ok so i am about to purchase a 98 z71 with a 5.7 vortec. it is getting a 4 inch lift and 20's wit 33 inch mud terrains. also the plan is headers, into high flow cats, true dual exhaust with flowmaster 40 series dumped. also taylor made wires, ngk plugs, custom tune, cold air. i'm also looking into rebuilding the transmission with a small stall and want to rebuild on the motor a little bit to help it get better gas mileage so on the rebuild what would you suggest for parts on the rebuild, as in intake, heads, pistons and cam. thanks

 

actually, if the motor is good, no smoking, noises and such, i would swap out the current injectors for the new mfi unit. did this on my tahoe, big difference. cost about $450 an 3 hours. power and mileage improved.

 

where can i find the mfi unit online?

 

http://www.oreillyauto.com/site/c/se...hoe&vi=1303872

part number 63886 is the mfi unit. you will need the bracket that's just above it as well. mine came with it, even tho it says it doesn't. it's cheap, get it anyway, return if not needed. the local store might even have the mfi in stock, you can look to see if bracket is in there then. don't forget a gasket kit too.

 

hey maxx, what is the difference between the mfi unit you put in the link up there and the one that is factory in my truck, 98 vortec 350? why is it more power and better mileage? is it the same part just new so it would work better or is it a more high performance part or somethin?

 

from the factory, the vortec is central port injected, meaning that all 8 injectors are located in the center of the manifold, right next to the fuel lines. what happens is that fuel comes in, gets released thru the injector, then travels down tubes towards the intake. at the end of these tubes at the intake ports, there's a poppet valve. this valve opens when the fuel hits a certain psi, allowing fuel in. as soon as the fuel pressure in the tube drops enough, the poppet valve closes. here's the problem. these poppet valves are prone to failure. gas builds up on them, and they tend to not close all the way. this allows fuel to leak past them when it shouldn't. you can replace these poppet valves, but it's generally a matter of time before they fail again. the mfi unit eliminates the troublesome poppets. what it does, it moves the actual injector from the center, down to each intake port. so essentially you end up with an actual multi port injected motor. so when the fuel comes in, it goes straight down each tube under pressure, then waits for the injector itself to squirt fuel directly into cylinder. no more poppets. this is a problem that gm recognized and started fixing awhile ago. according to MDTAHOE, when rigs come to his shop for this repair, they replace the stock injectors with the new mfi setup. it's way more reliable, better power, better economy.

 

i understand completely. yea, that sounds like a bunch of crap with the factory vortec. from my experience of working as a tech at the ford dealership for 3 years I can say that injectors on their own are prone enough to failure.. much less having some extra mechanical parts after the injectors. lol Well i think it would be cool to replace my setup with that new fuel injection setup. Sounds like a fun saturday project. i always though the factory injector spyder was setup with injectors right behind the valves like most fi systems. interesting. learn somethin new everyday. Thanks maxxman

 

i thought the same thing till my 'hoe started acting up. thought vortecs were still an mfi type. it took me 3 hours or so, minus the hour or so of cleaning everything. easy, well worth it.

 

cool cool.. yea, technically it is a multi port fuel injection system. It is just a dumb design.