Estimation of the Cd-reduction

[Kilpuri]

Hello all,

I happened to find this forum while seeking information of the everyday mods to reduce drag. Forum seemed to be extremely interesting! My (our) intention is not to save fuel. Our intention is to reduce lap times on racing. You can visit our web pages on http://mallasracing.info (Kuvia = Pictures).

Like you can see we are using ED-chassis (88-91) sedan Civic, 1.6i SOCH. From pictures you can see the "current" design.

I have planned following aero-modifications:

- Belly pan under engine (Belly pan under the elsewhere of the chassis is not allowed)
- Modification of the trunk bottom (diffuser)
- Nose piece to round up and close the upper surface (bumper to engine cover)

How much would you estimate these would reduce the Cd? I think current one is very close to the 0,31.

What else?

Car is lowered as much as possible and you have to keep in mind that we need to cool down the engine and transmission due to the fact that most of the 6h race we use rpm between 4000-6500 1/r. Also brakes needs to cool down.

Regards

- Mikko

[Gary Palmer]

With the objectives you have of keeping the engine/transmission running, I'd be pretty careful about doing anything in terms of a grill block, or even a belly pan under the engine.

If you do something with the grill, I'd test the daylights out of it. A grill block does seem to make a difference, in terms of mileage and it does seem to take a block of almost the whole grill before I see a temperature increase, on the highway. However, on my 89 Honda it is only turning 3,000 -3,800 if I'm pushing it at 80 mph, or so. However, that is all steady state driving, not mash it to the floor, then let up as late as possible, hammer the brakes and then do it over and over again.

You should check out the aerodynamics of Bassjoo's Honda. His boat-tail added more mileage than any other modification and it might be something you could give a try.

[Kilpuri]

Originally Posted by Gary Palmer

With the objectives you have of keeping the engine/transmission running, I'd be pretty careful about doing anything in terms of a grill block, or even a belly pan under the engine.

I have planned only to cover the small slot between the bumper and the hood. Grill of the bumber is totally open as the vents for brake "coolant hoses". I am not so worried of this grill block, I am mainly worried of the belly pan. Does anyone have some measured data how much it would affect? Should I let the exhaust pipes free of the cover? I have also planned to leave the trailing edge of the belly pan open, so some heat could escape under the car. So far we have not had any sign of over heating of the engine. Actually engine runs bit too cold, but more I am worried of the transmission.

We have also made an hole to the hood on the "low pressure leading edge" on top of the exhaust manifold to prevent the heat from engine compartment. We have also made some shark cut elsewhere.

I made sketch trying to clarify the current idea.

Originally Posted by Gary Palmer

You should check out the aerodynamics of Bassjoo's Honda. His boat-tail added more mileage than any other modification and it might be something you could give a try.

That kind of tail is not allowed. I would go ahead with the diffuser.(?)

[GasSavers_SD26]

Have you thought about an exhaust wrap to keep the heat in the exhaust system? Usually keeps exhaust velocity higher also; better scavenging in addition to reducing some of the under hood temps.

Are you using a good synthetic transmission oil? Might help.

[Kilpuri]

Originally Posted by SD26

Have you thought about an exhaust wrap to keep the heat in the exhaust system? Usually keeps exhaust velocity higher also; better scavenging in addition to reducing some of the under hood temps.

Are you using a good synthetic transmission oil? Might help.

This wrapping could be good idea.

But back to the topic. Does anybody have an idea how much these mods could affect to Cd-value? Which affects most? If you experts concider that there is no need to such mods, then the risk of the overheating might be concidered... ...might be.

[GasSavers_SD26]

I guess you have to look at it this way...

What you make won't be a bolt on item. So, you're gonna have to try to make some tests to really decide the value of what you do.

Manufacturers are looking at those things in improving their mileage numbers, so, certainly, it's worth looking at.


How much will it help? How far off the fastest times are you? Is it aerodynamics that is holding you back or something else?

[red91sit]

The bellypan will most certainly lower Cd, and raise downforce, I see no reason not to have it!

[basjoos]

It's hard to calculate exactly how much any particular mod will drop your Cd since it all depends on what your car's current shape is and how the new aero mod will change it. You can use coastdown tests to calculate your Cd using info at the following site:

http://www.instructables.com/id/Meas...t-of-your-car/

How likely your car is to overheat with a grill block in place is strongly dependent on the outside air temps and also how hard you you are pushing your engine. You could build a driver adjustable grill inlet into the nosepiece so you can monitor your radiator temps and tailor your cooling drag to the amount actually needed under the current conditions. Also check out the drag reduction mods used on the Bonneville Salt Flats speed record cars.

[Kilpuri]

Originally Posted by basjoos

How likely your car is to overheat with a grill block in place is strongly dependent on the outside air temps and also how hard you you are pushing your engine. You could build a driver adjustable grill inlet into the nosepiece so you can monitor your radiator temps and tailor your cooling drag to the amount actually needed under the current conditions. Also check out the drag reduction mods used on the Bonneville Salt Flats speed record cars.

I assume that the grill block does not affect due to the fact that actually a bit newer Civic (ED VTi) has hood which cover this shallow hole which we have actually already covered. There is huge grill on bumper which remains open.

The effect of the belly pan makes me wonder, because I do not have any experience of those. Outside temp is max. 25C and ofcourse we are pushing all the time on the max.

Actually I attached the pictures of the first step of the design change (nose piece). It sure is ugly, but hopefully some paint and fine tuning will help at least a bit! But who cares if it works. Feel free to comment! Note that on new desing there is huge additional cooling exit on the hood. Aerodynamically designed of course!

[The Toecutter]

I like the new nose. There's members here who would definately be able to make use of any information pertaining to how you built it and affixed it to the car!

Did you involve any books on aerodynamics in figuring out your design, or did you just go by looks and what you already knew about aerodynamics?