How do you keep the C3 from getting light above 120mph?
05-20-2017, 05:08 PM
#261
Le Mans Master
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Before too much is misread into the matter of engine weights...
Thanks to its location behind rather than above the front axle, C3 engine weight is split roughly 85% / 15% front to rear. An otherwise iron blocked BBC with aluminum heads, intake and water pump only weighs approx. 90# more than an L82 SBC, for example, which translates into an increase on the front axle of about 77# with the remaining 13# on the rear. This is on the order of ~1% difference in distribution to the front, and an all-aluminum BBC would actually tip the scales in the other direction. Not exactly the equivalent of having dropped a supermassive black hole in under the hood. Just saying.
Now, back to our regular programming...
Thanks to its location behind rather than above the front axle, C3 engine weight is split roughly 85% / 15% front to rear. An otherwise iron blocked BBC with aluminum heads, intake and water pump only weighs approx. 90# more than an L82 SBC, for example, which translates into an increase on the front axle of about 77# with the remaining 13# on the rear. This is on the order of ~1% difference in distribution to the front, and an all-aluminum BBC would actually tip the scales in the other direction. Not exactly the equivalent of having dropped a supermassive black hole in under the hood. Just saying.
Now, back to our regular programming...
05-20-2017, 06:53 PM
#262
Le Mans Master
I agree,. over the years people have said the big block cars didn't handle as well I always felt that was overblown but still it has to have some effect.
05-21-2017, 07:03 AM
#263
Melting Slicks
I have a tough time accepting that the Le Mans cars had that tiny lip on the end of the rear deck acting as a spoiler at 200mph?
Which brings me wondering what removing the rear window would do.
Would it act as a diffuser, or improve the aeros in some other way?
Those that have a removable rear claim the car is much quieter.
Anyone have some experience w/this?
R
Which brings me wondering what removing the rear window would do.
Would it act as a diffuser, or improve the aeros in some other way?
Those that have a removable rear claim the car is much quieter.
Anyone have some experience w/this?
R
Also one year at RA [HPDE] they made me run with the top up [6t8 roadster], to eliminate the parachute effect of canvas top we cut out the rear window, it was shot and couldn't see through it anyway, but just having the top up slowed me down 10mph. T
05-21-2017, 11:28 PM
#264
Drifting
Member Since: Aug 2015
Location: NSW, Australia
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C3 of Year Finalist (track prepared) 2019
I assumed his response was aimed at those saying it was too dangerous to travel at high speeds, not at you and the other useful responders to the thread, but I could be mistaken.
05-23-2017, 12:43 AM
#265
Pro
05-23-2017, 06:27 AM
#266
Drifting
05-23-2017, 01:22 PM
#267
Melting Slicks
See the little fins on the top of the Sundowner car that run the length of the roof. They are for stability.
Years ago I was Crew Chiefing for a customer of mine's land speed bike. A friend of his was pitted next to him with the world's fastest stock bodied VW Bug. The friend heard me trying to explain the importance of aerodynamics to my customer. He told a story of how his car was uncontrollable at speed. It was all over the track. He took the car to a aerodynamics engineer and he put the two little fins on the length of the roof on the Bug. He said it completely transformed the Bug. It was now stable at very high speeds.
The fins keep the air running straight along the roof instead of dropping of the sides haphazardly and making the car move around.
The lead in the Sundowner serves two purposes. One is to keep it from going airbound, but the other is for traction. Running on the salt is not like running on any type of pavement racing. Traction is not as good, especially with the skinny tires, and you run for long distances as compared to a drag strip or the straight on a road race track, so the weight doesn't hurt you for acceleration as bad. Except for maybe balancing a car for a race course, the extra weight would hurt handling and acceleration in most other forms of racing.
Mike
Years ago I was Crew Chiefing for a customer of mine's land speed bike. A friend of his was pitted next to him with the world's fastest stock bodied VW Bug. The friend heard me trying to explain the importance of aerodynamics to my customer. He told a story of how his car was uncontrollable at speed. It was all over the track. He took the car to a aerodynamics engineer and he put the two little fins on the length of the roof on the Bug. He said it completely transformed the Bug. It was now stable at very high speeds.
The fins keep the air running straight along the roof instead of dropping of the sides haphazardly and making the car move around.
The lead in the Sundowner serves two purposes. One is to keep it from going airbound, but the other is for traction. Running on the salt is not like running on any type of pavement racing. Traction is not as good, especially with the skinny tires, and you run for long distances as compared to a drag strip or the straight on a road race track, so the weight doesn't hurt you for acceleration as bad. Except for maybe balancing a car for a race course, the extra weight would hurt handling and acceleration in most other forms of racing.
Mike
Last edited by v2racing; 05-23-2017 at 05:06 PM.
05-23-2017, 02:56 PM
#268
Le Mans Master
05-23-2017, 04:09 PM
#269
Le Mans Master
Quite the opposite. The fastback bodystyle results in improved laminar flow towards the back of the car, whereas the notchback of the early models resulted in flow separation at the end of the rooftop. You don't want that because then you have a low pressure region that begins above the rear of the vehicle instead of behind it. Note the airflow when they put the smoke right behind the rear window on this C3 in a windtunnel at around 2:45:
Not good for either aero drag or downforce.
The best thing to do is look at the racecars and how the bodystyle changed towards the fastback in the later years. It happened for a reason.
Not good for either aero drag or downforce.
The best thing to do is look at the racecars and how the bodystyle changed towards the fastback in the later years. It happened for a reason.
Separation creates drag. So with attatched flow you will get better lift and less drag. If a spoiler is employed THEN you get down force with flow over the spoiler and also drag as the air separates aft of the spoiler. The whole reason spoilers need to be used is to counteract lift. Then the spoiler needs to be tall enough to reach the area of flow, that may be much higher off the body of the car due to some separation. If the separation includes burbling (notch back design) then the spoiler would have to be quite tall to reach the region of flowing air and would be more like a flying wing type design, similar to an elevator on an aircraft.
Race cars constantly have to balance drag with lift as does every car now. Less drag on cars makes for a better lifting body as well due to the lack of flow separation. So good in fact that Nascar (at least, others may as well) uses spoilers on their cars to keep them from getting airborne due to lift in a loss of control situation.
Last edited by REELAV8R; 05-23-2017 at 04:10 PM.
