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MG MGB GT V8 Factory Originals Technical - RV8 Exhuast Headers

Fellow V8ers,
Clem Spriggs

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Fellow V8ers,
I'm nearing the stage of my V8 conversion where I have to decide on exhuast manifold for my V8. I was thinking of putting in a RV8 exhuast to aid the cooling of the engine bay, what with Australia Summers!

Does anyone know exactly where the hole in the inner wing wall goes?

Does this conversion aid under bonnet temperatures that much?

Is it an easier option than a regualar exhuast manifold?

Clem Spriggs
Clem Spriggs

As you guys were so nice to the Queen during her visit, you obviously deserve help.

The RV8 manifolds necessitate a good size hole in each inner wing. This of course means the under-bonnet temp drops considerably when you are on the move. In order to help the engine stay cooler when at a standstill, I feel its worth putting vents of some sort in the bonnet. I fitted Escort Cosworth type units and now have the pleasure of seeing hot oil vapour escaping through them from the rocker vents when stuck in traffic!
There has been some correspondence recently about more powerful electric fans and putting a plastic fan assy on the water pump boss. All of these things are worth considering as is the fitting of an override switch to the fan thermostat switch.
Have a look at the V8 Conversion web site which is so well maintained by Mike at : -
I think you wil find it useful.
Fitting the RV8 manifolds is a case of "suck it and see", Im afraid. Just make sure you make the holes big enough so you can take the manifolds on and off without removing the engine!
good luck!
bob p

thanks for the advice I was considering bonnet vents as another additonal method to cooling the engine bay. Do you know of any problems or difficulties with this type of exhaust manifold ? Aside from the large hole which would require reinforcing.

Clem Spriggs

No problems. I fitted them to my factory GTV8 and to my ex Florida left hand drive Roadster V8. The GT has a single big bore exhaust and one silencer at the rear. The Roadster has a dual system with a balance pipe between the exhausts just behind the bell housing and again silencers at the rear. The dual system sounds fantastic! We also made up stainless steel fittings to go around the pipes where they pass through the inner wings to prevent a lot of crap blowing up from underneath in bad weather. As the cars only get driven when Im home in England in Summer they havent had much use!
By the way use Allen headed set screws to secure the manifolds to the head, they are MUCH easier to get at! My manifolds and exhaust sustems were supplied and or fabricated by mu old buddy Mike The Pipe 01-816-691719 in South London, who Im sure would be happy y send you a set. I think V8 conversions does them too.
Go for it mate!
bob p

These pictures may help. I am sure hole location varies based on who made the headers. But this should give you some idea.
Jim Miller

An alternative to using Allen head bolts to secure the headers is to use bolts with a twelve-point head.
A 3/8" bolt uses a 3/8" 12point socket and you have the option of using a (12pt) box wrench if needed. These type of bolts have a built in flange and you should use "high collar" lock washers. The same lock washer you would use for Allen head bolts.
Randy Forbes

I took a series of photos at the Faringdon body assembly facility for the RV8 with the specific intention of being able to use the photos to locate the position for the hole, its shape and the reinforcement ring. The very few spot welds for the ring are surprising. I will have to get these posted as they are of a bare steel shells.

I used these to create my holes and the resulting clearance has been even all round without being excessive. My manifolds are 'copies' of the originals but the principle is that all aftermarket manifolds should be of the same pattern. So the pictures of the holes in the inner wings should also equally apply.

Roger Parker

clem. to give you a start i took the measurements off my shell at the headers are from v 8 con and are supposed to be rv8 copies.both holes start 4"from the bulk head and 1.5" up from the chassis rail. the hole is 8" high by &.5 wide, with on mine a 0.625" wide reinforcing spot welded all round. hope this gives you a start. regards adrian
adrian salisbury

I forgot to say, that the circumference of my cars cutouts are reinforced and have captive nuts for the Crap baffles.
bob p

Hey Guys,
Thanks for the info on the Headers. I think I'm certain I'll use this option. I'm trying to source a pair of Manifolds in Australia or a pattern for one so I can get set made up. Does anyone have a pattern for a RV8 style manifold?

Clem Spriggs

G'Day Clem,

MG Workshops in Melbourne have RV8 style manifold but at the price they are asking, they must be made of gold. Last I heard that they wanted around $800 for them. You may be better off getting some from the UK such as Mike the Pipe.



The MGB Hive in the UK will do full stainless steel RV8 manifolds and single system with one muffler for around $1000 aussie dollars and includes all the brackets and bolts (mild steel would obviously be cheaper).Bonus is that you won't pay the 17.5% tax if you order from overseas.Allow about $250 for freight to Aussie. If you want a twin system you may have to find another source. I can't comment on the quality as I have not fitted mine to the car yet but they look fine. As far as cutting the holes, make sure you have the donk set up in its final resting place before you start cutting.


One further point which nearly caught me out, is if the headers are created as mirrors of each other, with no off-set the right side exits about an inch further back than the left. So don't cut one side and just copy it on the other.

This is due to the heads being off-set by just over the thickness of the conrods.

Nick Smallwood

Good point, I think that I would have fallen into that trap. I will remember that when the angle grinder comes out.

Clem Spriggs


I have updated my website with pictures of my RV8 inner wing holes. Should give you an idea of the size.


Nick Smallwood

Its a question of suck ita and see when fitting RV8 style manifolds - at least it was for me. Make sure you reinforce the circumference of the resulting hole though.
On the move ,you definitely get better cooling, and cooler air to the induction system. Put some vents in the bonnet too.
At a standstill I think more powerful blower fans plus even putting a plastic fan back on the water pump might be a good idea.
The RV8 manifolds are much more efficient.
The primary pipe dias are bigger, I believe 1.625 inches, and the angle that the pipe leaves the port is better.
I think MGB Hive has complete systems on sale at the moment - look in Safety Fast.
Good Luck.
noddy noddy

Hey guys,

I just opened up my box from M-T-P with my RV8 headers in it. I was expecting equal length primaries of about 30" as described by Bob Pulleyblank(Bob, I e-mailed you but it came back as undeliverable). These do not have equal primaries and are certainly not 30" in length (range from 12 to 18 inches). Did I misunderstand? Did I miscommunicate my order to M-T-P? Is this the only style available?

Mark Marchbanks

On somewhat of a different topic, has anyone seen or used side pipes (ala Cobra or late 60s Vette) on a B? Seems to me it might look pretty sharp.
Tom Burnley

I considered the "HOOKER MUFFLER" look when I made the headers for my MGBGT w/Buick 3.8 V6.
To be really sanitary, you would need to do some work to the rocker panels and the front fenders. Otherwise I think they would stick out to far.
I have another project in the "gathering parts" stage that already needs new sills and rockers anyway. This one is a 74&1/2 GT and I have a 302 and 5-speed to go in it...
Randy Forbes

This thread was discussed between 03/04/2000 and 14/06/2000

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