1969 MGB GT Build Log

Hello everyone!

I began a thread on this car on MGExp and I won't bother rehashing everything I have over there, but the short version of it is this. I bought the car about 3 years ago after graduating college as nothing more than a pretty clean shell with plans to completely redesign the front and rear suspension, engine swap it and build what I would like to think the engineers then would have liked to build now. Over the last few years a lot of work has happened in fits and starts as I grew my collection of tools, did design work and worked on things when I could. During that time my professional career in racing has gotten off the ground, I've gotten married and some health stuff, which took center stage for my wife and I, is starting to get resolved. The last few months I've been posting on the MGExp forum my progress on the car has been propelled forwards. Having the accountability to update people, whether they care or not, makes a huge difference. Much of what I post though I think is better suited for this forum and so for a while I'm going to post to both while I figure out where to go from here. To get up to speed I'd recommend reading through the MGExp log here. (Please let me know if I shouldn't link this directly)

The overall goals for the car are front and rear independent suspension with plenty of adjustability, a K series engine and a manual transmission and a total vehicle weight of 2000 lbs without a completely stripped interior. I don't have a huge need for anything be to super original to the car obviously. The car is not intended to be a track-only car but I'd like it to be comfortable there. This means making sure the brakes and cooling are up to the task of multiple laps.

The plan is to start on the rear suspension. This project is as much an exercise in project management as engineering and for this to not take forever I need to focus on one small assembly at a time. I want independent rear suspension and a front suspension designed to work well with the rear. I spent a few months designing the kinematics and few more months evaluating different subframe and control arm layouts in CAD/FEA to dial in the compliance as best I can. Both the front and the rear have the kinematics drafted in, but the rear is pretty much complete. The car will use S2000 uprights and a Ford 8.8 IRS diff in the rear. I just recently this week found a way to get Miata hubs to work with the S2000 uprights, and so it will have 245/45-r15 tires. The track is 55.5 inches which is very close to a Miata and so axles should also be usable with off the shelf options. The design of the rear suspension is nearly complete and the manufacturing is underway. Here are a few photos from along the way so far, I am going to try to update once a week. Let me know if there are things you would like me to focus on, or if you have any questions. Feedback of any kind helps keep this project going.

Also, this project needs a name, suggestions accepted.

Now I get to follow the build on two sites. Works for me.

As someone who owned an MGB GT for over 40 years, I like where this is going.

Excited to follow along!

Looking forward to your build!

Stop tempting me with this IRS setups!

The miata/8.8 axle option kind of fell through based on price, so I've been looking into other options. Does anyone know if an S2000 housing (to get better mounts and rear cover) with an NB miata torsen or clutch lsd would work? If so I can just run the stock miata axles which would be a lot cheaper and a bit lighter. The only difference on the stubs between the S2000 and the NB is the 26 vs 28 splines, the seal and the length and everything else is the same I believe. Alternatively I could use the 1.8 torsen and an s2000 rear cover and just work something out for the front mounts even if it is not ideal.

Still catching up on the original build thread, but this is super-cool!

Very similar idea to what I have in mind for my '73 BGT (still waffling between K series, Duratec, and possibly LFX/J-series on the grounds that since autocross is central to me, I don't need more power but having plenty of torque available at low revs is handy), but unlike yourself and Nukem all I have to show so far is a car that I want to finish baselining to stock-ish so I know what annoys me, and some good intentions. Looking forward very much to following along!

Anyhow, thanks for taking us along for the ride!

Nukem said:

Stop tempting me with this IRS setups!

As deep as you're in with your build, why not a little further?  Have you driven yours on the street? Mine is admittedly in need of fresh dampers, but it's hard not to notice over any significant bump that the rear unsprung weight is ~10% of the car...

This is awesome, I'm doing a Honda K20 swap in my MGB. My Instagram is @mr.byoung if you have one, I'd love to follow the build. I am building a cantilever rear suspension with the stock axle but would like to do irs eventually. I'm wanting to do similar with a street car build ready for the track.

Nukem said:

Stop tempting me with this IRS setups!

Do it... I've taken the last week to get some other things done to prevent burnout on this, but there is always room for scope creep. Your car is similarly over the top. I've got something very exciting coming home Friday too to get a bit distracted by. I'll post pictures when I get it uncrated.

Missed this earlier! 

DanielN said:

The miata/8.8 axle option kind of fell through based on price, so I've been looking into other options. Does anyone know if an S2000 housing (to get better mounts and rear cover) with an NB miata torsen or clutch lsd would work? If so I can just run the stock miata axles which would be a lot cheaper and a bit lighter. The only difference on the stubs between the S2000 and the NB is the 26 vs 28 splines, the seal and the length and everything else is the same I believe. Alternatively I could use the 1.8 torsen and an s2000 rear cover and just work something out for the front mounts even if it is not ideal.

IIRC the 2004-05 Mazdaspeed Miata used the S2000 splines in the diff.

As for track width, you're definitely going to need some bodywork. This is stock Miata track width under a GT with 195/50-15 tires on a +45 wheel.

With about 4" of flare.

My car sits at 2400 lbs wet with an LS1 and a T56. Miata front suspension (no separate subframe), rear axle is a GM 8.8 stick.

Keith,

Your car was no doubt an inspiration for this build just FYI. I think that's probably true for a lot of builds in here though. The possibly absurd track width is going to require some pretty extreme surgery to clear tires, but that's very visible in the cad. If the mazdaspeed axles were more available I'd use those with the s2000 diff and be done, but as far as I know they are the closest thing to unobtainium, is that true?

While we are at it, there is no way that cover in front of the shifter is covering a location the shift lever can be moved to?

Glad to hear my build is remembered :)

I don't know how unobtainable the MSM axles are these days. We used to have a pile of them from V8 swaps, not sure where they are now. I'll see what I can find out. It may be hard to buy a set without also buying the differential, as they're kinda a matched set.

I've never tried to shorten the trans. It would certainly be worth popping that cover off.

Last night I bit the bullet and ordered a lot of things I still need for the rear suspension and drivetrain. All the mechanical parts have now been purchased. I ended up buying an S2000 differential and aftermarket axles from Insane shafts. I also bought some stronger miata hubs, the rear powerlite brakes and soft lines, all the Mercedes spherical bearings and cups from SPC. I still needed the right side knuckle and upper ball joints so those have also been ordered. Going to be very exciting over the next week or so seeing all these parts come in. It's becoming real.

I still don't have a transmission so the complete drivetrain is not in, but I think I will use the NA generation 5 speed. That has an easily relocatable shifter apparently that just requires shortening the selector shaft and moving the mounts forward. It retains all the normal features without modification. That will help a lot in getting the engine as far back as possible without ruining the ergonomics in the driver seat. 

The laser cut sheet metal parts order for brackets etc. still needs to go out but that needs some more design work before it is ready and I need to find a way to turn the lower ball joint taper cups. The final pieces at that point are the fasteners and poly mounts. Budget-wise everything is still looking to be ok, so a slight sigh of relief there.

To follow up: all of our axles were sold to SNS Miata Parts about three weeks ago. They may have some MSM units. 

The engine is here! Hopefully I can test fit it in the engine bay this weekend and see what we are up against. The opportunity to buy it came up and I couldn't pass on it.

What, another MGB build?

Alright, fine. I'm in.

Still waiting on getting a whole bunch of parts in but I did get a chance to hang the engine in the engine bay. I know it's as empty as it will ever be, but honestly it doesn't seem like to tight of a squeeze. I'm a little worried about how to get it low enough, although I didn't have the engine canted over when I put it in for a trial. The oil pan is very low when the engine is at the height to clear the hood even with the engine hard to the back. I have nothing against a hood bump to clear, but I'd still like to get the engine as low as possible. I pulled off all the harness, accessories and clutch which required a couple trips to the store to get the right sockets. 

I wanted to confirm the clearance to the fuel tank so I scanned that in. Took a while to get it cleaned up and into the cad, but it should clear ok. I don't think I will use this specific tank though as it has been pretty damaged both from impacts under the car and when the car was slightly rear-ended. 

Once parts for the control arms and upright assemblies come in this week I will start jigging the control arms together and assembling the uprights. Once the diff comes in I'm going to see how it fits in the subframe in real life and see what I want to do for mounts. I may just scan it and work with it that way. It's the stock s2000 diff so it has the nicer forward mounts compared to the miata part.

I confirmed the axle plunge in Susprog3d and I think I'm probably alright. I don't know the max plunge available on the mazdaspeed miata axles though. I can always limit the bump to 2 inches if I need to.

Not a lot of progress on any particular item this week, but lots of little things and all in preparation for lots of parts arriving in a few days. The final thing is a change in tire size. 245/45-15 is not a size you can actually buy tires in. A bit unfortunate I didn't bother checking until now. The width is honestly getting a bit silly and so I've decided to go down to a 225/50-15. It's a very similar diameter to the stock tire, lots of sidewall still with the 50 aspect ratio and there is quite a bit more tire choice. I can go the re-71 direction for the street, proxes for the track or even throw a hoosier slick on if I feel like it. I think it looks pretty nice still from what you can gleen from this half-there picture.

Any consideration to 245/40/15?

I'm a proponent of silly tire width and played the same mental game re: tire availability. Eventually settled on 245/40/15 front and 275/35/15 rear. Nankang AR-1s are the only thing other than Hoosiers that are available in the 275/35/15 AFAIK, but the 245/40/15 readily available.

Joining in a little late, as usual for me. It's nice to see another MGB swap thread going--there are several of them here and every one of them brings new ideas forward.

I get the sense that maybe you did some FSAE in college?

245/40-r15 is for sure an option still, but fitting them under the car and still fitting a non-pushrod damper is probably not possible. @Carl, FSAE is definitely the root of all of this, I can't stop.

Assembled the first rear upright last night and ruined a wheel bearing. I forgot the circlip which while probably not the end of the world it is eclipsed by the second mistake. The stronger hubs are much thicker than the OEM parts and so the studs contact the upright before the hub bottoms out. Oops. I think a spacer will fix this but I need a chance to confirm the hub geometry relative to the S2000 part everything was originally designed with. The bearing works great though, it has an appropriate press fit and fits perfectly. I'll press the hub out tonight and see how far off we are.

Did not get to do much this week because my GTI decided to do VW things. The timing seems to have jumped a tooth even with the updated tensioner, and the turbo is dumping oil into the intake. Have to take time to fix those things. I did receive a bunch of the parts though to complete the rear suspension and got a chance to assemble them temporarily I only need a 1mm shim to clear the upright nicely with the back of the hub. The axles did fit nicely in the diff with no issues and are the perfect length so that was a win. Still waiting on all the parts from Summit, so I can't start assembling control arms until I get those in anyway. If the GTI didn't try so hard to put itself out of it's misery this weekend would have been getting the laser cut order out, but it had other plans.

I'll keep this short because there isn't a lot exciting to update. Lots has been going on making progress but much of it doesn't make for very good photos. I have most of the laser cut parts on order and they should be here within the next few days. I also went part by part and selected all the hardware and got that ordered. I still have a small collection of things to order but more and more is coming in. The last two weekends were mainly spent repairing my GTI which is now done, luckily it didn't completely jump time and so some new chains, tensioner and guides and it's back to running better than before. 

The calipers arrived and look incredible. Once I get a whole corner assembly together I'll get some nice photos of it. Still need to order the shims to deal with the thicker than expected hub flange and stud clearance issues. I weighted a lot of parts individually and the most up to date rear suspension weight with wheels and tires is 260lbs with 70lb of unsprung weight per corner. I'm pretty happy with that.

The final piece has been on the project management side, planning out the work for the next few months which while necessary is very boring and doesn't make for fun-to-share content. Next up is completing the subframe all the way through to paint before moving on to control arms. I already have lot of parts ready to work on for this upcoming weekend but I'll work this week on getting the remaining parts ordered and in some cases designed (diff mounts) for the following weekend where we can hopefully prep and paint it. Importantly though, this project has not ground to a halt, it's just in a phase that doesn't make for good content.

In reply to DanielN :

Engaging to share is as important on your side as ours, but I am curious how you're doing project management.

The tools I used for organizing software projects seem not quite right and also too heavy/expensive for my car stuff. I've dabbled with Trello and should probably just get better with spreadsheets. Still trying to find a solution to help organize timelines, dependencies, etc. I find there's a fairly low threshold for time and effort on these tools before I just wander off. I know you're working on your project management skills with this endeavor, and I suspect I'm not the only one who's curious about your tools and approach. But documenting that is also overhead, so no worries if you don't care to wade into it.

In reply to Jesse Ransom :

If I find a good solution, I'll let you know. I have a couple different spreadsheets tracking purchases and priority, another tracking tasks, none of it I'm particularly happy with. I use MS Project at work which is a very nice piece of software, but probably both too complex and expensive for what I want here. I've tried most of the SaaS online PM software and none of them seem quite targeted at projects like these. They focus on infinite integrations with slack etc but I want a few core things. The ability to give both forward and backward dependencies (and more complicated dependencies than a lag ie. this has to happen after this but can happen anytime as long as it happens before this date), track budget (not just hours, but parts and services) and address things like lead times vs working hours. It has to be less time though overall than just doing it in an excel sheet which is not something I've found yet. Some of the biggest challenges so far have been around reducing the number of orders and making sure you get all the parts that need to come from the same vendor designed even if they aren't all for the same exact system.