Big Lifted 95 Tahoe / LQ4 / Gen I NV4500 Conversion - detailed with part #'s

I spent nearly 3 weeks buried in my laptop trying to put all the info together to do this swap. Although the info is all over the intrawebs, it seemed many questions were still unanswered and part numbers left out when I needed them. I also spent a good amount of time finding the best prices for the parts I needed. I know most of you don't want to read a book but I cant tell you how many times I wish things weren't written so vague. So in this thread I will do my best to give you everything I learned in great detail.

OK so my 95 Tahoe had a 383 TBI Stroker that I was never able to properly tune. I did an NV4500 conversion a couple years back. The truck sports a 12" lift with a 14 bolt rear. Its only summer driven and got such poor fuel mileage with the 383 that I barely drove it. I was on vacation 160 miles from home towing my bike on the back of a trailer when piston #7 blew off the rod and the write pin breached the water jacket. After taking some time to learn about the numerous advancements made in the LS engines, It was pretty much a no brainer to go this route. As I am writing this header, the truck is in the shop having the exhaust tied together and the LQ4 is done. Here is a pic I took nearly 15 minutes before the engine failure while in NH. The 383's last uncompleted voyage.

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Finding an LSX

So I basically had to choose between the 5.3 and a 6.0. Bow auto parts in NH had a drop out 6.0 for $1500 but a 5.3 was only $850. I found a 5.3 I liked and planned to make the trip on a Saturday. At that point I was already expecting to need a few random parts for the conversion so I stopped by Everetts (my local self serve parts place) on my way home from work. Figured it wouldn’t hurt to ask and so I did. They had a 6.0 LQ4 from an 03 Yukon on the lot for only 650.00 with 103K. I decided 6.0 was the way to go and it was much closer. The guy at the counter claimed it had the harness but was separated from some of the outer accessories. I took a look and found the harness missing as well as a few small items that ultimately were available on parts trucks in the lot. I even took a few cell pics so I knew what I needed to get to complete it. The next day I went back with my tools and walked through the yard and pulled a bunch of stuff off a 5.3. On the return into the building, I told them I would take the engine. Since I was buying an engine, they said the parts I had grabbed were free. SCORE! In that bucket was a plethora of expensive goodies including the ECM, power steering pump and bracket, pulleys, starter and lots of hard to find parts. A couple days later I returned on a 90 degree day and filled another 5 gallon bucket with parts that I needed. They charged me 90 bucks. Again a score because I had the MAF and an bunch of OBS parts to help clean up my underhood. That day I came home with my "New to me" LQ4.

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Bolting up a manual tranny:

This was the first thing I needed to make sure of. It seemed all the forums had vague information and most people were not getting the answers they wanted about the swap. "Do it like this and it will work they said". I needed to be sure. I didn't want to have to pull the heavy NV4500 back out because I didn't do my homework. After nearly 6 hours of browsing forums I learned that the 99-2000 LS engines had a shorter crank than the SBC engines. Later on they became longer but were still a pinch short. Advance adapters sold a kit for nearly a grand but that was outrageous. The large price was because of a smaller bellhousing that would make up the difference in the crank length. An SBC clutch will bolt to the LS Flywheel as long as the dowel pins are removed. The only issue with using an LS flywheel is that the bolt holes are metric and the holes will need to be reamed out on the pressure plate. There was also an aftermarket flywheel for the cheap that was more designed for mating old trannys to the new engines as it was standard thread for the pressure plate bolts but metric holes for the connection at the crank. I went this route. Also the pilot bushing is different, use one from an LS2. Of course I had to wait until the flywheel and pilot bushing arrived and then take measurements to confirm. I probably dug into this too deep as I actually measured and confirmed the face of the new flywheel .2” closer to the engine and the pilot bearing .13” closer to the tranny. Since the input shaft end is very long, the pilot bushing was of no concern. At the time of the installation, all I could hope was that the .2” of clutch engagement would be made up by the hydraulic system. Once I was able to drive the truck, my presumptions were right and everything was fine. I was able to use my old NV4500 bell housing, clutch, pressure plate and slave cylinder. The only new purchase was the flywheel, flywheel bolts (don’t reuse old) and pilot bushing. It should also note that since the LSX engines are all metric, the bellhousing bolts I had were no longer going to work. Also when putting the engine on the engine stand, I had to dig up metric bolts to make the connection. Since the LSX engines don’t use one of the upper bellhousing bolts, I chose to move the upper arm on the stand to the lower bolt hole position, thereby keeping 4 bolts connected. Since I have the first gen NV4500, I have the external slave cylinder. This bolted right up, but was very very close to the plastic plug for the oil level in the oil pan. Most of us doing the conversion will not need to plug anything in here. If you plan on using it, make sure you don't have an external type slave cylinder.

Selecting motor mounts:

This was very confusing at first. There are half a dozen places that make these. The LSX engines are shorter than the SBC. I read of many people buying brackets that were supposed to keep the engine in the stock location and then after bolt up, they weren’t. Some people are upgrading to 4L80 Autos which are longer. In this case they need to be able to move the engine to make up the difference. I chose the Dirty Dingo mounts. They are the only ones that have adjustable bolt sleeves. They also eliminate the use of the old style bulky block brackets. I liked the ability to move things if need be or during future service. Since I have a stage 2 Cepek Lift, there are compression struts that mount to the transmission crossmember. This means I couldn’t really move it much. Also I custom fabbed my shifter offset so my Hurst T handle didn’t hit the dash or console. Bottom line, I needed my tranny to stay in the Exact same place. The dirty dingo mounts allow this and also aided in installation with regard to the transmission input shaft. Drop the engine in and slide it back into the tranny. This engine went into place easier than the 383 did both times prior.

Underhood:

After getting the 383 out, I started to realize how busy the area was under the hood. The ECM was going to have to go under the hood. The area on the passenger side fender I pretty much reserved for the intake. Most people just move the battery over to the drivers side and then use that space. I have 2 batteries. I had a makeshift dual battery tray that was jimmy rigged into place. I wondered if I had the proper battery tray, maybe I could hide the computer underneath. On my second trip to Everetts, I pulled a tray and realized the 96-99 trucks moved the fluid bottle to the area under the battery. Sweet. I never paid enough attention to the 96-99 to notice that change. This was perfect. I grabbed the tray, mounting bracket, fluid reservoir and hardware. Don’t forget the clip that’s on the inner fender. I gave myself a good foot of wire and hose off the reservoir so I could connect/plumb it into the old lines. On my truck, I removed my battery and scrapped the old junk tray. Next thing I noticed was the horn was going to be in the way. I removed it initially. The lower bracket went in first. The 2 core support holes were already there so that bolted right up. I had to drill 2 holes in the fender for the lower mounts. That was cake and since I grabbed the bolts from Everetts, it was simple. Then I slid in the reservoir. Went right in no prob. Don’t forget there is a little grommet in the bottom of the bottle that goes in the lower part of the bracket. Then the battery tray itself goes in last. I had to drill one more hole in the fender for the odd bolt in that tray. Look closely and you will see a divet in the fender where you need to drill the hole. Also there is a screw into clip connection in the inner fender. Next thing was I found plenty of room for the horn up against the core support. I flipped the horn and bracket around 180 degrees and used a self tapper to fasten it (apx. 2” to the left of the filler neck tube bolt). I bolted my air tank for the air horns to the new bracket and then the carbon canister next to it. (I removed the bracket that was on the canister and used a large hose clamp to attach it) Also cleaned up some of the E-fan wiring while I was in there. The old reservoir came out easy and opened up a space for the ecm. On a later trip to Everetts, I was able to score the factory 96-99 ECM bracket that mounts in that area. It wasn’t a perfect fit, but very neatly held the 2000+ ECM and it looks almost factory.

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Old TBI Harness:

I contacted Current Performance and had them make me a bare bones standalone harness (since no auto tranny). They needed to know that I had a 2000 (Red/Blue) ecm, and drive by cable throttle body. There was no need for fan control as my existing efan setup is independent of the engine management. In the old harness, there was a heavy ground that went to the back of the block. I kept it in the same space. Digging through the engine management part of the old TBI harness, I found 4 or 5 ground wires. I cut these all shorter and added a single yellow terminal to the end and grounded it on the same bolt as the “heavy ground” behind the block next to the oil sending unit. My oil sending unit plugged right in. I also retained the two ac compressor plugs and the coolant temp sender wire which I spliced into my extra wire on the coolant temp sensor. I should mention that I had purchased the 3 wire sensor and pigtail off ebay. When I was cutting out the old pigtails that weren’t needed, I found out that my former TPS plug was the same. I could have just used that one instead of buying a new one. Note that the old wire that used to be on the alternator was not needed. I was not sure if it was going to trigger a battery light. It didn’t so I cut the wire out. I also left alone the starter trigger wire. Currents harness plugged into everything pretty self explanatory. One thing I did not anticipate was different plugs for the O2 sensors. I had purchased the 03 ones thinking that was the way to go. The newer style sensors ground through the PCM. The older ones do not. Since I converted to drive by cable, that meant I had the old system and Current provided the flat plug connectors for the ground by pipe setup. I had to get the sensors for a 97 Corvette with the 5.7. As for the rest of the harness, they had a 4 wire hookup to complete it. For the tach wire, I spliced into the old white wire on the coils old “Black Plug”. For switched power, I spliced into the pink wire on the coils old “Black Plug”. For fuel pump, they recommend to bypass the entire relay system as the current harness has relays built in. I backtracked the grey wire that runs the pump and spliced into the wire where it begins its rise off the frame rail (down below the brake booster). The last wire was the check engine light. I found this brown with white stripe wire tucked in the old harness after it comes out of the plug on the passenger side of the firewall. All of the colors of the wires I spliced into matched the color that came on currents harness. Since my factory ECM is still tucked away behind the glove, the AC and DRAC modules are still working. On the first test drive, all gauges worked and the AC cycled properly. In the end the only wires that I cut out of the old harness were the injectors, IAC, TPS, CTS (for ecm), MAP, alternator, Coil and distributor. I didnt go as far as unpinning them from the ecm. I just taped them off individually and then hid the dead ends on the factory loom.

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Exhaust manifolds:

I decided to keep the manifolds. They aren’t as bad as the SBC manifolds. Sure headers would be neat., but I was doing this on a budget. I figured I could add them anytime. We noticed that the rearmost manifold stud was broken on both sides. I used an air gun to buzz out the other bolts. Trying to take these out by hand may increase the chance of breaking the stud. I prefer to use the gun. All the rest came out fine but I couldn’t figure out how to get the manifold around the oil dipstick. It was fused into the block. Mosquitoes were getting bad and I got frustrated so I just snapped the bracket off the upper part of the tube and slid the header off. Later on I did a repair by brazing the bracket back onto the tube. The stud on the drivers side came right out with PB Blaster and vice grips. The other side had broken flush. The solution was to mig weld a nut over the stud hole and then build up the center of the nut. Slow wire feed is key here. The aluminum wont bond to the steel so its pretty safe. Once the nut was welded onto the stud, let it cool then unscrew it. We got it on the second try and I owe my bud a 6 pack for teaching me this cool technique. The general consensus was to use factory GM gaskets as aftermarkets rarely do as good a job. I shopped around for the best price on GM gaskets and grabbed all new studs as well. Def didn’t want to reuse the old ones. I should note that when buying the gaskets from RockAuto (which had the best price), they didn’t identify if the price was for one gasket or two. All of the aftermarkets had a picture of both gaskets but the AC Delco ones did not have a picture. I searched the part number through summit and confirmed they were sold individually. Thus my order was for 2 of the AC Delco gaskets. I spray painted the manifold heat shield with black header paint before putting them back on. Here was the unseen kicker regarding the headers. When my truck made it to the exhaust shop, the phone rang instantly because they didn't have the flanges there to weld the new pipe to. No places locally had them either. In the end I had to buy the down pipes from each side and they had to cut the ends off to get the flanges. This was something I didn't find out in ANY of my reading on these forums. Had I known this, I could have pre-purchased the flanges from Speedway motors. When it was said and done, they money I spent retrofitting the stock manifolds was equal to what it would have cost to go with headers in the first place.

Intake Manifold:

Since my engine was missing parts, I had to look into what I needed for the intake. I didn’t have the plastic cover or the brackets. I saw one on a 5.3 in the salvage yard so I grabbed the cover and the little mount plate that bolts onto the intake. This should do for now until I decide whether I want the Vortec Max 3 piece covers or not. Note: the 3 piece ones need the mounting studs on the valve covers) My engine had a drive by wire throttle body. I chose to avoid this route as mounting the pedal is a pain and you have to alter the bend of the pedal to fit in the OBS. Drive by wire makes me nervous too. I like my foot physically connected to my intake. The salvage yard had a 5.3 with the cable throttle body. I grabbed that and the little bracket that goes on top of the intake to connect the cable. Cant forget that. I also learned that I needed a 96-99 style throttle cable. Grabbed one at the yard as well. My intake had a plug in the back where a brake booster would connect. The donor truck must have had hydroboost assist brakes. Since my truck needed a connection to the brake booster, I had to get the adapter. This was one of those items that I bought online before realizing they were so plentiful at the bone yard. No big deal, I only paid 5 bucks for the nipple. Before I forget, there was another difference between the DBC and DBW throttle bodies. The DBW unit on my LQ4 had a vacuum line coming off the top of the throttle body that went to the valve cover. Apparently the early throttle bodies had this line right on the throttle body. Later models they moved the line right onto the intake manifold and deleted it completely from the throttle body. Since I was swapping old onto new, I capped off the nipple coming off the throttle body. I also bent it down and out of the way. I should also note that there is a small hose nipple on top of the LSX intake. It comes from the factory with a break off tab in place so if you want to use the nipple, you will have to break off the tab. This can be a vacuum source for things like the AC diverter valve dashpot, carbon canister, evap component, or in my case, a mechanical vacuum gauge. I did some research on the steam lines. It seems that a line must come off the radiator (not the overflow line) and tie into the steam lines. The valve cover plumbing must be used, but the connection to the throttle body is not required. Well to me anyway. It is supposed to help with throttle bodies freezing in the winter. I chose to plug off both ports under the throttle body for now. If I have throttle issues later. It will take a mere minute to re-route the lines through the throttle body. I connected my plumbing directly to the extra port on the radiator. To make the change in hose size, I went to Home Depot and bought some brass fittings. A hose barb on each end for the proper hose size and a Coupler in the middle.

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Sensors and stuff:

This area got really confusing fast too. Here's the story. You have an oil pressure sender in the same area as the SBC. This is not needed by the ECM in any way to run the engine. Its sole purpose is to run the oil pressure gauge on the dash. There are 3 wires here. One is power, one is ground and the last is signal. I presume this sensor gets 12volts when the key is on and thus triggers the oil light on the dash. Once the truck is running, the pressure increases and the light goes off. OK so that being said the idea is to run the original SBC oil pressure sender in that location after removing the existing sensor. I couldn’t find an answer about just splicing the wires into the sensor in the LSX. Everyone is running their old sender so I decided to do the same. You will need an adapter to make this connection. Remember when I said everything was metric? Most people talk about the ones from S&P performance. They cost double because they are chrome. Auto Meter makes one for half the price so I went that route. There are also 2 other places you can steal oil pressure from. There is a plugged boss in the lower block an some have used the coolant line block off plate that has threads for running a sender. IM just using the one behind the intake because that’s where my factory harness plug is already. Use the other locations if you decide to add a second mechanical gauge.

You have a coolant temp sender on the passenger side of the engine. Don’t take this out unless its malfunctioning. Some have 2 wire units and some have 3 wire. The third wire (the one below the two that are side by side) can be wired directly to your dash gauge. I have heard there are discrepancies between the actual temp and indicated temp. If you only had a 2 wire sensor there, you can change to the 3. The part number is TX111 and the pigtail is S619. (Or use your former TPS plug if it’s a round style) I have a second mechanical water temp sensor. I could have put it anywhere really. Turns out GM was really good with giving us options. If you look on the drivers side in the back of the head, there should be a bung there. Again there is an adapter for metric to SAE on the S&P site, but the Autometer one was cheaper. This is probably a better place to put your dash gauge connection. Some have said it gets in the way of the spark plug wire. But it wasn’t an issue for me. I should note that I had to slightly drill out the adapter to fit the aftermarket probe inside for my added mechanical gauge.

My SBC had oil cooler lines. The new LSX engines don’t need this as much as the old engine so you can bypass it. Most do anyway. My engine used to have lines so I needed to cap off the 2 holes. There are 2 styles of block off plates from GM. One is just flat and is a basic block off. The other has a threaded boss for adding a sensor. It can be drilled and tapped for larger sensors. I believe they come threaded but not drilled all the way through. Should you want to add a sensor, just drill it out. There was a GM part for the cover, but I soon learned there was a separate number for the gasket and then another for the bolts. It was cheaper to buy the kit on ebay.

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Most people converting to LSX will opt for the Electric Fans. Its more efficient at cooling and less drag on the engine means more power. I had already done an Efan conversion years ago with a custom wiring harness and Rheostat to turn the system on. I could have tied it into my ECM but for now I am leaving it alone. Once I get this all dialed in setup electronics wise, ill upgrade the fan system if necessary

Regarding AC. Initially I was going to just abandon it, then when I got to the 11th hour of the install, I decided to just do it right. I should have sprung for the brackets initially. Prob is they were 300 bucks. I chose the dirty dingo ones as I had already done business with them for my motor mounts. I also didn’t have the hardware to mount my tensioner pully so buying their bracket not only gave me a mount for the compressor, but it included the pully. I didn’t even have to split the pressure lines off the compressor either. There were a few catches though. I found that the belt rode just along the edge of the tensioner pulley. To remedy this, I placed a 1/8” shim behind the tensioner pulley. You wont be able to go any more than 1/8” because the pin on the back of the tensioner must stay in the provided hole. The next issue was belt size. The one they sent me had an effective length of 105.77. I’m guessing that since I went with the 145amp alternator, I needed a larger belt. Gates K061066 was about an inch longer and worked great. Also Dayco 5061065 should work. There was even a little extra room to go longer so I think any 107” belt would work too.