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Learning how to build Lotus Seven replicas...together!
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PostPosted: July 3, 2019, 6:09 pm 
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Joined: June 25, 2019, 1:25 pm
Posts: 28
chrisser wrote:
Driven5 wrote:
I think your original thoughts are on the right path, and would probably try not overthink it too much beyond that.

Plenty of 7's (including Caterham's) have oil pans hanging lower than the frame and run up to 6" or so for frame clearance because of it. Probably the most common tire sizes have around a 23" diameter. So if you don't let the oil pan hang below the bottom of the frame and trade up to common 215/75-15 or 235/75-15 all-terrain tires, then that should immediately put you in the 8-9 inch clearance range without even changing anything else in the suspension.

The roll centers moving up with the sprung mass should be fine, and will mostly just help keep body roll in check. The only real geometry concerns I'd see are scrub radius decreasing and trail increasing in the front. Running a lower offset wheels should correct the scrub radius, and the mechanical trail increase shouldn't cause any significant issues. Obviously there are a few other (potential) tire to body/frame considerations to watch out for, but that just means a bit of planning ahead.

Alternatively...Jeep Cherokee donor? :mrgreen:


I haven't decided on uprights yet, although leaning towards front S-10 blazer all the way around or Solstice. I like that the Solstice are aluminum, but I also like that the the blazers come off a vehicle designed for 4wd. Blazers also came with 15" wheels IIRC. I think the stock Solstice brakes require a 16" wheel minimum (although there are obviously workarounds). Thinking I should maybe have longer control arms to preserve turning radius with larger diameter tires. I'll have to draw it out first.

I do plan on using the Cherokee xfer case. I have the NP242 in mine which has a differential to give what is essentially AWD and then has full time 4wd, full time 4wd lo and 2wd. I rarely, if ever, run mine on the differential, but it doesn't have enough power to spin the rear wheels unless I'm in a situation were 4wd makes sense. That could be different in a lighter vehicle with more power.

Still undecided on the drivetrain, but I'm leaning towards the Cadillac 4.9 because of the light weight and simple design, mated up to an AR5 out of a Colorado pickup.

But, at least in my mind, the drivetrain is the easy part. The rest of the package needs to be sorted in my head first.


Fun fact... the solstice front and rear spindles use the same hub assembly- both can be driven. I'm currently in the process of determining how to use cobalt hubs on the solstice spindles so that I can use 4x100 wheels and smaller caliper/rotors.


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PostPosted: November 25, 2019, 8:48 pm 
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Joined: June 21, 2010, 9:02 pm
Posts: 44
Location: Spencer WV
So this project is still alive. Some slight changes...

I've started acquiring some parts. Most notably a Solstice upright. Also been poking around CV axle and hub catalogs.

I'd like to use the front and rear independent differentials out of Explorers, circa 1996-2004 (that spans two generations but there's a fair amount of commonality). They seem to be more common than "standalone" GM and are aluminum. A lot of the GMs are integrated into the oil pan and use it to support part of the axle.

Don't know if any of you have the following knowledge, but if you do, the answers would save me a lot of experimental parts buying...

In the hub and CV axle catalogs, the spines of the outer joint are listed by spline count, with no diameters given.

The Solstice hubs have an uncommon bolt pattern and a different spine count than the Explorer CV axle outers. But there are many other GM hubs that will fit the uprights. I'm hoping I can find a hub that fits the uprights, has a common bolt pattern (something close to 5x4.5 ideally) and either fits the splines of the outer CVs of the Ford axles, or will take a GM outer CV that will fit the splines on the axle shaft.

So that's my question - if a CV, for example, shows as a 27 spline Ford and the hub shows being a 27 spline GM, are those two 27 splines the same? The hubs for old Buick Centuries (and Cadillac Allantes, oddly enough) are within a mm of the hole and bolt pattern in the uprights, have the metric equivalent of a 4.5x5 bolt pattern on the flange and have a 27 spline hole. The Ford front CVs have a 27 spine shaft. If those shafts fit those uprights, then I'm set on the front.

Likewise, are there a small number of spline counts for the axle shafts themselves and are they cross-compatible between the manufacturers? I can't find specs on the Ford rear CV axles but I believe the outer splines are a count that I can't find a corresponding GM hub to accommodate. Was hoping I could pop front outer CVs off and put them onto the back shafts, or find another outer with 27 splines and replace the outers. That would sort out the rear, all with OEM parts.

I'm thinking there is probably a fair amount of commonality involved, otherwise the CV and axle manufacturers would go bonkers and there have been so many cross applications in the last few decades (like GM switching to Ford-patterned T5s and Jeep using GM engines) that at least some of the parts can be swapped. The question is which ones.

Worse case, I'll either head to a wrecking yard or start buying individual pieces and seeing if they fit together.


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PostPosted: May 15, 2020, 4:37 pm 
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Joined: June 21, 2010, 9:02 pm
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Location: Spencer WV
Since my last post I've been doing a lot of thinking and research and started aquiring some parts.

Have a t5 out of a ~2000 V6 Mustang and the double-bubble bellhousing with the GM 60degree V6 pattern.

Couple of front uprights to evaluate (Solstice and Explorer).

Was originally going to use a Northstar, but they're getting hard to find and although the bugs are worked out, they're very expensive to rebuild. They also run best on premium, need about a $600 ECM/reprogramming for a M/T and the flywheel situation is sorta vague although probably the Fiero guys have it figured out. 4.0 shortstar has the same issues with less displacement.

Considered the Cadillac 4.1/4.5/4.9 and, while I love that engine, they are even harder to find these days than Northstars. Haven't been produced since 1995 - can you believe that was 25 years ago?

Also looked at the GM 60-degree V6 family - 2.8/3.1/3.4/3.5. The DOHC versions are getting hard to find. I thought about mixing and matching something but in the end, there's enough for me to do without building some Franken-engine. Plus, they're the same price from the junkyards as a 3.8 and as much as I like the idea of a 60degree V6, I like the displacement and reputation of the 3.8 more.

Almost went with the 3800 SC L67. I still may go that way, but the premium gas deal was kind of a dealbreaker and they're also getting harder to find although not as bad as the Northstar. Also needs ECM programming to run M/T and the flywheel situation is also a bit vague although less so than the Northstar.

Ended up picking up a 3800 out of a ~02 Park Avenue. Plentiful, runs on regular gas, 200HP/225FTLbs should be plenty of oomph even with the extra weight I'll have. Off-the-shelf flywheel (F-body) and ECM. V6s are short and I could always swap out the pieces to convert to the 300HP L67 if I need moar power. Plan is to try and run it off a bone-stock Camaro/Firebird 3.8 MT ECM. Right now it's just pushed into a corner until later. Going to try to run the FWD intake since that gives me the option to upgrade to the l67 later but worse case I can go with the F-body intake.

Eventual plan is to get a transfer case out of an XJ Cherokee and convert it to divorced (I'll have to machine a few parts), but since I already have one of those in my DD, I can get all the measurements off it. Basically I'm trying to accumulate the bare minimum of parts I need to answer all my questions and make some basic decisions before I commit to building, but so far I think I'm on the right path.

I need to get my differentials so I can get some width figures and then I should have enough info to work out the front suspension design and have some estimates of things like ride height, tire/wheel choice, wheelbase, etc. I already have some ideas on tires/wheels I want to use, and that's going to drive my final drive rations, so that's a bit of a circular reference, but I think I'm close with the tire diameter and that should get me close enough for the final drive. Worse case, I can always swap gears.


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