How will you go faster?

General engine tech -- Drag Racing to Circle Track

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David Redszus
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Re: How will you go faster?

Post by David Redszus »

Ken_Parkman wrote: Thu Dec 01, 2022 9:57 pm
David Redszus wrote: Wed Nov 30, 2022 11:29 pm
HP = Mass x Distance / Time
if:
Mass = 3000 lbs
Distance = 1320 ft
Time = 12 sec, then:

HP = 3000lbs x 1320ft /12sec = 330,000 lbft/s = 600HP
Horsepower is a valid indicator of how much power is needed for a 3000lb car, to cover 1320 ft, in 12 s.
But it does not tell us anything about acceleration in each gear, shift points, traction limits or gear selection.
Sorry David this is not the physics. Power = work/time. Above you have the power to lift 3000 lbs 1320 ft strait up in 12 sec.

You really might make a lot of 12 second car owners very happy telling them they have 600 hp, but unfortunately not.
Yes, you are right. My bad. :(

While the equation is correct, (force x distance is work), the input for mass is incorrect.
I based the calc on dragging 3000 lbs for 1320 ft in 12s. Actually, I should have used the rolling force instead of the dragging force. Since the required rolling force is much less, so is the power required.
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Re: How will you go faster?

Post by David Redszus »

My thanks to Ken Parkman for his eagle eye and catching my calculation error.
A careful examination of posted information is what maintains a high stanard of
accuracy and technical fact, compared to mere unfounded opinion.

Thanks Ken
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Re: How will you go faster?

Post by juuhanaa »

My colleague drives an old Volvo. I did a small scale Volvo 740 wind tunnel test and noticed that there could be less drag when reversing, but I don't think that alone will help him get to work faster. Perhaps some calculation and back to back testing is also needed. :-k

Screenshot_20221202-192120.jpg


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Re: How will you go faster?

Post by 289nate »

juuhanaa wrote: Fri Dec 02, 2022 2:28 pm My colleague drives an old Volvo. I did a small scale Volvo 740 wind tunnel test and noticed that there could be less drag when reversing, but I don't think that alone will help him get to work faster. Perhaps some calculation and back to back testing is also needed. :-k


Screenshot_20221202-192120.jpg



-juhana
Lol. Stickers will also make your car faster.
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Re: How will you go faster?

Post by juuhanaa »

289nate wrote: Fri Dec 02, 2022 11:27 pm
juuhanaa wrote: Fri Dec 02, 2022 2:28 pm My colleague drives an old Volvo. I did a small scale Volvo 740 wind tunnel test and noticed that there could be less drag when reversing, but I don't think that alone will help him get to work faster. Perhaps some calculation and back to back testing is also needed. :-k


Screenshot_20221202-192120.jpg



-juhana
Lol. Stickers will also make your car faster.
You have any 3D golfball stickers for sale?
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Re: How will you go faster?

Post by Firedome8 »

Speaking of area under the curve would it be correct to say that the horsepower at the shift point should equal the hp after the shift.. say you shift from 1 to 2 at 6500rpm and your hp is 300 at that point in the curve and after the shift your rpm is 5000 and the hp is 300 would that maximize the area..just thinking..
A good test is worth a thousand opinions.
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Re: How will you go faster?

Post by BobbyB »

David Redszus wrote: Tue Nov 15, 2022 12:33 pm It might be very interesting to examine what makes a drag car perform quicker and by how much.

Obviously, the engine size and state of tune is a starting point.
But several other factors will influence strip times.
Torque curve
Ambient air temperature
Ambient barometer
Humidity
Fuel energy
Air/Fuel ratio
Tire diameter
Tire traction
Rear end ratio
Gear set ratios
Torque converter
Weight
Frontal area
Drag Coefficient

How much does each factor contribute to ET?
Suppose we were to change each parameter by +-5%.

Which will produce the best bang for the buck?
OK Dave, after 20 pages of stuff about torque vs HP ... Can you address what can practically be done to a street/ strip hot rod that must handle curves very well and stop very well using 4 wheel disks...what can we do after sorting the engine and choosing the stickiest tires that are not drag radials?
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Re: How will you go faster?

Post by David Redszus »

How much does each factor contribute to ET?
Suppose we were to change each parameter by +-5%.

Which will produce the best bang for the buck?
OK Dave, after 20 pages of stuff about torque vs HP ... Can you address what can practically be done to a street/ strip hot rod that must handle curves very well and stop very well using 4 wheel disks...what can we do after sorting the engine and choosing the stickiest tires that are not drag radials?
This thread was never intended to provide optimization direction. It was intended to evaluate the contribution of various parameters to performance overall. It did not go that way. Personal experiences trumped quantitive analysis.

Initially, I constructed a spreadsheet that would calculate the performance contribution of each listed variable. And it does. Up to a point.

There is a big difference in launch methodology; automatics with torque converters vs stick shift with slipping clutches. They require separate analysis approaches and could benefit from different torque curves.

Setting that issue aside, I proceeded by constructing an analysis using a furnished torque curve and selected gearing for a five speed stick shift. After the issues concerning launch, weight is a very significant variable.
Using a weight range from 2000lbs to 4800lbs, I calculated 60 ft and 1320 ft times and speeds. Should be a simple linear curve, I thought.

To my surprise, I found data curves with peaks and valleys in performance, even with evenly spaced weight steps.
I am perplexed as to why that could be possible. Now I have retreated to the computer cave to review all the equations, data entry and calculations. Something is wrong; or is it?

As far as braking goes, that is a much easier problem set to solve; there are fewer variables.
We have the calcs for any vehicle brake system and performance optimization. Let me know if you are interested. Most racers don't care about brakes; they only slow you down. :(
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Re: How will you go faster?

Post by BobbyB »

David Redszus wrote: Wed Dec 07, 2022 1:20 pm
How much does each factor contribute to ET?
Suppose we were to change each parameter by +-5%.

Which will produce the best bang for the buck?
OK Dave, after 20 pages of stuff about torque vs HP ... Can you address what can practically be done to a street/ strip hot rod that must handle curves very well and stop very well using 4 wheel disks...what can we do after sorting the engine and choosing the stickiest tires that are not drag radials?
This thread was never intended to provide optimization direction. It was intended to evaluate the contribution of various parameters to performance overall. It did not go that way. Personal experiences trumped quantitive analysis.

Initially, I constructed a spreadsheet that would calculate the performance contribution of each listed variable. And it does. Up to a point.

There is a big difference in launch methodology; automatics with torque converters vs stick shift with slipping clutches. They require separate analysis approaches and could benefit from different torque curves.

Setting that issue aside, I proceeded by constructing an analysis using a furnished torque curve and selected gearing for a five speed stick shift. After the issues concerning launch, weight is a very significant variable.
Using a weight range from 2000lbs to 4800lbs, I calculated 60 ft and 1320 ft times and speeds. Should be a simple linear curve, I thought.

To my surprise, I found data curves with peaks and valleys in performance, even with evenly spaced weight steps.
I am perplexed as to why that could be possible. Now I have retreated to the computer cave to review all the equations, data entry and calculations. Something is wrong; or is it?

As far as braking goes, that is a much easier problem set to solve; there are fewer variables.
We have the calcs for any vehicle brake system and performance optimization. Let me know if you are interested. Most racers don't care about brakes; they only slow you down. :(
I would like to learn more about your brake stuff. Also, what can we do to reduce rolling resistance...how much does rolling resistance matter to acceleration performance?
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Re: How will you go faster?

Post by David Redszus »

...how much does rolling resistance matter to acceleration performance?
The contributing components to rolling resistance are: velocity, tire pressure, tire rolling diameter,
and temperature. Assuming hard concrete, and not soft sand or dirt, velocity is the most important
while the others are relatively minor.

The rolling resistance factor f, is given by the following equation.

f = 0.01 ( 1 + MPH/100)

so at 100 mph, f = 0.02.

The resistance factor is multiplied by the weight of the vehicle:
F (lbs) = 0.02 x 3000 lbs = 60lbs.

Obviously, the rolling resistance force will be increased by increased vehicle weight and higher speeds.
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