25 replies to this topic

[Pablo]

I am not a drag guy but occasionally find myself building a car here and there.

My question is, what pinion to use?

 

Motor will be a bone stock vintage Mabuchi 36D, sidewinder in a Dynamic chassis.

Body will be a 15 thou 1/24 Batmobile.

 

Spur 36T 48P. Wheel OD about .980"

 

Thanks for your help and opinions (get it - pinions?  )

 

Pablo

 

[chasbeeman]

People will ask you if you are racing 1/8 or 1/4 mile track?

[MSwiss]

Along with Dave Crevie, here are probably the only 2 regular Slotblog guys that can help you.

 

They will want to know tire diameter(which you provided) voltage the car will be run on, and possibly track length.

 

[Pablo]

Not sure who and where the car will go to at this point.

If it stays local here in Cleveland, TN the track is 1,000 feet.

I'd guess 16 volts but I will double check once the rest of the world wakes up today 

 

Thanks guys 

[Pablo]

16.4 volts

[Dave Crevie]

Which Mabuchi 36D? In drag racing, there are a lot of variables that can effect your best E.T.  Track condition not the least of it. Some places they glue the crap out of the track, others they don't allow any glue. With a Bobcat, a ten tooth pinion would be a good place to start. For bracket racing you want the motor to top out well before the traps. That gives you a little margin for error, to allow for variances in conditions.  For heads up, you want it to top out right at the traps. Remember, in bracket racing it's not the fastest car that wins. It's the one that can consistantly turn it's dial-in.

 

By the way, a .980 tire let's you run a pretty big spur. The bigger the gears the better better for mesh. But I don't remember how big you can go with that chassis and stay in the 3 to 1 - 3.5 to 1 range. Drag racing is a lot of trial and error. That's about all I can tell you.   

[Pablo]

Thanks Dave    Motor will be a Champion 36D from Professor Motor.

If you recommend a 10T to start that's fine with me. I was guessing 12.

 

I don't know what a "trap" is, or "heads up". Yes I am clueless  

 

The biggest spur gear size to be flush with bottom of chassis would be about .850

A 36T will be somewhat less than that. Close but not exactly at ground zero.

 

3 to 1 would be a 12T.  Looks like my choices are 10, 11, or 12T.

 

Thanks again Dave

[MSwiss]

The light bulb just went on with this.

 

A 36T, even in 48 P, with a 36D sidewinder, unless I'm missing something,  is not even remotely possible. 

 

I Googled 36D size and they are approx. 1.1" wide. 

 

The Cox car below is most likely geared 16-48.

 

[Dave Crevie]

16/48 is 3 to 1. You are running on a short drag strip. You might want to go up from that to the 47 tooth or 48 tooth (if it will fit, you have some adjustment).  Professor motor shows three different Cox 36D motors, only the NASCAR version shows RPM rating, at 32,000. PM has 12, 13, 16 and 17 tooth Cox pinions, and 46 and 47 tooth Cox spurs. That's all I know.   

[Pablo]

OK thanks guys. Looking at approx. 3 to 1 is ballpark enough for now.

The motor will arrive in a few days and I'll work it out.

[Bill Seitz]

Keep in mind that the 36D motor doesn't clear the axle by much with the stock 16/48 gears Cox used. This is where I'm sure Mike Swiss was coming from. A 10 or 12/36 won't work - not enough space motor to axle. My suggestion is to work from 16/48 and add teeth to one while subtracting from the other to keep the spacing. There's going to be a bit of a problem here because the .980 tire won't allow a spur much larger than 45 or 46, so it'll be impossible to get gears that provide the axle spacing the motor needs. The 36D sidewinders used 1.13 tires for a reason - getting gears big enough. I'd recommend going to the larger diameter Pro-Track tires.

 

I hadn't done anything 36D since the 80's, but a friend sent me a couple Classic Industries cars that got me playing with 36D again and considering building a chassis. A 36D can be used inline with .060 track clearance on 1" OD tires. This is where you can use those 10 and 12T, .091 pinions.

[Pablo]

Thanks Bill, I appreciate it  

[Martin]

This may not make much of a difference, but if you were to convert to a 3/32" axle you get another .015'' clearance to the motor.

And or you could make some fancy eccentrics to move the axle lower for smaller tires?.

I know that's probably more work than you want to do, but was just thinking

[Pablo]

Trying to keep it simple and stock    Something a youngster could have assembled with a screwdriver back in 1967 

[Ramcatlarry]

FYI:

"TRAPs"  A set of timing light at the finish line to measure the actual top speed of the car.

 

Drag racing is raced in two manners.  HEADS UP is when each lane/driver start at the same time when the lights turn GREEN/GO.  This is usually done when both competitors are racing same power components or car class.  Many times it is difficult to have a large enough pool of 'equal' competitors.

..Bracket racing is the alternative to heads up. Since EACH lane can be 'dialed in' to a ET (elapsed time) of their cars capabilities, a different starting time can be used to race.  The goal is to have both cars potentially finish their run at the same exact time.  The 'REACTION TIME' is how long it takes to process the GO light and make the car move from the staring line.

[Pablo]

Thanks Larry. 

 

And of course, Swiss is right - now that I have the motor in hand and a pile of gears, obviously it's going to need a massive pinion to reach the spur.

[Pablo]

I have a possible plan, please tell me if I'm way off.

 

Set screw rear axle, Russkit replica 1/2 wide wheels, H & R black donuts ground to 1.10" OD.

48P gears, Cox 44T spur, 16T pinion. (ratio 2.75/1) (FDR 2.50)

 

The spur will clear 1/16" but the chassis bottom will be slightly higher.

So I'm thinking, and hoping, it won't matter on a drag car (?) 

 

The Champion-labeled 36D Mabuchi is bone-stock. Lancer Batmobile body looks cool 

 

Please save me from myself if I'm making a big mistake here. There is not much room for gearing adjustment without an idler gear.

And I don't want to do that on a simple car like this. Unless I absolutely have to. 

 

I found this old Pablo build thread but it was a road course car, not a dragster:

 

Dynamic 36D Legend - Pablo's Builds - Slotblog

[MSwiss]

Drag cars usually have higher clearance but it shouldn't be an issue with a car that stiff and relatively slow.

 

Biggest thing with cars like that is that the car has enough nose weight and the tires are skinny enough that the nose stays in at launch and when it hits the the glue in the shutdown.

 

IOW, you don't want it it to be a hazard on the track, if it races other cars.

[Pablo]

Gotcha. Thanks a bunch. 1/2" wide rears should be OK I hope 

[MSwiss]

1/2" is pretty wide for a nobar car with a slow motor.

 

Of course, rubber compound and traction level on the particular track the car will run on, will be a determining factor.

[Pablo]

Thanks I'll keep that in mind. Switching to narrower wheels would be easy (I think)

[Pablo]

 1/2" is pretty wide for a nobar car with a slow motor.

 

Of course, rubber compound and traction level on the particular track the car will run on, will be a determining factor.

 

My usual disclaimer of Navy warship navigation thinking keeps me out of trouble once again -

"easier to deviate from a known plan than no plan at all".

 

Set screw wheels would make this rear end too wide. Slowly I turn, to a threaded axle setup.

Influenced by Swiss intel, 3/8" width Dynamic rims and a nylon 46T spur. 

 

Now I can have the ratio I want and it will fit the 3" width limitation of the body. 

16/46, 1.1" OD donuts. Good thing I have some small nuts here somewhere 

 

I appreciate Slotblog brain-power - without it, I'd be knitting sweaters  

[Tom Katsanis]

Yes 3 to 1 would be a good starting point with 1 3/16 tires maybe .400 or .435.
I'm running a rambuchi at the moment geared 2.8 to 1 & it runs 1.5s.

[Pablo]

This car is coming soon .........

[John Luongo]

great discussion and information, gentlemen. 36ds are alot of fun and can be in a class all by themselves. years ago i built a bracket racer out of an old belt drive 36d whisperjet rental car. modified a 1/2" aluminum front wheel into a drive pulley for a bit more top end, hard 1 1/8 rears, mounted a 40 ford body on it. my starting line prep was to remove glue and clean my lane, even used tiger milk on my tires to try and reduce drag. i used a release trigger for a "controller" and most always caught a 400 light. one finale had me pitted against a gr7 funny car. he didnt get the green until i was within a foot and a half of the trap lights, and he broke out. fun times