'90 3+3 12valve conversion

J

JAS3+390

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Oct 19, 2011
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Well so it begins! Going from tbi 454 and a granny 4 speed too..95 12v with new nv4500 and np 205. Now luckily this is the last of the square body chevys so from what I've read it will be a good match. My biggest question is what is the best way to run my fuel from the tank to the pump and is an air dog or fass necessary? And how easy is it making the cummins hook up to the hydroboost system. Any suggestions??

Thanks guys
 
A fass or air dog isnt nessary. Does the truck have duel tanks? And making the hydro boost work will be very simple have a line made up to go from your your pump to the hydroboost then there already should be a high press line to the stearing box then from the outlet of the stearing box it will go to return on the pump and you will have to t in the little low press return line from the hydro boost with the one that returns to the pump from the stearing box. Let's see some pics of the truck I was going to build a chev but lost interest
 
Cool thanks and all its got is the factory gas tanks. I've gotta flush em and I'm going to weld in fittings and put a leveler hose in between so I won't have to flip between the two anymore. And that sounds good on the hydroboost. Ill post pics asap. I've been running off of my phone and its not letting me put the pics up but The first chance I get on a pc ill have some up for sure.
 
Ya you got the rite idea about puting a crossover on the tanks then all you need is a pickup tube on the top of the lower of the two tanks and you will be set.
 
Take a look several vendors make crossmembers and mounts for the front of that chassis. That is a popular swap.. while you have the motor out reinforce the steering box if you havent already..

on your question of the fass the stock piston fuel pump is good to about 450hp.. maybe more if you are worried put a gauge it it.. most of them run 20psi.. to the injection pump..


also look at the mods to run the stock ac compressor, or use the peterbuilt bracket, or autoworld makes a bracket to run the stock gm ac compressor.

btw you will need a np205 off a first gen dodge with a stick.. input shaft is bigger than normal, so is the front bearing.. standard np205 rebuild kits come with the smaller bearing.. and when you make the rear drive shaft run the good spicer joints the cheep ones wont last with 800ft/lbs of torque.. learned that one the hard way...

also I hope you got the dana 80 out of the donar truck as the 14b in the chevy wont like big tires and a cummins for too long.. I run 410 gears and 35" tires and its a good combo if you dont tow alot.. if you tow alot smaller tires or more gear..

good luck PM me if you have any questions.. good luck you will have a great truck when you are done...
 
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just use an OEM mechanical lift pump. it will work perfectly and simplify your fuel system.

make sure your fuel tanks aren't galvanized!
 
All of these guys give great advise. I just completed the exact same conversion in question so I'll help if needed. As for adapting the gm np205 to the nv4500, I converted the dodge nv4500 2wd to a gm 4wd with a new shaft and rear housing. I then bought an "advanced adapters" adapter to bolt the two cases together. So you can use your factory np205. This is assuming your truck is already 4wd.
 
Thanks for all the info guys. As for the ac I won't have to worry about that unless I try to add it later. It didn't come factory on the truck just heat and defrost. I'm sure ill have to get my shafts redone and the spicers are the best way to go I agree. All I do with this truck is pull. I'm running 35s and 4:56 gears so I think it should do alright. I'm shooting for 450hp so well see. Do any of Yall know if there is a company that makes a gauge pillar for these old trucks?
 
No pillar gauge pod made specifically for them. Some have made their own out of fiberglass & others have modified one made for a 1st gen dodge.


Do you mean sled pulling is what you're building it for or pulling trailers for working/farm?
 
Alright ill see what a can come up with on the gauges. And we've only got one sled pull a year locally all my pulling is trailers and equipment....tractors, hay ect
 
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