engine needed a cam, crank, block, and an inframe kit.

Anyway brother, good luck with your engine and your truck!

Honestly I won't be helping on this one, anyone that has bought into the PP mind set is hard to help because some of what works doesn't jive with what they have read from Bruce.

Prime example, thinking that you can gain 50hp on a big cam without touching the pump.

There's no 25hp in that dual feed kit, maybe when your 700hp+. There's no free lunch at the charge air cooler either, going to need to increase fuel one way or the other.

Personally if this truck is your meal ticket I wouldn't bother. Reliability is king. To boot more fuel delivery almost guarantee's less fuel in the tank at the end of the day.

Other than changing turbo efficiency and making it burn cleaner, I don't see how adding fuel can ever add mileage.

Depends on how you drive and use any new found power.

Hey guys, especially smokin cat, I am here to learn. Forget about pp. I just have been reading.

I want to know what you guys that have done this think. If I am misinformed, then please steer me in the right direction.

Again, that is what I am here for.

SmokinCAT said:

Depends on how you drive and use any new found power.

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but you won't make any more power without more fuel, or burning current fuel more efficiently/make more torque lower in the powerband. You can have a 900hp truck, and but you'll still have to use the same fuel to make X amount of power to go X speed.

Well, I guess I just have it all backward. I am only looking for mileage, so maybe it's best to just let it be.

fld said:

Well, I guess I just have it all backward. I am only looking for mileage, so maybe it's best to just let it be.

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I don't know crap about these motors, so I'm not saying something like a better turbo and injector wouldn't help, I'm saying more fuel isn't necessarily the answer.

madmikeismad said:

Other than changing turbo efficiency and making it burn cleaner, I don't see how adding fuel can ever add mileage.

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My my dad works a Freightliner FLD with a Cat 3406C. When he got it, it was a stock 425. He averaged 7 mpg over the quarter. In the last 2 years he had got a bigger Borg Warner charger and played with the fuel screws. He lost mileage down below 6 mpg. Which made 500 hp on the dyno last spring.

Back the middle of the summer he put a new set of 25% over Cat injectors in it and left the pump the same. His fuel mileage jumped back up over 7 mpg.

fld said:

Thanks for the replies. Rockinram, That's amazing that you can run a zero button with no smoke. That engine must really pull!

you are fortunate that it was only a cam that you needed. My engine needed a cam, crank, block, and an inframe kit.

Anyway brother, good luck with your engine and your truck!

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Yeah it runs great now. However, it doesn't and won't keep up with the rest of the trucks in the class. It does well for what it is.

RockinRam96 said:

My my dad works a Freightliner FLD with a Cat 3406C. When he got it, it was a stock 425. He averaged 7 mpg over the quarter. In the last 2 years he had got a bigger Borg Warner charger and played with the fuel screws. He lost mileage down below 6 mpg. Which made 500 hp on the dyno last spring.

Back the middle of the summer he put a new set of 25% over Cat injectors in it and left the pump the same. His fuel mileage jumped back up over 7 mpg.

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Rockinram,

I think this is the best information that I could get, and that is exactly what I was looking for. Thank you.

You give that 400 about 215-220 PSI rail pressure and let the truck do all the work, you will gain MPG.

I assume it has a Holset charger?

SmokinCAT said:

Honestly I won't be helping on this one, anyone that has bought into the PP mind set is hard to help because some of what works doesn't jive with what they have read from Bruce.

Prime example, thinking that you can gain 50hp on a big cam without touching the pump.

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I think that if you actually read my post, I do a lot of saying, "is this correct?"
There is nowhere in there where I say, "hey guys, let me tell you the way that it is, I know all about this". Quite the contrary.

So I absolutely have no understanding of what your problem is. These forums are supposed to be about an exchange of information.

My attempt here was to gain a better fundamental understanding of turning up an engine. What is right, what is wrong, and the theory that this is based upon to make an informed decision. Just because you CAN do something does not mean that you should.

As far as pp, yes, I have read their articles. I have also read everything that I can find on the subject. There is a lot of conflicting information, which I believe that I said in my original post, so I came here seeking answers.

And I have to say to you, Mr smokin cat, I was very much looking forward to your response. I have read your posts on other forums, and I did have a healthy respect for what you have to say.

But after your reply, I feel quite differently. I came here asking, "is this correct?", and your response is to tell me that you are not going to help me because...????.... I am misinformed?... Because... I said something that you don't agree with?... Because... I received information from someone else before I asked you?... Because... you are Bruce's jilted lover??? I don't know, but your attitude problem makes zero sense to me.

These do not seem like reasons to not help someone. Furthermore, I have asked numerous direct questions in my post that could simply have been answered. I can only ascertain that you do not have the knowledge to answer those questions. So my real misinformation was thinking that you were the person to go to for help. Obviously not.

It's no wonder pp is so popular. If everyone asked a jerk like you for advice, I am sure that the masses would flock to Bruce.

Thank you to the guys that gave me good, helpful information.

Snedge said:

You give that 400 about 215-220 PSI rail pressure and let the truck do all the work, you will gain MPG.

I assume it has a Holset charger?

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That sounds like good information. Yes, it is a 3 series holset.

What is this PP your referring to? Pittsburg Power?


FLD, you said you had someone else rebuild your motor, correct? So you're in the same place I was last April when I started on my 855. Completely in the dark. These engines are stupidly simple to work on. Just take your time and change one thing at a time and see how things respond. Then if your happy with the results, change something else you think will make an improvement. You can't expect any of us to tell you to do this or do that and have the results you're looking for.

I think reliability is really something you shouldn't be concerned about. Especially since the motor has just been rebuilt and you're going to be the only one running it. Just don't abuse it and you'll be fine.