NTC 400

[Rod78]

So I just rebuilt this engine from the block up. It is a cpl 531. I set the static timing at -.069". It has an oversized turbo on it though. (Ht60).
I get 32 psi turbo boost at full load (110,000lbs). And I get 175psi fuel pressure. The truck originally had an ntc475 in it. I have a 15 speed overdrive with 3.55 diffs.
I have great power in the bottom 13 gears, but once I hit 14th gear I start running out of power at 1700rpm (45mph). It takes a couple miles of flat ground to get up to 55 or 60.

So my question is....is this all this engine should have for power or do I possibly have low power? Searching the internet says to maybe set the pump for a 625cpl engine. I can't really find anything on the 531 cpl. Maybe I'm expecting too much...
I am still waiting for my new pyrometer gauge to show up. Will take for a test drive to see what temps as soon as I get it installed.

Any input would be great thanks.

Rod

 

[RZucker]

So I just rebuilt this engine from the block up. It is a cpl 531. I set the static timing at -.069". It has an oversized turbo on it though. (Ht60).
I get 32 psi turbo boost at full load (110,000lbs). And I get 175psi fuel pressure. The truck originally had an ntc475 in it. I have a 15 speed overdrive with 3.55 diffs.
I have great power in the bottom 13 gears, but once I hit 14th gear I start running out of power at 1700rpm (45mph). It takes a couple miles of flat ground to get up to 55 or 60.

So my question is....is this all this engine should have for power or do I possibly have low power? Searching the internet says to maybe set the pump for a 625cpl engine. I can't really find anything on the 531 cpl. Maybe I'm expecting too much...
I am still waiting for my new pyrometer gauge to show up. Will take for a test drive to see what temps as soon as I get it installed.

Any input would be great thanks.

Rod

I'm thinking you need to get the fuel pressure up around 205-210 PSI. that should wake up the boost to about 40PSI, But you are really going to want to watch the EGT's. Don't monkey with the throttle shaft screw, you're going to need to drop a few button sizes.

 

[Truck Shop]

Well sort of-First off a RTO 15spd has a wide split in top hole and with 3.55 rears-she's pretty long legged. A better rear ratio with the 15 would be 3.90 rears pulling that kind of weight.
The 531 is a good CPL and the 625 is also. But here is where you can get some power, Do you still have the NTC 475? The 475 has a pump with a 1" gear and bigger orifice injectors.
Installed in a 400 with 14.1 compression it will give you basically an increase of hp to 444. Plus it will not have to high of rail pressure so the cam will live. The 400's used a pump with a
3/4" gear for reference. But you need the bigger injectors to keep the rail pressure around 200. The 475 pump and injectors should work well with the HT60 turbo

Removing the white plastic ball on the end of the throttle shaft and turning the rail screw for more fuel will increase fuel but it will also make for a sluggish throttle response. One thing that
is often over looked is having a pump shop double the setting on the anroid, it creates a little more smoke at the stack on shifts because it's not cutting the fuel back because of turbo lag.

 

[Rod78]

Yes I still have the 475. It's in pieces on 4 pallets in the corner of the shop. The fuel pump was just rebuilt before it dropped a valve. It's a future project to rebuild but other projects seem to be more important.

 

[Rod78]

Will the 475 injectors work with the 400 cam? The 475 injectors are fresh rebuilds sitting in a box in the corner of the shop as well. I thought the injectors were a longer stroke...

 

[Truck Shop]

I don't remember if the 475 injectors had a longer stroke but you can check with a pump shop to find out. I use Wentland Diesel in Milton Freewater, Ore. Funny I was just talking to
Loren Wentland today about 475 fuel parts in a 400. But I do know it was common to use the 475 pump with 400 injectors, I believe the pump is flowed to have a slightly lower rail
pressure.

 

[Rod78]

Well maybe once I get the new pyro installed it would be worth changing out the pumps then. Any idea what kind of fuel pressure I would see with stock injectors? The ht60 sure spools up at low rpm right now so I'm sure the engine would still burn clean with the larger pump.

 

[Rod78]

My diesel shop here in Canada says he can easily reflow the injectors and turn up the pump with a higher torque curve if I want.
I'm a bit confused on fuel pressure though. My 335 small cam is set at 167psi fuel pressure and the diesel shop says this 400 big cam stock fuel pressure is 158psi. Seems low to me. But he also tells me there is multiple fuel pump codes for the 531 cpl.
Building the engine feels like the easy part at the moment. Ha

 

[Truck Shop]

Cummins and there CPL codes for pump settings are all over the board. 158 is pretty standard for big cam fuel pressure, a few ran as high as 175 depending on other calibrations within the pump
and injectors. The key part is having the injectors flowed to match the pump to keep the pressure on the lower side. Years ago I built a BCIII for my own truck and I used a KT450 pump with
a 1" gear and the injectors were flowed using NTA420 injectors IIRC.

 

[DoyleX]

I've never monkeyed with a 475 but aren't they mvt. If the travel is the same they would be flowed for some good power. Your gonna want 230cc or so and at least 200psi of rail pressure. Id throw the pump and injectors from the 475 in and see what she dose.

Years back I built a mechanical N14 that was supposed to lift the left front. Started at 230cc and 250 on the rail, no fun. Went to 255cc and it pulled wheelies!

 

[Truck Shop]

Yes Doyle the 475 is variable time and twin turbo and those fuel parts will make 400 scoot. But one thing to consider for every 10% of over fuel for on pressure the load on the cam goes up 10%.
So 200 psi is a good area to stay focused on .

 

[Rod78]

When my 475 dropped the valve I was in a panic and bought this ntc 400 cpl531. The pump on the 400 was bad so i put the 475 pump on the 400. My pyro worked and egts were ok. I never had a boost or fuel pressure gauge installed then though. Within 5000 miles the piston sleeve bottom orings gave way and all my coolant dropped. The cam then welding to its bearings and spun in the block. So I found another block and rebuilt the 400 and the 400 fuel pump.
This probably didnt have anything to do with the 475 pump on the 400 engine but it sure makes me cautious.
So 200psi rail pressure should be max for decent engine life then??
Thanks for all the input. Keep it coming

 

[Truck Shop]

Years ago I had a friend that ran a 5 button in the pump on his BCII, stock button was a #42-a #40 is 5% over. Cams lasted about 1 1/2 years max. The fuel pressure ran around 280.
At 200 range you will be alright, but like most things it all depends on the right foot.

 

[Rod78]

So i found out the 475 has a high lift cam with injectors that have a .266" stroke compared to the 400 with a regular cam with injector lift of .224". I don't want to do anything too crazy with this engine. I'm proud that I built it from the ground up and know how much time it took. I'll see how it performs hauling grain over the mountain next week before I touch the fuel any. I'm thinking the smartest thing to do if I did anything would be to reflow injectors 10-20% over to keep the fuel pressure well below 200... thoughts???

 

[Truck Shop]

Correct.

 

[56wrench]

when I first got my super B grain trailers, I pulled them with a 400 big cam in a 79 w/star-38rears, 15 direct and 4.88? gears. grossed out at 63500kg(139700lbs). surprisingly, it didn't do too bad. I think some of your problem is the 3.55 gears. in my opinion, 4.10 gears(24.5 rubber) would be a better ratio for a 15 over. those old engines didn't like to lug as much as the newer ones. mine had a sweet spot at 1900 when at full load.

 

[Rod78]

You're absolutely right 56wrench. My gearing sure doesnt help. The original 475 twin turbo handled the load fine but with 75 less hp and 200lbft less torque now it sure shows itself. I dont need to break any speed records but I sure dont like driving with my foot mashed to the floor all the time either.

 

[Truck Shop]

The wide splits in the 15 doesn't help, truthfully I think a 13 would be a better gear box, but I like those 15's too.

 

[Rod78]

Yes, but unfortunately the 15 speed is still in really good shape. So I'm pretty sure it's not going to get changed out anytime soon. I do agree though. A 13 would be better

 

[Rod78]

This engine is in the 1981 western star that I have as my avatar.