whats the difference between the 2? Seems to me that its just the heatsink/fan and smaller wires on the 4cell version? Would be able to use a 4cell version in a 21.5 smc 3200 lipo pan car safely?

yes I used it in my lipo car for a long time you will probably never run long enough to drop the lipo below 6 volts. you will have to check but it may also have a lipo cutoff

Heres some specifics off Novaks site

http://www.teamnovak.com/products/esc/gtb_4cell/index.html

The 4-cell GTB does not have a lipo cut off but I,ve seen several being used in lipo applications with no problem. Heres info on a lipo cut-off if you choose to use one:

http://www.teamnovak.com/products/lipo_cutoff_module/index.html

you can use a 10.5 with a 4 cell speedo,anything hotter than that run the fan and heatsink
I used my leftover 4 cell gtb's with my 1\18th oval cars as well with the 300 series 8.5

Change wires to 14ga. or larger with lipo oval 10th scale oval stuff

ok thats basically what i figured. plan on running 21.5 lipo class here and need a speedo and motor still, want to keep my options open... Thanks all for the info

you can use a 10.5 with a 4 cell speedo,anything hotter than that run the fan and heatsink
Do you mean with a 6-cell pack or 2S LiPo? So I could run a 17.5 with a 4-cell GTB and 2S LiPo with no problems?

Do you mean with a 6-cell pack or 2S LiPo? So I could run a 17.5 with a 4-cell GTB and 2S LiPo with no problems?

Yeah,6 cell or 2c lipo

we were also using them in our 10.5 sprincars

Been using my 4c gtb w/lipo for a few months now in 10th pan oval and 10th sedan with a 10.5 Works great! speedo temps around 105-110 and have never used more than 2500mah so no need for cut-off.