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Another LS3, T-56 swap into 1981 C3

59K views 234 replies 22 participants last post by  zimmej51 
#1 ·
Greetings to all - I've been a member here for about a year but haven't posted anything until now. I know there have been quite a few threads regarding the LSx swap into a C3, but I thought I'd add my experiences to the wealth of information here!

I actually started my build a little less than a year ago, just in time for the Photo Bucket Phiasco that wiped out a lot of info just when I needed it the most! The car was kind of a "barn find", an 81 4-speed with 46K actual miles. No damage, no missing parts inside or out and most surprising no rust other than some surface rust here and there on the chassis. It was the condition of the car that prompted me to do a full resto-mod.

This is my first attempt at posting with pics by uploading them to DC. I'll probably mess up quite a bit here at first so bear with me! Advise and suggestions are welcomed! So here we go....
 
#175 ·
Everything is looking really good! I’ve been away from the forums and my own ‘81 LS3 swap for a bit while we finished part of our basement over the winter. I also put the Dakota Digital gauges in my setup and love them… they feel like good quality and well made. I got my car running in the fall enough to get it to an exhaust shop and get the first 150 miles on it. I found I had a tremendous amount of heat coming through the floor boards and firewall even with lizard skin applied to the exterior so I removed what interior I had in and have just got around to putting in Thermo-Tec’s Thermo Guard FR on the interior of the firewall and floor. I plan on putting some form of heat shield on the exhaust too and hope this combination solves my heat issue.

I am now revisiting and correcting a few things I cobbled together to get it up and running before winter. I like what you did with the Earl’s steam adapters… they must be a new product as I didn’t run cross them when I hooked my steam vents. Keep the posts coming!
 
#177 ·
Everything is looking really good! I’ve been away from the forums and my own ‘81 LS3 swap for a bit while we finished part of our basement over the winter. I also put the Dakota Digital gauges in my setup and love them… they feel like good quality and well made. I got my car running in the fall enough to get it to an exhaust shop and get the first 150 miles on it. I found I had a tremendous amount of heat coming through the floor boards and firewall even with lizard skin applied to the exterior so I removed what interior I had in and have just got around to putting in Thermo-Tec’s Thermo Guard FR on the interior of the firewall and floor. I plan on putting some form of heat shield on the exhaust too and hope this combination solves my heat issue.

I am now revisiting and correcting a few things I cobbled together to get it up and running before winter. I like what you did with the Earl’s steam adapters… they must be a new product as I didn’t run cross them when I hooked my steam vents. Keep the posts coming!
Goldata81 I'm very interested to hear of the heat problem you encountered. I'm at a good place right now to take some preventive action. I have a supply of Dynamat but have not installed it yet. My plan was to use the Dynamat inside and fab or adapt some heat shields of some sort over the pipes. But your experience is making rethink things. Maybe I should use something like Thermo Guard instead of the Dynamat? Does your LS have headers or stock exhaust manifolds? My plan is to retain the stock manifolds for the moment and fabricate the rest of the exhaust in a manner that I can adapt to headers as a future upgrade. If you get a chance, sure would like to see some pics of your exhaust system!
 
#176 ·
I hope you guys are all doing well during this crisis. I love the way this car is coming out and I really, really dig the color. But I am here now to share my bad thoughts about the GM filter/regulator. This was a relic of the LS1. And not just 97-04. Because in truth even some C5 cars had already upgraded to the C6 fuel system. This is because 350hp was a lot of demand to push through a filter under pressure. And also there was a realization that with such large fuel injectors if the particles can pass through the sock in the tank they will blow right through the injectors. At high flow rates that filter regulator will do a much better job at keeping 58psi between the pump ant the filter but the line running to the rail will be notably less. This is why by 2005 ALL corvettes switched to the new fuel system without a filter. And that was for the 6.0L LS2. It is a joke to think that filter regulator will happily fuel the 6.2L 450hp LS3. You need to swap the filter regulator for just a regulator. Be it from FAST or Aeromotive or w/e but you need to remove the restriction between the regulator and the fuel rail if you hope to fuel over 400hp worth of fuel.
 
#178 ·
Very interesting Autowiz, and makes a lot of sense to me. That must be why I see so many LSx swaps with just a regulator. I'll probably leave the filter/regulator in place for the moment, at least until I can get the car moving under it's own power. It shouldn't be a big problem to change to a regulator only. I'm not that crazy about where I installed the filter/regulator anyway. I appreciate your input! Reminds me of one of my favorite old sayings: "Learn from other peoples mistakes... You won't live long enough to make them all yourself!"
 
#182 ·
I am running the C3 Corvette LS Swap ceramic coated headers from ARH(bought through a different vendor). I mainly went with the headers for ease of putting on some form of exhaust until I could make it to a shop. Here is a pic of it on the lift all completed at the exhaust shop. I have some heat shielding for the exhaust on the way now as well.
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As for the heat, I had originally had both Fatmat(sound) and Reflectix on the inside of the firewall with only the Fatmat on the floor. Most of the Reflectix has been replaced with the Thermo-Tec products. I also threw some of Thermo-Tec's Suppressor Heat & Sound on top the the Fatmat since I ran across a good sale on some. Not sure if it was needed though. I now have Fatmat, Suppressor Heat & Sound, and the Thermo-Guard on the inside firewall on down covering the whole floor. Jury is still out on the interior temps but I feel confident. I've heard good things about Dynamat. I've never seen it but if it isn't too thick, you could use both. The only issue may be around the accel pedal. It looks like we're using the same pedal and mine is mounted very similar to yours. I haven't driven mine yet with all the heat products I've added and carpet in, but with all that installed the pedal can still be pressed to its physical stop right before it bottoms out with the flooring. If I run into issues, I'll have to revisit and do some trimming or adjust the pedal mount.

Here is a poor pic of my pedal during my wire cleanup attempt.
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#184 ·
I am running the C3 Corvette LS Swap ceramic coated headers from ARH(bought through a different vendor). I mainly went with the headers for ease of putting on some form of exhaust until I could make it to a shop. Here is a pic of it on the lift all completed at the exhaust shop. I have some heat shielding for the exhaust on the way now as well.
View attachment 103018

As for the heat, I had originally had both Fatmat(sound) and Reflectix on the inside of the firewall with only the Fatmat on the floor. Most of the Reflectix has been replaced with the Thermo-Tec products. I also threw some of Thermo-Tec's Suppressor Heat & Sound on top the the Fatmat since I ran across a good sale on some. Not sure if it was needed though. I now have Fatmat, Suppressor Heat & Sound, and the Thermo-Guard on the inside firewall on down covering the whole floor. Jury is still out on the interior temps but I feel confident. I've heard good things about Dynamat. I've never seen it but if it isn't too thick, you could use both. The only issue may be around the accel pedal. It looks like we're using the same pedal and mine is mounted very similar to yours. I haven't driven mine yet with all the heat products I've added and carpet in, but with all that installed the pedal can still be pressed to its physical stop right before it bottoms out with the flooring. If I run into issues, I'll have to revisit and do some trimming or adjust the pedal mount.

Here is a poor pic of my pedal during my wire cleanup attempt.
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Clever way to get past the deep driver's seat pan. I did it the hard way.... Replaced the seat pan with a shallow pan, like on the passenger side. I knew I wasn't going to retain the stock seats. Also fabbed up a new crossmember. These 2 things result in more room for the exhaust, but I'm not sure it's worth all the trouble!
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#185 ·
It's time for me to start getting serious about weatherstripping. I'll be replacing all of it. Previous research has me leaning toward CRC. Over the years I've gotten some really good stuff and some really bad stuff. I've never used CRC before, can anyone share their experience, good or bad, with CRC? I'm open to recommendations also. Thanks in advance!
 
#192 ·
1981 C3/LS3 swap, radiator hose question. I have a Dewitt 6139077M radiator on the way, thought I would tap the knowledge base here regarding the large radiator hoses. I have the Vintage Air Front Runner setup with the water pump they included with the kit. I attached a pic from early in the build that shows the water pump. Does anyone that has done a similar swap have any part numbers for the 2 large hoses? I'm no stranger to scrounging around and finding hoses that fit, or can be modified to fit, but would sure be a time and effort saver if someone could give me a starting point. Thanks in advance!

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#193 ·
Hi all, this isn't a big deal but thought I'd throw it out there anyway FWIW. This has to do with the horns and their location in the 81. When I started breaking down the car, I discovered that one of the horns (passenger side) was missing while the other was still in place on the driver side. I wanted to replace them but started getting crossed up on the correct bracket. That's when I discovered that the 81 assembly manual doesn't agree with the way my 81 was built. It shows one of the horns mounted near the center of the front hood opening and the other mounted to the big "crash plate" at the front of the bumper reinforcement. It's circled on one of the photos below. The correct location for my 81 is under the forward end of the fenders. That's where the wiring harness lines up as well. If you have done much with the assembly manual and service manual then you have probably discovered there are numerous inaccuracies. Like I said, no big thing, just thought I'd share.
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#194 ·
Been a month or 2 since my last post so here is what I've been doing. I have the seats, door panels, etc at the custom upholstery shop. Hopefully they will be done in 4 or 5 weeks. Meanwhile, one of my sons gave me a new 3D printer to mess with and it didn't take long to find something I needed to print. I have the optional manual control for the Dakota Digital gauge lights and since the knob looks a lot like a cig lighter I decided to make a mount for the control. That way I could use the existing hole where the cig lighter used to be. I drew up a 3D Cad drawing of the part I needed, sliced it and sent it to the printer. Worked perfectly, and I like the looks of the new knob. the pics below are the backside of the console bezel with the new mount bonded in place with ABS pipe cement. I got a little sloppy with the glue but it's on there for sure!
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I ran new 2-0 battery cable from the back and originally had it connected to the starter solenoid like OEM. The solenoid terminal is also where the two fusible links tapped into power and fed it to the fusebox. The 2-0 cable is flexible enough but it starts getting very crowded in that area real quick. The LS doesn't have a whole lot of space right above the starter. So, after wrestling with it for day or so I decided to install a remote distribution block from CE Autoelectric. It is a 4 post rated at 350 amps continuous. I connected the 2-0 AWG main supply cable to the block, ran a 4 AWG over to the starter (only about 18 inches long) and a 6 AWG up to the GMPP fuse panel. Made things WAY easier.

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Here's a few things I learned about the GMPP Electrical Center (fuse/circuit breaker panel) that comes with the GM kit for the LS3. I didn't want to use a bunch of in-line fuses for the radiator fans as well as other devices when the Electrical Center was just right there. So I popped the panel out of the case and did a little research. This may be well known but I'll share what I learned anyway. The GMPP LS3 kit uses the Delphi 12146281 Electrical Center as the basis for the fuse panel. As delivered, the panel uses only 4 of the 10 Maxi Fuse sockets. But the other 6 Maxi Fuse sockets do not have terminals in them. Only 1 side is connected to the power bus. After some serious digging I found the necessary terminals in the Delphi Connection Systems catalog. For the Maxi Fuse terminal that fits 10 AWG wire, you need Delphi P/N 12110127. Different size wire uses different P/N terminals. They are listed in a table in the catalog so consult the catalog for different size wire. There are also quite a few of the smaller fuse sockets that are not used, and like the Maxi Fuse sockets, there is no terminal in the small sockets. Only the bus side has terminals. These terminals are Series 280. For size 10 AWG you need the 280 series, tangless, unsealed, 16.2 mm spacing terminals, Delphi P/N 12110647. Some of the Delphi Electrical Centers use 15 mm spacing so pay attention to the table in the catalog. The terminals also have different P/Ns for different wire sizes.

Anyway, after all that, the object was to have all fuses in the GMPP Fuse Panel instead of inline fuses all over the place. The inline fuses work, and I've used a bucketful of them over the years, but I didn't want that on this car. To buy the Delphi terminals you may find it hard to find a source that doesn't have a 2,000 piece minimum purchase, but a little sleuthing will find a source for small quantities. I found the Maxi Fuse terminal P/N 12110127 on Amazon, min quantity 5. I found the 280 series terminal P/N 12110647 on ebay, min quantity 10. As hard as they were to find, they are a piece of cake to crimp onto the wire. Expanding the Delphi Electrical Center is an easy, clean way to add circuits. I recommend downloading the Delphi Connection Systems.

Here is the 800 series Maxi Fuse terminal:
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Here is the 280 series fuse terminal
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Here is the GMPP fuse panel with 2 additional Maxi Fuses for the cooling fans
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Getting late, more to come...
 
#195 · (Edited)
Thanks Zim, great post - I have been thinking about my electrical and stocking some misc parts. I knew from my initial look at the GM fuse panel that it had more capacity than it was plumbed for but I had not advanced my thinking that far yet. It's too easy to focus on point solutions, e.g. using the in-lines for the fan wiring, but then I usually end up re-doing stuff which costs me in the end.
 
#196 ·
Back again, stayed up past my bedtime last night.... BTW the end of my last post should have said "...download the
Delphi Connection Systems Catalog. I left off Catalog...

The DeWitt radiator came with dual SPAL fans but the GMPP output for the fan is fused at 30A and I was not sure that would be enough for 2 fans. It probably would have worked but I would feel better with 2 separate circuits/relays for each fan. Plus I wanted to use a trinary switch with the Vintage Air setup. In case you aren't familiar with the VA trinary switch, in addition to the hi pressure and low pressure safety switch, it also has a switch built in that closes at 245 psi on the discharge side to turn on the fans regardless of engine temp. So, I decided to make a relay panel that would have the relays and connections all in one place. It looks a little busy, but pretty simple really. Relays 1 and 2 run fans 1 and 2. They are essentially in parallel. Both relays are activated by the signal from the ECM. Relay 3 is activated by the trinary switch and will, in turn, activate relays 1 and 2.
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Next, finding a place to put it was a challenge. I wound up placing it next to the ECM on the back side of the passenger front wheel well. This made the wire runs pretty short. Kind of hard to see but here it is. The picture is looking straight down over the passenger side wheel.

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Between the time I started with the Vintage Air installation and now, VA released a kit for the 77-82 C3. I already had everything fabricated and installed except for the condenser. I was all set to order a condenser and make the mounts and hard lines, but when I called VA they told me about the kit. All I needed was the condenser kit (P/N 021074). I'll have to admit it was kind of nice not to have to make everything! It all fit very well, was a snap to install. All I need to complete the AC is to make up the flex hoses, I'll probably use beadlock fittings since I have the crimp tool.

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#197 ·
I'm going to post the Delphi Connection Systems catalog because it took me awhile to find it. If it isn't too big, and I'm not breaking any rules, here it is. I can't imagine Delphi having an issue with posting a catalog but you never know. The electrical center used in the GMPP LS3 kit starts on page 272. There is a wealth of information in the catalog, and once you kind of figure out how things are arranged it isn't too hard to find what you want. In addition to adding fuse circuits to the panels, there are many other components that can be added to the panels such as relays, diodes, etc. And using the Delphi panels is often easier than external circuits and gives everything a nice appearance.
 

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#198 ·
A little progress to report, the doors internals are all installed and tested. I replaced the window and lock motors, all rollers and just about everything that moves. The driver side regulator had the lower mount broken, pretty common on these. I used the repair kit from Zip, worked just fine. With everything cleaned and lubricated, I had forgotten how fast these windows go up and down! I also documented the disassembly and reassembly of everything in the door. There are lots of "how to's" around, but I recorded one or two tips that make assembly a bit easier. Also, the documentation is specifically for 81-82, and maybe 79-80. I have never been inside the doors for 79-80 but I suspect they are the same. If anyone is interested I'll be glad to share. Another box checked off!

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#199 · (Edited)
Those doors are looking great. And if your windows are rolling up and down fast then you have done an excellent job at aligning your tracks. Good on you. Cant wait to see pictures of them installed. Had a question about the fans. If you have both fans come on together from a standstill in parallel the sudden ~60 amp draw shock to the electrical system will cause the lights and stuff to momentarily dim when the fans come on each and every time. The way that GM handled this problem is to use 3 relays to control 2 fans just like you have but wired as such that these 3 relays have 2 turn on inputs at different temps to achieve low and high speeds by first bringing both fans on in series giving just half the current to each fan, or roughly 6v. Then when the higher temp is achieved the other 2 relays come on and switch the 2 fans from series to parallel, but since the fans are already spinning at half speed, the load applied at that point is equal to just one fan turning on and there is no hard shock to your electrical/charging system. And noise will be the only way you ever know the state of your engine's cooling fans. You already have all the parts for this, it is just in how you wire it up. In this setup you will have your vintage air trinary switch fan ckt wired to the 2 relays that bring on high speed. This way if the engine is cold and a/c pressure high the fan closest to the side of the condenser that the lines come in and out of will come on high speed by itself but if the engine is just warm it will bring up both fans in high speed. This is the manufacturer level way of doing this, not my own idea. But it is really slick and trick and will help your whole electrical system live a much longer and happier life. And also bring about greater creature comfort for the driver that doesn't have to deal with the sudden hard draw coming and going at seemingly random times.

Here is a diagram of what such wiring would look like. Your gen iv connect n cruise ecu will have 1 fan output and also an A/C input. You could get a fan switch set to like 185 on/175 off and use that to turn on low speed and then have the ecu drive the high speed at a higher temp you can change with software at will and wire the vintage air trinary switch fan relay control to that ckt.

 
#200 ·
Very informative post Autowiz, thank you! Since I was (still am) a little concerned about the fan current surge, I built the relay panel so that I could easily change up the triggers as you describe. To minimize the surge impact (hopefully) I ran 4 AWG from the 2-0 battery cable junction up into the ECM power relay box, just a little over 12". That's when I added the 2 fuses to the Delphi box with 10 AWG on each fan. I've tested by connecting a battery and so far haven't noticed anything but then again nothing else was turned on. Even if the surge doesn't cause a problem, I prefer the setup you described and will probably make the change once it gets on all 4 feet. I appreciate your input!
 
#201 ·
Moving to the interior while waiting on upholstery to get done. My first attempt at dashboard repair. The top was a mess, but the rest wasn't too bad. I used Polyvance materials and followed their instructions so didn't repeat them here. Worked a lot better than I thought it would. The color is 82 Dk Blue. A couple of the photos make it look a lot more blue than it is. At first glance it looks like charcoal, but there is a hint of blue. I bought a brand new 82 with this color interior and always liked it. Bumper Automotive exterior Auto part Furniture Table
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#204 ·
Looking for a little help here regarding interior colors. Back in 1982 I bought a brand new 82 Corvette with an exterior of Bright Blue (code 31) and interior of Dark Blue with cloth seats (code 22C). I definitely recall that the dashboard and other plastic parts almost looked like charcoal until out in the bright sun, only then could you detect a very slight dark blue tint to the color. I have duplicated the color on my current project but when I ordered a sample of the carpet it looks very blue. For the life of me I cannot remember what the carpet and cloth seats looked like in my 82 and of course I didn't take a single picture of the interior! Maybe the carpet color is correct but it sure seems too blue. The 31 Bright Blue exterior and 22C interior was not very popular and not many 82's were made with that color.

So it's kind of a long shot, but if anyone happens to have a picture of an 82 with the 22C interior I would be grateful to see it. Thanks!
 
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