Question about belly pans..

casioqv said:

I've heard that a full length smooth belly pan will significantly increase highway MPG.

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The partial belly pan on the 850 made a 10% difference on the highway. I'm building one for my 190e. It seems like every 190 I've seen lost its belly pan at some point along the way.

ErikS said:

Hot asphault on the highway has hot air right above it, if it is redirected to the rear of the car by a belly pan, its going to help keep the external engine temps down ...

What's so hard to understand about these concepts?

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Not so sure about that theory.


Breakdown of drag on a volvo, probably an S40 since the paper was released right before the S40 came out.


Break down of underside drag on a volvo.

http://autospeed.com.au/cms/title_Modifying-UnderCar-Airflow-Part-1/A_2455/article.html

tjts1 said:

Not so sure about that theory.

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Heat rises, guess at speed probably not a big deal, but sitting in rush hour traffic might.

Meh, I've got a belly pan and a skid plate, just thought I'd throw in my two cents.

Use duct tape. That's what Grumpy Jenkins(drag racer)did in the 70's to make the (then) new 1/4 mile recond top speed in Pro Stock back then. That's when duct tape became known as "200MPH Tape".

Not actually. Heat moves from a warmer to a cooler place. BTW, that heat is not gonna "penetrate" the hood. And it'll follow with the air flow. About the only time it'll rise in engine compartment, is when car is sitting still, with motor not running. Think again.

I think he meant to say hot air rises.

Hot air will rise, IF and only if, the temp above it is cooler than the hot air is. For example, if 90*F air is underneath 100*F air, the 90*F air WILL NOT rise. If 90*F hot air has 80*F air above it, the 90*F air WILL rise.

Most people say & think that hot air ALWAYS rises. Most of the time it does, merely because the air above it is cooler. But hot air does not always, or neccessarily rise.

It all depends on the temp of the air ABOVE it, next to it, or in the room beside it, what ever the case may be..

This is the FIRST thing taught in HVAC classes. Therefore one should ALWAYS say, air moves from a warmer to a cooler place. This way you'll always be correct. And not flunk HVAC classes.

YellowT5-r said:

John V.,

Do ya happen to recall if they bothered ducting that off of the radiator shroud up to the opening, or did the system rely exclusively on the low pressure right behind the front fascia to draw X% of the air flow out through the hood? I ask because one of my main concerns is radiant heat off of 5 18" long header tubes and an angry hot section that would be behind such a hood vent. Coatings and wraps aside for now, life would just be simpler with decent air flow around those bits.

In thinking about it, maybe some combination of through the hood vented radiator "exhaust" air and a lower front tray that would cause some % of the engine compartment air flow to be vented down by the tranny might be the ticket for track days. How pimp would a track day hood be anyways?

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Only poked my nose in 4-5 "400s" and say no special ducting.

And sure radiant heat is bad---I've had friends catch all sorts of crap on fire from insane heat---a T25 being forced to try and may 300 bhp (fawkin numb-skulls!!! They were toooooo smart to ask )
But aside from lighting stuff off if you insulate the firewall and the front part of the tunnel (even using like .032 sheet stainless or look at some modern Audis or VWs which have insulation mats stuck on which might be able to be forced to fit) and make sure you're getting in cold air to the intake, and do even a rudimentary pan it probably would be in some immeasurable way OK.
As said all the serious hard driving I've done is in a car designed by guys who didn't know better than to design the car super clean underneath and in say 1965 had a drag CD of 0,32 or so--full belly pan and engine compartment air vents in the inner fender wells, and for hot climates vents at the back of the hood.Wait here's some piccies:




At the back:


And here's what Saab called "tropical g?llar" or "tropical gills" at the back of the hood.



maybe it'd be easier to get a good car like a Saab 96 which manages air so well

good lord those are some ugly cars! like the vents tho

boosted12a said:

good lord those are some ugly cars! like the vents tho

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This sleek beauty is ugly?
This is my car, had it since 1985.


With this ugly car I have caught the reigning SCCA Pro Rally PGT Champion is less that 7 miles who started 1 minute ahead... Push rod V4 1730cc vs ST165 Celica All-Trac with the wonderful 3GSE 2 liter 16v turbo motor.
With this ugly car I have finished mere seconds behind a very experienced crew in a BMW M3 replica--M3 powerplant in a lesser shell updated to M3 specs----he with no mechaincals, me with a couple of serious problems which cost LOTS of time (rock wiping out brake hard line so loss of brear brakes and extremely dodgy brakes ---like 3 pumps for anything on a LONG stage---cost multiple minutes---loss of odo so driving blind for 1 stage)
A few seconds in total time of 2h 34m is in percent less than 01% diffference
88 M3 vs '69 Saab.
In snow caught the same guy inless than 4 miles with 1 minute gap.
So, maybe, MAYBE they're ugly but jeeeezus christ they work amazingly well.
And so easy to drive! (2000 lbs, 5.45 final drive, close ratio box, all steel LSD, 2.2 turns lock to lock stock rack---they go good!)

Oh and full belly pan---gotta keep it on topic!

Belly pan? The floor is so flat you could roll out your sleeping bag on it!

One thing you guys haven't argued about is the "ground effect".

smokeyfan1000 said:

Hot air will rise, IF and only if, the temp above it is cooler than the hot air is. For example, if 90*F air is underneath 100*F air, the 90*F air WILL NOT rise. If 90*F hot air has 80*F air above it, the 90*F air WILL rise.

Most people say & think that hot air ALWAYS rises. Most of the time it does, merely because the air above it is cooler. But hot air does not always, or neccessarily rise.

It all depends on the temp of the air ABOVE it, next to it, or in the room beside it, what ever the case may be..

This is the FIRST thing taught in HVAC classes. Therefore one should ALWAYS say, air moves from a warmer to a cooler place. This way you'll always be correct. And not flunk HVAC classes.

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Well since hot is a relative term, hot air always rises.

John V said:

This sleek beauty is ugly?
This is my car, had it since 1985.

With this ugly car I have caught the reigning SCCA Pro Rally PGT Champion is less that 7 miles who started 1 minute ahead... Push rod V4 1730cc vs ST165 Celica All-Trac with the wonderful 3GSE 2 liter 16v turbo motor.
With this ugly car I have finished mere seconds behind a very experienced crew in a BMW M3 replica--M3 powerplant in a lesser shell updated to M3 specs----he with no mechaincals, me with a couple of serious problems which cost LOTS of time (rock wiping out brake hard line so loss of brear brakes and extremely dodgy brakes ---like 3 pumps for anything on a LONG stage---cost multiple minutes---loss of odo so driving blind for 1 stage)
A few seconds in total time of 2h 34m is in percent less than 01% diffference
88 M3 vs '69 Saab.
In snow caught the same guy inless than 4 miles with 1 minute gap.
So, maybe, MAYBE they're ugly but jeeeezus christ they work amazingly well.
And so easy to drive! (2000 lbs, 5.45 final drive, close ratio box, all steel LSD, 2.2 turns lock to lock stock rack---they go good!)

Oh and full belly pan---gotta keep it on topic!

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it dosent look so bad in that pic but it stil looks like some italian thing from the 60s

John V said:

This sleek beauty is ugly?
This is my car, had it since 1985.

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No, it's not ugly. It's from the era of the last good looking Saabs. Still drive it regularly?

John V.,

I dunno if you've seen Project 755, so here's exactly the bits I'm talking about for decent air flow and heat extraction. As it stands, packaging with the 5-lung motor has plenty of room, I just want to make the best possible use of the space I have.

1) Used radiator air goes somewhere from here.



2) Here's where the hot bits lie where I think some air flow would help.



3) Here's the heat shielding to protect some tender bits and make a cold air intake.



4) Said soon to be hot bits include GT30/71R and this sexy beast: (header on a mock-up block yo give an idea of its radiant surface area.

I spy Dr. Pepper box.

Have to agree with John V. on the saab. I broke one in for a friend with 900 miles on it doing 90 mph for over an hour on an upstate New York interstate with him asleep in the passenger seat and my girlfriend terrified in the back seat. Wonderful car with the V-4. My present stock includes a 84 900S coupe with a dual cam motor and a turbo transmission, instead of a single cam/ stock tranny, a true snowmoble, along with a 89 740 turbo with 4 snow tires instead of 4 wheel drive for the Rocky Mountains. It is snowing today. I am planning on full front and rear belly pans for mileage, drag and top speed.

boosted12a said:

it dosent look so bad in that pic but it stil looks like some italian thing from the 60s

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Everybody was in love with Italian styling in the 60s! It's Swedish as can be, next thing you know you'll be dissing Amazons!!!


Is nothing sacred!!!???


Anyway, the car is really in the end a tool and seriously, the damn 96 shocked people here in USA for YEARS, especially as the conditions and weather got difficult.


But you know what they say: You can't keep all the people happy all the time...

Over on rallyanarchy a nice guy I've helped with his Fucus has realised how much fun rwd is, and especially how we can go out to wrecking yards and grab things like Borg Warner T5s, or Toyota 8" pick up axles for a few bucks and bang 'em in while he's has basically one choice to upgrade his MTX75 and he's looking at maybe $6400...it's insanity...


But he is resisting and squirming and dodging the obviousness of a 240---I found him several in Salt Lake City (he's in the Air farce stationed nearby there and currently in Afghanistan) He went so far to say "I'm kinda artsy-fartsy and I just can't see myself in a 240 cause they're so boxy! Howzabout a 140?"

240 too boxy, but 140 not???


Oi!

I thought that hot air rises because it is less dense and the colder, denser air pushes it up and out of the way, as in a hot air balloon. Same for a helium balloon.

I always wondered why when they calculate drag coefficient, they only include the silhouette of the vehicle and don't just extend it to the ground since I would think that all of the air under the car is just being dragged along with all of the junk hanging down under there.

If you have a full, flat belly pan, maybe it will increase lift, but the reduction of drag should more than be worth it. You just need a 45 degree trunk spoiler to get the air moving over the top of the car up, and out of the way.

I also believe that with an airplane wing, the angle of attach is way more important than the profile shape of the wing itself. That's why airplanes can fly upside down and not crash.

So, if you have a front spoiler down low, and a rear spoiler on top of the trunk up high, your angle of attach is a line from the bottom of the front spoiler to the top of the rear spoiler, thus no lift.

I was going to build a belly pan, but just went with the full front air dam and side skirts to keep all of that bad air from getting under the car in the first place.

Looks like there are a lot of examples of dirt cars being used here. The aero needs of a dirt car vs. a pavement car are different. I think there is always merit in adjusting the aero of a car to suit it's needs, but what are the real goals for this car?



John- Saabs are ugly. UGLY. But I like them.

cassidy said:

Have to agree with John V. on the saab. I broke one in for a friend with 900 miles on it doing 90 mph for over an hour on an upstate New York interstate with him asleep in the passenger seat and my girlfriend terrified in the back seat. Wonderful car with the V-4. My present stock includes a 84 900S coupe with a dual cam motor and a turbo transmission, instead of a single cam/ stock tranny, a true snowmoble, along with a 89 740 turbo with 4 snow tires instead of 4 wheel drive for the Rocky Mountains. It is snowing today. I am planning on full front and rear belly pans for mileage, drag and top speed.

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Hey if ever you want to have some more poop in your 900, and maybe build a bottom end nice and for amazingly cheap, call me.
EVERY Saab which has won a Group 2 title or individual National round has has the motor (and maybe gearbox, final drive, LSD, brakes springs, shocks clutch etc) supplied by little ol JVAB

Those wins were taken by G?ran ?stlund who drove an 8v B motor 99 Saab and was Nationala Champ in Gp2 in 1994
then Sam Bryan who won in 1995 with a 900 with 215 bhp normal aspirated 16 motor from ME! (and a LOT of other parts---he assembled all but the motor)

And my car in the photo above which I won 1995 SCCA Maine Summer Pro rally in Gp2---and I stress--after more than 2 years not sitting in the car on gravel and ALL the other cars from 1-about 15 had done full seasons in those previous 2 years.

(They just happen to all be from Seattle and were sponsored by a friend's large shop that I convinced to owener to get involved in rally as a co-driver then as sponsor)


it's funny but over the last couple of weeks the kid who has Ostlund car now locally and an old friend in Maine have both transferred the junk into 900s and FINALLY after seriously 10-13 years ofme bugging my eyes out and pulling my hair asking them "Do you have something against making easy power??? Do you want me to spank you in my ancient stuff AGAIN???", have decided to junk the stock intake manifolds which restrict power in NA to about 175 and not a skvatt more, only 10-13 years....