Building a wide body Porsche 962 with my scout

[DeoreDX]

My son is on his 3rd year of scouting and our Pinewood Derby is coming up. Each year as he grows in age and capabilities we have built progressively more complex cars. He tells me what he wants. I sketch up a design I think that he is capable of completing which he approves and he does most of the work. His designs haven't been ideal with respect to weight placement but with good wheel prep and me setting up to rail ride for him he's always been competitive (2nd in his Den both years) and has always finished just outside of the top 3 (4th and 5th) out of a pack of 70 kids.

7yo version of a Lamborghini Huracan

8yo Pokemon car

I asked him what he wants to make this year. His response was "I want a Porsche 962 like they raced in LeMans". After looking at some other pinewood derby cars he's decided he wants to build a wide body car with fenders. I took some artwork of a 962 and scaled it and started working on the design. Here is the car I have sketched up for him right now.

The wheelbase is 4.75" and the rear wheel is about 7/8" away from the end. That is about as far as I could stretch it without the scale being thrown off. The way I have it layed out is I will use his block for the main body and a 2nd block for the fenders.

I don't expect to win with this design but I would like to get him in the top 3 of his Den again so he can compete at the pack level. That's 3 places out of 11 kids which I think it doable based on past performance of the kids in the den. Most of the stuff I've read about is geared towards wedge/ladder/flat designs so I'm not sure how much is applicable to this style of car.

One question I have is for the fenders. I'm assuming all of the rail riding techniques are still applicable (Negative camber on the rears, positive camber on front drive wheel, etc). Because of the wheel hub the fenders will be just inside of the wheels themselves so they can contact the center rail first. Should we trim the fenders back so it rides on a wheel or would fender riding do the same thing?

Right now I have a hole designed in the bottom to remove weight (Orange part). Will skinning the underside for airflow make an appreciable difference? The image above will be used as the remplate to rough cut his car then it's off to rasp/file/sanding to get the final shape. Once we have it 90% shaped and glued together I'm going to see where else I can remove material. Right now I'm guessing we will be lucky if we were at 3 ounces after all the material is removed. I just wanted to run the design by some derby experts to see if I'm missing anything I should be doing with the design.

 

[Thinkin'Bout Racin]

My son is on his 3rd year of scouting and our Pinewood Derby is coming up. Each year as he grows in age and capabilities we have built progressively more complex cars. He tells me what he wants. I sketch up a design I think that he is capable of completing which he approves and he does most of the work. His designs haven't been ideal with respect to weight placement but with good wheel prep and me setting up to rail ride for him he's always been competitive (2nd in his Den both years) and has always finished just outside of the top 3 (4th and 5th) out of a pack of 70 kids.

7yo version of a Lamborghini Huracan

8yo Pokemon car

I asked him what he wants to make this year. His response was "I want a Porsche 962 like they raced in LeMans". After looking at some other pinewood derby cars he's decided he wants to build a wide body car with fenders. I took some artwork of a 962 and scaled it and started working on the design. Here is the car I have sketched up for him right now.

The wheelbase is 4.75" and the rear wheel is about 7/8" away from the end. That is about as far as I could stretch it without the scale being thrown off. The way I have it layed out is I will use his block for the main body and a 2nd block for the fenders.

I don't expect to win with this design but I would like to get him in the top 3 of his Den again so he can compete at the pack level. That's 3 places out of 11 kids which I think it doable based on past performance of the kids in the den. Most of the stuff I've read about is geared towards wedge/ladder/flat designs so I'm not sure how much is applicable to this style of car.

One question I have is for the fenders. I'm assuming all of the rail riding techniques are still applicable (Negative camber on the rears, positive camber on front drive wheel, etc). Because of the wheel hub the fenders will be just inside of the wheels themselves so they can contact the center rail first. Should we trim the fenders back so it rides on a wheel or would fender riding do the same thing?

Right now I have a hole designed in the bottom to remove weight (Orange part). Will skinning the underside for airflow make an appreciable difference? The image above will be used as the remplate to rough cut his car then it's off to rasp/file/sanding to get the final shape. Once we have it 90% shaped and glued together I'm going to see where else I can remove material. Right now I'm guessing we will be lucky if we were at 3 ounces after all the material is removed. I just wanted to run the design by some derby experts to see if I'm missing anything I should be doing with the design.

Good for you helping to build a design he wants! Consider balsa for the fenders and for the rear wing if you desire to do it. Go deeper into the canopy and extend the pocket closer to the front axles. You really only need 1/4" to 3/8" behind front axles for strength. Most here only leave a 1/4" total for the front axles I would guess that with weight reduction on the underside as you have it drawn and maybe in front of the front wheels, that you could be at or just under two ounces for the body.

 

[Corduroy Racing]

"One question I have is for the fenders. I'm assuming all of the rail riding techniques are still applicable (Negative camber on the rears, positive camber on front drive wheel, etc). Because of the wheel hub the fenders will be just inside of the wheels themselves so they can contact the center rail first. Should we trim the fenders back so it rides on a wheel or would fender riding do the same thing?"

Nice looking cars! Yes, you should trim the fenders --- on all four wheels. Only the DFW wheel should make contact with the rail.

Good luck!

 

[DeoreDX]

Rough cut it last night on the band saw. Used the belt sander to get the saw marks out. Still need to sand the wheel wells to get them to the proper dimensions. Total weight with wheels are tires was 102 grams (3.6 ounces, scale is only accurate to +/- 2 grams). 14g for wheels and nails. 30g for the fenders. 58g for the main body. We have a lot of material to remove yet as we haven't done any of the shaping yet.

I'd like to try to find some Balsa. I think I could shave at least 20g from the fenders with Balsa instead of the Pine. Couldn't find anything thicker than 1/8" Balsa at Hobby Lobby. Might have to laminate some together or find an alternative source. Will 1/2" thick Balsa cut on a band saw? I've only worked with thinner balsa and just used a razor knife to cut it as as it just splinters under a saw.

Here is where I plan on removing more material. I make the cut closer to the axles because I thought it would look better if the wheel wells were closed. I'll have to figure out if my scout is better with my dremel or with a hammer and chisel and let him to go town removing material. Not sure I trust him with a router just yet. I have 3oz of cylindrical tungsten weights. I plan on putting them towards the rear on the underside where the green dots are to get the car to 5oz.

 

[B_Regal Racing]

This is where I get Balsa from. I found a stick that would work for your application. $2.30

http://shop.balsausa.com/product_p/147.htm

 

[GravityX]

Looking at your initial mockup, I would extend the red markup, on the fenders, to the very front of the car to provide rail clearance, in front of the forward wheels. You don't want the fenders rubbing the rail at any point. Hollow out the body a little more if you can. I have seen a technique on YouTube where a guy hollows out a wooden car body, very similar to what you are doing here. This should help reduce the body weight so you can get a larger push from more tungsten at the rear of the car. Good luck.

 

[DeoreDX]

Looking at your initial mockup, I would extend the red markup, on the fenders, to the very front of the car to provide rail clearance, in front of the forward wheels. You don't want the fenders rubbing the rail at any point. Hollow out the body a little more if you can. I have seen a technique on YouTube where a guy hollows out a wooden car body, very similar to what you are doing here. This should help reduce the body weight so you can get a larger push from more tungsten at the rear of the car. Good luck.

That Youtube video was great. Never thought of using my drill press and router bits and I like the way he controlled the depth and used the rubber ball so he doesn't blow through the shell.

Son rounded out the cockpit last night and we built a second set of fenders out of balsa. He probably could have rounded it more but I think he got impatient with the process of rasp/file. Tried using the belt sander and a dremel but he couldn't use them very well and was just making gouged in the wood. Going to use some filler to smooth out the transition between the fender and hide the wheel well gap then we're sanding everything down. Balsa fenders knocked .63 ounces of the weight of the body. After rounding off the cockpit and changing to Balsa fenders we've gone from 3.1oz for the body to 2.25oz. I think I can get it below 2oz now and be able to use all 3oz of Tungsten we have.

 

[DeoreDX]

Son shaped the cockpit and smoothed out a lot of the edges. I came in and did some Bondo work for him to fill all of his file marks and he sanded that down. Two coats of high build primer. He cut out the spoiler and sanded the bevel in it but I cut out and fit the side parts of the spoiler as cutting those out required getting a little too close to the blade of the band saw for my comfort for a 9yo. Then a coat of gloss white. First coat looked like crap(gloss surface had cracks in the gloss layer) but my son was happy with it. After some urging he sanded it down and put on a second coat that looks much better. How he has to do the detail work. we have a vinyl cutter we can cut out most of the graphics. We will probably paint the cockpit.

 

[KyleBCostco]

Damn that is awesome!! Great job on both you and your son's part! Looks amazing!

 

[Vitamin K]

Mmmm, so smooth, so clean. Love it.

 

[Reecedad]

Very nice

 

[SuperSlow]

Yea very koool! Good job guys!
My club has a best design award, im sure this would take it hands down.

 

[DeoreDX]

Final touches completed yesterday and I help set up the track for the Friday evening test session and we ran the car several times. 3 of us who set up the track let our kids run their cars v. each other (Cub masters's two ids cars and a Tiger leader son's car). My son's came in last every time. I don't know the length but the track is long and we were running high 3.9's to low 4.0s. Other cars were running 3.8s. He were consistently right on their bumpers but always finished last. Son was disappointed and we went back home and took the wheels off to check everything over to make sure there wasn't and rubing.

Everything looked just fine but the wheels just didn't feel like they were spinning as freely as the wheels on his other two older cars. Took the dremel out with polishing compound and polished the axels. Before we stopped at 3k. Normally after I apply the graphite the wheel feels noticeably better but this time when applying graphite it never felt any better than without graphite. I couldn't find our hobby graphite/moly blend so I just gave my kid some stuff I found in my tool box I have no idea where it came from. Looked closer at the label and it is Graphite and Silica blend. It was late and I decided to just clean the wheels of old graphite and borrow some graphite from someone in the pack.

The format is round robin with everyone's car running 4 races once in each lane. 3 points for 1st, 2 for 2nd, 1 for 3rd. Pairings and race order is done randomly with software. Son's car went 4/4 winning 1st place in his den. The 2nd place kid in the den was one of the cars consistently beating him the night before at the testing. His and 2nd place cars ran neck and neck both times they faced each other. Both cars ran 3.8xx consistently in all 4 lanes My son's best was 3.83 and the 2nd place car's best was 3.810 both in the far left fast lane. Slow lane saw 3.86x's. The 2nd place car actually ran faster in a couple of the lanes but in the head to head matchups my son got the better lane placement.

The 3 cars he was testing against, One was the Weblo overall winner, one was the Tiger overall winner, and the other was the car he just beat out for his Den's championship. Turns out his car wasn't as bad as he thought as he was racing 3 of the fastest cars out of 60+ cars.

Winning the Den got him into the Bear finals. My son's car had 3 1sts and a 2nd. The 2nd place car from our Den beat him in the last race having the favorable lane in the head to head. On to the pack championship.

Won his first race but finished 3rd in the 2nd. He had an unfavorable lane and was in the same heat as the eventual #1 and #2 who were in the two faster lens. Then in his 3rd race he lost by 0.006 to a car in the fast outside left lane. He wasn't mathematically eliminated from a top 3 yet and the chips fell just right and he took the last race to get into a 4 way tie for 3rd place. There was a 2 way tie for 1st, both of the cub master's kids from the night before. My son dominated the 4 way race off for 3rd place sweeping all 4 races.

1-2 cars ran 4 times and it was 2-2. We completed a new timing system for the track earlier in the week but we didn't have time to update all of the spreadsheets to do time instead of giving points for places. Next year we plan on averaging all 4 times for places instead of the format we do now which is points for placing. Since it was just two cars we ran a 2 more runs in alternating lanes and average the time between the two. The 2nd place car from our Den too 1st overall by 0.001s. The 1-2-3 cars pretty much ran neck and neck all day. My son's car would always be a car length behind in most races when they make the turn at the bottom but would always pass the other cars at the end right in front of the finish line.

This was his first big trophy and he was quite excited. We put a lot of work into the car and he was hoping to get one of the design trophies but since he got a big one he didn't qualify for the others.