Joel’s SL-C Build Thread

Joel K

Supporter
This post covers the install of the interior tub close out panels which were fabricated and documented in post #318.

Here is a short video on the process…

Now that the tub placement is set, I took a couple measurements that I think will be useful to other builders. Basically after all the work involved with doing three body fitments it turned out the tub placement from the front vertical chassis members are virtually symmetrical. Measuring the distance between the crease in the tub and the chassis is about 1.2” on each side. This puts the rear cup holders about 1/4” behind the rear 2x6” chassis member.

Pic of the interior tub to front chassis measurements…
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The car was delivered with the body and tub screwed into the chassis. Turned out RCR mounted the tub 1/4” too far back on the driver’s side. This pivoted the rear of the body over to the passenger side so it took a bit of work to figure out why nothing was lining up.

Anyway, all is good now and the tub is centered and secured with 4 screws. Some additional mounting screws may be added at some point…
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Mounting the close out panels are a little tricky because there is a notch that needs to be cut out from the panel to clear a channel in the front of the tub. First clamped the panels in place to insure they sealed up well against the tub…
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Drilled a couple 1/8” holes and secured the panels with cleco fasteners…
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Next step was to trim the panels in order to clear the weld lines. To insure the panels lay nice and flat I spaced the holes 3” apart. This spacing worked well on the rear fuel tank area close out panel so figure I’d do the same thing for the side panels. Pic of the passenger side panel trimmed up and secured with clecos…
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Pic of both panels trimmed and mounting holes drilled…
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Panels all installed with weather stripping cut to size. Passenger side…
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Driver’s side…
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Pic with the tub out…
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On final install I’ll bond the panels in with silicone adhesive to add strength and seal up the interior tub. I’ll also add sound dampening and heat shielding too.

Time to finish up the fuel tank area.
 
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Joel K

Supporter
This post covers mounting the fuel tank. I got the fuel tank back from the welder during the summer. Really excited about how it all came out and finally ready to install it.

I like the fact that the fuel pump will be PWM controlled by the GM factory ECU and that the fuel pump has a self contained swirl pot, regulator, and fuel filters. Nice and simple. Hopefully not too noisy since it sits right behind the driver…
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There are many approaches to securing the fuel tank. I basically followed the approach recommended in the manual which uses rubber pads and brackets to hold the tank in place and provide isolation from vibration.

Here is a short video on the process…

1st step was to clean the frame rails with a stainless wire brush then wipe down with acetone to remove the oxidation layer. Nice and clean…
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Then installed the rubber cushions on the frame rails. Decided to use acrylic adhesive backed 1/4” x 2” silicone 50A Durometer medium rubber strips(McMaster Carr part number 1466N46). I selected silicone rubber since the oil tank is close to the fuel tank closeout panel and that could transfer heat to the frame. The adhesive on the silicone strip is rated for 300 degrees so figured that will do the job...
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Turns out the bottom of the fuel tank was not totally flat and it rocked back and forth when placed on the rubber pads. Looks like where the baffle was welded causes it to bow. So added 1/32” silicone strips to three corners of the tank and that steadied it...
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Used three aluminum angle pieces to hold the top of the fuel tank in place. To insure the top brackets apply some amount of clamping force on the tank I substituted a machined 7/32” plate instead of the 1/4” silicone pad when locating the holes. When secured, the brackets compress the top and bottom pads by 1/32”. Pic of the brackets held in place with Cleco fasteners…
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Used M6 bolts though the back of the rear cross brace for added strength. Pic of the brackets with the rubber pads installed. Nice and secure…
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For side cushioning on the passenger side used dual silicone strips on both the tank and the chassis. The strips are placed on the side of the tank(1/2”) and also the side of the chassis(3/8”). This combo provided the right distance to line up the tank center hole with the center chassis frame rail. Pic of the passenger side of the tank with the 1/2” strips…
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Did something similar on the driver’s side…
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Also used silicone pads behind and in front of the fuel tank. 1/2” in front, 3/8” bottom rear and 1/4” top rear. Used different sizes on the top and bottom since that is how the tank wants to sit.

This design creates a nice cradle for the tank to rest and prevent it from sliding around. The rear spacing is enough to accommodate Damplifier Pro on both the back of the tank and rear close out panel and also sandwich in a layer of Dynaliner. Pic of all the silicone pads in place…
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Pic of side tank brackets in place. One on the back side and another on the front. The front bracket is screwed into both plates in front of the tank and the rear bracket is bolted to the rear close out panel…
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All in all, this approach holds the tank very securely and isolates it well from vibration.

Lastly, the front close out panel will also secure the tank in place with additional silicone rubber strips attached to it. And considering I have an in tank fuel pump, I wanted to add access panel(s) for the fuel pump, fuel sender, and other components located next to the fuel tank. Before I close up the interior I’ll put some thought into modifying the tub and designing the close out panels.
 
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Ken Roberts

Supporter
Joel, where is the wiring connector for the fuel pump module fuel level sender? On my CTS-V fuel module I added a separate connector to the hat of the module (Yellow connector).

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Ken Roberts

Supporter
ATL also makes a nice bulkhead 2 wire connector. I was going to use it as a backup in case I couldn’t add a connector to the module hat.
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Ken Roberts

Supporter
Sorry I just realized the fuel sender wiring is in the stock hat 4 pin connector. I originally thought it was a twin pump like mine. All four pins are used for the two pumps.
 

Joel K

Supporter
Sorry I just realized the fuel sender wiring is in the stock hat 4 pin connector. I originally thought it was a twin pump like mine. All four pins are used for the two pumps.

Hey Ken, I had no idea but you are correct, it has a four pin connector on the hat. Here is a pic of the wiring…
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I haven’t thought much about how it all goes together electrically at this point but I assume the ECU reads the sender to know when it can perform an EVAP leak down test. I also have a fuel pump control module that I guess connects to both the ECU and the fuel pump. I figure who ever builds the stand alone harness will connect it all.
 
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Ken Roberts

Supporter
Keep in mind that you still need to install a fuel pressure sensor in the top of the tank. It measures the vacuum in the tank when a leak test is commanded. You can see in the second picture that the plate to hold the sensor should be about 5/16” thick.
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Ken Roberts

Supporter
It all depends on how far you want to take the evap system. The connect & cruise system as sold by GM uses a vapor canister and the solenoid that is attached to the engine. The solenoid opens based on different parameters (like fuel level) as you mentioned. When the solenoid opens it is creating a draw and will pull the vapours that have been stored in the vapor canister. Without this occasional regeneration the charcoal in the canister would become saturated and no longer able to function as designed.

If you want to go a step farther than a second solenoid is installed at the fresh air draw port on the vapor canister. This lets the system do a OBD2 test. It is testing for leaks. It commands the solenoid to open at the engine but also commands the solenoid at the vapor canister to close. A vacuum is now created as the engine is trying to draw air/vapor but the vapor canister is closed. As a result a vacuum is created in the fuel tank. The sensor I showed is measuring this condition and reports back the status. If all is well than a certain amount of vacuum will be created based on time and the level of fuel in the tank. If you accidentally left the fuel filler cap off than naturally the tank/ system would no longer be sealed and no vacuum would occur. Same situation as if the vacuum tube to the engine was cracked.

The OEM setup does the OBD2 tests as well. The connect & cruise system is a simplified version. It may be all that is needed. The OEM system just adds a bit of diagnostic/ reporting ability.
 

Joel K

Supporter
It all depends on how far you want to take the evap system. The connect & cruise system as sold by GM uses a vapor canister and the solenoid that is attached to the engine. The solenoid opens based on different parameters (like fuel level) as you mentioned. When the solenoid opens it is creating a draw and will pull the vapours that have been stored in the vapor canister. Without this occasional regeneration the charcoal in the canister would become saturated and no longer able to function as designed.

If you want to go a step farther than a second solenoid is installed at the fresh air draw port on the vapor canister. This lets the system do a OBD2 test. It is testing for leaks. It commands the solenoid to open at the engine but also commands the solenoid at the vapor canister to close. A vacuum is now created as the engine is trying to draw air/vapor but the vapor canister is closed. As a result a vacuum is created in the fuel tank. The sensor I showed is measuring this condition and reports back the status. If all is well than a certain amount of vacuum will be created based on time and the level of fuel in the tank. If you accidentally left the fuel filler cap off than naturally the tank/ system would no longer be sealed and no vacuum would occur. Same situation as if the vacuum tube to the engine was cracked.

The OEM setup does the OBD2 tests as well. The connect & cruise system is a simplified version. It may be all that is needed. The OEM system just adds a bit of diagnostic/ reporting ability.

I have to do the OBD2 version so have purchased all the EVAP components so the leak down test will be performed. From what I learned out about OBD2, only stock ECUs set the readiness flags for EVAP. Even the GM EROD engines do not. For NJ emissions it needs to pass ODB2 so I need a stock ECU which also means I need a standalone harness and not a GMPP harness.
 
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Ken Roberts

Supporter
One solenoid should be at the engine and the second one will be back at the fuel tank near the vapor canister. Perhaps the second one is also incorporated in the vapor canister. I will investigate this further.

The E-Rod is what I meant instead of, as I called it, connect and cruise.
 
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Ken Roberts

Supporter
Just make sure that whatever year tune you use as your operating system that all parts are pulled from that year. IE…..the ECM, FPCM and EVAP system parts.

From your picture I see that the vent control solenoid is independent of the canister…..:)
 

Joel K

Supporter
This post covers mounting the bottom fuel tank closeout panel fabricated back on post #263. Starting in 2018, all SL-Cs are delivered with the extended foot box and that leaves about a 6” uncovered portion at the back of the fuel tank area. I wanted to close this area up similar to prior year models.

I originally designed the panel to be welded in, but couldn’t get anyone to come to the house to do the work. Then I started to learn how to weld, but not ready to tackle this particular job which requires expert welding skills. So at this point decided to attach it with panel adhesive and screws and move on.

Pic of close out panel trimmed up to clear existing welds on the bottom of the chassis…
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First step was to drill 1/8” holes in the panel. The panel then becomes the pattern for the holes in the frame. Pic of the panel with initial 1/8” holes..
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I drilled the holes offset from those for the rear close out panel to help preserve the integrity of the lower rear chassis cross member. You can see the staggered positioning in this pic…
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First installed the cleco fasteners to the rear and interior frame rails…
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Decided to use M6 flat head screws in the panel since a 3/16” thick panel is thick enough to absorb the height of the screw heads. Used a 90 degree chamfer bit in the panel which matches the countersink angle of the screw heads…
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Pic of the 90 degree flute I used from Harbor freight. It costs $1.99. It works very well in a drill press with some cutting oil. It does not work all that well in a hand drill…
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Tapped the holes in the frame rails and temporarily installed the panel. Pic from underneath, the flathead screws work really well for this panel. I wanted the bottom to be smooth and happy with the result…
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Pic from the top…
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Before I install the sound deadening, I’ll attach and seal up the panel with RTV silicone. Will also install 1.25” silicone rubber plugs in each sub compartment. Just in case the area fills up with water or fuel.
 
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Joel K

Supporter
A minor update, but for the sake of completeness I am documenting this. One of the requirements to register a component car in NJ is emissions compliance. If using an engine newer than 1969, you need to install all available emissions equipment for the engine as when it was available. And if it is newer than 1996 it needs to pass emissions.

In my case, this car will need to pass ODBII emissions and have a full EVAP system. I’ll cover the workings of the EVAP system in a future post. This post simply covers the install of the EVAP canister.

The documentation for the dry sump LT4 engine states the engine is a replacement for the 2015-2016 ZO6 Corvette. So to be consistent I purchased the EVAP components for that year car. Here are the GM part numbers below:

Vapor Canister - GM# 22785596
Vapor Canister bracket - GM# 20958879
Vapor Canister Hose - GM# 22850205
Vent Control Solenoid - GM# 13576005

Here is a pic of the components…
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The vapor canister connects to one of the fuel tank vents/rollover valves and the vent control solenoid. It also houses the fuel tank pressure sensor which is used during the EVAP leak down test. Also purchased the factory mounting bracket due to the odd shape of the canister vs. fabricating up a custom bracket.

The bracket has some angled extensions to bolt it to the Corvette inner fender. I decided to trim those sections in order to mount it flat inside the fuel tank area against the frame…
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Further modified the bracket by splicing in an additional strap section. This moved the location of the bolt used to tighten/release the canister strap so it is easily accessible. The existing bolt is in the back corner and would be very difficult to get to in the case the canister needs to be removed. Used .03” thick stainless strip which worked well. Strong yet easy to shape and inexpensive. Pic of this modification…
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Installed the assembly next to the fuel tank…
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A wider angle pic…
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Since the vent control solenoid’s purpose is to allow fresh air into the fuel tank, it will be mounted outside of the fuel tank area so the hose will be routed through the rear fuel tank close out panel later in the build.

I’l find an exact place for it to be mounted after the return line cooling tubes and battery tray are installed. Time to move on to the engine compartment.
 
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