When the vehicles have been at rest, so that the brake is not charged, the brake pistons will have dropped to their lower position in the absence of a pressure differential ( as air will have leaked slowly into the upper part of the cylinder, destroying the vacuum ).

This was later cured by a switch to stronger pistons but the engine was also a mediocre performer offering no real economy benefit and it was dropped in 1973, to be replaced by the ‘ new ’ 3. 4.

This method of computing compression ratio cannot be used accurately for engines that have pistons with either domed or irregularly shaped heads.

** GT pistons into use in S4 also resulting true 10. 0: 1 compression ratio for all engines.

** 10. 4: 1 compression ratio pistons

This was achieved using different pistons which raised the S ' compression ratio from 9. 7: 1 to 10. 2: 1, the knock-on effect being an increase in the octane rating, up from 91 RON to 95.

Deflector pistons are used in two-stroke engines with crankcase compression, where the gas flow within the cylinder must be carefully directed in order to provide efficient scavenging.

Flat top pistons delivered the 10. 5: 1 compression ratio.

Petrol engines run at higher speeds than diesels, partially due to their lighter pistons, connecting rods and crankshaft ( a design efficiency made possible by lower compression ratios ) and due to petrol burning faster than diesel.

In the case of highly supercharged or high compression multi-cylinder engines particularly ones that use methanol ( or other fuels prone to pre-ignition ) pre-ignition can quickly melt or burn pistons since the power generated by other still functioning pistons will force the overheated ones along no matter how early the mix pre-ignites.

The compression remained the same as the Renault 12v, but the pistons differed, as did some of the timing gear, and the heads were re-engineered to allow easier maintenance ( the camshaft being fitted from the opposite end for example ).

Labyrinth seals are also found on pistons, which use them to store oil and seal against high pressure during compression and power strokes, as well as on other non-rotating shafts.

* Raising the compression ratio by reducing the size of the combustion chamber, which makes more efficient use of the cylinder pressure developed and leading to more rapid burning of fuel, by using larger compression height pistons or thinner head gaskets, or by using a milling machine or " shaving " the cylinder head.

The improvements in the " blacktop " engine included lighter rods, domed pistons for slightly higher compression, and an electric advance distributor ( the " browntop " came with a vacuum advance distributor ).

It has no crankshaft, and the pistons are returned after each firing stroke by compression and expansion of air in a separate cylinder.

Mechanically, the new Talon and Eclipse models were almost identical with the engines in the turbocharged versions receiving a modest increase in output thanks to a redesigned intake and exhaust, higher 8. 5 to 1 ( vs. 7. 8: 1 ) compression pistons, and new turbocharger.

The turbocharged version of the 4G63 ( sometimes referred to as the 4G63T ) is equipped with a lower compression ratio ( 7. 8 vs. 9. 0 in the naturally aspirated version ) and oil squirters under the pistons in order to better cope with the stress and extra heat caused by forced induction.

Shortly afterwards the 425cc was replaced by an improved 435cc engine and then in September 1968 M4 was replaced by an improved 602cc engine featuring higher compression pistons and forced induction from the engine fan giving slightly more power.

Although the displacement was the same, the KLZE had more durations on the cams, higher compression due to a different shape of pistons, and the intake manifold was different on the ZE.

The pistons ran cooler allowing higher compression ratios and higher engine speeds.

The Hyper Pak consisted of a very-long-ram intake manifold meant to accept a Carter AFB 4-barrel carburetor, the AFB carburetor itself and an appropriate air cleaner, dual ( front-3 and rear-3 ) cast-iron exhaust headers, a large-diameter exhaust Y-pipe to connect to these dual cast-iron headers, a larger muffler, a 276 °- duration camshaft with appropriate valve springs and pushrods, a heavier-duty clutch, a manual choke control, a starter motor modification template and, in the full-race version of the package, high-compression pistons designed to increase the engine's compression ratio to 10. 5 from the stock 8. 5.

Changes included a lower compression ratio, special pistons, high-strength valves, higher-pressure springs ( to avoid float ), better-sealing rings, a special cam, select-fit bearings, a special exhaust manifold, and a diecast aluminum cylinder head cover.

It uses an 8. 1: 1 compression ratio with Mahle cast eutectic aluminum alloy pistons, forged connecting rods with cracked caps and threaded-in 9 mm rod bolts, and a cast high-hardness steel crankshaft.

A four-bearing crankshaft was added, along with 6. 5: 1 compression pistons, for.

The drag pack required either the 3. 91: 1 or the 4. 30: 1 axle ratio, and included a 4-bolt main engine block, forged pistons, 780 CFM Holley carburetor, engine oil cooler, and a solid lifter cam.

Flat-topped pistons and high-lift camshaft gave a compression ratio of 10. 5: 1.

The pistons for the FS produce a compression ratio of 9. 1: 1 ( USDM ) but when FP pistons are used in the FS they yield 9. 7: 1 compression ratio.

Named " Swift Sport ", it is powered by a high-revving 1. 6-litre, naturally aspirated DOHC VVT four-cylinder engine with a 11. 1: 1 compression ratio, high lift cams, forged pistons, and strengthened valve springs.

The engine had hydraulic lifters, an oversquare bore: stroke ratio, a counterweighted forged crankshaft, aluminum pistons, floating wristpins, and a dual-plane intake manifold.

Changing the compression ratio on an Oldsmobile 215 required changing the heads, but on a Buick 215, only the pistons, which was less expensive and simpler.

The engine combustion chambers were redesigned and new " turbulator " pistons raised the compression ratio from 5. 9 to 6. 5: 1, resulting in an increase in horsepower to 141.

The compression ratio was raised from 6. 6: 1 to 7. 0: 1, the " turbulator " pistons were redesigned, smaller spark plugs were substituted for the previous type and “ Compound Carburetion ” was introduced.

The small piston, for a given distance of movement, displaces a smaller amount of volume than the large piston, which is proportional to the ratio of areas of the heads of the pistons.

The distance the large piston will move is the distance that the small piston is moved divided by the ratio of the areas of the heads of the pistons.

This engine used pistons with a static compression ratio of 22. 4: 1 and piston pins were 25mm OD.

The car additionally boasted the world's first production car engine with titanium connecting rods, forged pistons, and ultra high-revving capabilities — the redline was at a lofty 8, 000 rpm-all traits usually associated with track and race engineered motor cars.

In August 1963 VW introduced single-and twin-carburetor versions, respectively the Volkswagen 1500N, rated at, and the 1500S, which had high-compression ( 8. 5: 1 ) domed pistons and twin downdraught 32mm carburetors for more power.

The Stutz Motor Company used a modified T-head with 16 valves, twin-spark ignition and aluminium pistons to produce 80 bhp ( 59 kW ) at 2400 rpm from a 360. 8 cid ( 5. 8-liter ) straight-4 ( 0. 22 bhp per cubic inch ).

Within the meter, two figure " 8 " shaped lobes, the rotors ( also known as impellers or pistons ), spin in precise alignment.

In 1955, a 100M model was developed as well, with larger carburettors, a cold air box to increase air flow to the carburettors, high-lift camshaft and 8. 1: 1 compression pistons.

The L28E is the enlarged engine produced from 1975 to 1984 with dish-top pistons and a resulting compression ratio of 8. 3: 1.

For model year 1981 through model year 1983, the L28E received flat-top pistons and a high quench head, raising the compression ratio to 8. 8: 1, and thus increasing the power rating from ( 1975 – 1980 ) to ( 1981 – 1983 ).

The boost in displacement was obtained by boring the 2. 8 litre M104 block by 2. 1MM and using a highly modified version of the crankshaft from the 3. 5L OM603 to increase throw by 18. 9MM ; this necessitated the use of new forged pistons with shorter skirts.

In April, 1950, an engine with larger carburettors, inlet camshaft the same as the exhaust ( increased duration ) & higher compression ratio pistons ( 8. 16: 1 ) was " offered optionally ", as Aston Martin's first Vantage upgrade.

An optional high-output DBB engine with three twin-choke Weber 35 DCO 3 carburettors, special long duration camshafts, high compression 8. 6: 1 pistons and the dual-exhaust system boasted 195 hp ( 145 kW ), though this was rarer ( 10 cars thus equipped ) than the mid-level DBD option with triple SU 1. 75 " carbs and 180 hp ( 134 kW ) also with the dual exhaust system, fitted to 47 cars.

Several components had design changes, longer rods ( 152 mm c-c, longer ), pistons with a lower compression height, lower friction bearings ( smaller in size ), a crankshaft with 8 counterweights ( instead of 4 on the older Bxx engines ) and a heavy harmonic balancer in the crank pulley.

The engines with 2490 cc displacement, identified as the Volvo Penta AQ151 ( 8 valve ) and AQ171 ( dohc 16 valve ) models, got a forged crankshaft with a longer stroke ( 86 mm stroke ) together with pistons with a lower compression height.