(1) I would like to rebuild the turbo, or have it rebuilt. I thought about buying a new cartridge and swapping it with the old one. Any advice on a cost effective rebuild or rebuild service would be appreciated.
DDM and RPM Motorsports both offer rebuild services. I believe both also offer the option of increasing the size of the compressor wheel...a so called "big wheel" option. It's $500-700 last time I looked. The turbo is a Borg Warner K04 and is fairly common so you may find a shop local...if you trust them...to rebuild it. Since time isn't critical though I'd send it off to one of our vendors. I have a RPM Motorsports Big Wheel K04 they rebuilt for me...love it and no issues. (Just check your water plugs to make sure they were tightened when it was rebuilt.)
(2) Charge pipes. Is it worth it to buy these pre-made? (RPM for example, $450). Or could I achieve a quality result using a diy intercooler tube kits? Is there an optimal place to put the maf? It seems most of the mafs are right before the throttle body.
For charge pipes and intake, only the stock Redline "hot side" charge pipe (this is the pipe on the turbo going to the IC) is the same between both builds. For the intake and the "cold side" charge pipe you need something else other than the Redline charge pipes. On the intake, the differences are the MAF port and the PVC port that runs to the head. On the LE5, you don't need either and so if you USE a stock redline intake, you're going to have to block both those off.
On the "cold side" charge pipe, unless you're good at welding metal tubing, buy a charge pipe. I want to say DDM is aluminum and RPM uses steel but either will work. Just be sure your pipe on the cold side is between 2.75" and 3". Any smaller or larger and your stock LE5 MAF (which will go in this pipe...so you will need a GM MAF bung of the proper tube diameter if you're going to weld this yourself) tables will be WAY off. Martin's tuner HIGHLY suggests not to use anything smaller than a 2.75" pipe here since it will make it easier for you to run off your MAF table.
(3) turbo cat/downpipe. I do not need or want a cat, but would run a gutted cat for the time being. What is the most cost effective way to connect the turbo bits to the stock exhaust?
Most cost effective is to find someone with a Redline who has upgraded their stock cat and buy it from them then gut it. It's this or have a muffler shop get the flanges and weld something up but really, probably cost more than buying a stock cat from someone.
(4) Stock redline oil lines. I am planning to drill/tap the oil pan (I think that's the stock RL drain to location) so that I can just use the factory drain line. Any reason this is a stupid idea?
Not a stupid idea and really, I kind of wish I had done it. The ONLY drawback to this is that you must be VERY careful when you do it. RPM Motorsports does it this way and after they drill a very small pilot hole, they open it up with a larger drill bit PACKED with grease...not coated...PACKED...and they go VERY SLOWLY. What this does it the aluminum shavings that are coming off your block are caught by the grease in the drill bit. I believe they clean this and repack the bit as necessary as they go. This keeps the shavings out of your oil pan and THAT is the danger here. If you get shavings in there and they go through the oil system, you can have an oil passage blocked, have reduced oiling to part of the engine and have a catastrophic engine failure.
Also, you cannot take the oil pan off the engine while the engine is in the car. You have to remove the engine to remove the oil pan. So unless you're wanting to pull the engine, RPM's method or the DDM kit that sends the oil return line to the front of the engine and into the water pump timing cover are your oil return options.
(5) Bolts/fasteners. I do not want to pay the premium price for factory bolts. Any reason that I couldn't just use hardware store fasteners for the brackets? Any special fasteners for the plastic parts?
Not really anything special but really, there are very few nuts and bolts you HAVE to add. The ones on the intercooler brackets to the bumper are nothing special so as long as thread pitch and length are the same you're good. I WOULD, however, STRONGLY suggest to use OEM speed nuts where they are called for. Makes like SO much easier than trying to use regular nuts.
The downpipe to exhaust bolts/studs may break when you remove them because...well...they do that. You can replace them with standard bolts of the same thread pitch as stock IF you're using an OEM cat for your downpipe. If you go aftermarket, you will need bolts AND nuts but they will provide that with the aftermarket cat. The nuts that hold the downpipe to the turbo...THOSE I'd only buy as OEM.
(6) Intercooler. What is the most cost effective one to use?
If you can pick up a OEM intercooler used that is in good condition, this is going to be your cheapest option. The eBay ones will require a lot more work to route the charge pipes properly in our cars. the OEM and aftermarket intercoolers for our cars are made to route these charge pipes properly. I think you can pick up the used OEM intercoolers for not much more than you'd pay for the eBay ones and come out ahead money wise since you don't have to build the pipes.
(7) fuel system. I am planning on getting some 42 or 60 lb injectors. Still haven't decided which. Any need to change the stock pump, lines, etc?
You're fuel system isn't about going turbo but rather how big will you go in the future. For 7 psi on the LE5 with a K04 turbo you're going to be around 200-220 whp (guessing here as never dynoed when I was at that level) and the 42lb injectors will work fine. If you want to be around 10-12 psi and about 250 whp I would go 60 lb injectors.
FOR ME, my original target was much higher than that. I currently am at about 265 whp on 15 psi and without changing the head gasket, I wouldn't go any more than that. With that, I have 60lb injectors with the RPM in tank fuel pump (greater flow) feeding a modified DDM fuel rail that has been converted to make my fuel system a boost reference return style fuel system incorporating a fuel regulator on the rail that will raise and lower fuel pressure based on intake manifold pressure.
What does that mean and why did I do it? Simple, injectors are rated by how much fuel they flow for a given fuel pressure. HOWEVER, this fuel pressure number ISN'T the fuel pressure of the fuel in the rail but rather the pressure difference between the pressure of the fuel in the rail and the pressure of the chamber they're spraying into. SO, if you have a fuel pressure in the rail of 40psi, and a pressure in the manifold of 0 psi (no boost, no vacuum) then a 60lb injector flows at 60lbs of fuel per minute.
HOWEVER, your intake manifold when you're boosted is not at 0 psi very often. It's either below that (when you're off boost) or above that (when you make boost). So if you're at WOT and say at 10 psi, the pressure that the injectors are now flowing at isn't 40 psi. It's the 40 psi of fuel pressure minus the 10 psi of pressure in the manifold (your boost) and thus your injectors are flowing LESS than 60 lbs/min and thus must be spraying longer to get the same amount of fuel into the manifold.
With a boost reference return system like I have, the fuel regulator also sees what pressure the intake manifold is at and increases or decreases pressure accordingly. Thus, when my system sees 10 psi of boost, the regulator adds 10 psi more pressure to the fuel system. Thus my 60 lbs injectors would flow at 60 lbs/min regardless of how much boost I run because at 10 psi of manifold pressure my fuel pressure is now 50 psi rather than 40 psi and thus the pressure difference remains at 40 psi. (not my real numbers, btw...just for example).
Right now I run about 50 psi of pressure at 0 psi manifold pressure. The other thing this helps with is idle. The bigger injectors are a bit tougher to dial in at idle with the stock system because at idle, you're manifold is under vacuum. This means that 40 psi of pressure difference we talked about before could be 55-65 psi now. With greater pressure, the injectors flow MORE fuel than 60 lb/min and thus it's a bit tougher for the ECM to adjust fueling with the larger injectors. With my system, the fuel pressure at idle is LESS than my 50 psi and thus the ECM doesn't work as hard to maintain a smooth idle.
At my settings, at WOT the injectors are still "on" 70% of the time. When an injector is running at 90% of the time we say they are "maxed" and the user should be using a larger injector. My injectors and system will probably support close to 315 whp which was more inline with my original goal of 400 whp in stages. What I have now is about the furthest you can go on the LE5 with the K04 turbo. She just runs out of breath too soon. I make my max power at only 4600 RPMs.
Believe me, if you've read my build thread then you know I built my system for dirt cheap to start with. Some things you've left off...
A boost controller. Without one you're stuck at 5-6 psi max which is what the factory wastegate spring on the K04 will allow. Mechanical will get you higher but boost WILL drop off with RPM with the K04. I fought this for a LONG time and only with going with an eBoost2 Electronic Boost Controller (about $500 retail but I got mine used because I ball on a budget...homie...LOL) which will compensate for this did I finally fix it (didn't up my WHP max though because of the aforementioned breathing issue with the K04).
Tuning. You HAVE to tune this thing to make it work. This will probably be one of the larger expenses of the whole build. Again, I got lucky here and had friends with HPTuners and knew a bit how to get it in the ball park. This is going to be a $400+ expense depending on which route you go. HOWEVER, make SURE if you buy a tune from somewhere that you buy one where they scan and tune your car rather than a "canned" tune they just put on and say good enough. These LE5 turbo builds are quirky from what I've seen and you want a tune for YOUR setup in YOUR conditions using gas local to you.
Finally but most importantly, a Wide Band O2. We LE5 guys aren't blessed with a Wide Band (WB) O2 from the factory like those LNF (Redline/GXP) guys...jerks (LOL)...so we have to add one to get a proper air/fuel ratio(AFR) reading. You CAN do this build without one but if your wide open throttle (WOT) tuning is off and you're running super lean, you won't really know it without a WB. They're not cheap and you need a gauge pod (which means you can put in a boost gauge...and who wouldn't want to see the boost they added to their LE5, right?) but it is good insurance to make sure you don't make the engine go boom. I have the AEM wide band with gauge and it runs around $300. Well worth it in my opinion.
To me, having that O2 is why my engine is still running strong. I put the turbo on at about 77K miles and have 125K on it now without any major engine issues. All my issues have been little thing with the parts I've added.
Feel free to post more questions here as they come up and good luck with your build.