So I understand the difference between 1.6 and 1.7 ratio, I get the fundamentals of lever advantage ratio.

So my question is actually about the application to harley twin cam engines. Changing the ratio increases lift and the effective duration. However the centerline of the cam lobes stays the same. So the 'timing' of the cam is the same just increased lift and effective duration.

If one were starting from scratch ideally you would just get the cam with the lift, timing, duration, etc that you want but I am curious how they can be used with lower lift cams to get increased lift and duration. Say you already have the 1.7 roller rockers laying around.

I'm considering a set of 1.7s for my Tman 590 so lets use my configuration as an example:

1. Are they an effective tool across the board or are some cams best suited for this application?

2. Shoule I install on the intake and exhaust or just the intake?

3. What are the negatives of this type application?

 

From what I have read

1. Are they an effective tool across the board or are some cams best suited for this application? Some cams will benefit while other's probably not.. I think the stock epa cams are in the not category.

2. Shoule I install on the intake and exhaust or just the intake? Depends but for the most part both or just Intake. Most say when talking about OverSized Valves that the Twincams Intake is the key one.. obviously as you are trying to move up in power they both need it at some point. This thought seems to hold true for the Rockers as well.. get more air into the engine first, at least in the case of the Twincam

3. What are the negatives of this type application? I think mostly the same as Higher lift cams

One thread I'd seen says that Baisely will sell just Intake or Exhaust

 

.030" more lift, and aprrox. 2-3 degres more duration.
Some cams really like them, and others do not seem to.
S&S .585's and .570's, .510's, respond well, and Wood 6's do also.
Wood 9B's or the 9F's don't, just for instance.
Scott

 

SE204s respond well to the 1.7 rockers on the intakes; can't speak to any others as those are the only ones I have worked with.

 

Cool thanks for the replies.

I was working on a deal of used ones apparently it is not going to go through. If it does Guess I'll Call TR or Brandon and see if they know how the 590 works with the rockers.

 

Those do as well.
Client from Albany, NY has a set in a combo we did years ago.
Scott

 

Just curious why they would not work well on the epa cams? Have thought about doing this with stock cams as it cheap. But no use in doing it if no gain to be had.

 

It's not that they won't work. There will be a slight improvement but not enough to warrant the work....The shorter duration or epa cams won't because it's more about the amount of time the valves are open. Longer duration cams benefit better from the lift because of the length of time that they are open to an extent as Scott noted. More fill..

 

if your going to do it,do your math & re check all clearances

 

I think the 590s have plenty of lift and duration for any 107" build. If you still need more hp/tq, then it's time to bore the cases.