Right now I am building an A12 for a customer who is putting the engine in a 1200 coupe. The specifications are,"That the engine makes 120 hp (crankshaft) and is still streetable". Itried to talk him into an A15 as it would have been cheaper to get the grunt, but he loves his A12!!! A bit later he will take most of the A12 parts and put them on an A15 I thinK

I have used an A14 oval port head now fitted with 37 inlets and 31 exhausts and 24 cc chambers. This gives a comp of 10.2 approx. It has dual valve springs as well. New K lines inserts have fitted to the guides. The valves have been seated concentric to the seats. The head flows 132 hp (exhaust over inlet ratio 68%) at 480 thou lift.

I am fitting a special cam developed for the engine by clives cams. It is a modified 81A grind (231 degree @0.050" lift duration) with 106 degree lobe centreline. This will be street driveable, yet have lots of go. With the webers it probably go - "brump brump, brump brump, brump brump, brump brump" and perform excellently as well..

The engine has two 40DCOE webers with 32 chokes F16 emulsions 115 mains 160 airs 4.5 auxuiliary vents 45 F9 idles and 35 pumps.

The exhaust is Hi tech headers (HPC coated in and out) and a 580 cfm mufffle rsystem throuh 2.25" header pipes. An S2 bluebird dissy and coil complete the picture.

Performance at 5.8 kg/hp should make it able to produce enough to savage a stock WRX or S15 200SX.

The L16 runs to 9000. Shifts are normally done at 8500. The 8.2 figure was for 98 RON pump premium unleaded.

I would be looking at around 0.8 mm until I learnt how far the rods stretch.

If using a desktop dyno to do comparisons, set it up so it gives report on the range you want to use. If you have the option report on average torque and average power for the range.

I will dig up the block etc figures tomorrow. I dont have them here with me. Chamber volumes vary a bit with head casting mumbers

Pretty interesting thread and a very good link to the Cam Timing vs. Compression Analysis article. This was very readable.

One of the comments in the linked article hit it right on the head,
"To sum up - DCR a useful tool, but widely perceived to be of greater worth than can be supported by physics".

It was interesting to see how much variation there was between contributors for the idea of a safe? clearance between piston and head.

As mentioned previously in this sites thread, current technology allows the piston to kiss the head in race engines depending on head and piston design. The builders manage to keep them reliable by making the squish area larger and chamber smaller (within limits) to increase the shocker effect and increase burn speed.

The shock absorber effect means that the rate of resistance to movement of the gases (between piston and squish area) rises exponentially as the distance decreases between piston and head, if both suraces are parallel. It is this factor that allows the piston to kiss the carbon without doing damage.

I will watch that Mopar site in the future even though I dont know anything about the engines. Looks like some good tech stuff there occasionally.

On the L16 race engine I ran 0.020" squish clearance and when the engine was pulled down you could see the chamber shape in the carbon on piston.

In current V8 supercar and Porsche cup race engines they run down clearances to where the piston just about touches the head with rod stretch. The squish acts as a shock absorber on valve overlap when the rod receives maximum loading, and also gives maximum chamber turbulence on compressiion.

The 8.2 dynamic figure is based on the actual dynamic comp of an engine I ran. It had detonation at static 10.6, but ran fine at a static of 10.4. This translated to the 8.2 dynamic comp I gave you. Timing scatter and mixture control were the main reasons for the problem.

This dynamic figure will vary depending on the maximum RPM you intend to use. Higher Rpm allow you to use a higher dynamic comp due to increasing inlet inefficiencies at higher inlet velocities (100 m/sec and above) .

Running it through the heater should not be necessary if the cooling system is set up correctly with no problems. Running the coolant through the heater is usually just a band aid for a faulty cooling system. It usually indicates another problem is there but doing this masks it up.

I am including some cooling system thoughts that may make unserstanding what happens in your cooling system as bit easier.

When building any "Serious" engine you should hot caustic tank the block and head. This process helps remove scale and oil from the cooling system. Drill all the water gallery holes on the block deck to clean them of any corrossion.

If the head has been serviced correctly and there is no corrosion in the water jackets, you have a fighting chance of survival in a race engine.

The next most important thing is to keep the coolant pressure sufficiently high so steam bubbles do not form around the coolant galleries. This means that you must run a thermostat and give the coolant enough residence time to absorb as much heat as possible without being able to form steam bubbles.

The following is a simple diagnostic cooling test any one can do at no cost. It is suitable for A series, L series, CA FJ or SR's etc.

On the inlet side for coolant flow back into the block/head, fit the cap end of a 1.25 or 2 litre coke bottle into the hose on the block inlet side. Cut out the base of the coke bottle to make it like a funnel and fit the heater return line into the top of the funnel section. You may have to make an extension hose up to carry these tests out.

Half fill the funnel with water, then holding the bottle up, remove any air from the radiator cap. There should be sufficient water in the funnel so the coolant level remains relatively stable with the engine running. Top the coolant level in the funnel up with additional water to maintain the coolant level in the funnel at a constant level.

Bring the engine to a constant operating temperature. To test water pump pressure raise the coolant delivery hose into the funnel so the coolant from the heater return line falls in an arc into the top of the funnel. At approximately 800 rpm idle, the hose should be able to be raised 450 -600 mm before coolant flow stops. This indicates a coolant pressure of approximately 1 psi. If the flow level falls below 300mm before flow stops, the pump is not providing sufficient pressure for the system and the pump must be replaced.

Next look for pump cavitation by running the engine at 2000 rpm and looking at the changes that happen to the coolant. If it goes opaque or cloudy like the head on a freshly poured beer, you have some cavitation. If the cavitation is bad, large bubbles will appear in the funnel rather like the aerator bubbles in a fish tank.

If you have either symptom you should look at the water pump type you are using and the pump drive speed.

Often by slowing the pump or removing some pump blades or cutting them back, these symptoms will dissapear.

The tests were shown to me by "The Professor" John Bennet of Perfectune Engineering (Yella Terra) fame for those of you old enough to remember.

Hope the info helps.

I use 8.5:1 as a maximum dynamic CR and only if the ignition advance is programable.
For a dissy engine 8.2 is about the maximum .

Ceramic coating works. Be careful about the quality of any coating you get done though. Cheaper is not always the same quality. I spend around $400 on each four cylinder engine I get coated, and a further $160 on the exhaust headers inside and out.

Its interesting to see that most V8 supercar teams and top doorslammer and rail drag teams use ceramic insulation on chambers, valves and pistons. Some have been using it for 15 years.

HRT replace the bottom end on thier cars after 5000 race Km's and the pistons mostly show no appreciable wear after this distance.

Cooler engines and lower thermal stress on rings (allowing lower ring tensions) are the biggest benefits to performance and reliability.

Engine Analyser Pro v 3.3 is the only one I have seen worth putting any effort into. It takes account of bearing friction ring type and number and lots more. It takes a while to setup but produces good base data to compare likely effects. It is not going to give hard output nmbers but makes a good comparative tool.

No it is not a quote! It took me from about 6:30 am tilll about 8:00 am to get it the way I wanted and then I had an edit after that

Its hard to make it brief and keep on the plot. When there are so many variables, its ard to keep it from being a piece of techno_ speak that is not easily understandable. Its a great subject and I am always looking for ways to improve efficiency and performance.

I was going to put some info on ceramic coating of chambers and pistons in there as well as this has an effect on the compression ratio you can run. Ceramic coating reduces heat soak into the chamber and piston. This reduces potential for detonation at high engine speeds. Maybe that will come into another thread.

At least on this site, people are more interested in technical stuff and how to do things. Not the grand standing (mines better or bigger than yours) you get on other sites

Any one doing engineering, if you get to do thermodynamics: do it! This is one of the most useful "real world" sciences there is in my opinion.

The commodores also run lean burn at cruise. To maximise fuel economy the knock sensor does work flat out all the time during cruise and at full throttle. The ecu keeps spark timing just below the level where knocking occurs.

With normal combustion, the charge burn speed varies directly with charge density and the degree of charge turbulence. Higher compression increases charge density. Good port design and chamber shape helps determine the degree of chamber turbulence the fuel charge experiences. More charge turbulence exposes the mixture to the flame front more rapidly allowing it to burn in less time. Another factor varying burn speed is the amount of chamber squish. The squish area forces gases to be pushed through the already turbulent mixture. More squish usually means more turbulence and higher burn speed. One result of the faster burn speed is that less timing advance is required, reducing the chance of detonation under load.

For a given chamber, the Fuel burn speed remains nearly constant if there is a consistent quality fuel charge. This is in spite of engine speed variations. If the fuel charge burn takes an average of 4 milliseconds duration in the chamber- at 6000 rpm the burn duration available for 140 degrees of crank rotation in the burn cycle before the exhaust opens is only 3.888 milliseconds. This means the mixture is nearly completly burnt before the exhaust valve opens. - At 8000 rpm the burn duration available is only 2.916 millisecs, so only 2.916/4 * 100= 72.9% of the mixture is burnt by the time the exhaust valve is opened if the mixture was ignited at the same point as at 6000 rpm. This is known as burn lag. The burn lag is directly related to the burn speed. It is the relationship of the burn speed and ignition timing that determines where peak cylinder pressure occurs. It is where the peak cylinder pressure occurs in relation to the crank angle that determines how well an engine performs.

The wild card with choice of compression ratio is where the dynamic comp ratio is so high the fuel mixture is heated to a point it will spontaneously ignite. When this happens, there is a rapid combustion pressure rise before top dead centre is reached. Pressure increases further as TDC is reached. Chamber pressure becomes so high that now combustion is no longer controlled and the fuel charge explodes (detonates).

Instead of a constant push on top of the piston over a few milliseconds its like the piston being hit by a sledgehammer, with all combustion energy being released in less than a millisecond.

At higher engine speeds more heat is retained in the chamber and this makes detonation more likely with higher dynamic comp ratios.

The end result is the comp ratio you use will depend on -
1. Maintaining consistent fuel mixture quality
2. Having a good chamber design and fast burn speed through development of the squish area and chamber walls.
3. Accurate control of Ignition timing.

According to Ricardo's testing, for 98 ron 10.6 : 1 would be top CR

This is figure is available from a table in the book "Design and Tuning of competition engines" by Phil Smith.

There are none so blind as those that will not see.