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MG MGB GT V8 Factory Originals Technical - Inlet Manifold

I need the part no. for the Offenhauser dual port[the "lower" one] inlet manifold to fit a Edelbrock 1404 carb.,also need advice on which "low rider" air filter arrangement will suit my conversion to a mgb roadster.
My preference for the filter would be a K&N filter element but would appreciate learned advice.
I need to place this order with an overseas supplier thus need to be right the first time.
Finally,would a fitting kit be beneficial?
Thanks Trevor Burnett
t burnett

I was just refered to this site by Richard off the range rover group.


I presume you are talking about the Offy JWR dual port manifold that has the split runners.

Don't know whether power is that important but I saw some dyno results of that manifold on a 3.5 and it was costing a lot of power above 3000 RPM.

Back to back test against the Edelbrock Performer with the engine optimized for the Performer and it made a lot more power all the way to the red line at 6000RPM.

Whats your intended use for the car and what do you want to achieve. Are you intending to change the cam and modify the heads?

The usual air filter is the 14" x 2" Mr. Gasket Lowrider whci ch again can be somewhat restrictive because of the lid being so close to the top of the carb, but is usually all we have room for unless dramtic mods are done to the bonnet.


Kevin Jackson

Trevor, I'm using a Buick 215 inlet manifold, available from D&D Fabrications,( an Edelbrock 1404. It's as low as you'll get. As for the air cleaner,14" x 2" don't get one that has a "dished" top. It will foul the choke. For the Edelbrock carby, I found that the recommended rod jet set-up (1441 rods & 1422 jets) was a tad too rich & went one stage leaner in the cruise mode. 1423 jets & 1463 rods. BTW I had to fit a 1/2" phenolic spacer under the carb to aid hot starts, yet bonnet clearance is not an issue. The car is an RB, which does have a slightly higher bonnet profile than the CB cars. Barrie E
Barrie Egerton

Hi Trevor,
All the parts you need are available from Masterparts in Cape Town( Edelbrock 1404 four barrel carb, Edelbrock Performer Rover 3.5l inlet manifold,Holley blue top electric pump 5.5psi, 100 gals/hr and 14"x2" dropped bowl air filter with K & N filter element, straight 10mm banjo fitting for fuel line connection to the carb.)You will have to make up heater piping and an adaptor plate to mount the B heater valve at the rear of the manifold, and also to fabricate throttle and choke return spring fittings.They also stock K&N valve cover ventilation filters and thermostat outlet housings which can be made to fit.The calibration kit for the 1404 will have to be imported from the USA via Stateside autoparts; they can also order jets and rods as required for you .
The Edelbrock performer manifold is taller than the Offenhauser and you will have to do several trial fits with the engine mountings to get the bonnet to close without the need for a bulge (if that is your preference!)


Hi Tony,
Many thanks the info on the supplier,I definately want to go the Offenhauser manifold route due to the bonnet clearance issue,our local supplier Thundersports is extremely vague on the Offy manifold and am still waiting on info requested some four weeks ago hence my thread.
Rgds Trevor
t burnett

Hi Kevin,
Are you or any of the other readers able to guide me on the manifold preference vis-a-vie loss of power,etc,I do not want to bulge the bonnet and would like to retain the std. engine mounts,many thanks.
Rgds Trevor

t burnett


if you do not want to change the bonet and just cruising is on top of your list, the dual plane JWR manifold is just fine. It is the lowest one offered and it pronounces torque at engine speeds up to 3500 rpm, may be 4000 with the RV8 style exhaust manifolds. A 2 1/2" air cleaner should fit this installation.
When you want to have something more sporty, the Offy 360 seems to be the better decision, although you might have to cut out the strengthenig bar in the middel of the bonnet. The Offy 360 starts to limit the rpm range at beyond 5000 and works up to 6000 resonably while the JWR becomes very restrictive over 5000.
The Edelbrock performer is about 1" higher than the other manifolds, so it will not work under a stock bonnet when carb and filter are fitted.

I have the JWR on my car since more than 25 years but would not go for it a second time. It is simlpy insufficient and made tuning the Holley 390 a nightmare!
I tried to fit an Edelbrock once, but it was to high and I also wanted to keep the original shape of the bonnet. It seems to be first coice for Rovers and Range Rovers as for the Buick 215 powered saloons of the early 1960's.
Two friends of mine have tried the Offy 360 and were very satisfied even when racing, an other one decided for the JWR but on a B fitted with a LC Range Rover engine just for relaxed cruising but also has still to cure the problems with tuning his carb (jetting and springs for secondarys, accelerating pump cams and shooters).

There are also 4BBL original inlet manifolds for the Buick/Oldsmobile/Pontiac 215CuI engine offered in the USA. They also fit the Rover V8 and should be an interesting alternative concerning price and layout.

Some more details and pics are given here:


This thread was discussed between 06/03/2009 and 29/03/2009

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