1/10 mile clay track, box stock, flat head, purple plate, gear ratio question?

Bentleysautoparts

New member
Hello everyone, looking for your thoughts. 3 races into my 6 year olds racing career. His last race he really picked up some speed. He was about 4 mph, and roughly .5 second off from the leaders. It looked to me like he was coming out of the corners way faster then the others, but seemed to be slowing up at the end of the straight away. I have a thought that he has too much gear, that I cant shake. Right now he has a 11 TOOTH DRIVE on a single disc bully clutch, with a 72 TOOTH rear gear. Engine is a 5hp Briggs flat head methanol purple plate. older chassis, rocker kart, Burris 22's. 325 lb total weight. Track is a 1/10 mile clay track, low grip, slight banking. Pretty much, do you guys think that the 11-72 is to much gear, or should I let him tone his skills more before I Start dipping into the thought I have. I'm just worried because I don't want to hold him back, if he could be doing better. Also I don't know what rpm hes running, since we don't have a micron, and I also do not know what rpm his motor produces the most hp. Any thoughts would help, since everyone on here seems very knowledgeable. thanks
 
Your out to lunch with the gearing especially with a purple plate, you really need to get a tach even if it's just a cheap digitron that only reads R.P.M.
It's tough to say with just going off info listed but If it's close to a 1/10 mile you should NOT be any lower than a 12 front and any higher than a 64ish rear gear depending on how much momentum it carries it would not surprise me if a 13 front was the ticket.
Which track is it ? Do you know what gearing the SR Flatheads unrestricted are on ?
 

Bentleysautoparts

New member
racing promotor, Im not sure what the sr unrestricted are on. the track is Bartlett Bridge in lyman maine. Im pretty sure these purple plate kids are a lot of momentum. Im pretty sure they dont let off the whole way around the track. I talked to one guy, and im pretty sure he said they run a 70, but i never asked him about the drive. im thinking your correct, since his mph is much lower. I will check into that tach, thanks for your reply. I have someone in the next class up I can ask, but they run a l0206 engine, and are I think 350lb weight.
 

Bentleysautoparts

New member
Also, I think the reason for less gear on such a small track, is to stay in the power band. More rpm from more gear doesnt necessarily mean faster if its above the hp range. Am I correct on that?
 

flattop1

Dawg 89
Also, I think the reason for less gear on such a small track, is to stay in the power band. More rpm from more gear doesnt necessarily mean faster if its above the hp range. Am I correct on that?
Yes thats why it gave out at the end of the straightaway . Ran out of oomph .
 

OVALTECH1

Premium User
As said above in a plate it’s hard to build heat anyhow so unless your really off on the tuneup the tach itself will get you by. They have 30 dollar tachs on eBay that will give you a high rpm recall that will get you pointed in the right direction.
 
Also, I think the reason for less gear on such a small track, is to stay in the power band. More rpm from more gear doesnt necessarily mean faster if its above the hp range. Am I correct on that?
YES your correct on that, And when you get to far off you get gear bound then it's even worse, And with the 11/72 your big time gear bound.
 

1fasttiller

Member
Jump on Amazon and look at the tiny tach! $20 all day and works great on a kids kart. You will want that purple plate FH turning no more than 6000rpm. Try to stay 5800.
 

alvin l nunley

Premium User
Also, I think the reason for less gear on such a small track, is to stay in the power band. More rpm from more gear doesnt necessarily mean faster if its above the hp range. Am I correct on that?
In Sprint racing, adding one tooth to the axle means you have to pick up 200 RPM to be going the same speed. With the ratios you are running, if you added tooth to the axle, you have to pick up 100 RPM to be going the same speed. At exactly, but close. So try this; take one tooth off the axle, if you lose less than 100 RPM at the end of the straight, you're going faster.
That's why you need a tack!!
 

flattop1

Dawg 89
Your out to lunch with the gearing especially with a purple plate, you really need to get a tach even if it's just a cheap digitron that only reads R.P.M.
It's tough to say with just going off info listed but If it's close to a 1/10 mile you should NOT be any lower than a 12 front and any higher than a 64ish rear gear depending on how much momentum it carries it would not surprise me if a 13 front was the ticket.
Which track is it ? Do you know what gearing the SR Flatheads unrestricted are on ?
I'm on board with this . We ran 11 /72-82 on a 1/10 th mile track . Racing a modified flathead turning 7300- 8200 rpm .
Keep taking gear off till your rpms or lap times quit falling .
 
Im ordering up a 12 right now. That should be in by this weekend. i will let everyone know if it made it better..
We ran the purple plate class back in 2006 on a 1/10th dirt oval. We ran 12 x 63,64,65 depending on the track conditions. We only ran during the days. I will say this.. Get your 6 year old in a packing lot on days off to keep his foot into it. Good luck and kick ass!
 

Bentleysautoparts

New member
Update, were getting there. Last race I had the 12 tooth, and ran a 69 gear. gained 1.5 mph, and 4/10ths a lap faster. Im going to try a 65 next race and see whats up. We also had a whole new set up, and his line was getting better. Got 2nd in his heat, and led the feature for 10 laps. He got flustered when the fast guys were pressuring him, and kept coming down on them on the back stretch. Got blacked flagged for rough riding. Boy I cant wait till he figures out how to race others, and hold his line. Overall for a 6 year old racing older kids, and only 5 races under his belt, hes doing better then I was expecting him to.
 
Update, were getting there. Last race I had the 12 tooth, and ran a 69 gear. gained 1.5 mph, and 4/10ths a lap faster. Im going to try a 65 next race and see whats up. We also had a whole new set up, and his line was getting better. Got 2nd in his heat, and led the feature for 10 laps. He got flustered when the fast guys were pressuring him, and kept coming down on them on the back stretch. Got blacked flagged for rough riding. Boy I cant wait till he figures out how to race others, and hold his line. Overall for a 6 year old racing older kids, and only 5 races under his belt, hes doing better then I was expecting him to.
Let me give you some good advise to make things easier on you, until you get him driving his line and understanding momentum put a 67 on the rear with that 12 ( which is still not correct ) and leave gearing alone, Focus on him only pointing things out and preach momentum, momentum, momentum, and tires of course, walk him to the fence while older kids or Sr are racing that are front runners and have it figured out and point out what there doing right, reason being that will end up quickest method to making progress your looking for. I have set down with many little ones drawing the track in the dirt with 2 match box cars showing the line where they should be, and showing where there at and showing them when another kart has position on them and then what to do, bottom line show as much details with the match box cars as you can it really seems to help them with understanding it quicker than just telling them.

Good Luck !!
 
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