MG Sports Cars

In case you don't visit the "RaceCars" section... I know you won't want to miss this new article!

Al Pease's Supercharged 1962 MGB: the most successful MG in Canadian racing history

A few teaser snapshots:

There's been some weight loss on that xmbr!

Quote:

There's been some weight loss on that xmbr!

Now don't get any ideas and start drilling holes in that bionic hip.

Not to worry, Graham!

Love these stories of restorations of original racers.

Quote:

There's been some weight loss on that xmbr

Based on my experience notching one to fit a Ford, I'd say around 5 pounds. What do you think, Graham?

Not a lot, the stock x-member is not very heavy. Most of the weight is in the other parts. But a pound here and a pound there do add up.

JB

I think Jim is right - a couple of lbs at best, based on what is generally removed for Ford sump clearance.

Here's how I quickly estimated it:
~10 large round holes, each about 3" diameter, through 1/8" thick mild steel = ~8.84in³
~21 medium round holes, each about 2" diameter, through 1/8" thick mild steel = ~8.25in³
~24 small round holes, each about 1" diameter, through 1/8" thick mild steel = ~2.36in³
1 rectangular hole ~4" by ~13" through 1/8" mild steel = ~6.5in³

25.94 cubic inches of mild steel times 0.284#/in³ = 7.37 pounds

I think the material is probably thinner than 1/8", but the holes might be significantly larger than I estimated.

Good attempt Curtis, but it sounds optimistic to me. I think you might have guessed big on the holes.

JB

Has anyone calculated the weight difference when installing a 302? Mine still has pretty good suspension travel, and I was just wondering!

How much weight was removed is not the primary issue. The primary issue is that he removed as much as reasonably possible. An ounce of uneccessary weight is an ounce too much.

It also serves to invalidate concerns that notching the crossmember to fit a Ford creates a safety hazard. I think it's pretty clear that this crossmember has less strength than those we modify for the Ford, yet it had withstood far more stress than we'll ever put on them.

RE: "It also serves to invalidate concerns that notching the crossmember to fit a Ford creates a safety hazard. I think it's pretty clear that this crossmember has less strength than those we modify for the Ford, yet it had withstood far more stress than we'll ever put on them"

Amen to that Dan. When Curtis first posted the pics I thought about saying something witty about those holes not being possible because I was told I'd create a death trap if I notched the cross member for the 302... but I got side tracked & never came back to it.

I never took the opportunity to weigh the front crossmember when I had is stripped down, but many years ago Tony Barnhill tried to mimic what was done for a racer he was building, but he was a bit timid to go as far as the Pease MGB. He weighed the drilled version of the beam, a-arms, and spring pans he created, and had decreased about 6 pounds as I recall. The beam alone would be about 2/3 of that ... so about 4 pounds.
Maybe if Tony Barnill's "Autoist" (RIP) site is ever put back on-line I can find the bit that Tony wrote about lightening his front crossmember.

Mike Adams

Well obviously if Ted's front suspensions don't crack the cross beam anything heavier should be OK and that's a good thing. There are many front suspensions out there other than MG that are even lighter. I'll admit it, I have been in the camp of cautionists. Not so much for fear of collapse but for loss of body stiffness. I think that caution was and is justified and I'll tell you why. The stock crossmember constitutes a thin, large diameter tube fixed transversely across the front chassis frame rail extensions and this part of the monocoque structure has much less bracing and support than the rest of the body tub due to the outer wings being removable. This means that flexing, particularly in the vertical plane, is much more likely than elsewhere in the car, and such a tube effectively ties the frame extensions together in such a way that vertical flex is coupled from one side to the other, nearly doubling the flex resistance and reducing the deflection.

Is this flex an issue at all? I can now emphatically and categorically state that it is. As you know, I have removed what minimal amount of bracing is afforded by the bolted-on outer wings by conversion to a forward tilt assembly, and have added bracing to compensate, and over the years have had the chance to make some observations. The first of those was that the original supplemental bracing was inadequate as I began to see stress cracks in the skin of the inner wings at the point where the fenderwell headers passed through above the tires. Newer, stiffer bracing resolved that. However just a couple weeks ago I found a crack in the footwell area extending from the point where it joins the frame rail and this can only mean one thing, namely that the frame rails are still moving around enough to fatigue and crack the sheet metal. I have addressed this by welding up the crack and welding some new sheet metal into an adjoining area, returning the clutch fork "box" to the original configuration, and am softening up the front suspension a bit. Incidentally, the "box" could conceivably have contributed to the cracking by concentrating stress, but not by much and the movement had to be there regardless for cracking to occur. Note that my car's front sheet metal configuration, in terms of stress analysis, is stiffer than a car converted to fiberglass wings.

So the point is, as stout as the MGB tub has proven to be, this is an area to pay attention to. Not only are stress cracks bothersome, any loss of stiffness will loosen up the handling and make the car less precise in the twisties and it is clear that additional bracing between the frame rails and the bulkhead could be beneficial. But how far can you go without cracking? Hard to say. I've put a lot of miles on my car and they were almost all hard miles with a very stiff suspension. How you drive will matter a great deal. But one thing is for sure, it doesn't behave like a great bloody block of steel when you whack one corner of it, and the stiffness afforded by that relatively gargantuan cross member does indeed count for something.

JB

Pete and I weighed my (complete) stock rubber bumper xmbr and compared it to my FastCars xmbr.

The stock xmbr weighed #180...the FastCars xmbr #105