I just finished installing a LY6 in my ’76 GMC truck and thought I would make a little write up to hopefully help someone else down the road. I chose this motor because the truck has been in the family since new and the stock 350 was tired. I wanted a Gen IV to play with so I knew more what I was getting into when I did a LS Gen IV swap into my Chevelle. I have a L76 that I am about to start working on to go into the Chevelle in the next few months.
Motor: I got the motor, wiring harness and computer from a 2008 Silverado with 14,000 miles on it. $2,500 shipped to my door. I am using my stock TH350 for the time being until I swap a 6 speed manual into my Chevelle. I will then put my 4l80e in the truck behind the LY6. I used the exhaust manifolds off my L76 out f a Pontiac G8 GT since they hugged the motor closer.
Wiring: I did the wiring myself. Not too bad with a decent wiring diagram. I had a neat color Mitchell diagram that really helped. My harness had a bunch of cut wires and the motor came with the wrong drive by wire pedal. I had to get that all sorted out but that was the main problem. I then used a Current Performance stand alone fuse/relay module. I work in my garage so my swap had to be pretty quick so I set the motor up on a redneck test stand to crank it. I used a Silverado tank with internal pressure regulation so it was just one line up to the motor. I bought a copy of HPTuners and disable the VATS stuff and a few other things for initial crank. The first time the motor turned over it cranked right up and settled in a nice idle.
http://www.youtube.com/watch?v=D1Ct-eLNx44
Install: Once I got it up and running it was time to install. The actual install took about a day and a half with a lot of help from my dad. I used the stock Silverado 26 gallon tank and installed in the drivers side of the truck. This took me a full day to get it in place and run a fuel filler up through the cab and out by the drivers door like the older GMC’s. Pulling the old motor was the expected mess but easy. Spent half a day cleaning up the engine bay and repainting it. This will never be a show truck so nothing too pretty. I used Speedway Motors swap plates and stabbed the motor in for a test fit. We had to move the stock mounts back about an inch to keep the tranny in the same spot and not have a longer drive shaft. Firewall had to be dented in a good bit to clear the motor but no cutting was required. Used stock mounts, drilled new holes in the frame and the motor fit nicely. Stock A/C compressor would not fit with the Speedway Motor mounts so I will have to go with a Kwiki mount in the future if I want the A/C to work.
Other stuff: I used a stock air box and air intake. It was simple and I found that the MAF sensor was just about perfect when I went to tune it. I used the stock power steering return line and just cut off the stock LY6 power steering outlet hose and flared on the stock truck fitting so no need for a custom hose. I had exhaust pipes bent that you can see on the test stand. They were a guess but they work perfectly and I just dumped the exhaust through some Summit mufflers before the axle. I think I used a stock upper and lower radiator hose for the Silverado. One big electric fan is controlled by a thermostat, not the computer.
http://www.youtube.com/watch?v=LYq8h...eature=related

 

Up and running: First thing first, the VVT is nothing to be scared of. It works well and you can feel it. The computer advances the cam as the RPM climbs. Just like degreeing a cam in a small block but you get both the low end torque and the high end horsepower. GM does put a bunch of cam advance in for part throttle for emissions. I am going to remove this and see if it effects anything. The trucks do have a delay of sorts for power enrichment. Totally stock it was sluggish down below 4000rpm and would jump out of its skin from 4000 to 6000. I adjusted out most of the power enrichment limits so it totally depends on throttle angle and rpm to when power enrichment comes on. Huge difference. Motor is very responsive and tons of torque and power off the line. I have been playing with a bit more spark advance and so far see no knock reduction. I may just copy the high octane spark table from the L92 motor and try it. The stock LY6 runs 87 octane and a pretty conservative stock low and high octane table. Oh, for those who don’t know, the LY6 has a virtual speed density table. I am just running MAF so I have avoided the dreaded virtual speed density table thus far.
Conclusion: Great motor, deserving a far better home than my old truck. The motor has started ever time since I first fired it on the test stand. It is smooth and very happy behind the TH350 in normal driving. 15mpg thus far and that is not being very easy on it.
Hope this helps, please post any questions or suggestions.
Thanks!

 

You get the award for "best use of lumber during a engine swap" .... :-)


Glad to see/hear it runnning.

 

Thanks! I actually wound up using 8" wide piece of board to mount my drive by wire pedel in the truck to mock up where to place it.
Yea, the motor stand is as redneck as they come but I only spent about $4 for it. I bought lag bolts for the 4"x4"s and that was it. Radiator is my old spare Chevelle radiator. The trailer was the neat part, it allowed me to move it around to crank the motor outside. I would remove the motor and put it back on the engine stand then roll the trailer in the backyard.
My neighbors were just so thrilled to see that crazy *** contraption. And even more so when I cranked it up the first few times without any mufflers.

 

Awesome job. I think I am going to pull the plug on a Current Performance harness since I already have an E38 computer for my LY6. Sound really good too.

 

The Current Performance fuse/relay module worked pretty well but it is really meant for the LS1 motors. I had to decide what fuse to put injectors on, coils on, throttle servo etc. I also had to change the fuses around a bit to match it up to my LY6 needs.

 

What were the major steps with HPTuners to get that thing running? I would really like to see a how-to somewhere on getting a stock engine to run after a swap.

Looks great. I would love to do an LY6 in my Nova.

 

Buddyholly,
Good writeup. This is giving me more drive to get my LY6 buttoned up and hope my cheap E-bay set-back plates work with my BBC stands

Can you give me any more feedback on this enrichment you were referring to? I plan on having John @ www.Speartech.com do my harness and OEM computer reflash and I would like to have some idea on what to ask or request when I finally send my computer/order.

thanks,
Jim

 

I thought about doing a post just on some of the HPTuners stuff since it is so overwhelming. There are really not many great write ups on just what to do in HP Tuners and I can sort of understand. Lots of people make money tuning these things and giving away a step by step guide is giving too much away.
To be honest, there was not much to getting the motor to run software wise.
Here are some of the basic things I went checked off:
Operating System: VATS1 and 2 disabled: Starter check disabled:
Engine I had to set my tach output to "crank" with a high and low resolution of 15 to get my tach to work. I also had to add a tach wire from the e38 ecu and use a pull up circuit. The tach was a pain to get to work.
I also disabled the catalyst over temp and pretty much all of my torque management stuff since I am running the TH350 it is fair game for abuse.
I spent a lot of time disabling DTC(diagnostic trouble codes). Since i was not running a lot of stuff like rear O2's and fuel tank pressure sensors I disabled a ton of these codes. None that I know of will prevent the motor from running but they are reported.
That was about all I did just to get the motor to crank. When I got to tuning it there was a lot more stuff I changed. Using the stock airbox and intake pipe made the Mass Air Flow sensor almost perfect. I messed with it a few times and it was within a percent or two. I did use a wide band O2 sensor. I changed my air fuel ratio a bit to compensate for 10% ethanol at all the pumps. I also only run 92 octane and have pushed the high octane table up about 6 degrees with no knock reduction.
Power Enrichment OK this was a big one with my LY6. GM really wants you to not be able to break these motors. With tons of torque management to protect the tranny there are some delays built into the motor too is seems. Power Enrichment for those new to the game is where the ecu riches the mixture up when you need it. Stock LY6's have a lot of things that must be met to get PE so the motors are kinda sluggish. Mine required 87% of full throttle before Power Enrichment. It also had a pretty good ramp up delay before you got full power enrichment. I zeroed all my PE enable requirements and now have it so the throttle position sensor brings on PE at 48% up to 3000 and even lower after that.
VVT The LY6 has variable valve timing. It took me a while to understand exactly what was happening with this. It really is very simple and should, in my mind, require no tuning. The cam is held at zero at lower rpm, or the equivalent of advancing a cam in a motor for more low end. At the motor rpm goes up, the cam begins to retard above about 3000rpm. By 5600rpm it retards the cam to 8 degrees to give you that top end power. Simple and nothing to mess with...however...
GM has a huge spike at low rpm and part throttle where it retards the cam up to 25 degrees for emissions and fuel economy. It also changes the spark timing in this region by adding up to 13 degrees of spark. Once I changes my PE engagement I noticed a delay from part throttle cruising because the cam took a second to come back from 25 degrees. I smoothed out my table for the cam and removed this spike. I did the same and zeroed out the spark changes for the vvt. So now my vvt is nice and smooth going from 0 to 8 degrees retard by 5600rpm.
I hope this makes some sense and is hepeful. This is by no means everything and I have a more stuff to tweak but the motor now runs great. Great torque at tip end and you had better be aimed where you want to go by the time you hit 4000rpm because it is a rocket to 6200rpm with those L92 heads.
As always, questions and comments welcome.

 

where did you get the wiring diagram

 

The wiring diagram for this motor was from a Mitchell manual. Someone from the boards sent it to me and I pieced it together from 4 files and created a large .tiff photo. I printed it out in 8 parts and taped that together to make one huge color diagram. I would post a .jpeg version of it but is still over 1mb and I can't attach it through this site.
I bought a subscription to alldatadiy.com and found the diagram almost useless. It would tough to use in a stock vehicle but it did not show enough of the entire diagram to allow me to modify the harness. It was useful for identifying sensors and some other stuff but I would not recommend it.

 

buddy, thank you for the rundown - it's very helpful to read and learn from your experience. I can host the wiring diagram if you're willing to email it to me and it doesn't infringe on someone's copyrights. I'll send you a PM with my email address.

Did you keep track of your expenses in this build?

 

that's a nice build. I'll try me a vvt engine one day.

 

Buddy,
Thanks for the rundown. I look forward for more updates.

Jim

 

I don't have an exact total for cost on this build but I know the truck was more than the truck is worth!...Oh well the truck is family and I hope to use this motor for the next 20 years or so...Heck, the stock 350 lasted 34 years and is currently going into a friends 86 Chevy truck....
The motor was the major cost. $2500. Another $200 for the tank, pump, line and airbox. $100 for the current performance fuse/relay module. The crank/flexplate adapter to hook to the TH350 was expensive at around $75 for the adapter and six expensive GM bolts. The exhaust pipes were about $40 and another $50 for the Summit mufflers. Then about another $150 in hoses, fluid and all the other small crap. I installed a $30 tach and a $90 programable fuel gauge with a low fuel light from speedhut I use this same gauge in the Chevelle and like it so this was a splurge.
The main cost that one could avoid was buying a copy of HPTuners and a NGK wideband. This was an extra $700 I could have skipped but I will use them both to tune the L76 going into the Chevelle so I can ALMOST justify it...plus I just could not send my computer off and not know what someone had done to it. I already used the wideband to tune the Edelbrock Pro Flo in the Chevelle and it runs better than ever.
So, maybe $3200 without the software and wideband and maybe $3900 with it. I could have done this a bit cheaper but for how amazingly well this thing runs and how low mileage the motor is I am pretty happy and would defiantly do it again.

 

buddy, thanks for the additional info. I started putting estimates into an excel sheet and came up with a much higher estimate for my swap, but I'm including headers, an oil pan (champ/autokraft), and a few other odd & ends that are driving it up. I'm sure I could modify some of the stock components and avoid those costs - we'll see. Did you use the stock oil pan? What adapter did you buy from GM for the TH350 and did you have to modify the flexplate at all? I've read with some flexplates enlogating the torque converter holes is required while with others its not.

Thank you for emailing the wiring diagram. I was hoping to post it last night, but I didn't get a chance. I will try to do it this evening.

 

Yes, I tried to do this motor pretty cheaply. Header and a different oil pan would add quite a bit to it.
In the truck I used the stock oil pan. Since I moved the motor back there as no clearance problem, but I don't think it would have been any problem even a few inches forward.
I used the stock LY6 flex plate and the GM adapter and longer crank bolts:
Flexplate Spacer GM PART # 12563532
Longer crank bolts GM PART # 12563533
The bolts are expensive and you need six of them. And the spacer in my application went between the flex plate and the torque converter. Basically a support for the nose of the torque converter.
You can oblong the existing holes in the flex plate but I just rotated the converter a little ways and drilled 3 new holes.

 

About the Current Performance fuse and relay module, would you use it again for a Gen IV application? Or, would you try something else?

Reason I ask is I was going to use the module for my LY6 into a 72 Nova swap, but if it ends up being just as complicated as making one from scratch anyway, well then I will go ahead and make my own to begin with.

Thanks

 

Actually I am just about to order another one for my L76 swap into my Chevelle. The Current Performance fuse/relay module is pretty nice, but not really designed for the Gen IV motors. The twin fan, ac, etc relays are nice and it comes wiith a bunch of extra wire. My main issue was that the circuits did not mesh up too well with the Gen IV wiring harness. The Gen IV has a lot of stuff that the Gen III does not(well the drive by wire and the VVT in my case). Not a huge deal but I had to decide how to group the circuits based on the wiring diagram that told what amp fuse for each circuit. I think I had to go up from 10A to 15A on one or two circuits and the size of the wire in the module was a little thinner than I would have liked, but sufficent. So I would recommend it for the swap, but it would be nice if they updated the design a bit to make a better fit with the Gen IV's.

 

Alright, thank you for the info. That will help me out a good bit for when my focus goes over to the electrical work for my swap.