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Author Topic:   Repowering old truck
Dirt Forum Racer

Total posts: 95
posted January 06, 2004 09:41 AM  
Anybody ever re-power an older truck?
I have an '84 Chevy 3500 crew cab with 103k actual miles. The body is in good shape. (Great shape actually for an '84) However I am frustrated with the carbureted 7.4 engine. It is extremely cold blooded, you have to warm it up for 10 minutes or so or it wants to die. The milage is awful and it really isn't that responsive out on the road. I'm wondering how big of a mess it would be to get a modern 6.0 or 7.4 vortec injected engine from a salvage yard and swap out. How deep do you have to go? Do you have to also replace the transmission? What about fuel tanks, that could get messy as mine has the infamous gm "saddle" tanks and I believe the newer ones are designed to be mounted inside the frame. I'm just thinking if I could pull this off for even $5,000, I'd be ahead of paying $10,000+ to get a 100,000 mile + truck. Also, I should be able to get a few hundered out of my 7.4L for someone who was looking to a relatively cheap replacement for an older truck.
Any thoughts good or bad are welcome.

Dirt Full Roller

Total posts: 71
posted January 06, 2004 10:39 PM  
We recently converted a 6.5 Turbo diesel over to a 454 TBI. We had a wrecked '93 K25 that donated the 454 and the recipiant was also a '93 K25. The 454 engine mounts matched OK. Oil coolers were a little different, but almost all of the mechanical stuff interchanged pretty easily. The electronics turned into quite a job, even going '93 to '93. We had to use almost all of the wiring harness from the 454 Donor to get things to work. Computor had to be changed, Fuel tank had to be changed due to in tank fuel pump, fuel lines had to be changed, finally got everything to work except the tach. A lot of the wiring under the dash had to be changed. It's quite an undertaking. You will for sure have to have all the wiring and computor hookups. Probably fuel tank and pump. After doing this changeover, I don't think I'd want to tackle trying to convert the older truck to the GM fuel injected setup. It would probably be a lot easier to experiment with some different carburetion etc with your existing engine. It might be possible that there is an aftermarket wiring setup that would simplify the changeover to FI.

Dirt Freak

Total posts: 306
posted January 06, 2004 10:41 PM  
we were thinkin about this on a 46 chev pick-up and found out the best way to do this would to have a complete donner truck (crash victom) rite there next to it install engine trans combo then start with the computer stuff ie.wiring,sensers,cats,and anything else ya can think of lol so we dicthed the vortec infaver of a 283/pg combo

Dirt Forum Racer

Total posts: 95
posted January 06, 2004 11:04 PM  
That's what I was afraid I was going to hear. I have also looked into the Holley Pro-jection systems, but they seem pricy and I'm not sure if you improve things a lot or not. It's too bad someone like Holley, Moroso, etc., doesn't come up with a simplified swap kit. i.e. wiring, electronics, etc. needed to control the engine. That would basically be like what you get with the Pro-jection system to control that.

Dirt Freak

Total posts: 354
posted January 07, 2004 12:08 PM  
Check the Summit or Jegs catalog for a universal Chevy EFI swap wiring harness from companies like Painless Wiring. They make wiring harnesses for passenger car EFI swaps. They may also make later model truck harnesses. It might be worth a call to someone like Painless. (817)244-6898

Dirt Maniac

Total posts: 195
posted January 08, 2004 10:57 PM  
Gm performance parts catalog-502 cu in.
Gm actually sells a kit for your exct problem. Pricy though! The gas tanks can be had thru the aftermarket companies for about $120-$140 each.

Dirt Newbie

Total posts: 4
posted January 27, 2004 08:51 PM  
Assuming your motor is in good mechanical condition, only 103K, I would say go with the multiport kit (edelbrock i beleive) from summit (or whoever). this comes with a new intake manifold pre-assembled with injectors, fuel rails, throttle body, etc. and the sensors, wiring, and computer. There's a seperat, but specific, high pressure pump that you have to get also but I think thats cause of the single or dual tank trucks. If you get along with computers ( not a guy who yanks injection to replace it with a carb) I think this would solve your driveability and milage problems.

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