Hi guys, Barry, I follow the trail don't worry, I wouldn't miss it. I believe that Mats and Brian put a tombstone on a subject very impractical for most DIY's to deal with. To begin with, AR graced us with cars having Cx among the worst in the business! If memory serves me, the GTV toils around 0,39-0,41 and the 75 at 0,34-0,36 while a LOT of other common family-lugging machinery of similar age shows numbers around 0,29-0,32. Mats' arguments about the flat bottom are 100% valid-you'd have to drive wearing an asbestos suit! But MOST important, I find Brian's argument about DRIVING! I was driving karts for years and then the gtv and after that the 75, having logged umpteen track hours. I'm always looking for more power and planning for it, as well as handling, brakes etc. NOW, when Ron Simons comes down to Athens and drives MY car in "MY" track, I'm sure as hell that after a few recon laps he'll beat the sh*t out of MY best times and will keep improving! I really don't believe at this point that it's power I need or aero help! The man IS a race driver and thats what separates men from the boys. It takes a VERY 'together' person to admit that their car is FASTER than THEY are, but this is true in the vast majority of cases. Sorry if I'm stepping on some toes here, but looking for M3/M5 power out of a car begs the question: you really that good?(same goes for buyers of those M cars too!).
Power can be bought as it's always a question of $$ and sellers and peddlers abound, but MOST unfortunately TRUE ability is 'built-in' and can be honed further. In other words, if you've got it, you've got it and if you don't...you don't. It's also a matter of degree like none, some or a lot. Most people know this but it is seldom talked about,especially trackside! It's an ego thing,this driving,just remember the old saying: It's the driver that wins the race and the engineer/mechanic that lose it! I'm sure we all try our best to improve and always wrestle with the damn track beackons and we KNOW there IS room for improvement...that's what all the fun is about! If you had 100hp more, wouldn't things be exactly the same (allbeit in another class,with bigger boys!)??
To make a long story short and return to aero, the factory racers had adequate aids which will not look laughable on the street. I would personally settle for a decent kit and hours (many!) of track personal tutoring! Don't pick up the rocks just yet, let the above sink and think honestly!
Regards,
Jim K.
Lots of good points flowing here.
Back to my flat underbody. Making it totally flat is almost out of the question. However, any improvements here are really worthwhile. The Katz book is good, as is Hucho - Aerodynamics for road vehicles.
As Mats said, when you play with the airflow under the car you MUST consider heat issues.
When I made the front of the car flat the engine and oil temperature jumped a huge step on the scale. Actually enough to be a problem (solved of course).
What I did:
Flat plate under front air dam
Flat plates in the entire middle part between the skirts
Rear venturi as wide as fits between the tires
Tricks:
hot air from radiator is ducted 100% out through the FRONT of the hood (you're right as usuall Barry)
cooling air is ducted to the engine bay, oil cooler, oil pan and good care is taken that the hot air can escape without restriction
the exhaust is heat shielded (rock wool) and the tip exits through the sideskirt
the vented rear disks are not covered. The plates have holes for the hot air to escape. The rear brakes have cold air ducts as well.
the gearbox has cold air ducting and hot air escape (together with the brakes) above the venturi
the bottom is made of a combination of plywood and aluminum depending on how hot the place is.
there's still work to do but the concept definitely works. If anyone of you owns a wind tunnel we can make a gettogether and do some serious testing ower a couple of cold ones.
Back to my flat underbody. Making it totally flat is almost out of the question. However, any improvements here are really worthwhile. The Katz book is good, as is Hucho - Aerodynamics for road vehicles.
As Mats said, when you play with the airflow under the car you MUST consider heat issues.
When I made the front of the car flat the engine and oil temperature jumped a huge step on the scale. Actually enough to be a problem (solved of course).
What I did:
Flat plate under front air dam
Flat plates in the entire middle part between the skirts
Rear venturi as wide as fits between the tires
Tricks:
hot air from radiator is ducted 100% out through the FRONT of the hood (you're right as usuall Barry)
cooling air is ducted to the engine bay, oil cooler, oil pan and good care is taken that the hot air can escape without restriction
the exhaust is heat shielded (rock wool) and the tip exits through the sideskirt
the vented rear disks are not covered. The plates have holes for the hot air to escape. The rear brakes have cold air ducts as well.
the gearbox has cold air ducting and hot air escape (together with the brakes) above the venturi
the bottom is made of a combination of plywood and aluminum depending on how hot the place is.
there's still work to do but the concept definitely works. If anyone of you owns a wind tunnel we can make a gettogether and do some serious testing ower a couple of cold ones.
Micke!
Do You have any pictures You can share with us? You seem to be the one who has experimented most of us with this issue.
Mostly interested in the rear venturi and the flat bottom, but offcourse in all the other stuff aswell.
Very interesting thread this turnes in to....
Seb
Do You have any pictures You can share with us? You seem to be the one who has experimented most of us with this issue.
Mostly interested in the rear venturi and the flat bottom, but offcourse in all the other stuff aswell.
Very interesting thread this turnes in to....
Seb
Proud member of Team Rauk Race.
156 V6 24v -98
GTV6 3.0QV-83
75 3.0 Race Car "The raukster"
156 V6 24v -98
GTV6 3.0QV-83
75 3.0 Race Car "The raukster"
sorry,
the car is enjoying its winter sleep in a tent under a pile of snow. I'll try to get some next spring. I looked through my pics and all to old to show the underbody. You also need a hoist as ground clearance is 50 mm.
Speaking about the effect of the aerodynamics....
IMHO the answer to Zamani's original question is that with a small splitter and a wing off the shelf you do not get any gains you can feel.
In one race (first trial with my new - rear biased at the time - brakes) I managed to spin at ~160 km/h. No damage and I continued the race.
Next corner I spun. Weird, I thought.
Next one almost again....
Damn, are my tires muddy or what? Then I heard a new sound - WIND. I had lost my lid backing up.
Without my rear wing I was not able to do a corner at ~100-120 km/h without spinning. After this experience I can definitely tell you all IT WORKS!!
the car is enjoying its winter sleep in a tent under a pile of snow. I'll try to get some next spring. I looked through my pics and all to old to show the underbody. You also need a hoist as ground clearance is 50 mm.
Speaking about the effect of the aerodynamics....
IMHO the answer to Zamani's original question is that with a small splitter and a wing off the shelf you do not get any gains you can feel.
In one race (first trial with my new - rear biased at the time - brakes) I managed to spin at ~160 km/h. No damage and I continued the race.
Next corner I spun. Weird, I thought.
Next one almost again....
Damn, are my tires muddy or what? Then I heard a new sound - WIND. I had lost my lid backing up.
Without my rear wing I was not able to do a corner at ~100-120 km/h without spinning. After this experience I can definitely tell you all IT WORKS!!
It works!
It takes at least 5-10 km/h off the top speed at the end of the long straight.
The one I have is from a Volvo S40 Challange race car. I wouldn´t wanna drive a long fast turn without it anymore.
Seb
It takes at least 5-10 km/h off the top speed at the end of the long straight.
The one I have is from a Volvo S40 Challange race car. I wouldn´t wanna drive a long fast turn without it anymore.
Seb
- Attachments
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- MVC-003F.JPG (50.82 KiB) Viewed 9846 times
Proud member of Team Rauk Race.
156 V6 24v -98
GTV6 3.0QV-83
75 3.0 Race Car "The raukster"
156 V6 24v -98
GTV6 3.0QV-83
75 3.0 Race Car "The raukster"
Define "big turn"
the larger the radius (= higher speed) the bigger the effect of aerodynamics.
The effect is proportional to the speed^2.
I.e. if you have 500 N (50 kg) of rear downforce at 100 km/h you will have 4 times more or 200 kg aiming into the Schwedenkreuz with 200...
From this you probably also notice that the impact is bigger for light cars. My GTV weight on the rear wheels is 480 kg and YES, 50 kg of downforce makes a difference.
the larger the radius (= higher speed) the bigger the effect of aerodynamics.
The effect is proportional to the speed^2.
I.e. if you have 500 N (50 kg) of rear downforce at 100 km/h you will have 4 times more or 200 kg aiming into the Schwedenkreuz with 200...
From this you probably also notice that the impact is bigger for light cars. My GTV weight on the rear wheels is 480 kg and YES, 50 kg of downforce makes a difference.
- Attachments
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- Rear wing.jpg (24.3 KiB) Viewed 9775 times
Beats me - probably not.
Actually the biggest problem is that there are not enough original parts. This makes it a "new car" and should receive an appropriate tax!
It was street legal in Finland until some years ago anyway.
Now it doesn't make much difference as the ground clearance effectively prevents driving on the roads. If I need to "move it" I use temporary plates like on the picture (saves tax and insurance too).
Got too old (sensible !?!?!) to drive to the races like I did as a kid. I was pretty lucky though as I always drove home as well. Now I use a trailer like other adults.
Actually the biggest problem is that there are not enough original parts. This makes it a "new car" and should receive an appropriate tax!
It was street legal in Finland until some years ago anyway.
Now it doesn't make much difference as the ground clearance effectively prevents driving on the roads. If I need to "move it" I use temporary plates like on the picture (saves tax and insurance too).
Got too old (sensible !?!?!) to drive to the races like I did as a kid. I was pretty lucky though as I always drove home as well. Now I use a trailer like other adults.
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mikecudahy
- Silver
- Posts: 5
- Joined: Tue Aug 16, 2005 1:13 pm
- Location: Milwaukee, WI
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SydneyJules
- Verde
- Posts: 619
- Joined: Sun Dec 19, 2004 1:57 pm
- Location: Sydney
Let's wake up this topic.
The Evo set is recommended for 75's to improve aerodynamics. I would be very interested about those, but the budget for this winter is already about the limit.
What about the standard TS skirt and "spoiler" set, is there any real gains in Cd values or does it improve ground effect even noticeable amount? Do you think it is worth of it's weight?
I had TS skirts and fender arcs at last season, but wanna drop them to save some weight. What do you think?
The Evo set is recommended for 75's to improve aerodynamics. I would be very interested about those, but the budget for this winter is already about the limit.
What about the standard TS skirt and "spoiler" set, is there any real gains in Cd values or does it improve ground effect even noticeable amount? Do you think it is worth of it's weight?
I had TS skirts and fender arcs at last season, but wanna drop them to save some weight. What do you think?
Kimmo / alfatune.fi
If you are refferring to the stuff on the wheel arches and bottom of the doors you can drop them and not lose anything I believe.
Probably even will be better with that slightly smaller frontal area and weight...
Probably even will be better with that slightly smaller frontal area and weight...
Mats Strandberg
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-
GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-
GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
So, the front Evo bumper and in particular the splitter has a beneficial aero dynamic effect? Anyone know for sure? Can someone experienced in this area perhaps quantify in some way?
Jes
Jes
87 Milano Verde - daily driver - Juliet
87 Milano 3.0 Motronic - budget race car - Roxanne
87 Milano 3.7 24v - race car
(Repeat or do as I say at your own risk - be critical)
87 Milano 3.0 Motronic - budget race car - Roxanne
87 Milano 3.7 24v - race car
(Repeat or do as I say at your own risk - be critical)
Just what I ment. The plan is to drop them now. I see benefits in weight lossMats wrote:If you are refferring to the stuff on the wheel arches and bottom of the doors you can drop them and not lose anything I believe.
Probably even will be better with that slightly smaller frontal area and weight...
but will lose some racy look 
What comes to aerodynamics, I really would like to know.How about small rear spoiler? Could it be somewhat functional piece? I didn't had it installed on last season but may test it in future.
The difference on CD values between Standard 75 and EVO is claimed to be huge, 0.38 vs 0.33. Where it really comes from?
That's good question. I may test what TS skirts, wheel arches and rear spoiler do for laptimes, but don't unfortunately have any Evo parts..ar4me wrote:Can someone experienced in this area perhaps quantify in some way?
Kimmo / alfatune.fi