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Junior Member
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20 Posts
Discussion Starter #1
I have a 4mg77190 in a 379 Pete. The previous owner swapped it in there it's not the original engine which was supposed to be a 400hp. It was very underpowerd to pull 80k loads so I put a pump off of a 425 on it a few years back and also a turbo off a 400. It went from turning 1700 rpm no load to 2100 rpm no load. Also went from 17 lbs of boosts to 26. The truck ran great, no overheating and has never used any oil and only black smoked when going thru the gears until the boost got up enough to burn the fuel. Fuel mileage has allways been poor when loaded and even after changing the pump and turbo it still never performed loaded as well as the 425s I have driven. It burned a piston last week so I'm going to inframe it. What kit should I order to get the best pistons and also thinking of changing the injectors because I'm sure what's in there are pretty small it being a 310hp. Also should the timing be altered as well. Not looking for a hot rod but would like to go back with the right parts to get at least 425 hp out of her and 5mpg. Can anyone tell me the right pistons to use as well as what I need to do as far as injectors and timing? Thanks in advance. It's hard to find anyone around my area that knows b model cats.
 

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Junior Member
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20 Posts
Discussion Starter #2
I have done some reasearch and was thinking of going with 3421 injectors and 9y4004 pistons. Will they work with my current cam and pump and advance? What will the timing need to be set at?
 

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Junior Member
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168 Posts
3421's should be used with 14.5:1 compression pistons and a minimum of a 18° cam but preferable a 21° 7FB 425 pump cam or the best option being the 24° 7FB 400 cam. Someone got your timing too far advanced when your pump was changed if infact you have holes burnt in pistons
 

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Junior Member
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20 Posts
Discussion Starter #5
SO I NEED TO CHANGE THE CAM IN THE INJECTOR PUMP? OR THE ENGINE CAMSHAFT? OR BOTH? DO YOU HAVE PART NUMBERS? CAN I USE THE SAME ADVANCE?
 

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Junior Member
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168 Posts
Just the pump cam is different and id have to look it up to get ya the # and yes your advance is the same but just so ya know a pump cam is ,ike $2000-2200 and special tools are needed and at the very minimum a complete reseal kit for the pump and governor and lap the barrel and plungers to the bonnets. The whole pump us a very complicated, tedious project if your not familliar with them and dont have a service manual for the pump. It would be cheaper and easier for you to go to a salvage yard and get a pump from a 7FB 400 WJAC with a 24° cam or One from a 7FB 425 ATAAC With a 20 or 21°. The 24° is the best one but both are for 14.5:1 compression and 3421's and will deliver more fuel than if u used your 18° cam with the 3421's.
 
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