Keith SuperDork
11/2/08 3:32 p.m.

So, as some of you know, I have a little black MGB GT that my wife is demanding I desecrate. The original plan was to stuff a 302 in there - and then I got involved in this whole LS thing. So that's what it's going to get. And the simple "the MG axle will stand up to a stock 302" plan has turned into a plan to graft Miata suspension underneath front and rear. This is all at the urging of my wife - when it's for her, I'm allowed to spend 23 hours a day in the garage.

So I'm currently at the fun part of a project car - planning. And I'm looking for some input. The Miata front and rear suspension and steering are a given.

Should I go with an L33 (aluminum block 5.3, available for cheep) and stick on the appropriate LS1 parts to make it fit? Or is that not worthwhile by the time you've bought a new serpentine drive (as far as I can tell from the pictures), a new intake and oil pan? I'm looking at the math and I still think it's worth doing. I can get a 16,000 mile L33 for $1000, shipped. Can't do that with an LS1.

The plan was to use a T56 and the New and Improved Cadillac CTS rear end - that's the mix we have in the Miata. But since I'm gutting the entire rear end of the car, I actually have a lot of room to play with. And I'm starting to wonder about a Corvette transaxle. Anyone have any dimensions for these things? Words of warning or support for this part of the plan? Obviously, I'd have to deal with the torque tube and take about 13" out of the wheelbase, but I'm thinking that's gotta be possible.

Ian F
Ian F Reader
11/2/08 4:30 p.m.

A Miata under-pinned MGB has been done. Full Mac-strut front end and everything. I tried searching for the page but had no luck...

I would say go with the LS1/T56/CTS combo. Unless you plan on branching out into MGB V8 conversions, I'm guessing a more familiar combination would go together faster.

Sultan New Reader
11/2/08 4:50 p.m.

Keith, If you build this car can be your adopted kid? I know me being almost 48 would be a bit akward but think of the joy you would get watching me drive this car:-)

Sounds awesome and please do a build blog. Thanks. RS

Jensenman SuperDork
11/2/08 6:26 p.m.

The Miata suspended BGT which was floating around the 'net a while back was being done by installing a full width Miata subframe. Not a good idea since the Miata track is a lot wider and flaring the fenders enough to cover the rear tires would make it look really goofy. I suggest building a custom subframe and control arms, I narrowed a Miata subframe for my stillborn rotary Opel project and honestly the geometry was borderline once I narrowed it. The roll center change would have been rather weird. It was also necessary to cut enough of the stock Opel frame rails away that it would have been simpler to just cut out ths stock rear floorpan and build from scratch. I was working with a Challenge budget, in this case I guess that wouldn't be important.

In the front, it would be simplest to adapt Miata knuckles to the stock B subframe with custom control arms. I wouldn't go Mac strut for height and camber curve reasons, I'd do coilovers. Not to mention there is not a lot of room for struts when you have a V8 and headers. On the subject of headers, there's a lot of V8 Bs on with fenderwell headers. IMHO, that's not a real good way to go. There are some hotrod type block hugger headers that are available through Speedway Motors etc that will keep you from having to whack big holes in the fenderwells.,,_LS1-Tight-Fit-Headers.html?itemNo=9300114?itemNo=ls1%20headers

The 'Vette transaxle would be pretty cool and if you decide to go customsubframe I'd certainly give it strong consideration. Otherwise, there's plenty of room in the B's tranny tunnel for a T56 or similar.

Woody Dork
11/2/08 6:26 p.m.
Sultan wrote: Sounds awesome and please do a build blog. Thanks. RS

I think Keith prefers books over blogs...

Brust New Reader
11/2/08 7:36 p.m.

That sounds like a cool plan. I did the miata thing under my MG midget. I still don't have pictures of the rear (5 1/2 years later), but I ended up building my own subframe and using the miata a-arms. I narrowed the axles with my machinist uncle's help. I do have pictures of the front at I also have it up on the readers rides section. This is my third iteration. Were it my car and I actually wanted to drive it, I'd use the MGB components. I know you prefer to do things on the cheap, but for the pain and effort, I'd go with some proven parts so that you can enjoy the thing without constantly fiddling with it. Get some big brakes, get the coilover conversion that's floating around, and narrow the miata rear subframe using the bigger diff that you guys used for the LS miata. I know it's more expensive, but I've been there and remain- making a custom car inside a production body is more difficult than building a car from scratch. Ever build a ship in a bottle? Anyway, take it for what it's worth. And I'll look forward to what you come up with!


NOHOME New Reader
11/2/08 8:33 p.m.

You are going down a road I have been mapping for osme time.

The Miata suspension graft front and rear is a good idea but will require some serious flares. The best flares for the MGB are off of a old doge omni. Use the fronts flares and swap sides.

Myself, I would use a front end from "Fast Cars" that is designed for MGB V8 swaps. It will give you modern geometry and brakes that fit under a MGB.

Rear end, I would go with an 8" ford and around a 3.0 rear end gear (close as I could get) and Bill Guzmans' rear 4 link. (V6 conversions).

I would not bother with the T56 for two reasons. First, with the torque of a LS1 and the weight of an MGB, you need six speeds like a firsh needs a bycilce. Pointless. I would say a full manual powerglide would be a better choice. Myself, I like the T5 options from Tremek since ther is some adjustability for where the shifter is going to fall.

The car is gonna be wild.


Keith SuperDork
11/2/08 8:42 p.m.

I've been looking at the GT with the Miata underpinnings (no McPherson struts, of course, you won't find those on any Miata) for a while. I don't think the car ever went beyond the stage of sitting on the wheels. I have some concerns about the strength of the upper shock mounts in the front, and there never were any for the rear. But it's a good proof-of-concept setup. The owner's actually on this forum and I came close to buying it, actually :) I believe it was a stillborn Challenge car. For those who want to see:

In my case, I want to keep the body stock. So narrowing will be required. In the rear, that's dead easy. Unless I go with the transaxle, in which case I'll just make a custom subframe and hang the 'box in it. In the front, I'm expecting I'll probably have to build a subframe similar to the one that we use for LS conversions on the Miata. It'll give more room than a cut-down Miata one. I consider the Miata suspension components to be the proven ones in my case :) It's not just a matter of being cheap, it's a matter of being a platform I know extremely well. It'll also give me a good power steering rack. The "Fast cars" stuff is pretty, but it's mainly made for 302 swaps and it's spendy. I expect to spend some time sorting out the handling (that's a fun part of the build) and it really helps to have a garage that is stuffed with good Miata options. Others may come to different conclusions, but it's hard to ignore my own particular history and knowledge.

Jensenman, I'm not sure I see where the geometry problems come in. The roll centers will change due to the narrowed layout - as will the amount of weight transfer - but they shouldn't move around, which I think is the key. Will they? I need to spend some time with suspension layout programs. It looks as if I'm going to have to lose about 3" in the front and 4.5" in the rear.

It's expected that I'll be moving the steering column as part of the swap. So I'll either make things fit that way with a set of block-huggers (as in the Miata conversion) or more likely, poke through the fender wells. Making headers doesn't scare me, although making two sets will be a pain.

Six speeds is overkill, I know that from the 2500 lb LS Miata. But the T56 easily mates to the LS1 where the T5 does not, and there's no question about its strength in bone-stock form. I find myself skipping all over the box on the Miata, but it works and I love that super-tall 6th gear. Of course, I do have an issue of Car Craft here that tells me how to fit a T5 to my LS1...

I don't do "blogs". They're about people's cats, and the weather, and links to other blogs as far as I can tell. I do build diaries, have since my first major project car nearly 8 years ago. They're about building a car And the MG is no exception, it's already got the website up:

oldopelguy HalfDork
11/2/08 8:52 p.m.

From a packaging and a gear ratio availibility standpoint the hot ticket for transmission might be to get the adapter bell-housing from Advance Adapters and use a Toyota 5-speed. Much thinner overall and plenty strong, and the Supra ones have better racing ratios than any T5. Even with the adapter bell it would probably end up cheaper than a T56.

While you may not be able to find one to drive locally to find out for yourself (though I think I could get you in touch with someone) I'd actually recommend the Opel Manta front suspension, instead of the Miata, matched to the Miata rear. Already double wishbone, great handling (banned at most dirt tracks), and Lotus used a lot of the parts on one of their cars so there's brake upgrades and such out there already. It also helps that it's the same width as the Miata rear and shares the same bolt pattern. Slightly less great handling but tons easier to find and cheaper would be the Fiero/Chevette/Impulse front suspension, which is just slightly narrower, also the right bolt pattern (with Chevette, Opel, or Isuzu hubs) and also an easy to pull sub-assembly.

I know you know Miatie Keith, but if you're building a hybrid anyway you might as well make it a real freak.

Keith SuperDork
11/2/08 9:06 p.m.

My boss Bill (who's currently looking to start on his Miata-engined Opel GT with a RX7 GSL-SE rear end) had a few Mantas. I'll talk to him about that option.

It's so hard for me to get away from the Miata because I have a full set of control arms, several knuckles, at least two complete brake systems, a couple of steering racks and columns and lord knows what else in my garage at home. Meanwhile, at work, I have access to everything. We throw away subframes because we don't have room to store them all. So it's a good answer for me. They kinda sorta handle a bit in their original form too.

Good suggestion for the Toyota, I'll check that out. I like the idea of the smaller size. Is that a Supra trans? What's the magic otaku name for it?

MitchellC Reader
11/2/08 9:38 p.m.

Sounds like quite an undertaking... might as well start the MG mindset by getting a few cases of Old Speckled Hen:

oldopelguy HalfDork
11/3/08 12:39 a.m.

Obviously Bill hasn't measured where the Miata shifter will come out in a GT; it was why I decided the easiest way to hybrid the two would be to graft the GT nose and tail onto the Miata tub.

For the most part the Toyota transmissions with removable bell housings only had one of two bell housing to tranny bolt patterns. One of them is actually the same pattern as a slew of Jeeps, Dodges, and the new Solstice and Colorado, though input shaft lengths seem to vary a bit. A little searching around on the old board will get you some links with more information, we had a good thread going there for a bit.

Given what you have available to you in terms of used parts, Miata stuff probably is the way to go. As to the width issue, though, 3" extra width is only 35mm more offset on a set of custom racing wheels, which might be an option too. A 15 or 16" rim will probably clear all the arms on a Miata rear suspension no matter how far back it's offset is. Might not be super sexy looking rims but if it runs good....?

Osterkraut Reader
11/3/08 2:41 a.m.
MitchellC wrote: Sounds like quite an undertaking... might as well start the MG mindset by getting a few cases of Old Speckled Hen:

Which has disappeared from Gainesville...

Tim Baxter
Tim Baxter Online Editor
11/3/08 6:54 a.m.

Careful with the old Speckled Hen... drink enough of it and you'll decide the MG is perfect as it is, as God and Cecil Kimber intended it, as all MGs are, amen.

10 points to the first person who can tell me the OSH-MG connection.

bludroptop Dork
11/3/08 7:12 a.m.
Tim Baxter wrote: 10 points to the first person who can tell me the OSH-MG connection.

Too easy...

Tim Baxter
Tim Baxter Online Editor
11/3/08 7:14 a.m.

Damn. Left off "without googling"

Jensenman SuperDork
11/3/08 8:05 a.m.

I cut 5" out of the center of my subframe.

From my decidedly unprofessional pencil and paper figuring, the roll center would start out OK but would change quickly due to the long control arms mounted close together at the bottom. Of course, if the body doesn't roll much that wouldn't be a problem. The fix, again from unprofessional paper figgerin' was to shorten the control arms top and bottom. Since that wasn't in the budget, I decided to leave it as it was and stiffen the suspension.

Treb New Reader
11/3/08 9:08 a.m.

Right, and they named the ale after the car, and gave it an octagonal label after MG's octagonal logo.

donalson SuperDork
11/3/08 9:31 a.m.

just to drool... mmmmm

aeronca65t Reader
11/3/08 9:56 a.m.

This MGB-GT V8 ran at our recent ~VRG Vintage Races at NJMP.

It had a Rover (nee Buick) alum engine. Cool-looking car and sounded good too

Keith SuperDork
11/3/08 10:31 a.m.

It was a Rover-powered car that got me into this mess in the first place. Looked great, sounded awesome, probably couldn't have outrun a stock 1.6 Miata in a straight line.

Both of the cars above are fitted with the old Sebring flares. Historically appropriate but they don't work for me aesthetically. The Omni ones look okay and it might be a reasonable option to widen the car instead of narrowing the suspension. According to the British V8 board, they'll widen the car about 2" per corner. Perfect! Now I just have to convince my wife that it's how she wants her car to look - it would be a shame to lose that spear along the side.

I think going to a +75mm offset wheel might have some adverse effects on the scrub radius, more than potential handling problems from changes in roll center. I'll do the math on the former and see how much that's changed from the original Miata setup, but some initial. Oldopelguy, are you saying that any toyota transmission with a removable bellhousing is appropriate?

Ian F
Ian F Reader
11/3/08 11:39 a.m.

Keith wrote:

I've been looking at the GT with the Miata underpinnings (no McPherson struts, of course, you won't find those on any Miata) for a while. I don't think the car ever went beyond the stage of sitting on the wheels. I have some concerns about the strength of the upper shock mounts in the front, and there never were any for the rear. But it's a good proof-of-concept setup. The owner's actually on this forum and I came close to buying it, actually :) I believe it was a stillborn Challenge car. For those who want to see:

Yep... that's the car I was thinking of... probably saw it here... don't know why I thought Miatas have struts... I knew they didn't... have had BMWs, MINI's and Volvos on the brain lately, I guess... I wish I was "allowed" to get a Miata...

Master's wiring harness nearly drove me to insanity (or to drive down to TN with a loaded AK)... but his GT V8 is a beautiful piece of work.

MitchellC Reader
11/3/08 3:45 p.m.
Osterkraut wrote: Which has disappeared from Gainesville...

I got a sixer from ABC on Archer a few weeks back. I still have a few in my fridge.

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