If you look up some drag racing info, you may find some helpful tips there. I know that the drag racers do as much as possible to change the front end and to reduce the width of the front tires, as that's where majority of the drag is created.

It was my understanding, however, that the high Cd from the front wheels was due to the width of the tires, not the fact that they were spinning as the article that Chebosto linked suggests. It does make sense, though.

I do know that XKR will have more than enough power to reach his desired speed and comfort level at those speeds so the Cd shouldn't matter as much as downforce to keep the car planted. Still, it wouldn't hurt to look into reducing the Cd a bit more inconspicuously.

Here's a website that could be of help:
http://www.recumbents.com/car_aerodynamics/

 

I got what you were saying...

I know what you are saying....But there is a big gap where the stock muffler use to sit....3 of the shops that builds race cars said that its not got to leave it like that. And the 2 drivers that tested it said the samething. They think it will rip it off if I maintain high speed which could cause a problem with sudden change at that speed. Terry's setup will fix it...

Yes...you all are saying the samethings that Brian is saying....I guess thats why he is telling me to shut up......I dont care....you guys say it...and i am going to keep asking him.....Its my azz thats going to be in this car.......

With the entire suspension setup and wheels.....the car feels like I am driving at 100mph instead of 180+.....I will get videos the next outing

Thanks for the input guys.

 

the front wheels rolling and creating a ton of pressure in the wheel well is the main point of drag they create. that is why they have vents to help get that pressure from increasing drag.

 

We want DOWN FORCE. The stock diffuser does not generate much of that.

 

Mike, I sent you a revision to the drawing with the changes to the rakes.

 

not really. the article is stating that the majority of the drag on the car is the air flow through the front of the car, through the radiator, hitting the back of the engine/firewall area, etc..

there is no way to avoid this other than offering more venting for the engine bay. ie. cutting holes in the firewall toward the back of the engine and having air ducts on the side fenders for the air to escape..


the F-4 comes to mind along with this quote: "given enough power, a brick can fly"


i know he will have more than enough power to reach his goals, its about getting there efficiently.

 

I just re-read it twice to make sure I didn't miss anything.

I assumed, perhaps mistakingly, that the drag from air entering the engine compartment through the radiator would be reflected in the 33.4% figure for the cooling package drag. If not, I would expect the 3.1% figure for the engines percentage of drag to be higher. The article is not clear on this point. In fact, other than the chart, the only time the article mentions the engine is when it references the bits hanging down.

Anyway, it is what it is. Mike can push out the rear fenders a bit, and that should help.

 

ugh. sorry. now i know what u meant. i had read somethign else after i posted the first link..

yea. that 3% is engine bits in the airstream.. but, still if u can aleviate air pressure inside the engine bay, that would be beneficial too...

air flowing over the top of the car comes in varying pressure zones, u can create airflow escape using the right venting..

 

I think with all this info i shall begin project "greasy weesel"
I too am going to be fabricating my own flat undertray. I'll be using a product called alucobond. Its incredibly light and incredibly strong.
Are you guys going to be enclosing the exhaust with the undertray? and if so, are you going to heat wrap it. I think i'm going to heat wrap mine up to the muffler just to prevent any excess heat from building up under the car.
I'm also going to be making some little plates that will attach to the front end of the wheel wells to cover up as much of the tire as possible.

 

I agree....Thanks for the input...

Hmm.....Alucobond....very interesting...how is it to work with??

As far as my plans are right now is to close up the rear only.....because the exhaust pipes in the center is already setup a groove ....so if the rear works as well as expected.....thats it for me..

 

It's a bit of both I believe. The surface area exposed to the flow will generate drag. The flow pattern generated by the rapidly spinning tires will interact with the flow. High pressure in the wheel wells will generate lift on the body as well.

Terry

 

Mike, have you put some thought into gearing yet? Or tire diameter?

If you are running a 3.3diff (which I think you are right now)....to hit 200 in 5th you'll be at 8500rpm (just over actually), or 6th is 6200rpm range on a stock dia tire.....only issue with that, is I know some trans have big issues with pulling an overdrive gear (6th) that hard that long. Maybe someone thats looked into the trans (briguy maybe or sirpierre) could shed some light on how good the squirters/pump is in our trans to cool/lubricate gears

Just thoughts

Tom

 

So far I am sticking with the 3.3.....that may change later after I test it with the new setup.... I am sticking with the 20's so I should have much better numbers from the stock plus..Yokahama is sending me 3 sets plus a big azz sticker for my car

Dont forget now.....I will not be above 190 for long...2 reasons....1) My class will be in the 150 range....not open class 190+...dont forget that...2) There are only a few areas that will allow you to hold those speeds. The reason I opt for this much power..is to get me from say for example ..130 to 190 in under 15 sec.....and the monster brakes to get me back to 90 or 70 for the corner and then back up as quick as possible.

Say for example Tom you are running in my class and your cars real top speed is 170....all it would take for me to beat you is a few 180 or 190's to scrub tons of time off the clock. I think some people think that I will run at over 190 for 90 miles......not even my ####### could do that. The trick is not to scrub off too much and get DQ'ed.

I have received some PM's from people telling me that there is no way I can run a VQ 90 miles at 200mph......Not even a Ferrari or Lambo could do that..... But I told them I am not that crazy

Winning my class at the SSC would be nice....but there is a sub group that puts big BIG $$$ on the line......so thats my REAL reason


Tom...did you PM Sharif as yet???

 

I already have the exhaust caramic coated back to the muffler sections. Once we have the final position for the mufflers/exhaust tips hammered down and move them accordingly, I'm going to ceramic coat the reast of the exhaust back to the tips. I'm also ceramic coating the exhaust manifolds, turbine housings and downpipes.

In addition, we'll be using NACA ducts to provide air flow to the transmission and rear differential.

 

page 148 of Competition car aerodynamics , by Simon McBeath

 

Pretty much like the Top Secret and Amuse Sup. fenders

 

sounds good mike....no no pm's yet lol

I've only gone up and down real quick to speeds (somewhere well north of 160as the speedo only reads to there.......but well it was well above that is all I know lol).....I didn't look at any of the gauges too much....was concerned with staying on the road lol.....and it is pretty sick how quick we can get up to above speedo speeds with some of these setups isn't it lol.

Um Sharif.....I'm waaaaaiiiiiitttttiiinnnggggg....

Tom

 

OK....I finally got a response from the guy who built my GT1 car.....I sent him a bunch of pictures including the ones below and asked if he saw a problem in his opinion with running this car at high speeds. I did not tell him what was in question...

He first asked if it was a stock body. He wanted to know if I did anything to the rear for it to extended further than the front...Once I told him it was stock...he then said that the more rubber you have to the ground the better... he said to get the wheel/tire as close to the top of the fender as possible without rubbing.

He did say that if you widen the rear to extent further than the front....you will have to do extra to counter the negative effects......I take it he is talking about changing the direction of the air.

THEN I told him why I am asking.....He said even if he though my offset was wrong....the only time that would make a difference is if you had a track only pro car that had a limited HP in its bracket, limited weight and so on...where any little wrong direction of air would affect your times......but running a street car with insane hp will not even matter.


I have a car in my garage that comes with 355 from the factory and the bottom of the wheels extend a little further then mine......If the car was not steady at 180 plus....this is something I would address....I am sure it will be OK.

 

Hey so are you going to have a navigator with you? What are your plans for timing? Because you do have a "target speed" right? and are trying to finish at .000 I assume? I ran the BBORR this past April and by pure luck had an average speed of 124.952 in the 125 target speed class and ended up with a 3rd place trophy@ 1.3 seconds fast...which means there were two other competitors UNDER 1.3 seconds over 118 miles..CRAZEE! Believe it or not, I used a 10 dollar digital kitchen timer from walmart! LOL I set it up to count DOWN 28:32 for the first leg of 59 miles and deducted the 32 seconds fast that I was at the half way point..raced second leg and stopped the timer as I crossed the line. Couldn't freaking believe it read 0000 when I looked after I parked!.just curious what you're thinking. I assume you are planning on running the NORC next spring right? I have thought about doing the BBORR AND the norc next year..just not sure I can go to Nevada right after the BBORR. We'll see!

 

I searched, but unfortunately I could not find Amuse fenders for a G35. The TS vent is pretty small and pretty high up on the fenders. The Seibon fender's vent is a little larger, but still a little high up.


Someone needs to make those Amuse fenders for the G35, PPPLLLLEEEAAASSSEEEE.

Oh, and while their at it, make them 2" - 2.5" wider than stock, and make a rear fender kit that increases the width by the same amount. And please don't make us buy bumpers we won't use.