"overdrive" pulleys?

[smontanaro]

I own a 914/6 and frequent the 914club.com forums. Over there one of the topics turned to somewhat longer gears to reduce RPMs at cruising speeds. The concensus seems to be that a certain minimum RPM level is necessary to blow enough cooling air around. One of the folks there mentioned that "overdrive pulleys" must be available for /6's. Any suggestions where I might find such beasties?

Thanks,

Skip Montanaro

[911quest]

Overdrive pulleys are a compromise at best remember for more airflow at high speed you lose airflow in stop and go traffic.

[Grady Clay]

Skip,

Yes, this is a great solution for almost any 911 or six. The standard (pre-’75) ratio is 1.3:1. The ’75 and later 930 and many 911s have 1.82:1 ratio. This works great keeping the hottest and most important parts cooler – the heads and cylinders.

I have this configuration on my "street” six; 2.8S, MFI, 11.5:1 CR. I also have it on my ’68 2.0 original 130 hp.

The parts necessary are the 134 mm dia crank pulley and the 930 or ’80 -> 911 fan with the 84 mm split pulley. I have written extensively about this on Pelican, including part numbers, etc.

For track use the “Rubbermaid Solution” is best. Search Pelican.

Our 911s and sixes like to buzz along at relatively high rpm. Part of the reason if the engine cooling fan is rpm dependent and thus the cooling. Another is the oil system. You need sufficient rpm to keep the oil pressure (when hot) high. With lower pressures, there isn’t sufficient spray to the intake rockers and cam lobes and the piston cooling squirters don’t open. They need 3-4 bar (42-56 psi) to open.

Best,
Grady

[kenikh]

Interesting!

Slight hijack - do you run that 11.5:1 CR 2.8L on 93 octane pump gas (even with twin plugs)?!? If so, a summary of how would be appreciated.

[Grady Clay]

No; 112 octane leaded race gas. I keep two 55 gal drumbs at home and we have (15 min away) a drive-up gas station with up to 114 octane, road tax paid.

Best,
Grady

[kenikh]

Cool! Have you ever used Torco race gas concentrates to get your octane up? Race gas is a bit hard to come by around these parts.

[Grady Clay]

Try:
VP Racing Fuels
Pasco, Washington
Phone: 509-544-0306
Fax: 509-547-1687
E-Mail: vpnorthwest@msn.com
www.vpracingfuels.com

Best,
Grady