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Difference between Silver and Blacktop 20V 4AGE Engines

This is a guide for making a educated comparison between the 20V Silvertop and Blacktop engines with a description of the difference explained. Some smaller differences are not covered and there are also some differences between the first and second generation of Silvertop engines.

 

AIRBOX

– The Blacktop has a larger volume Airbox. The other key difference is the Silvertop airbox has a horizontal split between the lid and the base, as such the bolts are wound from the top down. The Blacktop has the opposite, it also has the difference of having the lid hook in to the bottom of the airbox base before swinging closed and being clamped down.

 

CAM BELT

Tooth shape: To reduce noise the Blacktop belt featured a slightly different shape teeth profile, this is on the belt only and the profile of the drive / driven pulleys(s) remains unchanged.

Belt length: To allow for the different cam belt tensioner (see “Camshafts belt tensioner”) the Blacktop cam belt is one tooth shorter at 110 compared to the 111 of the Silvertop. Normally the belts can’t be swapped between engines but if the entire tensioning system (16V / Silvertop: Oil pump, spring tensioner and tensioner post fitted to block) is changed / fitted then a Silvertop belt can be used on a Blacktop.

Belt width: Unlike all the other models of 4age belt that use a 19mm belt the Blacktop belt is wider at 21mm.

 

CAM BELT DRIVE AND MAIN CRANK PULLEY

Belt drive pulley width: To allow for the 2mm wider belt the Blacktop cam belt drive pulley on the crank is 1.7mm wider with a total width of 25.2mm compared to the 23.5mm pulley as used on both the 16V and 20V Silvertop engines.

 

Main pulley row offset: To maintain the same position / offset of the main crank pulleys inner row with it’s the wider belt / drive pulley there is 1.7mm less of an offset from the rear center face to the inner row with the Blacktop. See lower for conversion notes.

Spacing of the two belt rows: The Blacktop has a different spacing between the two belt drive rows on the main crank pulley compared to that of 16V / 20V Silvertop pulleys. See lower for conversion notes.

Harmonic dampening: 16V and Silvertop engines all use a rubber dampener between the inner part of the main crank pulley and the two outer rows. The Blacktop on the other hand only has dampening on the inner pulley. This visually gives the appearance of not being any dampening feature at all when they certainly do.

Conversion notes: It is possible to convert a 16V / 20V Silvertop crank pulley to be partially compatible with a Blacktop by machining 1.7mm of the rear center face, however the outer row will not be compatible due to the difference in distance between the two rows. For those not using the outer row- for example not using a Blacktop power steering pump or A/C components then there is no issue. A solution can be to either use the 16V / Silvertop brackets and pumps or even simpler a 4-Rib accessory belt instead of the original 5-rib, this lets the belt compensate for the difference by being one rib offset between the pulleys.

 

CAMSHAFT BELT TENSIONER

The Silvertop is identical to all previous A-series engines made before it in that it uses a simple and reliable sprung idler wheel to keep tension on the belt. The Blacktop’s use a hydraulic tensioner and it’s own unique belt tension pulley to match.

Conversion notes: The spung tensioning system can be swapped on to a Blacktop but it also requires the swap of various other components. In total the parts required from a Silvertop would be the oil pump, cam belt, cam belt tension pulley, tensioning spring, the steel post fitted into the block for the spring to loop over and lastly that the bottom and middle plastic belt covers either be adapted or changed to that as used on a Silvertop.

 

CAMSHAFTS

Both engines have virtually identical exhaust cams. However the Blacktop has 0.23mm higher lift on the intake. The cams can be swapped between the engines if the VVT cam gear is also swapped, but there would be no point as both cams are virtually identical so there would be no real gain. Blacktops cams also have an interesting feature in that the base circle (low side) of all the cam lobes have been machined such that they have only a small ridge for a friction surface. This is a simple yet clever way of facilitating additional oil to flow between each cam lobes and bucket, this lowers wear and friction. For specific 4age camshaft timings: Bill’s Stock 4AGE description page.

 

COMPRESSION RATIO

The Silvertop has a static compression ratio of 10.5:1 compared to the 11:1 of the black. Both the combustion chamber volumes and the piston shapes cause the change in the compression, see under “Pistons & Gudgeon pins-” and “Head (combustion chamber)” for more information.

 

CON-RODS

The Silvertop con-rods are very solidly built and with bolts weigh in at 506 grams each (without bearings). The Blacktop was fitted with thinner, lighter and weaker rods which are 485 grams each. Both are readily interchangeable and use the same fasteners for the main bearing cap, as such the ARP fastener upgrade also suits both as does a complete set of billet aftermarket rods. The difference in strength is only a factor with higher than original revs, as an example OEM Silvertop con-rods are normally able to be revved to a 8600RPM limit long term, something that is very much not suggested to do with Blacktop rods. However the limit of a Silvertop rod isn’t that much higher before fastener failure and stretching fatigue failures resulting from over-revving come into play.

 

CRANKSHAFT

Despite reports of differences all 20V engines and the later model 16V engines use the same part number for the crank.

 

ECU / EFI MANAGEMENT

These engines run different ECU’s and whist they have the same appearance as such the similarities end quickly after. They are not interchangeable without modifications to the wiring loom / harness. See out Workshop manual article for a guide on converting this Silvertop wiring loom / harness to be compatible with a Blacktop ECU.

Load metering: All ECU’s use various sensors to determine load. However the method used varies between engines as the Silvertop uses a simple Vane type airflow meter whilst the Blacktop uses a more complex vacuum (MAP) and throttle position (TPS) for larger throttle openings where there is no vacuum. The Blacktop engine featured no airflow meter as such but did have an additional vacuum sensor (MAP sensor). Please see under “Head (inlet face)” and “Inlet manifold” for more information.

 

HEAD (CASTING ABOVE EXHAUST PORTS):

The Silvertop features multiple cast ribs in the head above the exhaust ports. On the Blacktop this was significantly reduced to a more simple design. For comparison pictures: Bill’s Modified 4AGE Page.

 

HEAD (CAMSHAFT LOBE / BUCKET RECESSES)

The Silvertop engine featured a small recesses / shallow bevels leading into each side of the cam bucket recesses. This is to assist with the oiling of the bucket and provides additional clearance for taller cam lobes. In the Blacktops these were significant increased.

Aftermarket camshaft fitment notes: When fitting an aftermarket camshaft depending on the amount of lift some material may need to be removed from the head around this area, due to the deeper recesses of the Blacktop heads they are able to have cams with a higher lift fitted before modifications are necessary. Always test a camshaft for clearance between the lobes and the head by turning it over by hand, ideally without the buckets fitted.

 

HEAD (COMBUSTION CHAMBERS)

The combustion chambers between the engines are quite different in terms of their squish area. While their valve size and position are identical the Silvertop features a chamber with a squish area in every gap between the valves. The Blacktop on the other hand features all but the smallest flat section behind the exhaust ports. This led to a large difference between the combustion chamber volumes where the Silvertop is 35cc (reported by Arias) and the black at 37.8cc (measured by myself).

Pictured is a Silvertop chamber on the left and a Blacktop on the right:

 

HEAD (EXHAUST PORTS)

The Blacktop featured exhaust ports of a greater diameter (+3mm). For comparasin pictures: Bill’s Modified 4AGE Page.

 

HEAD (INLET FACE)

To allow for the Blacktops need for a vacuum signal (see “Load metering”) a larger section of metal was added on lower part of the flange face of the head to mate against the inlet manifold. Please see under “Inlet manifolds” for more information.

 

INLET PORTS

The Silvertop in its inlet ports has no set dividers as such and features a large internal volume. The Blacktop engine on the other hand has something more resembling three tubes with two dividers. Also the opening of the Blacktop inlet ports are approximately 4 to 5mm wider at their entrance over the Silvertop giving a larger cross sectional area.

Pictured on the left is the Silvertop port and the Blacktop port at the right, however the Blacktop head has received some porting to remove sharp edges internally.

Picture courtesy of Bill Sherwood (Billzilla)

 

INLET MANIFOLD

To allow for the Map reading of the Blacktop engine (see “load metering”) the inlet manifold has a wider face for the side of the head with an additional vacuum feed off every cylinder that leads to an integral chamber for a vacuum signal to feed the Map sensor. The Blacktop head featured a wider flange face to let these channels a solid surface to seal against. The Blacktop has an internal shape of the manifold in a more of a heart shape than the Silvertop’s circular inlets (see “Throttles”). The Blacktop inlets at the head side are also wider to allow for the larger inlet ports in the head. Please see “Throttles”, “Head (Inlet face)” and “Inlet manifold heat insulators” for more information.

Pictured are the head side of the two manifolds, the bottom manifold being the Blacktop, notice how it has 4 additional bleed points for the air into a common chamber.

Original owner of picture unknown.

 

INLET MANIFOLD HEAT INSULATORS

While both engines feature a thick gasket/heat insulator between the head and the inlet manifold the Blacktop and apparently the later Silvertop models feature a trapezoid cutout instead of a square cutout in provision for the fuel path out of the injector.

 

FLYWHEELS

The Silvertop flywheel is of a conventional design with a set of mounting points for the pressure plate extended further then the ring-gear, this flywheel weighs 6.9kg. The blacktop however has all the unnecessary sections of the outer lip machined off to reduce the weigh at its most influential point. This reduces the weight down to 5.9Kg. Both are readily interchangeable.

The left flywheel pictured is the earlier Silvertop design while the right is the lightened Blacktop.

Picture courtesy of Mr Acoustic.

 

INLET CAM PULLEYS

Both 20V engines run the simplest form of variable valve timing in the form of a twin position cam inlet pulley. Although physically interchangeable their locating dowels have a 5 degree difference in their angular position. As such they ARE NOT interchangeable between each other unless the matching VVT pulley is also fitted, for example there are no issues with fitting both the cam and VVT pulley intended for a Blacktop engine together on to a Silvertop. Please see the article “Working with VVT” for more information.

 

OIL PUMPS

To allow for the difference in cam belt tensioners the oil pump castings are different between the engines. They are interchangeable if all the other belt tensioning parts and cam belt are changed at the same time. Please see “Camshafts belt tensioners”, “Camshafts” and “Camshafts belts” for more information.

 

PISTONS & GUDGEON PINS

Even though the Blacktop head features a more open combustion chamber (see “Head combustion- chambers”) it still has a higher static compression ratio (see “compression ratio”), this is purely because of the piston design. The Silvertop piston features a very small dome with two deeply angled exhaust flycuts, two moderate inner flycuts and a moderate flat middle flycut for the middle intake valve. The Blacktop piston is very different, to accommodate for the larger chamber the dome is considerably higher with reduced flycuts. The exhaust flycuts are still present but more shallow and only the middle intake flycuts remains but even that is just a tiny flat circular dish machined out. A Blacktop engine is an interference engine unlike all other A series engines. Although the pistons are initially interchangeable physically they aren’t practically as a Silvertop with Blacktop pistons has a very high compression and quite low when the combination is reversed. Also of note is that the Silvertop piston is lighter at 308 grams without rings or a gudgeon pin installed compared to the 315.5g of the blacktop. The Blacktop does have a superior gudgeon pin design in that it has countersunk ends which give it a small 3g advantage bringing the weight difference slightly closer. The gudgeon pins them self are readily interchangeable.

 

THERMOSTAT

The silvertop shares the same 48mm diameter thermostat as the 16V models while the Blacktop uses a significantly larger 56mm.

 

THROTTLE BODIES

Blade / butterfly diameters: While both engines have round throttle blades, however the Blacktop throttle blades are larger at 45mm compared to the 43mm of the Silvertop. On paper this calculates to the Blacktop having a 9.5% larger cross sectional area. However due to having the same shaft width between them the actual difference in flow would be a little higher again.

Diameter of the main opening at the outer flange: This is the inner diameter of each the bore measured at the outer face (where the velocity stack bolts up), this is 49.5mm on a Blacktop. As for the Silvertops there was a difference between the Gen-1 and Gen-2 models, both had the same blade diameter but the opening diameter is smaller for the Gen-1 model. The diameters are close to 46.5mm for the Gen-1 and 47.5mm for the Gen-2.

Inside and outside profiles: The internal transition of the rear opening as seen at the rear flange casting of the throttle housing is different. The Silvertops have a simple round machined opening at the same 43mm diameter of the blade / throttle center bore while the Blacktop has more of a kidney shape to suit the different manifold (see “Inlet manifold”).

Velocity stack mounting: Measured from center to center between the fasting points used to mount the velocity stacks Silvertop throttles have a 73mm distance and 83mm for the Blacktop. This is the single easiest way to identify the model of a throttle set.

Conversion notes: While the throttle bodies can be swapped in terms of being able to be bolted down they have other incompatibility issues resulting from the different inside / outside profiles on both ends and different velocity stack mounting. So while they can be swapped when the matching velocity stacks are also fitted it is highly advisable to port match the throttles to suit the manifold  or vice versa where applicable. Also of note fitting larger Blacktop throttles to an engine will not necessarily increase the power as Silvertop throttles can already provide enough flow for most of the 4age engines out there.

 

VELOCITY STACKS

The Silvertop Velocity stacks / trumpets are formed out of a hard plastic while the Blacktop uses a firm rubber instead for their construction. They aren’t readily interchangeable because the two mounting bolts are further apart on the Blacktop trumpets. Please see “Throttle bodies” for more information.

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