I know the 21.5's are not actually in the racers hands yet, but does anyone that has tested them have and idea on how to gear them compared to 4 cell stock?

If on our 130' run line carpet track I gear 4 cell stock at 1.85 - 1.95, I would gear 21.5 LiPo at???

The testing at HotRod Hobbies (flat asphalt, I believe close to 200') with the 21.5 was

Roll Out 3.85
Tire Size 2.25
Gear 88/48
Temp at end of 5 minutes 187
Lap Times 5.4 -5.7
54 laps

I have never had to push a brushless motor hard enough to worry about temp. 187 seems kind of hot. Is 187 ok. What is a safe temp if you are trying to get your motor to last more then one race.

We've been trying to keep them under 180. The 10.5's have been running close to that...the 17.5 lipos are generally below 170 (depending on how hot it is outside)

I doubt you'll see most guys run the 21.5 over 155-160 degrees...in normal outdoor temps.

The testing at HotRod Hobbies (flat asphalt, I believe close to 200') with the 21.5 was

Roll Out 3.85
Tire Size 2.25
Gear 88/48
Temp at end of 5 minutes 187
Lap Times 5.4 -5.7
54 laps

What would 4 cell stock be at HotRod's?

I will be testing/running my 21.5/lipo on a 350+ asphalt track. Any suggestions for a starting rollout?

I will be testing/running my 21.5/lipo on a 350+ asphalt track. Any suggestions for a starting rollout?

Have you got yours already??? I,m still waiting.

350+ track try a 1.50 gear(with caps) and on the 130' try a 3.00 roll out should put you in the ballpark. My best guess having run every other motor combo.

Have you got yours already??? I,m still waiting.

It came in today. I ran the 17.5 w/4c in breakout and lap times were a bit faster than 27t. Hopefully 21.5/lipo is the ticket for this big track

@ Hot Rods we use a 225 Roll Out For Four Cell Stock. The track is Approx. 220ft run line

Thanks Buck,

I couldn't remember the Stock rollout, but I thought it was right there close...and I knew 200 was short, and I didn't look for my track notes.

That's only what....about 20 teeth lower than what the 21.5 needs.

My 21.5 came yesterday!!!!!!!!

Thanks to all, we should have a good baseline now. :woohoo:

Robert,

Let us know how you do with it...after you get it dialed in.

OK, ran the 21.5/LiPo today at Freddie's Hobbies. It's a 135 foot run line, flat carpet track. Everybody rolled out somewhere about 3.10. I ran a 3.10 and came off the track between 135° and 140°. We ran 6 minute heats and used about 1300 mah. Once we get the COT bodied cars dialed in ( they really are different) I bet we get up to 3.40 - 3.50.

I'll keep you posted.

So how is the speed of the 21.5/lipo compare too? Is it close to 13.5 /4 cell?

From what I have read on the threads for testing the 21.5 w/lipo is maybe slightly faster than a good stock motor on 4cells, the 17.5 on lipo is abouut the same as 10.5 on 4cells.....

B mullins,

so far we found the 21.5/LIPO to be almost 1/2 second a lap quicker than STOCK on our little CAPPED track...it took almost 3 laps to get upto speed...but it kept building momentum.

On flat asphalt w/ foams, there was a lot less notiicable speed increase.

We don't have a lot of 13.5 data to compare it too, because we never really got into running the 13.5's cause the first time we did, the TQ would have been I believe 3rd in the 10.5 class.

It should (The 21.5/LIPO) prove to be almost in the middle of a 4 cell STOCK and a 13.5 4 cell combo. Just a tick faster than I had originally hoped for, but very drivable.

Joe Myers
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thanks for the reply swtour

Well we were disapointed. the 21.5/lipo is the same speeds as 13.5/4cell maybe a tick faster. We ran it on an asphalt track with a 365' drive line with a 4.8 rollout and It ran 6.6 lap times and I'm sure those lap time will be improved apon. Lap times for 13.5 are 6.3 to 6.9 and our best stock times are 7.1 to 7.3. but we realy want to start using lipo batteries so we decided to move forward with the new class next season. We will be the first track in florida to legalize lipo batteries and we are excited about using lipo. I wander what the 18.5 would do on our track, aaah you probably couldn't find enough gear.

On a smaller track, the 21.5/lipo will run a lot closer to fast stock speeds. On a 365' track, the lipo's discharge curve really makes the motor perform well and will let it run fast. The bigger the track, the faster than stock it will go. On small tight tracks, the lack of torque in the 21.5 really slows it down.

Thats what I figured it was too. We love the 13.5 speeds. We were just hopeing our novice people would be able to take over when we moved up to 17.5 lipo.

stoneman,

That's why I was pushing more toward the 25.5 motor, but at that time ARCOR approved the 21.5 before we could finish testing it...and the early tests we did found the 21.5's FAST on CAPS yet just a tick faster than 4 cell stock on the short tracks.

I was hoping not to end up with another 13.5 speed class. *(Although I must say...the 21.5/LIPO although FAST...it's much easier to drive than the 13.5 ...which in itself isn't bad to drive... The 21.5 is about momentum..and KEEPING IT)

Joe Myers
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stoneman,

That's why I was pushing more toward the 25.5 motor, but at that time ARCOR approved the 21.5 before we could finish testing it...and the early tests we did found the 21.5's FAST on CAPS yet just a tick faster than 4 cell stock on the short tracks.

I was hoping not to end up with another 13.5 speed class. *(Although I must say...the 21.5/LIPO although FAST...it's much easier to drive than the 13.5 ...which in itself isn't bad to drive... The 21.5 is about momentum..and KEEPING IT)

Thats cool That would make it a little more like stock as far as staying out of trouble and off the pipes, things that will make you rebuild that momentum.

Hey Stoney we can build a medium size track just for the 21.5/lipo that will have the same speed as the 27t 4c. Just need to know that "ideal" size :drunk:

Looks like our intial testing was off a bit! What I had posted earlier was based on some initial testing on our local track. A few cars made it to a carpet track today and it looks like 21.5/lipo is going to run 2 or 3 laps faster than stock. My bad.

has anyone tested the 21.5 with 4 cell? and in comprarison what would be diff . in 17.5 to 21.5 rollout?

I never tried the 21.5 with 4 cell, since when I tested the 17.5's w/ 4 cell they were so close to a brushed 4 cell stock speed...

I did try the 25.5 on 4 cell, but only at a 88/50 ratio (I think it hit like 14 mph) I only got into the low 20's with the 25.5/LIPO and the same ratio.

So to get any speed at ALL out of a 21.5/4 cell - Try a 76/65 and see what that gets you...

The 21.5 is rated at 1800Kv where the 17.5 is rated at 2200Kv...so you'd probably roll out about 20% taller than a 17.5 (sorry - BRAIN is dead today...but I'm thinking another 4-5 teeth taller than what you'd put on the 17.5 to start)

Joe Myers
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Hey Stoney we can build a medium size track just for the 21.5/lipo that will have the same speed as the 27t 4c. Just need to know that "ideal" size :drunk:

Well we ran 21.5/lipo for the first time at our track last night and the times were the same speed as the fast stock guys. I don't know if you were looking at the right lap times Eugene but if you were your going to kick our butts.

Well we ran 21.5/lipo for the first time at our track last night and the times were the same speed as the fast stock guys. I don't know if you were looking at the right lap times Eugene but if you were your going to kick our butts.

Kevin was calling them out to me. I was the only car on the track and ran a wing. You guys had a field of cars w/o a wing. Its going to be interesting next Saturday during the day.

Kevin was calling them out to me. I was the only car on the track and ran a wing. You guys had a field of cars w/o a wing. Its going to be interesting next Saturday during the day.

Yes it is! I can't believe the different feel of this motor.It has alot of torque on take off then it kinda winds out and gives you the feel like your under geared. I ran a 4.1 and a 4.5 rollout and the speed never changed kevin was running a high 2 and a 3 rollout and his time when he got in a good lap was the same lap times as mine. Allthough when I ran the 4.5 rollout I used considerable more battery power. So you may be able to tell if your over geared by how much battery power you used in a heat.

I can't believe the different feel of this motor.It has alot of torque on take off then it kinda winds out and give you the feel like your under geared.

This is why I've had to tell guys to "LOOK AT THE LAP TIMES" and not go by what the car feels like...most think it feels way SLOWER than a regular 27t STOCK motor...

Joe Myers
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Maverick Oval Chassis (http://www.swiftracingproducts.com)
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McAllister Racing Bodies (http://www.mcallisterracing.com)
STICK E.T. Tire Sauces (http://www.arcor-rc.com/arcor2003/sticket.htm)

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