User avatar
Mats
Verde
Verde
Posts: 4059
Joined: Mon Nov 29, 2004 12:26 am
Location: Gothenburg, Sweden
Contact:

Post by Mats »

I can speculate, can't say I have any real numbers to back me up though.

-Lower ride height, less frontal area. (Is the Evo lower?)

-Front end moves the air around the car instead of under it. This is good, sides are way smoother then the floor. Probably increase cooling as well as the underfloor pressure is lower -> bigger pressure diff. over the radiators.

-The Evo front is wider in front of the wheels, this is very important as the wheels are a big source for drag. To be able to move the air around the wheels in a controlled way is extremely important, it also create a nice low pressure area outside of the wheels, this is very good for brake cooling.
The same goes for the rear wheels minus the brake cooling naturally.

-The rear bumper of the Evo kit is probably not better then the std. though, it's wider behind the wheels and this catches the air, for strict racing I'd use the std unit or possibly make some cut outs to let the pressure out of the wheelhouse.

-Rear spoiler is great. maybe not for drag though... :roll:
A friend here has a home made spoiler that looks like the IMSA one, he says it makes a huge difference in fast turns. A wing would be better for drag naturally.
The std "duck tail" on the 75 is terrible, REALLY heavy. the thin trims and a proper wing is lighter and much more efficient.

Time to re-read theat book... Race Car Aerodynamics by Joseph Katz. Very good book.
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!
kterkkila
Gold
Gold
Posts: 174
Joined: Tue Oct 18, 2005 11:00 am
Location: Finland
Contact:

Post by kterkkila »

Good thinking Mats 8)

Actually never though that help on cooling before.

What comes to spoilers and skirts, our rules allow to use only factory options or similar shape. That's why can't go to IMSA look. The material must be rubber or plastic. Only glass fibre reinforcement is allowed, but not any of advanced fibres.

This gives possibility to make own thin grp pieces, but to do that should first found evo set for copying it. That may not be easy.. Fortunately there isn't any hurry with this project.
Kimmo / alfatune.fi
User avatar
Mats
Verde
Verde
Posts: 4059
Joined: Mon Nov 29, 2004 12:26 am
Location: Gothenburg, Sweden
Contact:

Post by Mats »

I guess "similar shape" means identical shape but in another material? Otherwise you could do a lot of interesting stuff... :wink:

I personally believe that the biggast improvement you can do aerodynamically is to make a flat undercarriage, i.e. a flat floor. Rake that a couple of degrees and you will get less drag and some nice download.
Only then will it be important to have low side skirts. Probably will need some gearbox and brake cooling though. 8)
Is this allowed in your rules?

I think you can actually buy Evo skirts from the UK, in grp. Grp is the only thing you need btw, there are really no benefits at all with carbon fibre or aramid unless you use prepreg and autoclave but if you have that kind of budget I'm guessing you wouldn't be driving a 75 in a small local series. :wink:
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!
User avatar
Micke
Verde
Verde
Posts: 810
Joined: Sun Dec 05, 2004 11:33 pm
Location: Finland
Contact:

Post by Micke »

Mats is right on spot again. You done your homework as usual!

Even the Evo air dam doesn't do much good without something flat under it (or at least something to block airflow). Mostly you can see the ground through the front which means there's for sure a good way for the low pressure to escape.

The quoted difference in C_d is totally imaginary. With only the small plastic parts this is definitely not possible.

If Kimmo gets some interesting parts done we can always measure the drag in spring when weather permits.

In the Saloon class where Kimmo's driving nothing is allowed which would really help. Then cooling won't be an issue either. With real modifications it is 4 sure.
kterkkila
Gold
Gold
Posts: 174
Joined: Tue Oct 18, 2005 11:00 am
Location: Finland
Contact:

Post by kterkkila »

Mats wrote:I guess "similar shape" means identical shape but in another material? Otherwise you could do a lot of interesting stuff... :wink:
That’s what I ment, the shape must be identical. The rules are quite restrictive. But what’s in your mind when thinking “interesting stuff”? I’m curious on that ;)
Mats wrote: I personally believe that the biggast improvement you can do aerodynamically is to make a flat undercarriage, i.e. a flat floor...
...Is this allowed in your rules?
Unfortunately not, any kind of underfloor panels are forbidden, expect small protection shield under the engine :(
Mats wrote: I think you can actually buy Evo skirts from the UK, in grp. Grp is the only thing you need btw, there are really no benefits at all with carbon fibre or aramid unless you use prepreg and autoclave but if you have that kind of budget I'm guessing you wouldn't be driving a 75 in a small local series. :wink:
I may use vacuum curing (or not), but probably not autoclave. With good guality glass fabrics and epoxy resins, the grp pieces can be made light and strong enough for the purpose.

You're also right that aramids and carbons go out of my budget. But if I really would like to invest on this, would definetely prefer SP's sprint system than regular prepregs ;) They are easier to use, as they aren't so sticky (cutting, bending on edges). They also doesn't need external pressure of autoclaves, vacuum and heat is enough :)

Familiar with this?
http://www.spsystems.com/solutions/sprint.htm
Kimmo / alfatune.fi
kterkkila
Gold
Gold
Posts: 174
Joined: Tue Oct 18, 2005 11:00 am
Location: Finland
Contact:

Post by kterkkila »

Micke wrote:Even the Evo air dam doesn't do much good without something flat under it (or at least something to block airflow). Mostly you can see the ground through the front which means there's for sure a good way for the low pressure to escape.
Does the Evo have somekind of aerodynamic improvements under the car?
Micke wrote: The quoted difference in C_d is totally imaginary. With only the small plastic parts this is definitely not possible.
Might be, who knows :roll:
That's the only claim I've been found. Without better knowledge about accuracy of those values, can't do more than speculate. Although the claimed difference sound big also in my ears..
Micke wrote: If Kimmo gets some interesting parts done we can always measure the drag in spring when weather permits.
Guess not yet on coming season. I may do some lap time and coast down tests with actual TS parts, if not found Evo parts, but manufacturing own ones is not possible on this spring. I have too many project going which should be ready on summer (Engine mods, remapping ecu, transmission changes, small clutch, new flywheels, lightenings everywhere, a-arm mountings, dion bending...).
Micke wrote: In the Saloon class where Kimmo's driving nothing is allowed which would really help. Then cooling won't be an issue either. With real modifications it is 4 sure.
I agree, can't do things which REALLY helps, but smaller helps are welcome too. I guess that the evo bumber would make noticeable difference. Just look at the picture here, it will let lot of air under the car.

Image

What comes to the cooling, can you really say when there comes an "issue" or what is "real modifications"?

I don't see it so simple. I already had some problems with this issue, even when the engine was quite mild (+15hp). When driving at full speed (or about one or two seconds away from that per lap) several hours in hot wether, cooling capablities should really be sufficient. Now the plan is to use new, maybe a bit smaller, radiator and get more power out of the engine..
Kimmo / alfatune.fi
User avatar
Mats
Verde
Verde
Posts: 4059
Joined: Mon Nov 29, 2004 12:26 am
Location: Gothenburg, Sweden
Contact:

Post by Mats »

Kimmo, thanks for the link, it goes on my "to read" list. :)

Micke, thanks for that, nice to hear I remembered it correctly.

Interesting to hear about the rules, especially the "small protection shield under the engine", who decides how this "protection" may be designed? :twisted:
Are you allowed to make holes in the hood? A definite improvement would be to seal off all holes and such in the front to force all air going into the holes in the front through the radiator and then let it out (again ducted through an "air-tight" tunnel) through the front part of the hood, them you can gradually make the inlet hole smaller until you notice the engine running a little too warm (not much!) and make the inlet hole a little larger. All other air hitting the front should be guided to the sides or over the car. As much as 30% (!!) of the total resistance is from radiators.
No need to have holes in the front unless you really need it, brake cooling for instance might be a good idea.

Now, an Evo front end with a "protection" from the front lip extended back under the engine together with the above mentioned radiator improvement will produce quite a bit of download. The Evo front will for sure make the situation around the front wheels a lot better as well.

Now for the interesting parts, are you allowed to have any other "protective shields" under the car? I would think about getting a "protective Shield" for the gearbox and gas tank if I were you... :wink:

No more free tips for today. :)

Edit: I got some side-by-side shots of my turbo and a friends Evo at home, I'll try to remember to post them for front end comparison.
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!
kterkkila
Gold
Gold
Posts: 174
Joined: Tue Oct 18, 2005 11:00 am
Location: Finland
Contact:

Post by kterkkila »

Some years ago couple of cars on this class had air guides under the car. After that those came prohibited. Only protection plates under the engine were allowed. Now when I look again in rules, found that there isn't anything about that anymore. My mistake.

One of the basic rules says that you are not allowed to do any modification which is not specially allowed in the rule book. Other rule says that man can add any additional accessories, if they have nothing to do with handling, steering, transmission or brakes, and if they are not adding any engine power. There is also extra note that these accessories cannot affect on those mentioned even as "secondary" function. That can be red in several ways. I guess the engine bottom shield goes on that. The gearbox or tank shields could be too obvious.. We must have race tanks, so there is only cover of original tank under the car.

Quite restrictive rules, arent they :? This is the way how the budgets are kept in about reasonable level.

One max. 100mm cooling tube is allowed for each brake. There is also listed what kind of holes can be done to chassis.. Radiator, it's electric blower and it's mountings are free, but the position must stay. Maybe these free "mountings" could help on guiding airflow ;) Unneeded holes on the chassis can be blocked, which allows controlling of incoming air on the front. Have to think about it a bit.

What comes to the holes on the front bumber on the pic, they were like a emergence reliefs, when the temperature was rising bit too high. Guess they won't help a lot, but had to do something. We also changed coolant fluid mixture to pure water at the same time and that helped enough for that time. The radiator itselves looks good but is rather old. Also would like to have some amount lighter solution, so it need to be also smaller.

That pic would be nice :D
Kimmo / alfatune.fi
Post Reply