Autocross EVO - Street Modified Build
- First, a diffuser that seals up to the rear bumper and does not allow airflow over both above and below it's surface would not be considered a wing.
- The Voltex rear diffuser could be considered a wing, and Voltex actually calls it a "rear under wing". Therefore it is not allowed because it does not mount to the rear deck as defined in the wing rules.
- If one were to modify the rear bumper cover so it had an integral diffuser element and you could argue that the diffuser is part of the bumer cover, then you're golden!
EVOlutionary
- The Voltex rear diffuser could be considered a wing, and Voltex actually calls it a "rear under wing". Therefore it is not allowed because it does not mount to the rear deck as defined in the wing rules.
- If one were to modify the rear bumper cover so it had an integral diffuser element and you could argue that the diffuser is part of the bumer cover, then you're golden!
EVOlutionary
that was my thinking as well, but I still have questions about the legality as an aerodynamic aid.
9.5 is a bit narrow for 295? Also, how does the diameter/gearing compare?
That's my reasoning anyway. Seems logical, but this wouldn't be the first time the SEB did not agree with my reasoning . . . Best thing would be to draw a picture of a rear bumper/diffuser and ask the SEB for a clarification or ruling.
Next question - are you thinking of adding a diffuser to reduce drag, increase downforce, or look cool? If the answer is anything other than to reduce drag, I would save your money. Even in that case, I probably wouldn't waste my time and money on it as you will get better returns for your $$ elsewhere.
If it is to increase downforce think about this -- do you really need more rear traction?? Have you made the front end so grippy that you can't get enough grip in the rear with suspension, alignment, tire pressure changes to balance the car?
At autocross speeds, even with the most radical front aero treatment allowed by the rules I bet it will be hard to make so much front grip that the rear can't keep up without a wing and diffuser. Don't know though. Maybe I'll try running wingless next year . . .
I see where you're coming from. If the diffuser is an integral part of the rear bumper (as in molded in - one solid piece) then I think there is no question as to the legality, because there is no rule saying you can't make your car more aerodynamic. For example, you can modify the rear bumper by cutting holes in it to reduce the parachute effect. You can also cut it up and reshape it/redesign it. Doesn't matter if it ends up being more or less aerodynamic as there is no mention of aerodynamic properties in the rules.
That's my reasoning anyway. Seems logical, but this wouldn't be the first time the SEB did not agree with my reasoning . . . Best thing would be to draw a picture of a rear bumper/diffuser and ask the SEB for a clarification or ruling.
Next question - are you thinking of adding a diffuser to reduce drag, increase downforce, or look cool? If the answer is anything other than to reduce drag, I would save your money. Even in that case, I probably wouldn't waste my time and money on it as you will get better returns for your $$ elsewhere.
If it is to increase downforce think about this -- do you really need more rear traction?? Have you made the front end so grippy that you can't get enough grip in the rear with suspension, alignment, tire pressure changes to balance the car?
At autocross speeds, even with the most radical front aero treatment allowed by the rules I bet it will be hard to make so much front grip that the rear can't keep up without a wing and diffuser. Don't know though. Maybe I'll try running wingless next year . . .
That's my reasoning anyway. Seems logical, but this wouldn't be the first time the SEB did not agree with my reasoning . . . Best thing would be to draw a picture of a rear bumper/diffuser and ask the SEB for a clarification or ruling.
Next question - are you thinking of adding a diffuser to reduce drag, increase downforce, or look cool? If the answer is anything other than to reduce drag, I would save your money. Even in that case, I probably wouldn't waste my time and money on it as you will get better returns for your $$ elsewhere.
If it is to increase downforce think about this -- do you really need more rear traction?? Have you made the front end so grippy that you can't get enough grip in the rear with suspension, alignment, tire pressure changes to balance the car?
At autocross speeds, even with the most radical front aero treatment allowed by the rules I bet it will be hard to make so much front grip that the rear can't keep up without a wing and diffuser. Don't know though. Maybe I'll try running wingless next year . . .
I want it to reduce drag so I can get marginally better gas millage going to and from the events
However, the parachute effect from the rear bumper fasca can affect your times on course. I also like running my car pretty loose so I can pivot the rear end more in tight corners. If I can generate even a small amount of downforce that is useful in a slalom or a long sweeper, then the diffuser would be helpful.
that's the theory anyway, I am still designing my aero package for next year. My goal is to have something that maintains the downforce balence between the front and rear.
and yeah, I have been following your aero developments with more than a passing interest now that my EVO is not a daily driver anymore.
well noones been in here for a while so i thought i would revive it
what are peoples plans for next year??
POWER:
i am keeping this the same maybe with upgraded valve springs to rev to about 8000rpms get a map for 112 oct vs the 100 i used this year to try to up low end power and have my tuner smooth out the powerband
DRIVETRAIN:
I am doing clutch and flywheel as i am still on the stock units if anyone has advice on a daily drivable light combo let me know
I am tossing the acd and going with a quaife diff, supposed to be quite a bit lighter and helps the cars handling of course
SUSPENSION:
well in my search for shocks, i think i have found a set of used moton club sports that i want to pick up. i would take those do a test and tune day or two with my local race craft engineer and see where that can get me. plus my local guy has some different suspension geometry parts that we are going to test out.
WEIGHT:
as mentioned, light clutch, flywheel, diff. probably going to take out all i can think of, on the list is still putting on the ams mustache bar, maybe a new front cross member bar. removing motors for rear windows, removing sound deadening etc to try to get the car as close to the 2750 lb mark as possible (yes i am getting serious this year but my realistic goals for weight are about 2900lbs)
DRIVING:
i got myself a codriver. he was a stock champ in utah for 2005 and 2006 and this year in his stu sti he has been running with me. he drove my car for the first time last weekend and although i was about 4 seconds ahead of the rest of the utah sm pack (46.6 compared to 51's and 52's) he beat me by 1.2 seconds his first time driving my car! ( he ran a 45.4) hopefully this co-driving experience can make me better.
WHEELS:
i am definately going with 285/30/18 all around. i think 18x10.5 up front with a 18x9.5 in the back i think i will stick with kuhmo v710 since i already have a contengency check with them. if anyone has any ideas on good reasonably priced wheels in these sizes PLEASE let me know i want to find something different than your typical nt03+m's. i love the rpf1's but i dont think they come in the right size
what are all of you guys doing in the off season? who all is planning on going to nationals again next year?
what are peoples plans for next year??
POWER:
i am keeping this the same maybe with upgraded valve springs to rev to about 8000rpms get a map for 112 oct vs the 100 i used this year to try to up low end power and have my tuner smooth out the powerband
DRIVETRAIN:
I am doing clutch and flywheel as i am still on the stock units if anyone has advice on a daily drivable light combo let me know
I am tossing the acd and going with a quaife diff, supposed to be quite a bit lighter and helps the cars handling of course
SUSPENSION:
well in my search for shocks, i think i have found a set of used moton club sports that i want to pick up. i would take those do a test and tune day or two with my local race craft engineer and see where that can get me. plus my local guy has some different suspension geometry parts that we are going to test out.
WEIGHT:
as mentioned, light clutch, flywheel, diff. probably going to take out all i can think of, on the list is still putting on the ams mustache bar, maybe a new front cross member bar. removing motors for rear windows, removing sound deadening etc to try to get the car as close to the 2750 lb mark as possible (yes i am getting serious this year but my realistic goals for weight are about 2900lbs)
DRIVING:
i got myself a codriver. he was a stock champ in utah for 2005 and 2006 and this year in his stu sti he has been running with me. he drove my car for the first time last weekend and although i was about 4 seconds ahead of the rest of the utah sm pack (46.6 compared to 51's and 52's) he beat me by 1.2 seconds his first time driving my car! ( he ran a 45.4) hopefully this co-driving experience can make me better.
WHEELS:
i am definately going with 285/30/18 all around. i think 18x10.5 up front with a 18x9.5 in the back i think i will stick with kuhmo v710 since i already have a contengency check with them. if anyone has any ideas on good reasonably priced wheels in these sizes PLEASE let me know i want to find something different than your typical nt03+m's. i love the rpf1's but i dont think they come in the right size
what are all of you guys doing in the off season? who all is planning on going to nationals again next year?
What are the key differences in allowances between XP and FP? I think the most logical extension of SM is XP. Does FP have a splitter/wing rule or are they stuck with spoilers/air dams??? That may be the biggest difference. Dunno . . .
As for next year, I will do another Street Mod write up in the spring and start this whole thing over again. I learned ALOT the last 2 seasons. The 2006 season was the homework/trial and error stage. I learned what I did not want in a Street Mod car. The 2007 season was the building/buying/assembling stage. Built a car from scratch and got it 95% complete before the season was over and the money ran out. The 2008 season will be the the tweaking/testing/tuning stage. We will actually change some of the suspension/alignment settings from where they've been for 2 years and try to go faster. We will massage the powerband to make the car easier to drive fast. We will manipulate the driveline to make sure that every bit of power we are making is turned into forward momentum when called upon. That's it in a nutshell. This year we threw all the parts on the car (over the period of the whole season) and tried to learn to drive the car faster as-is. Next year we will change the car to make it go faster with the same driving (if that makes any sense?)
I hope you all had as fun of year as I did. Next year will be even better. Who knows, one of these days I may even get the thing out onto a road course for a HPDE!
Jarrod
As for next year, I will do another Street Mod write up in the spring and start this whole thing over again. I learned ALOT the last 2 seasons. The 2006 season was the homework/trial and error stage. I learned what I did not want in a Street Mod car. The 2007 season was the building/buying/assembling stage. Built a car from scratch and got it 95% complete before the season was over and the money ran out. The 2008 season will be the the tweaking/testing/tuning stage. We will actually change some of the suspension/alignment settings from where they've been for 2 years and try to go faster. We will massage the powerband to make the car easier to drive fast. We will manipulate the driveline to make sure that every bit of power we are making is turned into forward momentum when called upon. That's it in a nutshell. This year we threw all the parts on the car (over the period of the whole season) and tried to learn to drive the car faster as-is. Next year we will change the car to make it go faster with the same driving (if that makes any sense?)
I hope you all had as fun of year as I did. Next year will be even better. Who knows, one of these days I may even get the thing out onto a road course for a HPDE!
Jarrod
Yes XP allows you to have a wing....think APR, where FP would only allow the stock wing. XP also allows side skirts and a front splitter. FP or XP seems like the class for me, mostly from the point, where I could do what I want to (my own personal likes) and still run. SM just has too many small rules I don't want to adhere to. I will probably end up having an FP or XP car that looks like it could be in SM.
Last edited by TearItUpSports; Oct 10, 2007 at 07:47 PM.
Only minor changes for me, I think:
Power: FMIC, IC piping, 20g-LT with Ti internals (unless something better comes out)
Weight: might actually remove some things for real this time, but I'm not sure, since it will probably still be my daily driver. Mini battery to go with the IC piping at least. Remove wing. Maybe one of those tiny passenger seats and an actual race seat on the driver's side. I was maybe 200lbs heavier than Daddio this year, I think.
Suspension: just going to change the settings from a road course setup to an autox setup
Driver: probably only going to do Tours and Pros with maybe a few local events after changes to the car for practice
Power: FMIC, IC piping, 20g-LT with Ti internals (unless something better comes out)
Weight: might actually remove some things for real this time, but I'm not sure, since it will probably still be my daily driver. Mini battery to go with the IC piping at least. Remove wing. Maybe one of those tiny passenger seats and an actual race seat on the driver's side. I was maybe 200lbs heavier than Daddio this year, I think.
Suspension: just going to change the settings from a road course setup to an autox setup
Driver: probably only going to do Tours and Pros with maybe a few local events after changes to the car for practice
The thing I like best about XP is you can gut the interior and run carbon door skins with no windows, headlights, tail lights, etc. I don't know what the minumum weight for an EVO would be in that class, but I bet you could easily have a 2400-2500# EVO staying within the rules. THAT would be a blast to drive!!