Another Letter to the CRB on H Production Parity

Gary Wittman":2sko123t said:
I originally thought the SIR was a good way to help equalize cars in any particular class. Unfortunately, it just about killed GTL. I think the main reason was that many people just did not like the idea and just dropped out without giving it a chance or tried it and didn't like what they had to do to make it work.

If I had to do something to slow my car down and had various options, I would elect to reduce valve lift. One way to do that is changing the cam. Typically, cams are not that difficult to R & R and they can be reground or just replaced with a new one. I think cost would be comparable or less than an SIR and nothing new would be added to the engine compartment. That would eliminate having to fab up new components for installation. Dyno time would probably be needed but that is the norm for anyone that is serious about going fast with a new engine anyway.
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Having given it some thought cam lift does not sound that bad... Much less intrusive than compression or other internal items, and way less r&d than an SIR/plate. Many of the popular cars have multiple profiles to choose from off the shelf, and the regrind is always an option. I still favor weight from a cost standpoint, but this could be a reasonable alternative.
 
Jason@SportsCar":1awv3c3w said:
Having given it some thought cam lift does not sound that bad... Much less intrusive than compression or other internal items, and way less r&d than an SIR/plate. Many of the popular cars have multiple profiles to choose from off the shelf, and the regrind is always an option. I still favor weight from a cost standpoint, but this could be a reasonable alternative.
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Some LP prod car engines can't fully optimize the maximum cam lift they are given now.
 
Well - a 100 lb delta starting in February. While it's been a long time since i actually did any real engineering... First order approximation (F=MA) gives a 4.4% change in relative acceleration between the "tin tops" and the roadsters. Or another first order approximation based on the formula for kinetic energy (1/2mvv) and the 70 lb change indicates that in the time that the original weight tin top accelerated to 90 MPH it will now be down to 88 MPH. Relative cornering speeds should be affected along with achievable top speed, but much harder to easily approximate those impacts. Anyway, seems like a pretty significant change and should make for an interesting set of possibilities - Anyone know what Steve Sargis is doing with his Spitfire? :)
 
I guess they chose to use Jason Stine's letter which asks for the weight to be adjusted on the Honda instead of mine which asks for straight line performance to be adjusted on all of the faster cars in H. Weight changes don't get the job done. The Honda CRX already had 275 lbs added to it without appreciable effect. Weight changes only create a situation where the faster cars will have more tire management issues and the lighter cars won't be able to take any weight off anyway.

I'm just a dumb mechanical engineer, but maybe stevn37 can enlighten me as to how adding weight affects achievable top speed, especially at a track like Daytona, because I just don't see it.
 
Ron Bartell":192pl434 said:
I guess they chose to use Jason Stine's letter which asks for the weight to be adjusted on the Honda instead of mine which asks for straight line performance to be adjusted on all of the faster cars in H. Weight changes don't get the job done. The Honda CRX already had 275 lbs added to it without appreciable effect. Weight changes only create a situation where the faster cars will have more tire management issues and the lighter cars won't be able to take any weight off anyway.

I'm just a dumb mechanical engineer, but maybe stevn37 can enlighten me as to how adding weight affects achievable top speed, especially at a track like Daytona, because I just don't see it.
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I don't think weight limits top speed at tracks where cars are rpm/drag limited, but it does impact how long it takes to get there and how long you can spend there. If corner exit and acceleration is slowed you will get to that top speed later, and weight will force you to brake sooner. At tracks like MRLS I can't hit my top speed, so this weight slows the lap time.
 
I'm just a dumb mechanical engineer, but maybe stevn37 can enlighten me as to how adding weight affects achievable top speed, especially at a track like Daytona, because I just don't see it.[/quote]

Well, Wikipedia does a pretty good job of explaining why increasing weight will result in slower top speed. http://en.wikipedia.org/wiki/Rolling_resistance . Since rolling resistance is a function of the normal force (i.e., weight in this case), then increasing weight will increase rolling resistance, which in turn will result in a lower top speed, assuming power remains the same, of course

rolling resistance is defined by the following equation:[5]

\ F = C_{rr} N
where
F is the rolling resistance force,
C_{rr} is the dimensionless rolling resistance coefficient or coefficient of rolling friction (CRF), and
N is the normal force, the force perpendicular to the surface on which the wheel is rolling.

Since the coefficient of rolling resistance is most likely different for different cars and may take significant effort to determine, I didn't try to quantify it in my earlier comment. Besides, it may not even have a material impact, but theoretically will have an impact.

If you're interested, one way to determine the coefficient is to take a fish scale and use it to determine the steady state force required to keep the car rolling. Then knowing F and N (the weight), then one can calculate C. :) I'm planning to do this on my CRX in a few days. I'm sure this is part of everyone's typical development effort. :)
 
Jason@SportsCar":yhrxy2iz said:
I don't think weight limits top speed at tracks where cars are rpm/drag limited, but it does impact how long it takes to get there and how long you can spend there. If corner exit and acceleration is slowed you will get to that top speed later, and weight will force you to brake sooner. At tracks like MRLS I can't hit my top speed, so this weight slows the lap time.
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Jason - I get the whole F=MA thing, and realize it will take a little longer to get to the same top speed as before. Just don't think it will slow you guys down very much if you still have the same advantage on the straights, especially at Daytona.

stevn37":yhrxy2iz said:
..........rolling resistance.........
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stevn37 - Rolling resistance?? Really? Mounting a GoPro in the airstream slows the car down too, but I don't think it will help the Spridgets change places with the faster tin-tops.

I don't mean to pick on you, stevn37, but our competition board keeps doing the same thing and expecting different results. Over time, with the combination of weight being added to the Honda and taken off of the Spridget there has been almost a 400 lbs difference, and it has had very little effect on the problem. We now have another 100 lbs change. I can't help but think it won't be different this time either.
 
Topeka needs to invest in good simulator software (e.g., Bosch LapSim) to make these decisions more quantitative and less thumb in the air.

To see someone trotting out F=MA in describing a lap time is laughable.

-Kyle
 
The weight is not my concern at Daytona, its the big whole I have to punch in the air for a long time. At RA I lost about 4mph and 2secs a lap without a draft, going to be worse at Daytona. My car is stronger on mid speed tracks like MRLS, where I don't spend much time in 5th gear.

I think if you look back at RA results you will see that the Honda has gotten slower since it picked up weight.

Ron Bartell":2qagmcdv said:
Jason@SportsCar":2qagmcdv said:
I don't think weight limits top speed at tracks where cars are rpm/drag limited, but it does impact how long it takes to get there and how long you can spend there. If corner exit and acceleration is slowed you will get to that top speed later, and weight will force you to brake sooner. At tracks like MRLS I can't hit my top speed, so this weight slows the lap time.
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Jason - I get the whole F=MA thing, and realize it will take a little longer to get to the same top speed as before. Just don't think it will slow you guys down very much if you still have the same advantage on the straights, especially at Daytona.

stevn37":2qagmcdv said:
..........rolling resistance.........
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stevn37 - Rolling resistance?? Really? Mounting a GoPro in the airstream slows the car down too, but I don't think it will help the Spridgets change places with the faster tin-tops.

I don't mean to pick on you, stevn37, but our competition board keeps doing the same thing and expecting different results. Over time, with the combination of weight being added to the Honda and taken off of the Spridget there has been almost a 400 lbs difference, and it has had very little effect on the problem. We now have another 100 lbs change. I can't help but think it won't be different this time either.
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The SM guys like the fish scale. You are going to do that? I thought you had people for that? :wink:


stevn37":3adqjdf5 said:
Well, Wikipedia does a pretty good job of explaining why increasing weight will result in slower top speed. http://en.wikipedia.org/wiki/Rolling_resistance . Since rolling resistance is a function of the normal force (i.e., weight in this case), then increasing weight will increase rolling resistance, which in turn will result in a lower top speed, assuming power remains the same, of course

rolling resistance is defined by the following equation:[5]

\ F = C_{rr} N
where
F is the rolling resistance force,
C_{rr} is the dimensionless rolling resistance coefficient or coefficient of rolling friction (CRF), and
N is the normal force, the force perpendicular to the surface on which the wheel is rolling.

Since the coefficient of rolling resistance is most likely different for different cars and may take significant effort to determine, I didn't try to quantify it in my earlier comment. Besides, it may not even have a material impact, but theoretically will have an impact.

If you're interested, one way to determine the coefficient is to take a fish scale and use it to determine the steady state force required to keep the car rolling. Then knowing F and N (the weight), then one can calculate C. :) I'm planning to do this on my CRX in a few days. I'm sure this is part of everyone's typical development effort. :)
Click to expand...
 
Hey - not feeling picked on at all regarding rolling resistance. :) Didn't I say something like it's probably not a material impact? But you can't refute the engineering reality of it - unless you're one of those guys that thinks the sun revolves around the earth. :) Regardless, I think it is important in these kind of forums to try to keep things focused on data or engineering based discussions, which is certainly what I was trying to do. Hopefully that helps us to avoid the inevitable mean-spirited comments.

Personally, I was quite disappointed with the CRB action to add weight to the tin tops and had spoken to some friends just a little bit ago (before the CRB decision came out) that I thought the better solution would be to speed up the roadsters. Who wants to go slower on the race track? :) However, I don't have good personal insight on what would be the optimal approach to that, although my somewhat myopic view on that would be to give more carburetor (weber?) to the Spridgets.

Jason - regarding fish scale checking... you might be surprised at the things I do on my car. I actually torqued the lug bolts just the other day. :)
 
stevn37":3bygfc3m said:
although my somewhat myopic view on that would be to give more carburetor (weber?) to the Spridgets.

:)
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I think raising the compression ratio, say 1 point to 12.0 to 1, would be a better cost effective, and net result solution.
 
37, Dont be put off arguing physics. You are correct that more weight slows the car down, evry time, other than maybe at the salt flats/ice racing, where traction is more PSI related.
The issue is that weight moves times at different track in differing amounts.
50# wil slow the VW down about .5-.8 sec @ Daytona. and around the same @ Sebring.
The 275 # added to the Honda slowed that car down about 2sec @ Sebring.
I believe that our Board did a good job slowing the cars down to the "base car" that should(IMHO) be the 1275. I think that PROD's long term best interest is to keep those LBC cars running among us.
Adding some reward weight to the Hondas seems fair also, a they have proven to outperform the engineering expectations.
Keeping the field tight by making small weight adjustments annually makes a lot of sense and gives us little guys hope for continued tight fun racing .
Keep the class alive and competitive please.
 
Acme Speed Shop":pbpv6yic said:
I think raising the compression ratio, say 1 point to 12.0 to 1, would be a better cost effective, and net result solution.
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+1 tothat hap...another point of compression would be easiest solution.

Weight - now i have to go chop 40+ lbs out of my car (not sure where that's coming from)
Carbs - expensive to go to dual webers
cam - development cost for more lift

aaron
 
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