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MG MGB GT V8 Factory Originals Technical - Cast iron Manifold Questions

I have a couple of questions that maybe someone would be kind enough to answer. One, is there really much real-world difference between the efficiency of of OEM cast iron exhaust manifolds and block huggers? Most of the huggers that I've seen don't look all that great. I have a pair of iron ones and I'm a cheap skate who tends to use what I have, within reason. I also like the idea of the cast units transferring less heat and not having flimsy header flanges to worry about. Two, can the cast iron ones be installed with the engine in place? This particular project uses a mostly stock SD1 engine and I have ruled out RV8 headers because I don't want to cut up my RB GT . Many thanks to all.

From what Ive read, the manifolds need to be put on the engine while it is still half way out of the bay, then lowered into place. It has to do with the lower flange clearing the frame rails and steering rack.

The OE cast iron blockhuggers have two advantages -they are a little quieter and on this side, the standard OE exhaust system bolts up (with persuasion). On the down side; they are inefficient (lose about 13 BHP ) they crack, they heat up the engine bay, you need a heat shield for the starter motor and as Jake says, you need to raise the engine to instal them.

The tubular block huggers tend to be a little more efficient but they still heat up the engine bay, the inner wing needs some dressing to make them fit but otherwise the engine does not need to be moved to fit them. If they are stainless, you can also get them out easily but they may also crack.

The best solution is the RV8 route through the inner wings.
Roger Walker

Removing and replacing the cast manifolds is a diabolical task.

A couple of the holts are near impossible to get access to with a spanner.

Removal of the starter motor is made very difficult because you have to remove the right side manifold.

Removing either manifold necessitates lifting the engine from its mounts.

To undo the nut on the right side engine mount may require removal of the steering shaft which means removing the entire steering assembly.

I am happy with my stainless blockhugger manifolds from Clive. Either manifold can be removed in 20 minutes and the starter removed without touching the exhaust.

Sound attractive?

Ian Buckley

I suppose like most things there are tubular block huggers and tubular block huggers. Mine (I've had two sets now) can be removed without disturbing the engine but you do have to pull the rack to get the drivers-side one completely out, but I have that down to a fine art (removal of the drivers side mount can be done with the rack in situ, but it is fiddly). I have replaced the starter, surprisingly easily, just by removing the heat shield. Access to the top bolt was by using a set of 3/8" extension bars and universal joint between two of the pipes. The first set of tubulars did repeatedly crack at the middle siamese, but the cast iron are said to be prone to cracking through overtightening. Both sets of tubulars have given problems with warping. you can get them off OK but can't get them back on because the bolt holes no longer line up. Drilling and filing the holes overcomes this, but the flanges are still warped, I've now welded struts between the flanges. The holes in the flanges are much bigger than those in the head which avoids any problems of misalignment, but it means that the overlap can be very small so the gaskets can leak, and blow altogether unless you use metal-faced gaskets. Mine are very close to the right-hand inner wing, even with a couple of extra shims under that engine mount. Tubulars can be heat-wrapped, I have read that this will crack cast-iron. I've not used cast iron but certainly tubulars offer problems in getting to the bolts. Access to the rear two is very restricted, and one of the others is partly shrouded by the pipes meaning you have to use a very slim spanner and keep turning it over, and even then it only comes partly out until all the other bolts are loose. There are sets of alen-headed bolts that make access to the back two easier but still don't help with the shrouded bolt. Tubulars probably offer freer gas flow than the cast iron. If you scrap the cast iron you have to ditch the original lobster-claw air filters - if you still have them, and substiture K&Ns. This, together with the freer manifolds, alters the breathing so you have to use richer needles or suffer flat spots at medium throttle openings. I've been fighting my manifolds for nine years now. Original cast iron manifolds are said to be as rare as hen's teeth, if I still had them I'd still use them.
Paul Hunt

I have used the cast manifolds and stainless tubular block huggers. I now have Rv8's, they are far superior.
Better cooling, more power, no more fried starters.
I have cut holes in my factory V8 wings, its really not a problem.
Didnt notice much difference between cast and tubular huggers.


Why scrap the factory airboxes? The only parts that would be missing from the removal of the OE manifolds would be the heat collectors that bolt to the OE manifolds. The rest can still be used, perhaps with a cold air intake tube to each air filter. I have an OE induction manifold setup and airboxes, I haven't run the car much yet, but will see how much power is lost by using the airboxes as well as a set of K&N's as I plan to try both.

This is probably a good time to ask......
Finishing a V8 midget project (I didn't start it) The breathing is a bit of a concern. It has a Isky TR8 Works cam, Std SD1 Heads and Landrover cast iron 4 into one manifolds. It's never been started yet and I fear the high overlap offered by the cam may be subject to reversion at low rpm. Unfortunately I don't know the spec's of the cam other than it was run in this short block as a drag racing V8 (Martin Cowell was supposed to have done a 11 sec qtr mile in it. Any advice very welcome....

Note that the Midget means that any other manifolds mean quite a lot of work :(
Stuart Robson

Jake - true enough, I was thinking they mounted on the manifolds but of course they mount on the rocker covers and only the warm air shroud need be omitted. It's just that the two changes often seem to go together.
Paul Hunt


I'm going RV8 over Xmas and you are welcome to my block huggers although a bit knackered down by Y collector, may not be important to your conversion.

Paul Wiley

I too would like to go with the RV8 type headers as I can't seem to seal one exhaust port properly (right front, ie passanger side USA).
I had my block huggers Jet Hot coated and they look nice but they warpped when I removed them to send them out to be coated. My block huggers do not have the reinforcing strap between cylinder ports but I hear that don't help much anyway. Also my engine is the Olds 215 (although stroked to 269ci by Dan at D&D) so I'm asking cause the heads are angled differently will the RV8 headers still fit? Also here in the states who is the best source for the highest quality RV8 style headers? At this point cost is not an object, I just want the best!!!
Michael S. Domanowski

Normally left front right rear(ie same on both sides).
The only way I cured problem was High temp RTV Silicone sealant.

Money no object Clive Wheatley, although I'm having mine made up but similar to CW.

But as in US these may be of interest

Paul Wiley

The port angle is not different enough to cause you a problem. I've used my fenderwell headers with both Buick and Olds heads and I couldn't tell any difference. However, what *is* different is the spark plug angle, and I had to cut away the connecting straps between the ports because they hit the plugs.

Jim Blackwood


Thanks very much for the offer (Huggers). Unfortunately it's still too tight for them (I did have a set already but I had to pass them on too). There's a 4" cut out in the footwell tunnels for the cast iron ones and this does not impede pedel room at all. Going that tiny but further with the huggers may cause a problem with the clutch pedal and I want to really enjoy this car. Mind you losing 15 bhp with that power to weight ratio I can live with.....

Well for the moment anyway!

Thanks tho'

BTW Where are you in Surrey?
Stuart Robson

In the USA, as far as I can tell, all the Rv8 headers are made by Kirk, somewhere in the South, Alabama, maybe. These are sold by TSI, D & D, & Glen Towery. Prices are cometitive last time I checked. Imported RV8 headers should be available from the same sources, but I don't know why anyone would want to spend more money to get the imports. I have a standard set on my 3.5, and a set with 1 5/8" primaries on the Buick 300. Both sets were a good fit. The set from D & D had some grinding already done for improved access to the spark plugs & dip stick that I had to do myself on the first set. That may be because they were installed on the engine I bought from Dan.

If you buy a set of headers & are going to have them coated, install first & be sure you can get a socket on all the plugs, & that the dip stick clears before you have them coated.
Jim Stuart

Thanks much to both Jim and Jim, I should have known Dan at D&D could get them for me.
Michael S. Domanowski

Thanks to all who responded to my questions. I appreciate it. It seems like the best long term answer is to go to RV8 pipes, but I think I'll try the cast ones first since it appears that I won't completely strangle my engine with them even though installation and starter service appears to be a pain. Maybe using a gear reduction starter will free up some room. Thanks again.

This thread was discussed between 03/12/2003 and 08/12/2003

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