Hello everyone
I've fitted some time ago a LCR "lip" splitter on my 2005 LFR. At first, I thought it a purely cosmetic mod, but a mod which does nothing is hardly worth the money.
How do splitters work
A splitter is supposed to be the front axle counterpart of a rear wing - to generate downforce to keep the front wheels down. It works on the Bernoulli Principle - by narrowing the air gap between bumper and ground, air under the car gains speed and therefore looses pressure, while air above the splitter keeps the pressure and pushes down the nose of the car.
The lower bumper and plastic undertray of the LC / LFR is more or less an airfoil, aimed to narrow the gap between lower engine bay and ground - the same Bernoulli principle tells us by accelerating the speed and lowering the pressure of the air going under the engine, the pressure differential would "suck" the hot air from the engine bay and help the cooling. The pressure differential under a 4-door car at high speed is far more efficient compared to a pair of puny plastic fans.
Fitting a splitter would create a barrier in front of the car and narrow the air gap below the bumper, but it does also mess with the air coming below bumper. Splitters need a flat underbelly to work best, because they rely on air speed. Braking the air with under car obstacles is not a good idea.
Our cars
As I've had a plan to improve the Leon aerodynamics, studied how the bumper is made. (Factory Cx figure is 0.32).
There is a flat underbumper for the first 20cm or so, a central (black plastic) undertray dropping down in front of the engine sump, and 2 side panels. There are 2 large holes behind the bumper, below the intercooler and below the horns, about 35 x 20 cms each, which do the worst possible thing for the car's aerodynamics - the underbelly has to be as flat as possible to allow the air to flow.
Also, the Leon has outer door seals on the upper half of the doors, between front and rear door and on the lowest edge, but nothing on either rearmost edge or foremost edge of the doors.
Rear factory spoiler is functional, a rear wing has to be as high as possible to smooth out the airflow over the back.
The dirty work
1. Sealed the panel gaps as following:
- outer door seal on the fender's edge to seal the foremost edge of the front door;
- outer door seal on the rear fender to seal the rearmost edge of the rear door;
- seal between upper edge of the hatchback/spoiler and the body;
- seal between hatchback's rear window sides and body;
- seal between engine bonnet and fenders;
- seal between fender edge and A-pillar;
- also used red silicone caulking to seal the bumper to bodywork both front and rear and the edges of the headlamps to the bumper and fender.
All seals unless specified were made from triangular-section rubber recovered from wiping edge of wiper blades - it's the only easily available rubber which has the right section and size, looks OEM, is soft and flexible enough to follow edges and to be glued strongly.
From outside the car, is very hard to see the seals if you don't know specifically what to look for.
2. Modified the front bumper as following:
- used insulating foam plates to smooth out the transition between LCR plastic splitter and the flat section under the bumper - turn the "step" into an "incline";
- as the transition has been covered, used the same plates, cut with a sharp blade and glued, to make the underbelly (lower side of the bumper, engine side panels, engine undertray) as flat as possible;
- also formed a "channel" or a "venturi" behind the hole in the middle of the splitter back to the engine undertray;
- covered also the engine side plastic panels with the foamy material, to take opportunity to dampen engine noise;
- took a sandwich plastic panel for roofing (3 mm thick, 2 layers of plastic with a square-tube empty section between them) and cut 2 pieces to fit the holes behind the bumper, below the intercooler and below the horns; the left and right are different shapes and have to be trimmed, impossible to get the shape right from the first attempt;
- covered the exposed part of the plastic panels with the same foamy material to get surfaces of the lower bumper and panel at the same level, to avoid having "hills and valleys" on a surface that has to be flat;
- fit the panels with self-threading screws in the plastic of the bumper and engine side panels;
- filled the minor gaps with strong silicone caulking.
Right now, the lower surface from splitter back to the front wheels and inner fenders on the sides and engine sump in the middle is a flat continuous panel. (Unfortunately, is not flat as in "straight edge flat", there is a slight concavity, for the shape of the engine underbelly was complex and working on your back with glues and screwdrivers in a 20 cm space is not a way for fine adjustments
for this reason I didn't take any pictures, there was no angle to do it.)
The bumper/underbelly mod is 100% invisible from outside the car. Only by crawling under it, or raising the car, can it be seen.
Results
1. The sealing of the panel gaps yielded no discernible results. Maybe outer noises were a bit muffled.
2. Water ingress between door and door frame is reduced to almost nonexistent.
3. The underbelly modification yielded some surprisingly good results for a job made with no calculations or aerodynamic tools: coasting seems easier and turn-in seems slightly better - in curves taken at 60 to 80 km/h, that is. (No time to make any experiments on an open road.)
Right now, seeing how the bumper of a LC/LFR is made (split just at the lower front edge to feed air in the SMIC and opposite side hole) and having also the splitter and panels behind, it has the very approximate shape of a F1 nose wing, so it has the reasons to provide some results.
There should be also possible to continue behind engine with a flat plastic underbelly from head to tail, leaving a channel in the middle for the exhaust to run. Some racing cars and supercars use flat undertrays for better ground effect and downforce.
Best Regards,
~Nautilus
I've fitted some time ago a LCR "lip" splitter on my 2005 LFR. At first, I thought it a purely cosmetic mod, but a mod which does nothing is hardly worth the money.
How do splitters work
A splitter is supposed to be the front axle counterpart of a rear wing - to generate downforce to keep the front wheels down. It works on the Bernoulli Principle - by narrowing the air gap between bumper and ground, air under the car gains speed and therefore looses pressure, while air above the splitter keeps the pressure and pushes down the nose of the car.
The lower bumper and plastic undertray of the LC / LFR is more or less an airfoil, aimed to narrow the gap between lower engine bay and ground - the same Bernoulli principle tells us by accelerating the speed and lowering the pressure of the air going under the engine, the pressure differential would "suck" the hot air from the engine bay and help the cooling. The pressure differential under a 4-door car at high speed is far more efficient compared to a pair of puny plastic fans.
Fitting a splitter would create a barrier in front of the car and narrow the air gap below the bumper, but it does also mess with the air coming below bumper. Splitters need a flat underbelly to work best, because they rely on air speed. Braking the air with under car obstacles is not a good idea.
Our cars
As I've had a plan to improve the Leon aerodynamics, studied how the bumper is made. (Factory Cx figure is 0.32).
There is a flat underbumper for the first 20cm or so, a central (black plastic) undertray dropping down in front of the engine sump, and 2 side panels. There are 2 large holes behind the bumper, below the intercooler and below the horns, about 35 x 20 cms each, which do the worst possible thing for the car's aerodynamics - the underbelly has to be as flat as possible to allow the air to flow.
Also, the Leon has outer door seals on the upper half of the doors, between front and rear door and on the lowest edge, but nothing on either rearmost edge or foremost edge of the doors.
Rear factory spoiler is functional, a rear wing has to be as high as possible to smooth out the airflow over the back.
The dirty work
1. Sealed the panel gaps as following:
- outer door seal on the fender's edge to seal the foremost edge of the front door;
- outer door seal on the rear fender to seal the rearmost edge of the rear door;
- seal between upper edge of the hatchback/spoiler and the body;
- seal between hatchback's rear window sides and body;
- seal between engine bonnet and fenders;
- seal between fender edge and A-pillar;
- also used red silicone caulking to seal the bumper to bodywork both front and rear and the edges of the headlamps to the bumper and fender.
All seals unless specified were made from triangular-section rubber recovered from wiping edge of wiper blades - it's the only easily available rubber which has the right section and size, looks OEM, is soft and flexible enough to follow edges and to be glued strongly.
From outside the car, is very hard to see the seals if you don't know specifically what to look for.
2. Modified the front bumper as following:
- used insulating foam plates to smooth out the transition between LCR plastic splitter and the flat section under the bumper - turn the "step" into an "incline";
- as the transition has been covered, used the same plates, cut with a sharp blade and glued, to make the underbelly (lower side of the bumper, engine side panels, engine undertray) as flat as possible;
- also formed a "channel" or a "venturi" behind the hole in the middle of the splitter back to the engine undertray;
- covered also the engine side plastic panels with the foamy material, to take opportunity to dampen engine noise;
- took a sandwich plastic panel for roofing (3 mm thick, 2 layers of plastic with a square-tube empty section between them) and cut 2 pieces to fit the holes behind the bumper, below the intercooler and below the horns; the left and right are different shapes and have to be trimmed, impossible to get the shape right from the first attempt;
- covered the exposed part of the plastic panels with the same foamy material to get surfaces of the lower bumper and panel at the same level, to avoid having "hills and valleys" on a surface that has to be flat;
- fit the panels with self-threading screws in the plastic of the bumper and engine side panels;
- filled the minor gaps with strong silicone caulking.
Right now, the lower surface from splitter back to the front wheels and inner fenders on the sides and engine sump in the middle is a flat continuous panel. (Unfortunately, is not flat as in "straight edge flat", there is a slight concavity, for the shape of the engine underbelly was complex and working on your back with glues and screwdrivers in a 20 cm space is not a way for fine adjustments
for this reason I didn't take any pictures, there was no angle to do it.)The bumper/underbelly mod is 100% invisible from outside the car. Only by crawling under it, or raising the car, can it be seen.
Results
1. The sealing of the panel gaps yielded no discernible results. Maybe outer noises were a bit muffled.
2. Water ingress between door and door frame is reduced to almost nonexistent.
3. The underbelly modification yielded some surprisingly good results for a job made with no calculations or aerodynamic tools: coasting seems easier and turn-in seems slightly better - in curves taken at 60 to 80 km/h, that is. (No time to make any experiments on an open road.)
Right now, seeing how the bumper of a LC/LFR is made (split just at the lower front edge to feed air in the SMIC and opposite side hole) and having also the splitter and panels behind, it has the very approximate shape of a F1 nose wing, so it has the reasons to provide some results.
There should be also possible to continue behind engine with a flat plastic underbelly from head to tail, leaving a channel in the middle for the exhaust to run. Some racing cars and supercars use flat undertrays for better ground effect and downforce.
Best Regards,
~Nautilus
