Here, we will investigate the characteristics of this engine by referring to the data of the KF type naturally aspirated engine installed in Toyota’s LA700A type Pixis Mega D 2015/07 model.
KF Engine type naturally aspirated specifications
LA700A type Pixis Mega
|Vehicle model||DBA-LA700A type|
|Car name & grade||Pixis Mega |
|Inner diameter x stroke||63.0mm x 70.4mm|
|Bore stroke ratio||1.12|
|Single cylinder volume||219.4cc|
|Intake method||Naturally aspirated|
|Fuel used||Regular gasoline|
|Maximum output||52PS / 6800rpm|
|Maximum torque||6.1kgm / 5200rpm|
First of all, as a basic structure, the KF type engine is a long stroke type engine with a bore (inner diameter) of 63.0 mm, a stroke (stroke) of 70.4 mm, and a bore stroke ratio of 1.12 (the stroke amount is larger than the piston diameter).
When the displacement and the number of cylinders are the same, the engine has better torque characteristics in the low rpm range than the short stroke type and is easy to handle, but in the high rpm range, the filling efficiency deteriorates and the sliding resistance increases. There is a concern that the output will drop.
Moreover, when the number of revolutions is the same, the average piston speed tends to be higher than that of the short stroke type, so the load on the engine tends to be heavier.
Among the models registered on this site, the oldest model equipped with the KF type naturally aspirated engine is the first Pixis Space [L575A type | 2011/09] released from 2011/09 , and the newest model is 2015. It is the first Pixis Mega [LA700A type | 2021/05] released from 07 , and 24 types of NA cars are registered.
Evaluation from the viewpoint of transient characteristics and liter equivalent horsepower
|Image of engine performance curve|
|Changes in horsepower||44.3PS → 52PS|
|Transition of torque||6.1kgm → 5.5kgm|
|Liter horsepower||79.03 PS / L|
|Liter torque||9.3kgm / L|
The Pixis Mega in-line 3-cylinder 658cc engine with a compression ratio of 11.3 and regular gasoline specifications, which is the reference vehicle for this time, produces a maximum output of 52 horsepower at 6800 rpm and a maximum torque of 6.1 kgm at 6800 rpm.
If you know the horsepower and the number of revolutions, you can know the torque, and if you know the torque and the number of revolutions, you can know the horsepower. The torque at 6800 rpm is 5.5kgm.
The horsepower per liter of displacement is 79.03PS / L and the torque is 9.3kgm / L, and the horsepower per cylinder (single cylinder volume 219.4cc) is 17.3PS and the torque is 2.0kgm.
When the KF type naturally aspirated engine is applied to a 10-step evaluation based on the deviation value aggregated from all NA vehicles registered on this site, the evaluation is ” quite good” with a converted horsepower of [ 7 ] and a converted torque of [ 5 ]. It is categorized as ” High power engine “.
By the way, among the models equipped with the KF type naturally aspirated engine, the one with the highest output was the LA700A type Pixis Mega 52PS / 6.1kgm, and the smallest was the LA350A type Pixis Epoch 49PS / 5.8kgm.
Displacement increase, compression ratio increase, bore stroke ratio change
|Normal displacement and compression ratio|
|Bore||Stroke||Displacement||Compression ratio||B / S ratio|
|Displacement expansion by bore up|
|Displacement expansion by increasing stroke|
There are three factors that determine the engine displacement: the number of cylinders, the bore diameter, and the stroke amount. By increasing or decreasing these, engines with various displacements are created.
Here, regardless of whether it is actually possible, the displacement when the piston diameter is expanded from the genuine 63.0 mm to 66.0 mm in 0.5 mm increments and when the stroke is extended from the genuine 70.4 mm to 75.4 mm in 1 mm increments. And, the change of the compression ratio when it is assumed that the combustion chamber volume does not change is listed.
* It is easy to say stroke up, but if you want to make a long stroke, you need a crankshaft and a compatible connecting rod, and if you can not divert it, you have to make it in one-off, so it is expensive anyway. It is a menu that requires considerable preparedness to put out.
Regarding the compression ratio, in most cases, the uneven capacity of the top surface of the piston changes as the diameter of the piston increases, so the compression ratio values in the list do not match, but the displacement. Please enjoy the atmosphere that the compression ratio will naturally increase as you increase the size.
The B / S ratio is an abbreviation for the bore stroke ratio, and as the bore diameter is widened, the characteristics of the long stroke type, square type, or short stroke type are approached. In the case of KF type engine, the ratio changes from 1.12 to 1.07 when the bore is increased by +3.0mm from the genuine piston.
Increased displacement with engines with similar piston diameters
There are 8 engines with pistons that are similar in size to the KF type engine with a piston diameter of 63.0 mm, so as a side note, let’s calculate the displacement when the piston is diverted and the bore is raised.
|Eg model||Piston diameter||Displacement|
As engines with similar piston diameters, Nissan: R06A type 658cc 64.0mm mounted on MG33S type Moco, Honda: S07A type 658cc 64.0mm mounted on JF1 type N-BOX, Nissan: H82W type Otti 3G83 type 657cc 65.0mm, Mazda: F6A type 657cc 65.0mm mounted on DA52W type Every Wagon, Nissan: 3B20 type 659cc 65.4mm mounted on HA1W type Days Roox, Honda: mounted on PA1 type Z E07Z type 656cc 66.0mm etc. is applicable.
(Although the number of people who find pleasure in such a quest has decreased) No matter how close the diameter is, there are factors such as the diameter of the piston pin, the height of the piston, and the convenience of valve recess, so if possible, the same manufacturer, If possible, if you choose the same fuel and the same intake method, and if possible, the one with a similar displacement, the possibility of genuine diversion may increase.
Average piston speed
Next, let’s look at the average piston speed. The average piston speed at 6800 rpm, where an engine with a stroke of 70.4 mm produces maximum output, is 16.0 m / s , which is a piston speed that travels a distance of 16.0 meters per second (57.6 km / h at speed). It means that is moving up and down.
The average speed is 17.2 m / s at 5200 rpm, which produces the maximum torque, and 17.1 m / s when the rev limit is assumed to be 7300 rpm, which is 500 rpm higher than the 6800 rpm where the maximum output is generated.
For reference, I calculated the change in piston speed when a KF engine with a stroke of 70.4 mm is rotated up to 10000 rpm. Looking at this, it seems that the speed increases by approximately 4.70 m / s as the number of revolutions increases by 2000 revolutions.
Considering only 20.0 m / s, which is a guideline for a general engine assuming mass production, it is mechanical to set the upper limit of high rpm to about 8520 rpm (whether it rotates or not). It seems to be preferred both mentally.