The most common question I am asked is about four barrel carburettors and inlet manifolds for the Rover V8 engine, so here's a few notes for you all:
There are basically 6 different after market (OEM) inlet manifolds to choose from:
JWR Offenhauser dual port A very low, flat manifold specifically designed for cars with a very low bonnet line. The manifold sits well down in the valley but does not perform so well at high revs. I have driven a 3500cc TR7V8 with one fitted and to be honest it was fine. Particularly suited where there is limited bonnet clearance such as in the TR7, Stag and for Capri and Cortina conversions. The JWR part of the name comes from John Woolf Racing (no connection) who worked in collaboration with Offenhauser to design a Rover V8 (Buick 215) inlet manifold that would fit under the bonnet of typically smaller British cars. It has an unusual dual port design.
JWR Offenhauser Dual Port
Offenhauser 360 Their main Buick 215 manifold, a good manifold for street or off-road use. Fine for racing provided you're keeping under about 6000 rpm. Still listed at about £270, but you might have to ring around to get one.
Offenhauser thermostat housing
Edelbrock performer Edelbrock's famous design that has been around for years now. Still made today and available from a number of UK suppliers at about £200 and for a similar price from various performance suppliers in the US. Again, perfectly OK for racing provided you're keeping under about 6000 rpm. According to Edelbrock, this manifold works best under 5500 rpm.
Harcourt single plane An Australian designed, hi-rise, single plane manifold which requires considerable under-bonnet space. It has a separate thermostat housing fitted to the manifold by two short heater hoses. If you buy one but find that the thermostat housing is missing, you can buy a similar item from John Eales for about £50. I believe the manifolds are no longer made, but there are a few unused ones about. As with all single plane manifolds, not ideal for road use as low end torque is compromised for top-end power.
Harcourt single-plane manifold
Wildcat single plane A development of the Harcourt with the manifold and thermostat housing cast as one unit. This is the favoured manifold for serious race use. Available new from Wildcat Engineering or from DJE in Nuneaton for about £360.
Wildcat single plane manifold
Huffaker single plane The manifold used by Leyland on the early TR7V8 rally cars (later cars used fuel injection). Quite rare. Many that I have seen have been modified by drag racers to take Nitrous Oxide.
Lastly is the modified, pent-roof SU/Stromberg manifold. These can work surprisingly well but it requires considerable skill and time to modify one of these manifolds to take a 4 barrel carb and, it's probably better to by a new Edelbrock performer if you can afford it. I have seen a few around but not surprisingly the quality is variable.
Jon's choice: For the road, the Edelbrock performer, for the track the Wildcat.
Holley King of the street and track. The choice of all the professional racers in the USA, can be difficult to set up, but without doubt the best of the bunch. On a road-going 3500cc engine stick to a 390 cfm vacuum secondary unit. If racing the choice is 454 or 600 cfm, ideally as a double pumper. It's impossible to say which to use as you have to determine the dynamics and air flow requirements of your own engine. For example a 5.0 litre race engine with heavily modified heads would almost certainly need a 650 cfm unit. So you know the difference, a double pumper has throttle pumps on all 4 barrels and the second pair of barrels open mechanically. On the other types the secondary barrels are sucked open and the throttle pumps are only in the 2 primary barrels. There are several models available with a different application for each, see their excellent web site. Big double pumper = huge fuel consumption; my race car uses a gallon every 5 minutes which equates to about 6 mpg.
Holley 4150, 390cfm double-pumper (Keith Dorton special edition)
Edelbrock An excellent street performance carburetor, but not seriously used for competition in the UK. The main choice is the 500 which has the advantages of being cheaper than a Holley and easier to set up. Also sold in the UK as a Weber 500.
Edelbrock 1404 model 500 cfm carburettor
Carter A less expensive but capable 4 barrel carburettor. Very common in the US, less so in the UK.
Jon's choice: You get what you pay for. Holley is far superior, but you do need it set up correctly.
Essential on a road car; bigger the better, ideally with a cold air feed from outside.
For weirdness, you could try the 4 x SU setup on a Boxer manifold. Quite rare but apparently surprisingly good! I've never used one so can't comment on it's effectiveness.
Rover V8 showing the Boxer, 4 x SU inlet manifold
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