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Project Infiniti G20 Racecar: Making it Stick With APR’s Wing and Splitter

by Steve Rockwood

Project G20 is an aerodynamic disaster. Blockish shape, steep windshield and rear glass, and open bumpers all lead to a car that makes masonry look sleek. As a result of poor aero combined with suspension balance set up in line with Grandma Paule’s saying of “loose is fast, don’t be a <sissy>”, Project G20 is a minor tremendous ridiculous handful at anything above 75mph. Four wheel drifts on the oval at Auto Club Speedway, while entertaining, aren’t a good long-term survivability plan. When Kojima spun our car in turn one his first lap out, we knew it was time to tame Project G20’s inner bucking bronco with some aero bits from APR.

 

All the aerodynamic panache of a cinderblock.

Indeed, the competition probably appreciates G20’s aerodynamic efforts. After a particularly heated battle with Justin Taylor in the Rockstar Garage S2000, who was running about 1-2 seconds a lap quicker than Project G20 at the time, I asked him why he didn’t push for a pass sooner. His response: “honestly, I was just waiting for you to crash, but it never happened.” Huh.

 

“Will. You. Just. Crash!” - Justin

Downforce is one of those vacuous (see what I did there?) terms that gets thrown around too much. Some refer to downforce directly created by wings, canards, splitters, and other accoutrements, while others refer to the net effect on the vehicle from various aerodynamic aids as well as demerits. For the sake of sanity, and this article, we were primarily after making the car less floaty and dangerous at speed, so actual measurement values didn’t matter to us much (which is nice, seeing as MotoIQ hasn’t bought a wind tunnel yet). We’ll just trend this article towards measurable data from manufacturer’s spreadsheets and lap times, as well as subjective results on the car’s behavior. While selecting our aero mods, we needed to be mindful of creating too much aerodynamic wake with our vehicle, as its brickish shape already makes for easy passes on long straights by drafting competitors. Lastly, let’s be honest: Project G20 does not look like a racecar. At all. Our guess is more people looked at our car on the trailer and wondered why we put stickers all over Mom’s car than thought “hey, look at that racecar!” Now they’ll look at it and wonder if mom gets angry driving a car with stickers and wings on it. Sort of a win?

 

Does Mom know you’re racing her car?

To begin our aerodynamic aids, we needed to look at the major problem areas that need addressing. First and foremost on the list was the plastic rectangular parachute known as the rear bumper. Since the P10 chassis was designed in the late 80s, Nissan didn’t bother to do anything with the airflow exiting the ass end of the vehicle because (1) gas was a whopping buck a gallon, and (2) the government wasn’t breathing down manufacturer’s necks quite as badly so 30mpg highway was good enough. As a result, the rear bumper is a giant scoop perfect for catching wayward air and lots and lots of dead leaves. Add in the giant hole left behind by the ectomied muffler, and we’ve got the previously described parachute. This no doubt contributed quite a bit to the vehicle’s overall drag number, it also probably made a shit-ton of lift. Terrible.

 

Yep. Any air coming under the car on the sides will be trapped in that pocket where the muffler used to be.
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Comments
rawkus
rawkuslink
Monday, March 31, 2014 10:41 PM
This reminds me of the first time we mounted a Kognition wing to the back of the Evo. It was so amazing. Definitely a "come to Jesus" moment.
Supercharged111
Supercharged111link
Tuesday, April 01, 2014 9:14 AM
With the rare Nismo bumper and custom aero, do you have a contingency plan if you end up doing some landscaping? My class won't allow aero, but I hear it can be a ~$1,500 trip through the weeds when it happens.
jeffball610
jeffball610link
Tuesday, April 01, 2014 9:28 AM
I'm always surprised that more people don't run some sort of belly pan. The air going under the front end has to cause all kinds of turbulence in the engine bay. It's no wonder that modern cars have it from the factory. I'm contemplating making an entire flat bottom for my 4G63 Datsun 510 project at some point.
Rockwood
Rockwoodlink
Tuesday, April 01, 2014 10:19 AM
@ rawkus: yep. I resisted aero for the longest time, thinking that while it was faster, it wasn't that necessary and a liability when it came to farming trips. The biggest gain wasn't in qualifying times, but in consistency. The car just doesn't get upset by bumps and other stuff nearly as much as it used to, so I can knock out consistent laps pretty easily.

@ Supercharged111: That NISMO bumper, when viewed in person, has had its (un)fair share of agricultural excursions and other stuff. As a result, it is currently held together by our new splitter, and previously by Gorilla Tape (note the custom "racing stripe" it has in the middle). We haven't gone through the weeds (yet) with this new setup, but we did have a temporary plywood/fiberglass belly pan (no splitter) that was destroyed ITS FIRST RACE by a slower out of class car attempting to divebomb pass me under braking into the infield at Autoclub Speedway.

@ Jeff: yep, though the most common excuse (which was my own) was that it'll just get destroyed.
Crousti
Croustilink
Wednesday, April 02, 2014 3:03 AM
About the gurney flap removal; basically it means you have too much downforce rear compared to front. did you consider moving the front splitter a bit further front ? You still have room for 2" considering regulations, and it should add more front end grip.

did you try harder springs to counteract downforce ? As the rear adds more than the front, they may be too soft now, resulting in a "leaned back position" at speed, creating some front lift and canceling the effect the splitter has.

Just my 2 cents, i am fascinated with aero stuff and how it interacts with suspension and handling. someday i will do a splitter too and belly pan setup too, but i have to make some holes in the hood first to evacuate heat . I wanted to dump hot air on the sides (make an opening near the firewall, where high pressure is found, and dump between door and wing panel ) but that is too much work for me. And hood venting should be fine, too.
Rockwood
Rockwoodlink
Wednesday, April 02, 2014 7:25 AM
@ Crousti: Moving the splitter farther forward, with it already sticking out about 4", probably would not have netted much downforce, especially given the amount of work it would've required to get it there. The longer splitter also would've made getting a jack under the front of the car impossible (it currently barely clears when on blocks), and I'm not the hugest fan of jacking from the sides.

Harder rear springs are in the cards. However, we did not have extras while testing, and removing the gurney flap seemed an easy solution. It was affixed with 3M double sided tape, so it is a simple process to reinstall. As for compressing the rear suspension, that is unlikely to come into play. The APR wing, at our AOA and max speeds (140-ish mph, hard to tell since the speedo tops out before then), is making about 170lbs of downforce. With the rear spring rate being 500in-lbs, we're maybe lowering the car 1/2" in the rear even if the front weren't making any downforce. Wheel rates for our car are about the same, front:back, so the ride height delta front:back is likely negligible. I'm no expert on aero though, so even a small change in pitch (maybe 1/8-1/4" over the wheelbase) may be significant, but my gut tells me it's not.

We plan on eventually adding a hood vent as well, which should increase net downforce up front, at which point we may need that Gurney flap again.
Mike Kojima
Mike Kojimalink
Wednesday, April 02, 2014 8:41 AM
More than 4" is the point of diminishing returns with splitters in general.
Crousti
Croustilink
Wednesday, April 02, 2014 10:20 AM
@Rockwood: ok ,thanks. If you ever try with harder springs rear, tell me the how it goes. That wing adds a fat man worth of weight on the rearmost of the car when at speed, so i was thinking harder springs (and damping) should be worth trying if the tracks you are on have mostly high speed corners. Just a thought, i don't know if it would be noticeable, or if the driver can take advantage of it.

If you still have too much downforce rear, maybe you can try removing the side plates. I know they are used to prevent air going around the sides instead of top and bottom. Removing them has the same effect as using a smaller wing, and the faster you go, the "smaller" the wing becomes. That is why airbus fits side plates on plane wings, so my guess is it has the same function on a car wing.

@Mike thanks ! Now i know where to stop .
ginsu
ginsulink
Wednesday, April 02, 2014 3:02 PM
Another good reason to mount on the quarter panels is because of 'wing flutter'. I've seen plenty of evidence of this happening in videos where the wings are mounted directly to the trunk lid. Trunk lids were just not meant to take high frequency load variations at all. A nice stable wing down load is the idealized performance of an inverted wing, but aerodynamics just don't work that way.

Also, any thoughts on running vortex generators along the rear to gain some pressure recovery to reduce drag and possibly improve rear wing performance?

Additionally, how about adding front and rear tire strakes? It does alot for the CoD and it's a very cheap and easy mod too.

Also, I've convinced my self that the 'JDM hood Prop' is the cheapest and easiest way to vent on my car. From what I've seen it can lower engine bay temps by, at least, 15 deg and is could potentially lower drag as well when considering the change to front stagnation pressure ahead of the radiator inlets.
ginsu
ginsulink
Wednesday, April 02, 2014 3:16 PM
Just noticed that 5 deg AoA has the highest efficiency on the data provided (is this is a L/D coefficient?).

Although, one could argue that because the flow coming down from the roof is likely to have a downward component, that you are approximately running at ~5deg AoA wrt the flowfield anyway (assuming these are all negative AoA's since we're trying to maximize downforce not lift).
Rockwood
Rockwoodlink
Wednesday, April 02, 2014 5:26 PM
@ ginsu: I didn't even think about relative airflow!
We've got it running flat and figured we couldn't go any farther.

We're planning on an aero pt II for additional items. Btw, what're strakes?
bru1212
bru1212link
Wednesday, April 02, 2014 6:07 PM
Just noticed your license plate, love it!
Monkius
Monkiuslink
Wednesday, April 02, 2014 7:24 PM
"Strakes" are those little gurney flaps right infront of a wheel (and offset a bit laterally), that you see on most modern cars...

The "JDM hood prop" is basically a cheap cowl induction hood. Since there is a high-pressure area right in front of the windshield, raising the hood there is more likely to let air /into/ the engine compartment than /out/ of it. So: lower temps maybe, lower drag no.

ginsu
ginsulink
Wednesday, April 02, 2014 11:56 PM
Monkius summed it up, you see them on a lot of Acuras, Lexii and I know on the front and, I think, rear of the S2000. Since you're not an OEM you can go a bit bigger on them as well. You can also go out to maybe a 1/2" outside of the fender like a vertical gurney flap in front the wheel well (I've seen this done on production Corvettes).

I'll add that you can also attach some strakes to the control arms as well to block flow from entering the wheel well from underneath, maybe even angling them to use the diverted flow to help with brake cooling

The ones I made for my car use a flat mudflap and they are riveted to the rear edge of the bumper for support. On the rear, I riveted them to the rear edge of the side sill.
ginsu
ginsulink
Thursday, April 03, 2014 12:04 AM
@Monkius - I don't think we can say definitively the flow is going to enter into the engine bay from above the hood. Personally, I see a bit of a 'Coanda Effect' happening in that area. I'm actually worried I'll get more engine bay smells pulled into the fresh air vent and stink up the interior of my car.

I guess you could attach a line of wool tufts on the edge of the hood and see if any get sucked into the bay at speed. This is probably worth doing since you can actually see it all happen while you're driving really easily.
Crousti
Croustilink
Thursday, April 03, 2014 1:25 AM
@ginsu actually yes, it does on most blocky shaped cars. At least renault and bwm (in europe) put air intake at at that very place when they produced block shaped cars, and it worked very well.

I made some trials on my S chassis, raising the rear of the hood works when driving under 80mph. Makes nothing from 80 to 100 (approx), then the faster i went, the higher the engine temp, compared to a closed hood.

The wool tuft is going to be hard to use (you dont want to be checking where the wool tuft is while driving 100+, and turbulences will make it go in and out), but a (home made) differential pressure gauge can be used. Use a long oil resistant transparent hose, bend it in a U shape, add oil in it, stick the U part in the car, stick one side of the hose under the hood and the other outside, near the windshield, job done.

Not long ago i bought a second hand hood, that i planned to cut to vent right after the radiator. But since i installed it, i noticed a decrease in temperature, which was odd.
It turns out the hood a little bent from a fontal crash, and when watched from the side, on the car, you can see the middle got a little raised. This creates 2 long yet not tall opening on the sides. I assume the temperature drop comes from that. Maybe it creates less drap than chopping the top of the hood, so i might not cut it if i don't need to.

Rockwood
Rockwoodlink
Thursday, April 03, 2014 8:25 AM
Ah, yes, those. Yeah, Pt II will most likely feature those when we add skirts and a belly pan. Might also work on a diffuser, but that may be beyond my fab skills. Plan on doing all of it in house with common tools, so we'll see.

And yes, the EVO-style vortex generators will need to be tested as well. We'll make sure to tuft test as much as we can, as well as quantify lap times.

Anyone have any other suggestions they'd like to see tried?
radrandy55
radrandy55link
Thursday, April 03, 2014 3:34 PM
Nice plates!!
Rockwood
Rockwoodlink
Thursday, April 03, 2014 3:40 PM
Lol. Can't take life too seriously, right? :)
nissannx
nissannxlink
Thursday, April 03, 2014 4:26 PM
Awesome Article. When I have time and money I'd like to do something similar to the NX. Great inspiration.
ginsu
ginsulink
Thursday, April 03, 2014 10:39 PM
I think there is a good chance for the hot stagnant engine bay air to get pulled into the cooler high velocity flowfield above the hood and attach to the flow going up the windshield due to the coanda effect. This is a diagram of a similar situation on an F1 car showing the flow through an exit duct being driven passively using the coanda effect.

coanda
ginsu
ginsulink
Thursday, April 03, 2014 10:44 PM
Also just found out about these 'air curtains' that BMW uses, which would be interesting to design some ducting for.

aircurtain
Rockwood
Rockwoodlink
Friday, April 04, 2014 12:06 AM
I was thinking of a flap in front of the wheel well.

That, or just run canards.
Ztaal3
Ztaal3link
Monday, April 07, 2014 7:37 PM
awesome update for you g20, and as always an inspiration for my primera :P
btw that front bumper is not a nismo part as far as I know here it was standard on all the 95-96 models SE, the SRI and GT got the same but just one big hole on the driver side, in the GT it had ducts pushing air to the gearbox which had cooling fins on the case. My plane for those three holes are brake cooling for the small ones and gear and CAI for the engine. need any more of those bumpers just look over to the EUDM cars :P

My car will also get a rear wing, rear diffuser, splitter, evo like roof vortex things, canards and if any heat issues arise there will be some hood venting, but sadly my rear wing have to go on the rear deck lid so need to reinforce that just a bit ...

@Rockwood could I bother you guys just a bit? you wouldn't happen to have ha picture of the complete backside of the front bumper? wanna see if I can steal some ideas of your mounting system ;)
Rockwood
Rockwoodlink
Tuesday, April 08, 2014 5:50 PM
You can sort of see how we mounted it from the back on page 4. I'll try to dig up something better.
sr20ve
sr20velink
Thursday, May 08, 2014 5:27 AM
You may covered this before but have you had any oil starvation problems when cornering? If so, what was your solution?
Rockwood
Rockwoodlink
Thursday, May 08, 2014 6:57 AM
Surprisingly, no. We just do the standard SER guy overfill to 4 quarts (well, 5 due to added capacity from the oil cooler).
1nvisib1e Sadd1e
1nvisib1e Sadd1elink
Saturday, August 08, 2015 3:07 AM
I was always curious what you did for replacing the passenger and driver side engine/trans mounts.

It seems there is no clear viable replacement solution other the custom on a lathe.
Rockwood
Rockwoodlink
Saturday, August 08, 2015 1:01 PM
Being old SER guys, we collected many many parts that got thrown at this car: Place Racing (now defunct) motor mounts, solid poly.
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