MG Sports Cars

I was a little disappointed with the Beemer diff. Physically it will fit into the space OK, but the ring gear is about a 7-1/2 to 7-3/4" piece. I do not doubt that they are excellent parts, made of the finest materials, but personally I feel that is a bit small for this application. The stock 340 puts out 365 ft/lbs of torque and with the blower it is completely within reason to forsee 450 ft/lbs or more, and I have my doubts that any ring and pinion of less than 8" diameter is going to last long under that kind of stress. IIRC the stock MG ring is not much under 8" itself.

So that leaves me looking at the Mopar, the Nissan, and the Ford 8.8 and possibly Jag (Dana 44). John did have a big selection of half shafts and I may have to go back and look at those again.

The Nissan diff having a 200mm ring is also under 8" at 7.87" or about 7-7/8" but possibly close enough. I consider it just a little marginal for this engine, but still a possiblilty.

The Mopar 8-3/4 still looks quite attractive. Carl, would you happen to know what cars used this axle? It would need some machine work on the housing but it's feasible to do this.

Still watching for the right 8.8 housing, so far no luck. Ford production numbers would sure be handy.

The Jag is still in the running. Recent fitting on the Roadmaster suggests it can meet the installation requirements, and could end up being the best choice still. Needs to be converted to CV half-shafts and have an upper link in order to have a modern suspension, but that may not be all that difficult.

Jim



Edited 1 time(s). Last edit at 02/06/2008 09:25AM by BlownMGB-V8.

Jim
Are you planning on modifing the Mopar 8 3/4" for IRS?

Bill

That would have to be considered as an option Bill. I see that these axles were widely used until 1974 and there could still be a large number of them available at reasonable cost. Since they used a formed steel housing (banjo type) the modifications would include cutting off the tubes and welding on bearing housings close to the center and the addition of mounting brackets. All in all not a terrible lot of modification. I do not think an aluminum carrier is or will ever be available for them but I could be wrong. At any rate, it looks feasible. I wonder what stub shafts and bearings/bearing housings are used on the 9" ford IRS center sections?

Jim

Jim,
More info.

The V6 and i-Force 4.7 V8 Tundra models' rear differential uses a 9.5-inch ring gear, and the i-Force 5.7 models step up to a 10.5-inch ring gear - one of the largest in the segment. All Tundra differentials are made using new machining technology: "face hob" gear cutting for ring and pinion gears yields stronger tooth form and a greater engagement area for increased torque capacity and reduced gear noise.

I have a Tundra and it does ride smooth.

Couldn't you work on the R230 and take off some of the front mounts so it wouldn't be so wide at the mounting area around the pinion, and fab out some king of bracket. The front of the R200 is about the same as the R230. 8 1/2 '' that isn't that far off from 7"
...3/4" of an inch on both sides.

Just a thought.
Calvin

See that was the attraction of the long nose 200 Calvin, no need to modify or cut down the housing. I feel a lot more comfortable modifying a banjo housing than a cast piece if I'm going to have to do that. Any welds are a lot more likely to be sound and tolerate abuse. I also think any ring gear over 9" is going to be serious overkill even with something like the Roadmaster. The ring of the 230 is certainly big enough, but it won't fit the available space without some pretty serious modification and I doubt the average builder is going to want to make those mods. Had they made a 215 or 220 long nose or even a short unit with bolt on side pinion mount that would have been ideal I expect.

Personally I think the goal here is for a shippable kit that does not include heavy items like the pumpkin. A very short banjo housing is reasonable, a cast housing, not so much. One that uses a stock unmodified center section, even better. Unfortunately the universe of housings meeting the requirements is very small at present. I was pretty happy to see the mopar as an alternative. I've learned that it came in 3 basic configurations and perhaps the "A" body unit is the best choice. It is likely to have a light weight housing. The pinion is smaller at 1-3/8" diameter but this should be adequate and the axle bolt circle is 4" where the larger housings use a 4-1/2" BC, but that isn't terribly relevant to this application. Plus with the drop out center section it is very easy to set up the gears and differential. Much, much easier in fact than for instance a Dana.


This is a "B" body housing. The tapered sections on either side of the housing may cause difficulties but otherwise cutting the tubes and re-welding the bearing carriers would not be much trouble. I don't know which carrier is pictured, but from this perspective it seems to be deeper from the differential bearings to where the case narrows appreciably than it has to be. That could be a problem, so test fitting will be required befort deciding to go that way. Incidentally, I just discovered that an aluminum carrier as well as an aluminum yoke are available. Pricey, and the weight reduction is only maybe 15 lbs, but some folks would be interested I'm sure.
[www.jimsautoparts.com]

On the other hand, the Jag unit is readily available at fair prices and is already configured for mounts and inboard brakes. That's a significant advantage. There are good reasons why it is the most popular package for IRS.

Jim



Edited 2 time(s). Last edit at 02/05/2008 09:58AM by BlownMGB-V8.

Jim,

Jag IRS on ebay.

[cgi.ebay.com]

Calvin

"Carl, would you happen to know what cars used this axle?"

Uh, lots & lots of Mopars? :)

Best pumpkins are the 742 & 489.

Great summary here:

[www.usaimports.co.uk]

Jim, the rear from a Corvette was mentioned early in the discussion. I've been doing some checking and this might be one to consider. There's a good selection of ratios available, the ring gear is about 8" and they did hold up behind the big block Vette's of the early 70s so they can stand some torque. There are a couple of rear covers available that eliminate the original spring mount and tighten up the size quite a bit and IIRC the nose isn't too wide to fit between the battery boxes. Or you could have a steel plate cut that would mount on the rear cover bolts and then use a really close fitting sheet steel cover for minimum size. The plate would then be the rear mount. You're still stuck with a U-joint half shaft with the stock stub axles, but that's something that is pretty easy to adapt if you really want to go to CV joints. The conversion of a banjo style housing to an IRS center can be done, the early Heidt type rear ends for the street rodders were based on a modified Ford 9" housing, they now have a custom alloy housing which is a bit narrower.

Jim
When I had the machine shop narrow my 8 3/4". He chucked up the housing in a large lathe, at the center points where the bearings fit. Then built up the housing tubes at the point of cuts, with welding beads. Then machined the welded area true, this "true's up" the outer surface to the bearing surface. From there it was just a matter of cutting the flanges off and matching the outer surface, then weld them up. This process corrects the stamped housing to the center point of the axles.
He cut the stock axles and re-splined them.
Been running that same rear end since 1982 with no problems, although it was probably over-kill for my previous engine combos. I'm glad that I have it for the S/C engine now.
B body drum brakes are 10" x 1 3/4" (same as MGB), but are a dual sevro type. So you get more braking power then with the same sized expanding shoe type MGB brake. There are 13/16" wheel cylinders (same as MGB GT) available to fit the Mopar brakes. I believe they were from a early 70's Dodge 1/2 ton PU.
Quite a few 8 3/4" rears came with a limited slip diff, combined a wide selection of gear ratios, is why I chose to go with the Mopar.


Bill



Edited 1 time(s). Last edit at 02/05/2008 10:13PM by MG four six eight.

Good find Calvin, one a little closer would be nice. Maine is a long drive for a local pick-up. Good info on the 8-3/4 Carl. So far I haven't seen anything on housing weights but one from an A body might be a good choice since it would be hard to break even the 741 in an MGB.

Bill, I seem to recall that the early Vette diff is a Dana 44 also (at least some years). The ring diameter on those is 8-1/2" so they are plenty strong enough for the MGB. In fact, that size is probably near perfect for a high powered MG. The Corvette rear could be made to work. I think it would be more difficult to mount than the Jag version.

Jim

Bill J. Thanks, I just about missed your post. Sounds like a very good axle for a S/C setup. There is indeed an aluminum center section available, see earlier post. The price I saw was around nine hundred so a little expensive for 11 to14 lbs. There may be others.

Jim

Believe it or not, I've been looking at a Ford Expedition/Navi 9.75" IRS diff. It seems almost inconceivable that one of those could be small enough to fit the available space, but it may be and they aren't hard to find. It has a side mounting pad for the pinion mount which is reportedly 3-1/2" from the pinion centerline, meaning that a 1/2" offset should be enough to give adequate clearance. The rear mounts are on the cover very much like the Mustang 8.8" unit and the distance from axle centerline to the back of the rear cover is about 5 to 5-1/2", meaning that it may fit.

Now it's very obvious that this is massive overkill in terms of strength and that probably means extra weight which we don't need. But on the plus side, it is sprung weight, it shifts the weight balance a bit to the rear which isn't a bad thing, and then there's the clutch type posi unit to consider. These units as a rule tend to be less effective than we'd like due to a small clutch area and rapid wear, and are often marginally effective within sometimes as little as 20,000 miles. A bigger unit in a lighter car means it will be under stressed and should work better and last longer, both very good things. In addition, the pinion mount point is very beefy, being designed for a 3 ton vehicle so building a strong enough mounting system should be pretty easy.

My truck should have the same diff, though a solid axle instead of IRS. So in the next few days I hope to have a chance to drive it up on the maintenance pit and take some measurements. Then we'll have a better idea if it's a viable candidate.

Jim

I didn't buy the 9.75" unit. The more I thought about it the more it just seemed too big. The pinion mount surface would have been flush with the battery box unless the diff was offset and then the handbrake would be in the way of the driveshaft and then there is all that weight.

Instead I've been looking at a new approach to the Jag unit. The Dana 44 used in the Jag IRS has an ideal ring size at 8-1/2". It isn't that much bigger (heavier) than the stock MGB unit but it will handle any engine and transmission we could reasonably put in the car. It can be mounted without undue fuss and bother, using a method that will allow pinion angle adjustment, and it comes with inboard brakes. What it does not come with is an upper control arm of any sort and because of this it is much heavier than it might otherwise be. These shortcomings can be remedied.

As I mentioned on the Roadmaster thread, Spicer sells slip yokes which can be used in combination with U-joints, driveshaft flanges and stub shafts to make up short units that can take the place of the Jag half shaft. I will have to do some checking on specific parts but this gets us the push-pull capability that is inherent in CV type half shafts and allows the use of an upper control arm (UCA). Based on past experience with 4 wheel drive and divorced transfer cases I'm confident that the right combination of parts can be found.

Once we're free to use a UCA the logical next step is to triangulate it so that it can transfer thrust loads to the body. By doing this we achieve two very important things in addition to locating the top of the wheel. First we remove the torque loading of the upright which is inherent in the original design. Second we split the thrust load between the lower and upper control arms, allowing the use of lighter, thinner materials. These two changes mean that the combined weight of both CA's is now significantly less than what is needed to prevent deformation of the original LCA. In the process we can eliminate the radius rods used in the original installation as well, with their engineered in binding and slop.

At this point I still plan to use the uprights that I had waterjet cut for the T-bird IRS, which move the outer pivot points outwards to the point that they are actually inside the rim itself, thereby allowing the use of longer control arms for better suspension geometry. By the time it's put together I could decide that a built up unit will work as well or better but since I have these I might as well use them. I will probably stick pretty close to the T-bird arm length and pickup points, and may even use the T-bird bushings for adjustability and because in the lighter car they will be stiffer and therefore more precise. For hubs I haven't decided. I need a compact hub that uses a cartridge bearing and a chevy lug pattern, but there should be several choices for that. A four bolt flange on the stub shaft or a U-joint yoke either one should work.

Jim

Turns out my quest for tires may be marginally easier than I had thought, I'll know more after I do some searching. Could be no better. But I made a mistake. Don't even know how or why but somehow I'd gotten the notion that there was a 1:2 relationship between tread width and tire height. Not so! The BFG 265/50-14 is 10" wide mounted on a 7" rim and tread width is slightly less, say 9-1/2 depending on where in the curve you say the edge is. So while the search is still difficult it may not be impossible. There may be a 15" wheel and tire that will do the trick.

Jim

Big news in the engine department. Mike Tomaszewski of TA Performance has informed me that he is looking into making a set of heads to fit the Rover engine. This came about due to the inquiries of one of our Australian friends, who asked Mike if he could make a product to compete with Wildcat or Wilpower. It turns out of course that TA's existing high performance aluminum head for the Buick V6 is easily converted back into a V8 head by the simple expedient of combining parts of two existing V6 molds, resulting in a Rover head that has every feature of TA's formidable V6 heads. Naturally this head would also fit the 215 provided the valves would clear the bore, but more importantly, it would fit the 300 and the mighty 340! Remember also that the 340 is only a .050" overbore from being a 350, so a lightweight 350 with tremendous performance potential is well within reach. Even more interesting, by the simple expedient of using a 340 cam, intake and exhaust, these heads will bolt right up to the Buick 350 block! (some of the cam bearings will need to be sleeved to fit the block) Buick 350's are both plentiful and cheap, as well as being a bit lighter than either the 300 or 340.

How's that for some news you can use? The release date hasn't been set, in fact Mike is still considering the idea. But once the decision has been made the road to sales should be a short one.

Jim

I will be continuing on with my plan to use the '64 300 heads. Dale has those heads and is working on them now, so probably he will send them along with the engine for the Roadmaster when that comes back next month.

I got the roadster back down on it's wheels today, new brakes and all. It's still too muddy to get it out and see how the suspension is going to act, as it sits the rear is stiff and high. But I expect it to loosen up and settle after it's been driven. Gives it a rather rakish appearance, not that it needed it. Once we get past the tax returns I'm planning on putting down gravel and the mud will no longer interfere with my driving, which would be real nice on days like today.

I've learned a lot about tires lately, and wheels. Exactly what that'll mean on setting up this car is yet to be determined, but one thing I know, I can go a LOT bigger on the rear tires.

Jim

so did you do an IRS or put it back on the ground using your existing axle? What tires did you put on it?

I won't get the IRS done until after the one in the Roadmaster, so it's still sitting on the stock axle and the old hard 265/50-14 BFG's. I've got a whole new drivetrain in the works, front to back but it'll take a good bit of time to put it all together and there are still IRS parts to buy and to design. In the meantime I'll have to decide whether to stick with the ford lug pattern or go chevy, look for suitable rear wheels, decide on the rear tire size but I'm thinking that a 315/35-17 would fit just about right. The Sumitomo HTR Z at $99 for an ultra high performance summer radial seems like a good choice, but finding the right wheels won't be easy. Anyway before I go there I still need to find the right differential. I'm not seeing a lot of good choices on ebay right now so that's holding up the project. Did see a sweet Corvette dana 44 3.55 posi aluminum case unit but at 2500 bucks, ouch, not for me. So I'm still looking.

Jim

Not much new to report, but with the weather getting warmer that should change soon. I did however get a couple of rolls of 1/8" stainless tubing ordered. This will be used to plumb the hydraulics for the front tilt assembly. I will attempt to use the existing gas charged cylinders (maybe I should say gas leaked cylinders) and plumb them for the hydraulic lines. The remaining challenges will be the valves and accumulators. This will connect to the tilt/trim pump in the trunk. In this way I hope to finally have the tilt assembly fitting the same way it did before I took it off to paint it. Somehow it has never fit quite as well since and I think it has to do with the force applied by the gas struts.

Dale Spooner is working on the 300 heads and they will be coming back with the 455 engine for the Roadmaster project in about a month and a half. At that point I will tear down the reman shortblock and reassemble using ARP rod bolts and making whatever other changes seem appropriate, and then install heads, valve covers, pan and front cover. Focus will then shift to the blower intake and the transmission.

In the meantime all I need to be able to drive the car is fresh gravel on the driveway to the lab and that's just waiting on the weather.

Jim

Jim,
So I guess I willbe picking up, from Dale, the 455 block, crank, heads, pistons, rods and 2 340 heads?
Just trying to decide what trailer to drag along. I would prefer the luggage trailer. Think all that will fit?
Also, do you need another engine stand? I could bring it along also. If so it will probably be the open trialer.
I think I will be picking it up on April 24 if Dale has it all ready.

Steve