V-Belt or Serpentine Belt for Road Racing

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V-Belt or Serpentine Belt for Road Racing

Post by VW&MGman » Sun Sep 24, 2017 6:57 am

Hi All,

I need your advice...especially those of you who road race.

Currently I have a serpentine belt system with a push on sand seal and a welded fan. On the straights I usually hit ~ 6500 rpm and hold it there till I have to slow down. This could be as long as 10 seconds.

Based on what I read, the serpentine belt system seems to blow up fans.

So here are my questions:

If convert back to a V-belt set up, how tight should I keep the belt?

Are V-belts prone to jump/skip off and if so, how could this be prevented?

Any of you running a power pulley? (ie: 5 3/4" crank pulley)

I run an alternator. Is the stock generator pulley the same for the alternator v-belt pulleys?

What size belt do you run?

What brand?

Thanks in advance

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Re: V-Belt or Serpentine Belt for Road Racing

Post by Thenoj » Sun Sep 24, 2017 9:28 am

I can tell you what doesn't work so you don't have to retrace my steps. I ran a v belt with power pulley on a road race 1600 that was spun to 7200rpm. I had issues with the belt flipping over or popping off because I was trying to run the least amount of tension possible to induce slippage at high rpm. I did so based on the theory that when the fan reaches its maximum design rpm it stops increasing air flow and exponentially increases parasitic drag on the engine as rpm increase. I don't know if this theory has been tested and (dis)proven. I didn't race long enough to find a reliable way to regulate fan rpm and drag.

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Re: V-Belt or Serpentine Belt for Road Racing

Post by Marc » Sun Sep 24, 2017 8:36 pm


12V (and large-diameter 6V) generator pulleys will interchange with alternator pulleys. The width of the belt was increased on alternator-equipped cars to transmit more power without increased slippage. The increased width necessitated making them slightly longer as well, 11.3x912 versus 9.5x905mm.

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Re: V-Belt or Serpentine Belt for Road Racing

Post by fabo » Mon Sep 25, 2017 7:59 am

I used to race a hipo hillclimb circuit beetle for years,8000rpm and threw a few v belts and in the end threw a rod..we think because it threw a belt and I didn't realise,no3 piston got hot locked up the rest is history...our theory...now a guy I know races hillclimbs,and used to do long tarmac rallies and he uses a v belt but also uses a serpentine tension pulley just to stop the vbelt from flexing and potentially coming off....he never has issues....

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Re: V-Belt or Serpentine Belt for Road Racing

Post by 74baja1915 » Wed Sep 27, 2017 3:56 pm

I have used both and the only time one popped of was the serpentine belt going down the highway. It was a cheaper kit and after that happened I noticed that the tesioner bracket would flex under load. So if you do go non V belt make sure you get a quality kit.
P.S. I got home that day with a belt made out of rags some 20 miles

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