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MG MGB GT V8 Factory Originals Technical - Chassis brace with RV8 manifolds

Anyone about to fit a through the wing exhaust might benefit from the following.
About 2 yrs ago I fitted Rv8 manifolds to my GT and to help keep the chassis taught I made a brace similar to a strut brace which attaches to the wing fitting bolts either side of the engine bay, just in front of the air cleaner, above the exhaust holes in the inner wings. The car has regularly been abused on the track (and the road)with no sign of flexing at all.
I have not heard of anyone doing this modification which is very simple.

Views anyone?


Mark Rawlins

Good idea Mark although the cars are very strong by modern standards and some of us are not convinced that the RV8 strengthening is not primarily intended as a placebo.

I believe it is Glen Towery who has cut holes for RV8 manifolds and has operated with them for some considerable time without any strengthening ?
I expect he will confirm.

Glad to read you (ab)use your car properly


Sounds like one of those ideas where there's just no reason not to do it.

I had my car converted to a V8 three years ago by a very, very knowledgable pro and he set up everything just as per my specs, except he flatly refused to install RV8-style headers as I had asked for, as he was absolutely convinced that the strength and stiffness of the entire front clip would be compromised by cutting holes in the inner fenders. I think he thought there was a chance that handling could be compromised. After all, most modern tuners go out of there way to keep the front of the car as stiff as humanly possible, what with shock tower braces and the like.

So I got block-huggers!
Brian Jameson

The more force transferred to the mass of the car during an accidend, the less transferred to yours truly- handling aside! It sounds to me like it would induce good force transfer in most side impact collisions if it's not too stiff, but how might it fold in head on/off collision situations. Could it come in and getcha? Anyone ever seen a crash test of a B? How and where does it crumple? Do I really want to live with crushed legs anyway?...Probably.

The way I figured it the strut is stressed torsionally. (ie. the wings are trying to fold outwards) and so Ive used a small dia tube apprix 12mm which is above the engine and well away from the cockpit. I suppose one could use steel cable with a turnbuckle and do the same job.

Mark Rawlins

From my work with tilt front ends, I can tell you that the biggest problem from weakening the inner fenderwells is not the handling, but cracking of the inner fenderwells, and possible distortion in the fenderwell and fender areas (bending of the car's front end). The unibody structure is quite strong however and considering the location of the holes for the RV8 headers and the amount of sheet metal above the cutout, (as well as the boxed sections) I really do not see any problem with it whatsoever. The outer fender provides a certain amount of reinforcement, and is actually very stiff in the lateral direction. The inner fenderwell is still substantial enough even with the cutout to give very good support in both the vertical and longitudinal axis' and the angle it sits at gives very good torsional bracing. I wouldn't worry about it. Kurt Schley has run the cutouts for ventilation purposes for several years now without any trouble, I'd be much more concerned with edge treatment of the hole itself. Ideally a good sized wire would be beaded into the edge, or at least welded or brazed to it to avoid any chance of crack propogation, but flanging and smoothing the edge would help considerably.

I have cutouts through the top rail of the inner fenderwells right in front of the triangulated box sections large enough for the header tubes to pass through. Together with unbolting the outer fender from the inner fender, this significantly weakens the front of the car and supplemental reinforcement is required. Initially I used white oak stringers bolted to the top rails and while they gave adequate reinforcement to avoid failure, they also allowed enough movement to allow stress cracks to begin propagating. (I was occasionally jumping the car, and the suspension is stiff. I could get pretty good air at one favorite spot, with a somewhat sideways landing to set up for the other half of the downhill "S") These stringers were replaced with stainless steel bar stock braced into the fender stubs and I've had no more trouble. As I said, I wouldn't worry about it.
Jim Blackwood

It is not that you have a V8 that matters wether this is usefullt it is how much power or more importantly torque the motor is producing. I am hjoping I can find a way to stiffen up my front end as I know my chassis is flexing when I am really having fun. I mean the front of rth car comes up strong when I get on her and the driver side goes a touch higher.

These chassis ARE incredibly strong, but again, not designed to have 300ft/lbs of motor in them either. I would be very interested in seeing pictures of whatever you guys have done to stiffen your front chassis.
Larry Embrey

"Anyone ever seen a crash test of a B? How and where does it crumple?"

There is a picture of a factory 30mph crash test in David Knowles' 'The Untold Story'. It crumples at the front, which isn't being clever, since a modern car will crumple throughout to varying degrees at a relatively low speed. There has been a well-documented case on this site of a racing accident where an MGB hit a solid concrete wall at an estimated 130kph. The car had 0.75 metres of crush, but none of this was in the passenger compartment.

It is to add strengthening around the hole cut in the inner wing.
Paul Hunt

anthony barnhill


I had the misfortune to hit a lamppost with my V8 mgb roadster in 1999.

I hit the kerb, shattered the nearside front wheel (LE/ Stag type) and burst the tyre causing the car to run along the kerb.

The broken rim hit a metal lamppost which had been positioned at the edge of the pavement, the wing was only damaged to a depth of about 6" ( the distance from the kerb to the lamppost) but the car stopped dead from about 30mph, I guess, swinging 90 degrees around.Impact was sufficient to dislodge glasses.

I had not done any strengthening of the body , but had welded new sills, and seam welded the floors, and the shell had only been restored a couple of years, so there was no rust corrosion to weaken the structure.

The nearside chassis rail took most of the shock, it buckled badly just behind the crossmember.
The crossmsmber itself was banana shaped, and there was a small depression in the passenger footwell where the wheel or tyre had impacted.
The shell had twisted and sprung the boot catch.

Slight bruising to passenger and myself from seatbelts.
Small bruise to passengers leg where it impacted footwell
Massive damage to my ego !!!!!

We were both surprised at the strength of the bodyshell, and the comparatively little damage the passenger compartment sufferred, I had always believed MGB's were tough cars, unfortunately I managed to prove it!

Michael barnfather

"Impact was sufficient to dislodge glasses"

Reminds me of a newspaper headline after someone crashed a Bell X-craft in the 60s: "X-15 explodes: Pilot wets pants" (in fact the water had been sprayed by fire crews and came in through the hatch as it was opened).
Paul Hunt

I have to put in a comment for the strength of the B.
I had the missfortune to wreck one as a teenager (many moons ago) by bouncing it off of an oak tree. Damaged the the front body work and bent the RF suspension but the car did bounce off the tree! The impact was hard enough that my freind in the car behind me (yes I was winning) saw the bottom of the car as it spun up from the impact. I was wearing a seat belt, got out of the car , said damn.
Then the painful part. I had to call my Dad.

Two weeks later, after I replaced a shock and hammered out the wing, it was back on the road. A little uglier but driving.
I've thought about that night a lot because I've just given my 16 year old son one of my old Bs. He's good about wearing his seat belt too. No V8 for him though. That's mine!


In my former occupation I have seen quite a few bodies in MGBs. Those killed in cars that stayed upright were often dead from impacting the dash areas through not wearing belts, but not all. What is most apparent is that even where rusty sills were present the deformation was very limited and much as Mike describes above. One of the disadvantages of this is that the energy is not dissipated into the structure but passed along it to the first energy sponges - the humans inside, and even with largely intact interiors and normal looking corpses their insides were real mess.

It is a very good structure but one with the 1950s viewpoint of the more solid the better. We know now that this has only limited value.

Roger Parker

Thank you Roger !

I was just eating my sandwich at lunchtime when I read that.

Michael barnfather

Roger, this underlines my comments that it was unlikely the holes would hurt anything. Larry may be seeing some twist on very hard launches, but so far it's the first I've heard of that.
Jim Blackwood

heh Very well put Jim. and YES my car does see hard launches. The evidence I am seeing is a slight washboard look just in front of the brake booster on my US spec '78 Not to bad yet, but I hope to address it this winter. This could also be contributed to by my poor worn shocks and springs letting the car get all out of shape as well.
Larry Embrey you have any photos of your setup?
anthony barnhill

Larry, wait, that washboard thing is common even in 4-cyl. MGBs ... did yours have it pre-conversion? I think it's just the way the panels were pressed. Can't imagine the engine bay is particularly stressed by the presence or absence of a V8.

Can confirm about the washboard thing, my ex-Californian'75 has this on the LHS innner guard but not the RHS. Some teathing problems with pressing the new (then) shape of the inner guard maybe.

... exactly as Peter said, they're in the LHS but not the RHS. Basically the area where the brake plumbing sits in a LHD car.

This thread was discussed between 31/10/2002 and 06/11/2002

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