Aerodynamics of a brick.

[Fast Guy]

Do you think my car has the aerodynamics of a brick?

1st picture is my car. (can't remember why I photoshopped those wheels on)
2nd picture is a side profile (someone else's car) to show the rear end.


I've done a few subtle mods since then. The mods are intended to make me go faster up the 1/4, but hopefully they help with aerodynamics/drag as well.
I'll upload some pictures when I've resized them.

[Christ]

That spoiler is probably doing nothing for you, except slowing you down... you ever see a professional drag racer with a spoiler like that?

Same with that hideous hood scoop... and those vents on the hood most likely aren't helping anything either.

Other than that, you have a halfway decent hood/windshield angle, but the rest of your aero is lost in the design phase..

[Christ]

What exactly have you done to make it faster up the 1/4 mile?

Hopefully you've removed those stick-on chunks of plastic on the hood... the vent/scoop, particularly. Neither is necessary, and from the looks of it, I'd be willing to bet that they're not even functional... the US equivalent of "Rice".

[lunarhighway]

i'm not sure what you want to achieve

are you looking for information that will make your car more efficient on the road, or just a little faster in a dragrace? and how important are the looks of features like the hoodscoop and the spoiler (would you keep them if they did nothing good because they look cool?)

i won't claim to know much about race car aero but the rear spoiler looks as though it's gonna add quite some drag, it might create some downforce but i wonder if a FWD car needs that for acceleration. The only benefit it could have is that it helps at extreme cornering speeds, but you'll only need them when going very fast around a track, and if you're into that perhaps a suspention upgrage might be something to look at first. unless you really like it's look and are willing to sacrifice topspeed, acceleration and FE for that i'd considder something more subtle.

for on road use and drag raceing i think id go for a lip spoiler or kammback, the big cavity below the kammback might actially generate some downfoce (wich again i don't think you're going to miss at normal speeds or even on the highway), it will reduce drag, make the car more stable at speeds, and it will help your on road FE. plus a well designed one will set your car appart form the crowd...

autospeeds.com has some interesting articles on hood scoops and undertrays, so if they hoodscoop is functional you might look at how to make it perform better. it it's just for looks, see if you can close of the intake so it adds less drag or convert it into an extraction vent by placeing a shield in front of the opening wich is open at the top... youd create something like a smokestack on a ship where the high speed air passing over the opening extracts warm air from under the hood... this might actually improve cooling and if you install an undertray keep air from spilling out under the car and create drag there.

[Fast Guy]

I take it no one is familiar with that car.

The car is as Nissan designed it for Group A rallying. It's a 4wd car. The bonnet scoop feeds a top mounted intercooler, so it was needed, but I'm not sure how much benefit the side vents are. They may let a little air out of the bonnet, I don't know for certain. In fact from the factory they have blanks fitted which you can remove (I did). I don't know how much the rear spoiler works, if I remember, I'm going to try and remove it next time I go to the strip to find out.

As standard the car will hit 60mph in about 5.1s and do the 1/4 in the high 13s. The car will now hit 60mph in 3.7s, do the 1/4 in 12.4 at 110mph and it can go round corners pretty fast

I found the Autospeed website a few years ago, it's been in my favourites ever since. There's some good stuffon there.

The mods I done to the car since I bought it are, lightweight bonnet (now with a larger central vent, rather than scoop as I replaced the top mount intercooler with a front mount) lightweight wheels and smaller diammeter tyres. The after market exhaust saved 13kg, lightweight flywheel saved 5kg, lightweight engine pulleys, fibreglass hatchback, lexan windows, removing complete aircon saved 23kg, DTM style mirrors to replace the standard slabs, a rear diffuser waiting to be fitted. Carbon fibre drivers seat saved 10kg.
I have kevlar/fibreglass doors to go on, they'll save about 12kg each.
I also turned the boost up abit to get more power. 290bhp now against 215bhp standard.

I've lost a good 80kg for daily use and about 120kg when I remove the interior to go drag racing.

What I'm trying to achieve is to make the car go as fast as I can without spending too much money on the engine. To me that means reducing weight and reducing drag if possible.

The last day out I had averaged about 29mpg whilst travelling at the motorway speed limit of 70mph It was certainly my best mpg yet returning a good 40miles more before I started worrying about filling up.

[Fast Guy]

This is my car as it looks now.

I had a Toyota Celica GT4 vent fitted to my fibreglass bonnet. I'm hoping it helps vent some of the air that goes through the radiator and intercooler then onto the turbo and exhaust manifold.

The mirrors I fitted to cut drag a little. Wether they work or not I don't know, but they look like they should

Hopefully when the weather is better I'll get the rear diffuser fitted.

[wyatt]

A couple things I see that could help fuel economy by improving your aerodynamics would be:
1. An bellypan for under your engine. I have heard numbers between 3 and 5% better FE, and I have heard better downforce, better cooling, and less drag. I can't say for sure how well they work, but if nothing else, an aluminum bellypan would help protect your engine and keep things a bit cleaner.
2. I don't know how vital your huge "mouth" opening is, but I would guess that in cooler weather and normal driving you could block most of it off. Your car will warm up faster and keep the engine bay warmer during winter type driving. You might even be able to fit something more "beak like" there that will force air OVER the vehicle.
You can find out more about these and other modifications by looking at the "60+ Vehice Modications" at the top of the page (or using the link here).

[Christ]

That "mouth" isn't for the radiator, it's for an intercooler. Keeps the intake charge from the turbo from overheating and causing detonation as it is compressed in the engine. Colder air charge = more power, when tuning is correct.

OP, when you're not racing, you could certainly cover that up though. Unless you rev high all the time. Your Turbo shouldn't even really be spooling in street driving, so it's not really heating up enough to utilize an intercooler that much.

[rav]

The mirrors are awesome, where did you get them from?

Ravi

[dichotomous]

do you have tunable engine management with boost control? thats how you could get some great numbers, tweaking the exact fuel shot into each cyl for each throttle input % and rpm and boost level, and keeping boost to about 1psi or so would help so that there is no "suck" portion of "suck-squish-bang-blow"