simpleton's question...

[littlegearl]

is there some trick i'm missing? or am i just being a numpty? but can someone explain to me the following:

1. why on a transverse layout FWD-only car with a crossflow head the exhaust ports are on the leading edge of the block and the inlet on the back?

surely it would make more sense to have the air intakes at the front to create a ram-air effect and have the exhaust exiting straight underneath the car, i understand this would probably cause hugh complication's on a transverse 4WD layout but it seems the majority of cars / engines that have never been designed for 4WD transmissions still have it this way.

i've heard a rumour that in the 1990's when Vauxhall was using its XE engine for the Cavalier BTCC campaign they turned the head round to do this, would this even be possible?

2. on the same style car, why is the engine always on the left (as you look into the engine bay) and the gearbox on the right?

is this to do with the bulk of cars being LHD so when they switch over to FWD happened and people such as VW and Opel started making transverse gearboxes they mounted the heavier engine on the opposite side to the driver to try and improve lateral weight distribution? or again am i missing some simple trick here?

cheers in advance...

[r1ot]

I can answer the first one you had to go really fast to benefit from the ram air effect at lot faster than is legal. Some manufacturers do have the intakes towards the front of the engine the puma engine for example.

[Alex@POD]

Also I have seen some cars (can't remember what sorry) with the engine "on the right"... Very good questions though. I would hasard a guess and say that the heat from the exhaust is best kept away from the bulkhead in tight engine bays... It must also be easier to route the intake to the back with an airbox on the side, as it would prove very tight or twisty the other way around...
Just wild guesses in any case...

[littlegearl]

'suppose it could just be that it is actually easier to do this way round, though it seems illogical to me it may be cheaper to manufacture!?!

[Mattt]

Could also consider exhaust manifold branch lengths - i.e. you have more to play with if it comes out the front.

[paolow]

just logical speculation but the xaust is probably to the front to avoid issues with heatsoak through the bulkead etc. If it were to the rear there would be phenomenal heat build up, Also, from a purely practical point of view, exhausts not only have to come off more often than inlets, but are also more problematic when they do with corroded bolts etc so it makes it easier to do if theres more room, and there is at the front.
But then look at my car - the MR2 has the xhaust on the cabin side becasue of the mid engine. having said that - its the same engine as the celica where its the 'right' way round.
WRT the gearbox question - let me havea think....
Hmmmm, out of the box thinking has me believe this is a hangover from RWD designs. engines almost always (in fact i cant think of an exception) run clockwise. put a gearbox on that and to get fourth - ie - 1:1 ratio (usually) the power goes straight through the box and out of the output shaft and this of course goes directly to the wheels. ergo this effectively decides which way round the engine and box go ( i think).
I dont know the definitive answer to both - im a policeman - but thats my thinking...

[Mikey G]

paolow said:

Hmmmm, out of the box thinking has me believe this is a hangover from RWD designs. engines almost always (in fact i cant think of an exception) run clockwise. put a gearbox on that and to get fourth - ie - 1:1 ratio (usually) the power goes straight through the box and out of the output shaft and this of course goes directly to the wheels. ergo this effectively decides which way round the engine and box go ( i think).
I dont know the definitive answer to both - im a policeman - but thats my thinking...

Early Hondas run anticlockwise and the engine is the other way around to most other FWD cars. Later units such as the Civic type R run conventionaly clockwise and the engine has now been turned around to the normal way.
It may well be something to do with the design of the gearbox otherwise it would need an extra shaft to get the differential turning the correct way.

[Arif110]

Could it also be anything to do with a preference over which direction the engine exerts a force on the chassis, as it rev's?


Just my 2p's-worth...!

[leorest]

paolow said:

... let me havea think....
Hmmmm, out of the box thinking has me believe this is a hangover from RWD designs. engines almost always (in fact i cant think of an exception) run clockwise. put a gearbox on that and to get fourth - ie - 1:1 ratio (usually) the power goes straight through the box and out of the output shaft and this of course goes directly to the wheels. ergo this effectively decides which way round the engine and box go ( i think).
I dont know the definitive answer to both - im a policeman - but thats my thinking...

Nice thinking but can't the diff be arranged such that it can change the drive direction?
Memories of playing with RWD RC cars and installing the diff upside down and getting it to go really fast backwards

[leorest]

... Oh and in the good old clockwork days the carb was put on the back of the engine to protect it from "carb icing" so may be a hangover from the golden era.
Modern efi is obviously less prone to icing but it might be a factor.

[badders]

All the PSA XU's run with inlets facing fowards.

[paolow]

badders said:

All the PSA XU's run with inlets facing fowards.

very true - but ive also been told that they suffer from heat build up which is hard on ancilliaries which is interesting.

[littlegearl]

an interesting side thought, as my knowledge is very limited i've been thinking about the cars i do know...

my mk 1 cavalier (longitudinal, rwd) has a non-crossflow block which has the carb and exhuast on the driver's side of the engine bay.

my mk 1 astra (transverse, fwd) has a crossflow head with the inlet at the back and exhaust at the front as previously mentioned, if you turn the block 90 degrees to run north-south (as i have done in my mk 1 cavalier) then you get the inlet on driver's side, exhaust on passenger's side

not very interesting in itself, but when you consider the above (crossflow) engine i am referring to is the vauxhall xe engine which is effectively a 2.0 16v version of the 1800cc 8v engine first used in the opel manta / mk 2 cavalier... ie, it was designed for both types of installment

so perhaps as i touched on earlier in the thread manufacturer's just stuck with what they knew, plus combined with the rotation of the crank they had their hand dictated!?!

as mentioned by Paolow the engine his MR2 has originally came out of a FWD car, so went from a Front-FWD layout to a mid-RWD layout so Toyota had to deal with possible heat soak issues otherwise they would have a 5-reverse geared MR2 if they turned it round through 180 degrees...