BG-33P
27-03-2013, 12:01 PM
Hey guys,
I've been thinking about undertrays for a while now and have started researching this topic along with general vehicle aerodynamics. I'm looking to develop an undertray for my 1996 del sol and wanted to get other peoples thoughts, input and ideas.
The Car
My car is only used on the street and occassionally sees some 'spirited' driving which is kept well within my limits, the cars limits and the legal limits.
The car has the following mods which may influence the discussion in this thread:
Engine:
B16A2 - Stock block / head / gearbox
ITR intake arm and box, ducted to behind the front bumper
Stock header + cat + cat back
Competition Clutch + Ultra Light Flywheel
Hasport engine mounts
Wheels / Suspension:
Enkei RPF01 16x7
Toyo T1R 205/45
Tokico Coilovers - not super low or stiff. Can go lower and stiffer if needed to aide the objectives of this exercise
Slotted Brake Discs Front & Rear with performance pads. OEM Sizes.
Energy Suspension Bushes throughout apart from new oem honda rear trailing arm bushes
ITR Front strut bar
ITR Rear sway bar
ASR Rear subframe brace
ETD Traction bars
Stock upper and lower control arms
Aero / Body:
OEM EG Civic front lip - Might switch to the EM1 lip as its shape might have a positive effect on the aero going under the front of the car.
Stock bumpers
Stock rear wing
Stock hood
Stock mudflaps + sideskirts
Goals / Expectations
Initially I was thinking that this project would give me a small but noticeable increase in fuel efficiency. However, upon further research its apparent that I could also gain a little downforce (through reduction of lift generated under the car), and increased effeciency of the cooling systems in the car.
The aspirations of extra downforce don't really bother me as I'd probably need to be driving outside of my current scope/abilities to see the difference anyway. The cooling benefits are something that I am interested in maximizing throughout this process along with reduced drag/lift from the underbody so I will concentrate on those elements.
Ultimately I'm looking forward to researching, developing and building a custom item for my car. I've always done my own work on the car and haven't had the time / space to do stuff like this in a long time so it should be fun.
Restrictions
Throughout the process I'm working with the following restrictions:
No drilling of holes in the body of the car. Original holes should be used for mounting points.
All work should be completely undable. (no cutting of panels etc)
Ride height and all work should remain legal within victoria.
Stock appearance should be maintained as much as possible.
Any new parts should be made to a standard that looks factory.
Reducing Drag
Ultimately the aerodynamics of the del sol are pretty ****ed because of the low pressure area behind the rear window that disrupts alot of flow coming off the back of the roof and over the bootlid. There is little I feel I could do here but some day i might experiment with different roof lips / diffusers etc. For now I'm just concentrating on the underside of the car.
Based on the research I've done so far the way to reduce drag from the underside of the car is to have the entire under body completely flat. Some benefit can be had by shaping and sloping areas of the underbody to produce lower / higher pressures where required but the basic idea of a flat / smooth underbody still remains.
A completely sealed underbody looks to be the most effective design however that generates problems of its own. The biggest problem here is heat management. You've got lots of heat that needs to be removed from the engine bay as well as lots of heat generated from the exhaust system.
For the under body I'd probably split it up into three pieces:
Front - from the front lip to the firewall / front subframe area
Middle - from the front subframe to the rear subframe
Rear - from the rear subframe to the rear lip
Front Undertray
The front undertray needs to serve a few purposes:
Stop turbulent air making its way up into the engine bay from underneath the car
Channel hot air out of the engine compartment
Duct air to the places where I want it rather then letting it find its own way through the frame rails
The mere presence of a flat undertray will stop most of the air making its way up into the engine bay which ticks the first box there. This should create a lower air pressure environment in the engine compartment which will help air flow through the cooling cores.
Removing the hot air from the engine compartment now becomes an issue though. I've seen panels which have rear facing louvers in their front undertray behind where the sump / gearbox would be which allows air to be sucked out of the engine bay by the air passing underneath the car. This sounds like it would work once there is air passing under the car. I'm concerned about the airflow at idle and when in traffic though. I'm also contemplating an upward bend in the panel behind the sump/gearbox where the louvers will be situated as it approaches the firewall to increase the natural suction effect from the air passing under the car. Yes it will comprimise the effect of the undertrays aero but it could have a positive effect on the cooling attributes of the car.
Ducting of the air is pretty simple. I'm thinking of having some form of opening in the front of the car to channel air to the air box. Probably near the front lip off to the side where the lip starts to turn down.
I'm also thinking of putting naca ducts in the front undertray for numerous uses. One such use would be to duct air to the brakes. Not that they absolutely need it but it would be cool to have. (wank factor yo). Another use might also be to get some extra air blowing across the sump / exhaust / gear box and then have it go out the louvers in the undertray. This may have a negative effect though cause the extra air in the engine bay could cause higher pressure and reduce the suction effect happening on the rear louvers.
Middle Undertray
The middle undertray would be rather simple. Just a big flat sheet that sits under the car. running the full width of the vehicle and pretty much the lenght of the side skirts. The major concerns here are to do with the exhaust piping. Do i enclose it? Do i leave it open? Do i enclose it and supply a couple of naca ducts for cooling? Some design changes may need to be made to stop it from hitting the exhaust. or i could just space the undertray lower so it clears everything.
Some underbodies have vertical pieces that help keep the air flowing straight down the body or to help air channel inwards towards the rear diffuser and away from the rear wheels.
Rear Undertray
There are plenty of possibilites for the under tray from the rear subframe to the rear of the car, as well as some designs that influence the aero in different ways. Different degrees of incline leading to the rear bumper produce different results for drag and downforce. ultimately I'm wanting to get a smooth flow of air out the back of the car whilst reducing drag as much as possible. The turbulent air from the rear wheels needs to be kept seperated from the (hopefully) smooth air running through the under body.
The reduction of the parachute effect will obviously help reduce the drag on the car.
Cooling efficiencies
The cooling differences should be noticeable because of the bigger pressure differences between the front of the car and the engine bay once the under tray is on. If the theory is correct, and the design does what its supposed to do, i should see an increase in efficiency of the radiator and air con core.
Testing
In order to actually measure any difference i'm going to have to take temperature and pressure readings before and after. I'll have to get my hands on some test equipment but i'm thinking of the following measurements:
Pressure before and after the radiator. (this should give me an indication of how much air is flowing through the radiator - the bigger the difference the better as far as I'm aware)
Pressure readings in a couple of areas in the engine bay, particularly when I'm expecting presure changes induced by the undertray
temperature readings of the sump & gear box drain bolts (trying to get a good indication of oil temps without installing proper sensors)
air temp readings of different areas inside and outside of the engine bay.
Any ideas / info on this stuff would be good as I've only done preliminary research at the moment.
Construction
Initially it will be done with cheap / shitty / potentially inapproriate materials just for testing purposes and to provide a quicker iteration time for changes. Prototyping yo!.
Once I get closer to the final design I'm thinking of using a mix of plastics and metals. The heat sensitive areas will probably need to be some form of metal. This could also help the undertray act as a heat sink to get some of the heat off the components. I have access to 3D printing hardware as well so I'm think of producing any ducts / openings using printed plastics which all seem to have different properties for heat & fexibility. All of which so far seem to be quite usable for what I want to do.
For finishing I'm thinking the whole thing should be painted matte / satin black with nice round edges on all the corners for a nicer oem style. I could vynl wrap the rear diffuser with fake carbon for some wank factor too lol. Although I probably wont do that.
If you've gotten this far you should be rewarded cause I've written one hell of an essay here. Any info, ideas, tips, etc are totally welcome. I'll be back to post some pictures that help support parts of my 'essay' above. Pictures make things easier.
Let the discussion begin.
J
I've been thinking about undertrays for a while now and have started researching this topic along with general vehicle aerodynamics. I'm looking to develop an undertray for my 1996 del sol and wanted to get other peoples thoughts, input and ideas.
The Car
My car is only used on the street and occassionally sees some 'spirited' driving which is kept well within my limits, the cars limits and the legal limits.
The car has the following mods which may influence the discussion in this thread:
Engine:
B16A2 - Stock block / head / gearbox
ITR intake arm and box, ducted to behind the front bumper
Stock header + cat + cat back
Competition Clutch + Ultra Light Flywheel
Hasport engine mounts
Wheels / Suspension:
Enkei RPF01 16x7
Toyo T1R 205/45
Tokico Coilovers - not super low or stiff. Can go lower and stiffer if needed to aide the objectives of this exercise
Slotted Brake Discs Front & Rear with performance pads. OEM Sizes.
Energy Suspension Bushes throughout apart from new oem honda rear trailing arm bushes
ITR Front strut bar
ITR Rear sway bar
ASR Rear subframe brace
ETD Traction bars
Stock upper and lower control arms
Aero / Body:
OEM EG Civic front lip - Might switch to the EM1 lip as its shape might have a positive effect on the aero going under the front of the car.
Stock bumpers
Stock rear wing
Stock hood
Stock mudflaps + sideskirts
Goals / Expectations
Initially I was thinking that this project would give me a small but noticeable increase in fuel efficiency. However, upon further research its apparent that I could also gain a little downforce (through reduction of lift generated under the car), and increased effeciency of the cooling systems in the car.
The aspirations of extra downforce don't really bother me as I'd probably need to be driving outside of my current scope/abilities to see the difference anyway. The cooling benefits are something that I am interested in maximizing throughout this process along with reduced drag/lift from the underbody so I will concentrate on those elements.
Ultimately I'm looking forward to researching, developing and building a custom item for my car. I've always done my own work on the car and haven't had the time / space to do stuff like this in a long time so it should be fun.
Restrictions
Throughout the process I'm working with the following restrictions:
No drilling of holes in the body of the car. Original holes should be used for mounting points.
All work should be completely undable. (no cutting of panels etc)
Ride height and all work should remain legal within victoria.
Stock appearance should be maintained as much as possible.
Any new parts should be made to a standard that looks factory.
Reducing Drag
Ultimately the aerodynamics of the del sol are pretty ****ed because of the low pressure area behind the rear window that disrupts alot of flow coming off the back of the roof and over the bootlid. There is little I feel I could do here but some day i might experiment with different roof lips / diffusers etc. For now I'm just concentrating on the underside of the car.
Based on the research I've done so far the way to reduce drag from the underside of the car is to have the entire under body completely flat. Some benefit can be had by shaping and sloping areas of the underbody to produce lower / higher pressures where required but the basic idea of a flat / smooth underbody still remains.
A completely sealed underbody looks to be the most effective design however that generates problems of its own. The biggest problem here is heat management. You've got lots of heat that needs to be removed from the engine bay as well as lots of heat generated from the exhaust system.
For the under body I'd probably split it up into three pieces:
Front - from the front lip to the firewall / front subframe area
Middle - from the front subframe to the rear subframe
Rear - from the rear subframe to the rear lip
Front Undertray
The front undertray needs to serve a few purposes:
Stop turbulent air making its way up into the engine bay from underneath the car
Channel hot air out of the engine compartment
Duct air to the places where I want it rather then letting it find its own way through the frame rails
The mere presence of a flat undertray will stop most of the air making its way up into the engine bay which ticks the first box there. This should create a lower air pressure environment in the engine compartment which will help air flow through the cooling cores.
Removing the hot air from the engine compartment now becomes an issue though. I've seen panels which have rear facing louvers in their front undertray behind where the sump / gearbox would be which allows air to be sucked out of the engine bay by the air passing underneath the car. This sounds like it would work once there is air passing under the car. I'm concerned about the airflow at idle and when in traffic though. I'm also contemplating an upward bend in the panel behind the sump/gearbox where the louvers will be situated as it approaches the firewall to increase the natural suction effect from the air passing under the car. Yes it will comprimise the effect of the undertrays aero but it could have a positive effect on the cooling attributes of the car.
Ducting of the air is pretty simple. I'm thinking of having some form of opening in the front of the car to channel air to the air box. Probably near the front lip off to the side where the lip starts to turn down.
I'm also thinking of putting naca ducts in the front undertray for numerous uses. One such use would be to duct air to the brakes. Not that they absolutely need it but it would be cool to have. (wank factor yo). Another use might also be to get some extra air blowing across the sump / exhaust / gear box and then have it go out the louvers in the undertray. This may have a negative effect though cause the extra air in the engine bay could cause higher pressure and reduce the suction effect happening on the rear louvers.
Middle Undertray
The middle undertray would be rather simple. Just a big flat sheet that sits under the car. running the full width of the vehicle and pretty much the lenght of the side skirts. The major concerns here are to do with the exhaust piping. Do i enclose it? Do i leave it open? Do i enclose it and supply a couple of naca ducts for cooling? Some design changes may need to be made to stop it from hitting the exhaust. or i could just space the undertray lower so it clears everything.
Some underbodies have vertical pieces that help keep the air flowing straight down the body or to help air channel inwards towards the rear diffuser and away from the rear wheels.
Rear Undertray
There are plenty of possibilites for the under tray from the rear subframe to the rear of the car, as well as some designs that influence the aero in different ways. Different degrees of incline leading to the rear bumper produce different results for drag and downforce. ultimately I'm wanting to get a smooth flow of air out the back of the car whilst reducing drag as much as possible. The turbulent air from the rear wheels needs to be kept seperated from the (hopefully) smooth air running through the under body.
The reduction of the parachute effect will obviously help reduce the drag on the car.
Cooling efficiencies
The cooling differences should be noticeable because of the bigger pressure differences between the front of the car and the engine bay once the under tray is on. If the theory is correct, and the design does what its supposed to do, i should see an increase in efficiency of the radiator and air con core.
Testing
In order to actually measure any difference i'm going to have to take temperature and pressure readings before and after. I'll have to get my hands on some test equipment but i'm thinking of the following measurements:
Pressure before and after the radiator. (this should give me an indication of how much air is flowing through the radiator - the bigger the difference the better as far as I'm aware)
Pressure readings in a couple of areas in the engine bay, particularly when I'm expecting presure changes induced by the undertray
temperature readings of the sump & gear box drain bolts (trying to get a good indication of oil temps without installing proper sensors)
air temp readings of different areas inside and outside of the engine bay.
Any ideas / info on this stuff would be good as I've only done preliminary research at the moment.
Construction
Initially it will be done with cheap / shitty / potentially inapproriate materials just for testing purposes and to provide a quicker iteration time for changes. Prototyping yo!.
Once I get closer to the final design I'm thinking of using a mix of plastics and metals. The heat sensitive areas will probably need to be some form of metal. This could also help the undertray act as a heat sink to get some of the heat off the components. I have access to 3D printing hardware as well so I'm think of producing any ducts / openings using printed plastics which all seem to have different properties for heat & fexibility. All of which so far seem to be quite usable for what I want to do.
For finishing I'm thinking the whole thing should be painted matte / satin black with nice round edges on all the corners for a nicer oem style. I could vynl wrap the rear diffuser with fake carbon for some wank factor too lol. Although I probably wont do that.
If you've gotten this far you should be rewarded cause I've written one hell of an essay here. Any info, ideas, tips, etc are totally welcome. I'll be back to post some pictures that help support parts of my 'essay' above. Pictures make things easier.
Let the discussion begin.
J