Impact of top speed from a functional rear diffuser?

[azynneo]

Is the top speed impacted by installing a rear functional diffuser?

[ryoma]

would it really affect you if your top speed is actually impacted? lol. I highly doubt you'll be driving over 120 MPH constantly to find out if the top speed is lower by 5 MPH in order for it to affect you. and if you do, good luck to you sir

[azynneo]

Originally Posted by ryoma

would it really affect you if your top speed is actually impacted? lol. I highly doubt you'll be driving over 120 MPH constantly to find out if the top speed is lower by 5 MPH in order for it to affect you. and if you do, good luck to you sir

Let me reword that , will I lose acceleration.

Also, what about front canards would those be overkill. I don't plan on getting a wing since I heard it's pretty much dead weight at the power were making.

[ryoma]

I highly doubt you will lose any noticeable acceleration, if any at all. though, you will gain more stability at speed. I am not a specialist in this area so if you want in depth info, wait until someone else chimes in like Velox (they make rear diffusers and front splitters). though, if you want to get canards, you might as well get a front splitter as well. makes everything go together if you want that race car look. as long as you think your car looks good, there's nothing wrong with getting a wing either. do what you want since it's your car and don't let others opinions affect you (that much) lol

[azynneo]

Originally Posted by ryoma

I highly doubt you will lose any noticeable acceleration, if any at all. though, you will gain more stability at speed. I am not a specialist in this area so if you want in depth info, wait until someone else chimes in like Velox (they make rear diffusers and front splitters). though, if you want to get canards, you might as well get a front splitter as well. makes everything go together if you want that race car look. as long as you think your car looks good, there's nothing wrong with getting a wing either. do what you want since it's your car and don't let others opinions affect you (that much) lol

I got my functional splitter, functional side skirts, carbon fiber hood, now all thats left is diffuser and wing LOL. Well I don't deny it looks good, but I was actually going function over that. Debating on underpanels as well..

[Gunman]

The effect of aero increases as speed increases, roughly a square function, ie 2x the speed equals 4x the downforce. Your drag penalty is going to be similar. The drag penalty for underbody areo is less than over body, so the canards, aka dive planes, would induce more drag than the diffuser (diffuser may even reduce it).

As for a wing working, it would depend on the design, and angle of attack. A properly designed wing could easily improve the downforce at autocross speeds, but would reduce top end due to drag. It all depends on what you are doing with the car. When I worked on the Viper GTLM design, we had a completely different wing for Lemans, since drag was a concern there, but not so much on US tracks.

[azynneo]

Originally Posted by Gunman

The effect of aero increases as speed increases, roughly a square function, ie 2x the speed equals 4x the downforce. Your drag penalty is going to be similar. The drag penalty for underbody areo is less than over body, so the canards, aka dive planes, would induce more drag than the diffuser (diffuser may even reduce it).

As for a wing working, it would depend on the design, and angle of attack. A properly designed wing could easily improve the downforce at autocross speeds, but would reduce top end due to drag. It all depends on what you are doing with the car. When I worked on the Viper GTLM design, we had a completely different wing for Lemans, since drag was a concern there, but not so much on US tracks.

what do you think of aluminum based side skirts?

[plucas]

Originally Posted by azynneo

Is the top speed impacted by installing a rear functional diffuser?

Yes if it works.

F = 0.5 * rho * v^2 * cd *A
That is the equation for the force of drag

Now if you talk about top speed, that includes the power for the car...

P = F * v

If you decrease drag, the force will be decreased which will decrease the power need to go a certain speed. It will also raise your top speed aerodynamically with no added additional power.

[azynneo]

Originally Posted by plucas

Yes if it works.

F = 0.5 * rho * v^2 * cd *A
That is the equation for the force of drag

Now if you talk about top speed, that includes the power for the car...

P = F * v

If you decrease drag, the force will be decreased which will decrease the power need to go a certain speed. It will also raise your top speed aerodynamically with no added additional power.

what about acceleration? does the car have to put in more effort to get to a certain speed quicker?

[totopo]

Originally Posted by azynneo

what about acceleration? does the car have to put in more effort to get to a certain speed quicker?

yes. The negative force, as people have said, is proportional to the speed^2. You can convert the force into power with the function provided from plucas.

I don't know what the actual values would look like, i'll maybe calculate/look it up later. For example say at x speed, the net effect of drag is 40hp, and lets say rolling resistance is another.... 10hp??? so at x speed you have to use 50hp of your ~170whp to not slow down. So you have 120hp left to accelerate.

Now lets say you increase your speed by 20%. The power requirement goes up by ^3 = ~72%. So now you need ~70hp for drag and... like i dunno 12 hp for rolling resistance. So now you are down to 90whp or so to accelerate.

So you can plot a graph of your drag+rolling resistance vs. speed and it should look exponential, with % increases in cd shifting the curve that % upwards. Or alternatively you can plot a graph of your hp-(drag+rolling resistance) for effective whp at any given speed and the point at which it crosses 0 is your theoretical top speed. and again, a % increase in your cd shifts that curve that % downwards.

edit: other considerations: don't forget you have a shifty transmission, not a CVT, so when you shift and are at the bottom of your rpm, your power could be considerably less than peak. Also, dyno hp is a terrible metric for this type of steady state questions because of the stupid necessarily ass-backwards way they work, so the car may actually put out more than 170hp steady state to the wheels, contrary to dyno whp measurements.

[Gunman]

Originally Posted by azynneo

what do you think of aluminum based side skirts?

Proper design will work, regardless of the material. Material is more a function of cost, and potential damage they may incur.

For pure function, parachute material worked great on indy cars back in the day

[stevesnj]

Do want to get to top speed faster?