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Inner Fenders 

 

to run them, or not to run them? What is the general consensus? I would think not running them would keep temps down by allowing the air to exit the engine bay after passing through the radiator easier. 

 

Running a S-10. 

 

 

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Non structural inner fenders are usually cut out, mostly to prevent the tire from eating them when you have "racing contact". 

 

For cars that need them to support the fenders (some frame cars), you either need to make some supports and potentially used some points (or repurpose parts) or just leave it alone. 

Edited by Black Magic
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17 minutes ago, Black Magic said:

Non structural inner fenders are usually cut out, mostly to prevent the tire from eating them when you have "racing contact". 

 

For cars that need them to support the fenders (some frame cars), you either need to make some supports and potentially used some points (or repurpose parts) or just leave it alone. 

Fenders have 5 or 6 mounting points to the cab, and 3 to the front radiator support. Might add another front support location and call it good. 
 

I was worried more what people thought in the event of racing in the rain. 

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Some are part of the car's structure... If so you could use a 3" hole saw and lighten the load some and get some more air in, keep in mind if you race in the rain water is going to get all over the engine. Electronics don't like wet.

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We th a Malibu without inner fenders.  Never had an issue n the rain.

 

The bigger issue is the gap at the front of the door on some cars allowing the tire to spray water all over the driver.  Plus, opr gets in there and makes the car a mess.

 

It's probably not great for aero, but I don't actually know what the flow looks like through that area.

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1 hour ago, wvumtnbkr said:

We th a Malibu without inner fenders.  Never had an issue n the rain.

 

The bigger issue is the gap at the front of the door on some cars allowing the tire to spray water all over the driver.  Plus, opr gets in there and makes the car a mess.

 

It's probably not great for aero, but I don't actually know what the flow looks like through that area.

Not great for aero having them installed or not great having them removed? 
 

min not worries about the driver or cab getting messy the way the door seals. We should have enough wiring to get the computer located inside the cab beyond the firewall as well. 

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Unless you duct things, radiator, out the hood it should help airflow removing them. All the air going under the hood has to go somewhere and if the inner fenders are in place about the only exit for the air is under the car. Not good as it will cause lift.

 

Note that Nascar stock cars do not have front inner fenders.

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34 minutes ago, Bandit said:

Unless you duct things, radiator, out the hood it should help airflow removing them. All the air going under the hood has to go somewhere and if the inner fenders are in place about the only exit for the air is under the car. Not good as it will cause lift.

 

Note that Nascar stock cars do not have front inner fenders.

Planned on louvering the hood for air movement, and sealing off all the front except some brake ducking. 
 

Thanks for the info!

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4 hours ago, Bandit said:

Unless you duct things, radiator, out the hood it should help airflow removing them. All the air going under the hood has to go somewhere and if the inner fenders are in place about the only exit for the air is under the car. Not good as it will cause lift.

 

Note that Nascar stock cars do not have front inner fenders.

Fast moving air under the car is what you want for downforce.

 

Big amounts of air squished into a tiny space creates faster flow.  Faster flow has lower pressure.

 

I'm not disagreeing with you, just clarifying my p.o.v.  not sure if that air would be fast moving or not.

3 hours ago, mgoblue06 said:

Planned on louvering the hood for air movement, and sealing off all the front except some brake ducking. 
 

Thanks for the info!

Add a little lip to the front of your hood ducting.  It will help extract air from the hood.

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1 hour ago, wvumtnbkr said:

Fast moving air under the car is what you want for downforce.

 

Big amounts of air squished into a tiny space creates faster flow.  Faster flow has lower pressure.

 

I'm not disagreeing with you, just clarifying my p.o.v.  not sure if that air would be fast moving or not.

Yes, fast moving is good however it is fast moving due to the low pressure. A splitter is more effective the closer it is to the ground as it allows less air under the car.  One doesn't want to add air under the car as that raises the pressure. That is the idea behind splitters and side skirts as they keep the air out. High pressure above the car body and low pressure below it is what gives downforce.

 

I can't find it now but there is a pic of a C5 Corvette, what one considers a pretty aerodynamic car, going through one of the speed traps in the Silver State Challenge or similar with the front of the car not only riding high, but the hood is bowed and lifted as well due to all the pressure under it. Mark Steilow recently said the 2008 CTS-V had 300 pounds of force pushing up on the hood latch at 190mph. Granted much faster than here, but it shows that trapped air is not good. The lift is still there at lower speeds, just not to the same extent and lift is bad for grip.

 

edit to add-That is why in racing series where it is allowed the radiators are sealed from the engine compartment with the hood duct. The wheels wells are also a high pressure area, hence the louvers to relieve that pressure.

spacer.png

Edited by Bandit
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3 hours ago, mender said:

I think that's the front end of a Fiero...

KIMG1108.jpg.7e9a183c2b83c125e26b531269af395c.jpg

 

Oops, sorry, wrong colour.

Little easier on a Fiero with no engine in the way.

 

What's up with the sewer grate? Keeping critters out? 🙂

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3 minutes ago, Bandit said:

Little easier on a Fiero with no engine in the way.

 

What's up with the sewer grate? Keeping critters out? 🙂

That's so you don't drop tools and they hit the radiator.  At least that's my reason for it on my car....

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3 minutes ago, Bandit said:

Little easier on a Fiero with no engine in the way.

 

What's up with the sewer grate? Keeping critters out? 🙂

We strap hot dogs onto it during the race so we'll have something to eat after...

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3 minutes ago, mender said:

We strap hot dogs onto it during the race so we'll have something to eat after...

Good thinking. Very green.

 

That Vette pic has me looking into fiberglass molding.

Edited by Bandit
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I always look at it like flow in a pipe.

 

If you make the pipe smaller, the fluid will flow faster and have a lower pressure.   This is only true if there is a way for the air to escape and meet back with itself.

 

There is definitely a point where the amount of air being crammed in can't escape fast enough and the pressure will build and the flow will slow.

 

If you have fast movement of fluid, it will have a lower pressure.

 

I like to think of it like the molecules only have sooo much energy.  They can either exert force (pressure) or go fast.  Can't do both.

 

Edit to add....  we had our hood much like lenders and our temps went UP!  Found out the flow wasn't terrific in that area of the hood and air wanted to go IN!  Arggghhhh.   We added a little gurney flap at the front of the opening and that made everything better!  I see the corvette has a little lip at the front too!

Edited by wvumtnbkr
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2 minutes ago, wvumtnbkr said:

I always look at it like flow in a pipe.

 

If you make the pipe smaller, the fluid will flow faster and have a lower pressure.   This is only true if there is a way for the air to escape and meet back with itself.

 

There is definitely a point where the amount of air being crammed in can't escape fast enough and the pressure will build and the flow will slow.

 

If you have fast movement of fluid, it will have a lower pressure.

 

I like to think of it like the molecules only have sooo much energy.  They can either exert force (pressure) or go fast.  Can't do both.

Venturi effect. I think I have seen where that is used in undertrays and such. That is likely the effect one is getting with the slight rake that is recommended for aero as well. Related anyway.

 

Like you say, there is a point when there is too much air, plus it isn't really controlled or directed at all when it is just dumped into a cluttered engine compartment. Turbulent air is no good.

 

I noticed that all the newer stuff has the splitter higher in the middle. Apparently that is so they don't stall when the splitter inevitably hits the track. Limiting air is good but completely blocking it suddenly kills the downforce unsticking the front end or causing the car to porpoise.

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29 minutes ago, wvumtnbkr said:

That's so you don't drop tools and they hit the radiator.  At least that's my reason for it on my car....

Keeps the cheese out, don't want De Brie in there...

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1 hour ago, wvumtnbkr said:

Edit to add....  we had our hood much like menders and our temps went UP!  Found out the flow wasn't terrific in that area of the hood and air wanted to go IN!  Arggghhhh.   We added a little gurney flap at the front of the opening and that made everything better!  I see the corvette has a little lip at the front too!

I have reasonably good rad ducting at the front and it all seems to work well, no problem with water temp with the stock rad despite more power. High speed stability is also good, so avoiding two issues that Fieros usually have. Directing the air up and over works better than jamming it under, at least for now.

KIMG1107.jpg.7a136303eaee72d9cbcbec3ffe06c099.jpg

 

I'll be adding an air dam and splitter before it hits the track again.  And no, the M-B V12 under that radiator is not going into the Fiero despite the potentially wonderful sounds. :)

Edited by mender
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This really turned into a nice aero thread. lol. 
 

With good venting I’ll probably throw some vents in the fenders as well. 
 

If we have time we were going to get crazy and do a flat bottom as well. Does any of this have effect on that?

 

 

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From my understanding, a flat bottom is more about how the air is "conditioned" to work with a rear diffuser but drag can be reduced as well. Past a certain level, the underside of the car can be a major contributor to the downforce with only a minor increase in drag. The basic premise is high pressure over the car and low pressure under the car = downforce, so whatever the car needs in mods to increase the pressure differential adds downforce.

 

Partsbadger posted a link to their car build, it answers some of the questions:

https://ruggedbadger.com/the-car-build/

Good information on there. :)

 

I have most of the race car aero books and as usual have been reading up but my practical experience so far has been limited to rad ducting and hood vent on the Fiero, and splitter, air dam and rear wing on the Civic. The Fiero's mods work well for what they were meant to accomplish, mainly getting air to and away from the radiator for cooling.

 

The Civic was a decent car without the aero, getting good reviews from my various drivers about the recent upgrades that put it in contention with the faster cars around here. I swapped the engine and installed the aero at the same time and meant to do some testing with and without the aero to validate improvements but ended up doing a race with it instead of a test and tune. I went about a second faster on a short low speed track and my other driver went about two seconds faster, closing the gap between us to about a second and a quarter.

 

The next race was at a high speed track, and I upgraded to 245s from 225s. I only had a few laps during practice (crew chief = I do the work when things start to go wrong = no seat time) but I was surprised at how fast the car was. Lots of grip from the bigger tires and the aero, so much so that I was well below the car's capability which doesn't usually happen. I was really looking forward to pushing the car after everyone else got a few laps in but the third driver came in with the water temp gauge pegged.

 

The next day went better and the drivers were very happy with the car, being able to place it wherever they wanted and push hard. The aero definitely helped, and I will be making improvements for this year. The plan:

1. Extending the splitter forward and to the sides.

2. Covering the front tires better now that the 245s are sticking out beyond the lower edges of the fenders.

3. Covering the headlight openings for lower drag and more air over the car.

4. Better rad ducting and hood venting to reduce pressure buildup under the hood (had substantial hood flex from that!).

5. Might see about some underbody panels to smooth the airflow plus some thoughts about a rear diffuser.

6. Side skirts.

7. Increase the adjustment range on the rear wing; already maxed out the amount that I thought would be too much (7 degrees AOA).

 

I've been wanting to play with aero for quite a long time but believed the naysayers that claimed the speed that we are at is too low to see any real benefits. After only one year using basic aero I can see that they were wrong! 

Edited by mender
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58 minutes ago, mender said:

I was surprised at how fast the car was. Lots of grip from the bigger tires and the aero, so much so that I was well below the car's capability which doesn't usually happen. 

 Snip*

 

Yep.  Same experience here.  The car wa actually way faster into and through the corners than I was comfortable with.  I had to "recalibrate" my ohcrapometer.

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