Pushing the limits

[flying farmer]

Boredom has set in.

For the first time in about 10 years I am not restoring a Triumph, and I needed something to do.

Since I finished my Stag project, it has left my Stag engine TR feeling a little sluggish, even if this is a false feeling with the TR weighing about a quarter of a ton less than the Stag.
I decided the solution would be to build it another engine, and recycle the old one through one of my other Triumphs.

I never expected to get the 246bhp I achieved with the Stag project, and I also never expected it to be quite happy on regular unleaded with a 10.5 : 1 compression ratio, especially since I am running a maximum advance of 31 degrees.

This gives the possibility of squeezing a bit more out of the Stag engine.

To this end I have been slowly accumulating bits over the last 12 months with the intention of starting when I ran out of other things to do, which has now happened.

The idea is to build this engine to a very similar specification to the last one, but with a bit more compression and to try something a bit more radical with the head porting while still retaining standard size valves.

I don't have the benefit of high compression pistons this time, so getting the higher compression required is going to need a little more imagination on the machining of the pistons and block. To this end I have acquired a new set of 40 thou pistons as I have a block that is bored 20 thou over but which needs two liners replacing due to corrosion.
This block came from a mate who bought it to replace the RV8 in his Stag, but the pits in the bores were actually full of body filler!

The idea is to get a bit more swept volume which will help raising the compression. The block is currently away for a rebore and new liners. I had already replaced one liner that was hopelessly pitted but the pitting in the other was a bit too much to be taken out with the rebore. This block had already had 8 liners fitted so swapping a new one was simply a matter of grinding though one side with a carbide cutter then winding in a new one using an old brake disc as a flat surface and a large section threaded rod to do the pulling.

So far I have spent a lot of time over the last few weeks porting the heads using my home made flow bench.

When I say a lot of time, I am probably getting on for 100 hours so far. I am actually doing 3 heads, one is rather corroded but hopefully saveable, and the intention at the moment is to be able to use this for future reference just in case I ever do another pair of heads.

Unfortunately I cannot do a straight comparison with the heads of my project Stag as one of my original old flowbench hoovers went bang while using it as a hoover!
I have also done some porting work on my flowbench as there were a number of restrictions that needed removing. This tends to raise vacuum levels at high valve lift and so gives the impression of less effective porting of the inlet tract.

I shall keep updating this thread as work progresses, but I don't intend rushing it as I am not intending to fit the completed engine until next Winter.

Neil

[mjheathcote]

Regarding swept volume, would have loved to know how TM Garages did their 'big bore' Stag engine in the 90's.
Think it was around 3.5L, they also did a twin timing chain conversion too.
Without looking at piston diameters, it couldn't have been as simple as boring and fitting say 2lt TR7 pistons maybe?

[kev100]

Good stuff Neil ...

I am interested in doing what is necessary to my engine with the goal of better fuel economy rather than improved power, but I am sure there are some crossovers here .. will keep an eye on this thread ..

I have just taken possession of a 60sqm unit, so finally will be able to get my Stag out of the paddock it has been sitting in for nearly a year, and begin the restoration process .. although I have rented the unit as a store for materials and to keep my tools in, the main reason was so I would have a good space for the restoration, my stag will now be sitting in a new home of about 40sqm of that space ... happy days.

[Carboy0]

Marked this one up for subscription.

Very interested in ideas for future enhancements for my own.

Chris

[StagManiac]

Likewise, watching with great interest.

Paul

[mole42]

Me too, although my 'aspirations' are rather more modest.

(see what I did there?)

Richard

[Ian F]

Neil

If I'd known you were so bored, you could have had a play with my Stag engine!

Currently bog bog standard and measured at 112.5 hp when I last went to Enginuity and you were there with your Stag engined TR - some 5-6 years ago.

Busy year this year however, including E S M I hope, but likely to need attention soon as it's now covered 93k with little or no major attention to my knowledge.

Shame you've got a new project now though, maybe reserve me a space next time? LOL

Ian

[mole42]

I have just taken possession of a 60sqm unit

That's a pretty big engine!!

[kev100]

That's a pretty big engine!!

The price was right ..

[flying farmer]

Regarding swept volume, would have loved to know how TM Garages did their 'big bore' Stag engine in the 90's.
Think it was around 3.5L, they also did a twin timing chain conversion too.
Without looking at piston diameters, it couldn't have been as simple as boring and fitting say 2lt TR7 pistons maybe?

Can't say I have ever heard of this big bore conversion, but I wasn't a member of the SOC back then.

I would have doubted it would be as simple as using another Triumph piston. I had some Dolomite Sprint pistons somewhere, but I don't think the castings would be thick enough to take the required bore. Also the pistons are much heavier and this would require some serious counter weighting of the crank.
On my last Stag it cost an extra £100 ish quid to get the crank weighted up to account for the +20 pistons.
I have lightenened the con rods for this next build as it has +40 pistons that are even heavier.

I remember someone on here from the USA had some bespoke pistons manufactured, but IIRC the cost was over $1000.

Neil

[flying farmer]

Some of you will have seen similar pictures before from my last Stag project, but the secret of success in extracting power from the Stag engine is to make it breath better.

The only way of finding whether the porting work undertaken is doing any good is to measure the airflow though the port, and for this a flow bench is required.

Although it is possible to measure the flow in cubic feet per minute this requires expensive calibration equipment, and it is simpler to measure the pressure drop in the cylinder by attaching a water filled U tube to a spark plug with the centre knocked out and replaced with a small diameter bit of pipe.
To generate the airflow I am using two rather knackered vacuum cleaners. These are joined with a T piece to the crown of an old piston wedged into the bottom of no2 cylinder of a spare Stag cylinder block.
I use this cylinder for all the tests, but I have to keep making reference to an old head gasket to ensure that the valves are located correctly relative to the cylinder bore, then use whichever head stud/bolt positions are available to ensure it remains aligned.
The first photo below shows the piston in the block, since I last used it I have cut down the piston so only the crown remains. This was because the gudgeon pin bosses were partially obstructing the pipe. The pipe is just a bit of 1"galvanised steel water pipe fibreglassed into the crown, and the rubber T piece I am using pushes directly onto this pipe.
I may yet increase the size of this pipe as it is probably still too restrictive, and then re test all the finished ports

The second photo shows the U tube, the colour for the water comes from OAT antifreeze. The wooden ruler is used for measuring the pressure differential between the cylinder bore and the atmospheric pressure. The height of water raised is double the reading obtained from the left hand tube next to the ruler. I did wonder if there was a difference to be found between testing on a high pressure day and a low pressure one, so I did log the atmospheric pressure for a while but did not seem to find a particular link.
Mains voltage is very significant however, hence the voltmeter resting on top of the electric socket. Some days it can be as low as 232 volts, other days as high as 241 volts and this can easily give a difference in reading of half an inch of water at maximum valve lift, and a lot more at lower valve lifts.

As the airflow increases due to porting work, the pressure in the cylinder will decrease so I am aiming to get the lowest figures possible while removing as little metal as possible.
Picture 3 shows the mount I have made for my dial gauge, the large screw presses down the valve the required amount, and picture 4 shows the dial gauge attached to its magnetic base. Dropping the magnetic base does it no good at all, hence the orange tape holding it together!
The steel plates bolted where the inlet manifolds fit may form the basis for the inlet manifold, or I may just retain them as templates. The throats of the inlet ports have had the top sides raised by 2 or 3 mm which is about as far as I dare safely go due to a waterway that starts about 10mm in from the manifold face.
The last picture shows the trumpet I use to smooth the airflow into the port, I simply hold this in place over the mouth of the port when testing. I have had to enlarge the head end of this compared to the one I used on my last Stag engine due to opening up the ends of the port a little.
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[mike@thenook]

This is seriously interesting stuff Neil, you never fail to impress with your abilities and knowledge on engines, if only I had the same and the time to play!

Cheers!

[flying farmer]

I am still suffering from the lurgy so garage time is non existent at the moment. However, when modifying a head you have to know where you are starting from, and whether it is safe to start grinding out lumps of metal.

When I did my last engine I cut up a scrap head to check the thickness of the castings, but I never took any photos of an unmodified head, but this time I remembered.
The first two pictures show what I am using as my spare reference head before I started work on it. I forgot to photograph the best pair of heads before I started work on these.

It can be seen that the standard casting has some pretty enormous ridges in the port just below the valve and it is not difficult to remove these. Somewhere I have some flow test results that show the percentage improvement just by removing these, and I shall come back to these at a later date. On the picture of the sectioned head, the results of the previous "remove the obvious lumps porting job" can be seen on the port as brighter bands. This is about as much as is useful if still using the Stag inlet manifold as it is the manifold that is the major restriction rather than the porting job. The Stromberg fed engine in my Estate will have this sort of porting job, and that makes 162bhp with Stag type tubular manifolds and straight through silencers.

The last picture shows a section through an inlet port. This head had previously been used on one of my early efi engines, and there is a notch cut out of the inlet manifold face to clear the injectors on the top side of the port. This is ordinarily just a 90 degree angle.

What can be seen is that the port is slightly narrower at the manifold face than before the valve guide boss. On my last engine I didn't touch the roof of the port and left it more or less as it came from the factory. A waterway can be seen running over the top of the port which limits the amount that can be taken out.
As it happens grinding a small amount out of here has major implications on the design of the inlet manifold, which again will be covered at a later date.
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When looking at the sectioned head above, the really obvious restriction looks to be the valve guide boss. This is where the flowbench comes into its own, as I have discovered that grinding away the valve guide boss is a sure way of killing flow through the port. This is when a scrap head is invaluable, as when the flow figures suddenly take a turn for the worse the situation can be remedied with body filler. Again, and again and again until I get it somewhere near right! Taking too much out of the good heads is a serious PITA as the only remedy is to weld the missing metal back in again. That could be expensive. It is pretty damn soul destroying to get the flow figures of a single port nearly as good as the last port that you did, then removing a fraction more makes the flow massively worse at a single stroke. I have spent at least two weekends sorting out single ports where I have done just this!
Neil

[Ian928]

Taking too much out of the good heads is a serious PITA as the only remedy is to weld the missing metal back in again.

I know many use Epoxy to add material in the intake port. I am not sure about ultimate longevity though.

I must say I am shocked when I see the way these heads look! The only heads I have done was to ease out some very small imperfections between valve seat and port on my Porsche 928S, those were just big enough to catch a fingernail. I have looked at the ports in my Triumph Spitfire and I am sure they look a lot better than this. The upside of course is that there probably are gains to be had! Do you have any numbers indicating performance gains just by cleaning up the ports?

[flying farmer]

I dread to think what would happen if a lump of epoxy fell out of an inlet port! Might as well chuck a pebble into the cylinder, at least at the thickness required to even out a Stag port.
The Triumph 4 and 6 pot cars are far better than the Stag as regards the regularity of the castings, I have had a play with both of these in the past. The Stag castings vary a lot from one casting to another, so I assume there was a fair variation in the construction of the moulds.

This does make the porting extremely difficult, because what works brilliantly on one port is extremely difficult to transfer to another port. I have made numerous profile templates of the better flowing ports, but when you try and grind another one to the same profile it simply doesn't work!

I eventually arrived at a series of templates that removed the minimum amount of metal that seemed to do the job on most ports. This is not helped by the fact there are 4 right hand curved ports and 4 left hand curved ones, and in addition to this the end ports on both heads are different to the middle ones particularly with reference to how far to one side of the valve stem that the ports are biased.

This gives 4 different port designs over 8 ports. Nothing like keeping it simple!

Despite all this, the basic design of the ports and combustion chambers are actually very clever. I think I read somewhere that the heads were developed by Ricardo Engineering who were big in head and combustion chamber design back in the fifties and sixties.
The exhaust ports are extremely good as cast, and very little can be done to improve them. I did wonder whether the relatively narrow gap between the valve and the cylinder wall side of the head on the inlets could be a restriction, so I tried grinding a bigger gap on a scrap head with no improvements whatsoever. It looks like the combustion chamber design is about as good as could be hoped for.
The ports themselves have a huge bias towards the cylinder wall side. This at first sight looks as though it will try and force the inlet charge through the narrowest part of the valve to head gap. The 1st photo below I have borrowed from my last Stag engine project, and this shows the general direction of the flow. If anything I have been rather too conservative with the amount the arrows wrap around the back of the valve stem. I reckon the airflow around both sides of the valve actually meets at least 45 degrees to the left of the valve in the diagram. This has the effect of making the mixture swirl around the cylinder at high speed before it is compressed which is very good for fuel efficiency and resistance to detonation. This might explain why I can get my Stag engine to run smoothly on mixtures as weak as 18:1, and on hot starts it is often about 20 :1. My Rover V8 goes rough past 16:1.
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The picture above also shows how I was having problems with turbulent flow reversal on the inside of the port with the last engine. The picture below, also borrowed from the last project, also shows how I was having flow reversal problems along the floor of the port which I cured by angling the port downwards by about 20 degrees.
This time I opened up the entry to the port, mostly upwards but also towards the turbulent area on the wall.

This smoothed out the airflow nicely, and hopefully without increasing the port size enough to drop the gas velocity which would damage low speed torque. We will find the answer to this when the engine eventually gets onto the rolling road! The trumpet I use for testing still had a 20 degree end to it when I started enlarging the port upwards. This now kills the flow stone dead and the air now has to enter the head at 90 degrees to the mounting face. This will have implications when I build the inlet manifold as I was able to keep the runners straight until they met the bottom of the plenum, then another slight kink from the plenum floor to the trumpet finished the job This time I will have to design in a bend.
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