Which is lower, flat or in line
Discussion
As the title.
Which is the lower engine in a normal car instalation, i.e. Subaru versus any other FWD I4 or V6
I'm not talking about centre of gravity, just overall height.
This question was prompted by another thread in which someone pointed out how the requirement to allow 100mm of room between the bonnet and the engine was forcing tall bonnet lines in new cars. If a flat four or six is lower will they become more widespread as car maker try to keep the look of lower, sporty, models? Not so long ago IIRC a Jaguar stylist mentioned how hard a sporty bonnet line was becomming to design, Will it be a case of "fat or flat"?
At first I thought the flat engine would easily win but when you allow room for the exhaust under it and all the induction and ancilliaries above it is there any difference?
Which is the lower engine in a normal car instalation, i.e. Subaru versus any other FWD I4 or V6
I'm not talking about centre of gravity, just overall height.
This question was prompted by another thread in which someone pointed out how the requirement to allow 100mm of room between the bonnet and the engine was forcing tall bonnet lines in new cars. If a flat four or six is lower will they become more widespread as car maker try to keep the look of lower, sporty, models? Not so long ago IIRC a Jaguar stylist mentioned how hard a sporty bonnet line was becomming to design, Will it be a case of "fat or flat"?
At first I thought the flat engine would easily win but when you allow room for the exhaust under it and all the induction and ancilliaries above it is there any difference?
It depends on the induction and valvetrain arrangement, really. An Alfa Boxer engine with downdraught carbs and an air filter casing on top of the carbs will be taller than some in-line engines with pushrod valvegear and sidedraught induction, but it's certainly possible to make the boxer configuration lower if this is a definite design criteria. Exhaust manifolds don't cause a huge problem as they come out the bottom of the cylinder heads then bend round to run backwards within the depth of the sump, or only a little below it. You could also make an induction plenum a deformable structure, if you wanted to, and duct the air in from a filter in the nose of the car.
The tendency has been for inline engines to become taller over recent years, because virtually everything is now DOHC, in order to acheive the sort of efficiency demanded by modern regulations, and many have fancy variable lift/timing valvegear that can make the heads even taller.
The Scooby flat 4 is an incredibly compact little engine, but the main problem with boxers for front engine applications is that they can be so wide that they restrict available steering lock... but again, as cars have grown ever bigger, this has become less of an issue.
The tendency has been for inline engines to become taller over recent years, because virtually everything is now DOHC, in order to acheive the sort of efficiency demanded by modern regulations, and many have fancy variable lift/timing valvegear that can make the heads even taller.
The Scooby flat 4 is an incredibly compact little engine, but the main problem with boxers for front engine applications is that they can be so wide that they restrict available steering lock... but again, as cars have grown ever bigger, this has become less of an issue.
cymtriks said:
This question was prompted by another thread in which someone pointed out how the requirement to allow 100mm of room between the bonnet and the engine was forcing tall bonnet lines in new cars.
There was a manufacturer (possibly citroen) testing the idea of having the bonnet pop up when it detects an impact. So you could have the low bonnet and pass pedestraian safety.
The problem with a wide angle V or making an engine that's close to a compact "cube" is that it ignores the effect of mounting the intake and anciliaries above a flat or wide V engine block.
The problem with a pop up bonnet is making certain that it will pop up and that it will do this at the right time. It just won't work right every time.
Back to height take a simple comparison as follows along the lines of Audi/Subaru-
height to wheel/diff centre about 11.5 inches
height from diff centre to clutch centre about 3.5 inches
so we have a fixed crank centre of about 15 inches
for the I4 engine the block and head are about 8 inches each giving a total ground to top height of 31 inches.
for the flat four assume the block is 8 inches deep which puts the intake gasket at 19 inches high. So if the intake system and all of the anciliries are less than 12 inches high it's lower overall. So you might save 2 to 4 inches overall.
For something like a big GT Jag XK, Ferrari 599 or Aston Vanquish that will certainly allow more styling and aerodynamic freedom. Taking into account the width of these cars, and the extent that the exhaust adds to the current V engines, the width of a flat engine might not be a problem.
Alfa, Ferrari, VW, Lancia and Citroen have made flat engines but no longer do so. I wonder if any of them will now reconsider as the width issue gets less important and the height gets more so.
The problem with a pop up bonnet is making certain that it will pop up and that it will do this at the right time. It just won't work right every time.
Back to height take a simple comparison as follows along the lines of Audi/Subaru-
height to wheel/diff centre about 11.5 inches
height from diff centre to clutch centre about 3.5 inches
so we have a fixed crank centre of about 15 inches
for the I4 engine the block and head are about 8 inches each giving a total ground to top height of 31 inches.
for the flat four assume the block is 8 inches deep which puts the intake gasket at 19 inches high. So if the intake system and all of the anciliries are less than 12 inches high it's lower overall. So you might save 2 to 4 inches overall.
For something like a big GT Jag XK, Ferrari 599 or Aston Vanquish that will certainly allow more styling and aerodynamic freedom. Taking into account the width of these cars, and the extent that the exhaust adds to the current V engines, the width of a flat engine might not be a problem.
Alfa, Ferrari, VW, Lancia and Citroen have made flat engines but no longer do so. I wonder if any of them will now reconsider as the width issue gets less important and the height gets more so.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff