Honda K20A & Toyota 2ZZ-GE
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The K20A has cemented it's status as a legendary four cylinder platform. For all out naturally aspirated power screaming to stratospheric redlines, there is nothing better quantitatively.
However, there is a quiet gem born of Toyota's collaboration with Yamaha in the 90's, which in my opinion was designed to take on Honda's dominance of naturally aspirated small displacement motors. One of the principal sources of information is a report titled "Development of the High Speed 2ZZ-GE Engine" published by Toyota in March 2000. They had several specific design objectives:
1. Provide high speed performance
2. Retain low speed flexibility
3. Maintain same bore pitch as base engine (1ZZ)
4. This was to keep the same outer dimensions
5. Maintain same emission standard as base engine (TLEV)
6. Achieve best power to weight ratio in the field
The date of this report tells a story. The K20 engine was launched in 2001, and it is highly likely that the 2ZZ engine was benchmarked against the Honda B18C.
The Toyota engineers worked extremely hard to make a lightweight yet powerful engine. However evidence I found suggests that the K20 and the 2ZZ engine and transmission packages have a approximately 20kg weight difference with the 2ZZ being lighter. Here are some other dimentions that show the difference in size of the two engines
2ZZ vs K20A
Bore: 79mm vs 86mm
Bore Spacing: 87.5mm vs 94mm
Deck Height: 212mm vs 212mm
(note K24 is 231mm deck height)
The bore of the 2ZZ is 79mm vs the 86mm of the K20A, and the bore spacing for the 2ZZ is 87.5mm vs the K20A which is 94mm. The block height for the 2
I found this compelling post by Fluffyninja on S2Ki to back up this research:
"Just for some background I was the engineer responsible for our ZZ assembly line from September 2000~End of 2004, I look after engine testing of all engine types we build, I made all the engine test standards (including engine weights all the major varients) upto the end of ZZ production.
I was responsible for Cylinder block machining, cylinder head machining, block/head casting and periodically assisted with cam, rod and crank machining. You might say I know a thing or two about this engine family. Now I will admit we didn't deal with 2ZZ (we built 1ZZ, 3ZZ and 4ZZ) but I do happen to know that a fully dressed 1ZZ engine was approx 105Kgs."
The technical paper itself quotes the engine weight at 115kg the diagram below in the study shows how much they focused on lightweight as a part of the design.
Speaking of area under the curve, let's study torque per litre (lbft per liter). This will give us an idea of how the 2ZZ and the K20 stack up against other engines, particularly the bottom end.
Honda S2000 AP1
153 / 1.997 = 76.6 lbft/l
Honda S2000 AP2
162 / 2.157 = 75.1 lbft/l
BMW E46 M3
262 / 3.246 = 80.7 lbft/l
Ferrari F430
343 / 4.308 = 79.6 lbft/l
Toyota 2ZZ
133/1.796 = 75.1 lbft/l
Honda K20
152/1.997 = 76.6 lbft/l
In terms of torque per litre, they are comparable, with a slight advantage to the K20. The additional torque produced by the displacement difference is only the beginning of why Honda produced a superior engine. Let's get into the top end of the engine.
The bore size of of the K20 is 4mm larger than the 2ZZ (86mm vs 82mm). The bigger bore in the Honda allows for larger valves to be fitted to the cylinder head of the K20. The shorter stroke also allows an engine to rev higher, which creates more horsepower.
Valve Sizes:
K20 in= 35mm, 2ZZ in= 34mm
K20 ex=30mm, 2ZZ ex=29mm
If you imagine air flowing through a wide angle port of a cylinder head, the more horizontal it is, the closer to a 90 degree angle it has to turn to go into the vertical inline combustion chamber. A narrow angle port design allows the air to flow more naturally into the engine, as it moves along the straighter path.
As the revs rise, the K20 uses roller followers for all 3 of its cam lobes (two low-speed, one high-speed). The 2ZZ uses rollers for the low-speed lobe and fingers for the high-speed. While the 2ZZ is an incredible engine, it is outgunned by the K20 at the higher RPMs from a design point of view.
The 2ZZ head employs the VVT-i system uses engine speed, intake air volume, throttle position and water temperature to calculate optimal cam timing. They then added a changeover mechanism that utilises 8 lobes and a linked rocker arm assembly to move to the different profile.
This is in contrast to the Honda VTEC system which required 16 lobes that each activates one valve to perform the switch over, reducing overall weight in the valve-train. In addition, The Honda VTEC system uses 2 low-speed, 1 high-speed roller followers, while the Toyota 2ZZ uses rollers for the low-speed lobe and fingers for the high-speed which means less friction on the K20 valve-train.
The 2ZZ has metal matrix cylinder liners that are usually replaced by cylinder sleeves. Because the bore spacing is very tight, there is not much room over any overbore. Cylinder sleeves allow for longer life and sealing and replaces the metal matrix bore. It needs to be machined for valve clearance as well. Engine builders sometimes remove the plugs in the oil galleys which usually have a pressed ball bearing. These are drilled out and a threaded part is inserted for easier servicing.
While it's rod ratio is not as optimal for high rpm performance, tuners have been pushing the engine to about 240hp, by solving it's main problem - oiling. The 2ZZ’s stock oil pump gears can fail if the engine is over-reved or even sometimes for no reason at all.
The 2ZZ is known for excessive camshaft wear due to oiling issues, and there are 3 actions that reduced the chances of this occurring. Firstly, engine oil has to be warmed up to operating temperature before use. Secondly, a baffle plate should be installed in the oil pan (although in the technical paper, they avoided this to speed up oil flow back to the sump as the engine was reliable up to 1.0G).
Finally, upgrading the oil pump helps ensure more consistent flow. Although there is no definite evidence, WPC treatment of the camshaft should help long term durability of the cam shaft. The Toyota factor balanced the rotating mass to around 10grams of tolerance, and a good engine builder should be able to balance it to 0.5 grams instead.
While the torque potential of the cars per liter is somewhat comparable, the significant advantages of the cylinder head design of the K20A leaves the 2ZZ in the dust, which is clear since it was designed in an era where the Honda B18C was it's competition. It would have been amazing if Toyota continued development of the 2ZZ and perhaps produced a response to the K20, but even Honda moved onto forced induction engines, so we are likely left with the swansong to naturally aspirated 4 cylinder engines from both manufacturers.
References:
Toyota ZZ: Everything You Need to Know
Development of the High Speed 2ZZ-GE Engine
DOI: https://doi.org/10.4271/2000-01-0671
Citation: Shikida, T., Nakamura, Y., Nakakubo, T., and Kawase, H., "Development of the High Speed 2ZZ-GE Engine," SAE Technical Paper 2000-01-0671, 2000, https://doi.org/10.4271/2000-01-0671.
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