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Old 10-06-2019, 11:23 AM
Mrmonk7663 Mrmonk7663 is offline
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Default Torque converter Garter springs

Trying to pick Garter Springs for best performance. 212 non hemi. Flat top piston. .030 shave. Mod2 cam. Billet rod/flywheel. Header. Intake. 22mm mikuni. Ported/polished head. 22lb springs. Champion rockers.

Tires-18
Gearing 6:1 or 6.75:1

Lightweight single seater kart.

30 series. Green Driven spring.

The question...taking into consideration the above build, would the white garter springs (3100rpm engagement) be appropriate over the std. blue (2200rpms)

Also, assuming a 6 driven, is the middle or third hole recommended?

I have 7 drivens and a 44 magnum comet also at my disposal but would like to try the 30 series first due to packaging constraints in the frame.

Thanks!
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Old 10-06-2019, 01:45 PM
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picking the right garter weight combination is fairly straight forward..
IF you know the peak torque rpms of your engine that is..

namely stay just below (say 200-300 rpms) and you'd be good;
that way at engagement you have a good amount of torque already and once fully locked
the engine just enters peak torque and you'll have the best possible accelerative power at your disposal.

Now, if you have a fairly pointy torque curve,
you want the TC to stay in low gear as long as possible ..
with a very flat curve (or very flat and paved terrain)
you can have it shift up as quickly as possible..
and inbetween for inbetweens
Something you will need to test if you don't have a dyno graph for your engine,
what works best in your area.

IF you do not know about the torque of your engine (when, where and how much)
you need to start guessing..
with a roughly 6500 -6800 rpms maxspeed, a 3100 engagement speed is not too bad of an idea..
but simply put: as long as you don't test it you'll never know what's ideal...
unless you find the guy that tested for you (i.e. has the exact same built engine)

gearing then is again a totally different topic..
18" and 6:1 is tough .. high engagement speed makes that worse...
but while it's a bit on the tough side and as long
as you don't plan to go slower than ~11mph
I don't see an issue with a 6:1 ratio (I think 6.75:1 is a better idea though)
If you plan going offroad mostly however (18" wheels sound like off road to me)
gear as low as possible.

'sid
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Last edited by itsid; 10-06-2019 at 10:15 PM. Reason: cosmetics ;)
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Old 10-06-2019, 04:23 PM
Mrmonk7663 Mrmonk7663 is offline
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I appreciate the response. It’s exactly what I needed. It Helps-out a ton.
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Old 10-07-2019, 04:08 AM
Mrmonk7663 Mrmonk7663 is offline
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Hey Sid, or anyone else that knows...

You mentioned the 6:1 gearing might be fine if I stayed above 11mph...how did you determine the lowest acceptable speed that will not burn up the belt? I woukd Love to know how to determine that myself.

Also for 18” tires I know that generally 6:1 is the accepted minimum and more gear is better for the belts...what about other tire sizes...how do you determine proper gearing for smaller and larger tires? Everything I have built so far has had 18-20” tires but I have a few projects that will be using 15” and 16” tires too.

Thanks man!
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Old 10-07-2019, 09:57 AM
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Well knowing the series30 has a low ratio of 2.7:1
I just added a hair of safety margin and raised that to 2.6
(since as soon as the belt is fully engaged it wants to raise on the driver)
that times the chain ratio gives us a
final ratio of 15.6:1
with 3100 rpms (full lock rpms) and 18" wheels that means we talk 10.64 mph
Or if you want it the other way around:
take the 2.7:1 low ratio completely to get to 16.2:1 overall ratio
and add the safety margin to your rpms (+100 rpms)
and with 3200 rpms on 16.2:1 and 18" wheels we get to a calculated speed of 10.58 mph

both round to be roughly 11 mph.
any slower than that and the clutch might want to start disengaging again (burning the belt/shoes)

Wheel size is an essential part of the gear ratio, most people forget about that.
since in the end you want the engine to push you along a road not just spin a wheel, right?

If you alter the wheelsize of an existing setup you mostly want to adapt your ratio to that.
And in such cases it's fairly easy to do..
take the ratio you got and divide by the wheeldiameter you got
then multiply with the wheeldiameter you want (6/18)* 15
and you end up at 5:1
So 6:1 on 18" wheels behaves almost the same as 5:1 on 15" wheels
(acceleration, top speed etc. all calculate to the same values)

here some generic kart/engine setup with 18" on 6:1 and 15" on 5:1 for comparision
(keep in mind clutch engagement here is assumed to be 2200 rpms)
KartInfo by kartcalc.net:
Code:

KART
RW diameter: 45.72 cm | 18 in Total weight: 200 kg | 440.92 lbs
ENGINE
Original HP: 7 Asummed HP: ~7 Torque: 13.85 Nm | 10.21 ft lbf RPM: 3600
TRANSMISSION
Final ratio: 6:1 TC type: series 30 6" driven Lowest ratio: 16.2:1 Highest ratio: 5.4:1
PERFORMANCE
Max Wheel Torque: 224.37 Nm | 165.49 ft lbf Min Wheel Torque: 74.79 Nm | 55.16 ft lbf Acceleration: 2.79 m/s | 9.15 ft/s Top Speed: 57.45 km/h | 35.7 mph
KartInfo by kartcalc.net:
Code:

KART
RW diameter: 38.1 cm | 15 in Total weight: 200 kg | 440.92 lbs
ENGINE
Original HP: 7 Asummed HP: ~7 Torque: 13.85 Nm | 10.21 ft lbf RPM: 3600
TRANSMISSION
Final ratio: 5:1 TC type: series 30 6" driven Lowest ratio: 13.5:1 Highest ratio: 4.5:1
PERFORMANCE
Max Wheel Torque: 186.98 Nm | 137.91 ft lbf Min Wheel Torque: 62.33 Nm | 45.97 ft lbf Acceleration: 2.79 m/s | 9.15 ft/s Top Speed: 57.45 km/h | 35.7 mph
Side note:
Wheel torque here is the torque the wheels are driven by (engine->chain->wheel);
the torque the wheels pushing against the road with - again is identical
224.37Nm (doesn't matter which one you pick really)
times 15 divided by 18 turns out to be 186.975 (some rounding involved )
same mathematical concept as above
that's why acceleration doesn't change..


'sid
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Old 10-07-2019, 03:03 PM
Mrmonk7663 Mrmonk7663 is offline
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Thank you for the lesson. It will definitely come in very handy. Awesome work.
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