Black goo

[quattro]

Whilst tarting up the engine recently, I changed the inlet manifold bolts for some nice stainless ones. The rear offside bolt had a strange black goo on it much like a butyl sealant, or the old gum gum type non setting sealant. I have found this substance in various places around the car, including sealing a makeshift gearshift boot to the tunnel, and fixing the fuel pressure gauge into its housing.

A few days ago, a heat dissipator gasket arrived and I set about fitting it. The rear offside bolt holding the carb down was also covered in this black goo

I took the carb off to find that the gasket used was the wrong one. The carb is a four barrel on a twin port mainfold, meaning that the front two feed all 8 cylinders, whilst the rear two feed just 4 each on their own side. They should not be allowed to interfere with each other so a four hole gasket should be used. The gasket pictured is a square hole gasket and does not seal the barrels independently. The angled plate here has another square hole gasket on the other side.

Just as a precaution I took the inlet manifold off as I was concerned about the black substance.

It appears it was just sealing the bolt hole itself as there was no sign of it on the composite gasket, although the waterway at the rear was discoloured slightly. I have to wonder if the sealed off waterway (No access for it in the manifold) was leaking up the bolt hole :?:

All back together now, new valley gasket hylomared in, new heat gasket, in place of the old angled plate (hoping I don't need that), running just a little smoother now and hopefully will be able to tune the fuel system better. I did get hold of a Boach Lambda sensor and fitted it to the nearside manifold when I had the engine apart. Fit that to a gauge and I can get some real time A/F readings very soon.

 

[ghce]

??? what Carb are you using, your discription has got me somewhat confused. I am running an Edelbrock dual plane inlet on mine, each of the 2 ports just supplies 4 cylinders only and on my Weber carb1 primary and 1 secondary feed 1 of the of the 2 inlet manifold ports ie 4 cylinders only the other primary and secondary run the other 4 cylinders. this is pretty standard stuff but what you are saying is a wee bit different than that.

Ps Nice photos

Graeme

 

[quattro]

It's an Edelbrock (Weber) 500 carb, but the difference is the 'Dual Port' Manifold. This is different from the Dual Plane manifold :shock:

The port is split into two parts and the primaries feed the lower ones. As they enter into a single void, they feed all 8 cylinders and run at a very high speed (apparently).The secondaries feed the upper part of the port when they are open. Left feeding left, right feeding right. I thought this strange so have had a look around on the net. It seems to be a good mainifold for small V8s, like the Rover, as it gives good power and helps with fuel consumption.

I will post up some pics later.

 

[quattro]

It's upside down but you can see how the port is split into two ports per cylinder.

 

[ghce]

All sounds a little weird, I presume that it is an input pulse of charged air/ timing and flow thing :? The only 4 port setups I have seen were for seperate carbs, if you find any good links to write ups on it I would love to see them.

Graeme

 

[ghce]

that photo makes it a bit clearer, I can see how that would work! still would like to see the tech explanation for it esp as how it applies to torque and MPG.

Graeme

 

[quattro]

I haven't found any write ups, just little snippets as to what they are all about - like this one

Offenhauser Dual Port intake manifolds feature completely separate runner systems for the primaries and secondaries. At low-load, the primaries feed the fuel-air charge through the smaller bottom passages at near sonic speed, improving power and efficiency. When the secondaries open, their charge goes through the bigger, cooler upper passages. Then, in turn, it is rammed into the cylinders when it encounters the high-velocity mix from the primaries. The result is better fuel economy and a 15-30 percent power increase across the whole rpm range.

and this

Offenhauser Dual Port manifolds vs. dual plane manifolds

There is a lot of confusion regarding the differences between the Offenhauser dual port manifolds and other companies’ dual plane manifolds. Their names are similar, but their designs are distinctly different. Both manifolds are designed to increase torque output in the lower RPM range of an engine. This is mainly for street performance or towing application where engine RPM does not regularly exceed 6,000 RPM. In this lower operating RPM range; air velocity in the manifold is critical to increasing torque output.

The dual plane manifolds tackles this issue by dividing the manifold lengthwise creating two plenums in the manifold. The manifold then has runners that overlap each other on different planes; this where the name dual plane comes from. On a four barrel manifold, one primary and one secondary venturi of the carburetor supplies the air/fuel mixture to each plenum. The size of the plenums and runners decrease the volume in the manifold and increases the air velocity. The performance trade off in this design is in the runners themselves. Air, like water, likes to follow the path of least resistance. The runners create barriers in the manifold that the air/fuel mixture must navigate on its way to the cylinder head. As the air/fuel mixture follows the path of the runner, centrifugal force acts on the air/fuel mixture causing fuel to drop out of suspension and pool in the runner. Also, with each plenum sharing a primary and secondary venturi from the carburetor; as the secondary opens air velocity is decreased in the plenum until engine RPM is increased restoring the lost air/fuel mixture velocity.

The Dual Port manifold takes a different approach to improve engine efficiency at lower RPM. Understanding the dynamics of air flow and the flaws of the dual plane manifolds, Offenhauser engineered the dual port manifold to increase air velocity without sacrificing air/fuel mixture. The Dual Port manifold is basically two manifolds placed on top of one another. The carburetor is split between the primary and secondary venturies; with the primary supplying one plenum and the secondary supplying the other separately. The primary plenum is place on the bottom of the manifold and the secondary plenum is on top of the primary. Each plenum is separated from the carburetor all the way to the head flange. When looking at the head flange, there are two ports exiting the manifold (one primary and one secondary) for each intake opening on the cylinder head; this is where the name Dual Port comes from. In order to increase air velocity, the primary plenum is smaller in size than the secondary plenum. The smaller area of volume in the primary plenum increases the air/fuel mixture velocity to near sonic speed. The increased speed of the air/fuel mixture allows more air and fuel to move pass the intake valve when it is open. Also, without runners like the dual plane manifolds, the dual port does not have fuel leave suspension and maintains air/fuel ratio from the carburetor to the engine. When the secondaries of the carburetor open, the air/fuel mixture travels at a slower speed than in the primary plenum. As the slower moving air/fuel mixture meets the faster air/fuel mixture at the cylinder head; the faster air/fuel mixture flow pulls the slower air/fuel mixture into the cylinder with a ram effect. In addition, placement of the primary plenum below the secondary plenum adds additional benefits. The faster moving air/fuel mixture insulates the secondary plenum from engine heat. This allows the secondary air/fuel mixture to be colder and denser for increased engine efficiency. This increase in engine efficiency has the benefit of reducing fuel consumption and exhaust emissions.

The Dual Port manifold by the nature of its design is a superior manifold when compared to the dual plane manifold. The benefits of the manifold are a proven fact, not marketing hype. Complaints about the Dual Port manifold can easily be traced back to one of two things; inflated expectations or using the manifold on the wrong application. The later of which, is a subject all to itself.

All very interesting and news to me - I didn't even know this type of thing existed.

Problem is, that at near sonic speed, the primaries are going to sucking fuel and air from the secondaries, when you have the wrong gaskets :evil:

This is what the open intake looks like

 

[ghce]

Pretty much the explanation I was expecting, quite exciting too. I would be keen to see what the new RPM VS torque graph looks like when compared to the dual plane not to mention fuel economy at town and country running.

Down to the nitty gritty, the Edelbrock dual plane which I have is plug in replacement to the Rover OEM in terms of thermostat (P5 housing) and temp sensors for the P6 setup, what nasty adaptions do you need to make to get this beast fit in with P6B.

Graeme

 

[ghce]

In my searching found this site http://www.mez.co.uk/ms12.html

Graeme

 

[quattro]

Down to the nitty gritty, the Edelbrock dual plane which I have is plug in replacement to the Rover OEM in terms of thermostat (P5 housing) and temp sensors for the P6 setup, what nasty adaptions do you need to make to get this beast fit in with P6B.

Graeme

I didn't fit it, it was on there when I bought the car.

Looking at it, you need a different thermostat housing, but it is fitted with the original P6 thermostat.

The heater hose which used to go underneath the P6 manifold used to go over the Offenhauser and rocker covers but I have rerouted this to go through a pipe (modified from a 2200TC) which is now bolted to the rocker covers. Looked a right mess with that huge hose there.

The vacuum for the brakes comes out of the back, just under the rear of the carb, and the temp guage is in the same place as the P6 mani. Looks failry simple to be honest.

 

[quattro]

Just as a matter of interest for anyone using this type of set up and having starting problems.

I have been told that the engine heat can boil the fuel out of the carb making it difficult to start, so get hold of one of these heat dissipator gaskets and this will cure it.

I got hold of a 1/2" Mr Gasket 98, and it now starts on the button every time.