Question for Cat gurus

Bullrack

Bullrack

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Sep 24, 2006
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What all needs to be done to a 400B WJAC to make it as strong as a 425B ATAAC? I found a set of Jakes already. I know the 425 has a bedplate that the 400 doesn't have, and I know about the narrower mains on the 400. I found another 359 Pete I want to put in our heavy haul fleet, it has the 400WJAC/15over/3.70 rears. I ran with our '92 379 425ATAAC/15over/3.90 rears last weekend......mine is '13 W900L ISX550/18spd/3.70 rears. Anyway, only a few times did I have to back out of throttle on hills when I was following him. My combo has 8 axles and his is a 6 axle combo, I weigh a good 8K more than him and we had identical machines on. I've forgotten how stout those 425's were! And no, the 425 is a crate reman with the seal on the pump, it hasn't been jacked with. What can I do to this other 400WJAC to make it pull like this?
 
Bring everything performance related back up to par before you start making changes.
Check boost pressure
check lift pump pressure
Check fuel settings
Verify injection timing. The timing tends to slip over time.

After everything is back FLS and FTS can be adjusted and you can mod from there without having to go backwards to fix something.

Reaper of Threads
 
The only difference between the 400 and the 425 is the charge air cooler. The 425 obviously has air to air and the 400 has a jacket cooler. Now there are subtle differences in the injection pumps, but a 400 is basically the same thing as the 425, if they are both 3406Bs. I'm guessing the prefix on the 400 is 7FB and the prefix on the 425 is 4MG.

I want to put a Cat in my Kenworth, and if I do it will be a 7FB.
 
That's why I think it needs checked out/over

Reaper of Threads
 
Haven't got my hands on it yet, but will check it out. I thought the 425 had a bedplate/spacer above the oil pan that the 400 didn't have, could be wrong. I might be thinking of A vs. B. So, what all is involved with changing it over to ATAAC? If this part isn't very simple to do, I'll leave this truck alone.
 
I'm not sure what you means by a bed plate. Do you mean a girdle or block stiffener?

To make it air to air you'll need a charge air cooler, piping from the charger to the cooler, them from the cooler to the intake manifold and you'll need a manifold off of an air to air motor.

Sure that the motor you have isn't a 3406A?
 
Never laid eyes on it yet. That's what throwing me about this truck! I'm gonna wait to get my hands on it before I assume anything. It's an '86 Pete with the original engine, just gone through by Cat, same guy has owned it since new. He should know what he has, but it's possible he doesn't. I do know it's painted white instead of Yellow. He claims it to be a 3406B with WJAC. I keep thinking it could be a A maybe? Peterbilt did some really weird things to trucks in that era! LOL
 
Unless it was transplanted it's not an A, and it being white is a Paccar thing for that era, though I thought it was phased out earlier than that. My 7FB is out of a 88 international and it is air to water.

The stiffening plates didn't come around till the E models came out and even then the mechanicals that were being made didn't get them.

You would also need the block off plates for the front water opening and the one on the block, also factory air to air engines were timed different than the air to water. Factory set on a 7fb ata is 21* were as the atw is 24*.

What makes you think that the air to water won't run like the air to air engine that you ran against.
 
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Will need to cap the water jackets.
Parts nos for caps and gaskets below.

All of the mechanicals I have played with have this spacer plate. Also below.

I would rather see both coolers run. Flip the inlet to the jwac and shove an elbow in it. Plumb your ataac into it.

Reaper of Threads
 

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And if you install the pan without the spacer the pan will crack on the gears.

Reaper of Threads
 
Unless you want to get real crazy there's plenty of room to make power in an wjac, no need for ata.

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My engine does not have a spacer of any sort.

Why would you want to heat the air charge back up after shoving it through an air to air then right back into the water cooler which would take it back to the engine temp.
 
chevota84 said:
Unless you want to get real crazy there's plenty of room to make power in an wjac, no need for ata.

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Click to expand...

My thoughts exactly, the injection pump is still the limiting factor on making HP.
 
At what power level is a 3406 out of fuel??? I saw a pretty strong 3406 make 750 hp on the dyno with a set of injectors and a charger.
 
That's more than injector/turbo/pump mods

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biggy238 said:
Data to prove inlet temps?

Reaper of Threads
Click to expand...

What inlet temps? With the water jacket or air to air?

With a good air to air intake temps should never exceed 150*F at even 50psi. An air to water will not be able to take the intake temps below the engine water temp.

The air to air temps are being pulled from a C15 that runs at around 860hp to the ground. The guy is meticulous about IATs and has the setup to monitor them properly.
 
I asked because I thought you would know.
It wasnt my intention to run jacket water through it any longer.

Reaper of Threads
 
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