Joel’s SL-C Build Thread

Joel K

Supporter
Time for the next update. I recently fabricated the Supercharger Plenum Intake extension and it is ready for welding.

The LT4 requires you to relocate the throttle body since in its stock location it butts right up against the firewall and there is no room for an intake tube. Most builders cut out a section of the rear brace/cross member and modify the seatbelt bar attached to the roll cage, but I prefer to leave the frame as-is.

By sliding the engine back 1.5” I now have enough room behind the firewall for a custom supercharger intake extension and think I’ll also be able to change the supercharger belt and water pump without having to remove the engine. The compromise being a little more rear weight bias. Since I am not going to track the SL-C I don’t think this will materially affect the handling of the car.

Originally I was going to use a 4” silicone Cobra-head intake tube but after getting the engine in the car there is just not enough room. After thinking about the approach a bit, I would have preferred to do what the other builders do and use a 120 degree 4” intake elbow but there is still not enough room for that without modifying the chassis due to the placement of the supercharger plenum opening.

To make it all work I decided to fab up a cobra-head style aluminum intake extension thinking it will provide enough airflow to run a stock tune and be compact enough to fit behind the firewall without modifying the chassis.

Here are pics of the actual cobra-head elbow and my protype made out of plywood, duct tape, and aluminum duct material...
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Here is a detailed discussion on the approach....


Here are the raw materials and parts needed to fab up the elbow. Two 2.25” 120 degree elbows, 4” aluminum tube and Holley throttle body flanges...
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Scribed and cut the elbows in half...
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Made the cobra-head shape...
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Fabricated the front and back panels...
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Milled out the throttle body flanges to fit the 4” tubes...
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Joel K

Supporter
Here is a discussion of the fabrication process, this was more work that I thought it would be, but at least it’s ready for the welder.


Here are more pics of the fabrication...

Making the first pattern for the longer throttle body tube out of A/C ducting and painters tape to get a rough form...
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Then due to complexity of the shape decided to fabricate the back half of the tube separate from the front...
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Adding the front
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Now made a pattern out of the two pieces...
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And the final product, hopefully it flows enough air so the engine runs without throwing codes, if not I’ll re think this in 18-24 months when I am in go-cart stage...
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Nice and compact and squeezes in between the supercharger plenum and firewall. There should be enough room even with some sound deadening and heat shield in place....
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Not planning to weld this up for a while since I want to be 100% sure if I will run the throttle body over or under the frame.

Next step will be to fabricate rear engine mounts to accommodate the slightly shifted location of the LT4 in the chassis.
 
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Joel K

Supporter
The next step in the process is to fab up new rear engine mount brackets.

Here is a video and discussion on the topic...

Originally I was simply going to add a 1.5” steel spacer between the stock brackets and the trans plate but it turned out the LT4 stock oil cooler interferes with that approach. Also, the stock rear engine mount brackets placed the engine 1/3” too low. The LT4 oil pan peaked out from under the frame rails which could be an issue passing NJ safety inspection.

I could have ditched the stock oil cooler and added an air to oil cooler, but still had the height issue so decided to make up new brackets

The bracket design needed to move the engine back 1.5” and up about .33”.

What I came up with is a bracket with two 45 degree bends instead of a deeper bracket with a single 90 degree bend.

Paper template...
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Mocked the brackets up out of plywood...
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Standard bracket depth is 1.5” deep...
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New bracket is 3” deep...
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Here is a rear view of the brackets in position...
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Top view...
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The metal is at the fabricators and should be ready next week. Looking forward to finally securing the LT4 in the chassis.

In the meantime I’v been fitting the seats in the car so I can position and install the EPAS steering column.
 

Joel K

Supporter
The next custom item I want to tackle is installing an EPAS steering column, more on that in a following update. My build order is based on getting as much of the time consuming custom work done first, then do the more standard items and get the car to go cart stage.

In preparation to install the EPAS steering column I wanted to fit the seats in the car and align the steering column appropriately before I start drilling holes in the chassis. So a prerequisite is to mount the RCR seat brackets onto the seats and place them in the car.

Here is the first video discussing the seat fitment....

Here is a pic of the seat showing the recline angle necessary to get my 6’2” frame in the car. I actually find the seats very comfortable and in all likelihood will use these seats and add some seat cushion pads to finish them....
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Turns out by using the standard brackets, the seats foul the mounting plate area where the custom track day/side impact bars attach to the floor pan.

There are four mounting holes for the side impact bar mounting plate...
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Standard brackets cover two of the holes...
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Here is the second video discussing the requirement for custom brackets and the resulting fitment...

Thus, a bit of custom work is necessary to bring the seat brackets inboard about .75” per side in order to get the seat closer to the center console and allow them to also clear the side impact bars.

Custom prototype bracket made out of plywood...
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Seat and brackets now clear the side impact mounting holes...
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At this point, these brackets will serve their purpose. That is, to figure out where I will sit in the car so I can align the steering column and angle it properly.

Later in the build, if I choose to stay with these seats I’ll finalize the design and fab them up out of 3/16” aluminum.

Thanks to Howard and the other forum members who provided input on finding a way forward. I always appreciate everyone’s help.
 
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Dan Carter

Supporter
Joel

I’m 6-2 as well and thought I would share. I too am using the stock seats. On the inside of your seat I did not see any reinforcement for the bolts. Perhaps you have one already, but I cut some aluminum plate the shape of that interior oval. It spread my weight over more of the fiberglass as I found it wasn’t as strong as I thought. On the passenger side I had to lean the seat inboard with a minor outboard shim at the floor to help clear the door. Now I did keep that seat more upright for my smaller 5-3 passenger. If you cut a hole for the dive belt, the seats are two piece so be ready to fill that gap. I’m guessing you know all this already, so disregard if you experienced this already.
 

Joel K

Supporter
Joel

I’m 6-2 as well and thought I would share. I too am using the stock seats. On the inside of your seat I did not see any reinforcement for the bolts. Perhaps you have one already, but I cut some aluminum plate the shape of that interior oval. It spread my weight over more of the fiberglass as I found it wasn’t as strong as I thought. On the passenger side I had to lean the seat inboard with a minor outboard shim at the floor to help clear the door. Now I did keep that seat more upright for my smaller 5-3 passenger. If you cut a hole for the dive belt, the seats are two piece so be ready to fill that gap. I’m guessing you know all this already, so disregard if you experienced this already.
Thanks Dan,

On my seats the fiberglass seems pretty thick and was planning to fab up aluminum discs like Kurtiss did on his GT-R build for added support. Here are two pics of what he did.

Here are the discs...
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Then he epoxied them on...
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One area that I am still unsure about is where to cut out the holes for the belts. All the pictures and instructions on mounting the lap belts I have seen show they get anchored behind the drivers hips, but the way these seats are designed that area is where the rear bolt for the bracket goes. Any input and pics you have on how you ran the lap belts would be appreciated.
 

Joel K

Supporter
Here are some before and after photos on how the updated brackets help position the seats in the chassis. Spending time on this helped me better understand where to place the steering column and also get a sense if these seats would work for me regarding how much of an recline I would need to have in order to fit in the car. All in all I think they will work out fine. They certainly look great in the car.

Standard seat.....
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Gentleman’s Seat...
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Gentleman’s Seat with custom bracket...
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Seats can now be mounted more inboard and close to the center console....
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I placed the rear bulkhead just to check seat height and everything seems to line up well. You can also see the side impacts bars in this pic....
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Dan Carter

Supporter
joel

Here are pictures of what I had to do to get as close to a perfect hip pull back as I could. The lap belt obviously comes thru the slot and covers my hips at nearly the perfect placement. I anchored the belt ends to the car frame at angles close to what the belt manufacturer suggests (only a few degrees off). Its not absolutely perfect, but it is a close as I could get with these seats. You can see the cutout for the dive belt.....holds this boy in place. I know I'm not going anywhere if I ever need the belts to hold me in.

I'm
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intrigued by your seat mount design. Got any more picks?

Dan
 
I know you know this, but be sure to test fit the roll bar and spider before making the final determination of where you mount your seats.
 

Joel K

Supporter
I know you know this, but be sure to test fit the roll bar and spider before making the final determination of where you mount your seats.
Thanks John, point well taken. Based on this exercise it gave me a real good sense for where the seats will go so I could mount the steering column. The steering column has a bit of adjustability so for now not planning on permanently mounting the seats. As you recommend, after the body and head-liner is installed makes a lot of sense.
 

Joel K

Supporter
joel

Here are pictures of what I had to do to get as close to a perfect hip pull back as I could. The lap belt obviously comes thru the slot and covers my hips at nearly the perfect placement. I anchored the belt ends to the car frame at angles close to what the belt manufacturer suggests (only a few degrees off). Its not absolutely perfect, but it is a close as I could get with these seats. You can see the cutout for the dive belt.....holds this boy in place. I know I'm not going anywhere if I ever need the belts to hold me in.

I'mView attachment 100265View attachment 100266 intrigued by your seat mount design. Got any more picks?

Dan
Thanks Dan, this is very helpful

Here are some more pics of the design...for now just plywood. I have a few ideas on modifying them somewhat, but won’t get to that till I focus on the interior,

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Joel K

Supporter
Ok, a huge milestone on my SL-C Build. I drilled my first hole in the chassis and actually installed something!

Time to install the EPAS steering column. Having power steering was important to me and I looked at a number of options. I settled on a unit from DCE Motorsport Electronics. The model is call the Pro Street Column with speed sensitive assist. I mainly want assist for parking and driving real slow and there are not many aftermarket systems which provide it. Also, this steering column is very compact and fits the limited space in an SLC quite well.

Here is a pic of the EPAS column, it is very compact...
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Here is the first video describing the system and showing it side by side with the stock column.....

Here is the 2nd video showing the steering column installed....

I had to figure out where I wanted to mount the column relative to the stock column whose hole locations were marked on my chassis. I chose 1/3” to the left and a 1.5 degree angle to center the column in the binnacle and get it center to the wider stock seat. The is a little tricky since the column is not centered between the four mounting holes on the assembly. I must have measured this 10 times. Sat in the car stared at the alignment etc. My first holes needed to be correct!

Since the holes on the steering column are slotted I still have some adjustability if necessary.

Showing the steering column angle...
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Measured this about 10 times...
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Actually drilled some holes in the chassis...
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Machined up 1.25” aluminum hex spacers for the M12 bolts...
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The column mounted perfectly in the chassis....
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Here it is with the wheel bolted on just for kicks, will worry about final steering wheel placement later in the build, but looks pretty good and very happy with the result...
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A few final comments on the steering column.

Since the back of the column is lower than the stock unit, I may need to add a section of 3/4” DD rod and use a pillow block to raise the back of the steering shaft above the pedals. Right now the steering shaft looks like it will be right between the clutch and the brake and may interfere with my feet. A simple fix if needed and I can put the DD u-joint provided in the kit to good use.

The other item is the stock steering wheel and quick disconnect will work fine with this column. I am not sure if this column is collapsible. If not I may use a Momo collapsible steering wheel boss and an different quick disconnect. Either way I think this will work out well.
 
Best of luck paving the way for the rest of us with regards to power steering in the SL-C. It looks like it's going great so far. This has been something I was looking into for the future as well. I used to own a 2010 Camaro 2SS/RS with a decent size cam. Fun car to drive, however, the power steering went out... didn't work for about a 2 years! Never got around to fixing it before I sold the car, but I always wish I got around to fixing it. It was an all around more enjoyable car to drive when it worked so i think you are on the right track! Really enjoying the updates Joel!
 

Joel K

Supporter
Best of luck paving the way for the rest of us with regards to power steering in the SL-C. It looks like it's going great so far. This has been something I was looking into for the future as well. I used to own a 2010 Camaro 2SS/RS with a decent size cam. Fun car to drive, however, the power steering went out... didn't work for about a 2 years! Never got around to fixing it before I sold the car, but I always wish I got around to fixing it. It was an all around more enjoyable car to drive when it worked so i think you are on the right track! Really enjoying the updates Joel!
Thanks for the feedback Cody, power brakes are my next to do. That will be more challenging than the EPAS.
 

Scott

Lifetime Supporter
Joel.

I have a Pro Street EPAS and a Pro 102 tilt column on order. My understanding is that the column is collapsible. I have heard that if you keep the race version at full lock the unit gets pretty hot (max draw of 70 amps). The pro version is rated at 40 amps so it won't get as hot, but you might not want to keep it at full lock. I'm also replacing the rack with one with a quicker ratio.
 

Joel K

Supporter
Joel.

I have a Pro Street EPAS and a Pro 102 tilt column on order. My understanding is that the column is collapsible. I have heard that if you keep the race version at full lock the unit gets pretty hot (max draw of 70 amps). The pro version is rated at 40 amps so it won't get as hot, but you might not want to keep it at full lock. I'm also replacing the rack with one with a quicker ratio.
Thanks Scott. Nice to hear others are planning on using this as well. Glad it is collapsible.

I did speak to DCE when I ordered this and they explained that for racing I may want to upgrade to the race version which is more powerful. From what I remember the motor does not change and the electrics do, but I think you lose the speed sensitive feature. Since this will be a street machine I am thinking this will work ok.

Not sure about the stock ratio with EPAS, but I guess that is easy enough to change after the fact if I think the steering is too slow.
 
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