Further efforts to limit the effects of under-bonnet temperature in a TC – update from Steve Priston

This is an update from Steve Priston’s article in Issue 58. Following publication of this article there were some comments made as to why the modifications carried out by Steve were necessary. A couple of members said that they had not, so far, experienced any overheating problems.

The following are some extracts from what Steve said in reply:

Please do not feel in any way that these modifications are necessary, if you are not experiencing any difficulties with the way your car is behaving, after all, everybody has a different driving style and certainly expects or hopes for different things from a car.

I come from a classic/vintage motorcycling background and am a time served Mechanical Fitter so make reversible changes, realising that our current fuel situation is not going to get any easier for our vehicles to cope with.

As with everything that I do, to try to improve the reliability of my car, I ensure that it is reversible. Unfortunately, in many cases, it can only be a compromise. Like trying to keep the modern fuel cool, in a small engine bay, with a great lump of hot cast iron radiating heat, with only a vented cooling system and large radiator to cool things down.

So, this sets the scene for what follows by way of update from him – over to Steve……

Want something neat to deflect the heat?

Following on from the write-up in issue 58, I have given the under-bonnet heat situation some more thought, first deciding to trim down my 3mm thick alloy heatshield so that it resembled the profile of the commercially available stainless-steel ones because its centre, upper portion, looked to be directing some of the heat from the middle of the exhaust header, onto the inlet manifold or at least impeding the airflow.

Photo shows Steve’s original 3mm thick alloy heatshield as shown in issue 58, which he subsequently decided to reshape.

Having re-shaped the shield, I then spotted that it might just be possible to fit an additional smaller shield, between the manifold, the edge of the cylinder head and of course those two centre exhaust outlets, directly below.

This involved a bit of cardboard folding and cutting, having decided first, that some light gauge, 2 inch alloy angle section that I had, might just do it, which it did, after a bit of adjustment, as can be seen from the photos.

Photos show two views of the additional smaller shield to locate as described above.

The additional smaller shield is attached via two cylindrical alloy spacers, to the larger shield, in an effort to better transfer some of the heat it would collect, then hopefully these would help to dissipate it better, looking at the small amount of space between these components, you will appreciate how this is quite fiddly, to get it in.

Please be aware, that I also employ a pair of Tufnol insulating spacers, between the carburettor flanges and the main heatshield.

Ed’s note: A picture showing the additional shield in situ is included under the next heading.

Want to move it out there for cooler air?

Another change that I have made, is to my pancake air filter arrangement, by adding an alloy spacer, to move out the rear filter, getting it away from the shielding effect of the front one, by moving it one and a half inches over to the offside.

Sometimes when checking the spark plug colours, I had noticed that the front two appeared to be very slightly weaker, than the following pair, this was the motivation for the change.

Above picture shows back filter moved out by one and a half inches. Picture below shows tapered bore of the spacer.

As can be seen from the photo, the spacer has a tapered bore, as an attempt to compensate for the extra distance that the filtered air has to travel, over its neighbour, its ‘octagon’ shape was an after- thought!

As suggested recently by Paul Ireland, it is connected to the rocker cover breather, via some 6mm bore PTFE tube.

Want to keep your fuel cool and still blended as intended?

It had been suggested to me by more than one friend, that the best thing I could do, to help cope with this change in our fuel, was to somehow get the fuel to return back to the petrol tank – so how do you do that, without doing something irreversible to the car?

Well, I already use a rear mounted fuel pump, also having a fuel pressure regulator. So, I cast my mind back to my last carburetted car, a 1986 Vauxhall Astra 1300, which had two different sized fuel lines, in a nylon type material, running along the underside of the car. My recollection of this was only because at some point the rubber hoses at each end had needed replacing.

Nylon now, would of course be no good, but using PTFE tubing instead would; this giving the advantage of being able to be threaded along the inside of the chassis rail, rather than having to fabricate the lines in rigid stainless steel, then attaching it to the outside of the rail, where the two lines would be visible.

Next, having had a good look at the underside of the petrol tank, I decided that the returned fuel would have to go back into the tank via the 3/8 BSP drain plug port so I would need to make up some sort of snorkel tube, to discharge the fuel into the very top of the tank. For this, I bought some 8mm outside diameter stainless steel tube, creating what can be seen in the photo, the pipe resembling something like a bow.

The requirement for this curved shape, was due to the sloping rear panel of the tank because I didn’t want this new internal pipe, to touch the inside of the tank; but it would have to reach the top inch or so of head space, allowing it to discharge fuel, without any risk of syphoning, thereby avoiding any need for a non-return valve.

The fitting used for the tank connection, is something that I modified to suit but could be bought as an 8mm to 3/8 BSP nipple, that is then simply drilled to allow the 8mm pipe to pass right through; its olive was tightened onto the tube before fitting it into the tank, to make that job easier, then the compression nut was slackened off, before fitting it into the tank.

This was achieved by first jacking-up the rear of the car, then by leaving the compression nut on the fitting loose, it could be screwed into the port, with the bent tube remaining stationary up inside the tank. To get an effective seal on the olive, without the need for it to be excessively tight, I over-taped the olive, with plumber’s PTFE tape, a trick from years of working on sterilisers, that had to pass stringent leak tests.

This then left me with no easy means of draining the tank, which now it seemed, more than ever would need addressing, as we are advised not to leave ethanol fuel for too long in our vehicles.

This time however, I did actually drill and tap an 1/8 BSP thread into the side of the large hexagon brass tank outlet fitting, which at the time also required a replacement gauze; the extra threaded hole could simply be plugged, if needed.

This new tapping allowed me to add a ¼ inch ball type drain valve, to which I have fitted an additional plug, as shown (below), to prevent accidental draining, now making this task both simple and safe.

Photo showing the addition of ¼ inch ball type drain valve to which an additional plug has been fitted to prevent accidental draining.

This tank part of the job, had been what had put me off of attempting returning the fuel for a good while, so the worst was now hopefully solved.

My attention then turned to what fittings I could lay my hands on, to sort out the other end, under the bonnet, as can be seen in one or more of the pictures, with the smaller 1/4″ bore return line, passing over the top of the 3/8″ bore supply hose.

Ed’s note: Some under-bonnet ‘shots’ follow:

I decided that by ensuring that the fuel should remain cool, when pumped to the float chambers, that I would swap back the float chamber tops, reverting to the standard arrangement, with the hoses running closer to the cylinder head, having felt previously, that the front banjo fitting was perhaps a little vulnerable, should the car have a shunt.

It had also been suggested, that to be able to control the supply to the carburettors, that I retained the fuel pressure regulator, only this time it should be in the return line so I dismantled it, to alter its flow direction but expect that this was not really necessary.

With opposite ends of the system ready, I decided that I could also both simplify and tidy things up, by moving the fuel pump inboard of the chassis rail.

Having thought briefly about the pipe sizes for the run along the chassis rail, I seemed to remember that the Astra had an 8mm bore supply, with a 6mm return so this is what I went for, meaning 10mm and 8mm PTFE outside diameter tubing was required.

When using compression fittings with this type of tubing, I decided to make up some short lengths of very thin-walled stainless steel lining tube so that the olives would work as intended and once again over taped them, also where the SAE J30 R9 rubber hose joined the 10mm PTFE tube, I fitted a longer piece of liner tube for where the hose was double clipped.

The pump was mounted between two pieces of hose, with both being covered with some nylon mesh sleeving, as a form of extra protection.

The two lengths of PTFE tubing are protected by lower specification rubber hose, which I cut along its length, then pushed over the tube, clipping it in place, this in turn being routed along the chassis rail, clipped up as required. 

Now, by simply opening the filler cap, with the pump running, you can both hear and just see the fuel as it returns into the main body of the fuel in the tank below.

One last thing that I felt I should do, was to fit a manual fuel pump switch, simply so that when ending a journey, it would allow me to run down the amount of fuel in the engine bay, by running the engine until it stopped, hopefully lessening the possible issues of corrosion slightly.

Please note, if having just read this article in disbelief, of what I have done to my car, my justification is simply because it gave me something to do but also, I hope has helped to “future proof” it for a while, as fuel becomes less suitable. Also, please be aware that I haven’t yet had my car anywhere near as long as many of you reading this, having only acquired it at the age of 50, in 2017 so will have to hopefully put up with it for a while yet!                                    Steve Priston

Editor’s note: Just to close, a couple of underneath the car ‘shots’:

Revised fuel pipe routing, no longer outboard of chassis rail.

Reliable, less expensive, modern Facet fuel pump, well out of harm’s way. https://www.fuelpumpsonline.co.uk/facet-guide-27-w.asp

Editor’s further note:

The article was sent to Paul Ireland for comment, at Steve’s request.

Paul had some reservations based on his son’s experience of fitting a fuel injected engine into his Lotus Europa. He had a lot of problems with his Facet fuel pumps failing. The problem arose because these must be mounted horizontally otherwise the pump rollers run on and wear the side face. This can cause the pump to jam.

With such an arrangement it is very important to fit a fuel filter between the fuel tank and pump. Facet pumps are very susceptible to dirt in the fuel. He was not sure where Steve fitted the fuel filter.

He added that Steve mentioned the pressure regulator but he did not see where he fitted it nor its pressure setting. With such an arrangement the regulator needs to be fitted on the fuel return path to the tank. It must also be set to the same pressure that a normal pump would generate. Too high a pressure may cause the needle valves in the float chambers to fail.

Modern cars that are fitted with a system to continually return the petrol tank also include a swirl pot on the fuel feed to the pump. The purpose of this is to remove air from the fuel before it is pumped into the high pressure circuit. In the case of the MG RV8 for example, the swirl pot is fitted inside the petrol tank.

Given this swirl pot arrangement Paul is not certain what the effect of air in the fuel line would have in Steve’s arrangement.

Paul’s comments were fed back to Steve, who replied as follows:

“There are significant differences between the high pressure re-circulating systems as used on modern fuel injected vehicles and those used for my more simple low pressure application, because the high pressure systems employ more complex components that are totally unsuitable.

There are many versions of both fuel pumps and regulators available, even those specifically for retro fitting carburettors to an engine already using a turbo with a high pressure system for injectors, so you need to study the relevant application of these for safety’s sake.

I have used a Facet Posi-Flow 60106, 4 to 6 psi pump, with a Malpassi  PKA, 1.5 to 5 psi regulator; combined they cost less than an SU pump alone.

The Facet pump used is only rated at 4-6 psi; the instructions clearly describe that it should be mounted as I have done, being inclined at an angle, to prevent cavitation within the pump, having its own inline, replaceable filter simply screwed into the inlet port.

The fuel pressure regulator is of course positioned within the return fuel line and is not a multi ported version of the Malpassi unit, just having in/out ports because that is all it needs, unlike those for fuel injection, it also is their lowest pressure version, as required by the SU’s, with its sole purpose now being to create resistance to the fuel flow, above that of just returning it in a smaller bore pipe.

The regulator must be thought of in its current application, as more of a chicane, with the pipe system being the race track, in actual fact no matter what setting it has been tried on, it doesn’t upset the running of the car one bit, so has no effect on the float needles seating.

As far as issues through the return fuel carrying air bubbles that it has collected at the float chamber interface, well, this is part of the reason for the snorkel in the petrol tank having its exit end cut half way through, then bent over to approximately 90 degrees, to produce something of a spray at a time of higher pressure and with the exit at the top of the tank, it should help to de-aerate it.

With the tank vented, as they are, there is little chance, if any of a pressure build-up within it and in my experience of purified water systems, the feed water is supplied via a “spray ball”, into the tank, to de-aerate, like a showerhead. Please be mindful of the fact that what I have done to my fuel system has been through advice and guidance, from a retired Ricardo employee, his role with the company, was as their “engine rigger”, in other words, the person who rigged up the test beds for all manner of engines, setting up all of their supplies of fuel, oil and coolant, addressing any special requirements, as discovered, during the extended test periods.

The retired Ricardo employee did mention the use of a swill or swirl pot, but only if I had a problem, as they are more of a race track fitment, unless a vehicle suffers from issues that they can cure, as I understand the later carburetted VW Golfs did.

I think that as the SU float chambers have their own unsealed tickler units built into the chamber caps, that this should not be discounted as a means of effectively venting off vapour, should it build up: also, that in my car’s particular case, the temperature build-up, within its float chambers is very small, due to the effectiveness of using both heat shields and Tufnol insulating spacers combined.

As we currently live on the south coast, with its well-known appalling traffic problems, our return journey very often includes the last mile and a half, in heavy, slow moving or often stationary traffic, where I experience no issue whatsoever, with the behaviour of the car, even to the point that if the weather is very hot, I tend to switch off the engine, whilst waiting at traffic lights, before joining the “merry throng” westwards because of how confident I am of it restarting, without issues.”

Ricardo plc: https://ricardo.com/about-us