Hood vent to reduce front end lift for the Showcar.

[nissanfanatic]

I spent a day this past week making a hood vent. I noticed that the hood was lifting a lot at speed. To no suprise, this helped a lot.







I placed it in a location that supported flow in a straight line to the roof. I used fishing line to test this. I did a little trig to put the scoop at an 11* angle, which is what most wings are put at. The hole is 27" by 4". The idea is to vent the underhood area to mitigate lift and allow for better cooling. The scoop sits right over my CHRA, so it should vent some heat from the turbocharger. It should also allow water to run directly onto my engine during rain... So it has one design flaw.

This design seemed to have the lowest pressure to drag ratio. It also seemed to disrupt the boundary layer a lot less according to Joseph Katz.

From driving experience, the hood no longer lifts up, and I bottom out at higher speeds on areas where I didn't before. I can't wait for a 12kg/10kg coilover setup, R compounds, and some downforce.

[syncline803]

Lets hope you have the car in the garage at all times then.

[jarhead]

Nice work bro. Looks good

[kb240]

looks pretty nice. id paint it though or something

[nelson240sx]

I can't wait for a 12kg/10kg coilover setup, R compounds, and some downforce.

Holy spring rates batman.

[jarhead]

Lmao... yeah with that kind of setup and as much power as he makes he's gonna need some pretty stout brakes for the track

[titanoh]

If its a problem for you to drive in the rain, why isn't it bad for hot/street/rat rod guys to drive with a fully exposed engine?

[jholman05]

Have you tried making a splitter? I started last weekend, made it go from directly behind my pignose lip to mid transmission area. I also am putting vents in my hood, but they are from an old 280z the one side has a naca duct that will blow air onto the turbo. Im glad to hear other ka-t people are into aerodynamics. Maybe you should start an aerodynamic thread.

[emo_tactical9]

From my admittedly little knowledge about aerodynamics, wouldn't this design not create enough of a low pressure zone over the vent to actually do any good?

Next step is to seal off the engine bay, save for the radiator and intercooler, to make it more effective.

[savatoge]

The idea is to vent the underhood area to mitigate lift and allow for better cooling.

This design seemed to have the lowest pressure to drag ratio. It also seemed to disrupt the boundary layer a lot less according to Joseph Katz.

From driving experience, the hood no longer lifts up, and I bottom out at higher speeds on areas where I didn't before.

Typically, a low pressure area develops from the headlight/hood meeting point to around the middle of the hood. Adding a vent in the middle of the hood (especially one like yours which vents at such a small angle into the existing air flow) will decrease the overall drag force on the front of the car because the vent minimizes this low pressure area...minimizing the pressure difference between the front of the hood and the rear of the hood minimizes flow separation, which in turn reduces drag.

However, studies have shown that the introduction of a vent will also increase the lifting force on the front of the car, unless some form of additional venting is put in place out the bottom/lower sides of the engine bay.

Your design is different from most others in that you have boxed off the sides of your vent. This is interesting in that these boxed ends will generate vortices...and the spiral effect will most likely aid in providing an additional pull on air coming out of the ends of the vent, as well as also helping in minimizing flow separation along those sections of the hood. It would be interesting to see what real effect is going on with your design in a wind tunnel and/or computer sim.

Maybe you should start an aerodynamic thread.

Vented hoods have been discussed here before.

[ispentallmymoneyontires]

"hey guys look at the dumb ricer and his silly hood vent... pssh like you could get any cowl induction like that"





[/sarcasim]

I <3 your car

[nissanfanatic]

Based on crude observations, my hood no longer lifts up and down as it did before. This to me says that I no longer have air trapped inside the engine bay lifting on the hood. I don't think this vent alone is enough considering my radiator inlet.I suppose small gurney flaps on the trailing edge of my scoop sides and top would aid even more in a lower pressure at the vent exit.

Based on my findings in Race Car Aerodynamics by Joseph Katz, this is a good design to create a low pressure and drag coefficient.

And yea, I definitely can't wait for the ricer comments when I have a wing and front splitter.

I don't have much of a problem with brakes right now. Although, I don't run full on track events, or haven't yet.

I made some plugs for the hood scoop when I have to park it outside.

[bubbles]

i will say one thing.. unless you are going to drive this on a prepared track 12/10 kg coilovers are almost too stiff.. i have some now and when i get into a high speed corner if there are any bumps it will make my car loose traction and under or over steer into the corner.. which of course can be unexpected and slow you down a bit... possibly even spin you in a corner.. my coils are nice but they are really almost too stiff..

like i said i would imagine on a prepped track that they would do fine. I have not had a chance to try them on a track yet though.

if i could redo my coilovers again i would buy something with like a 8/6 kg combo because its still stiff but can handle the bumps without jumping the car in the air in a high speed corner

just my 2 cents

[1wheelwonder]

Nice work Cory!

[nissanfanatic]

i will say one thing.. unless you are going to drive this on a prepared track 12/10 kg coilovers are almost too stiff.. i have some now and when i get into a high speed corner if there are any bumps it will make my car loose traction and under or over steer into the corner.. which of course can be unexpected and slow you down a bit... possibly even spin you in a corner.. my coils are nice but they are really almost too stiff..

like i said i would imagine on a prepped track that they would do fine. I have not had a chance to try them on a track yet though.

if i could redo my coilovers again i would buy something with like a 8/6 kg combo because its still stiff but can handle the bumps without jumping the car in the air in a high speed corner

just my 2 cents

I agree. But 8kg/6kg coilovers will bottom out extremely easy with 460lbs of force in the rear, plus whatever I end up with in the front.

[Liger]

Where are you getting this 460 lbs of force?

[nissanfanatic]

APR GTC-300. It is CFD based, but "240sxTTE" was hitting the bumpstops on 9kg/7kg Tein RAs with this wing.

I will also be using diver flaps, a front splitter, and a different vented hood up front. The engine bay will be blocked off on the bottom.

[bubbles]

again is the car going to be on a prepped track all the time though.. or a parking lot running autocross or something?

[emo_tactical9]

Oh, i thought i saw you today!
It was a ricey looking sentra, with canards, a splitter, and ***** up wing. It said R-tune on the side. Ricer tune!!!

[syncline803]

^^ it begins!!!!

haha

[nissanfanatic]

again is the car going to be on a prepped track all the time though.. or a parking lot running autocross or something?

It is going to be driven on the street a lot and on the track when there are track days. I'll deal with the roughness, just like ACR Viper owners do, to have downforce. I can't have my car bottoming out due to downforce like it does now. With a simple hood vent, my car scrapes the front air dam at 140mph.

And if I'm a ricer, then all of you have a long way to go before you even make it to ricer status... You need to make 532whp on a stock internal KA and have a car that pulls 1.1g lateral acceleration on street tires.

[adamky]

And if I'm a ricer, then all of you have a long way to go before you even make it to ricer status... You need to make 532whp on a stock internal KA and have a car that pulls 1.1g lateral acceleration on street tires.

I thought the ricer comment was a joke, but I don't think you took it that way...

[nissanfanatic]

So was my comment. But I guess you guys didn't take it that way.

I rarely take the internet seriously.

[emo_tactical9]

That was a joke. I thought that was in there.
I'm sure my car will pull at least 1.0g.
So does this mean you are going to start tracking the car? Or are you just doing it because you like all the engineering stuff?

[nissanfanatic]

I don't like competitions.. I am more or less doing it for the same reasons I made a lot of power. I just want to see what its like. Most of the handling stuff I do is on the street. It is fun to go to our little local test and tune road course events and put down good times though.

I am doing the aero stuff after reading a good book on the subject. It awakened me to what aero can do for a car. It looks like the introduction of aerodynamic downforce came about in 1965. Maximum lateral accel went from about 1.3g (which is still pretty much all you can expect from mechanical grip even today) to somewhere around 3.8g in 1994-ish. It is a graph that slaps Enzo Ferrari in the face for his retarded quote.

To me, it is a fascinating subject.