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MG MGB GT V8 Factory Originals Technical - Alloy vs. steel bonnets

I know this is the n-th time this inquiry has appeared here but can we get to the bottom of it:

1. is the alloy bonnet from the earlier cars really bowed less than the later steel bonnets?; and

2. how much lighter than the steel one is the alloy bonnet?

Is there any downside to putting an alloy bonnet on a V8?

I just measured my original 64 aluminium bonnet and a 1971 (black grille) bonnet I now have on the car and they have the same bulge above where the carburettors would be on a factory v8. That is in the centre halfway between the cross brace and the rear of the bonnet. Hope that makes sense. I understand the bonnets from rubbernose cars are more bulged.

I don't have a clearance problem and I could have either bonnet fitted. I just thought I would 'save' the aluminium one. I just weighed the aluminium one at 16 lbs or 7 kg.

Aluminium bonnets don't have the large holes near the locking mechanism which are handy for a hidden bonnet safety strap. I never drive anywhere without the bonnet 'tied' down. That is why the aluminiun one has lasted me 30 years!! I suggest putting the holes in.
Ian Buckley

Tell us more about the hidden strap ystem. I've always been a bit aprehensive of a bonnet coming up but I don't want to spoil the appearance of the car

I'll echo that Marc. If you could describe your strap Ian, or even post a picture, you'd be doing us all a service.

Terrance, FYI I have an ali. bonnet fitted to a factory V8 (1974) with no clearance problems.

Ian Thomson
ian thomson

... oh, I forgot to ask, is the frame of the alloy bonnets steel or aluminum? I ask because I want to know if the frame can be re-welded (I wish to move the x-member forward to clear my 14" carb and I'd like to weld on a hood prop tab).

Like Ian Thomson I have an ali bonnet on a 1974 factory BGT V8 - no clearance problems. Very much lighter - I'd say around 1/2 the weight of a steel item. However, be aware that the metal is VERY soft and can be dented very easily - especially the front couple of inches. I filled the gap between the bonnet and the frame in this area with expanding foam (builder merchants) which provides a little extra support. It's next to impossible to "undent" this area if someone has used excessive force to close the bonnet, simply leaned on it, or it's been hit by something which would simply cause a stone chip on a steel bonnet.

Arthur Mitchell

They are indeed a bit fragile but I'm sure many will agree, they are one of the things that makes an MG an MG! I believe they are about 17 pounds lighter than the steel version, and when you think about it, on a 2200 pound car that's a decent amount of weight, in a not-so-great place. The foam in front sounds like a pretty good idea.

I believe the frame is aluminum. So in order to screw on tangs for props, etc., you'd want to put in nutserts first.

Confusion on confusion. Sources talk of all bonnets being changed for commonisation when the V8 was introduced although that has always been open to question. Since the carbs are so far back, any increase in height/curvature of the bonnet to clear them *must* have also needed a corresponding change in the panel between the bonnet and the windscreen. This panel (panel, shroud, top) is shown for the roadster only, and it *was* changed for the rubber bumper cars. There were originally seperate bonnets for V8 and non V8, both which went NLA, to be replaced with a common bonnet, which is shown as a direct replacement for both earlier bonnets. As far as I can tell the curvature and height at the back of the bonnet and shroud is the same on both my 73 roadster and 75 V8. Whilst the bonnets may have been changed the shrouds are almost certainly original.
Paul Hunt


I replaced a 1973 steel bonnet for a current heritage bonnet a year or so back and there is definitely a greater clearance over the carbs - about an extra 3/16.

The shroud line is exactly the same, so the extra height must come from a greater curvature to the centre part of the panel.
Chris Betson


This thread was discussed between 24/04/2002 and 27/04/2002

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