Newbie here, hello and some questions

[Rich]

Hi,

I've been lurking on GT40s.com for years, before I ever knew what an SLC was, but decided to break my silence today. I've been interested in building a mid-engined component car for at least 10 years.

I currently own a Lotus Elise that I've completely pulled apart and put back together twice over the last 3 years. It has an aftermarket TVS blower on its tiny motor and is quite fast! But it's tiny, and is a bit twitchy, and I love the way it drives.

Anyhow, I am considering building an SLC for my next car, although the 917 is my all time favorite car and RCR does make a nice kit, and an LS motor fits, I am guessing that the SLC is a better actual car.

Questions regarding the SLC:

I've never seen the method of construction for the SLC's chassis discussed, but most aluminum monocoque chassis I've seen or read about were made by bonding sheets and/or extrusions with epoxy and rivets since you can spread loads over the entire interface between bonded components, and retain the annealed strength of the original materials. My understanding is that SLCs are constructed of TIG welded sheet aluminum; how does this compare for fatigue and strength, specifically around the welds, over time to a bonded aluminum chassis?

What is the ride height range for acceptable suspension geometry? And are lowered uprights available?

Can someone post a picture of the underside of the car? I am guessing it is flat, but I've never been able to find a picture. Has anyone attempted to make ground effect tunnels for the rear underbody work, or are there frame components in the way?

What are common options people generally get when ordering a kit?

I'm guessing the grazziano transaxles are like $10Kish +; how do these compare to inverted Porsche transaxles for durability and feel? The Toyota C6x that is in my Lotus is far from my favorite transmission I've had (favorite would be on my 1st gen miata!) and I'd like my next car to have a more rewarding transmission.

I'd probably do an LS376, and this would probably see some track use. Would you recommend a dry sump for a streetable track car, or would an accusump and baffled pan be sufficient? I'm not too familiar with LS motors and their oiling.

I think that's it, thanks for reading!

Rich

 

[Jack]

Hi Rich,
Welcome to the forum. Lots of good info to be found here.
The SL-C chassis is what I have termed "jewelry". Other than a slightly
dropped floorpan it is flat on the underside. There will be no issues with fatigue.
Not the typical thin aluminum panels that are riveted and bonded. The SL-C chassis
is well engineered and constructed. You need to go to see Fran Hall at RCR.

 

[Will Campbell]

There are several SL-Cs in your area, including mine. Contact me via PM if you want to come over and see mine.

 

[PeteB]

On the lowered uprights question - stock it's only got 4-5 inches of ground clearance. I don't think you could actually drive it if you made it any lower.

 

[Cam]

There are a few good photos of the aluminum frame floating around. They are boxed sections of aluminum and sheet. Welds are localized so the heat affected zone shouldn't be very large. Welding only affects material strength locally and not the entire piece. Based on what I've seen I don't believe a heat treating of the entire frame is necessary, though I don't know what grade the material is or what the designed margins are.

As others have stated, underside is basically flat with the exception of the seat area if you opt to go with the dropped floor pan. It's optional so if you want a completely flat bottom don't order that. The engine compartment is open at the bottom so this area is exposed to the ground. At the rear both the street and race versions have a diffuser though the race version appears to be more functional (to me). At the front the street splitter can be modified with tunnels which are already incorporated into the race version. I know a few folks have added close outs to the bottom of their engine compartment to keep airflow undisturbed beneath the car, just need to watch for heat build up.

Common options - not sure there is such a thing! How deep are your pockets and what do you want the car to do/look like? The latest revision of the website does a great job showing what the options are. If you go through the various build threads some people have listed their options near the beginning. I have a thread back when I was debating what options to go with and I stepped through some of my thought process back then.

Can't comment on the Graz VS Porsche trans as I don't have any direct experience. I would say you're comparing an oem transaxle which has thousands of durability and test hours behind it versus one which has been flipped and modified to make work (if that's the Porsche option you're going with).

The debate of dry sump, wet, or Accusump has been going on for quite a while over in the LS engine forums. These motors do seem to be particularly sensitive to high g sustained turns. I believe the other Cam is running a wet + Accusump in his 376/480 and he frequently hits the track. I'm planning on very limited track use (1 per year maybe) so I opted to go wet with no Accusump. I am however planning to go with a decently baffled oil pan and overfilling oil by 1 qt. I won't be driving the car hard if I take it to the track.

Good luck!

 

[Aaron H.]

Underside photo...

 

[Cam]

Aaron - looks like you strong armed that into the air! Did you coat the underside with something?

 

[Rich]

Hi Rich,
Welcome to the forum. Lots of good info to be found here.
The SL-C chassis is what I have termed "jewelry". Other than a slightly
dropped floorpan it is flat on the underside. There will be no issues with fatigue.
Not the typical thin aluminum panels that are riveted and bonded. The SL-C chassis
is well engineered and constructed. You need to go to see Fran Hall at RCR.

Thank you!

There are several SL-Cs in your area, including mine. Contact me via PM if you want to come over and see mine.

I will soon! Where in NoVA are you?

On the lowered uprights question - stock it's only got 4-5 inches of ground clearance. I don't think you could actually drive it if you made it any lower.

Thanks! My Lotus is at ~120mm or about 4.7 inches of ground clearance, and I don't really have any clearance-related issues with anything but the steepest of driveways. That is close to the bottom of the sweet spot for geometry on that car, before you start looking at doing long balljoints or dropped uprights.

I was primarily curious if the suspension geometry was compromised for street ride-heights (which having dropped uprights available would indicate) or if I wanted to take the thing racing for serious and wanted to drop it a bit more, it would still articulate without excessive static camber et. al. It sounds like the SLC is less compromised than my car. How bad is it with ground clearance? It has a longer snout than I am used to, so I am curious how often and badly people scrape the front.

There are a few good photos of the aluminum frame floating around. They are boxed sections of aluminum and sheet. Welds are localized so the heat affected zone shouldn't be very large. Welding only affects material strength locally and not the entire piece. Based on what I've seen I don't believe a heat treating of the entire frame is necessary, though I don't know what grade the material is or what the designed margins are.

As others have stated, underside is basically flat with the exception of the seat area if you opt to go with the dropped floor pan. It's optional so if you want a completely flat bottom don't order that. The engine compartment is open at the bottom so this area is exposed to the ground. At the rear both the street and race versions have a diffuser though the race version appears to be more functional (to me). At the front the street splitter can be modified with tunnels which are already incorporated into the race version. I know a few folks have added close outs to the bottom of their engine compartment to keep airflow undisturbed beneath the car, just need to watch for heat build up.

Common options - not sure there is such a thing! How deep are your pockets and what do you want the car to do/look like? The latest revision of the website does a great job showing what the options are. If you go through the various build threads some people have listed their options near the beginning. I have a thread back when I was debating what options to go with and I stepped through some of my thought process back then.

Can't comment on the Graz VS Porsche trans as I don't have any direct experience. I would say you're comparing an oem transaxle which has thousands of durability and test hours behind it versus one which has been flipped and modified to make work (if that's the Porsche option you're going with).

The debate of dry sump, wet, or Accusump has been going on for quite a while over in the LS engine forums. These motors do seem to be particularly sensitive to high g sustained turns. I believe the other Cam is running a wet + Accusump in his 376/480 and he frequently hits the track. I'm planning on very limited track use (1 per year maybe) so I opted to go wet with no Accusump. I am however planning to go with a decently baffled oil pan and overfilling oil by 1 qt. I won't be driving the car hard if I take it to the track.

Good luck!

Thanks! I found some better pictures of the chassis, it looks like a hybrid between welded square aluminum tube and a monocoque, with most of the welds between thick chunks of aluminum tube. I have a buddy that had the welds fail on one of the upper a-arm mounts in his FF roadster while driving and he experienced a catastrophic failure; since then I am extra weary about the way things are tacked together. I'd imagine that if this were a common point of failure, I would have read about it here.

FWIW, when you heat 6061 over ~400 or 500 degrees F (e.g. welding), if the heated area was T6 or T4, it is now T nothing, so the strength of the de-annealed aluminum is 1/2 to 1/3 what is was when heat treated previously. I don't know what alloys are used in SLC, nor do I pretend to know much more about metallurgy than that, but presumably the tube sections and welds are big enough to make this a non-issue.

Thanks regarding the oiling, I'm in the early stages of planning but I want to make sure I know weaknesses so I can plan around them.

View attachment 83093Underside photo...

Awesome, thanks! Has anyone covered up the void below the rear sub-frame? And are you just holding the car up in the air with one arm while snapping a photo with the other!?!?!

Aaron - looks like you strong armed that into the air! Did you coat the underside with something?

Ditto!

 

[Fran Hall RCR]

Contact Raver Motorsports and ask Dan , the SLC driver about his chassis strength feelings after having a 125mph plus solid impact with the wall at NJMP....

 

[Alex]

Thanks! I found some better pictures of the chassis, it looks like a hybrid between welded square aluminum tube and a monocoque, with most of the welds between thick chunks of aluminum tube. I have a buddy that had the welds fail on one of the upper a-arm mounts in his FF roadster while driving and he experienced a catastrophic failure; since then I am extra weary about the way things are tacked together. I'd imagine that if this were a common point of failure, I would have read about it here.

FF Cobras are notorious for UCA mount failures - if the UCA seizes up (not greased regularily, pivot points not loosened during alignment, there was also a bad batch at one point I think), instead of doing its job the UCA stays solid and the mount becomes the bending point....if you started bending a tab up and down, no matter how it's welded, it will fail.

 

[PeteB]

Thanks! My Lotus is at ~120mm or about 4.7 inches of ground clearance, and I don't really have any clearance-related issues with anything but the steepest of driveways. That is close to the bottom of the sweet spot for geometry on that car, before you start looking at doing long balljoints or dropped uprights.

I was primarily curious if the suspension geometry was compromised for street ride-heights (which having dropped uprights available would indicate) or if I wanted to take the thing racing for serious and wanted to drop it a bit more, it would still articulate without excessive static camber et. al. It sounds like the SLC is less compromised than my car. How bad is it with ground clearance? It has a longer snout than I am used to, so I am curious how often and badly people scrape the front.

Highly recommend the hydraulic lift kit for a street car. I can't get into my driveway without lifting the front. I've been pretty good at watching where I'm going and raising the front to get into parking lots, speed bumps, etc, and haven't had any bad scrapes with the front splitter. The lowest point on my car are the bolts for the seats - I've scraped them several times in uneven parking lots. The sound is horrendous.

 

[Rich]

Contact Raver Motorsports and ask Dan , the SLC driver about his chassis strength feelings after having a 125mph plus solid impact with the wall at NJMP....

I found their post on Facebook where they describe the crash and put up some pictures. It will definitely buff right out . But seriously, it looks like the chassis did what it was supposed to.

FF Cobras are notorious for UCA mount failures - if the UCA seizes up (not greased regularily, pivot points not loosened during alignment, there was also a bad batch at one point I think), instead of doing its job the UCA stays solid and the mount becomes the bending point....if you started bending a tab up and down, no matter how it's welded, it will fail.

Makes sense, and I think I've read that is a failure point for some of the older FF cobras especially.

Highly recommend the hydraulic lift kit for a street car. I can't get into my driveway without lifting the front. I've been pretty good at watching where I'm going and raising the front to get into parking lots, speed bumps, etc, and haven't had any bad scrapes with the front splitter. The lowest point on my car are the bolts for the seats - I've scraped them several times in uneven parking lots. The sound is horrendous.

Good to know, thanks! And maybe fasten a strip of delrin or other strong plastic to the underside of your car next to the bolts?