I'm getting conflicting advice on a cam installation. I'm looking at going with a woods 6 and gear drive for my 88 inch twinkie. One builder recommends a 4* advance key, the other says it's not needed. I know it degrees the cam 4* advance but can someone explain why that is necessary or why it is not.

JW

 

it may be needed if your compression is not high enough, like if you are at stock compression.

if you are pulling the heads off and bringing it up to 10:1 or so, you'll be fine without advancing the cam. at least that's my $.02

 

"Depends on what you are looking for. Advancing the cam can make cylinder pressures rise, produce torque earlier in the rpm range, but will also reduce the peak rpm range of the engine. You can take a compression test (with the throttle open) and see where the cylinder pressures are now. We typically don't want to see anything higher than 175 psi or so for a street bike to run on pump gas" That is the answer I got from a tech at a large cam company. Although I have heard of people running more comp. on the street. I'm thinking about this with my 37h's. I just want to make sure it isn't overkill.

 

A +4 cam gear is used when you are trying to use a cam at lower compression then what it likes. It will move the power band lower in the RPM range, while in turn it will reduce top-end power.

The Woods TW-6 likes around 10:1 - 10.2:1 CR, at that CR you wouldn't need to use a +4 gear. But if you are trying to run it at stock CR, then the +4 gear would be a good idea to get the power where you want it.

Steve

 

As others have said, , the +4 advance key will raise CCP, effectively giveing the cam and ealier intake close, raising CCP and moving the peak torque lower in the rpm range. Torque is a function of both CCP and statis CR, and cams are designed to operate with a certain CR to produce peak torque at a certain rpm. The longer duration/overlap of a cam, the lower CCP you will have so you compensate by raising CR, or in this case, advancing the cam timing to bring CCP up.

I am not a proponent of using advance keys, I believe in running a cam that fits your application and riding style, although others have no issue with it.