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[NaughtyNigel]

I should have mentioned yesterday -

The ports should be smoothed, but not polished, and finished with very fine (1,000 or 2,000 grit) wet or dry with a bit of light oil on it.

Polishing creates turbulence, whereas a smooth surface encourages laminar flow (= more inlet charge).

The key objective here is to smooth the inlet tract, so any gaskets should be trimmed back, and inlet ducts aligned with the inlet ports. This might mean ADDING material such as Devcon, rather than cutting it away. 

The idea here is to assemble the engine exactly as the designer intended (AKA 'Blueprinting'), rather than how the assembly line does it.

If you are really keen, the compression ratios of all six cylinders should be matched (by measuring head capacity at TDC), and skimming a fraction off of the piston crowns as required.

You might also check the 'squish band' around the periphery of each piston, using a piece of solder to measure the gap at TDC. Anything more than 25 thou encourages detonation and pre - ignition, but most assembly lines work to much wider clearances for safety. Don’t forget to check the gap between the valves (when fully open) and the piston crowns at TDC too.

Most petrol engines will safely run with much higher compression ratios (= more power for the same amount of fuel) if the squish band is correct.

Many competition engines are blueprinted, rather than 'tuned', as this provides greater power and economy with better reliability. The difficulty is that production lines simply don't allow for this kind of assembly.

NN

[Martin_1962]

Have the later 3.2 ones, Martin

I know - I was answering other questions

[Martin_1962]

I should have mentioned yesterday -

The ports should be smoothed, but not polished, and finished with very fine (1,000 or 2,000 grit) wet or dry with a bit of light oil on it.

Polishing creates turbulence, whereas a smooth surface encourages laminar flow (= more inlet charge).

The key objective here is to smooth the inlet tract, so any gaskets should be trimmed back, and inlet ducts aligned with the inlet ports. This might mean ADDING material such as Devcon, rather than cutting it away. 

The idea here is to assemble the engine exactly as the designer intended (AKA 'Blueprinting'), rather than how the assembly line does it.

If you are really keen, the compression ratios of all six cylinders should be matched (by measuring head capacity at TDC), and skimming a fraction off of the piston crowns as required.

You might also check the 'squish band' around the periphery of each piston, using a piece of solder to measure the gap at TDC. Anything more than 25 thou encourages detonation and pre - ignition, but most assembly lines work to much wider clearances for safety. Don’t forget to check the gap between the valves (when fully open) and the piston crowns at TDC too.

Most petrol engines will safely run with much higher compression ratios (= more power for the same amount of fuel) if the squish band is correct.

Many competition engines are blueprinted, rather than 'tuned', as this provides greater power and economy with better reliability. The difficulty is that production lines simply don't allow for this kind of assembly.

NN

On my Sunbeam I had 60 thou machined off the head - in fact it right up to the edge of the plug thread.

I considered a head skim on the 2.6 but that was too difficult being both V and over head cam

[NaughtyNigel]

I should have mentioned yesterday -

The ports should be smoothed, but not polished, and finished with very fine (1,000 or 2,000 grit) wet or dry with a bit of light oil on it.

Polishing creates turbulence, whereas a smooth surface encourages laminar flow (= more inlet charge).

The key objective here is to smooth the inlet tract, so any gaskets should be trimmed back, and inlet ducts aligned with the inlet ports. This might mean ADDING material such as Devcon, rather than cutting it away. 

The idea here is to assemble the engine exactly as the designer intended (AKA 'Blueprinting'), rather than how the assembly line does it.

If you are really keen, the compression ratios of all six cylinders should be matched (by measuring head capacity at TDC), and skimming a fraction off of the piston crowns as required.

You might also check the 'squish band' around the periphery of each piston, using a piece of solder to measure the gap at TDC. Anything more than 25 thou encourages detonation and pre - ignition, but most assembly lines work to much wider clearances for safety. Don’t forget to check the gap between the valves (when fully open) and the piston crowns at TDC too.

Most petrol engines will safely run with much higher compression ratios (= more power for the same amount of fuel) if the squish band is correct.

Many competition engines are blueprinted, rather than 'tuned', as this provides greater power and economy with better reliability. The difficulty is that production lines simply don't allow for this kind of assembly.

NN

On my Sunbeam I had 60 thou machined off the head - in fact it right up to the edge of the plug thread.

I considered a head skim on the 2.6 but that was too difficult being both V and over head cam

I assume that was a Sunbeam car?

60 thou is quite a lot, but many production engines don't run anywhere near as high compression ratio as the manufacturers claim.

We had the head skimmed by 20 thou on our old 1.6 16v Astra (when the head gasket went), and it made a noticable improvement to both power and economy.

I had about 25 thou skimmed off the heads of my 249 TZ Yamaha, and bronze squish rings fitted. This allowed much higher CR, and prevented seizing caused by overheating - a constant problem in engines running at 12,000 RPM.

I used to run it on a mixture of 50% 115 LL AvGas, regular pump fuel and an Acetone/Toluene mix (to further boost octane and prevent the Castor Oil from dropping out of solution).

It was quick (155 + MPH), and also used to smell gorgeous (so I am told), especialy during early moring practice on closed public roads. 

NN

[feeutfo]

I should have mentioned yesterday -

The ports should be smoothed, but not polished, and finished with very fine (1,000 or 2,000 grit) wet or dry with a bit of light oil on it.

Polishing creates turbulence, whereas a smooth surface encourages laminar flow (= more inlet charge).

The key objective here is to smooth the inlet tract, so any gaskets should be trimmed back, and inlet ducts aligned with the inlet ports. This might mean ADDING material such as Devcon, rather than cutting it away. 

The idea here is to assemble the engine exactly as the designer intended (AKA 'Blueprinting'), rather than how the assembly line does it.

If you are really keen, the compression ratios of all six cylinders should be matched (by measuring head capacity at TDC), and skimming a fraction off of the piston crowns as required.

You might also check the 'squish band' around the periphery of each piston, using a piece of solder to measure the gap at TDC. Anything more than 25 thou encourages detonation and pre - ignition, but most assembly lines work to much wider clearances for safety. Dont forget to check the gap between the valves (when fully open) and the piston crowns at TDC too.

Most petrol engines will safely run with much higher compression ratios (= more power for the same amount of fuel) if the squish band is correct.

Many competition engines are blueprinted, rather than 'tuned', as this provides greater power and economy with better reliability. The difficulty is that production lines simply don't allow for this kind of assembly.

NN

On my Sunbeam I had 60 thou machined off the head - in fact it right up to the edge of the plug thread.

I considered a head skim on the 2.6 but that was too difficult being both V and over head cam

Fit adjustable bottom pulley to sort the timing perhaps?

Must be a way to match the inlet wedge to the new head position, can the porting process take out the difference? Struggling to visualise it, been a while since i was in there.

[Martin_1962]

1600cc Sunbeam hatch

As to the V6 2.6 you have the bolts for the cam belt backing plate, and the inlet divider making things awkwards

[NaughtyNigel]

Fit adjustable bottom pulley to sort the timing perhaps?

Must be a way to match the inlet wedge to the new head position, can the porting process take out the difference? Struggling to visualise it, been a while since i was in there.

Should be possible. Port smoothness is more important than port diameter, which is why you sometimes need to use Devcon to add metal where it is needed.

If the heads are set up properly, you shouldn't need to retard timing. That one is a bit of a falacy in my view. Most people only retard timing because they cannot think of a better way to prevent detonation.

Colder spark plugs also help, as the standard plus are usually chosen to run a bit hot to cope with any oil coming up the bores. That is rarely a problem in V6 Omegas. 

NN

[Kevin Wood]

Fit adjustable bottom pulley to sort the timing perhaps?

Must be a way to match the inlet wedge to the new head position, can the porting process take out the difference? Struggling to visualise it, been a while since i was in there.

Timing is already continuously variable if you fit the 2.5/3.0 bottom idler.

Failing that verniers on the cam sprockets would give you full flexibility to tweak the cam timing.

Ignition timing is fixed, of course, unless you can re-map the ECU.

Finding some pistons that aren't dished would probably be the best route to up compression on the 2.6.

"Four stroke performance tuning" by Graham Bell (IIRC) is an excellent, if slightly US-biased book on the subject, IMHO, if anyone fancies some bedtime reading.

Kevin

[feeutfo]

Fit adjustable bottom pulley to sort the timing perhaps?

Must be a way to match the inlet wedge to the new head position, can the porting process take out the difference? Struggling to visualise it, been a while since i was in there.

Timing is already continuously variable if you fit the 2.5/3.0 bottom idler.

Failing that verniers on the cam sprockets would give you full flexibility to tweak the cam timing.

Ignition timing is fixed, of course, unless you can re-map the ECU.

Finding some pistons that aren't dished would probably be the best route to up compression on the 2.6.

"Four stroke performance tuning" by Graham Bell (IIRC) is an excellent, if slightly US-biased book on the subject, IMHO, if anyone fancies some bedtime reading.

Kevin

Best offer i've had for a while Kev. 

[zirk]

A file is enough - aluminium is soft

A file? Have you got electric out your way Martin? 24 ports with one file....? And about 3 weeks in the garage.

Also as a general point, is it not better to have the polishing or machining strokes at 90 degrees to the air flow direction?

Ive heard this as well, think they call it The Ball Bearing effect of air stream over a slightly groved surface,  (something about creating a slight turbualance over the inner surface area to improve central air flow).

Exactly that, would imply i dremal type tool would be best for diy. If there is any truth in if of course.

Any port "polishing" i've seen has been done across the flow as opposed to with the flow. Porting/gas flowing or shaping of the ports them selves is, i beleive, something of a black art. Getting each inlet port to flow exactly the same and improve the basic design. When talking in general terms of course, i've no direct experience with it.

Specifically with the omega, re shaping, i guess we are simply talking about matching inlet mating surface faces to the plastic inlet(and inlet manifold?) and removing lips or edges along with a general clean up and polish as the inlet is not restrictive as such....?

I mentioned 24 ports earlier, but are we just talking inlet? Is there much to be done with exhaust ports?

Exhaust Ports, No, (apart from deburring), Exhaust Manifold, maybe, to improve any retrictions or burring, but dont port the head to match the Exhaust diamiter, most Exhaust / Gaskets are larger than the Head port, this ridge gives a mini Dam effect allowing any Exhaust back presure gas to be restrictive towards the Head. 

[NaughtyNigel]

Any port "polishing" i've seen has been done across the flow as opposed to with the flow. Porting/gas flowing or shaping of the ports them selves is, i beleive, something of a black art. Getting each inlet port to flow exactly the same and improve the basic design. When talking in general terms of course, i've no direct experience with it.

Specifically with the omega, re shaping, i guess we are simply talking about matching inlet mating surface faces to the plastic inlet(and inlet manifold?) and removing lips or edges along with a general clean up and polish as the inlet is not restrictive as such....?

I mentioned 24 ports earlier, but are we just talking inlet? Is there much to be done with exhaust ports?

Exhaust Ports, No, (apart from deburring), Exhaust Manifold, maybe, to improve any retrictions or burring, but dont port the head to match the Exhaust diamiter, most Exhaust / Gaskets are larger than the Head port, this ridge gives a mini Dam effect allowing any Exhaust back presure gas to be restrictive towards the Head. 

Port polishing is usually across the flow because that is the only way you can get a tool (or your finger) in the hole to do it! 

The objective when porting road car engines should be to make it how the designer intended, by smoothing the ports, removing obstructions, and generally helping gas to get in, and out of the engine.

Radical porting needs skill and a sound understanding of engineering, (I'm talking about inlet tract and exhaust system design here), which is much more involved than simply providing large diameter pipes. Modern car designers are very clever people, but they have to work with cost constraints, and within production line schedules.

Port smoothing takes time, and time is money; although in fairness, most modern engines are very well put together. Whatever you do though, never ever think that the designer didn’t know what he or she was doing. They do know what they are doing, and everything they do is done for a reason!

Radical porting may provide an increase in peak power output, (probably at higher RPM than is desired), but will almost certainly reduce torque at lower engine speeds, which is far from ideal in a two ton car.

Turbo-charging (or to give it it’s correct title, turbo-supercharging) tends to be a more popular route to increasing power output nowadays because it provides increased torque across the rev range, provides greater tractability, and doesn't need as much brain power to understand. 

NN

[Kevin Wood]

Port smoothing takes time, and time is money; although in fairness, most modern engines are very well put together. Whatever you do though, never ever think that the designer didn’t know what he or she was doing. They do know what they are doing, and everything they do is done for a reason!

Very true. In addition the designer was working with different constraints to us. Emissions and fuel economy are such big issues these days that every percent they can shave off the figures counts. And of course he would have been unpopular, to say the least, if he specified an army of people spending hours smoothing the ports with emery cloth at Ellesmere port!

Radical porting may provide an increase in peak power output, (probably at higher RPM than is desired), but will almost certainly reduce torque at lower engine speeds, which is far from ideal in a two ton car.

Yep. One of the noticeable things about modern engines compared with engines a couple of decades ago, IME, is that ports are matched to power output.

Being over generous with the port dimensions slows the flow of the air-fuel mixture leading to fuel dropping out of the vapour and condensing on the port walls. Bad for emissions and fuel economy (see above!) so that is avoided.

This means that "Radical porting" is probably needed at an earlier stage in the tuning, but probably not until more radical cams are being considered.

.. and airflow restrictions typically are only evident at high RPM where airflow peaks, so this is why the improvements are at high RPM. Low to mid RPM performance is much more down to basics (cubes) and tuning (resonance) of the intake and exhaust system, which is why it's easy to mess this up by taking huge chunks of metal out.

If you're doing it properly, you only do that by the time you've got a set of lairy cams to go in, at which point you'll be throwing away flexibility anyway.

Kevin