Cummins 400 turbo boost and temp question

I just got an M915A1 with a Cummins 400. I want to add boost and pyro gages but don't know what ranges to get. Is the 400 in vacuum at idle and what is the maximum boost that a stock 400 will see. Also, what is the max temp the exhaust should see?

I wouyld get 1 from 1000 to 1600 range most turbo engine run in the 1200 degree when there working hard.

a diesel has no throttle plate to cause vacuum. The air inlet restriction will go up as the rpm and boost are rased due to air filter or piping restrictions between the air filter and the turbo. Cummins NTC 400 factory spec boost would max out at 21. Cummins used to say that any boost over 25 was overboost and caused more power loss to compress the air in cylinders that you gained. ( that is B.S.) so the boost gauge needs to be a 0 to 30 or so stock engine. you should find a 1/4 inch pipe plug fitting in the air crossover pipe between the turbo and the after cooler to screw the gauge line into. the only vacuum is between the air filter and turbo and the would be the air filter restriction gage.

I use this rule on my big cam 3. No more than 3 minutes at 1350 degrees. this is with the probe in the down pipe coming out of the turbo I have a ht4b holset 35 plus pounds of boost

Thanks for the info. Now I know what to buy.

roy jones said:

I use this rule on my big cam 3. No more than 3 minutes at 1350 degrees. this is with the probe in the down pipe coming out of the turbo ...

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that's really hot pre-turbo. wouldn't be surprised if that's 1800°F.

does one typically check EGT's before or after the turbo with a diesel?

I'd assume before, just like a gas engine but wasnt sure.

Obviously this is ideal, i know without some fab work its not always feasible to have the probe right where you want it.

Ideally, before AND after.
Before the turbo really helps you keep from melting down the turbo.
After the turbo is what you should be reading to make sure you are cooling the turbo down properly.

And 1350 AFTER the turbo is WAY too hot!

That motor can take 1350 all day long, the turbo on the other hand wont, i ran a ntc 400 non turbo once it got crazy hot

atvcat33 said:

, i ran a ntc 400 non turbo once it got crazy hot

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?? NTC...New head,4 valve, Turbocharged, Custom rated.

I believe one inch if possible from the head exhaust port. Piston will have problems before turbo. Would be nice to know hottest cylinder and place probe there if possible.

atvcat33 said:

That motor can take 1350 all day long, ...

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not post-turbo temps, it can't...

My 915 makes about 20psi boost, 1050 degrees pre turbo and 165 psi fuel pressure (I am straight piped, my EGT's did run slightly higher with the muffler)

on my 818 i have the biggist turbo availible stock for a ntc 400 or 420 and i can only get 10 psi of boost now those are non cooled pistions and no intercooler and the truck never sees operating temperature, im sticking injecters and a fuel pump in it, then its time to watch the gauges. you can do crazy things to these motors as long as you watch the gauges, and as far as me running that ntc non turbo we took the turbo off that truck and swapped the parts fro mthe 818 to the international truck, just to see how it was different

NTC is New head ,Turbo ,afterCooled 400 350 or what ever is the HP it was built with.

Sounds like alot of inexperience here to me....

Yup, you can throw parts together and things will work just not correctly.

On the M915A1 which cylinder is likely to be the hottest? Anyone got an opinion or should just plan on 6 probes?

I am going to hazard a guess and say the rear most cylinder. I am not basing on experience. I just know that it is warmer back there and the pt pump feeds from the back off the head. Rear cylinder should get a little more fuel.

I seem to recall cylinder 3 and 4 are the hottest. I'm no expert, though.