EVO Aerodynamics Review
Jul 10, 2007, 10:26 PM
#1
EVO Aerodynamics Review
The following is a review of multiple aerodynamic parts I have tested and/or installed on my EVOs over the past few years. I think it will be of interest to folks who track or race thier EVOs.
#1 – DHP Composites (DHPcomp@gmail.com) prototype front splittter/undertray for the EVO VIII front bumper.
This was installed on my ’04 EVO VIII in 2006 and ran all through the autocross season. It consists of a base layer of aluminum, center layer of foam core (except for the splitter/lip area), and a top layer of carbon fiber. There is an air duct/venturi on each side that ducts air toward the wheel wells. There is a vertical lip that extends up from the splitter about 1.5” to seal it off against the bottom of the front bumper. This unit weighed an estimated 20 pounds. Initial durability and resistance to damage was very good. Misjudging the angle of attack to get into steep driveways would result in the splitter flexing and the aluminum bottom scraping on the ground, taking the majority of the abuse. Durability and repairability of larger impacts was not so great. Once I hit a curb with the side of it. The aluminum and carbon layers separated and the aluminum bent up while the carbon just flexed. We were able to bend the aluminum back to flat and re-epoxy the layers together. Much more of an impact and it may not have been repairable.
This unit was added to a neutral handling Street Modified class autocross car. The effect was immediately noticeable. The front end had a lot more grip than before and the rear end was much more active in corners. Oversteer could be induced either by lift-throttle/braking in tight corners or power-on acceleration through larger sweepers. The power oversteer was something that was completely new to me! As speeds increased the rear end got progressively more unstable causing some difficulty in high speed slaloms and quick transitions. The front just had so much more grip that the rear could not keep up. . .
#2 – Voltex front bumper/Voltex twin canards/Voltex undertray.
This was installed on my new ’06 EVO IX RS which was being built from the ground up for competition in SCCA Solo2 Street Modifed class. I wanted every aerodynamic advantage the rulebook allows, so I went with Voltex based on their racing history, work with EVO aerodynamics, and wind tunnel testing of all their parts.
These 3 pieces came as one unit already assembled. Fitment was VERY good as far as body kits go. I had to take a sander to a little spot by the drivers side headlight to keep it from scratching up the light. Other than that, it was just painted and installed. It came with pre-cut mesh for the two upper sets of holes, and mesh already installed in the very bottom small holes. The directions for all Voltex stuff are in Japanese with only a couple pictures. It would be a good idea for Voltex to maybe re-write them in English for it’s North American market. The Voltex pieces can be installed just by going off the pictures and using some common sense, though.
First thing I noticed is that while the fiberglass bumper is strong and rigid, it is quite a bit less flexible and pliable than the urethane stock unit. The bottom of the bumper sits a bit lower than the stock unit. With it, I scraped on some driveways that I never scraped on before. It has a splitter-like element built into the bottom area of it. The center hole is huge and makes the stock intercooler look puny. The ARC wide model fills the hole perfectly, as does the Blitz intercooler. No trimming was necessary to fit the ARC model. The front bumper support does not fit as-is with the Voltex front bumper. The intercooler hole is taller than the stock bumper. You can modify the front support beam by cutting out a 1”t x 18”w x 3”d section from the bottom of it and it will fit perfectly. That is what I did. I also welded some strips of sheet metal back onto so that you don’t have hollow openings where you cut. It looks stock now and weighs the same as the stocker.
The undertray is fairly thin and flexible (~1/8”), although the craftsmanship is superb! It mounts to the bottom of the bumper with 13 bolts, and also to several brackets that attach to the chassis. The undertray IS functional. I could feel quite a difference in front end grip with it mounted vs. with it off. Also, at speed on the highway the front end just felt more “planted”. For a daily driver street car I feel this is a perfect setup, and when my car is off the track for extended times it will definitely go back on in place of the larger splitter/undertray (see below). This unit helped take me to a 2nd place finish in the Winged Warrior 3 autocross, even low on power running stock boost and pump gas!
#3 – DHP splitter/undertray for Voltex front bumper.
This unit is made to match up with the Voltex front bumper. It has a top and bottom layer of carbon sandwiching a foam core. It is much thicker and stiffer than the prototype I ran earlier, while weighing only about 1/3 what the prototype did. Weight is approx. 6 pounds for the unit itself, 8 pounds with mounting hardware. Finish is very good to excellent. Durability for this unit should be very good for a track car, but for a street car you will need to be very careful with driveways and curbs. One good thing – this should be easier to repair if need be than the one with the aluminum base.
It is hard to say which splitter/undertray would make more actual downforce since I had them on 2 totally different cars. The new car with the Voltex front end and the new splitter handled very well. It had a ton of turn in grip and rotated very well. After driving it in several races, including a higher speed Solo Trials, I came to realize that it was rear traction at higher speeds that was limiting the potential. It felt as though I could throw the car into turns faster and the front would stick, but the rear would want to come around. Also, in slaloms and quick transitions it felt as though if we pushed too hard the rear end would come around. Time for some rear downforce!!
#4 – DHP rear wing for EVO VIII or IX.
This unit is made to work with the DHP front splitter, matching downforce front and rear. The wing element weighs about 5-6 pounds, plus the aluminum mounts. It can be set to different angles of attack based on intended use. Right now I have it set at max angle for the most downforce at autocross speeds.
After adding the wing the car developed horrible push all through the corners. Corner entry and exit. We made some other changes at the same time as adding the wing so we tried to adjust those. With no real results, we decided to go to the sway bar. Just a simple modification to the swaybar made the car a whole new beast! In slow speed corners the front bites, the rear end rotates and gets you pointed the way you want to go. In high speed sweepers and slaloms the car just sticks!
Getting late. More to come soon. . .
#1 – DHP Composites (DHPcomp@gmail.com) prototype front splittter/undertray for the EVO VIII front bumper.
This was installed on my ’04 EVO VIII in 2006 and ran all through the autocross season. It consists of a base layer of aluminum, center layer of foam core (except for the splitter/lip area), and a top layer of carbon fiber. There is an air duct/venturi on each side that ducts air toward the wheel wells. There is a vertical lip that extends up from the splitter about 1.5” to seal it off against the bottom of the front bumper. This unit weighed an estimated 20 pounds. Initial durability and resistance to damage was very good. Misjudging the angle of attack to get into steep driveways would result in the splitter flexing and the aluminum bottom scraping on the ground, taking the majority of the abuse. Durability and repairability of larger impacts was not so great. Once I hit a curb with the side of it. The aluminum and carbon layers separated and the aluminum bent up while the carbon just flexed. We were able to bend the aluminum back to flat and re-epoxy the layers together. Much more of an impact and it may not have been repairable.
This unit was added to a neutral handling Street Modified class autocross car. The effect was immediately noticeable. The front end had a lot more grip than before and the rear end was much more active in corners. Oversteer could be induced either by lift-throttle/braking in tight corners or power-on acceleration through larger sweepers. The power oversteer was something that was completely new to me! As speeds increased the rear end got progressively more unstable causing some difficulty in high speed slaloms and quick transitions. The front just had so much more grip that the rear could not keep up. . .
#2 – Voltex front bumper/Voltex twin canards/Voltex undertray.
This was installed on my new ’06 EVO IX RS which was being built from the ground up for competition in SCCA Solo2 Street Modifed class. I wanted every aerodynamic advantage the rulebook allows, so I went with Voltex based on their racing history, work with EVO aerodynamics, and wind tunnel testing of all their parts.
These 3 pieces came as one unit already assembled. Fitment was VERY good as far as body kits go. I had to take a sander to a little spot by the drivers side headlight to keep it from scratching up the light. Other than that, it was just painted and installed. It came with pre-cut mesh for the two upper sets of holes, and mesh already installed in the very bottom small holes. The directions for all Voltex stuff are in Japanese with only a couple pictures. It would be a good idea for Voltex to maybe re-write them in English for it’s North American market. The Voltex pieces can be installed just by going off the pictures and using some common sense, though.
First thing I noticed is that while the fiberglass bumper is strong and rigid, it is quite a bit less flexible and pliable than the urethane stock unit. The bottom of the bumper sits a bit lower than the stock unit. With it, I scraped on some driveways that I never scraped on before. It has a splitter-like element built into the bottom area of it. The center hole is huge and makes the stock intercooler look puny. The ARC wide model fills the hole perfectly, as does the Blitz intercooler. No trimming was necessary to fit the ARC model. The front bumper support does not fit as-is with the Voltex front bumper. The intercooler hole is taller than the stock bumper. You can modify the front support beam by cutting out a 1”t x 18”w x 3”d section from the bottom of it and it will fit perfectly. That is what I did. I also welded some strips of sheet metal back onto so that you don’t have hollow openings where you cut. It looks stock now and weighs the same as the stocker.
The undertray is fairly thin and flexible (~1/8”), although the craftsmanship is superb! It mounts to the bottom of the bumper with 13 bolts, and also to several brackets that attach to the chassis. The undertray IS functional. I could feel quite a difference in front end grip with it mounted vs. with it off. Also, at speed on the highway the front end just felt more “planted”. For a daily driver street car I feel this is a perfect setup, and when my car is off the track for extended times it will definitely go back on in place of the larger splitter/undertray (see below). This unit helped take me to a 2nd place finish in the Winged Warrior 3 autocross, even low on power running stock boost and pump gas!
#3 – DHP splitter/undertray for Voltex front bumper.
This unit is made to match up with the Voltex front bumper. It has a top and bottom layer of carbon sandwiching a foam core. It is much thicker and stiffer than the prototype I ran earlier, while weighing only about 1/3 what the prototype did. Weight is approx. 6 pounds for the unit itself, 8 pounds with mounting hardware. Finish is very good to excellent. Durability for this unit should be very good for a track car, but for a street car you will need to be very careful with driveways and curbs. One good thing – this should be easier to repair if need be than the one with the aluminum base.
It is hard to say which splitter/undertray would make more actual downforce since I had them on 2 totally different cars. The new car with the Voltex front end and the new splitter handled very well. It had a ton of turn in grip and rotated very well. After driving it in several races, including a higher speed Solo Trials, I came to realize that it was rear traction at higher speeds that was limiting the potential. It felt as though I could throw the car into turns faster and the front would stick, but the rear would want to come around. Also, in slaloms and quick transitions it felt as though if we pushed too hard the rear end would come around. Time for some rear downforce!!
#4 – DHP rear wing for EVO VIII or IX.
This unit is made to work with the DHP front splitter, matching downforce front and rear. The wing element weighs about 5-6 pounds, plus the aluminum mounts. It can be set to different angles of attack based on intended use. Right now I have it set at max angle for the most downforce at autocross speeds.
After adding the wing the car developed horrible push all through the corners. Corner entry and exit. We made some other changes at the same time as adding the wing so we tried to adjust those. With no real results, we decided to go to the sway bar. Just a simple modification to the swaybar made the car a whole new beast! In slow speed corners the front bites, the rear end rotates and gets you pointed the way you want to go. In high speed sweepers and slaloms the car just sticks!
Getting late. More to come soon. . .
Last edited by EVOlutionary; Dec 25, 2010 at 08:47 AM.
Jul 11, 2007, 06:58 AM
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Nice write up...
did you have to make any spring rate changes or valving? have you done any track testing (not autox)?
I have the Voltex full dry carbon undertray / wing and i'm thinking I will need to go up 3-400lbs in the front and 200 in the rear.
-Kyle
did you have to make any spring rate changes or valving? have you done any track testing (not autox)?
I have the Voltex full dry carbon undertray / wing and i'm thinking I will need to go up 3-400lbs in the front and 200 in the rear.
-Kyle
Jul 11, 2007, 07:24 AM
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Great write-up, thanks for sharing!
What happened to the other thread? Was it (and all of it's valuable information) deleted by over-zealous moderators who could have just removed a few posts?
What happened to the other thread? Was it (and all of it's valuable information) deleted by over-zealous moderators who could have just removed a few posts?
Jul 11, 2007, 07:50 AM
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neat review, but we need pics!! 
anyhow, here is more useful info on the stock aerodynamics (comparing an evo to an STI)
https://www.evolutionm.net/forums/sh...ht=wind+tunnel
anyhow, here is more useful info on the stock aerodynamics (comparing an evo to an STI)
https://www.evolutionm.net/forums/sh...ht=wind+tunnel
Jul 11, 2007, 07:58 AM
#5
No spring rate changes yet, but they have not been ruled out as we continue to sort the car. We are already on the high side compared to many other cars out there. . .
My guess is that someone had a fit because the guy building custom parts in his garage is not a "Vendor", and was talking about selling said parts and pricing, etc. . . If that's the problem, then hopefully they will just delete and sales oriented posts and leave the rest up. . .
EVOlutionary
Jul 16, 2007, 07:27 PM
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Thank you for contributing this type of thread...Aerodynamics are often overlooked and not discussed often enough...Anyone who says aerodynamics are useless should be directed to this thread...Your review is concise and accurate...Voltex aero parts are not only the best-looking parts in the industry, they are engineered for the fastest autos...The front splitter from DHP looks like a well-crafted piece, I would like to see comparison shots (if you have them) to the Voltex piece you were talking about...Also, have you considered running front canards?...Your problem now is that the rear has too much downforce, making the car push (understeer)...Evasive had a great deal of success installing the Voltex front canards...From what I remember reading, there was enough downforce to create a gap between the factory bumper and fenders...I see them in the earlier pictures, without the wing, but not with...From one SCCA member to another, I salute your efforts...Thanks again, keep us all posted...
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Jul 19, 2007, 11:43 PM
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This is the Voltex Dry Carbon SPL Splitter thats on the time attack cyber evo front bumper. Its about an inch thick dry carbon and it bolted on the frame itself to hold 900+ pounds of downforce.
Jul 20, 2007, 06:44 AM
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I'm waiting for my new Voltex bumper so I can have my proper downforce! 
I'll have lots of pics once I get it installed, and lots of pics from Road America, if I get it before my NASA weekend, August 4th & 5th.
I'll have lots of pics once I get it installed, and lots of pics from Road America, if I get it before my NASA weekend, August 4th & 5th.
Aug 3, 2007, 01:45 PM
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One of the aerodynamic "features" that I would like to correct on my 03 is the parachute effect of the rear bumper cover. I was convinced to get the APR rear diffuser to direct air beneath the rear cover when I noticed the rear of the AMS time attack car:
https://www.evolutionm.net/forums/sh...d.php?t=286343
According to the AMS website, they are using the APR wide body kit. This doesn't seem to include any kind of diffuser or cover under the rear area. Instead, the bumper cover has a much higher bottom edge. It wouldn't catch the under-car airflow nearly as much as the stocker. This might be an easier way to remove the parachute effect of the stock cover and be more tolerant of muffler size/placement and exhaust routing.
Is this a reasonable approach? Does anyone know of a stand-alone rear bumper cover that is cut high like the APR wide body kit?
https://www.evolutionm.net/forums/sh...d.php?t=286343
According to the AMS website, they are using the APR wide body kit. This doesn't seem to include any kind of diffuser or cover under the rear area. Instead, the bumper cover has a much higher bottom edge. It wouldn't catch the under-car airflow nearly as much as the stocker. This might be an easier way to remove the parachute effect of the stock cover and be more tolerant of muffler size/placement and exhaust routing.
Is this a reasonable approach? Does anyone know of a stand-alone rear bumper cover that is cut high like the APR wide body kit?
Aug 3, 2007, 06:22 PM
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LOL
Aug 4, 2007, 06:42 AM
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...brake cooling maybe?
