Rover V8 Twin Throttle Bodies

Rover V8 Throttle Bodies

I’ve been looking into fitting Rover V8 Twin Throttle Bodies. Rover did it on a limited number SD1 Vitesse’s. I wanted to modify a Thor Manifold; for it’s looks and height; to twin plenums.

The trouble was, I had no idea what size throttle bodies I needed.

These people have been doing similar to what I intend to do:

Modified Thor manifold

You can view numerous different manifolds at this site:

Optimum Throttle Body Size

There are those that reckon a Rover V8 with a 72mm throttle body and 41mm inlet trumpets is good for 360bhp. 

By using A = πr2 alone I’d be looking for a pair of throttle bodies about 50mm diameter. If I copied a 4.6L Mustang, I’d be looking for a pair at 60mm Ø. If I went for 65mm, there’s a strong chance road manners would be compromised, but 48 could starve air flow. – confused

So I decided to do some maths, but firstly I read this Designing, Modifying and Building Intake Manifolds.

The velocity in the plenum intake pipe should not be higher than 180ft/sec at maximum rpm. The formula to figure out the diameter inlet, for a given velocity is:

D = √ ((CID × VE × RPM) ÷ ( V × 1130))

Where:
D = Pipe Diameter
CID = Cubic Inch Displacement
VE = Volumetric Efficiency
V = Velocity in ft/sec

A 4.6L (4538cc) Rover V8 is 276.9ci. Power drops off above 5750rpm, whilst many reckon to keep the hydraulic tappets healthy 5500rpm is a good red-line.

Diameter(Ø) = √ ((276.9 × 0.85 × 5750) ÷ (180 × 1130)) = 2.58″ (65.5mm)
Area = 3371.8mm2

The throttle flap mechanism takes up part of the area, so the 68mm Thor Throttle body, on a single plenum aligns reasonably with these sums. Even though the hydraulic tappets won’t like it, the Rover V8 will rev to nearly 6250rpm, taking the diameter up to 68.3mm. 

Each bank of 4 cylinders is 138.5ci.

A 138.5ci cylinder bank with a 85% VE, revving to 5750rpm with a desired 180ft/sec air speed through the intake pipe would look like this:

Diameter(Ø) = √ ((138.5 × 0.85 × 5750) ÷ (180 × 1130)) = 1.82″ (46.3mm)

I’d need an intake that has a 46.3mm inside diameter to have 180ft/sec air velocity at 5750rpm. Adjust that to take out the throttle flap and increase the rpm to 6250 and your at 48.3mm.

Currently, my Rover V8 is not tuned, so I plan on using a pair of alloy 48mm MGF alloy throttle bodies. If they are too small I can increase to 52mm or even up to a pair of 60mm CNC after-market throttle bodies.

Single Plenum and Firing Order

With a shared plenum each cylinder bank shares the same throttle body. Each Inlet is sucking through a 65mm throttle body. There will always be some overlap in valve opening times, meaning 2 inlets are simultaneously drawing through the same body.

Firing order : 1, 8, 4, 3, 6, 5, 7, 2

As the inlet valve on cylinder 1 is closing, the inlet on 8 will be opening.

Rover V8 Firing Order

By switching to a modified Thor manifold, each cylinder bank has it’s own plenum. There will be no inlet opening overlap, so the throttle body size could be reduced slightly.

By going to a modified Thor manifold I’ll also need two Inlet Air Controllers (IAC), which will probably mean I’ll need to upgrade the driver FET inside the Megasquirt.

Rover V8 P38 GEMS Plenum

The standard SD1 through P38 GEMS manifolds use a 65mm Throttle Body built into the plenum chamber.

Area = 3318.3mm2

Rover V8 Plenum

If performance was my goal, then boring out this manifold to 72mm would be the best option. If however, like me, height was the primary factor then a modified Thor manifold might be an option.

Rover V8 Thor Throttle Body

The Thor manifold uses a separate 68mm throttle body (MHB000240).

Area = 3631.7mm2

Rover V8 Thor Manifold

Rover SD1 Vitesse Twin Plenum

The SD1 Vitesse Twin plenum had either twin 65mm (prototype) or 68mm (road) built into the plenum chamber.

Twin 65mm Area = 2 x 3318.3mm2 = 6636.6mm2
Twin 68mm Area = 2 x 3631.7mm2 = 7263.4mm2

Rover SD1 Twin Plenum

Mustang 4.6Ltr 2V Throttle Bodies (JQMT60CRB02)

The similar capacity 16valve 4.6Litre Mustang uses a pair of 60mm throttle bodies (JQMT60CRB02).

Twin 65mm Area = 2 x 2827.4mm2 = 5654.9mm2

Mustang 60mm Throttle Body

MG / Rover / Lotus Throttle Bodies

The K series Rover engine uses 48mm and 52mm throttle bodies.

MHB000261 – alloy

MHB000261 Throttle Body

d = 52mm
A ≈ 2123.7mm2
2123.7 x 2 = 4247.4mm2

MHB102121 – plastic
MHB000080 – alloy
MHB102121 Throttle Body

d = 48mm
A ≈ 1809.6mm2
1809.6 x 2 = 3619.1mm2

Whilst I’m planning the inlet manifold changes, I’ve still got the stainless exhausts to sort out.

Megasquirt MS1/Extra Rover V8 - Troubles Starting

Broken Bosch Ignition Driver LegsAs many regular readers know, I'd had my Megasquirt MS1/Extra Rover V8 starting within a couple turns of they crank. So why the picture above? - Once you spot it, it's obvious! The next evening, with 2 wires on the idle valve reversed, I tried again. Absolutely nothing. It didn't ...

Rover V8 Engine Mounts

I was fed up with that old Rover V8 falling off its jacks, so I made up some engine mounts. One time, when the engine fell off its mounts it managed to drop right through the chassis rails in such a way that it managed to hit the floor. What ...

Rover V8 Short Water Pump

A lot of people know the P6 water pump is much shorter than the SD1 but what is the super short water pump on the right? On the left is the standard Rover SD1 Water Pump. On the right is the Rover V8 Serpentine Water Pump. As you can see, ...

Rover V8 to MT75 Adaptor - part 4

This is an MT75 4x4 gearbox from a 2.0lt turbo Sierra Sapphire Cosworth. The bell-housing bolt pattern is much smaller than that of the Rover V8. Unfortunately, the bell-housing is not removable, so I am cutting it off with a hacksaw. It may seem a little Low-Tech and indeed there ...

Rover V8 Inlet Trumpets

Many people modify the length of the Rover V8 Inlet Trumpets within the plenum. However, until I get my Rover V8 up and running I keep mine as Land Rover intended. The first job for me was to get it drawn up into CAD. - Basically an excuse not to ...

Rover V8 Timing Chain Cover - Part2

Is this a Timing Cover Issue? or Is it a Front Diff Issue? It's definitely a space issue. After drawing up the standard Rover SD1 style timing cover housing, I found that the oil pump was trying to occupy the same space as the front prop shaft and Sierra Front ...

Rover V8 to MT75 Adaptor Plate - part2

Will the Borg Warner 35 Auto bellhousing mate to the MT75 manual? Can I cut it up to make a Rover V8 to MT75 adaptor plate? I was having one of those mental blind-spots. For some reason, because I was trying to mate the Sierra Cosworth MT75 manual gearbox to the ...

Rover V8 to MT75 Adaptor Plate

The goal is to mate the Rover V8 up to a Ford MT75 gearbox. Therefore I had 2 choices: Use an Rover V8 to MT75 adaptor plate Use a complete LT77 bell-housing and remove the integral MT75 bell-housing and weld on a mounting plate. Seeing as I could not find anyone ...

Translate »

Web Design by Go Web Solutions