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FC: main underdrive pulley users?

Old 05-14-09, 07:09 PM
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FC: main underdrive pulley users?

Are there any track dogs that run a main underdrive pulley on N/A?

Last Track day at Buttowillow Raceway I got happy with the downshifts towards the end of the day and apparently boiled my coolant. My S5 gauge had begun to move off the middle, but as soon as I noticed the gauge, I dialed it down and the needle began to return to the center immediately. Cruised back into the paddock and the upper rad hose had collapsed, but the engine cooled down just fine. After it cooled I didn't have to put that much coolant back in, maybe a pint. That was 6 weeks ago, and no sign of coolant seal failure, even after two bouts of Auto-X.

I think my radiator cap might have been bad, so I went ahead and replaced it.

I'm interested in installing a main underdrive pulley to help with the high RPM cavitation, but have noticed a lot of static regarding them being bad for "street" cars. No real data, just a lot of ghost stories. FWIW, the my 7 never sees "stop-and-go" duty. It's my weekender, and only driven in anger.

Does anyone have one, and their car overheats while idling in the pits? Or does anyone run one on the street with no complaints?

Thanks for reading.
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Old 05-14-09, 10:01 PM
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I have a main underdrive on my Turbo II and I've never had a problem in traffic or idling. I do have the coolant jacket mod but I don't think it makes that much of a difference. However do not combine a main underdrive and an alternator underdrive on an FC or you won't have enough juice at idle.

Also you should get a real temp gauge, the S5 one is worthless. I like the SPA dual digital gauge with oil and water temp, it's a little spendy but it's nice and I find I can read it at a glance better than I could with my old autometer analog temp gauge. You can also program a flashing alert light for whatever threshold temp you want.
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Old 05-15-09, 07:49 AM
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I have the main and alternator underdrive pulleys, got the alternator so I could run 2 belts. Works just fine. Also have an electric fan for when it gets too hot sitting on grid.

Pulleys are just a tiny fraction of the cooling system. These things are a b*tch to keep cool on track. Even with the above pulleys, I have to run a AWR radiator, 40 Below and have custom ducting to keep temps in line.

I do recommend at least the main underdrive, I ran with a stock pulley one time and had belt slippage, the belt was getting eaten up literally.
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Old 05-15-09, 09:00 AM
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Originally Posted by SCCAITS View Post
I have the main and alternator underdrive pulleys, got the alternator so I could run 2 belts. Works just fine. Also have an electric fan for when it gets too hot sitting on grid.

Pulleys are just a tiny fraction of the cooling system. These things are a b*tch to keep cool on track. Even with the above pulleys, I have to run a AWR radiator, 40 Below and have custom ducting to keep temps in line.

I do recommend at least the main underdrive, I ran with a stock pulley one time and had belt slippage, the belt was getting eaten up literally.
Mine is an occasionally street driven car that's mostly a track beast at this point... The problems came up if I had the headlights, wipers, radio, blower, etc going, it's not a stripped out race car I also have dual belts, I got a stock size dual pulley for the alternator.

Still a bitch to keep cool though. I don't really have water temp problems with my fluidyne radiator but my oil gets too hot and forces me to take a cool down lap during DE depending on the weather. Need to make ducting for the oil cooler...
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Old 05-15-09, 08:33 PM
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Thank you for the replies.

Originally Posted by Gene View Post
However do not combine a main underdrive and an alternator underdrive on an FC or you won't have enough juice at idle.
I have a machinist friend who is going to make me an "overdrive" pulley for my Alt so I can get the cooling benefits without the electrical trade-off.

Originally Posted by Gene View Post
Also you should get a real temp gauge, the S5 one is worthless.
Yes, I was already aware of the nature of the S5 gauge. A full sweep electric gauge with warning is in the mail. It would be interesting to know what the "tipping" point for the S5 gauge is to know how hot it did get.


Originally Posted by SCCAITS View Post
Also have an electric fan for when it gets too hot sitting on grid.

Pulleys are just a tiny fraction of the cooling system. These things are a b*tch to keep cool on track. Even with the above pulleys, I have to run a AWR radiator, 40 Below and have custom ducting to keep temps in line.
I do plan to go with an Al radiator, and do some ducting work when I replace my cracked bumper.

Do you run just distilled water and the 40-below? Would that be fine year-round in a non-freezing climate with no-A/C in the car?


Any experience with the main underdrive, and the 5" water pump underdrive from Mazdatrix? anybody?
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Old 05-16-09, 07:18 AM
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Originally Posted by HotRodMex View Post
Do you run just distilled water and the 40-below? Would that be fine year-round in a non-freezing climate with no-A/C in the car?
Yes, just distilled water and 40 below. Fine for a race car, for a street car I think I'd add some antifreeze to it. FWIW, I also replace my mixture about 2x a year just because. There was a thread about this recently in this section, look back and you'll probably see it.
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